JP7661832B2 - Shrinkage ratio estimation device, shrinkage ratio estimation method, program, recording medium, shrinkage ratio estimation system, and method for manufacturing extrusion molded product - Google Patents

Description

The present invention relates to a shrinkage rate estimation technology for estimating the shrinkage rate of an extrusion molded product.

JP 2020-44695 A (Patent Document 1) describes a technology that detects the torque generated in the rotating screw of a rubber extruder and estimates the viscosity of the rubber material based on this detected torque data.

JP 2020-44695 A

For example, a cable, which is a typical extrusion molded product, has a structure in which the conductor wire is coated with resin to ensure insulation, and the resin that coats the conductor wire is formed, for example, by extrusion molding technology. The resin formed by extrusion molding technology is then annealed, but it is known that the cable shrinks after annealing. For example, if the resin shrinks in the longitudinal direction of the cable, this can cause fluctuations in the outer diameter, making the outer diameter of the cable thicker, or can cause problems such as the conductor wire (core wire) being exposed from the end of the cable. For this reason, it is desirable to reduce the shrinkage rate of cables.

Regarding this point, currently, it is not possible to grasp the shrinkage rate (dimensions after annealing) of an extrusion molded product that contains the resin extruded from the extruder as a constituent material at the time of extrusion. This causes defects after annealing, resulting in a decrease in manufacturing yield and an increase in lead time. Therefore, from the perspective of improving the productivity of extrusion molded products, a technology that can estimate the shrinkage rate at the time of extrusion is desired.

For example, if it becomes possible to estimate the shrinkage rate during extrusion, a technology is desired that can modify the manufacturing process of the extrusion molded product based on the estimated shrinkage rate so that the shrinkage rate is equal to or less than a predetermined value. This is because if the manufacturing process of the extrusion molded product can be modified so that the shrinkage rate is equal to or less than a predetermined value, the production of extrusion molded products with a shrinkage rate greater than the predetermined value can be suppressed, thereby improving the productivity of high-quality extrusion molded products.

The shrinkage rate estimation device in one embodiment includes a shrinkage rate estimation unit that estimates a shrinkage rate based on a relational equation that relates the torque current of a motor provided in an extruder to the shrinkage rate of an extrusion molded product that contains a resin extruded from the extruder as a constituent material, the relational equation including a constant parameter, and a numerical value change unit that changes the value of the constant parameter to a first value that makes the value of the shrinkage rate equal to or less than the predetermined value when the shrinkage rate estimated by the shrinkage rate estimation unit is greater than a predetermined value, or changes the value of the constant parameter to a first value that makes the value of the shrinkage rate smaller than the predetermined value when the shrinkage rate estimated by the shrinkage rate estimation unit is equal to or greater than the predetermined value.

The shrinkage rate estimation method in one embodiment includes a shrinkage rate estimation process that estimates a shrinkage rate based on a relational equation that relates the torque current of a motor provided in an extruder to the shrinkage rate of an extrusion molded product that contains a resin extruded from the extruder as a constituent material, the relational equation including a constant parameter, and a numerical value change process that changes the value of the constant parameter to a first value that makes the value of the shrinkage rate equal to or less than the predetermined value when the shrinkage rate estimated in the shrinkage rate estimation process is greater than a predetermined value, or changes the value of the constant parameter to a first value that makes the value of the shrinkage rate smaller than the predetermined value when the shrinkage rate estimated in the shrinkage rate estimation unit is equal to or greater than the predetermined value.

This shrinkage rate estimation method can be realized by having a computer execute a process for estimating the shrinkage rate of an extrusion molded product using a program. For example, this program includes a shrinkage rate estimation process that estimates the shrinkage rate based on a relational equation that relates the torque current of a motor provided in an extruder to the shrinkage rate and includes a constant parameter, and a numerical value change process that changes the value of the constant parameter to a first value that makes the value of the shrinkage rate equal to or less than the predetermined value when the shrinkage rate estimated by the shrinkage rate estimation process is greater than a predetermined value, or a numerical value change process that changes the value of the constant parameter to a first value that makes the value of the shrinkage rate smaller than the predetermined value when the shrinkage rate estimated by the shrinkage rate estimation unit is equal to or greater than the predetermined value. The program in one embodiment can be recorded, for example, on a computer-readable recording medium.

In one embodiment, the shrinkage rate estimation system includes an extruder that extrudes resin, a water tank that cools the resin extruded from the extruder, a distance adjustment unit that can adjust the drop distance between the extruder and the water tank, and a shrinkage rate estimation device that estimates the shrinkage rate of the extrusion molded product.

The shrinkage rate estimation device includes a shrinkage rate estimation unit that estimates the shrinkage rate based on a relational equation that relates the torque current of the motor in the extruder to the shrinkage rate of the extrusion molded product and includes distance as a constant parameter, and a distance value change unit that changes the value of the withdrawal distance to a first value at which the value of the shrinkage rate is equal to or less than the predetermined value when the shrinkage rate estimated by the shrinkage rate estimation unit is greater than a predetermined value, or changes the value of the withdrawal distance to a first value at which the value of the shrinkage rate is less than the predetermined value when the shrinkage rate estimated by the shrinkage rate estimation unit is equal to or greater than the predetermined value. The distance adjustment unit adjusts the position of the water tank so that the withdrawal distance becomes the first value changed by the distance value change unit.

The manufacturing method of the extrusion molding product in one embodiment includes a shrinkage rate estimation step of estimating the shrinkage rate based on a relational equation that relates the torque current of the motor provided in the extruder to the shrinkage rate of the extrusion molding product, the relational equation including, as constant parameters, a configuration parameter that defines the configuration of the extrusion molding system that manufactures the extrusion molding product or a part of a condition parameter that defines the extrusion conditions in the extruder; a numerical value change step of changing the value of the constant parameter to a first value that makes the value of the shrinkage rate equal to or less than a predetermined value when the shrinkage rate estimated in the shrinkage rate estimation step is greater than a predetermined value, or a numerical value change step of changing the value of the constant parameter to a first value that makes the value of the shrinkage rate smaller than the predetermined value when the shrinkage rate estimated in the shrinkage rate estimation unit is equal to or greater than the predetermined value; a step of changing the configuration parameter or the condition parameter to reflect in the extrusion molding system that the constant parameter has been changed to the first value; and a molding step of extruding resin in the extrusion molding system after the configuration parameter or the condition parameter has been changed.

According to one embodiment, it is possible to produce extrusion molded products of excellent quality.

5A to 5C are schematic diagrams illustrating an extrusion molding process for covering the outer periphery of a conductor wire with resin. 1 is a schematic diagram showing a state in which a conductor wire is covered with a resin extruded from a die. FIG. 1 is a graph showing measurement results (experimental data) of the temperature of a resin. 1 is a graph showing the time dependence of viscosity (shown in black) calculated based on experimental data, and the time dependence of torque current output from an extruder (shown in gray). FIG. 1 is a diagram illustrating the validity of the existence of a correlation between "torque current" and the shrinkage rate of an extrusion molded product. FIG. 13 is a diagram showing a procedure for formulating the correlation between the “torque current” and the contraction rate. FIG. 2 is a schematic diagram illustrating “strain rate.” 1 is a graph plotting actual measurement data. 1 is a flowchart for explaining a development concept. FIG. 1 is a schematic diagram showing a configuration of a shrinkage rate estimation system. FIG. 2 is a diagram illustrating an example of a hardware configuration of a shrinkage ratio estimation device. 1 is a graph showing the relationship between "pulling distance" and shrinkage rate. FIG. 2 is a functional block diagram showing a functional configuration of the shrinkage rate estimation device. 4 is a flowchart illustrating an operation of the shrinkage rate estimation device. 1 is a flowchart showing a manufacturing process of an extrusion molded product.

In all drawings used to explain the embodiments, the same components are generally given the same reference numerals, and repeated explanations will be omitted. In addition, hatching may be used even in plan views to make the drawings easier to understand.

<Cable manufacturing method>
In this embodiment, a process for covering the outer periphery of a conductor with resin using an extrusion molding technique will be described as part of a method for manufacturing a cable in which the conductor is covered with resin.

Figure 1 is a schematic diagram illustrating the extrusion molding process for covering the outer circumference of a conductor with resin.

In FIG. 1, raw material pellets 10, which are the raw material for the coating material, are fed into an extruder 11 and kneaded, and molten resin is extruded from a die 13 via a crosshead 12. The extruded resin coats the surface of a conductor 14 moving along a travel line. The resin coating the surface of the conductor 14 is then air-cooled immediately after being extruded from the die 13, and then water-cooled in a water tank 15. In this way, the resin extruded from the die 13 solidifies during the cooling process by air and water cooling. Here, the conductor 14 is composed of copper twisted wire, etc. The raw material pellets (plastic material) 10 are composed of a thermoplastic polyurethane resin, etc.

Then, an annealing process is performed on the extrusion molded product, which contains the resin formed by the extrusion molding technology as a constituent material, but it is known that the extrusion molded product shrinks after the annealing process. Since the shrinkage of the extrusion molded product has a negative effect on the quality of the extrusion molded product, it is desirable to reduce the shrinkage rate of the extrusion molded product.

In this regard, for example, if it were possible to grasp the shrinkage rate (dimensions after annealing) of an extrusion molded product in real time during extrusion molding, it would be possible to improve manufacturing yields and reduce lead times. In other words, from the perspective of improving the productivity of extrusion molded products, there is a demand for technology that can estimate the shrinkage rate in real time.

<Basic Concept of the Embodiment>
The basic idea of the present embodiment is to estimate the shrinkage rate of an extrusion molded product in real time, not by directly estimating the shrinkage rate itself, but by focusing on a physical quantity that is correlated with the shrinkage rate and estimating this physical quantity to indirectly estimate the shrinkage rate. In particular, if a physical quantity that can be grasped in real time as a physical quantity that is correlated with the shrinkage rate can be found, it is considered that the shrinkage rate can be estimated in real time based on this physical quantity.

This basic concept has the following advantages:

For example, to estimate the shrinkage rate itself with high accuracy, it is necessary to take into account both the extrusion conditions and the material properties of the resin. However, with shrinkage rate estimation technology that formulates the shrinkage rate itself, not only is it difficult to formulate the shrinkage rate itself by taking into account both the extrusion conditions and the material properties of the resin, but it also includes a parameter called "crystallinity" that needs to be measured. As a result, it is difficult to introduce technology that formulates the shrinkage rate itself in real time into the manufacturing process of extrusion molded products.

In contrast, according to the basic concept, there is no need to formulate the shrinkage rate itself, and if a physical quantity that is correlated with the shrinkage rate can be formulated, the shrinkage rate can be indirectly estimated from the formulated physical quantity. In this case, if it is easy to consider both the extrusion conditions and the material properties of the resin in formulating the physical quantity, and if the formulation can be done without including the parameter "crystallinity" that requires measurement, the shrinkage rate can be estimated with high accuracy and can be introduced in real time in the manufacturing process of extrusion molded products. In other words, if a physical quantity that is correlated with the shrinkage rate can be grasped in real time and can be formulated taking into account the extrusion conditions and material properties, the shrinkage rate can be estimated with high accuracy and can be introduced in real time in the manufacturing process of extrusion molded products.

The inventors conducted extensive research to find such a physical quantity, and as a result, they focused on a physical quantity called "torque current." In the following, we will explain "torque current."

<"Torque current">
In the extrusion molding process, an extruder is used. In the extruder, raw material pellets, which are the raw material of the coating material, are kneaded with a rotating screw. Then, the kneaded molten resin is extruded from the outlet of the die to cover the outer periphery of the conductor with the resin. Here, the screw is rotated by a motor provided in the extruder. At this time, the load current flowing through the motor that rotates the screw is the "torque current". The inventor has newly discovered that this "torque current" is a physical quantity that is correlated with the shrinkage rate of the extrusion molded product. In particular, the "torque current" is a current that flows through the motor that rotates the screw that kneads the resin, and the extruder is configured to be able to detect abnormal rotation of the screw by constantly monitoring this "torque current". For this reason, the "torque current" is a physical quantity that can be grasped in real time in the extrusion molding process. Therefore, if the "torque current" is correlated with the shrinkage rate of the extrusion molded product, it is possible to estimate the shrinkage rate of the extrusion molded product in real time from the "torque current".

Here, it is not clear that there is a correlation between the "torque current" and the shrinkage rate of the extrusion molded product. Therefore, below, we will first qualitatively explain that there is a correlation between the "torque current" and the shrinkage rate of the extrusion molded product.

<Qualitative understanding of correlation>
<<Explanation of "Drawdown Stress">>
In order to explain the existence of a correlation between the "torque current" and the shrinkage rate of an extrusion molded product, the "drawing stress" plays an important role. Therefore, the "drawing stress" will be explained.

Figure 2 is a schematic diagram showing how the conductor wire is coated with resin extruded from the die.

In FIG. 2, molten resin 20R extruded from the outlet of die 13 is coated onto the surface of conductor 14, which moves at a constant linear speed. The molten resin 20R coated onto the surface of conductor 14 is then cooled in water tank 15 and crystallized. At this time, as shown in FIG. 2, molten resin 20R extruded from the outlet of die 13 is pulled by conductor 14, which moves along the travel line. As a result, the stress applied diagonally to molten resin 20R from the time it is extruded from the outlet of die 13 until it coats conductor 14 is the "drawdown stress σ."

The inventors speculate that this "drawdown stress" correlates with the shrinkage rate of the extrusion molded product. In this regard, the reasons why the inventors speculated that there is a correlation between "drawdown stress" and shrinkage rate will be explained. The inventors speculated that there is a correlation between "drawdown stress" and shrinkage rate as a result of understanding the shrinkage mechanism shown below.

Here, we explain the shrinkage mechanism that the inventors have discovered.

In extrusion molding technology, molten resin extruded from a die is stretched to produce a product (extrusion molded product) of the desired dimensions. At this time, the "drawdown stress" applied to the extruded molten resin stretches the polymer chains of the polymer that constitutes the molten resin, and the molten resin is water-cooled in the stretched state. When the resin is then exposed to a high temperature again by annealing, the "drawdown stress" applied to the resin is eliminated, causing the resin to shrink. The resin shrinks due to the above mechanism. Therefore, according to this mechanism, it can be seen that the "drawdown stress" is one of the factors that causes the shrinkage of extrusion molded products that contain resin as a constituent material. Taking this into consideration, the inventor has come to surmise that there is a correlation between the "drawdown stress" and the shrinkage rate.

<<Relationship between "Drawdown Stress" and Viscosity>>
Next, it will be explained that the "draw stress" is correlated with viscosity. According to the above-mentioned mechanism, the "draw stress" applied to the extruded molten resin causes the polymer chains of the polymers that are the constituent materials of the molten resin to elongate. Therefore, it can be considered that the "draw stress" is influenced by the material properties of the resin. In particular, since it is considered that the "draw stress" is greatly influenced by the fluidity of the resin, it is presumed that the "draw stress" is correlated with the viscosity that represents the fluidity of the resin. For example, since it is understood that the "draw stress" also increases qualitatively as the viscosity increases, it is reasonable to presume that there is a correlation between the "draw stress" and the viscosity.

<<Relationship between viscosity and "torque current">>
Next, it will be explained that viscosity has a correlation with "torque current". For example, kneading of resin is performed by rotating a screw with a motor. At this time, if the viscosity of the resin is high, the energy required to rotate the screw to knead the resin is large. This means that a large load is applied to the motor that rotates the screw, and as a result, the "torque current" for rotating the motor is large. On the other hand, if the viscosity of the resin is low, the load applied to the motor to knead the resin is small. This means that the "torque current" is small. Therefore, it can be considered reasonable that a correlation exists between viscosity and "torque current".

Below, experimental results showing that there is a correlation between viscosity and "torque current" will be described. First, the viscosity is calculated. Specifically, the viscosity can be expressed by (Formula I) described later, and the viscosity can be calculated based on this (Formula I). For example, based on the resin and extrusion conditions of the extruder used in the experiment, the "viscosity constant η ₀ " included in (Formula I) is 9.11×10 ¹¹ (Pa·s ⁿ ), the "temperature coefficient α" is 8.42×10 ² (1/° C.), and the "viscosity index n" is 0.225.

In the case of the viscosity of the resin being extruded from the extruder and stretched, the (dγ/dt) in (Formula I) is the "strain rate." In contrast, in the case of the viscosity of the resin being kneaded inside the extruder, the (dγ/dt) in (Formula I) is the "shear rate."

If we assume that the "shear rate" is constant inside the extruder, and consider it to be a constant, the viscosity η can be calculated from the resin temperature T based on (Formula I).

Therefore, the temperature of the resin extruded from the extruder is measured. Specifically, a thermocouple was inserted into a hole drilled at the tip of the extruder to measure the temperature of the resin. Figure 3 is a graph showing the measurement results (experimental data) of the resin temperature.

Then, the viscosity is calculated by substituting the experimental data shown in Figure 3 into (Formula I). Figure 4 is a graph showing the time dependence of the viscosity calculated based on the experimental data (shown in black) and the time dependence of the torque current output from the extruder (shown in gray).

As shown in Figure 4, if you focus on the peak positions circled, you can see that there is a correlation between the calculated viscosity value and the torque current value. From the above experimental results, it is considered reasonable that a correlation exists between viscosity and "torque current."

The above is summarized as shown in FIG. 5. FIG. 5 is a diagram explaining the validity of the existence of a correlation between the "torque current" and the shrinkage rate of the extrusion molded product. In FIG. 5, from the above-mentioned qualitative explanation, first, it is presumed that there is a correlation (first correlation) between the "drawdown stress" and the shrinkage rate. Then, it is presumed that there is a correlation (second correlation) between the "drawdown stress" and the viscosity, and also that there is a correlation (third correlation) between the viscosity and the "torque current". Therefore, when these first correlation, second correlation, and third correlation are taken into consideration comprehensively, it is presumed that there is a correlation between the "torque current" and the shrinkage rate of the extrusion molded product. In other words, when the first correlation, second correlation, and third correlation are taken into consideration, it can be presumed that the "torque current" and the shrinkage rate are mutually correlated through the viscosity and the "drawdown stress". In this way, it is qualitatively understood that there is a correlation between the "torque current" and the shrinkage rate of the extrusion molded product.

<Formulation of correlation>
Furthermore, the present inventors have attempted to go one step beyond the qualitative understanding of the correlation between the "torque current" and the shrinkage rate of the extrusion molded product and to formulate the correlation, and this point will be explained.

Figure 6 shows the procedure for formulating the correlation between "torque current" and contraction rate.

As shown in Figure 6, the first step is to formulate the correlation between viscosity and "torque current". Then, the second step is to formulate the correlation between "pull-down stress" and "torque current", and the third step is to formulate the correlation between contraction rate and "torque current".

Below, we explain how the correlation between contraction rate and "torque current" can ultimately be formulated by following the procedure shown in Figure 6.

<<Step 1: Formulation of the correlation between viscosity and "torque current">>
Generally, viscosity is expressed by the following formula (I):

Where:
t: Time η: Viscosity η ₀ : Viscosity constant α: Temperature coefficient T: Resin temperature dγ/dt: Strain rate n: Viscosity index

<<<<Explanation of strain rate>>>>
Here, the "strain rate" included in (Equation I) will be explained.

Figure 7 is a schematic diagram explaining "strain rate."

In Fig. 7, the cross-sectional area of the outlet of the die 13 is indicated by " _Sd ". Molten resin 20R is extruded from the outlet of the die 13. At this time, the average flow velocity of the molten resin 20R extruded from the outlet of the die 13 is " _vd ". The molten resin 20R extruded from the outlet of the die 13 at the average flow velocity " _vd " is stretched by the addition of a linear velocity " _vf ". Here, " _Sf " shown in Fig. 7 is the cross-sectional area of a molded product made of a conductor coated with molten resin 20R. Also, "L" shown in Fig. 7 is the distance (draw-down distance) from the outlet of the die 13 to the water tank 15.

In such a configuration, the "strain rate" is expressed as follows (Equation II):

Where:
dγ/dt: strain rate v _d : average flow velocity of molten resin at the die outlet v _f : linear velocity L: distance from the die outlet to the water tank (draw-down distance)

That is, the "strain rate" is defined as a physical quantity obtained by dividing the difference between the average flow velocity " _vd " and the linear velocity " _vf " by the distance "L" from the outlet of the die 13 to the water tank 15. The "strain rate" defined in this way is zero, for example, if the average flow velocity " _vd " and the linear velocity " _vf " are equal. In other words, when the average flow velocity " _vd " and the linear velocity " _vf " are equal, it can be considered that no distortion is qualitatively applied to the molten resin 20R, so it can be understood that the "strain rate", which is a physical quantity related to the distortion of the molten resin 20R, is zero. In addition, it can be considered that the greater the difference between the average flow velocity " _vd " and the linear velocity " _vf ", the greater the distortion applied to the molten resin, so it is appropriate that the "strain rate" is expressed by (Formula II).

<<<<Linearity Assumption>>>
Next, in formulating the correlation between the viscosity and the "torque current" expressed by the above (Equation I), the linearity of the viscosity and the "torque current" is assumed. This assumption is appropriate because it is consistent with the qualitative understanding that, for example, as the viscosity increases, the "torque current" also increases. Based on this assumption, the viscosity is expressed by the following (Equation III).

Where:
t: time η: viscosity a: constant τ: torque current b: constant

According to the inventors' investigations, it has been found, as a new finding, that when the "torque current" is changed, the average flow velocity (v _d ), linear velocity (v _f ), draw distance (L) from the die exit to the water tank, temperature (T) of the resin, temperature coefficient (α), and viscosity index (n) are almost constant, whereas the viscosity constant (η ₀ ) of the resin mainly changes.

Based on this knowledge, the linearity between the viscosity and the "torque current" expressed by (Equation III) is approximately equivalent to expressing the viscosity constant (η ₀ ) by (Equation IV) shown below.

Where:
t: time η ₀ : viscosity constant a ₀ : constant τ: torque current b ₀ : constant

In this way, the correlation between viscosity and "torque current" can be formulated.

<<Second stage: Formulation of the correlation between "pull-down stress" and "torque current">>
Next, the formulation of the correlation between the "pull-down stress" and the "torque current" will be described.

The correlation between "pull-down stress" and viscosity is expressed by the following formula (Equation V):

Where:
t: time σ: pull-down stress η: viscosity dγ/dt: strain rate η ₀ : viscosity constant α: temperature coefficient T: resin temperature n: viscosity index

For example, the formulation of "pulling stress σ" (Formula V) includes "viscosity η" and expresses the relationship "pulling stress σ" ∝ "viscosity η". In this way, the formulation of "pulling stress" (Formula V) takes into account the material property of the resin's viscosity and the extrusion conditions including temperature and strain rate, and since it can be considered that qualitatively as the viscosity increases, the "pulling stress" also increases, the formulation using (Formula V) can be said to be consistent with a qualitative understanding.

The formula for "pull-down stress" (Equation V) has the following usefulness:

(1) (Formula V) is a relational equation that takes into account both the material property of the resin, namely its viscosity, and the extrusion conditions, namely the resin temperature and strain rate. This makes it possible to estimate the "drawdown stress" with a high degree of accuracy, compared to formulations that only consider the material properties or formulations that only consider the extrusion conditions. This means that if there is a high correlation between the "drawdown stress" and the "shrinkage rate" of the extrusion molded product, then it is possible to estimate the "shrinkage rate" with a high degree of accuracy, taking into account both the material properties and the extrusion conditions. For this reason, the formulation using (Formula V) is very significant.

(2) Next, the formula (Formula V) for formulating the "drawing stress" does not include the degree of crystallinity. This is because, as shown in FIG. 2, the resin extruded from the die 13 (for example, the temperature of the resin is 180°C to 200°C) is molten resin 20R, which is cooled and crystallized in the water tank 15. Therefore, before reaching the water tank 15, the resin is in a molten state and there is no need to consider the degree of crystallinity. In other words, the "drawing stress" is significant in that it does not include the degree of crystallinity as a parameter. In other words, the formula (Formula V) for formulating the "drawing stress" with a focus on the "drawing stress" does not include the parameter "degree of crystallinity" that requires measurement, and therefore it can be said to be significant in that it can be easily introduced in real time in the manufacturing process of extrusion molded products.

Next, by substituting the relationship of (Formula IV) for the viscosity constant (η ₀ ) included in (Formula V) representing the “drawdown stress”, the following (Formula VI) is obtained.

Where:
t: time σ: pull-down stress a ₀ : constant τ: torque current b ₀ : constant α: temperature coefficient T: resin temperature dγ/dt: strain rate n: viscosity index

In this way, the correlation between "pull-down stress" and "torque current" can be formulated.

<<Third step: Formulation of correlation between contraction rate and "torque current">>
Next, the formulation of the correlation between the contraction rate and the "torque current" will be described.

As mentioned above, it is presumed that the shrinkage rate is correlated with the "drawdown stress". Therefore, the present inventor proposes to assume linearity in the correlation between the shrinkage rate and the "drawdown stress". For example, according to the shrinkage mechanism, the "drawdown stress" causes the polymer chains of the polymers that are the constituent materials of the molten resin to elongate. It is considered that the degree of this elongation increases as the "drawdown stress" increases. When the resin is exposed to a high temperature condition by annealing, the "drawdown stress" applied to the resin is eliminated, and as a result, the resin shrinks. Considering this, it is understood that the greater the degree of elongation, the greater the shrinkage rate. In other words, it is considered that the greater the "drawdown stress", the greater the shrinkage rate of the extrusion molded product that contains the resin as a constituent material. Therefore, it is reasonable to assume linearity between the "drawdown stress" and the shrinkage rate of the extrusion molded product.

Assuming this linearity, the correlation between "pull down stress" and shrinkage rate is expressed as shown below (Equation VII).

Where:
t: time ε: shrinkage rate A: constant σ: pull-down stress C: constant

Then, by substituting the "pull-down stress" expressed by (Formula VI) into (Formula VII), we obtain (Formula VIII) shown below.

Where:
t: time ε: shrinkage rate A ₀ = Aa ₀ : constant τ: torque current B ₀ = Ab ₀ : constant α: temperature coefficient T: resin temperature dγ/dt: strain rate n: viscosity index C: constant

In this manner, the correlation between the shrinkage rate and the "torque current" can be formulated. According to the thus formulated (Formula VIII), if the constants _A0 , _B0 , C, temperature coefficient α, and viscosity index n are known, the shrinkage rate (ε) of the extrusion molded product can be estimated based on the extrusion conditions consisting of the resin temperature (T) and strain rate (dγ/dt) and the "torque current."

<Results of correlation verification>
Below, we will explain the verification results that support the present inventor's insight that there is a correlation between the shrinkage rate of the extrusion molded product and the "torque current". In other words, we will explain the verification results that support the existence of a high correlation between the shrinkage rate and the "torque current".

To verify the correlation between the shrinkage rate and the "torque current," an extrusion experiment is carried out using, for example, an extrusion molding system having the configuration shown in Figure 1. Specifically, in the extrusion experiment, a thermoplastic polyurethane resin is used, and the resin temperature and strain rate are adopted as the extrusion conditions.

Specifically, a crosshead was attached to an extruder equipped with a full-flight screw with an outer diameter of 40 mm, and a die with a hole diameter of 2.25 mm was used to produce a string-like sample consisting of an extrusion molded product (cable) with an outer diameter of 1.5 mm at a linear speed of 20 m/min. At this time, the temperature of the crosshead and die (corresponding to the temperature of the resin) was changed to 185°C, 190°C, and 195°C, and the "torque current" during extrusion was recorded every second with a data logger. This allows data to be obtained for a string-like sample whose viscosity has been changed by changing the temperature of the resin. The shrinkage rate was measured using the string-like sample obtained in this way.

Specifically, string-like samples were taken every 600 seconds during extrusion and cut to approximately 500 mm. The lengths of the cut string-like samples were then measured before and after annealing at 130°C for three hours, and the shrinkage rate was calculated based on the formula "(length before annealing) - (length after annealing)}/(length before annealing) x 100." This allows for the acquisition of actual measurement data showing the relationship between shrinkage rate and "torque current."

Figure 8 is a graph plotting the actual measured data.

In Figure 8, the horizontal axis indicates "torque current" (A), while the vertical axis indicates the shrinkage rate (%). The circles in Figure 8 indicate data for a resin temperature of 185°C, the diamonds indicate data for a resin temperature of 190°C, and the crosses indicate data for a resin temperature of 195°C.

As shown in FIG. 8, the correlation coefficient (R) between the "torque current" and the contraction rate is "0.89". Considering that the closer the correlation coefficient is to 1, the higher the correlation, it can be seen that there is a high correlation between the "torque current" and the contraction rate. In particular, it can be seen that the actual measurement data has a roughly linear relationship as shown by the dashed line, and therefore it can be seen that the formulation of the correlation between the contraction rate and the "torque current" using (Equation VIII) is valid.

The above experimental results support the existence of a high correlation between the "torque current" and the shrinkage rate, and confirm the inventor's assumption that a high correlation exists between the "torque current" and the shrinkage rate. Therefore, it can be seen that the technical idea of estimating the shrinkage rate of an extrusion molded product based on the "torque current" formulated in (Equation VIII) is extremely useful in that it takes into account both the material properties and the extrusion conditions, and that it can be introduced in real time into the manufacturing process of the extrusion molded product.

For example, if we take the example of an insulating resin that covers a conductor as an extrusion molded product, being able to estimate the shrinkage rate of the insulating resin in real time means being able to continuously grasp the shrinkage rate in the longitudinal direction of the insulating resin as it is extruded from the extruder.

<Further consideration>
According to the basic concept of the present embodiment described above, for example, the shrinkage rate of the extrusion molded product can be estimated in real time in the manufacturing process of the extrusion molded product based on the formula (VIII). However, in the basic concept described above, if the estimated shrinkage rate is larger than a predetermined value, it can be known that the quality of the extrusion molded product manufactured in the manufacturing process of the extrusion molded product is poor, but it does not take into consideration the prevention of the production of poor quality extrusion molded products.

Therefore, the inventors have gone one step further from the basic concept and devised a method to prevent the production of poor quality extrusion molded products even when the estimated shrinkage rate is greater than a predetermined value, thereby ensuring the quality of the extrusion molded products produced in the extrusion molded product manufacturing process.

The following explains the development ideas behind this embodiment.

<Development Concept in the Embodiment>
The developed idea in this embodiment is a relational equation that relates the torque current of a motor provided in the extruder to the shrinkage rate of an extrusion molded product that contains a resin extruded from the extruder as a constituent material, and is premised on estimating the shrinkage rate based on the relational equation that includes a constant parameter. The developed idea is that when the estimated shrinkage rate is greater than a predetermined value (e.g., 5%), the value of the constant parameter is changed to a first value that makes the value of the shrinkage rate equal to or less than the predetermined value, and then the extrusion molding system that reflects the change of the constant parameter to the first value continues to manufacture the extrusion molded product.

As a result, according to the developed concept, even if the estimated shrinkage rate is greater than a predetermined value, the extrusion molding system can be modified so that the shrinkage rate is equal to or less than the predetermined value, thereby preventing the production of poor quality extrusion molded products with shrinkage rates greater than the predetermined value. In other words, according to the developed concept, the quality of the extrusion molded products manufactured can be ensured by feedback controlling the extrusion molding system based on the estimated shrinkage rate.

For example, the above-mentioned relational expression can be expressed by (Formula VIII). (Formula VIII) is an expression that relates the variables "torque current τ(t)" and "contraction rate ε(t)", and (Formula VIII) includes a "constant" and a "constant parameter".

In this specification, a distinction is made between "constants" and "constant parameters", so this point will be explained. The "constants" included in (Formula VIII) mean "constant A ₀ ", "constant B ₀ ", "constant C", "temperature coefficient α", and "viscosity index n". On the other hand, the "constant parameters" included in (Formula VIII) mean "resin temperature T" and "strain rate dγ/dt". Furthermore, considering that "strain rate dγ/dt" is expressed by (Formula II), the "constant parameters" mean "resin temperature T", "average flow rate v _d of molten resin at the outlet of the die", "linear speed v _f ", and "draw-down distance L". Therefore, the "constant parameters" can be considered to be included in the configuration parameters (e.g., "draw-down distance L") that define the configuration of the extrusion molding system that produces the extrusion molded product, or the condition parameters (e.g., "resin temperature T", "average flow rate v _d of molten resin at the outlet of the die", "linear speed v _f ") that define the extrusion conditions in the extruder.

The following is a flowchart explaining the development concept of this embodiment.

Figure 9 is a flowchart to explain the development concept.

In FIG. 9, first, for example, the shrinkage rate is estimated by using (Formula VIII) as a relational expression (S101). Specifically, the torque current output from the motor of the extruder is input in real time and substituted into (Formula VIII), so that the real-time shrinkage rate can be estimated. Then, it is determined whether the estimated shrinkage rate is greater than a predetermined value (S102). At this time, if the estimated shrinkage rate is greater than a predetermined value (threshold value), if the production of the extrusion molding is continued as it is, there is a high possibility that a poor-quality extrusion molding with a shrinkage rate greater than the threshold value will be produced. For this reason, in the developed idea, the value of the "constant parameter" included in (Formula VIII) is changed. That is, in the developed idea, after finding the value (first value) of the "constant parameter" that makes the value of the shrinkage rate equal to or less than the predetermined value, the value of the "constant parameter" in (Formula VIII) used for the estimation is changed from the original value used for the estimation to the "first value" (S103).

Then, the change of the "constant parameter" to the "first value" is reflected in the extrusion molding system (S104). Here, it is possible to reflect the change of the "constant parameter" to the "first value" in the extrusion molding system because the "constant parameter" is a parameter belonging to the configuration parameters that define the configuration of the extrusion molding system or the condition parameters that define the extrusion conditions in the extruder. Next, resin extrusion molding is performed in the extrusion molding system after the reflection (S105). This means that resin extrusion molding is performed in the extrusion molding system that has been changed so that the shrinkage rate is equal to or less than a predetermined value, and therefore the production of poor quality extrusion molded products with a shrinkage rate greater than the predetermined value is suppressed.

If extrusion molding is to be continued, the process returns to step S101 (S106), whereas if extrusion molding is to be terminated, the process terminates the extrusion molding. Here, in step S101 to which the process returns, the shrinkage rate is estimated by using the changed "first value" as the "constant parameter" of (Equation VIII).

If the estimated shrinkage rate is equal to or less than a predetermined value (threshold value) in step S102, extrusion molding of the resin is performed using the current extrusion molding system, since there is a low possibility that an extrusion molding product with a shrinkage rate greater than the predetermined value and poor quality will be produced even if the extrusion molding is performed using the current extrusion molding system (S105). Then, if extrusion molding is to be continued, the process returns to step S101 (S106), whereas if extrusion molding is to be terminated, extrusion molding is terminated.

As described above, according to the developed concept of this embodiment, even if the estimated shrinkage rate is greater than a predetermined value, the extrusion molding system can be changed so that the shrinkage rate is equal to or less than the predetermined value, thereby preventing the production of poor quality extrusion molded products with shrinkage rates greater than the predetermined value. In other words, according to the developed concept, the quality of the extrusion molded products produced can be ensured by changing the extrusion molding system based on the estimated shrinkage rate.

<Selecting "Constant parameters">
As the "constant parameters" for realizing the above-mentioned developmental idea, configuration parameters (e.g., "draw-down distance L") that define the configuration of the extrusion molding system that produces the extrusion molded product, or condition parameters (e.g., "resin temperature T", "average flow velocity v _d of the molten resin at the die outlet", "linear velocity v _f ") that define the extrusion conditions in the extruder can be used.

However, according to the inventor's investigation, the "pull-down distance L" is preferable as a "constant parameter" that makes it easier to realize the developed idea. The reason for this will be explained below.

For example, when "resin temperature T" is used as the "constant parameter," if the estimated shrinkage rate is greater than a predetermined value (threshold value), for example, based on a group of data showing the relationship between the previously acquired "resin temperature T" value and the "shrinkage rate" value, a value of "resin temperature T" (say T1) at which the shrinkage rate value is equal to or less than a predetermined value is found, and then the value of "resin temperature T" in (Formula VIII) used for the estimation is changed from the original value used for the estimation to "T1." The change in "resin temperature T" to "T1" is then reflected in the extrusion molding system. Specifically, this means controlling the temperature of the resin being injected into the extruder.

However, it is difficult to control the temperature of the resin being injected into the extruder in order to change the value of "resin temperature T" to "T1". For example, even if you try to set the temperature of the resin being injected into the extruder to "T1", it takes time for the value of "resin temperature T" to actually stabilize at "T1" after the setting. As a result, there is a time lag between setting the value of the resin temperature to "T1" and the actual value of the resin temperature becoming "T1". Therefore, it is difficult to reflect the change of "resin temperature T" to "T1" in real time in the extrusion molding system. For this reason, if "resin temperature T" is selected as a "constant parameter", it is difficult to easily embody the above-mentioned developmental idea.

Furthermore, when "average flow velocity v _d of molten resin at the die outlet" is used as the "constant parameter", for example, the cross-sectional area "S _d " at the die outlet shown in Fig. 7 is fixed, so it is difficult to reflect changes in "average flow velocity v _d of molten resin at the die outlet" in the extrusion molding system. Furthermore, when "linear speed v _f " is used as the "constant parameter", it is considered difficult to change "linear speed v _f " over time in real time.

On the other hand, if the "withdrawal distance L" is used as the "constant parameter," changing the "withdrawal distance L" can be easily achieved by changing the position of the water tank.

Therefore, the developed idea in this embodiment can use as a "constant parameter" a configuration parameter (e.g., "draw-down distance L") that defines the configuration of an extrusion molding system that produces an extrusion molded product, or a condition parameter (e.g., "resin temperature T,""average flow velocity v _d of molten resin at the die outlet,""linear velocity v _f ") that defines the extrusion conditions in the extruder, but from the viewpoint of easily embodying the developed idea in practice, it is found that it is desirable to adopt the "draw-down distance L" as the "constant parameter." Therefore, hereinafter, a shrinkage rate estimation system that embodies the developed idea by adopting the "draw-down distance L" as the "constant parameter" will be described.

<Configuration of shrinkage rate estimation system>
FIG. 10 is a schematic diagram showing the configuration of a shrinkage ratio estimation system 500. As shown in FIG.

In FIG. 10, the shrinkage rate estimation system 500 includes an extruder 11 that extrudes resin, a crosshead 12 attached to the extruder 11, a die 13 attached to the crosshead 12, a conductor 14 that moves along a travel line, and a water tank 15 for water-cooling the resin. Furthermore, the shrinkage rate estimation system 500 includes a shrinkage rate estimation device 100 that estimates the shrinkage rate by inputting the torque current output from the extruder 11, a distance adjustment unit 20 that adjusts the position of the water tank 15 based on the output from the shrinkage rate estimation device 100, and a drive unit 30 attached to the water tank 15. In this manner, the shrinkage rate estimation system 500 is configured.

<Operation of the shrinkage ratio estimation system>
Next, the operation of the shrinkage ratio estimation system 500 will be briefly described.

In FIG. 10, raw pellets, which are the raw material for the coating material, are fed into an extruder 11 and kneaded, and molten resin is extruded from a die 13 via a crosshead 12. The extruded resin coats the surface of a conductor 14 moving along a travel line. The resin coated on the surface of the conductor 14 is then air-cooled immediately after being extruded from the die 13, and then water-cooled in a water tank 15. At this time, the distance from the exit of the die 13 to the water tank 15 is the "draw-down distance L."

Here, the extruder 11 outputs the torque current value to the shrinkage estimation device 100. The shrinkage estimation device 100 estimates the shrinkage based on the torque current value input from the extruder 11 and the relational expression shown in (Formula VIII). If it is determined that the estimated shrinkage is greater than a predetermined value (threshold value), it changes the "draw-down distance L" and outputs it to the distance adjustment unit 20. When the distance adjustment unit 20 inputs the changed "draw-down distance L" from the shrinkage estimation device 100, it controls the drive unit 30 attached to the water tank 15 to adjust the position of the water tank 15 so that the "draw-down distance L" becomes the value changed by the shrinkage estimation device 100. Then, the extrusion molding is manufactured at the adjusted position of the water tank 15.

In this way, the shrinkage rate estimation system 500 of this embodiment operates to produce high-quality extrusion molded products with a shrinkage rate below a predetermined value.

<Configuration of the shrinkage ratio estimation device>
Next, the configuration of the shrinkage ratio estimation device 100, which is a component of the above-mentioned shrinkage ratio estimation system 500, will be described with reference to the drawings.

<<Hardware configuration>>
First, the hardware configuration of the shrinkage ratio estimation device according to this embodiment will be described.

Figure 11 is a diagram showing an example of the hardware configuration of the contraction ratio estimation device 100 in this embodiment. Note that the configuration shown in Figure 11 is merely an example of the hardware configuration of the contraction ratio estimation device 100, and the hardware configuration of the contraction ratio estimation device 100 is not limited to the configuration shown in Figure 11, and may be other configurations.

In FIG. 11, the shrinkage rate estimation device 100 includes a CPU (Central Processing Unit) 101 that executes a program. This CPU 101 is electrically connected to, for example, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, and a hard disk drive 112 via a bus 113, and is configured to control these hardware devices.

The CPU 101 is also connected to input devices and output devices via the bus 113. Examples of input devices include the keyboard 105, the mouse 106, the communication board 107, and the scanner 111. Examples of output devices include the display 104, the communication board 107, and the printer 110. The CPU 101 may also be connected to, for example, a removable disk device 108 and a CD/DVD-ROM device 109.

The contraction ratio estimation device 100 may be connected to a network, for example. For example, when the contraction ratio estimation device 100 is connected to other external devices via a network, the communication board 107 constituting a part of the contraction ratio estimation device 100 is connected to a LAN (local area network), a WAN (wide area network), or the Internet.

RAM 103 is an example of a volatile memory, and the recording media ROM 102, removable disk device 108, CD/DVD-ROM device 109, and hard disk device 112 are examples of non-volatile memory. These volatile and non-volatile memories constitute the storage device of the shrinkage rate estimation device 100.

The hard disk device 112 stores, for example, an operating system (OS) 201, a group of programs 202, and a group of files 203. The programs included in the group of programs 202 are executed by the CPU 101 using the operating system 201. The RAM 103 also temporarily stores at least some of the programs of the operating system 201 and application programs executed by the CPU 101, as well as various data required for processing by the CPU 101.

The ROM 102 stores a BIOS (Basic Input Output System) program, and the hard disk drive 112 stores a boot program. When the shrinkage rate estimation device 100 is started, the BIOS program stored in the ROM 102 and the boot program stored in the hard disk drive 112 are executed, and the operating system 201 is started by the BIOS program and the boot program.

The program group 202 stores programs that realize the functions of the shrinkage rate estimation device 100, and these programs are read and executed by the CPU 101. In addition, the file group 203 stores information, data, signal values, variable values, and parameters that indicate the results of processing by the CPU 101 as each item of a file.

The files are recorded on a recording medium such as the hard disk drive 112 or memory. The information, data, signal values, variable values, and parameters recorded on the recording medium such as the hard disk drive 112 or memory are read by the CPU 101 into the main memory or cache memory, and are used for the operations of the CPU 101, such as extraction, search, reference, comparison, calculation, processing, editing, output, printing, and display. For example, during the above-mentioned operations of the CPU 101, the information, data, signal values, variable values, and parameters are primarily stored in the main memory, registers, cache memory, buffer memory, etc.

The functions of the shrinkage rate estimation device 100 may be realized by firmware stored in ROM 102, or may be realized by software alone, by hardware alone such as elements, devices, boards, and wiring, a combination of software and hardware, or even a combination with firmware. The firmware and software are recorded as programs on a recording medium such as the hard disk drive 112, a removable disk, a CD-ROM, or a DVD-ROM. The programs are read and executed by the CPU 101. In other words, the programs cause the computer to function as the shrinkage rate estimation device 100.

In this way, the contraction rate estimation device 100 is a computer equipped with a CPU 101 as a processing device, a hard disk drive 112 and memory as storage devices, a keyboard 105, a mouse 106, and a communication board 107 as input devices, and a display 104, a printer 110, and a communication board 107 as output devices. The functions of the contraction rate estimation device 100 are realized by utilizing the processing device, the storage device, the input device, and the output device.

<<Prerequisites>>
Next, a functional block configuration of the shrinkage ratio estimation device 100 will be described, but before that, a prerequisite will be described. The shrinkage ratio estimation device 100 estimates the shrinkage ratio by substituting the value of the torque current input from the extruder into (Equation VIII).

Here, (Formula VIII) includes "constants" such as "constant A ₀ ", "constant B ₀ ", "constant C ", "temperature coefficient α ", and "viscosity index n". These five "constants" are determined, for example, by the method described in the inventor's prior application (Patent Application No. 2020-216933). In addition, (Formula VIII) includes "resin temperature T" and "strain rate dγ/dt", and considering that "strain rate dγ/dt" is expressed by (Formula II), the "constant parameters" include "resin temperature T", "average flow velocity v _d of the molten resin at the outlet of the die", "linear velocity v _f ", and "drawdown distance L".

In this embodiment, these "constant parameters" are set to constant values. In other words, (Formula VIII) is a formula for estimating the contraction rate using the torque current as a variable, and the "constant parameters" included in (Formula VIII) are set to constant values.

However, the "constant parameter" is a parameter that belongs to the configuration parameters that define the configuration of the extrusion molding system that produces the extrusion molded product, or the condition parameters that define the extrusion conditions in the extruder. Taking this into consideration, it is considered that changing the value of the "constant parameter" in (Equation VIII) will change the value of the shrinkage rate.

Therefore, in the developed concept of this embodiment, the relationship between the value of the "constant parameter" and the value of the shrinkage rate is acquired in advance. For example, a group of data showing the relationship between the value of the "constant parameter" and the value of the shrinkage rate is acquired in advance, and this group of data is stored as a database.

Specifically, in this embodiment, a group of data showing the relationship between the value of "pull-down distance L" and the value of the shrinkage rate is acquired in advance. For example, FIG. 12 is a graph showing the relationship between "pull-down distance L" and the shrinkage rate. In this embodiment, a group of data corresponding to the graph shown in FIG. 12 is acquired, and, for example, this group of data is stored as a database.

<<Function block configuration>>
FIG. 13 is a functional block diagram showing the functional configuration of the shrinkage ratio estimation device 100.

The shrinkage ratio estimation device 100 has an input unit 301, a shrinkage ratio estimation unit 302, a determination unit 303, a distance value change unit 304, an output unit 305, and a data storage unit 306.

First, the data storage unit 306 stores (Equation VIII) in which the "constants" and "constant parameters" have been determined, as explained in the prerequisites above.

The data storage unit 306 also stores, for example, a "shrinkage rate-withdrawal distance related data group" corresponding to the graph shown in FIG. 12.

The input unit 301 has the function of inputting various data, and is configured to input, for example, the value of the torque current output from the extruder.

The contraction rate estimation unit 302 is configured to estimate the contraction rate by acquiring (Formula VIII) stored in the data storage unit 306, and then substituting the value of the torque current input to the input unit 301 into (Formula VIII).

The determination unit 303 is configured to determine whether the shrinkage rate estimated by the shrinkage rate estimation unit 302 is greater than a predetermined value (threshold value).

The distance value change unit 304 is configured to change the value of the "drop distance L" included in (Formula VIII) based on the result of the determination by the determination unit 303.

Specifically, when the determination unit 303 determines that the shrinkage rate estimated by the shrinkage rate estimation unit 302 is greater than a predetermined value (threshold value), the distance value change unit 304 is configured to change the value of "withdrawal distance L" in (Formula VIII) from the original value used for estimation to a value that makes the shrinkage rate value equal to or less than the predetermined value, based on the "shrinkage rate-withdrawal distance related data group" stored in the data storage unit 306.

However, the distance value change unit 304 is not limited to being configured to change the "withdrawal distance L" based on the "shrinkage rate-withdrawal distance related data group", and may be configured to change the "withdrawal distance L" using, for example, (Formula VIII).

Specifically, the distance value change unit 304 can be configured to change the original "drop distance L" value used for the estimation to a "drop distance L" value calculated as a result of substituting the torque current value input to the input unit 301 and the shrinkage rate value equal to or less than a predetermined value into (Formula VIII).

The output unit 305 is configured to output the value of the "withdrawal distance L" (the "first value") changed by the distance value change unit 304.

<Operation of the shrinkage ratio estimation device>
The shrinkage ratio estimation apparatus 100 in this embodiment is configured as described above. The operation of the shrinkage ratio estimation apparatus 100 will be described below with reference to FIG.

Figure 14 is a flowchart explaining the operation of the shrinkage rate estimation device 100.

In FIG. 14, the input unit 301 inputs, for example, the value of the torque current output from the extruder (S201). Then, the shrinkage rate estimation unit 302 estimates the shrinkage rate by substituting the value of the torque current input to the input unit 301 into (Equation VIII) (S202).

Next, the determination unit 303 determines whether the value of the shrinkage ratio estimated by the shrinkage ratio estimation unit 302 is greater than a predetermined value (S203).

When the determination unit 303 determines that the value of the shrinkage rate estimated by the shrinkage rate estimation unit 302 is greater than a predetermined value, the distance value change unit 304 changes the value of the "drop distance L" (S204).

As a specific example, the distance value change unit 304 changes the value of "withdrawal distance L" in (Formula VIII) from the original value used for estimation based on the "shrinkage rate-withdrawal distance related data group" stored in the data storage unit 306 to a value that makes the shrinkage rate value equal to or less than a predetermined value (a value smaller than the predetermined value or a value equal to the predetermined value).

As another specific example, the distance value change unit 304 changes the original "drop distance L" value used for the estimation to the "drop distance L" value calculated as a result of substituting the torque current value input to the input unit 301 and an arbitrary shrinkage rate value equal to or less than a predetermined value into (Formula VIII).

Then, the output unit 305 outputs the changed value of "withdrawal distance L" (S205).

On the other hand, if the determination unit 303 determines that the value of the shrinkage ratio estimated by the shrinkage ratio estimation unit 302 is equal to or less than the predetermined value, the processing of steps S204 and S205 is not performed.

Next, if the operation of the contraction ratio estimation device 100 is to be continued (S206), the process returns to step S201. On the other hand, if the operation of the contraction ratio estimation device 100 is to be ended (S206), the process in the contraction ratio estimation device 100 is ended.

Note that S203 in FIG. 14 may be changed to "Shrinkage ratio ≧predetermined value?" In other words, the determination unit 303 may be changed to determine whether the value of the shrinkage ratio estimated by the shrinkage ratio estimation unit 302 is equal to or greater than a predetermined value (a value greater than or equal to the predetermined value). If the determination unit 303 determines that the value of the shrinkage ratio estimated by the shrinkage ratio estimation unit 302 is equal to or greater than the predetermined value, the distance value change unit 304 changes the value of "pull-down distance L" so that the value of the shrinkage ratio becomes smaller than the predetermined value. If the determination unit 303 determines that the value of the shrinkage ratio estimated by the shrinkage ratio estimation unit 302 is smaller than the predetermined value, the processes of steps S204 and S205 are not performed.

By operating the shrinkage rate estimation device 100 in the manner described above, the shrinkage rate estimation method of this embodiment is realized.

<Shrinkage rate estimation program>
The shrinkage ratio estimation method performed by the above-described shrinkage ratio estimation device 100 can be realized by a shrinkage ratio estimation program that causes a computer to execute a shrinkage ratio estimation process.

For example, in the contraction ratio estimation device 100 consisting of a computer shown in FIG. 11, the contraction ratio estimation program in this embodiment can be introduced as one of the program group 202 stored in the hard disk device 112. Then, by having the computer that is the contraction ratio estimation device 100 execute this contraction ratio estimation program, the contraction ratio estimation method in this embodiment can be realized.

The shrinkage rate estimation program that causes a computer to execute each process for creating data related to the shrinkage rate estimation process can be recorded on a computer-readable recording medium and distributed. Recording media include, for example, magnetic storage media such as hard disks and flexible disks, optical storage media such as CD-ROMs and DVD-ROMs, and hardware devices such as non-volatile memories such as ROMs and EEPROMs.

<Method of manufacturing extrusion molded product>
For example, in the past, there was no shrinkage rate estimation technique that could be introduced in real time into the manufacturing process of extrusion molded products, so the shrinkage rate was reduced by adjusting the extrusion conditions based on the experience of the workers. In this regard, according to the technical idea of the present embodiment, it is possible to introduce an objectively accurate shrinkage rate estimation technique into the manufacturing process (manufacturing line) of extrusion molded products without relying on the experience of the workers.

Furthermore, according to the technical idea of this embodiment, even if the estimated shrinkage rate is greater than a predetermined value, the extrusion molding system can be modified so that the shrinkage rate is equal to or less than the predetermined value, thereby preventing the production of poor quality extrusion molded products with a shrinkage rate greater than the predetermined value. As a result, according to this embodiment, it is possible to reduce the amount of waste of resin material and extrusion molded products (e.g., cables) and improve production efficiency. In other words, the technical idea of this embodiment is to introduce shrinkage rate estimation technology to the extrusion molding production line in real time and to make it possible to modify the extrusion molding system based on the estimated shrinkage rate, thereby achieving the remarkable effect of improving the manufacturing yield of extrusion molded products.

Therefore, below, we will explain the manufacturing process of an extrusion molded product using the shrinkage rate estimation system 500 (extrusion molding system) shown in Figure 10.

Figure 15 is a flowchart showing the manufacturing process for extrusion molded products.

As shown in FIG. 15, first, when the extruder 11 is operated, the extruder 11 outputs the torque current value of the motor provided in the extruder 11 to the shrinkage ratio estimation device 100 (S301).

Next, when the shrinkage ratio estimation device 100 receives the torque current value output from the extruder 11 (S401), it estimates the shrinkage ratio by substituting the torque current value into (Equation VIII) (S402). After that, if the estimated shrinkage ratio value is greater than a predetermined value, the shrinkage ratio estimation device 100 changes the value of "withdrawal distance L" so that a shrinkage ratio equal to or less than the predetermined value is achieved (S403). Then, the shrinkage ratio estimation device 100 outputs the changed value of "withdrawal distance L" to the distance adjustment unit 20 (S404).

Next, when the distance adjustment unit 20 inputs the value of "pull-down distance L" output from the shrinkage rate estimation device 100 (S501), it controls the drive unit 30 attached to the water tank 15 to adjust the position of the water tank 15 so that the input value of "pull-down distance L" is realized. After that, the extrusion molded product is manufactured at the position of the water tank 15 adjusted by the distance adjustment unit 20.

In this way, the manufacturing method for extrusion molded products in this embodiment makes it possible to manufacture extrusion molded products of excellent quality with a shrinkage rate below a specified value.

In addition, in S403 in FIG. 15, when the estimated shrinkage ratio value is equal to or greater than a predetermined value (a value greater than or equal to the predetermined value), the shrinkage ratio estimation device 100 may change the value of "withdrawal distance L" so that a shrinkage ratio smaller than the predetermined value is achieved. In this case as well, the changed value of "withdrawal distance L" is output from the shrinkage ratio estimation device 100 to the distance adjustment unit 20.

<Effects of the embodiment>
According to the technical idea of this embodiment, even if the estimated shrinkage rate is greater than a predetermined value, the extrusion molding system can be changed so that the shrinkage rate is equal to or less than the predetermined value, thereby preventing the production of poor quality extrusion molded products having a shrinkage rate greater than the predetermined value. In other words, according to the developed idea, the extrusion molding system can be changed based on the estimated shrinkage rate, which has great technical significance in that the quality of the extrusion molded products produced can be ensured.

The invention made by the inventor has been specifically described above based on the embodiment thereof, but it goes without saying that the invention is not limited to the above embodiment and can be modified in various ways without departing from the gist of the invention.

For example, the "torque current" of the motor in an extruder varies depending on the type of motor and the shape of the screw, but if a value under standard extrusion conditions (molding conditions) is determined, it is possible to determine the increase or decrease in the shrinkage rate of the extrusion molded product from the relative value. For this reason, as long as the standard conditions of the extruder are known, it is possible to apply the technical ideas in the above-mentioned embodiments to any type of extruder. However, in the case of a full-flight screw, the screw structure is simple, so the technical ideas in the above-mentioned embodiments can be easily applied.

The technical ideas in the above-described embodiments are applicable to a wide variety of resins, including plastics and rubber, and are not limited to, for example, thermoplastic polyurethane resin. In addition, the technical ideas in the above-described embodiments are applicable to a wide variety of extrusion forms, regardless of tube extrusion, wire extrusion, or die shape. Furthermore, the extrusion molded products (products) manufactured by the manufacturing method for extrusion molded products to which the technical ideas in the above-described embodiments are applied can be of any shape or type, such as a sheet, irregular shape, or cable (electric wire).

REFERENCE SIGNS LIST 10 Raw material pellets 11 Extruder 12 Crosshead 13 Die 14 Conductive wire 15 Water tank 20 Distance adjustment unit 20R Molten resin 30 Driving unit 100 Shrinkage ratio estimation device 101 CPU
102 ROM
103 RAM
REFERENCE SIGNS LIST 104 Display 105 Keyboard 106 Mouse 107 Communication board 108 Removable disk device 109 CD/DVD-ROM device 110 Printer 111 Scanner 112 Hard disk device 201 Operating system 202 Program group 203 File group 301 Input section 302 Shrinkage ratio estimation section 303 Determination section 304 Distance value change section 305 Output section 306 Data storage section

Claims (12)

a shrinkage rate estimation unit that estimates the shrinkage rate based on a relational expression that relates a torque current of a motor provided in the extruder to a shrinkage rate of an extrusion molded product that contains a resin extruded from the extruder as a constituent material, the relational expression including a constant parameter;
a numerical value changing unit that changes a value of the constant parameter to a first value that makes the value of the shrinkage ratio equal to or smaller than the predetermined value when the shrinkage ratio estimated by the shrinkage ratio estimating unit is greater than a predetermined value, or changes a value of the constant parameter to a first value that makes the value of the shrinkage ratio smaller than the predetermined value when the shrinkage ratio estimated by the shrinkage ratio estimating unit is equal to or larger than the predetermined value;
A shrinkage rate estimation device comprising: 2. The shrinkage ratio estimation device according to claim 1,
The numerical value change unit changes the value of the constant parameter to the first value based on a data group indicating a relationship between the value of the constant parameter and the value of the shrinkage ratio. 2. The shrinkage ratio estimation device according to claim 1,
The numerical value change unit changes the value of the constant parameter to the first value based on the relational expression. 2. The shrinkage ratio estimation device according to claim 1,
The shrinkage ratio estimation unit estimates the shrinkage ratio of the extrusion molded product based on the relational expression formed by Equation 1 shown below.

Where:
t: Time ε(t): Shrinkage rate A ₀ : Constant τ(t): Torque current B ₀ : Constant α: Temperature coefficient T: Resin temperature dγ/dt: Strain rate n: Viscosity index C: Constant 5. The shrinkage ratio estimation device according to claim 4,
The strain rate is expressed by the following equation 2.

Where:
dγ/dt: strain rate v _d : average flow velocity of molten resin at the die outlet v _f : linear velocity L: distance from the die outlet to the water tank (draw-down distance) 6. The shrinkage ratio estimation device according to claim 5,
The constant parameter is L included in the formula 2. a shrinkage rate estimation step of estimating the shrinkage rate based on a relational expression that relates a torque current of a motor provided in an extruder to a shrinkage rate of an extrusion molded product that contains a resin extruded from the extruder as a constituent material, the relational expression including a constant parameter;
a numerical value changing step of changing the value of the constant parameter to a first value that makes the value of the shrinkage ratio equal to or smaller than the predetermined value when the shrinkage ratio estimated in the shrinkage ratio estimating step is greater than a predetermined value, or a numerical value changing step of changing the value of the constant parameter to a first value that makes the value of the shrinkage ratio smaller than the predetermined value when the shrinkage ratio estimated in the shrinkage ratio estimating unit is equal to or greater than the predetermined value;
A method for estimating shrinkage ratio comprising: A program for causing a computer to execute a process for estimating a shrinkage rate of an extrusion molded product containing a resin extruded from an extruder as a constituent material, the program comprising:
a shrinkage ratio estimation process for estimating the shrinkage ratio based on a relational expression that relates a torque current of a motor provided in the extruder to the shrinkage ratio and that includes a constant parameter;
a numerical value changing process for changing a value of the constant parameter to a first value that makes the value of the shrinkage ratio equal to or smaller than the predetermined value when the shrinkage ratio estimated by the shrinkage ratio estimation process is greater than a predetermined value, or a numerical value changing process for changing a value of the constant parameter to a first value that makes the value of the shrinkage ratio smaller than the predetermined value when the shrinkage ratio estimated by the shrinkage ratio estimation unit is equal to or larger than the predetermined value;
A program that includes: A computer-readable recording medium having the program according to claim 8 recorded thereon. An extruder for extruding resin;
A water tank for cooling the resin extruded from the extruder;
a distance adjustment unit capable of adjusting a drop distance between the extruder and the water tank;
a shrinkage rate estimation device for estimating a shrinkage rate of an extrusion molded product containing the resin as a constituent material;
A shrinkage estimation system comprising:
The shrinkage rate estimation device comprises:
a shrinkage rate estimation unit that estimates the shrinkage rate based on a relational expression that relates a torque current of a motor provided in the extruder to the shrinkage rate of the extrusion molded product, the relational expression including the distance as a constant parameter;
a distance value change unit that changes the value of the withdrawal distance to a first value that makes the value of the shrinkage rate equal to or less than the predetermined value when the shrinkage rate estimated by the shrinkage rate estimation unit is greater than a predetermined value, or a distance value change unit that changes the value of the withdrawal distance to a first value that makes the value of the shrinkage rate smaller than the predetermined value when the shrinkage rate estimated by the shrinkage rate estimation unit is equal to or greater than the predetermined value;
having
The distance adjustment unit adjusts a position of the water tank so that the drop distance becomes the first value changed by the distance value change unit. A method for producing an extrusion molded product containing a resin extruded from an extruder as a constituent material, comprising the steps of:
a shrinkage rate estimation step of estimating the shrinkage rate based on a relational expression relating a torque current of a motor provided in the extruder and a shrinkage rate of the extrusion molded product, the relational expression including, as constant parameters, a part of a configuration parameter that defines a configuration of an extrusion molding system for manufacturing the extrusion molded product or a condition parameter that defines an extrusion condition in the extruder;
a numerical value changing step of changing the value of the constant parameter to a first value that makes the value of the shrinkage ratio equal to or smaller than the predetermined value when the shrinkage ratio estimated in the shrinkage ratio estimating step is greater than a predetermined value, or a numerical value changing step of changing the value of the constant parameter to a first value that makes the value of the shrinkage ratio smaller than the predetermined value when the shrinkage ratio estimated in the shrinkage ratio estimating unit is equal to or greater than the predetermined value;
modifying the configuration parameter or the condition parameter to reflect in the extrusion molding system that the constant parameter has been changed to the first value;
a molding step of extruding the resin in the extrusion molding system after the configuration parameters or the condition parameters are changed;
A method for producing an extrusion molded product comprising the steps of: The method for producing an extrusion molded product according to claim 11,
The extrusion molding system comprises:
The extruder;
A water tank for cooling the resin extruded from the extruder;
a distance adjustment unit capable of adjusting a drop distance between the extruder and the water tank;
A shrinkage rate estimation device for estimating a shrinkage rate of the extrusion molded product;
Including,
The constant parameters include the drop distance, which is one of the configuration parameters;
the shrinkage rate estimation step is performed by the shrinkage rate estimation device,
The constant value changing step is performed by the shrinkage ratio estimating device,
A method for manufacturing an extrusion molded product, wherein the step of changing the configuration parameters or the condition parameters is carried out in the distance adjustment unit.

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