JPH0320845B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an automatic control method for an insulation extrusion molding line using a computer, the purpose of which is to control the outer diameter and capacitance of foamed plastic insulated cables to constant values. The present invention relates to an automatically controlled method for extruding a two-layer plastic insulated cable having a foam layer and an outer solid layer. Here, the two-layer plastic insulated cable is one that is mainly used as a communication cable core, and as shown in Fig. 3, a foam layer a is provided around the conductor 1, and a A thin non-foamed layer, that is, a solid layer b, is extruded at the same time. As shown in FIG. 4, this cable is provided with a foamed plastic layer a and a solid layer b concentrically by one common crosshead 42. Now, as a typical method for controlling the extrusion molding of plastic insulated cables, there is the following method. (a) Measure the outer diameter of the cable and the amount of resin coating, calculate the degree of foaming, and artificially adjust the extruder rotation speed, set temperature, and position of the cooling tank for adjusting the degree of foaming to manufacture a cable with predetermined characteristics. Method. (b) A capacitance meter is installed on the extrusion line, and the capacitance of the cable is continuously measured, and the servo motor is driven according to the deviation from the target capacitance, and the position of the cooling tank in the pass line direction and the extrusion How to automatically control machine temperature. (c) Automatically calculates the resin adhesion amount and degree of foaming based on data from the capacitance meter and outer diameter measuring device, and automatically adjusts the extruder rotation speed, temperature, and cooling tank position according to the deviation from the target value. How to control. However, automation of the extrusion process has conventionally been applied only to single-layer extrusion, and automation of two-layer extrusion molding is generally difficult for the following reasons. That is, it is known that the formula W=KN approximately holds true, where W is the extrusion amount in an extruder, N is the screw rotation speed of the extruder, and K is an empirically determined proportionality constant. In the case of single-layer extrusion molding, by adjusting the extruder screw rotation speed using a control method using this formula, it was relatively easy to automatically control the extrusion amount as well as the cable outer diameter capacitance. . However, the 2
In layered plastic insulated cables, W
=KN has not been applied to control the extrusion amount of each layer. Table 1 shows an example of experimental results regarding the relationship between screw rotation speed and extrusion amount in a two-layer extruder.

[Table] As shown in the experimental results in Table 1, when the screw rotation speed of the solid layer extruder is increased to increase the extrusion amount, the extrusion amount of the foam layer decreases. For this reason, it is extremely difficult to apply the formula W=KN to each extruder individually to control two-layer extrusion molding. The reason why this phenomenon occurs is that two extruders 4 are connected to the same crosshead 42.
0.41, it is thought that a change in the extrusion rate of one extruder changes the extrusion pressure of the other extruder, thereby affecting the extrusion rate. Therefore, conventionally, when manufacturing two-layer plastic insulated cables, the cross section of the cable was observed using a projector to measure the wall thickness of the solid layer and the foam layer, and static measurement was performed based on this value. Capacity and outer diameter were controlled, but this is artificial and depends on the skill level of the operator, so there is a large time lag between when a fluctuation appears and when it is corrected. Loss and local product defects were unavoidable. As a result of many attempts to adjust the extrusion amount, the inventor found that
Foam layer extruder rotation speed for double layer insulated cable
N _f (rpm) Full layer extruder rotation speed N _S (rpm), foam layer resin adhesion amount W _f (g/m), solid layer resin adhesion amount W _S
(g/m), and the empirically determined proportionality constant is K, we found that there is a high degree of correlation between these values: W _f /W _s = K × N _f /N _s . That is, if W _f =0.151, W _ss =0.121, N _f =39, and N _s =25 are substituted into the above equation based on the data values shown in Table 1, K = 0.151/0.121×25/39. , K≒0.79996. On the other hand, W _f =0.149, W _s =
Substituting 0.124, N _f = 39, N _S 26 into the above equation, we get
K=0.149/0.124×26/39, and K≒0.80108. In this way, it can be understood that both have almost the same constant of proportionality, and therefore there is a correlation of W _f /W _s =K×N _f /N _s . Note that this value of K is a characteristic value of the extrusion molding machine that is empirically determined for each specific cable,
The value varies depending on the type of cable. The present invention has been made based on this knowledge, and the gist of the present invention is to adjust the extruder screws of a foam layer extruder and a solid layer extruder based on a predetermined calculation method using a computer. An automatic control method for extrusion molding a two-layer plastic insulated cable, which calculates each modification amount of rotation speed, extrusion temperature, and auxiliary cooling water tank position, and further controls cable capacitance and cable outer diameter to design values. ,
Extruder screw rotation speed N _s of the solid bed extruder
(rpm) and the extruder screw rotation speed N _f (rpm) of the foam layer extruder, the resin adhesion amount W _s of the outer solid layer b and the resin adhesion amount W _f of the inner layer and foam layer a can be adjusted. and controlling such that the ratio of the extruder screw rotation speed N _f to the extruder screw rotation speed _{N s} is proportional to the ratio of the resin adhesion amount W _r to the resin adhesion amount W s. The present invention is characterized by an automatic control method for extrusion molding a two-layer plastic insulated cable. Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic diagram of a two-layer plastic insulated cable production line. In the conductor 1, the foam layer a is formed by an inner layer extruder 40, and the solid layer b is formed by an outer layer extruder 41, respectively, by the same crosshead 42.
Layers are extruded. On the downstream side of the extruder, a cooling water tank 8 and an auxiliary cooling tank 7 are arranged in line in the pass line direction with respect to the cooling water tank 8 in order to change the cooling hardening point of the extruded resin and adjust the degree of foaming. Furthermore, the auxiliary cooling water tank 7 includes a position detector 5 and a servo motor 6 for moving the auxiliary cooling water tank 7 in the pass line direction. Note that a capacitance monitor 9 is attached to the cooling water tank 8. The foam layer resin foaming degree, which is the main element of cable capacitance, is determined by the servo motor 6 being driven according to the control signal from the computer and adjusting the position of the auxiliary cooling water tank 7 in the pass line direction. It is controlled by the capacitance value. In addition, the measuring instruments include a known capacitance meter and a non-contact outer diameter measuring device 1.
0 is set. Now, to explain the input/output to the computer in Fig. 2, the force data for controlling the outer diameter is mainly the cable outer diameter 26, the screw rotation speeds 22 and 24 of the extruder for each layer, and mainly the degree of foaming. Capacitance 2 as data for adjustment
5. There are seven types of input data: extrusion temperature 21, 23 of each layer extruder, and position 27 of the auxiliary cooling water tank. On the other hand, the output data includes a total of five types of output data, including the rotational speed 30 and 32 of the screw drive motor of each layer extruder, the position of the auxiliary cooling water tank by the servo motor 33, and the set temperature of the temperature controllers 29 and 31 of each layer extruder. be. Here, the process of determining the control amount using a computer will be explained. The strand diameter d ₁ is used as immediate data before starting production.
(mm), non-permittivity ε _b of resin, resin density ρ (g/cm ³ ),
Insulation outer diameter d ₂ (mm) Capacitance C as data continuously input from a measuring device installed on the line
(PF/m), the outer diameter of the foam layer obtained by calculation is defined as d ₃ (mm), and the control amount to be obtained is W _f
(g/m) W _s (g/m) and the degree of foaming of the foam layer is η _f (%), then the following five well-known equations hold true. C=ε/18・l _o (d ₂ /d ₁ )×10 ³ ...(1) ε=ε _f・ε _{b lo} (d ₂ /d ₁ )/ε _f・l _o (d ₂ /d ₃ ) + ε _b
・l _o (d ₃ /d ₁ )……(2) ε _b −ε _f /ε _b −1=2ε _b +ε _b /2ε _b +1×η _f /100
...(3) W _s = π/4 (d ₂ ² − d ₃ ² )・ρ ...(4) η _f = {1−W _f /π/4・(d ₃ ² − _{d 1} ² )・ρ} × 100 ... (5) Using the above formula and W _f /W _s = K × N _f /N _s ... (6), calculate the W _f of the cable at a certain point in time,
W _s , η _f , and d ₃ can be easily calculated using a computer. This calculation result is compared with the cable design value, and the extruder rotation speed of each layer and the position of the auxiliary cooling water tank are adjusted several times at regular intervals using a feedback control method based on the above six formulas. In addition, a comparison was made between the insulation outer diameter d ₂ , capacitance C, resin adhesion amount W _f , W _s , foaming degree η _f , and foam layer outer diameter d ₃
Correct it to within the cable design tolerance range. At this time, find d ₃ as follows. First of all,
Each symbol in equations (1) to (6) is classified into immediately known numbers and unknown numbers as follows. (Known quantity) C: Capacitance measured by signal 25 of capacitance monitor 9. d ₁ : The outer diameter of the supplied conductor 1, which is naturally a known number. d ₂ : The outer diameter of the final product having two insulating layers, which is measured by the non-contact outer diameter measuring device 10. ε _b : The relative dielectric constant of the resin (base resin), which is naturally known. ρ: Density of the resin (base resin), which is also known as a matter of course. K: is a constant of proportionality found in the present invention. N _f : Inner layer extruder for extrusion molding foam layer a
40 screw rotation speed is 22. N _s : Screw rotation speed 24 of the outer layer extruder 41 for extrusion molding the solid layer b. (Unknown quantity) ε: Total permittivity of foam layer a and solid layer b (equivalent permittivity) ε _f : Dielectric constant of foam layer d ₃ : Outer diameter of foam layer a η _f : Degree of foaming of foam layer a W _f : Adhering amount W _f of foam layer a : Adhering amount W f : Adhering amount W f : Adhering amount W f : Adhering amount W f : Adhering amount W f : Adhering amount W You can ask for everything. In addition, for short period and small fluctuations in the degree of foaming, the servo motor 6 is driven to change the distance between the auxiliary cooling water tank and the extruder and adjust the cooling hardening point to adjust the degree of foaming to the target value. However, for long periods,
The program also includes a control method characterized by adjusting the degree of foaming by changing the extrusion temperature in response to wide fluctuations. As described above, according to the present invention, cable design values are calculated by continuously inputting and monitoring data on the cable outer diameter and capacitance into a computer in the extrusion molding line for two-layer plastic insulated cables. If a deviation occurs, the optimum correction amounts for the extruder screw rotation speed, extruder temperature, and foaming degree for each layer are calculated to minimize the deviation width, and the results of this calculation are immediately The output from the computer automatically controls the screw drive motor of each layer extruder, the set temperature of each layer extruder, and the position of the auxiliary cooling water tank, resulting in uniform capacitance and uniformity that could not be obtained with conventional artificial manufacturing methods. This allows for the automatic production of double-layer plastic insulated cables having an outer diameter of approximately 100 mm.

[Brief explanation of the drawing]

Figure 1 is a schematic side view showing a production line for two-layer plastic insulated cables, Figure 2 is a diagram showing input/output data to a computer, Figure 3 is a cross-sectional view of two-layer plastic insulated cables, and Figure 4 is a two-layer plastic insulated cable production line. FIG. 2 is a sectional view showing the vicinity of the crosshead of a two-layer extruder used for manufacturing a layered plastic insulated cable. In the figure, 1 is a conductor, 6 is a servo motor,
7 is an auxiliary cooling water tank, 8 is a cooling water tank, 9 is a monitor, 10 is a non-contact outer diameter measuring device, 28 is a calculator,
40 is an inner layer extruder, 41 is an outer layer extruder, 42 is a crosshead, a is a foam layer, and b is a solid layer.

Claims (1)

[Claims] 1. Calculate each correction amount of the extruder screw rotation speed, extrusion temperature, and auxiliary cooling water tank position of the foam layer extruder and the solid layer extruder based on a predetermined calculation method using a computer. , an automatic control method for extrusion molding a two-layer plastic insulated cable, further controlling the cable capacitance and cable outer diameter to design values, the extruder screw rotation speed N _s (rpm) of the solid layer extruder being By adjusting the extruder screw rotation speed N _f (rpm) of the foam layer extruder, the resin adhesion amount W _s of the outer solid layer b and the resin adhesion amount W _f of the inner foam layer a are controlled. When doing so, the extruder screw rotation speed of the solid bed extruder
The ratio of the extruder screw rotation speed N _f of the foam layer extruder to N _s and the ratio of the resin adhesion amount W _f of the foam layer a to the resin adhesion amount W _s of the solid layer b are stored in advance in the computer. An automatic control method for extrusion molding a two-layer plastic insulated cable, characterized in that the characteristic value K of an octopus extruder is controlled so as to be proportional as a proportionality constant. 2. There is a method of adjusting the degree of foaming by adjusting the position of the auxiliary cooling water tank in the pass line direction for small fluctuations in the degree of foaming, and by adjusting the extrusion temperature for large fluctuations. An automatically controlled method for extruding a two-layer plastic insulated cable according to claim 1.