JPS597572B2 - Parison wall thickness control method in blow molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for controlling the wall thickness distribution in the longitudinal direction of parison, that is, an extrusion direction, in parison molding using a plastic blow molding machine. The present invention relates to a method for controlling parison wall thickness in blow molding that can be formed by program control.

In blow molding, according to a preset control program, during injection or extrusion of the parison, a servo cylinder moves the mandrel up and down, changes the nozzle slit that injects resin, and controls the thickness of the parison as it changes in the extrusion direction. The method is known.

In the conventional method, the entire stroke XT of the plunger F, which injects the resin supplied from the extruder D from the nozzle E, is divided into N equal parts (FIG. 1A), as shown in FIGS.
), the wall thickness t of the parison G corresponding to the length ΔX of each equally divided section and the nozzle slit s proportional to the wall thickness are set as shown in Fig. 1B using a pin board, etc., and this setting profile is Program control based on

Here, the symbol Xi is the length of i-1 sections from the injection origin, ≠i! The position of each section of the setting profile corresponding to '1tXi, g indicates the entire section of the setting profile, and h indicates a partial section. In this setting method, the length of a certain section of the stroke X of the plunger F is Δx (Δx=XT/N
), the profile of the parison formed as shown in FIG. 1C is short in thick sections and long in thin sections.

Therefore, for the ratio h/g between the length of a certain section and the total length of the set profile, the ratio of the section length IB of the corresponding parison formed in FIG. 1C to the total length IA of the parison is: , and the configuration profile (Fig. 1, B)
and the parison profile (Fig. 1, C) are not directly proportional and are distorted. Therefore, it is difficult to set a setting profile that matches the profile of a desired parison, and it is necessary to find the setting profile through repeated trial and error. In addition, when changing the wall thickness of a part of the parison, if you make change 1 shown in the dotted line in Figure 1B on the setting profile, the shape of the formed parison will be as shown in the dotted line p in Figure 1C. As shown, the section length of the changed part becomes shorter, and the length IB up to the section without changes changes to 1d.If the injection amount is further increased or decreased so that the total length of the parison does not change, this time the change The thickness of the sections that do not need to be increased or decreased,
In any case, the setting profile must be completely revised, and a great deal of effort and time is spent on correcting the setting profile, resulting in wasted resin used for trial molding. The concept of the present invention for solving the above-mentioned problems will be explained below with reference to FIGS. 4A, B, and C and FIG. 5.
In the present invention, the conventional method takes the injection stroke (hereinafter referred to as stroke) as a reference, uses this as an independent variable, converts the nozzle slit corresponding to the thickness of the parison, and further converts the nozzle slit into the position of the mandrel, which becomes the dependent variable. In contrast to setting a function form and performing program control using this, the length l of the parison is taken as a reference, and the longitudinal wall thickness distribution, nozzle slit, and stroke position of the parison are grasped as a function of the length of the parison. Next, a function form is set in which the stroke position is used as an independent variable, the nozzle slit is converted into the position of the mandrel, and the nozzle slit is converted into the position of the mandrel as a dependent variable, and a program is created. From this point on, servo control is performed according to the conventional method. The procedure for creating the above program will be explained in detail below. [1] First, the total length IA of the parison is divided into N equal parts, and the wall thickness t is determined for each section length Δl, and input into the parison profile setting device 13 and stored.

(2) Next, by utilizing the fact that the wall thickness swell ratio k1 is approximately constant for a given resin and nozzle, the wall thickness t is converted into the nozzle slit s using the following equation (1). Here, Si and ti represent the nozzle slit and the thickness of the parison, respectively, corresponding to the i-th section of the parison.

Swell is a property of resin molecules when they are deformed based on their viscoelastic effect. For example, when flowing through a nozzle, the dimension in the direction that once shrinks due to shear stress with the wall surface expands by springback after passing through the nozzle. On the other hand, the dimension in the elongated direction refers to the property of shrinking.

Normally, the wall thickness and diameter expand and contract by that amount in the longitudinal direction of extrusion. In addition, the volumetric compressibility is approximately 10% for every 1000 kg/CTl of pressure in the case of a normal resin in a molten state (for example, polyethylene). However, during blow molding, the pressure applied to the resin is 100 to 200
Since it is K9/a, in the normal case, volumetric compression and expansion can be ignored and the behavior inside and outside the nozzle can be considered as incompressible. The through nozzle slit Si shown in equation (1) is proportional to the wall thickness Ti.

Next, the constants α, β, a that indicate the shape of the nozzle shown in Figure 3 are
, move the nozzle slit s to the vertical position y of the mandrel 8.
Convert to [3] Known parison wall thickness swell ratio K
, and the diameter d of the diameter swell ratio K2J and the number of divisions N, the required stroke amount Δx is determined for each equally divided division unit Δ2(Δl-.A) by using the following equation.

Here, APLG: Plunger cross-sectional area k1: Wall thickness swell ratio (Depending on the type of resin, the wall thickness of the parison after exiting the nozzle expands 2 to 3 times compared to before injection, and this expansion ratio refers to this) K2: Parison diameter swell ratio (a constant determined by the shape of the nozzle and the type of resin in the radial ratio of expansion described above) Si: Nozzle slit (opening degree) Ti: Wall thickness of the parison From equation (4), 1 of the parison It can be seen that the stroke length ΔXi required to push out the parison for each section length Δ2 is directly proportional to the wall thickness Ti of the parison in that section, and also directly proportional to the required injection amount of resin in that section.

(4) According to the steps [2] and 3 above, the stroke
When calculating the length ΔXi of each section for the entire section (+1 to ◆N), we can use each section Δ1i of the parison as an intermediary, and over the entire length of the parison, the stroke Xi is an independent variable, and the vertical position Yi of the mandrel is a dependent variable. It's good because you can set the function form to do.

As mentioned above, in the process of thinking, even though we first selected the length l of the parison as an independent variable, in the end we decided to use the stroke position as an independent variable and convert the mandrel position into a function form. In order to detect the length of the parison online, it is necessary to line up a large number of phototubes, which increases the cost. On the other hand, the stroke position can be easily detected with an inexpensive potentiometer, and the nozzle slit s and The reason for measuring the wall thickness t of the parison is that it is difficult to directly detect the nozzle slit through which resin is injected at high temperature during injection of the parison, and to continuously detect the thickness of the parison at high speed.

Detecting the position Xi of each section of the plunger as the parison is ejected and operating the mandrel based on this signal is the same as conventional parison control, but the stroke position that determines the mandrel position Yi in the present invention Xi
It should be noted that the positions are not equidistant, but are irregularly spaced as shown in equations (4) and (5).

In actual control, the stroke position Xi is stored in the computers of the profile setters 13 and 14 together with the mandrel position Yil and the wall thickness Til nozzle slit Si of the parison for each section of the length of the parison. Furthermore, if a parison is actually injected using the above settings, and the length or wall thickness of the parison is different from what was planned due to the inaccuracy of the swell data, the swell ratios Kl and k2 must be corrected to match the actual values. do. If it is desired to change the total length IA of the parison after correcting Kl and k2, the total length h can be changed using the vane foot of the parison profile setting device 13. To summarize the features of the present invention as described above, injection proceeds while injecting the amount of resin required for the product in each section of the injection strobe, so the shape of the parison to be molded is different from that in the conventional method. There is no deviation shown in Figure 1 B (wall thickness setting profile) and Figure 1 C (molded wall thickness profile), and they are the same as shown in Figure 4 B and C. .

That is, n cedar B is 1\- (FIG. 1, B, C) in the conventional method, and H = RI (FIG. 4, B, C) in the method of the present invention.

Furthermore, due to the above-mentioned characteristics, if part of the wall thickness is to be changed as shown by the dotted line q in Fig. 4C during trial molding of the wall thickness profile of the parison, the set profile should be changed as shown by the dotted line r in Fig. 4B. and change the stroke as shown by the dotted line u in Figure 4A, so that the total stroke becomes XT'
If you change it to , it will not adversely affect the wall thickness of other parts of the product.

In addition, although the profile is roughly set in a step-like manner in FIG. 4, this is to explain the idea of the invention in an easy-to-understand manner, and in reality, the dividing points in the longitudinal direction of the parison are roughly set. Since the number of points reaches approximately 500 to 1000, it goes without saying that the profile is set as a smooth curve. However, setting all the points as described above is cumbersome, so only the minimum points necessary to represent the unevenness are given, and a curved line (broken line) connecting the points with straight lines is used instead. However, it is also possible to simplify it. These operations are
You may use a method of displaying the set point on a CRT screen attached to the computer, for example, if you keep pressing a key in the positive direction, the set point moves in the direction of increasing the thickness of the parison. It can be done easily. Based on the above considerations, the present invention improves the drawbacks of the conventional parison wall thickness control method in blow molding, obtains a parison profile with the same shape as the nozzle slit setting profile, and makes program setting extremely easy. This was done for the purpose of providing a method for controlling the thickness of a parison, and its gist is to divide the entire length of the parison into equal parts, and for each divided section, to create a parison with the desired thickness distribution. Each injection stroke of the plunger that can inject the required amount of resin for molding and the nozzle slit that is proportional to the wall thickness of the parison are determined over the entire length of the parison, and then, using the correspondence between the positions of the nozzle slit and the mandrel, , characterized in that the position of the mandrel is controlled according to the stroke position by converting the nozzle slit into the position of the mandrel and setting a correspondence between each injection stroke and the position of the mandrel for each section of the parison, Furthermore, the present invention is characterized in that the position of the mandrel is controlled according to the elapsed time of the stroke by using the stroke time instead of the length of the stroke section in the above feature.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the method of the present invention will be described in detail below with reference to the attached block diagrams illustrating control procedures.

In FIG. 5, 6 is a plastic blow molding machine head;
7 is a plunger, and 8 is a mandrel. When resin is introduced into the head body 10 from an extruder (not shown) through the resin inlet 9, the resin is ejected from the nozzle slit s by the downward movement of the plunger 7, and the parison 11 to form.

In order to give the parison the desired wall thickness distribution t, the entire length IA of the parison is divided into equal parts with the required roughness, the wall thickness Ti is set for each divided section 111, and the CRTl is adjusted as necessary.
2, etc., to store the wall thickness distribution state in the parison profile setting device 13. Next, by taking the wall thickness swell ratio k1 determined depending on the resin and nozzle used, the above formula (
1), the nozzle slit Si corresponding to each wall thickness Ti
Stroke nozzle slit profile setting device 14 (
(hereinafter referred to as a stroke setting device) and stored. Next, each stroke section length ΔXi of the plunger corresponding to the amount of resin contained in each section 1i of the parison 11 is calculated by the stroke profile setter 14 using equation (4) and stored. At this time, various values necessary for calculating equations (1) and (4), namely, wall thickness swell ratio (k1), parison warp swell ratio (K2'). The diameter (d) of the nozzle is stored in advance, and for other values, the data provided by the parison profile setting device 13 is used as is.
Or process and use. In this way, the stroke profile setter 14 obtains all combinations of each stroke section length ΔX, and nozzle slit Si over the entire length of the parison, using each section Δ11 of the parison as an intermediary.

Therefore, by integrating the stroke section length ΔXi, a functional form is set in which the stroke length X1 is an independent variable and the nozzle slit s is a dependent variable. Here, the stroke profile setter 14 further performs the calculation and converts the wall thickness t into the position y of the mandrel 8 of the molding machine using various values α, β, and a related to the shape of the nozzle shown in FIG. , finally the injection stroke position Xi and the mandrel position Y
Create a functional form with i and use it in the program setting device 20.
1 to set the control program for the molding machine. The subsequent control operations are the same as the conventional one.

That is, as the plunger 7 injects resin, each stroke position Xi of the plunger 7 is detected by the stroke position detector 15, and each mandrel position Y is detected according to the program.
The servo bulk 17 is actuated by the servo controller 16 for the mandrel 8 to match the servo cylinder 1.
8 to move the mandrel 8 up and down, its position is detected by the mandrel position detector 19, and feedback control is performed by sending a signal <y> so that there is no difference from the set value Yi.
Mandrel 8 is operated according to the program. Then the second
As an example, a program setting method for a continuous extrusion blow molding machine will be described. The setting of the parison wall thickness distribution and the setting of the nozzle slit profile and stroke profile corresponding to the wall thickness distribution are the same as in the first embodiment. In this method, the extrusion time of the parison is used instead of the stroke x described above, and a function form is set using the stroke setting device 14, with the extrusion time and the independent variable being the nozzle slit as the dependent variable, and then the nozzle slit is set at the position of the mandrel. After that, the extrusion time is integrated, and the position of the mandrel is set relative to the elapsed time of the extrusion stroke to form a control program for the forming mold, and the servo control is performed while feeding back the position of the mandrel relative to the elapsed time. As described above, when setting the profile of the nozzle slit, a parison with the desired thickness distribution can be formed by setting the nozzle slit profile according to the desired thickness distribution distributed in the longitudinal direction of the parison. The wall thickness of some of the parisons has also been changed.
Only some changes to the nozzle slit profile need to be made.

It should be noted that the present invention is not limited only to the above-described embodiments, and it goes without saying that various changes can be made without departing from the gist of the present invention.

Since the parison wall thickness control method in blow molding of the present invention has the above-described configuration, it exhibits the following effects.

(1) By directly setting the wall thickness distribution obtained for each fixed section length of the parison as the nozzle slit profile, a wall thickness profile that is the same or similar to the set profile can be obtained, so the profile setting is easy. There is no need to repeat trial and error as in the past, and labor and resin resources can be saved.

(Ii) When changing part of the wall thickness of the parison, the desired thickness distribution can be obtained by simply changing the nozzle slit profile of the part to be changed, and the wall thickness setting profile can be changed as before. There is no need to completely change the
Partial plan changes in wall thickness can be easily made.

[Brief explanation of the drawing]

Figure 1 A, B, and C are explanatory diagrams showing the relationship between the plunger stroke, set profile, and molded wall thickness distribution when setting the wall thickness distribution of a conventional parison, and Figure 2 is the vicinity of the plunger of a plastic blow molding machine. 3 is a partially enlarged view of the vicinity of the nozzle slit in FIG. 2, and FIG. 4 A, B, and C are plunger strokes, set profiles, and forming when setting the thickness distribution of the parison in the method of the present invention. FIG. 5 is a block diagram of a parison wall thickness control method showing an embodiment of the present invention. In the figure, 7 is a plunger, 8 is a mandrel, 11 is a parison, 13 is a parison profile setting device, 14 is a stroke/nozzle slit profile setting device, IA is the total length of the parison, Δl is the section length of the parison, s is the nozzle slit, t is the wall thickness of the parison, x is the injection stroke position, Δx is the length of each section of the injection stroke, and y is the position of the mandrel.

Claims (1)

[Claims] 1. The entire length of the parison is divided into equal parts, and each injection stroke of the plunger is capable of injecting the required amount of resin for forming a parison having a desired wall thickness distribution in each divided section; and a nozzle slit proportional to the wall thickness of the parison, respectively, are determined over the entire length of the parison, and then, using the correspondence relationship between the nozzle slit and the mandrel position, the nozzle slit is converted to the mandrel position, and the nozzle slit is proportional to the wall thickness of the parison. A parison wall thickness control method in blow molding, characterized in that the position of the mandrel is controlled according to the stroke position by setting the correspondence between each injection stroke and the position of the mandrel for each section. 2 Divide the entire length of the parison into equal parts, store the wall thickness of the parison with the desired wall thickness distribution for each divided section in the parison profile setting device, and set the required thickness for forming the parison for each section. Each injection stroke capable of injecting a resin amount and a nozzle slit proportional to the wall thickness of the parison are each set by a stroke/nozzle slit setting device using the wall thickness distribution settings stored in the parison profile setting device. , calculate and store the nozzle slit correspondence relationship with the stroke position as its own variable by integrating the above-mentioned injection stroke lengths, and set the correspondence relationship between the nozzle slit and the mandrel position in a step-like function form. 2. A parison wall thickness control method in blow molding according to claim 1, wherein a correspondence relationship between an injection stroke position and a mandrel position is set using the above method. 3 Divide the entire length of the parison into equal parts, and calculate the injection stroke time for each divided section to inject the required amount of resin to mold the parison with the desired thickness distribution, and the thickness of the parison. Proportional nozzle slits are determined respectively over the entire length of the parison, and then, using the correspondence between nozzle slit and mandrel positions, said nozzle slits are converted to mandrel positions, and each injection time is calculated for each said section of the parison. A method for controlling parison wall thickness in blow molding, characterized in that the position of the mandrel is controlled according to the elapsed time of injection by setting the correspondence between the position of the mandrel and the position of the mandrel.