JPH0446724B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a method for automatically adjusting the length of a parison.

(b) Prior Art As a conventional parison extrusion molding method, for example, there is a method shown in Japanese Patent Publication No. 7572/1983. This involves dividing the entire length of the parison into equal parts, and each injection stroke of the plunger capable of injecting the required amount of resin in each divided section to mold the parison with the desired wall thickness distribution, and each injection stroke of the parison. A nozzle slit proportional to the wall thickness of the parison is determined over the entire length of the parison, and then, using the correspondence between the nozzle slit and the mandrel position, the nozzle slit is converted to a mandrel position, and each injection is performed for each section of the parison. A parison extrusion molding method is shown in which the position of the mandrel is controlled according to the stroke position by setting a correspondence between the stroke and the position of the mandrel.

(c) Problems to be Solved by the Invention However, in the conventional parison extrusion molding method as described above, when the target parison wall thickness is changed or when the molding cycle time is changed, the extrusion amount increases. If it remained constant, the total length of the parison would change, so in order to prevent this, it was necessary for an operator to operate the extruder and adjust the amount of extrusion.
This adjustment work was time consuming and wasted materials. The present invention aims to solve these problems.

(d) Means for solving the problem The first invention of the present application solves the above problem by adjusting the extrusion amount according to the change in the average wall thickness. That is, the parison length automatic adjustment method according to the first invention uses a polygonal line that shows the target wall thickness change after the change with respect to the average wall thickness that is obtained using the polygonal line that shows the target wall thickness change before the change. The extrusion rate of the molten resin is adjusted so that the extrusion rate of the molten resin after the thickness change is obtained by multiplying the average wall thickness ratio obtained by the above process by the extrusion rate of the molten resin before the thickness change.

Moreover, in the second invention, the extrusion amount is controlled according to changes in molding cycle time. That is, in the parison length automatic adjustment method of the second invention, the ratio of the molding cycle time before the change to the molding cycle time after the change is multiplied by the extrusion amount of molten resin before changing the wall thickness. The extrusion amount of the molten resin is adjusted so as to correspond to the extrusion amount of the molten resin after changing the thickness.

(e) Effect When the target parison wall thickness is changed, the parison length will change if the extrusion amount is the same. That is, the thinner the wall thickness, the longer the parison length, and conversely, the thicker the wall thickness, the shorter the parison length. In the case of the first invention, since the extrusion amount is changed according to the change in the average wall thickness, the parison length is maintained constant even if the wall thickness changes. The extrusion amount can be adjusted by changing the rotation speed of the extruder depending on the ratio of the average wall thickness after the change to the average wall thickness before the change.
This makes it possible to always obtain a parison of the desired length. Regarding the second invention, similar effects can be obtained based on the molding cycle time before and after the change.

(f) Example (Example of the first invention) FIG. 1 shows a parison extrusion molding apparatus. die 1
A core 12 is provided in the opening of 0, and this core 12 can be moved up and down by a hydraulic cylinder 14. Molten resin can be supplied to the gap 13 between the die 10 and the core 12 from an extruder (not shown).
The operation of the hydraulic cylinder 14 is controlled by a hydraulic servo valve 16. Hydraulic servo valve 16 is actuated by a signal from servo amplifier 18 . Also, core 1
The position of 2 is detected by a potentiometer 20, and its detection signal is fed back to the servo amplifier 18. The servo amplifier 18 includes a CPU 22 that constitutes a microcomputer.
A command signal from (central processing unit) is input.
The CPU 22 also outputs a command signal to the extruder control device 31. Connected to the CPU 22 are an input device 24, such as a keyboard, a storage device 26, and a display device 28.

FIG. 2 shows a routine for wall thickness control among the controls executed by the CPU 22. This routine is executed by an interrupt signal every 20 msec, for example. First, a target value a of wall thickness for the calculated parison length is calculated from a data table by interpolation (step 100). For example, data as shown in FIG. 3 is input into the data table. That is, the desired wall thickness A relative to the parison length L is shown by a polygonal line. In the case of the example shown in Fig. 3, P ₀ (parison length L ₀ =0, wall thickness A ₀ =4), P ₁
(L ₁ = 0.3, A ₁ = 8), P ₂ (L ₂ = 0.5, A ₂ = 8), P ₃
(L ₃ = 0.7, A ₃ = 4), and P ₄ (L ₄ = 1.0, A ₄ = 4)
The five points are input from the input device 24 and stored in the storage device 26. In addition, parison length L
is shown with the total length as 1, and the wall thickness A is mm
It is shown in units. From this table, a target value a of wall thickness for a given calculated parison length is calculated by interpolation. In the first routine =
Since it is 0, a=4. In the second and subsequent routines, a target value a of wall thickness corresponding to the parison length calculated in step 106, which will be described later, is calculated. Next, core 1 is calculated from the calculated wall thickness target value a.
The stroke Cs of step 2 is calculated (step 102).
The wall thickness of the parison to be extruded and the stroke Cs of the core 12 have a predetermined relationship depending on the shapes of the die 10 and the core 12; for example, Cs=2.2·K·
a-5 (K is a constant). Then,
The calculated core stroke Cs is output from the CPU 22 to the servo amplifier 18 (step 104). As a result, the servo amplifier 18 controls the hydraulic cylinder 14 via the hydraulic servo valve 16 to achieve the given core stroke Cs. The movement of the core 12 is controlled by the potentiometer 20 to the servo amplifier 1.
8, the core 12 is moved to the given core stroke Cs. Following the output of the core stroke Cs, the calculated parison length is calculated (step 106). The calculation is performed based on the following formula. That is, =+(Δt/T)·(a ₀ /a) Δt is the unit time during which this routine is executed, which in this embodiment is 20 msec as described above.
T is the extrusion cycle time, which is the time until the entire length of the parison is extruded. a ₀ is the average wall thickness, and corresponds to the area of the shaded area shown in FIG. 3 divided by the total length of the parison (=1). In addition,
During parison extrusion molding, the extruder is operated at a constant rotation speed and always discharges a constant amount of molten resin, so Δt/T is the melt discharged in time Δt relative to the total molten resin required for one parison. It will show the ratio of resin. Next, it is determined whether the calculated parison length has reached the full length, that is, whether it is ≧1 (step 108), and if the full length has not been completed, the process returns, and if the full length has been completed, the calculated parison length is The value is reset to 0 (step 110) and the process returns.

By repeating the routine shown in Figure 2,
The actual wall thickness of the parison 15 extruded through the gap 13 between the die 10 and the core 12 is as set as shown in FIG. In this example, the process is set to end when the calculated parison length reaches the full length, but the same effect can be obtained by setting the process to end when the actual elapsed time from the start of extrusion reaches the cycle time. I can do it.

FIG. 4 shows a parison length control routine among the controls executed by the CPU 22. This routine will be executed when the target thickness of the parison is changed. First, determine whether the target wall thickness has changed (step
202), returns if it has not been changed, and returns if it has changed (for example, assume that the polygonal line characteristic shown in FIG. 3 has been changed to that shown in FIG. 5, that is, P ₁ (L ₁ = 0.3, A ₁ = 8) is P ₁ ′ (L ₁ =
0.3, A ₁ = 6)), the average wall thickness before the change a ₀ (corresponds to the area of the slope in Figure 3)
is calculated (step 204). In this case, a ₀ =
It is 5.8mm. Next, the changed average wall thickness a ₁ (corresponding to the area of the shaded area in FIG. 5) is calculated (step 206). In this case, a ₁ =5.3mm. Next, calculations are performed to correct the rotational speed N of the extruder (step 208). That is, the rotational speed N is corrected according to the ratio of the average wall thickness a ₁ to the average wall thickness a ₀ . In this case, N=0.914N. Then, the corrected rotational speed N is output (step 210).
As a result, as in this example, when a _{1 <a 0, the rotation speed of the extruder decreases, and conversely, when a 1 >} a ₀ , the rotation speed increases. As a result, extrusion molding is performed with the wall thickness as shown in Figure 5, and the parison length is
Since extrusion molding is completed when the thickness reaches 1.0, it is possible to obtain a parison with the same length as before changing the wall thickness. Therefore, when the target parison wall thickness is changed, the parison length is automatically maintained at the initial state.

(Embodiment of the second invention) FIG. 6 shows an embodiment of the second invention. In this example, the molding cycle time is changed from T ₀ to T ₁ , and the rotation speed of the extruder is set according to the ratio of the old molding cycle time to the new molding cycle time T ₁ . This means that, for example, if the molding cycle time becomes longer (i.e., T ₁ > T ₀ ), the rotational speed will decrease, and the parison length at T ₁ hours will be the same as the parison length after T ₀ hours at the old rotational speed. be the same. That is, a constant parison length can be maintained regardless of changes in molding cycle time.

(G) Effects of the Invention As explained above, according to the present invention, the extrusion amount is controlled according to the ratio of change in the average wall thickness of the parison or the molding cycle time.
Even if the target parison wall thickness is partially changed or the molding cycle time is changed, parisons of the same length can be automatically obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an apparatus for carrying out the method of the present invention;
Figure 2 is a diagram showing the parison wall thickness control routine;
Figure 3 shows the target parison shape, Figure 4
FIG. 5 is a diagram showing a parison length control routine according to the first invention, FIG. 5 is a diagram showing a target parison shape after modification, and FIG. 6 is a diagram showing a parison length control routine according to the second invention. 10...Die, 12...Core, 13...Gap, 14...Hydraulic cylinder, 15...Parison,
16... Hydraulic servo valve, 18... Servo amplifier,
20...Potentiometer, 22...CPU, 2
4...Input device, 26...Storage device, 31...Extruder control device.

Claims (1)

[Claims] 1. The parison length and wall thickness values at the bending point of the polygonal line indicating the target wall thickness change of the parison are stored in advance in a storage device, and the parison is calculated at regular intervals during extrusion molding of the parison. The target value of the wall thickness for the length is calculated based on the above value stored in the storage device, and the gap between the die and the core is adjusted to obtain the target value of the wall thickness. Calculate the elongation of the parison length that should occur within the above fixed time from the target value and the amount of molten resin extruded,
The calculated value of the parison length increase is added to the previous parison length as the new calculated parison length, and the above operation is repeated until the calculated parison length reaches the pre-stored total length of the parison. In the parison length automatic adjustment method when the parison is extrusion molded by repeating the molding cycle until a preset molding cycle time elapses, and the polygon line indicating the target wall thickness change is changed, the target before the change The ratio of the average wall thickness obtained by the polygonal line showing the target wall thickness change after the change to the average wall thickness obtained by the polygonal line showing the target wall thickness change after the change is calculated as follows: A parison length automatic adjustment method characterized by adjusting the extrusion amount of molten resin so that the amount multiplied by the amount becomes the extrusion amount of molten resin after changing the wall thickness. 2. Store the parison length and wall thickness values at the bending point of the polygonal line that indicates the target wall thickness change in the parison in advance in a storage device, and calculate the wall thickness for the calculated parison length at regular intervals during parison extrusion molding. The target value is calculated based on the above value stored in the storage device, the gap between the die and the core is adjusted to obtain the target value of wall thickness, and the target value of wall thickness and molten resin extrusion are calculated. Calculate the elongation of the parison length that should occur within the above certain period of time from the amount,
The calculated value of the parison length increase is added to the previous parison length as the new calculated parison length, and the above operation is repeated until the calculated parison length reaches the pre-stored total length of the parison. In the case of extrusion molding a parison by repeating the process until a preset molding cycle time elapses, and when the molding cycle time is changed, the parison length automatic adjustment method is as follows: The extrusion amount of the molten resin is adjusted so that the extrusion amount of the molten resin after the wall thickness change is obtained by multiplying the extrusion amount of the molten resin before the wall thickness change by the ratio of the molding cycle time. automatic parison length adjustment method.