JPH0788945A - Wall thickness control method for parison - Google Patents

Abstract

(57) [Summary] [Purpose] Using a pre-existing parison pattern, a modified parison pattern in which the die gap amount of the pre-existing parison pattern is corrected only in a specified section with an injection stroke can be created easily in a short time. Based on the above, we propose a method for controlling the thickness of parison that can immediately restart the actual operation. A method for controlling a wall thickness of a parison P formed by extruding a molten resin from a nozzle slit 7 of a blow molding machine 1, which is an injection stroke during molding and the nozzle slit 7
The die gap amount is controlled on the basis of a parison pattern preset on two orthogonal axes, and the gain function that specifies the wall thickness change in the specified section of the injection stroke of the existing parison pattern is defined. The die gap amount is controlled based on the modified parison pattern obtained by multiplying the function of the existing parison pattern.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the thickness of a parison in a blow molding machine, in which an existing parison pattern is specified in addition to a parison thickness characteristic curve (hereinafter referred to as a parison pattern) which is set in particular. The present invention relates to a wall thickness control method for a parison in which a similar parison pattern in which the wall thickness is corrected only in the injection stroke section is simply created and immediately put into actual operation.

[0002]

2. Description of the Related Art A parison made of a molten resin extruded from a blow molding machine and hung down is not uniform in the longitudinal direction of the parison depending on the intended product shape, and is formed by changing the wall thickness as necessary. . One of the methods conventionally used as a method for controlling the thickness of the parison in this case is to set the parison thickness characteristic curve in which the injection stroke amount (or molding time) and the die gap adjustment amount are preset on the screen on two orthogonal axes. A so-called parison pattern control method is adopted, in which the die gap (in other words, the required wall thickness) setting value for each set point obtained by dividing this molding time into multiple equal parts is taken out and the downward movement of the extrusion plunger is controlled over time. It had been.

[0003]

As described above, in the above-described control method using the parison pattern, the shape of the product is once determined, and the wall thickness is increased or decreased as necessary according to the strength of the product. It is very simple and efficient in the case of mass production of one kind in which a different parison pattern is formed and the same product having the same shape and the same wall thickness variation is repeatedly molded. However, when making a slight correction by looking at the situation of the on-site product or making a slight change to the existing parison pattern due to production reasons to create a product with a new parison pattern, the screen on the two orthogonal axes described above is re-created. He had to recreate a new pattern from the beginning and start producing with a new parison pattern, and he was forced to change all settings. In particular, it is often necessary to increase or decrease the wall thickness only in a certain section of the injection stroke. Rebuilding a new parison pattern from the beginning each time requires a lot of labor and time. In short, it hindered productivity.

[0004]

In order to solve the following problems, in the present invention, the molten resin supplied to the gap formed between the mandrel and the blow head is operated by an injection cylinder to lower the gap. Is a method of controlling the wall thickness of a parison that is extruded from the nozzle slit of
In addition, while controlling the die gap amount based on a parison thickness characteristic curve preset on a screen on two orthogonal axes with the horizontal axis representing the injection stroke during molding and the vertical axis representing the die gap amount of the nozzle slit, It is obtained by multiplying the existing parison thickness characteristic curve that has already been set by the set value of the die gap amount in the specified section of the injection stroke on the horizontal axis by the correction value calculated based on the function of the injection stroke specified in advance. The die gap amount is controlled on the basis of a modified parison thickness characteristic curve formed from the modified set values.

[0005]

According to the present invention, only a part of the existing parison pattern is corrected by multiplying the correction value calculated on the basis of a predetermined function of the die gap amount by the set value of the existing die gap amount to obtain the correction value. New molding can be restarted in a short time by using the locally modified parison pattern, which reduces the loss of molding time and improves the productivity.

[0006]

Embodiments of the present invention will now be described in detail with reference to the drawings. 1 to 4 relate to an embodiment of the present invention,
FIG. 1 is a block diagram of a parison thickness control device, FIG. 2 is a modified parison characteristic curve (parison pattern) diagram, FIG. 3 is an explanatory view showing an embodiment of a local correction function, and FIG. 4 is another local correction function. It is explanatory drawing which shows an Example. As shown in Figure 1,
The blow molding machine 1 has a core 3 which is fitted to a mandrel 3A provided in the center of the inside of a die 2 having a rectangular cross section of a blow head 2a and a nozzle 2b connected thereto and which expands downward in diameter. The rod 3a is connected to the Parison cylinder 8 so as to be reciprocally movable in the vertical direction.
The molten resin supplied to the resin passage 2c in the die 2 by the extruder 6 is extruded downward by the operation of the injection cylinder 5 of the injection device 4 from the nozzle slit 7 formed in the gap between the core 3 and the nozzle 2b, and the parison P is formed. Configured to form. The gap at the lowermost end of the nozzle slit 7 is particularly called a die gap (or die gap amount), and regulates the wall thickness of the parison P to be extruded. Parison cylinder 8
The servo valve 10 for supplying hydraulic oil to the die, the die gap detector 9 for detecting the operation amount of the rod 3a of the Parison cylinder 8 and the position detector 5b for detecting the operation amount of the piston rod 5a of the injection cylinder 5 are all parison meats. It is connected to the thickness control device 16. The parison thickness control device 16 has a built-in command signal setting unit 11 for setting a parison curve, a deviation calculation unit 12, and a PID control calculation setting unit 13, and is connected to a display device 14 and an input device 15 to detect the parison P being discharged. It is constructed so that the wall thickness can be controlled arbitrarily.

Next, the operating procedure of the parison thickness control method according to the embodiment of the present invention will be described. The display device 14 and the input device 15 are used to display a parison thickness characteristic curve (parison curve) on a screen on two orthogonal axes with the die gap amount G on the vertical axis and the injection stroke S on the horizontal axis as shown in FIG. Alternatively, what is called a parison curve is shown as curve A in the figure, and a function G = f (s) waveform is created. The parison pattern is created by the injection stroke S on the horizontal axis.
Is divided into a plurality of equal control areas, and the set value (die gap amount G) at the start point or center point of each control area is set, and the straight line connecting these is interpolated into a smooth curve to make a corrected curve. create. This is the set parison pattern, which is stored and stored in the command signal setting unit 11 in the parison thickness control device 16, and in actual operation, the die at the injection stroke S position of the injection cylinder 5 input from the position detector 5 is input. Gap amount set value G ₁ and die gap amount measured value G detected by the die gap detector 9.
The deviation e from ₂ is calculated by the deviation calculator 12. Deviation e obtained
The PID control calculation setting unit 13 performs the PID calculation using, and outputs the result to the servo valve 10 to operate the Parison cylinder 8. By repeating these operations moment by moment, the injection cylinder 5 and the Parison cylinder 8 are operated in accordance with a preset parison pattern, and the die gap amount G is increased or decreased in accordance with a prescribed waveform. The parison P molded in this manner becomes a parison having the same thickness change as the parison pattern set in the longitudinal direction. On the other hand, at a production site where molded products are molded according to these set parison patterns, local correction is performed to increase or decrease the wall thickness in a certain section in the longitudinal direction of the parison from the condition of the finished product. Sometimes it is necessary. In such a case, it is complicated to recreate all the parison patterns from the beginning, and it takes a lot of time and labor, which is a factor that hinders productivity. Therefore, in the present invention, in order to reduce such complexity, a new parison pattern in which an existing parison pattern is locally modified is simply created, and by utilizing this, production can be immediately restarted to contribute to improvement in productivity. I chose The correction procedure will be specifically described below.

In FIG. 2, the existing set parison pattern (A curve represented by a solid line, function G = f
(S) (for (s)), a parison pattern with a slightly thicker parison pattern is corrected as shown by the B curve shown by the dotted line in FIG. 2 only in the designated section (between S = a to c) of the horizontal axis injection stroke S. If you want to create, except in the specified section a to c (that is, when the injection stroke S is less than a, or more than c)
1, and a gain function y = α (x) that is a function of the injection stroke x is defined between the designated sections a to c. Then, y = 1 at both ends between the designated sections a to c, that is, S = a and S = c, and y = k (however, k at the center between the designated sections a to c (this is the point b)). Is a constant slightly larger than 1 and usually a function such that k = 1.1 to 1.5) is adopted. As the simplest function,
As shown in, the linear function can be adopted as the gain function y = α (x). In this case, a straight line connecting point (a, 1) and point (b, k) and point (b, k) and point (c,
It becomes a straight line connecting 1) and. The function G = g (s) of the B curve having the die gap amount G corrected between the designated sections a to c using the gain function y = α (x) thus defined.
Becomes g (s) = α (x) × f (s). When a first-order function is used for the gain function α (x) as described above,
Generally, the left and right differential coefficients at the start point S = a and the end point S = c of the specified section of the modified parison pattern do not match, and the right differential coefficient is larger than the left differential coefficient at the start point and conversely, the left differential coefficient is at the end point. The coefficient becomes smaller. However, as mentioned above, the increase in wall thickness is very small compared to the original waveform,
As long as a value of k = 1.1 to 1.5 is selected, the difference in the differential coefficient is very small and there is no practical problem. Furthermore, when a product with high accuracy is required and a molded product having a smooth wall thickness variation in which the left and right differential coefficients at the start point and end point of the specified section are matched, it is necessary to use the above first-order function instead. A gain function having a function of second order or higher is used. The gain function in this case passes through three points (a.1), (b, k), (c, 1) as shown in FIG. 4, and the left and right differential coefficients of the start point and end point of the specified section are the same. Use a function of degree 2 or higher. The modified parison pattern in the case where the wall thickness is slightly increased in the designated section has been described above. However, when the wall thickness is reduced, the setting constant k is selected in the range of k = 0.80 to 0.99, for example.

As described above, a corrected parison pattern, which is locally corrected only in the designated section of the injection stroke, is newly created through the display device 14 and the input device 15, and is re-registered in the command signal setting portion 11 of the parison control device 16. In addition, it is possible to obtain a desired molded product while adjusting the die gap amount G by the above-described operation procedure.
As described above, according to the present invention, it is possible to easily create a modified parison pattern in which the wall thickness is corrected only in a desired designated section with respect to the original waveform through a gain function defined by a first-order function or a second-order function or more. Therefore, the work time required for changing the molding conditions (local changes in the parison thickness) is greatly reduced.

[0010]

As described above, according to the thickness control method of the parison of the present invention, the time required for changing the molding conditions is significantly shortened and the actual operating rate is increased, so that productivity is improved and Driving operability is improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a parison thickness control device according to an embodiment of the present invention.

FIG. 2 is a modified parison characteristic curve diagram according to an embodiment of the present invention.

FIG. 3 is 1 of a locally modified function (gain function) according to the present invention.
It is explanatory drawing which shows an Example.

FIG. 4 is an explanatory diagram showing another embodiment of a local correction function (gain function) according to the present invention.

[Explanation of symbols]

1 Blow Molding Machine 2 Die 2a Blow Head 2b Nozzle 2c Resin Passage 3 Core 3A Mandrel 3a Rod 4 Injection Device 5 Injection Cylinder 5a Piston Rod 5b Position Detector 6 Extruder 7 Nozzle Slit 8 Paricon Cylinder 9 Die Gap Detector 10 Servo Valve 11 command signal setting unit 12 deviation calculation unit 13 PID control calculation setting unit 14 display device 15 input device 16 parison thickness control device A parison pattern (original waveform) B parison pattern (corrected waveform) G die gap amount S injection stroke α ( x) Gain function e Deviation G ₁ Die gap amount set value G ₂ Die gap amount measured value

Claims (1)

[Claims] 1. A method for controlling the wall thickness of a parison, which is formed by extruding a molten resin supplied into a gap formed between a mandrel and a blow head from a nozzle slit at the lower end of the gap by operating an injection cylinder, and , The injection stroke during molding is the horizontal axis, and the die gap amount of the nozzle slit is the vertical axis. The die gap amount is controlled based on a preset parison thickness characteristic curve on a screen on two orthogonal axes. It is obtained by multiplying the set existing parison wall thickness characteristic curve by the set value of the die gap amount in the specified section of the injection stroke on the horizontal axis by the correction value calculated based on the function of the injection stroke specified in advance. A method for controlling a wall thickness of a parison, wherein the die gap amount is controlled based on a corrected parison thickness characteristic curve formed from a corrected set value.