JPS5925649B2 - Method for controlling cross-sectional area distribution of parison for blow molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the cross-sectional area distribution 9 of a parison in a blow molding machine.

In blow molding, a parison extruded into a cylindrical shape from a nozzle is sandwiched between molds, and gas is blown into the parison to cause it to expand, stick to the inner wall of the mold, and solidify to form a hollow product. .

Therefore, the wall thickness of the molded product is largely influenced by the distribution of the longitudinal cross section/9 product of the parison that is sandwiched between the upper and lower parts of the mold and enters the mold.

Even if parisons have the same cross-sectional area, the wall thickness distribution of the molded product will change depending on the size of the diameter, but as long as a given nozzle is used, the parison diameter will hardly change and this effect can be ignored in practice. It is also possible to change the parison diameter by pre-processing, but this is not normally used because the diameter is unstable.
To control the cross-sectional area of the parison, measure both the thickness Tp and the diameter Dp of the parison, and calculate the cross-sectional area Ap from the relational expression Apeπ・Dp−Tp. How to ask.

@ Analyze both the speed at which the parison is extruded υ, d and the extrusion amount G, and calculate the cross-sectional area Ap of the parison by GAp2? A method of finding it from the relational expression.

υPd There are two methods.

Method 4 is possible if an ultrasonic thickness meter is used, but it has the drawback that if the parison develops vertical wrinkles as a result of a curtaining phenomenon, the diameter of the parison cannot be measured at all.

Although curtaining phenomenon is easy to occur, it is particularly difficult in large-scale blow molding. Similar to O's method, ``In a continuous extrusion blow molding machine, the time when the lower end of the parison passes a specific height is measured with multiple phototubes arranged in the vertical direction of the mold, and the extrusion speed υPd of the parison is determined. , IKV method (Kunst
Offberater9VOl22, black 2, 78-87
, 2/1977).

However, this method cannot be applied to an accumulator type blow molding machine and cannot control the cross-sectional area.

The reasons for this are: (a) the viscoelastic properties of the parison change due to disturbances such as differences in resin rods and changes in temperature, and the cross-sectional area cannot be kept constant; (5) to compensate for the drawbacks of (a). It is necessary to measure the amount of extrusion and change the nozzle slit to obtain a parison with a constant volume, but continuous measurement of the amount of extrusion requires a gear pump for molten plastic to be installed in front of the head, which is expensive. Therefore, normal blow molding is not economically viable.

(c) The shape of the parison is a sharp shape from the previous molding, and it is rarely a horizontal shape, but usually has an irregular shape with jagged edges.

For this reason, it is not possible to finely control the thickness distribution in the longitudinal direction of the parison based on the passage time of the lower end. (d) Arranging a large number of detectors such as phototubes requires time and effort to adjust them, and it is inconvenient to take out molded products, attach accessory devices, etc. In addition, in an accumulator type blow molding machine, the length and weight (
In other words, the following methods are available for keeping the average cross-sectional area constant.

In other words, the amount of injection is limited in advance to keep the weight constant, and the time when the plunger reaches a certain position at the lower end of the parison is compared with the time when the plunger reaches the injection limit, and the opening degree of the nozzle slit is changed to control the parison. There is one in which the length is controlled to be constant (Japanese Patent Publication No. 55-16816).

However, with this method, it is not possible to keep the cross-sectional area and length of each part of the parison divided into two or more parts constant in the longitudinal direction. cannot be controlled.

As described above, conventionally, the cross-sectional area has not been measured at each position in the longitudinal direction of the parison, and therefore no attempt has been made to control the cross-sectional area distribution that changes in the longitudinal direction as set.

Conventionally, there was no way to measure the wall thickness, outer diameter, or cross-sectional area of the extruded parison, so it was difficult to know whether the parison had reached the set shape or whether a certain parison continued to come out. This could only be confirmed indirectly from measurements of the complex wall thickness distribution of molded products.

The present invention attempts to measure and control the longitudinal cross-sectional area distribution of the parison while extruding the parison. A marker is provided directly under the nozzle near where the parison passes, and a mark detector is installed below the marker. Two detectors are installed at close intervals in the vertical direction so that a detection signal is emitted each moment the mark passes through the two detectors, and input/output for setting the cross-sectional area distribution in the longitudinal direction of the parison can be performed. In an accumulator blow molding machine that has a microcomputer and a servo control system that performs balisong control using signals from the microcomputer, the extruded parison is intermittently marked with a marker, and the mark is detected on two machines. The time it takes to pass between the containers is measured to find the moving speed of the parison, and at the same time the stroke speed of the extrusion plunger is measured to find the extrusion flow rate, and this is divided by the moving speed of the parison to calculate the flow rate perpendicular to the longitudinal direction of the parison. Find the cross-sectional area, then find the nozzle opening area from the nozzle slit and the nozzle diameter, and divide the cross-sectional area of the parison by this value to find the product of the wall thickness swell ratio and the diameter swell ratio. Convert the relationship between the position of the plunger and its cross-sectional area from the relationship where the volume of the resin is constant to the relationship between the stroke position of the plunger and the cross-sectional area, and adjust the above so that the set cross-sectional area is reached each time the position of the plunger changes. The slit value to be used is determined from the data immediately before the obtained swell ratio product data, or the value near the same plunger position obtained during the previous extrusion, or the slit value and swell value used during the previous injection. The nozzle slit was calculated using the value determined by interpolation or extrapolation of the corresponding swell value, the position of the mandrel was controlled to achieve the nozzle slit, and the cross-sectional area distribution at multiple points in the longitudinal direction of the parison was set. It is characterized by the fact that it can be controlled according to the conditions.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of an accumulator type professional molding machine for carrying out the method of the present invention, in which 1 is a head, 2 is a plunger, 3 is a mandrel, 4 is a position detector for the plunger 2, and 5 is a servo cylinder, 6 is a servo valve,
7 is a position detector for the mandrel 3, 8 is a marker for attaching a mark 10 to the parison 9, 11 is a mark detector, 1
2 is a microcomputer connected to receive signals from the position detectors 4, 7 and mark detector 11, and to output a current to drive the servo valve 6 and an activation signal to the marker 8, and is used to set functions. It has the characteristics of being able to remember things, do calculations, and keep track of time.

13 is a nozzle slit, 14 is a resin inlet, 15 is an accumulator, and 16 is a nozzle portion.

Note that the mark detector 11 outputs a confirmation signal when a mark 10 made with the marker 9 (made with black magic ink, silver paint pastel, etc.) enters the field of view of the mark detector. Two upper and lower mark detectors 1 arranged with a vertical interval T8 smaller than the distance of
1 is set as one set, and they are installed under the nozzle slit 13 and immediately below the marker 8.

The method for attaching the above mark is JP-A-56-2883.
There is also method number 0. Further, the above mark detector is commercially available. In the method of the present invention implemented with the above configuration (
1) First, the principle of measuring the cross-sectional area of a parison will be explained.

When a mark 10 is placed on the parison 9 that is being pushed out by the marker 8, this mark 10 is immediately detected by the upper mark detector 11 and a detection signal is sent to the microcomputer 12.
The mark 10 that has passed through the interval T8 is detected by the lower mark detector 11, and a detection signal of the same mark 10 is sent to the microcomputer 12.

The microcomputer 12 calculates the time Δt between the two signals using a built-in clock, and calculates the time Δt between the two signals.
The moving speed (extrusion speed) υ,d of the parison in the marked portion is determined from the interval T8 between 1 and 1 by the following equation.

On the other hand, at the same time that the mark 10 is placed, the moving speed υI of the plunger 2 is also measured from the rate of change of the signal from the position detector 4 by being sent to the microcomputer 12.

As a result, assuming that the cross-sectional area of the plunger 2 in the extrusion direction is AI, the cross-sectional area A of the parison can be determined from the following equation based on the constant volume relationship. In this way, the cross-sectional area Ap of all marked points on the parison can be determined during extrusion of the parison. When extruding parison 9 with plunger 2, if the screw extruder is stopped,
Equation 2 is strictly correct.

However, even if the extruder is in continuous operation, the flow rate at which the plunger 2 extrudes the resin stored in the accumulator 15 is, for example, 3000 cc/s, whereas the amount of extrusion from the extruder is 100 cc/s, which is 1/30 It is generally assumed that two equations hold true. Next, the principle of controlling the cross-sectional area of the parison as set will be explained.

Parison thickness swell ratio Rtl diameter swell ratio Rh
l The thickness of the parison is TPl The nozzle slit is S1 The nozzle diameter is DNl The parison diameter is D, The cross-sectional area of the parison is A.
Then, there is the following relationship.

As is clear from this relationship, in order to control A,
(Rt-Rh), DN. All you have to do is know the value of S and change one of them.

The nozzle diameter DN is a constant, and the nozzle slit S can be freely controlled by the vertical position of the mandrel. Swell ratio (Rt-
Rh) changes depending on physical properties, flow path shape, and extrusion conditions and cannot be controlled, and its value and tendency cannot be accurately estimated before molding. However, the swell ratio (Rt-Rh)
Once the nozzle and the resin to be used are determined, it will only change slightly due to changes in the opening degree of the nozzle slit S and pressure accompanying changes in S. Therefore, in order to control the cross-sectional area A, of the parison, first assume the swell ratio (Rt-Rh), calculate S for A from equation 5, and then mold the parison with this nozzle slit S to obtain the actual cross-section. :Ni-drop? This means that it is sufficient to calculate ze71↑ζ=≠ and use this value as immediate feedback to the subsequent extrusion.

By calculating (Rt-Rh) at several locations (the more the better) during one parison extrusion, and using them to back-calculate the nearby nozzle slit S (formula 5), the cross-sectional area of the parison can be adjusted as set. can be controlled.

Regarding the method of measuring the cross-sectional area of the parison, see (1) above.
It is stated in ([[I) A method for controlling the cross-sectional area distribution in the longitudinal direction of the parison according to a set value from 1 or more will now be described with reference to FIG.

FIG. 2 is a flowchart showing control in the steps of setting, start of extrusion, parison formation, and end of extrusion. 1. First, the distribution of the cross-sectional area A along the position t in the longitudinal direction of the parison is set as a relationship between points P A,i-t of several bends.

A, i=f(Ti) (1=1~N)...02.
On the other hand, based on the relationship between the amount pushed out by the plunger and the volume of the parison, the following relationship exists between the length Ti of the parison and the stroke position Xi of the plunger.

However, the interval between Ti atoms is constant at Δt (i.e., Ti, +1-Ti=ΔTi=1~N-1).

11Xi = Mutual monopoly A, kΔt (1=1 to N)...[F] From the [stock] formula, the relationship Xi-TiyAPi-Xi is obtained.

3. The setting points of the above A, i-Xi relationships are far from each other, and unless they are complemented by connecting them with straight lines, a smooth parison shape cannot be obtained. The interpolated values A, j−Xj for each interval Δx are determined after the start of extrusion (j=1 to NJ, NJ>>N).

4. Next, for each stroke position Xj of the plunger detected by the position detector 4, a nozzle slit Sj that can produce the set cross-sectional area A, j of the parison is determined by the following equation assuming a swell ratio (Rt-Rh)j.

The nozzle slit Sj is converted to the mandrel position Y by a simple geometrical relation.

Yj←Sj...0 From now on, Yj corresponding to Xj will be output.

5. On the other hand, if we decide to attach marks at ΔTm at integral multiples of Δt as marking interval settings, then Tl, . Xi
(for example, i
= 2, 4, 6...).

Xi used when marking is referred to as XMi.

6. When the parison is extruded in this way, XMj
According to the principle of (1) above, the actual cross-sectional area A of the parison is
, ′ are measured.

From this measured Ap' and equation 6, the true swell ratio (Rt
-Rh)' is obtained.

' Immediately move this (Rt-Rh) to the next stroke position Xj+
This is used to calculate the nozzle slit Sj+1 and the mandrel position Yj+1 by substituting it into Equations 1 to 9.

This process is continued until a new (Rt-Rh)' is obtained at the next mark point. 'Also, if (Rt-Rh)' is not determined in the next extrusion, the previously determined values for each Xj are used as they are.

The value until the 1'th mark is (Rt-Rh)
Use the value of Xi=1.

In this way, the cross-sectional area A of the parison is measured the next time the parison is extruded, but even without changing the p nozzle slit S, the nozzle slit Sj-Yj is based on the true swell ratio, so the cross-sectional area A of the parison is measured as set. In addition to the cross-sectional area A,j, the relationship between the length Ti of the parison and the cross-sectional area A,i is also automatically satisfied from the relationship of Equation 8.

7. Regarding the effect that the swell ratio changes somewhat due to the modification of the nozzle slit Si, please refer to 4. above. ~6. Repeat steps.

8. Once you can make a parison according to the settings,
In order to confirm that the molding is stable, the cross-sectional area A, is measured and controlled at certain intervals, but if A is not measured, the mandrel is The position y of is program-controlled, and the calculation of the slit S based on the swell ratio (Rt-Rh) is omitted.

Note that the above is an example of the method of the present invention, and the method is not limited thereto, and the following method may also be used.

That is, during extrusion of 4 parisons, the swell ratio (Rt.Rh
) was not corrected, but was corrected during the next extrusion (Rt-
Rh) can also be used.

Furthermore, it is also possible to use a value determined by interpolating or extrapolating the swell value corresponding to the slit to be used from the slit value and swell value used during the previous injection.

In this case, although there is a drawback that the control is not performed during the first extrusion, molding conditions can be automatically set because the calculation speed of the microcomputer is fast.

Most of the various disturbances during long-term operation, such as differences in QlO resin rods and changes in temperature, can be automatically corrected.
A constant parison shape is always obtained.

This increases molding stability and eliminates the need for monitoring. This allows for labor savings.

(1V) By measuring the moving speed υ, d of the parison at the heights of the upper, middle and lower parts of the suspended parison, it is possible to measure the tendency of drawdown. It is also possible to create a cross-sectional area distribution.

Therefore, it becomes easier to mold resins that have severe drawdown and for which it is difficult to set an appropriate nozzle slit.

It can produce excellent effects such as

[Brief explanation of drawings]

FIG. 1 is a sectional view of an accumulator blow molding machine for carrying out the method of the present invention, and FIG. 2 is a flowchart of the method of the present invention. 1...Head, 2...Pransha,
3... Mandrel, 4, 7... Position detector, 8... Marker, 9... Parison, 10... Mark, 11 ...Mark detector, 12...Microcomputer, 13.
...Nozzle slit, 15...Accumulator.

Claims (1)

[Claims] 1. A marker is provided directly below the nozzle near where the parison passes, and two mark detectors are installed vertically at close intervals below the marker, and the detection signal is obtained at each moment when the mark passes through the two detectors. In an accumulator type blow molding machine, the accumulator type blow molding machine has a microcomputer capable of inputting and outputting information for setting the cross-sectional area distribution in the longitudinal direction of the parison, and a servo control system that controls the parison using signals from the microcomputer. The parison being extruded is intermittently marked with a marker, the time it takes for the mark to pass between two detectors is measured, the movement speed of the parison is determined, and at the same time the stroke speed of the extrusion plunger is measured. Determine the extrusion flow rate, divide this by the moving speed of the parison to determine the cross-sectional area perpendicular to the longitudinal direction of the parison, then determine the nozzle opening area from the nozzle slit and nozzle diameter, and use this value to calculate the cross-sectional area of the parison. The product of the wall thickness swell ratio and the diameter swell ratio is obtained by dividing the ratio, and on the other hand, the relationship between the longitudinal position of the set parison and its cross-sectional area is calculated by calculating the relationship between the stroke position of the plunger and the cross-sectional area based on the relationship that the volume of the resin is constant. Convert it into a relationship, and each time the plunger position changes, set the cross-sectional area immediately before the swell ratio product data obtained above, or change it to the same plunger position obtained during the previous extrusion. Calculate the nozzle slit using the closest value or the swell value that corresponds to the slit value used during the previous injection and interpolate or extrapolate it from the swell value and the swell value used during the previous injection. A method for controlling the cross-sectional area distribution of a parison for blow molding, characterized in that the position of a mandrel is controlled so as to form a slit, and the cross-sectional area distribution at multiple locations in the longitudinal direction of the parison is controlled as set.