JPS5919809B2 - Parison wall thickness adjustment device in blow molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for adjusting the wall thickness of parylin in blow molding, vacuum molding, or other hollow molding.

For example, when a bottle having the shape shown in FIG. 3 is molded by the blow molding method, the amount of deformation during molding is different between the mouth portion 12 and the shoulder portion 14, which has a larger diameter. This causes variations in product wall thickness.

In order to compensate for this, it has conventionally been customary to increase the wall thickness of the part of the parylin that corresponds to the part of the product that bulges out during molding. However, in parts where the cross-sectional shape of the product is flat, such as an ellipse or a rectangle as shown in Figure 13, a thin part often occurs near the end of the major axis of the ellipse (near point B). This is noticeable in flat ellipses with a large ratio of major axis to minor axis. For example, according to actual measurements of a molded product having a cross-sectional portion as shown in Fig. 4, it was found that although the desired average thickness of 0.7 to 0.8 mm was obtained in other approximately circular cross-sectional portions, In this elliptical cross section, there is a significant imbalance in wall thickness, 1.1 to 1.3 mm near the end of the short axis and 0.3 to 0.6 mm near the end of the long axis. The problem cannot be solved by the Parylin wall thickness adjustment device. The present invention was made in order to solve the conventional disadvantages, and in addition to adjusting the wall thickness of Parylin according to the amount of swelling of the product, the present invention also allows the cross-sectional shape of the product to be oval or rectangular. The purpose of the present invention is to provide a wall thickness adjustment device for Pariline which adjusts the shape of Pariline to an elliptical shape with an appropriate size corresponding to the flattened portion.

That is, as shown in Figure 5a, the cross section has an inner diameter of X and an outer diameter of R.
Particularly in the part corresponding to the product part with a flat elliptical cross section, the thickness of Parylin in the shape of a circular ring with a thickness of . The idea of the present invention is to adjust the cross-sectional outer circumferential shape of the parison to an elliptical shape so that the thickness is increased by δ in the short axis direction where the product is thick.

An embodiment of the present invention illustrated in the drawings will be described below.

First, an example of the apparatus of the present invention will be described with reference to FIGS. 1 and 2. FIG.

In the figure, reference numeral 1 denotes an extrusion die casing having a hollow cylindrical shape, and an extrusion cylinder 2 for extruding molten resin opens in the side wall of this die casing.
A circular support ring 5 is attached directly below the opening of the extrusion cylinder 2 of the casing 1, and the upper end opening of a thin-walled cylindrical external mouthpiece 4 is fixed to the inner circumference of the support ring 5. .
The external mouthpiece 4 is made of a suitable metal material that is heat resistant and has high tensile strength, such as a stainless steel plate, and is provided below the opening of the extrusion cylinder 2 coaxially with the casing. The upper end opening of this external mouthpiece 4 is a resin inlet communicating with the opening of the extrusion cylinder 2.
The cross-sectional shape is held constant and fixed so as not to be deformed, and the lower end opening, which is the resin outlet, is pressed and deformed by pressing blocks 6, which will be described later. An internal cap 3 is mounted coaxially within the external cap 4 so as to be movable in the axial direction. The internal cap 3 has a truncated conical shape with a taper that expands downward, and defines a molten resin passage p with a circular cross section with the external cap 4. The conventional technique is to adjust only the width or narrowness of this resin passage through motion. Two pressing blocks 6, 6 are disposed between the outer periphery of the lower end opening of the external cap 4 and the casing 1. As is clear in FIG. The track is formed so as to have a predetermined elliptical inner circumference 6a that surrounds the entire outer circumference of the lower end opening of the outer cap 4 when the outer cap 4 is in a state in which the inner circumference of the outer cap 4 is They are disposed in close contact with the outer periphery of the cylinders and spaced apart from each other by a predetermined distance in the radial direction, in this case by 2δ. The pair of pressing blocks 6, 6 has an elliptical inner circumferential portion 6a having a circumferential length equal to the outer circumferential length of the lower end opening of the external mouthpiece 4. Here, the elliptical shape formed by both pressing blocks 6, 6 is created by increasing the outer diameter of the resin, that is, the parison, extruded from the lower end opening of the external mouthpiece 4 in a predetermined direction by an amount ε, as described above. The diameter in the perpendicular direction corresponds to an ellipse shortened by an amount δ, and the thickness of the material of the external cap 4 is t.
', then the major axis is 2 (R+ε+t') and the minor axis is 2 (R-
δ+t') is an ellipse. A pressing rod 7, 7 is attached to the pressing rods 6, 6, respectively, in a straight line at one diameter position of the external mouthpiece 4.

The pressure rods 7, 7 each extend outside the casing 1, one pressure rod 7 being connected to a hydraulic cylinder 8, for example.
The other pressing rod is connected directly to the piston at point 11.
The lever 9 is connected to one end of a lever 10 with an arm length ratio of 1:1 that rotates around , and is mounted between the other end of the lever 10 and the piston in the opposite direction to the former pressing rod 7. is configured to move the same distance. The above is an example of a device for pressing the pressing blocks 6, 6.
This mechanism may optionally be replaced by other mechanical or electromagnetic devices. A case will be described in which the thickness of a parison is adjusted using the apparatus of the present invention described above.

When the pressing blocks 6, 6 are not pressed, the shape of the molten resin passage p is as shown in FIG. When the cross section of the product is not particularly flat and there is no need for adjustment, the resin is extruded from the lower end opening of the external die while the circular path remains as it is, and a parison is obtained. Of course, the thickness of the resin passage p can be varied by moving the internal cap 3 up or down, that is, by varying the above-mentioned X, as in the conventional case. Then, when the resin is sequentially extruded in the axial direction from the lower end opening of the external mouthpiece 4 and the product reaches a part where the cross section becomes a particularly flat ellipse, the fluid pressure cylinder 8 may be actuated. In this way, the pressing blocks 6, 6 crush the lower end of the external die 4 from both sides, and the outer shape of the extrusion passage becomes an ellipse as shown in FIG. 5b. In this case, since the internal mouthpiece 3 does not change at all, it becomes thicker in the major axis direction and thinner in the minor axis direction, and as described above, it is possible to correct the imbalance in the thickness of the product. Therefore, the external cap 4 has a cylindrical shape, and the upper end opening is held constant and fixed without deforming its cross-sectional shape (perfect circular shape), and the lower end opening is fixed by the pressing blocks 6, 6. It is designed to be deformed by pressure.

That is, the external cap 4 has a wall portion that continues linearly along the axial direction between the upper opening and the lower end opening,
There are no other members or steps between the openings at both ends. Furthermore, when the lower end opening of the external cap 4 is deformed into an oval shape by the pressing blocks 6, 6, the cross-sectional shape of the external cap 4 gradually changes from a perfect circle to an ellipse along the axial direction from the upper end opening to the lower end opening. As a result, the cross-sectional area also changes slowly and continuously along the axial direction. Therefore, the resin passage p formed inside the external cap 4 between the upper end opening and the lower end opening has a wall portion that continues linearly along the axial direction, and the lower end opening is shaped like an ellipse. When deformed to The cross-sectional shape and cross-sectional area will not change drastically due to the difference between the parts. Therefore, the resin discharged from the opening of the extrusion cylinder 2 is transferred from the upper end opening of the external mouthpiece 4 to the outer mouthpiece 4.
During the process of being extruded from the lower end opening through the resin passageway, the resin can flow smoothly and continuously within the external mouthpiece 4 without sticking or stagnation. It is possible to prevent problems such as stopping and causing problems in parison molding or adversely affecting the quality of the parison. Here, the amount of increase in the wall thickness in the major axis direction ε} and the decrease amount in the minor axis direction δ may be set experimentally.

However, since the circumference of the lower end of the external cap 4 does not change and is constant, the circumference of the ellipse after deformation should be calculated by elliptic integral using the major axis value 2 (R + ε) and the minor axis value 2 (Rδ). The condition that the length must be equal to the original circumference 2πR is essential. The values of ε and δ are determined experimentally as described above, but their magnitudes are on the order of (10)-1 at most, and with this degree of deformation, the external cap 4 The material and its axial length and thickness should be selected so that the stress generated in the material does not exceed the elastic limit of the material. In this way, the cross-sectional area of the parison is changed by deforming the parison into an elliptical shape having a circumferential length equal to the circumferential length of the outer circumferential portion of the product in accordance with the flattened portion of the cross-section of the product. The pressing blocks 6, 6 each have an elliptical inner circumferential portion 6 having a circumferential length equal to the outer circumferential length of the lower end opening of the external mouthpiece 4.
a and press deforms the external cap 4 by surrounding the entire outer periphery of the lower end opening of the external cap 4, so that the lower end opening of the external cap 4 has an elliptical shape with no corners and continuous curves around the entire circumference. It can be transformed easily.

Therefore, by extruding the resin from the lower end opening of the external mouthpiece 4, a parison having an elliptical cross-sectional shape with continuous curves over the entire circumference can be obtained. By molding this parison into a container by blow molding, it is possible to obtain a good container with no corners along the axial direction and a continuous curved surface. In addition, in the above-mentioned embodiment, the outer cap 4 was explained as having a hollow cylindrical shape.
It may also have a hollow truncated conical shape with the same taper.

In addition, if there is a problem in which the middle part of the body bulges due to the extrusion pressure of the molten resin as a result of reducing the wall thickness of the external mouthpiece 4 and increasing its length in the axial direction, the casing 1
It is also advisable to fill the gap 15 between the external cap 4 with a fluid but incompressible material such as slippery powder such as molybdenum disulfide or oil. The device according to the invention can of course be controlled completely automatically.
Although not shown, for example, if a container is to be molded having a flat elliptical cross section starting at a distance y from the upper opening and extending over a distance l, then For example, a phototube is provided at the bottom, and when the lower end of the parison comes to this position and blocks the light, a solenoid valve is actuated to activate the fluid pressure cylinder 8, and another detection device is placed further downward at a distance l. The wall thickness of the parison relative to the container can be automatically adjusted by deactivating the hydraulic cylinder and returning it when the lower end of the parison reaches this point. Similarly, it is easy to adjust the thickness of the parison for containers with more complex shapes. As described in detail above, according to the device of the present invention, the shape of the outer periphery of the cross section of the lower end opening of the external mouthpiece is shaped into an elliptical shape having a circumference equal to the original outer periphery, corresponding to the flat part of the product. This method changes the cross-sectional area of the parison by changing the thickness of the parison and changing the cross-section of the outer circumference into an elliptical shape, which is different from the conventional ring-shaped cross-section. This has the effect of almost completely resolving the thickness imbalance in a flat cross section, which could not be resolved by adjusting the wall thickness as is or by increasing or decreasing the wall thickness only in one diameter direction.

In addition, in the device of the present invention, even when the lower end opening of the external cap is changed to an elliptical shape, the cross-sectional shape and cross-sectional area of the external cap can be changed gently and continuously along the axial direction, so that the resin can be It is possible to obtain flow continuity and to obtain a parison having an elliptical cross-sectional shape with no corners and continuous curves over the entire circumference, which is a favorable result in terms of parison molding and quality improvement of molded products. is obtained.

[Brief explanation of drawings]

FIG. 1 is a side sectional view showing one embodiment of the device of the present invention, FIG. 2 is a cross-sectional view taken along the line in FIG. 1, and FIG. 3 is a simplified perspective view showing an example of a product container made by blow molding. 4 is a plan view showing the bottom surface of the container shown in FIG. 3, and FIGS. 5A and 5B are simplified plan views illustrating changes in the extrusion port for molten resin. 1... Extrusion mouth metal casing, 2... Extrusion cylinder,
3... Internal cap, 4... External cap, 6... Pressing block, 6a... Oval inner peripheral portion of the pressing block, 7,
8, 9, 10, 11...pressing device.

Claims (1)

[Claims] 1. An upper end opening provided below the resin extrusion cylinder opening in the extrusion die casing in the coaxial direction with the casing and communicating with the extrusion cylinder opening is fixed while maintaining a constant cross-sectional shape, and a lower end opening is fixed. an external cap with a cylindrical shape that can be pressed and deformed; an internal cap with a truncated conical shape provided coaxially with the external cap so as to be movable in the vertical direction; and a lower end opening of the external cap. a pair of pressing blocks that surround the outer periphery of the external mouthpiece and are movably disposed opposite to each other on the diameter line of the lower end opening to press and deform the lower end opening of the external mouthpiece; a pressing device that applies a pressing force by moving toward and away from the outer base, and the pair of pressing blocks each have an elliptical inner circumferential portion having a circumferential length equal to the outer circumferential length of the lower end opening of the external base. A parison wall thickness adjustment device in blow molding, characterized by having: