JPH0261373B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for heat setting plastic pipes that can be applied to a stretch pipe forming machine.

Recently, metal cans, paper composite cans, plastic bottles, etc. have been used as containers for foods and the like. In particular, metal cans (aluminum cans, steel cans) have excellent airtightness and strength, and are used for various beverage cans, but they have drawbacks such as being expensive and being opaque, making it difficult to see the contents. Paper composite cans have problems in terms of strength.

On the other hand, biaxially stretch-molded polyester bottles have begun to be used as plastic bottles with excellent strength and transparency. In the case of bottles, the shape of the bottle is complex and the degree of stretching differs depending on each part of the bottle body, so the overall molding process is complicated.

A plastic can that solves these drawbacks is a plastic can that has a simple plastic pipe body and a metal cap.
This plastic can body member is uniaxially or biaxially stretched by blowing, drawing, etc., and then heat-set to impart heat resistance.

Figure 1 shows the conventional heat-setting method for plastic pipes. In FIG. 1, 1 is a plastic pipe, 2 is a heat-setting mold, 2a is an inner wall of the heat-setting mold 2, 3a is a pipe gripping device having a fluid passage 4,
3b is a pipe gripping device without a fluid passage, 4 is a fluid passage, 5 is a fluid pressure adjustment device, and 6 is a heating means.

However, the conventional heat setting method has the following drawbacks. That is, the plastic pipe 1 to be heat-set is brought into close contact with the inner wall 2a of a heat-setting mold, which is heated to a high temperature by a fluid (generally air) whose pressure is set by a pressure regulating device, and is heat-set by the heat of the mold. be done.

Thereafter, the mold 2 is cooled, the fluid pressure is released, and the heat-fixed pipe 1 is taken out. That is, the mold inner wall 2a
Remove the fluid pressure while maintaining the temperature and place pipe 1 into mold 2.
When taken out from the mold, the outer diameter of the pipe 1 becomes smaller than the inner diameter of the mold inner wall 2a due to heat contraction.
It is necessary to lower the temperature of the pipe 1 to a temperature at which thermal contraction does not occur by lowering the temperature of the mold inner wall 2a before releasing the fluid pressure. Therefore, the outer diameter dimension of the pipe 1 is determined by the dimension of the inner wall 2a of the mold 2.

Therefore, according to this method, it is necessary to repeatedly heat and cool the temperature of the heat-setting mold in one heat-setting operation (one cycle), which makes the mold complicated and requires heating and cooling of a mold with a large heat capacity. Since it takes a long time, productivity is poor. Another disadvantage is that the dimensions of the inner wall of the mold must be changed every time the required outer diameter of the pipe changes.

The present invention has been proposed in order to solve the above-mentioned conventional drawbacks, and in the heat-setting operation of plastic pipes, the heat-setting operation time can be shortened by using a mold with a simple structure, and the same size (inner wall size) can be fixed. The object of the present invention is to provide a heat-setting method for obtaining plastic pipes with different outer diameters using molds.

In order to achieve the above-mentioned object, the present invention maintains a heat-setting mold at a constant high temperature when heat-setting a plastic pipe molded in uniaxial or biaxial directions, and heats the pipe in close contact with the inner wall of the mold. By applying secondary pressure to the inside of the pipe, the pipe is heated and strain removed, and the pressure inside the pipe is reduced to secondary pressure.The mold is then opened to cool the pipe, and then the internal pressure is removed and the pipe is heated. Take out the
Furthermore, by arbitrarily selecting the secondary pressure and utilizing the pipe's thermal contraction force and the pipe's expansion force due to internal pressure, an arbitrary heat-fixed pipe can be obtained without changing the inner wall diameter of the heat-fixing mold. It is characterized by this.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows an example of an apparatus for carrying out the heat setting method of the present invention. In the figure, 11 is a plastic pipe to be heat-set, 9 and 10 are heat-setting molds (hereinafter referred to as molds) having heating means 6, and 13a
is a device for airtightly gripping the end of the pipe 11,
The pipe has a flow path 14 through which fluid is to be passed. 1
3b is the same airtight gripping device as the device 13a, but it does not have the flow path 14.

Reference numeral 15 indicates a main control valve for fluid pressure applied from the fluid pressure source 19 into the pipe 11, and reference numerals 16, 17, and 18 indicate pilot pressure control valves for operating the main control valve 15, which control the primary pressure, secondary pressure, and atmospheric pressure release, respectively. Has a setting function.

FIGS. 3 and 4 show the molds 9 and 10 opened while maintaining the secondary pressures at PA and PB, respectively. In addition, Figures 5 and 6 show the state of the heat-set final product plastic pipes, which were heat-set under the conditions shown in Figures 3 and 4, respectively.
Cut it along the line shown and use it.

Next, to explain the operation, first, the plastic pipe 11 cut to the required length is held in the airtight gripping device 1.
3a and 13b and held in the molds 9 and 10. The pilot pressure control valve 16 then actuates the main control 15 to control the primary pressure Pi from the fluid pressure source 19.
A controlled fluid pressure acts on the inside of the pipe 11. This pressure brings the pipe 11 into close contact with the mold inner walls 9a, 10a.

The molds 9 and 10 are heated to a high temperature by the heating means 6 and 6, and the pipes 11 that are in close contact with each other are thermally fixed (eliminate molding distortion) by the heat. In addition, unless the pressure Pi (primary pressure) at this time is such that the pipe 11 can be sufficiently expanded and deformed at the heat setting temperature, the pipe 11 will not come into sufficient contact with the mold inner walls 9a, 10a.

Next, by operating the pilot pressure control valve 17, the pressure inside the pipe 11 is reduced to a secondary pressure (for example,
PA, PB). This secondary pressure is the pressure that allows the pipe 11 to withstand thermal contraction at the heat-fixing temperature, and the pressure that prevents the pipe 11 from expanding and deforming due to internal pressure even if the outer restraining molds 9 and 10 are opened (balance pressure). set nearby. Next, the molds 9 and 10 are opened.

The pipe 11 is left to cool while its internal pressure is maintained at the secondary pressure. Although not shown in the drawings, cooling may be performed using a forced cooling device or the like to save time. Here, the internal pressure is set to a pressure slightly higher than the balance pressure mentioned above.
When set to PA, the pipe 11 expands and deforms to a diameter DA that is slightly larger than the mold inner wall diameter di, and the pipe shape 11a balances the internal pressure PA.

Also, if the pressure PB is set slightly lower than the balance pressure mentioned above, the diameter DB is slightly smaller than the mold inner wall diameter di.
The pipe shape of 11b balances the internal pressure PB. That is, even if the inner wall of the heat-setting mold is the same, the outer diameter of the pipe after heat-setting can be arbitrarily selected by selecting this secondary pressure.

Next, when the temperature of the pipe 11 drops to a temperature at which it does not deform even if the internal pressure is removed, the pilot pressure control valve 18 is activated and the pipe internal pressure is released to the atmosphere.
Next, the airtight gripping devices 13a and 13b are released and the pipe 11 is taken out. The pipe that has been heat-fixed is the fifth one.
6, so if a straight pipe section is required, it can be used by cutting it along line A to A as shown in the figure.

Since the present invention is constructed as described above in detail, heat fixing with different diameter dimensions can be achieved by selecting the secondary pressure without changing the inner wall dimensions of the heat fixing mold (in other words, with the same mold). A plastic pipe is obtained. Furthermore, by keeping the temperature of the heat-setting mold at a constant high temperature, the cycle time of heat-setting can be shortened, and production can be significantly improved.

Hereinafter, the present invention will be further explained in detail with reference to the following specific examples.

Example A biaxially oriented polyethylene terephthalate pipe (outer diameter 55 mm, wall thickness 0.4 mm) was heat-set by the method of the present invention under the following conditions.

Heat fixing mold: inner wall diameter 55mm, by electric heater
Maintained at 150℃ Primary pressure: Air pressure 4Kg/cm ² G, held for 20 seconds Secondary pressure and pipe outer diameter: 0.6Kg/cm ² G, air cooled
Pipe outer diameter 54.0 mm at 20 seconds 1.4Kg/cm ² G, pipe outer diameter 56.0 mm at air cooling 20 seconds Also, if cooling is performed at a different position from the heat setting mold position, secondary pressure can be maintained and cooled. At the time, another pipe can be heat set at the mold position, so heat setting in the case can be carried out in 25-30 seconds. However, according to the conventional method, the temperature of the heat setting mold is 150℃→70℃→150℃
→ Heating and cooling will be performed, which will take from several minutes to more than ten minutes. Furthermore, the outer diameter of the resulting pipe is around 55 mm, which is determined by the inner wall dimensions of the mold, and the dimensions cannot be controlled.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view explaining a conventional heat-setting method for plastic pipes, FIG. 2 is a cross-sectional view explaining a heat-setting method for plastic pipes showing an embodiment of the present invention, and FIGS. 3 and 4 are respectively Figure 5 is a cross-sectional view of the mold opened while maintaining secondary pressure.
6 is a sectional view of a pipe obtained by the method shown in FIG. 4. FIG. 6 is a sectional view of a pipe obtained by the method shown in FIG. Explanation of main parts of the figure, 6... Heating means, 9, 1
0... Heat fixing mold, 11, 11a, 11b...
Plastic pipe, 13a, 13b...A device for airtightly gripping the end of the pipe.

Claims (1)

[Claims] 1. When heat-setting plastic pipes molded in uniaxial or biaxial directions, the heat-setting mold is held at a constant high temperature, and primary pressure is applied to the inside of the pipe to bring the pipe into close contact with the inner wall of the mold. After heating the pipe to remove strain and reduce the pressure inside the pipe to secondary pressure, the mold is opened and the pipe is cooled, the internal pressure is removed and the pipe is taken out, and the secondary pressure is adjusted to an arbitrary value. The plastic pipe is characterized in that it is possible to obtain any heat-set pipe without changing the inner wall diameter of the heat-fixing mold by using the heat-shrinking force of the pipe and the expansion force of the pipe due to internal pressure. Heat fixing method.