JPS5818889B2 - plastic magarican no seikeihouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of forming a bent plastic tube.

When molding a bent plastic tube, as shown in Figure 3, a heated plastic tube is introduced into a mold for molding the bent tube, both ends of the plastic tube are sealed with airtight plugs, and high pressure air is injected into the plastic tube. A so-called blow molding method is sometimes used, in which the plastic tube is expanded along the inner surface of the mold and bent.

In this molding method, if the diameter of the plastic tube introduced into the mold is sufficiently smaller than the inner diameter of the mold, the plastic tube will be expanded at a constant expansion rate, so the plastic tube will have a considerable amount of expansion. Tension acts.

Therefore, the bending compressive stress on the inside of the bend caused by the bending deformation of the plastic tube is canceled out by the expansion tension, and the generation of wrinkles on the inside of the bend can be prevented.

However, due to the large coefficient of expansion, the bent pipe becomes considerably thinner, especially on the outside of the bend, where the thinning due to bending tensile stress due to bending deformation and the thinning due to the expansion mentioned above combine to cause the bent pipe to become significantly thinner. There is.

One possible way to prevent this is to make the diameter of the plastic tube introduced into the mold equal to the inner diameter of the mold to reduce the above expansion rate as much as possible, but in this case, When pressurized air is blown into the plastic tube, the straight tube inside the bend expands and is first pressed against the inner surface of the mold.
As a result, both sides of the plastic tube (see C in the figure) are restrained by the mold, and as a result, by blowing air afterwards, the folded plastic tube part inside the facing part is folded, and the mold is closed. It will be pressed against the inside of the curved part.

For this reason, there is a problem in that wrinkles are likely to occur inside the bent portion of the bent plastic tube.

The method for molding a bent plastic tube according to the present invention can effectively prevent the formation of wrinkles inside the bent portion of the bent tube, even if the expansion coefficient of the plastic tube is reduced.
A plastic pipe whose inner diameter and outer diameter are approximately equal is introduced into a mold for forming a bent pipe, and inside the plastic pipe,
When a pressurized medium is injected while the plastic tube is heated to expand the plastic tube until it contacts the inner surface of the mold, at least one end of the plastic tube is pulled from the outside, and then the pressurized medium is injected. It is characterized by performing the following.

The present invention will be explained below with reference to the drawings.

゛In Figures 1 to 3, 1 is a mold for forming bent pipes;
Numerals 2 and 2 are seal plugs, and 3 and 3 are clamp fittings for gripping the end of the plastic tube with the seal plugs 2 and 2.

These seal plugs 2, 2 are provided with pressurized air blowing nozzles 21.
21 has been introduced.

Furthermore, either the seal plugs 2, 2 or the clamp fittings 3, 3 is provided with a pulling means for pulling the plastic tube, but this is not shown.

To carry out the present invention, first, as shown in FIG. Finish 3.

A plastic tube P whose outer diameter is approximately equal to the inner diameter of the mold 1 is used.

When this plastic tube P is introduced into the mold 1,
The inner side C of the bent portion of the plastic pipe P is folded toward the outer side of the bend due to compressive bending strain.

After introducing the plastic pipe P into the mold 1, as shown in FIG. It is brought into close contact with the inner side 10 of the curved part.

In this case, it is desirable to pull the plastic pipe P by pulling both ends of the plastic pipe P, but it is also possible to pull only one end of the plastic pipe P.

Moreover, there is no problem even if some gap remains between the inside bend part 9' of the plastic tube P and the inside bend part 10 of the mold 1.

After pulling the plastic pipe P in this way and removing the wrinkles C (Fig. 1) on the inside of the bend, high-pressure air is blown into the plastic pipe P to form the plastic pipe as shown in Fig. 3. Expand p until it comes into close contact with the inner surface of whole red 1.

Before this expansion, some gap remains between the inside bend C' of the plastic pipe P and the inside bend 10 of the mold 1 (see Figure 2). Even if the wrinkles are not removed reliably, they can be easily removed by expanding the plastic tube P.

After the plastic pipe P is expanded in this manner, the plastic pipe P is cooled and solidified while maintaining the pressurization of high-pressure air, and then demolded to complete the work.

As described above, the method for forming a bent plastic tube according to the present invention involves introducing a heated plastic tube into a mold for forming a bent tube, pulling the plastic tube, removing wrinkles inside the straight portion of the plastic tube, and then This is a so-called blower molding method for plastic pipes by blowing high-pressure air into the mold, and even if the outside diameter of the plastic pipe introduced into the mold is approximately equal to the inside diameter of the mold, it can be bent without wrinkles and with a good appearance. You can get the tube.

In addition, the thinning of the plastic tube due to stretching of the plastic tube can be kept to a sufficiently low level compared to the case where a small diameter plastic tube is introduced into the mold and its expansion rate is increased to prevent the above wrinkles from occurring. .

Therefore, according to the present invention, it is possible to obtain a good plastic bent tube that has a small expansion processing rate, that is, has sufficient wall thickness and is free from wrinkles inside the bent portion.

[Brief explanation of drawings]

1 to 3 are explanatory diagrams showing the molding procedure in the present invention. In the figure, 1 is a mold, 2 and 2 are seal plugs, 21 and 21 are air blowing nozzles, 3 and 3 are clamp fittings, and P is a plastic pipe.

Claims (1)

[Claims] 1. A plastic tube whose inner diameter and outer diameter are approximately equal is introduced into a mold for forming a bent tube, and a pressurized medium is blown into the plastic tube while heating the plastic tube to transform the plastic tube into a plastic tube. A method for molding a bent plastic tube, characterized in that when the tube is expanded until it contacts the inner surface of the mold, at least one end of the plastic tube is pulled from the outside and then the pressurized medium is blown into the tube.