JPS5837130B2 - plastic magarikanno seikeihouhou narabini souchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for shaping a bent plastic pipe and a molding apparatus used in the method.

When forming bent plastic pipes, two commonly used methods are filling the plastic pipe with heated sand and then bending the pipe, and inserting a rubber core into the plastic pipe, heating the plastic pipe, and then bending the pipe. However, these methods have drawbacks such as the time it takes to put in and take out the heated sand and to attach and detach the rubber core.In addition, these methods do not effectively eliminate the compressive stress on the inside of the bend that occurs when the plastic pipe is bent and deformed. Since there is no means for this, there is also the problem that wrinkles are likely to occur on the inside of the bent plastic tube.

In addition, after inserting a heated plastic tube into the bending mold and sealing both ends of the plastic tube with airtight plugs,
A method of blowing high-pressure air into a plastic tube to expand and bend the plastic tube along the inner surface of a mold is known as a so-called blow molding method.

In this molding method, the diameter of the plastic tube introduced into the mold is made sufficiently small compared to the inside diameter of the mold, and the plastic tube is expanded at a constant expansion rate and subjected to a considerably large axial tensile stress. As a result, the bending compressive stress on the inside of the bend caused by the bending deformation of the plastic pipe is canceled out by the above-mentioned axial tensile stress, and the generation of wrinkles on the inside of the bend can be prevented.

However, due to the large expansion rate, the bending part is considerably thinned, and especially on the outside of the bend, the thinning caused by the bending tensile stress due to bending deformation overlaps with the thinning caused by the above-mentioned axial tensile stress. There is an inconvenience that it becomes extremely thin.

The present invention proposes a method and apparatus for molding a plastic bent pipe, which can sufficiently prevent the above-mentioned wrinkles and thinning of the pipe, and can mold the bent pipe with simple operations.

That is, the method for forming a bent plastic tube according to the present invention heats only the central portion of the plastic tube, grips both ends of the plastic tube with clamps, and encloses pressurized air inside the plastic tube while being gripped. Then, by operating the clamp, a bending force and a tensile force are simultaneously applied to the central portion of the plastic tube, thereby bending the central portion of the plastic tube along a bending mold. In this plastic bent pipe forming apparatus, clamps for holding both ends of the plastic pipe to be bent are arranged so as to face the outside of the plastic pipe at approximately the center along the axial direction. The tip of the side arm provided on the bending mold is connected via a link to the bending mold, and when the plastic straight pipe is gripped by the clamp, the pivot position of each link and the side arm is fixed. It is characterized in that it is located closer to the bending die than the pivot position between each clamp and each link.

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

FIG. 1A is a side view showing a plastic straight pipe supported by a molding device, and FIG. 1B is a top view of FIG. 1A.

In FIG. 1 and FIG. 1B, P1 is a straight plastic tube that is bent or shaped.

1 is a mold for bending, such as a wooden mold, a metal mold, or a resin mold, and side arms 2 2 are attached to both sides,
It is arranged so as to face the outside of approximately the central portion along the axial direction of the pipe P1 to be bent.

Numerals 3 and 3 are two-split clamp fittings that hold both ends of the plastic pipe P1, and 4, 4 and 4, 4 are links that connect the clamp fitting 3 and the side arm 2. Each link 4 and side arm 2
are rotatably connected by pins 6, 6, . . . and 5, 5 in parallel.

The pin 5 that pivotally connects each link 4 and the side arm 2 includes
After the stopper 5/ is screwed and the plastic pipe P1 is gripped by the clamp fittings 3, 3, the stopper 5' is tightened and set so that the links 4, 4... can be rotated without sideways vibration. Ru.

In addition, the pivot positions of each clamp fitting 3 and each link 4 are as follows:
At the vertical center position of the clamp fitting 3, that is, when the plastic straight pipe P1 is gripped, it is set to be at the same level as the center line C of the plastic straight pipe P1, and on the other hand, each link 4 and the side arm The pivot position with 2 is a little more than the center line C of the plastic straight tube P1 when the plastic straight tube P1 is gripped.
It is set to occupy a position offset to the mold 1.

In bending a plastic pipe according to the present invention, a plastic straight pipe P1 cut to a predetermined length is used.
The central part of the plastic tube P1 is heated, the central part is placed on the mold 1, and both ends of the plastic straight tube P1 are gripped with clamp fittings 3, 3, as shown in FIG.

Next, both ends of the plastic straight tube P1 are sealed with seal plugs 7, 7, and air is pressurized through an air pressure pipe 8 connected to one of the seal plugs 7.

This press-in of air is to appropriately prevent the plastic tube from flattening during bending and forming, which will be described later, and is usually carried out under a pressure of 0.2 to 0.5 kg/i.

After air is pressurized into the plastic tube P1 as described above, the links 4, 4, . . . are rotated to bend and deform the plastic tube P1, as shown in FIG.

In this case, the connection point 6 between the link 4 and the clamp 3 metal fitting is rotated along the trajectory M in FIG. 1A, and the horizontal length L between this connection point 6 and the pipe bending center 0 is centered on point 0 The plastic tube is bent and deformed while being elongated by the difference between the hypothetical locus N during pure bending with radius L and the aforementioned locus M.

Therefore, the plastic pipe is bent and deformed while being subjected to tensile force, and the bending compressive stress on the inside of the bend of the plastic pipe can be sufficiently canceled out by the tensile stress generated during this bending deformation, and the occurrence of wrinkles on the inside of the bend of the plastic pipe is prevented. can be prevented.

After the plastic tube is bent and deformed in this manner, the pressure of air sealed inside the plastic tube is increased to shape the cross section of the bent portion of the plastic tube into a perfect circle.

In this case, since both ends of the plastic tube are held by the clamp fittings, no axial tensile force is applied to the bent portion of the plastic tube.

Therefore, the bent portion will not be thinned due to axial tension and can be well rounded under sufficient pressure.

After this rounding, the plastic tube is forcibly cooled by water cooling, the air inside the plastic tube is exhausted, and the molding operation is completed.

In addition, in the above, air is directly pressurized inside the plastic pipe to pressurize the inside of the plastic pipe.
It is also possible to pressurize the inside of the plastic tube by inserting a tubular rubber bag into the plastic tube and pressurizing air into the rubber bag.

In addition, in the above example, only the lower mold is used, but the upper mold can also be used when rounding the bent part of the plastic. In this case, the sealed air pressure can be increased, so rounding can be more easily achieved. It becomes even easier.

In the method for bending or shaping a plastic pipe according to the present invention, as described above, pressurized air is sealed inside the plastic pipe while both ends of the plastic pipe are held with clamps.
As a result of this pressurization, the bent portion at the center of the plastic tube is not subjected to axial tension, and the air pressure can be selected to a pressure that can appropriately prevent flattening during bending deformation of the plastic tube.

Furthermore, since the plastic tube is bent and deformed while applying a tensile force when bending the plastic tube, the bending compressive stress generated inside the bent portion of the plastic tube is eliminated by the stress caused by the tensile force.

Therefore, according to the present invention, prevention of flattening during pipe bending and prevention of bending compressive stress can be performed independently of each other. The curved portion will not become extremely thin due to excessive axial tensile force acting on it, and the generation of wrinkles will be well prevented.

Further, the molding device of the present invention is configured to be able to apply external bending force and external tensile force to the plastic tube simply by rotating the link after gripping the plastic tube with a clamp, and is capable of carrying out the molding method of the present invention. It is fully useful for simplifying the work involved.

[Brief explanation of the drawing]

FIG. 1A is a side view showing a plastic straight tube supported by a molding device in the molding method of the present invention, FIG. 1B is a top view of FIG. 1A, and FIG. 2 is a side view of the plastic tube in the molding method of the present invention. It is a side view which shows after bending processing. In the figure, P1 is a plastic pipe, 1 is a bent type,
3, 3 are clamps, 4, 4... are links, 5, 5 and 6, 6... are pins, 7, 7 are seal plugs, and 8 is a pneumatic man pipe.

Claims (1)

[Claims] 1. Heating only the central part of the plastic tube, gripping both ends of the plastic tube with clamps, sealing pressurized air into the plastic tube while holding the plastic tube, and then operating the clamps. A method for forming a bent plastic pipe, characterized in that a bending force and a tensile force are simultaneously applied to the central part of the plastic pipe to bend the central part of the plastic pipe along a bending die. 2. Clamps for gripping both ends of the plastic tube to be bent are placed in a bending mold that is placed facing the outside of the plastic tube at approximately the center along the axial direction of the plastic tube. It is connected to the tip of the side arm provided in the mold via the link, and when the plastic straight tube is gripped by the clamp, the pivot position between each link and the side arm is the pivot position between each clamp and each link. A plastic bent pipe forming device characterized in that the forming device is disposed unevenly on the side of the bending mold.