JPH0156893B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for processing plastic pipes, and more particularly to a method for forming sockets on the ends of PVC pipes.

[Conventional technology]

By heating and softening the end of the PVC pipe and press-fitting the end onto the socket molding core,
It is known to mold sockets into the ends of PVC pipes.

However, the above method has disadvantages in that thinning of the wall of the socket tube and occurrence of noticeable wrinkles on the outer surface of the socket cannot be avoided.

In order to eliminate this disadvantage, an outer mold is placed on the socket molding core, and the thickness of the gap between the core and the outer mold is reduced.
The wall thickness of the PVC pipe to be expanded is approximately equal to the wall thickness of the opening to be formed, and the heated end of the PVC pipe is press-fitted into this gap. A method has been proposed in which a socket is formed at the end of a PVC pipe by filling the void by applying pressure in the same direction (Japanese Unexamined Patent Publication Nos. 53-136076 and 53-13679). .

FIGS. 1A to 1D show the socket molding method according to the second method described above. Figure 1A to 1st
In Figure D, a' indicates a tapered stepped portion, b' indicates a straight portion, and c' indicates a chevron-shaped portion.

p′ indicates the end of the heat-softened PVC pipe,
It is pushed into the gap between both molds, as shown in Figure 1A.
When the tip reaches the inclined stepped portion a', it receives an axial compressive force f and is thickened.

After that, as the press-fit progresses, the axial compressive force increases and the pipe cross-sectional area increases, but the pipe diameter also increases, so the wall thickness of the pipe portion where the diameter has increased decreases, as shown in Figure 1. As shown in B, the straight section
A gap g′ is generated between the inner surface of the outer mold and the outer surface of the pipe at b′. The thickness d of this gap g' can be qualitatively understood as follows.

That is, in FIG. 1B, at point P ₀
If the cross-sectional area of the PVC pipe considering the cross-sectional increase rate α is S(1+α) and the pipe inner diameter is r, the pipe outer diameter R is π(R ² − r ² )=S(1+α) Therefore, It is.

If the size of the gap between both molds is t, the thickness of the gap d is is given by

The end of the above PVC pipe is further pushed in,
As shown in Fig. 1C, when the tip of the pipe reaches the first step _C1 ' of the chevron section, the axial compressive force f at the end of the pipe increases, so the thickness increases at a rapid pace. As shown in Figure 1D, the straight part
A PVC pipe is thickened due to the axial compressive force f.

[Problems with conventional technology]

However, according to the observation results of the present inventors, because the gap d on the straight section PVC pipe is large,
Seats occur in the straight PVC pipe at the initial stage when the straight PVC pipe is thickened due to axial compression force.
I learned that this seat causes wrinkles to appear on the outer surface of the socket.

[Problem to be solved by the invention]

The present invention is intended to reduce or close the gap d to suppress the occurrence of the above-mentioned buckling and to prevent the occurrence of wrinkles on the outer surface of the socket. Specifically, in the first equation, in order to increase the pipe cross-sectional area S, the pipe end is thickened in advance, and d in the first equation is decreased.

[Technology to solve problems]

The plastic pipe processing method according to the present invention is as follows:
This method was invented based on the above results, and the diameter is expanded by pushing a plastic pipe onto the core, which has a first diameter-expanding sloping step at the front and a second diameter-expanding sloping step at the rear. When molding a socket, an outer mold is placed on the core with a gap approximately equal to the necessary wall thickness of the expanded diameter socket to be molded on the core, and the expanded diameter socket is formed. A state in which the end of a plastic pipe whose end is formed into a thick wall is heated and softened and pushed from the front of the core, and the plastic pipe that is pushed into the gap between the core and the outer mold always fills the gap. It is characterized by being pushed into the rear part.

[Effect]

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

In the present invention, since the processing of plastic pipes is based on expanding the diameter using a core,
As the diameter increases, the wall thickness decreases. Therefore, in order to eliminate the difference in wall thickness between the plastic pipe and the unprocessed part due to the decrease in wall thickness, it is necessary to increase the thickness of the processed part that is to be used as the expanded diameter socket of the plastic pipe in advance. FIG. 2 shows a PVC pipe p with its thickened end e.

During PVC pipe extrusion, the pipe take-up speed is reduced at regular intervals or the extrusion amount is increased, so that the thickened part e' is produced at regular intervals as shown in FIG. , e′...
Extrude the PVC pipe, and in conjunction with this extrusion, cut it at the thickened end e'' as shown in Figure 3B, or cut it at the center e of the thickened part and the thickened end e'' as shown in Figure 3C. It can be obtained by cutting the center m between the meat parts.

In the case of FIG. 3B and the case of FIG. 3C, the distances L and L' between the thickened parts and the thickened widths E and E' are different, and their ratios L/L' and E/E' is approximately 1/2.

In addition, other than the processed parts according to the present invention, for example,
If the wall thickness decreases due to separate tensioning, bending, etc. after socket molding, the entire tube should be increased in thickness compared to the final molded product, without separately molding the thickened and thinned parts as described above. It is said to have a certain thickness.

In Figure 4A to Figure 4B, 1 is the core, 2
is the outer mold, and the gap between them is the after-machining
It is made approximately equal to the pipe wall thickness W of the PVC pipe, that is, the PVC pipe as a finished product. Specifically, when only socket molding is performed, the thickness is 0.9 to 1.2 times the wall thickness W of the unprocessed PVC pipe. That is, the length of the thickened portion of the thickened portion is determined based on the length and volume of the socket in its completed state as an enlarged diameter socket.

A indicates the first diameter-expanding inclined step of the core 1, and b indicates an intermediate surface between both inclined steps, and the illustrated one is a reversely inclined surface. This intermediate plane may be a horizontal plane. The shape of the core 1 is determined according to the shape of the socket to be processed into the end of the PVC pipe.

The angle of the first diameter-enlarging inclined step part A and the angle of the second diameter-enlarging inclined step part b are usually 30 to 45 degrees, and
The angle is between 0 and 5 degrees.

According to the present invention, in order to process the end of the PVC pipe, the thickened end of the PVC pipe is heated to soften it, and a driving force is applied to the PVC pipe, as shown in FIG. 4A.
As shown in the figure, the thickened end e of the pipe is pushed into the gap between the core 1 and the outer mold 2.

FIG. 4B shows a stage in which the insertion has progressed considerably.

The cross-sectional area of the PVC pipe at each position of the core 1 in FIG. 4B is increased by the axial compressive force f acting on the PVC pipe.

Now, if the cross-sectional area of the thickened end e of the pipe is s, and the rate of increase in the pipe cross-sectional area on the core intermediate surface due to the above-mentioned axial compressive force f is α, then the pipe cross-section on the core intermediate surface C is The area is S(1+α). Therefore, if the cross-sectional area of the gap between the core 1 and the outer mold 2 on the intermediate plane C of the core is T, then by bringing S(1+α) closer to T, the virtual It is possible to reduce or eliminate the gap between the core 1 and the outer mold 2 shown in FIG. In order to bring S(1+α) closer to T, the cross-sectional area S of the end of the PVC pipe may be increased in advance. According to the invention, therefore:
It is possible to press the end of the PVC pipe into the core intermediate surface C without forming a gap between the outer surface of the pipe and the inner surface of the outer mold.

When the pipe end is not thickened in advance, that is, when the cross-sectional area of the pipe end is equal to the pipe cross-sectional area, the above-mentioned T/S is usually 1.2 to 1.3.

Therefore, the increase ratio of the pipe cross-sectional area mentioned above is 1+
Since α is 1.2 or less, the occurrence of the gap d hypothetically shown in FIG. 4B cannot be avoided.

As described above, according to the present invention, the end of the pipe can be pushed onto the intermediate surface of the core without creating a gap between the outer surface of the pipe and the inner surface of the core.

In particular, when the intermediate surface of the core is a reversely tapered surface, the outer diameter of the core decreases in the pipe insertion direction, so that the gap can be reduced even more effectively. That is, in the first equation, the rate of decrease in the gap d due to the core outer diameter decreasing by Δr is It is clear that the above-mentioned gap can also be reduced by making the middle surface of the core into a reverse tapered surface.

FIG. 4C shows the state in which the PVC pipe is pushed in at the final stage, and the pushing pressure is greater than the pushing pressure at the intermediate stage as shown in FIG. 4B.

If there is a gap hypothetically shown at d at the intermediate stage of pushing in in Figure 4B, the
The present invention eliminates the disadvantage that the PVC pipe may wave through the gap before the final pushing step of FIG. It can be avoided.

〔Example〕

Next, embodiments of the invention will be described.

For a core with an inclination angle of 30° for the first diameter-expanding inclined step, a 30° inclination for the second diameter-expanding inclined step, and a total length of 300 mm, the gap from the inlet to the first diameter-expanding inclined step is 10.5 mm. Gap 8.6 from the 1st diameter enlarged slope step to the 2nd diameter enlarged slope step
Place the outer mold in mm, and for this mold, the outer diameter is 114 mm,
A PVC pipe with a wall thickness of 7.1 mm and a wall thickness of 10.3 mm at the end.
After softening the thick part of the tube end by heating, a socket was formed by pressing between the core and the outer mold.

After pushing the plastic pipe into the mold, allowing it to cool down and removing the mold, we observed the molding socket, and found that no wrinkles were observed on the outer circumferential surface, and the wall thickness matched the gap between the core and outer mold. Obtained.

The tube end wall thickness was set to 9.0 mm and processed in the same manner as above, but in this case as well, no wrinkles were observed on the outer circumferential surface, and the wall thickness matched between the core and the outer mold.

〔effect〕

As described above, according to the present invention, the end of a PVC pipe can be processed into a socket having a desired thickness with excellent mechanical properties and having no wrinkles on the outer surface by the push-forming method. .

[Brief explanation of drawings]

Figure 1A, Figure 1B, Figure 1C, and Figure 1D
2 is an explanatory diagram showing the conventional processing method for plastic pipes, FIG. 2 is an explanatory diagram showing the thickened end of the plastic pipe processed by the present invention, and FIG. 3A,
3B and 3C are explanatory diagrams showing the method for manufacturing the pipe shown in FIG. FIG. In the figure, 1 is a core, 2 is an outer mold, a is a first diameter-enlarging sloped step, b is a second diameter-expanding sloped step, P is a plastic pipe, and e is a thickened end.

Claims (1)

[Claims] 1 A first diameter-expanding slope step part is provided in the front part, and a second diameter enlarged step part is provided in the rear part.
When a plastic pipe is pushed onto a core having diameter-enlarging inclined steps to form an enlarged-diameter socket, a gap approximately equal to the required wall thickness of the enlarged-diameter socket to be molded on the core is spaced. Then, an outer mold is placed on the core, and the end of the plastic pipe with the end that is to be used as the diameter expansion socket is heated and softened and pushed in from the front of the core to separate the core and the outer mold. A method for processing a plastic pipe, characterized in that the plastic pipe is pushed into the gap between the mold and the mold, and the plastic pipe is pushed into the rear part while always filling the gap.