JPS6233935B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for processing plastic pipes,
More specifically, it is a method of forming a socket at the end of a PVC pipe.

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, this method has the disadvantage that thinning of the wall of the socket tube 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.
A method has been proposed in which a socket is formed at the end of a PVC pipe by making the thickness approximately equal to the wall thickness of the PVC pipe and press-fitting the heated end of the PVC pipe into this gap.

FIGS. 1A to 1D show the socket molding method according to the second method. In Figures 1A to 1D, a' indicates the inclined step part, b' indicates the straight part,
c′ indicates each chevron.

P′ indicates the end of the heat-softened PVC pipe,
When the tip is pushed into the gap between the two molds and reaches the inclined step a' as shown in Figure 1A, an axial compressive force f is generated.
The meat is increased as a result.

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 is S and the pipe inner diameter is r, then the pipe outer diameter R is π(R ² − r ² )=S Therefore, It is.

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

The end of the PVC pipe is pushed in further, and the first
As shown in Figure C, when the pipe tip reaches the first step _c1 ' of the chevron c', the axial compressive force f at the pipe end increases further, so the thickness increases at a rapid pace. As shown in Figure 1D, the straight section
A PVC pipe is thickened due to the axial compressive force f.

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

The present invention aims to suppress the occurrence of the above-mentioned spots and prevent the occurrence of wrinkles on the outer surface of the socket by reducing the above-mentioned gap d. Specifically, the core diameter r is made small by making the above-mentioned straight part into a reversely inclined surface, and d in the first equation is made small.

From the first equation, It is clear that the thickness d of the void can be reduced by decreasing the core diameter r.

The plastic pipe processing method according to the present invention is as follows:
This method was invented in view of the above-mentioned points, and is a method in which a step between both inclined step portions of a core having a first diameter-enlarging inclined step portion at the front portion and a second diameter-enlarging inclined step portion at the rear portion is moved forwardly. The outer diameter of the outer mold is arranged on the inner core with a gap approximately equal to the wall thickness of the plastic pipe to be processed. This method is characterized by pushing the heated end of the plastic pipe into the core from the front side.

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

In Figure 2A and Figure 2B, 1 is a core;
2 is an outer mold, and the gap therebetween is made approximately equal to the wall thickness of the PVC pipe to be processed.

A indicates the first diameter-expanding inclined step portion of the core, c indicates the second diameter-expanding inclined step portion, and b indicates the reverse inclined surface. 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 c are usually 30 to 45 degrees. The angle of the reversely inclined surface b is 1 to 5 degrees.

According to the present invention, in order to process the end of the PVC pipe, the end of the PVC pipe is heated and softened, and the end of the PVC pipe is processed by applying the driving force of the PVC pipe to the core 1 and the outer mold 2. Push into the gap between the

FIG. 2A shows a stage in which the insertion has progressed considerably.

The amount of increase in the cross-sectional area of the PVC pipe P at each position of the core 1 in FIG. 2A differs depending on the axial compressive force acting on the PVC pipe. In Figure 2A, the PVC pipe on the reverse slope b of core 1 has the following:
Due to the presence of the second diameter-expanding inclined step c, a considerably large axial compressive force f acts, and the cross-sectional area of the PVC pipe is larger than that of the PVC pipe before processing. The increase in cross-sectional area has not reached the point where the gap between the core 1 and the outer diameter 2 is completely closed. Therefore, a gap g exists between the outer surface of the PVC pipe on the reverse slope b and the outer diameter 2.

However, the thickness d of this gap g is
As mentioned above, can be made smaller than when it is made horizontally.

FIG. 2B 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. 2A.

At this final stage, the gap g at the intermediate stage in FIG. 2A is crushed.

On the reverse inclined plane at the intermediate stage of Fig. 2A
The length of the gap g between the outer surface of the PVC pipe and the outer mold is large, so if the gap g is thick, the PVC pipe will become extremely This causes undulations and wrinkles, but in the present invention, such gaps can be made thinner, so such problems can be avoided.

As described above, according to the present invention, the end of the PVC pipe is thickened to a desired thickness by the indentation thickening method.
Moreover, it can be processed into a socket without wrinkles on the outer surface.

[Brief explanation of the drawing]

Figure 1A, Figure 1B, Figure 1C, and Figure 1D
2A and 2B are explanatory diagrams showing a conventional method for processing a plastic pipe, and FIGS. 2A and 2B are explanatory diagrams showing a method for processing a plastic pipe according to the present invention. In the figure, 1 is a core, 2 is an outer mold, a is a first diameter-enlarging sloped step, b is a reverse slope, c is a second diameter-expanding slope, and P is a plastic pipe.

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.
The space between the two inclined stepped portions of the core, each having diameter-enlarging inclined stepped portions, is an inverted inclined surface in which the outer diameter becomes smaller toward the front, and the outer mold is placed on the core, and the gap between these is covered. A method for processing a plastic pipe, characterized in that the plastic pipe is arranged so as to have a wall thickness approximately equal to the thickness of the processed plastic pipe, and the heated end of the plastic pipe is inserted into the gap from the front side of the core.