JPS6348696B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for molding a plastic pipe socket.

When molding a socket on the end of a plastic pipe, such as a PVC pipe, place the outer mold on the socket molding core and fill the gap between the core and the outer mold.
It is known to make the gap slightly larger than the wall thickness of the PVC pipe and to push the heated end of the PVC pipe into this gap.

1A to 1D illustrate the socket molding method described above.

In FIGS. 1A to 1D, a' indicates an inclined 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 the two molds 1' and 2', and when the tip reaches the inclined step a' as shown in FIG. 1A, it is subjected to an axial compressive force f and is thickened.

Thereafter, as press-fitting progresses, the axial compressive force f increases and the pipe cross-sectional area increases, but the pipe diameter also increases, so the wall thickness of the pipe portion whose diameter has increased decreases, and the first As shown in Figure 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
The cross-sectional area of the PVC pipe is determined by the thickness increase rate (cross-sectional area increase rate)
Taking α into account, S(1+α), and the pipe inner diameter as 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 1' and 2' is t, the thickness d of the gap is: is given by

The insertion of the PVC pipe end further progresses, 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
The PVC pipe on b' 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 PVC pipe in the straight section b' is large, the PVC pipe on the straight section b' is straightened at the initial stage when the thickness is increased by the axial compressive force f. I learned that a seat is formed on the PVC pipe, and that this seat causes wrinkles to appear on the outer surface of the socket.

In addition, in the socket formed as above,
The final thickness increase rate is large, and due to the degree of processing of the plastic, the hardness is significantly different from that of the unprocessed part. Therefore, there is a socket in the socket, that is, an unprocessed
In actual use with the end of a PVC pipe inserted, if a load is applied to the socket, the ring-shaped gap between the socket and the socket will become uneven, and this change in gap will cause the gap between the socket and the socket to become uneven. There is also a disadvantage that the deformation of the rubber ring cannot be followed and the sealing performance of the rubber ring cannot be ensured.

The present invention aims to suppress the occurrence of the above-mentioned buckling and prevent the occurrence of wrinkles on the outside of the socket by reducing the gap d.

Specifically, by making the above-mentioned straight part a reversely inclined surface and reducing the core diameter r, and by reducing the gap t or increasing the pipe cross-sectional area S, d in the first equation can be reduced. It should be small.

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

Also, from the first equation, it is clear that the thickness d of the void can be reduced by decreasing t or increasing S.

If t is made small or S is made large, the wall thickness increase rate of the socket, which is the final molded product, relative to the original pipe will not be so high, and the above-mentioned change in the hardness of the socket can be sufficiently alleviated.

The plastic pipe socket forming method according to the present invention was invented as a result of the above studies, and
An outer mold is placed on a socket molding core which has a first diameter-enlarging sloped step part on the rear side and a second diameter-expanding sloped step part on the front side, and has a reverse sloped surface part between these two step parts, This method is characterized in that the gap between them is made slightly smaller than the wall thickness of the plastic pipe to be processed, and the end of the plastic pipe to be processed is pushed into the gap.

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

In Figures 2A to 2C, P is the workpiece
1 shows the PVC pipe, 1 shows the socket molding core, and 2 shows the outer mold.

The core 1 includes a first diameter-enlarging sloped step part a at the rear, a second diameter-expanding sloped step part c at the front, and a reversely sloped surface part b at the middle.
The inclined step portions a and c have an inclination angle of 45 to 60°, and the inclination angle of the reverse inclined surface portion b is 1 to 5°.

The gap t between the core 1 and the outer mold 2 is slightly smaller than the wall thickness W of the PVC pipe P, specifically t=0.85 to 0.95W.

To carry out the invention, the end of the PVC pipe P is heated and the pipe end is
As shown in Figure B, it is pushed between the core 1 and the outer mold 2.

In this case, a gap g is created between the outer surface of the PVC pipe on the reverse slope b and the inner surface of the outer mold 2, but due to the reverse slope b, as the core outer diameter reaches the front of the core, As is clear from the second equation, the thickness d of the gap g can be made small, and the gap T between the core 1 and the outer mold 2 is small.
Since the original cross-sectional area S of the PVC pipe is large, the thickness d of the gap g can be made small (or even zero), as is clear from the first equation above.

Figure 2C shows the final pushing stage;
The gap g shown in Figure B is completely closed due to the plastic deformation of the PVC pipe.

Since the gap g in FIG. 2B is very small,
Even if the PVC pipe directly below this gap is subjected to an axial compressive force f, the waving of the PVC pipe can be well prevented, and wrinkles can be avoided at the socket that is formed in the final stage of FIG. 2C.

In addition, in the socket corrugated as described above, the socket body has an inversely tapered shape, the diameter of the body is small as a whole, and the cross-sectional area thereof is small; Because the thickness of the pipe is smaller than that of the original pipe, the processing rate (thickness increase rate) of the socket body is relatively small, and changes in the hardness of the socket body can be kept small. .

As described above, according to the present invention, the end portion of a PVC pipe can be formed into a socket with a good appearance without wrinkles and less deformation in hardness with respect to the original pipe by the indentation thickening method.

[Brief explanation of the drawing]

Figure 1A, Figure 1B, Figure 1C, and Figure 1D
2A, 2B, and 2 are explanatory diagrams showing the conventional socket forming method for plastic pipes.
FIG. C is an explanatory view showing the method of forming a socket for a plastic pipe according to the present invention. In the figure, 1 is a socket molding core, 2 is an outer mold,
a is a first diameter-enlarging inclined step portion, b is a reversely inclined surface portion, c is a second diameter-enlarging inclined step portion, and P is a plastic pipe to be processed.

Claims (1)

[Claims] 1. An outer mold is placed on a socket molding core that has a first diameter-enlarging sloped step part on the rear side and a second diameter-expanding sloped step part on the front side, and has a reverse sloped surface part between these two step parts. A plastic pipe socket forming method characterized in that the gap between these is made slightly smaller than the wall thickness of the plastic pipe to be processed, and the end of the plastic pipe to be processed is pushed into the gap. Method.