JPS6235901B2 - - Google Patents

Description

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

Various shapes of plastic pipe sockets have been proposed.

FIG. 1 shows a socket for a PVC pipe already proposed by the present applicant, in which a reverse slope 3' is formed between the rubber ring groove 1' and the sloped part 2' at the rear end of the socket.

In this socket, the pipe socket shown by the dotted line can also be rotated through a large swing angle, and the flexibility of the pipe joint can be improved. Therefore, it is advantageous against earthquakes, ground subsidence, etc.

Conventionally, one method of forming a socket at the end of a plastic pipe is to heat the end of the plastic pipe and press-fit the heated end onto a core for molding the socket. .

FIGS. 2A and 2B show how to form the above-mentioned specially shaped socket by this method.

FIG. 2A shows a relatively early forming stage, and when the heated PVC pipe end passes through the first diameter expansion slope step a, the diameter is expanded at a large diameter expansion rate, and this diameter expansion causes Large tensile stress occurs in the circumferential direction. As the end of the plastic pipe passes through the reversely inclined surface c of the core, the diameter of the plastic pipe becomes smaller, so the above-mentioned circumferential tensile stress gradually decreases. Plastic in a heated state is not an elastic body, and the stress due to strain disappears over time due to plastic deformation of the plastic, so this stress reduction effect over time is equivalent to the stress reduction effect caused by the above-mentioned reverse slope c. Superimpose the second
The circumferential stress remaining in the plastic pipe portion passing through the low point _b0 of the diameter-expanding inclined step b is relatively small.

Therefore, in FIG. 2B, the circumferential tensile stress of the plastic pipe portion passing through the low point b ₀ of the second diameter-expanding inclined step b is small, and the so-called stress on the core 1 of the plastic pipe portion P ₀ is small. The tightness is loose;
The occurrence of a gap g is unavoidable.

This gap g reduces the inner dimensional accuracy of the rubber apple groove. In particular, the rubber ring groove portion corresponding to the gap g is as shown in FIG.
The rubber ring R is the part that receives the water pressure P in the pipe, and the abnormal shape of the rubber ring groove part d at that point causes the rubber ring R to be abnormally deformed, which is a serious problem in ensuring the watertightness of the pipe joint. effect.

As mentioned above, when the socket is molded by the core press-fitting method, the shape of the socket is special, so conventional socket molding cannot avoid unexpected disadvantages.

The present invention provides a method for molding the above-mentioned specially shaped socket by a core press-fitting method without the above-mentioned disadvantages.

That is, in the method for forming a socket for a plastic pipe according to the present invention, the first diameter-expanding inclined step portion is provided at the rear;
A plastic pipe is inserted from the rear side of the core onto the socket molding core, which has a second diameter-enlarging sloped step at the front, and is a reversely sloped surface where the diameter becomes smaller as the distance between both steps gets closer to the front. Press-fit the heated end of the second
This method is characterized in that at least a portion of the plastic pipe in the vicinity of the lower part of the diameter-expanding inclined stepped portion is rolled and formed using a circumferential rotary former.

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

In FIGS. 2A to 2C, 1 indicates a socket molding core, which includes a first diameter-enlarging inclined step part a at the rear, a second diameter-enlarging inclined step part b at the front, and a reverse slope between them. It has surface c.

FIG. 3 shows a socket formed according to the present invention.
End E of the PVC pipe is shown and has been thickened.
Regarding this thickening, when extruding the PVC pipe, the pipe take-up speed should be periodically reduced, or
The PVC extrusion amount is increased periodically to extrude a pipe having thickened parts at regular intervals, and in conjunction with this extrusion, the pipe is cut to a fixed length so that one end has the thickened part. , a known method can be used.

According to the present invention, in order to form a socket at the end of a plastic pipe, the thickened end described above is heated;
This heating end is press-fitted onto the core 1 as shown in FIGS. 2A to 2B. In this case, the plastic pipe portion P ₀ is located above the low point b ₀ of the second diameter-expanding inclined step portion b.
As mentioned above, the circumferential tensile force at is relatively small, and a gap g occurs. Further, on the second diameter-expanding inclined step portion b, the axial compressive force acting on the plastic pipe is large, and the rate of increase in the cross-sectional area of the plastic pipe due to this axial compressive force is large. Therefore, the wall thickness of the plastic pipe becomes locally slightly thicker on the second diameter-enlarging inclined step b.

After the end of the plastic pipe is press-fitted onto the core 1 as described above, as shown in FIG.
22 in the circumferential direction of the pipe to collapse the above-mentioned gap above the low point _b0 of the second diameter-expanding inclined step b. By this compression, the inner surface of the rubber ring mounting groove of the socket is molded to a predetermined precision on the outer surface of the core.

The compression ratio of the rolls 21 and 22 is set to a value that corresponds to the diameter expansion ratio of the plastic pipe, in other words, it is set to a value that alleviates the restoring elastic force that occurs when the plastic pipe is expanded.

Therefore, this roll compression treatment does not substantially increase the circumferential length of the enlarged diameter portion of the plastic pipe, and results in a stretching treatment.

As a result, the plastic in contact with the rolls is stretched in the circumferential direction, and an increase in the circumferential tensile strength of the plastic pipe in this area can be expected.

In the socket molded according to the present invention, as shown in FIG. The increase in the circumferential tensile strength of the enlarged diameter stepped portion 11' is significant due to the effect of not only the mounting pressure of R but also the pressure f that causes the rubber ring R to expand in the thickness direction due to the water pressure P inside the pipe. It is valid.

In the above, the roll 22 is used for shaping the tip of the socket, and can be omitted.

When forming with the above-mentioned circumferential rotary forming element, the second
In order to equalize the local thick portion m on the second diameter-expanding inclined step portion b in FIG. It is also possible to apply pressure or tilt the roll 21 slightly with respect to the direction of the tube axis to flow a part of the plastic in the thick portion m to the thin portion n.

In addition, in this casting, in addition to setting the compression ratio of the roll 21 to a value corresponding to the diameter expansion ratio of the plastic pipe as described above, the pressing force of the spring 23 is adjusted from the lower point b ₀ of the second diameter expansion slope step b. The pressurizing force is slightly larger than the diameter expansion rate of the plastic pipe leading to the upper part, and the increase in the circumferential length and axial direction of the diameter-expanding inclined step part b due to the pressurizing force is absorbed by the tensile force generated in the thin wall part n. It is done by letting

Moreover, instead of the roll, a spatula or the like that rotates in the circumferential direction of the pipe can also be used.

In the present invention, as shown in FIG. 4, the core may be one in which the rubber ring mounting groove is formed by one step of the second diameter-enlarging inclined step part b.

In addition, in order to equalize the pressure insertion resistance of the pipe in each section on the core as much as possible and to equalize the thickness increase over the entire length of the socket, the core is divided in the longitudinal direction, and the pipe in each section is It is also possible to adjust the insertion resistance by changing the core material or temperature.

As described above, according to the present invention, a specially shaped socket shown in FIG. 1 is provided at the end of a plastic pipe.
By the so-called core press-fitting method, it is possible to mold without any problems, and the rubber ring sealability of the socket can be ensured without being affected by the molding process.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a socket molded according to the present invention; FIGS. 2A, 2B, and 2C are explanatory diagrams showing a method for molding a plastic pipe socket according to the present invention; FIG. 3 is an explanatory view showing the end of a plastic pipe into which a socket is formed according to the present invention, and FIG. 4 is an explanatory view showing another example of the core used in the present invention. In the figure, 1 is the core, a is the first diameter-expanding inclined step, b is the second diameter-expanding inclined step, c is the reverse slope, E is the end of the plastic pipe, and 21 is the circumferential rotary molding element. be.

Claims (1)

[Claims] 1 At the rear there is a first diameter-expanding sloped step, and at the front there is a second
The heating end of the plastic pipe is inserted from the rear side of the core onto the socket molding core, which has an inversely sloped surface with diameter-enlarging sloping steps and the diameter decreases toward the front between the two steps. A method for forming a socket of a plastic pipe, which comprises press-fitting the plastic pipe, and then rolling-forming at least a portion of the plastic pipe in the vicinity of the lower part of the second diameter-expanding inclined step using a circumferential rotary forming tool.