JP3024705B2 - Tube with integral socket - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to the production of tubes of molecularly oriented plastics material, in particular molecularly oriented plastics tubes with integrally formed sockets.

BACKGROUND ART It is well known that molecularly oriented plastic materials can provide increased mechanical properties. Molecular orientation is achieved by stretching or stretching under appropriate temperature conditions. Numerous methods have already been proposed, in particular to apply this principle to plastic pipes in order to increase the burst strength due to internal pressure by circumferential stretching (expansion).

British Patent No. 1,382,580 discloses that circumferentially oriented PVC is provided by the expansion of a tubular material by means of a cylindrical mold.
The production of (polyvinyl chloride) tubes is described.

In such an approach, there are difficulties in providing a socket for connecting the tubes together. There are a number of joints and coupling devices that serve this purpose, and the preferred method is to form an integrally enlarged bell-shaped section at one end of the tube, into which the other tube end or spigot is placed. It can be inserted and connected by providing a suitable sealing device such as an adhesive or a rubber gasket. Such tube sockets must be large in diameter and strong relative to the body due to fluid pressure, and the need to be able to withstand the various other loads experienced by the tube socket is generally Is considered. The usual method is to make the socket wall thicker than the tube body wall in proportion to its diameter.

GB 1,432,539 describes expanding a material tube in a female mold in such a way as to create a molecular orientation in the circumferential direction to form an enlarged diameter socket. This method is not sufficient due to the reduced wall thickness of the socket, and the applicant's next application describes an alternative method. That is, in Australian Patent No. 29086/77, the socket is made with thickened walls, while the Australian Patent No.
In 2908/77, a sleeve is placed over the socket to counteract the reduced wall thickness.

However, the preceding proposals are cumbersome and have not led to effective manufacturing. That is, thickening the material makes dimensional control difficult, and accurate control of cutting of the extrudate is required to ensure correct positioning of the thickened portion. Sleeve fitting requires the production and installation of the sleeve by a secondary process.

A further problem exists with molecularly oriented tubes if it is necessary to provide mounting members to support axial thrust, such as bends or T-type fittings that secure the tube to the tube. Occurs. Such means can also be used for non-oriented plastic pipes, provided that the axial strength of the pipe can be adapted to the usage burden. In a tube made of a molecularly-oriented material, the axial strength is suitably increased by introducing an axial orientation.

In the method described in U.S. Pat. No. 4,499,045, the method described in U.S. Pat. No. 1,382,580 is modified by using a sleeve that moves sequentially along a material tube to control expansion. The friction between this sleeve and the material tube is such that in a tube oriented in two axes,
Creates a longitudinal stretch (orientation) of the tube. The method described here has the disadvantage that the degree of axial elongation of the material tube cannot be actively controlled, and provides a solution to the problem of providing a satisfactory socket by an economical manufacturing method. Can not.

It is an object of the present invention to provide a method for producing a molecularly oriented plastic tube having at one end an integral socket having the required increased strength and wall thickness without the need for pre-thickening the material wall in the socket. Is to do. The present invention provides for each desired thickness and properties,
It is characterized by controlling the axial stretching of the material tube to apply different degrees of axial stretching to the socket and the body of the tube.

DISCLOSURE OF THE INVENTION The present invention provides a circumferentially or biaxially molecularly oriented plastic tube having at one end an integral socket having a wall with a lower degree of axial extension than the body of the tube. It is. Further, the present invention provides a method for manufacturing a plastic tube comprising the following steps.

(A) heating the material tube to a required molecular orientation temperature; (b) forming a socket by stretching (expanding) a portion of the material tube in the circumferential direction at a first axial stretching degree; c) forming the body of the tube by circumferentially stretching (expanding) the material tube at a second axial stretching degree, wherein the first axial stretching degree is the second axial stretching degree. It is characterized by being smaller than.

The term "axial stretching" as used herein refers to the elongation in the longitudinal direction achieved by circumferential stretching (expansion) at the free end. In the circumferential extension at the free end, both ends of the material tube are not constrained in the axial direction,
Reducing the length and wall thickness of the tube by a factor approximately equal to the square root of the increasing rate of diameter,
There is a reduction in the length and wall thickness of the material tube. In contrast,
In the circumferential extension (expansion) at the fixed end, the length is constant and the wall thickness is reduced by a factor equal to the increase in diameter. Thus, stretching at the fixed end results in a thinner wall compared to stretching at the free end and a positive (plus) degree of axial stretching, and the stretching is performed at the appropriate orientation temperature. In some cases, the plastic material tube is provided with an axial molecular orientation.

In one form of the invention, the socket can have zero axial stretch and the body of the tube can have some positive axial stretch.
In another form, the socket may have some positive (plus) degree of axial stretching, and the body of the tube may have a greater degree of axial stretching than the socket. In yet another form, the socket may have a negative (negative) degree of axial stretching, ie, compression rather than stretching, and the body of the tube may have some positive (positive) degree of axial stretching. be able to.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional view of an apparatus for manufacturing a tube having an integral socket from a material tube in accordance with the method of the present invention. FIG. 2 is the same as FIG. FIG. 3 is a schematic cross-sectional view of an apparatus similar to FIG. 2 showing a cooling step of the socket after expansion of the socket, and FIG. 4 is a cross-sectional schematic view of the main body of the material pipe. FIG. 5 is a schematic cross-sectional view of an apparatus similar to FIG. 2; FIG. 5 is a schematic cross-sectional view of an apparatus similar to FIG. 4 showing one modification of the manufacturing process; FIG. 5 is a schematic sectional view of an apparatus similar to FIG. 4 showing an example.

BEST MODE FOR CARRYING OUT THE INVENTION Preferably, the wall of the socket of the tube has a circumferential orientation and the main body of the tube has a biaxial orientation. A production apparatus which can achieve different degrees of axial stretching combined with circumferential stretching (expansion) is shown in FIG. The mold 1 has an inside diameter approximately equal to the final outside diameter desired for the finished tube. The end of the mold 1, i.e., the socket part 2, is substantially formed in the desired outer shape of the tube socket, and a groove (not shown) for forming a groove in the tube socket is appropriately formed so as to include an elastic seal. Is provided. The socket part 2 is configured such that it can be opened laterally or axially to remove the completed tube.

The material pipe 3 partially or wholly preheated to a predetermined molecular orientation temperature is supported and covered by a sleeve 4 or another supporting device, and guided into the mold 1. A conical flange 5 fixed to the end of the sleeve 4 is slidable on the mold 1.
And is connected to the sleeve 4. The sleeve 4 is first moved so that its conical flange 5 is located adjacent the rear part 6 of the socket part 2 of the mold 1 as shown in FIG. One end of the material tube 3 engages an end cover 10 which fits around the outer diameter of the material tube 3 into the mold 1 and the other end allows the material tube 3 to move into the sleeve 4. , A chuck 9 attached to a rod 9.

The fluid at the appropriate temperature is appropriately controlled to maintain the material tube 3 at the always uniform temperature required for stretching, so that the holes 11, 11.
It is circulated in and out of the material tube 3 via 12, 13, 14, and 15.
The pressure exerted by the fluid from the holes 11 is only as much as necessary for circumferential extension or expansion in the socket part 2 in order to form a socket in the material tube 3 as shown in FIG. Pressure is increased. On the other hand, holes 13, 14, 16, 17
From the heating fluid. During this process, the material tube 3 is only pulled in the sleeve 4 toward the end cover 10 without restraint, and the material forming the socket in the material tube 3 is not pulled in the axial direction at all. Optionally, the end of the material tube 3 is gripped by the chuck 8 and the material tube 3 is connected to the material tube 3 via the chuck 8 and the rod 9 to which the chuck 8 is fixed so as to perform the required degree of axial extension in the expanded socket. A tensile force can be applied. Optionally, chuck 8
Compressing the material tube 3 by applying a compressive force to the material tube 3 via the rod 9 to which the material tube 3 is fixed, that is, giving a negative (negative) degree of extension, and increasing the thickness of the socket and the wall of the main body of the tube. Can also.

A self-sealing or fluid-operated resilient seal may be provided on sleeve 4 or end cap 10 to assist in inflating the socket.

Upon completion of the expansion of the socket, a cooling fluid may be supplied from the holes 17 to the cooling jacket 18 around the socket portion 2 of the mold 1 to stop or fix the material molecular orientation of the socket portion. Then, in order to allow relaxation of the material tube 3 main body portion in the sleeve 4, the fluid is discharged from the hole 12 to reduce the pressure in the material tube 3.

The sleeve 4 can be partially withdrawn from the mold 1 during this step and, as shown in FIG.
It can also be pulled completely out of. Next to FIG. 3, a pressure fluid is supplied from the hole 11, and the main body of the material tube 3 is expanded as shown in FIG. Such inflation starts naturally from the already inflated socket and moves towards the other end. The tensile force applied to the material tube 3 via the chuck 8 and the rod 9 prevents the length of the material tube 3 from shrinking in the circumferential expansion, and ensures a thin wall and a reliable axial extension, that is, Causes molecular orientation.

At the completion of the expansion of the material tube 3, the material tube 3 is supplied through the cooling fluid holes 11 and 12 to fix the molecular orientation, and then the material tube 3 is released from the chuck 8 and the end cover 10 of the mold 1 is removed from the socket portion 2. And the material tube 3 can be taken out.
Both ends of the processed material tube are appropriately trimmed to form a finished product.

In one deformation step shown in FIG. 5, the chuck 8 is pulled out via a rod 9 so that a further axial stretching is exerted on the socket or the material pipe to the required degree of stretching, whereby the material pipe 3 is drawn. Is further subjected to a tensile force.
This additional stretching can be applied before or during circumferential expansion.

In a further variant step shown in FIG. 6, the material is pulled out of the sleeve 4 so as to control the axial stretching, as described in the aforementioned US Pat. No. 4,499,045. By maintaining the pressure in the tube, friction between the material tube 3 and a supporting device such as the sleeve 4 provided with the seal 19 can be utilized. in this way,
Also, the rod 9 and the chuck 8 can be omitted, and the movement of the axial sleeve 4 and the conical flange 5 in the mold 1 before or during the expansion of the socket is used to move the socket in the required axial direction. The degree of stretching can be obtained.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI F16L 9/12 F16L 9/12 B29L 23:00 31:24 (72) Inventor Makovaz, George Australia, New South Wales, Australia 21 20, Cherrybrook, Myson Drive 16 (72) Inventor Chapman, Peter Granville Australia, New South Wales 20 65, Greenwich, Ronald Avenue 45 (72) Inventor Jarvenkira, Yuri Jae Horora 15780, Tapionttier 4 in Finland 4 (56) References JP-A-56-2131 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 49/00-49/80 B29C 55/22-55/26

Claims (22)

(57) [Claims] 1. A connecting socket integrally formed at one end of a body, the socket having a diameter greater than the diameter of the body, the socket having a lesser degree of axial extension than the body of the tube. A plastic tube having a molecular orientation in a circumferential direction or a biaxial direction. 2. The plastic tube of claim 1 wherein the socket wall is circumferentially molecular oriented with a greater degree of stretching than the tube body wall. 3. The plastic tube of claim 1 wherein the wall of the socket is stretched so that the degree of axial stretching is zero and the body of the tube has a positive degree of axial stretching. 4. A plastic tube according to claim 1, wherein the wall of the socket has a molecular orientation in the circumferential direction and the body of the tube has a biaxial molecular orientation. 5. The plastic tube of claim 1 wherein the axial extension of the wall of the socket is positive and the axial extension of the body of the tube is extended to a greater extent than the wall of the socket. 6. The plastic tube of claim 1 wherein the wall of the socket has a negative degree of axial stretching and the wall of the body of the tube has a zero or positive degree of axial stretching. 7. The plastic tube according to claim 1, wherein the tube is stretched so that the degree of axial stretching of the tube body is positive. 8. A socket is formed by (a) heating the material tube to a required molecular orientation temperature, and (b) stretching a portion of the material tube in a circumferential direction at a first axial stretching degree. (C) forming the body of the tube by circumferentially stretching the material tube at a second axial stretching degree, wherein the first axial stretching degree is greater than the second axial stretching degree. A method for producing a plastic tube, characterized by being small. 9. The method according to claim 8, wherein the material tube has a substantially constant wall thickness over its entire length. 10. The method of claim 8, wherein the socket is formed prior to molding the body. 11. The method according to claim 10, wherein the socket is cooled below a predetermined molecular orientation temperature in order to fix the molecular orientation brought about by stretching before forming the body. 12. The method according to claim 10, wherein the circumferential extension of the material tube proceeds along the entire length of the tube so as to form the body of the tube. 13. The method of claim 12, wherein the circumferential extension is advanced toward the end of the tube opposite the socket. 14. The method according to claim 13, wherein the portion of the material tube which is to be the body of the tube is supported in the sleeve prior to circumferential extension. 15. The method according to claim 14, wherein the sleeve is drawn out before the circumferential stretching step. 16. The method of claim 15, wherein the friction between the sleeve and the material tube causes at least a portion of the axial extension.
The manufacturing method as described. 17. The method according to claim 8, wherein the socket is stretched with an axial stretching degree of zero, and the main body is stretched with an axial stretching degree of positive. 18. The method of claim 17, wherein the socket is formed by circumferential extension at a free end. 19. The method of claim 17, wherein the body is formed by circumferential extension at a fixed end. 20. The method of claim 18, wherein the body is formed by circumferential stretching at a fixed end with additional axial stretching. 21. The method according to claim 19, wherein the additional axial stretching is effected by gripping the end of the material tube opposite the socket and by stretching during the circumferential stretching forming the body of the material tube. Item 20. The production method according to Item 20, 22. The method of claim 17 wherein the positive degree of axial stretching acts on the tube simultaneously with the circumferential stretching to produce a biaxially molecularly oriented body.