Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1998-05-08
1999-07-27
Ball, Michael W.
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
1562733, 156294, 264492, 264249, 264296, 264322, 425393, 425DIG218, B29C 5704
Patent
active
059284510
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of socketing a pipe of oriented plastic having an annular groove inside the socket. This groove is provided to receive an elastic gasket for sealing between the socket and a spigot end of another pipe when two pipes are to be interconnected.
2. Description of Related Art
The common method in forming a socket or bell on a pipe of plastic which is not oriented, and at the same time providing an annular groove inside the socket comprises heating of an end portion of the pipe to a temperature substantially above the glass transition temperature of amorphous plastic or the crystalline melting point of crystalline plastic, respectively, and pushing the heated end portion of the pipe onto a mandrel having a collapsible core for forming said groove. The core is in the expanded condition when the end portion is pushed onto the mandrel. After cooling of the end portion the core is collapsed and the socketed pipe is withdrawn from the mandrel.
It is also prior art to slip a sealing ring or gasket onto the mandrel and to form the groove in the end portion of the pipe over the sealing ring which is left in the groove and is withdrawn from the mandrel together with the pipe.
When the socket shall be formed on a pipe of oriented plastic, particularly of MOPVC (molecular oriented polyvinylchloride) two problems are encountered which do not exist in case of pipes of non-oriented plastics material, viz. in the region where the groove shall be formed (the material is more sensitive to cracking around the periphery than normally because draw normally is higher in the hoop direction than in the axial direction), and socketing thus avoiding unnecessary compression that might reduce the elongation at break,
These problems are overcome by the method of the present invention.
SUMMARY OF THE INVENTION
When the oriented plastic is heated much over the glass transition temperature or the crystalline melting point, respectively, it will shrink onto the mandrel, which increases the friction between the pipe and the mandrel. The heated material also is softer, and by the combination of softer material and increased friction the plastic will be compressed when the heated end portion is pushed onto the mandrel. Heating of the end portion of the pipe is necessary because the forces required to push the end portion over the expanded collapsible core, the sealing ring, or a prefabricated groove core, respectively, will be too high if the temperature of the plastic is below the glass transition temperature or the crystalline melting point, respectively. However, in the method of the invention the compression of the plastic is well controlled and limited mainly to the region of the end portion of the pipe wherein the groove inside the socket is to be located, and thus the forces necessary to move the end portion of the pipe over the core or the sealing ring, respectively, can still be kept at a low and acceptable value. If the pipe is manufactured with axial draw then the heating of the end portion of the pipe will cause axial draw of the pipe to be reduced which provides an increase of the wall thickness in said region sufficient to compensate for the hoop streching of the pipe wall not only where the groove is located but also in the cylindrical part of the pipe.
By limiting the heating of the plastic above the glass transition temperature or the crystalline melting point, respectively, to the region wherein the groove inside the socket is to be located the two problems mentioned above thus will be overcome.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in more detail below reference being made to the accompanying drawings disclosing illustrative embodiments of the invention and wherein
FIGS. 1-3 and 4A are side views of a mandrel with a pipe shown in axial cross sectional view and disclose successive steps in the method of the invention in one embodiment thereof,
FIGS. 4B and 4C are fragmentary views of the mandrel in F
REFERENCES:
patent: 3852016 (1974-12-01), Delauzun
patent: 4276010 (1981-06-01), Shartzer
patent: 4428900 (1984-01-01), Riley et al.
patent: 4643658 (1987-02-01), Gordon
patent: 5527503 (1996-06-01), Rowley
Jarvenkyla Jyri
Johansson Mats
Ball Michael W.
LaPointe Dennis G.
Mason, Jr. Joseph C.
Tolin Michael A
Uponor B.V.
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