Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Plural sequential shaping or molding steps on same workpiece
Patent
1996-03-27
1998-04-28
Silbaugh, Jan H.
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Plural sequential shaping or molding steps on same workpiece
264323, 425393, 425DIG218, B29C 5704
Patent
active
057440859
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method and to a tool for expanding a pipe-end.
BACKGROND OF THE INVENTION
A method of the kind referred to is often used to establish pipe connections, and then primarily for expanding plastic pipes which have a memory capacity, i.e. pipes which automatically strive to return essentially to their original shape and form after having been expanded. One example in this regard is found in pipes that are manufactured from cross-linked polyolefins, and particularly pipes that are manufactured from cross-linked polyethylene, such as so-called PEX-pipes, which possess an active memory capacity at temperatures as low as room temperature. A pipe connection is established by expanding one end of such a pipe and inserting into the widened pipe-end a flanged connector which performs part of a pipe-connecting piece, normally made of metal, and which is retained in said pipe-end until the pipe is shrunk to an extent at which it is able to firmly grip the connecting piece. Optionally, a clamping sleeve made of a resilient material, for instance metal or plastic, which may be the same plastic material as that from which the pipe is made, is expanded and shrunk over the pipe-end in order to further enhance the holding and sealing pressure at the pipe connecting region. The clamping sleeve can be expanded at the same time as the pipe-end is expanded, with the clamping sleeve in position around said pipe-end.
One drawback with those expanding methods and expanding tools of the kind defined in the introduction and known hitherto is that the opposing edges of the outer jaw surfaces, which are generally circular-arcuate in cross-section, tend to produce on the inner surface of the pipe-end as said pipe-end expands pronounced, continuous grooves or score lines which extend in the direction of the longitudinal axis of the pipe. When fluid under pressure flows through a pipe connection that has been established by the expansion method, the fluid tends to follow the aforesaid score lines and therewith seep through the pipe connection. This deficiency in the tightness of the joint is particularly accentuated during the hours immediately after the pipe connection has been made.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a novel and advantageous method and tool which will eliminate the aforesaid drawback at least to a substantial extent.
To this end, there is proposed a method and a tool of the kind defined in the introduction. The pipe-end is thus expanded in stages, i.e. the mutually retracted jaws are inserted to a given distance in a pipe-end and then brought to an expanded state while expanding the pipe-end to a relatively small extent, whereafter the jaws are again brought together or retracted and inserted further into the pipe-end. The jaws are then again brought to an expanding state while further expanding the pipe-end. The method is repeated until the pipe-end has been expanded to the extent desired, for instance until the outer jaw surfaces have been inserted to their full length into the pipe-end and brought to an expanded state, whereupon the jaws are withdrawn from said pipe-end after having been returned to their retracted state or position. Because the pipe-end is expanded in stages with only small expansion movements of the jaws, the longitudinally extending edges of the delimiting outer jaw surfaces are always moved only a small distance apart and therewith produce no or only insignificant score lines in the inner surface of the pipe-end. This avoids the aforedescribed leakage problem.
The invention will now be described in more detail with reference to the accompanying drawings, in which
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a vertical section view of the most important part of an expansion tool for carrying out the inventive method;
FIG. 2 is a sectional view taken on the line II--II in FIG. 1 although with a modified design;
FIG. 3 is a sectional view taken on the line III--III in FIG. 1; and
FIG. 4 is a cros
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Eashoo Mark
Silbaugh Jan H.
Wirsbo Bruks AB
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