Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Reshaping running or indefinite-length work
Patent
1997-11-19
1999-11-09
Vargot, Mathieu D.
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Reshaping running or indefinite-length work
264269, 425392, B29C 5320, B29C 6334
Patent
active
059808071
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to apparatus and methods for reducing the width of plastics pipes, and more particularly to such apparatus and methods for reducing temporarily the width of plastics liner pipes for use in relining old or damaged fluid transport pipelines, such as mains water or drainage water pipelines.
The provision of such plastics liner pipes in these circumstances is a known area of technology utilising a variety of ways of fitting the liner pipes into the existing pipework system. The present invention relates to a technique, hereinafter referred to as the "roll-down" technique, in which a liner pipe, either in a continuous length as formed on extrusion, or as separate plastics pipes butt-welded together to a continuous length, and having an appropriate width for eventually fitting tightly within the pipeline to be relined is pushed through a sequence of roller sets to reduce the width of the liner temporarily so that it may then be fed into and through the pipeline system to be relined and subsequently allowed to expand, possibly with the help of pressurised fluids and/or heat, to its original width so as to fit tightly within the original pipework.
In such a roll down system, the pipe liner is physically driven from the upstream end through a succession of curved profile rolls each of which, in end view, is somewhat half-circular in configuration, the basic principle being that the pipe liner, of larger diameter than a first pair of opposed rolls having a somewhat circular roll throat in front view, is, subject to the thrusting force from upstream, caused to reduce in diameter on passage through that set of rolls, and then on through a second pair of rolls, usually rotatable at right angles to the first set of rolls, and possibly even a third pair of rolls, again having their axes of rotation at right angles to the previous set of rolls.
It has been found in such an arrangement that a straightforward reduction in diameter of the liner pipe in passing through a set of such rolls, if the rolls exert a truly circular radial force on the incoming pipes, and therefore result in the output of a truly circular reduced pipe from the first rolls, can result in collapse of the pipe liner during passage therethrough inwardly into a configuration generally known as a "heart collapse" (from its collapsed configuration of a somewhat heart-shaped nature). When this occurs, there is quite clearly a failure of the rolling technique.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome or at least to significantly reduce this problem.
According to one aspect of the present invention there is provided apparatus for producing reduction in width in plastics lining pipes including at least one pair of reducing rolls through which in use the liner pipe is forced from the upstream thereof, the rolls being disposed and configured to present a roll throat of effective ovality having a percentage of the difference between the maximum dimension normal to the axes of rotation and the maximum dimension parallel to the axes of rotation toward the last mentioned dimension in the range of 5% and 30%.
In accordance with another aspect of the present invention there is provided a method for reducing in width plastics liner pipes for inserting into pipework comprising the steps of forcing the pipe from upstream thereof through at least one pair of reducing rolls, being disposed and configured to present a roll throat of effective ovality having a percentage of the difference between the maximum dimension normal to the axes of rotation and the maximum dimension parallel to the axes of rotation toward the last mentioned dimension in the range of 5% and 30%.
The or each set of rolls may be freely rotatable.
With relatively small plastics liner pipes, which may preferably be made of polyethylene, of initial diameter of the order of 4 inches (104 mm diameter), two roll sets may be provided in succession with their successive axes of rotation at right angles, the rolls in each
REFERENCES:
patent: 4504171 (1985-03-01), Florence, Jr.
patent: 5114634 (1992-05-01), McMillan et al.
patent: 5340524 (1994-08-01), McMillan et al.
patent: 5626801 (1997-05-01), McMillan et al.
Subterra Limited
Vargot Mathieu D.
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