Plastic article or earthenware shaping or treating: apparatus – Preform reshaping or resizing means: or vulcanizing means... – Convoluting or twisting means
Reexamination Certificate
1999-02-23
2001-06-26
Nguyen, Nam (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Preform reshaping or resizing means: or vulcanizing means...
Convoluting or twisting means
C156S429000, C156S431000, C425S321000, C425S322000, C425S325000, C425S402000
Reexamination Certificate
active
06250908
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to the field of apparatuses for the formation of large-diameter ducts, pipes, conduits or the like, generally cylindrical in shape, from an extruded thermoplastic strip. U.S. Pat. No. 4,033,808 to Petzetakis discloses an apparatus for making large-diameter pipe from thermoplastic resin, the disclosure of which is hereby incorporated by reference. A synthetic-resin, hollow-profile strip is extruded and coiled helically around a winding drum to make a continuous tube. Adjacent turns of the helix are thermally fused together with axial pressure being applied on the strip so as to make a liquid-tight tube which can be used for a number of applications, particularly for subterranean use, e.g. as a waste or sewer conduit, storm sewer, or any other liquid conveyance.
The previous apparatus includes a drum for forming the conduit therearound, and the drum includes a core tube surrounded by a plurality of rollers upon which the extruded thermoplastic rolls as it rotates around the drum. The drum of the previous apparatus is fixed in diameter so only one diameter of pipe may be produced with each apparatus. Since a typical manufacturer of pipe manufactures conduit or pipe of several different diameters, it would be necessary to purchase and maintain several such apparatuses, which would involve considerable investment and ongoing expense.
In a conventional conduit-making process, “residence time” is the period in which plastic remains on the drum during the manufacturing process. Since the rate of manufacture is limited by residence time, it would be desirable to shorten this interval by increasing the drum speed. Typical manufacturing rates can range from 300 to 3500 lbs./hr. depending on the size of the pipe. Usually, large-diameter pipe or conduit is manufactured at about 1000-2000 lbs./hr. As the rate is increased, however, the conduit may not be completely cooled when coming off the drum. This makes the conduit shrink slightly inward, undesirably decreasing the final conduit diameter by a small, yet significant, amount.
SUMMARY OF THE INVENTION
In view of the above-indicated drawbacks with the previous device apparatus, there is therefore a need for a pipe or conduit apparatus which preserves the advantages of the previous device while manufacturing large diameter pipe and conduit of more than one diameter.
There is also a need for an apparatus having a drum that permits precision variations in pipe/conduit diameter to allow for the decreasing of residence time, thereby increasing the rate of manufacture.
These needs and others are satisfied by the present invention in which an apparatus for making a conduit is disclosed. An extruder is provided for producing a strip or ribbon of continuous thermoplastic. A winding drum receives the strip from the extruder in a pliable, fusible, substantially melted state, and helically winds the strip around the drum's perimeter to form a conduit having an inner diameter corresponding to the outer diameter of the drum. The drum includes a core tube surrounded by a plurality of rollers which define the outer diameter of the drum. The rollers rotate to advance the strip around the drum.
A plurality of support columns are used to support the rollers at each end. A hub assembly is used to movably support the support columns in slidable engagement. The support columns are radially displaced along the hub assembly between two positions, in order to vary the outer diameter of the drum between two diameters.
As will be appreciated, the invention is capable of other and different embodiments, and its several details are capable of modifications in various respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive.
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Jones Day Reavis & Pogue
Leyson Joseph
Nguyen Nam
The Lamson & Sessions Co.
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