Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Corrugating
Patent
1996-06-19
1998-04-28
Thurlow, Jeffery R.
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Corrugating
264166, 264515, 264540, 425532, 425336, 425393, 425396, B29C 4904
Patent
active
057440913
DESCRIPTION:
BRIEF SUMMARY
This invention relates to apparatus and a method for making annularly or helically ribbed plastic pipe and method of making such pipe.
Semi-rigid thermoplastic, annularly profiled pipe such as corrugated or ribbed pipe or substantially smooth walled pipe, has traditionally been made in a travelling mold tunnel. Conventional travelling mold tunnels comprise two endless tracks of hot mold blocks which come together along a forward run of the tunnel to provide a cylindrical mold travelling in the direction of extrusion. Such travelling mold tunnels with two endless tracks of half mold blocks are complex pieces of machinery requiring precise synchronization of the tracks. Moreover, they require a very great deal of space to accommodate the return runs of the tracks. This use of space becomes excessive when large diameter pipe is being molded. To best utilize the space available some conventional travelling mold tunnels have been made with one run above the other rather than in side by side relationship.
Various attempts have been made to provide travelling mold tunnels of other types. Thus, for example, Manfred A. A. Lupke in U.S. patent application Ser. No. 854,988 directed to hinged mold blocks, provides an apparatus in which mold blocks are hinged together and follow a return path in the same plane as the operating run without the need to change the orientation of the mold blocks during their return.
Another example of an early type of travelling mold tunnel which does not involve a return run along a different path is disclosed in Canadian Patent No. 962,412 issued Feb. 11, 1975 to Industriele Orderneming Wavin N.V. In that Canadian patent there is disclosed a mold tunnel which comprises only two pieces. Each piece is a longitudinal half of the whole tunnel. In operation the two piece mold is closed and moves forwardly at extrusion speed. At intervals it opens and moves rearwardly so that they never advance so far forward as to leave the molding region. That type of arrangement involved accurate precise movement of heavy long mold halves. It was necessary that he halves have appreciable length to support the pipe molded therein during cooling and setting.
A later mold tunnel of a somewhat similar type is disclosed in U.S. Pat. Nos. 4,911,633 and 5,017,321 issued Mar. 27, 1990 and May 21, 1991 respectively to Gordon A. Comfort. These patents disclose a method and apparatus for using a small number of mold blocks, e.g. two or three mold blocks in a mold tunnel. Each mold block is divided into two longitudinal halves. As one mold block, with its halves closed in molding configuration, advances the other (or others) leapfrog over it on a second parallel path to take up an upstream position. Such an arrangement allows for smaller, higher, more maneuverable mold blocks than those of Wavin, but it does not provide for return of the blocks without displacing them from the production track.
The present inventor has addressed the problem of still further space consideration. He has also addressed the problem of opening the mold blocks without the need for hinging in a system where mold block return is without change of orientation of mold blocks themselves. He has still further addressed the problems that exist in returning the mold blocks along the same path as that of their advance.
He has, therefore, attempted to provide a system in which the return path of the mold blocks is not laterally displaced from the operating paths.
According to the invention there is provided apparatus and a method for molding profiled, thermoplastic pipe. The apparatus comprises A travelling mold tunnel for the molding of pipe therein in an operating run, the mold tunnel comprising at last two mold blocks each having a tubular mold surface in a closed condition and being openable into an open condition to release pipe molded therein, in which individual mold blocks of the mold tunnel are returnable in steps at regular intervals along a return path whose longitudinal axis is contiguous with the longitudinal axis of the operating run. Th
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