Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Corrugating
Patent
1985-07-08
1987-12-01
Thurlow, Jeffery
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Corrugating
15624414, 15624415, 156500, 264511, 264514, 264566, 264568, 2642094, 264284, 264286, 425504, 4251311, 4253261, 425388, 425396, B29C 4730
Patent
active
047103370
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a single-wall pipe, tube or like conduit of a heat-mouldable or pressure-mouldable material, the conduit having smooth inner surfaces and a mechanical-strength enhancing pattern on the outer surface thereof. The invention further relates to a method and apparatus for manufacturing such conduits.
Such smooth inner-wall conduits are used in underground trenches as a means for protecting electric cables, in heat-exchangers etc. where the presence of irregularities, such as corrugations, on the inner surfaces of the conduits may create difficulties and/or in the cases where the conduit is subjected to relatively high mechanical streeses from externally of the conduit. A conduit manufactured in accordance with the method of the present invention can be used to advantage in those cases where a conventional corrugated or non-corrugated, smooth, conduit could otherwise be used, since a conduit produced in accordance with the invention for a similar throughflow area and external stresses, is cheaper to manufacture and lighter in weight, due to the fact that, inter alia, it incorporates less material per unit length.
Smooth inner-wall conduits having flanges or like protruberances on their outer surfaces are known to the art, inter alia manufactured by continuous extrusion. One method of manufacturing such conduits is described in Swedish Patent Application No. 7407555-7, according to which a conventional corrugated conduit is formed in a conventional manner by pressing a plasticized or molten material by means of air under positive or negative pressure against a moulding tool having the configuration desired of the moulded conduit, there being obtained a conduit which is patterned on both the inside and the outer side thereof. Further material is then introduced into the inside of the corrugated conduit, through an extrusion nozzle. This material forms a smooth sleeve whose outer surface bonds to the inner surface of the conduit. The conduit thus produced is not, however, a single-wall conduit, and the method by which the conduit is manufactured is encumbered with several disadvantages.
According to another method known for example from Swedish Pat. No. 7314295-2, material extruded by an extruder is fed to the space between two corrugated mould-jaw or die chains and is pressed into the corrugations of the dies with the aid of a conical mandril, the greatest external diameter of which determines the inner diameter of the conduit under manufacture. It is difficult with this method to produce single-wall conduits of good all-round quality. Because the material is pressed into the corrugation-forming or flange-forming cavities in the dies with the aid of an inflexible mechanical mandril, instead of with the aid of resilient prssurized air, it is difficult to fill all the cavities uniformly, so as to obtain fully formed corrugations or flanges. When the material is pressed into the aforesaid cavities, pockets of air readily form at the bottoms thereof, these pockets being empty of filling material. This is one of the reasons why incomplete or non-uniform flanges are formed. Furthermore, strong restrictions are placed on the height and form of the flanges, since it must be possible to release the moulded conduit from the moulding jawa or tools downstream of the moulding line in which the conduit is produced.
Light-weight conduits or pipes may be designed in the two principally different ways described above in order to achieve low weight and reasonable strength. However, different, in certain respects entirely different, products are obtained. In one case a single-wall pipe comprising outer, strengthening flanges is obtained while in the other case a double-wall pipe having hollow parts is obtained. It is obvious that the egg-shell design of the double-wall pipe makes the pipe less resistent to blows etc. than the flanged, single-wall pipe. Thus the single-wall pipe is especially suitable for pipes made of hard, brittle materials. The double-wall pipe comprising hollow parts is suitable f
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Thurlow Jeffery
Uponor AB
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