Pipe joints or couplings – Packed – Socket
Patent
1993-07-22
1995-07-04
Arola, Dave W.
Pipe joints or couplings
Packed
Socket
285423, 285915, F16L 1706
Patent
active
054293987
DESCRIPTION:
BRIEF SUMMARY
The invention relates to semi-rigid plastics material tube having a ribbed outer surface and having ends adapted to couple one tube to another.
BACKGROUND ART
Thermoplastic, semi-rigid tube has a variety of uses such as for underground drainage or for carrying electrical wiring. For various applications it has been found that corrugated tube, either double walled or single walled has advantages and, more recently, the use of a ribbed wall tube has become widespread. The ribs of such tube are usually annular or helical ribs upstanding from the tube wall by a height appreciably in excess of the thickness of the tube. The use of such ribbed tube gives good compression strength in comparison with solid walled tubes but utilizing less weight than plastics materials.
Ribbed tube has significantly larger outside diameter than plan walled tube and if they are to be joined together, coupling members of large internal diameter are generally unsuitable for joining ribbed tube with plain walled tube. For joining ribbed tubes, it is necessary to provide sealing means which must fill the entire gap between the ribbed tube base wall and the coupling sleeve. If the ribs upstand to any great degree this gap may be extensive. For example, if ribs upstand from the base wall of the tube by 2.5 cm or more, the seal must effectively seal an annular gap of at least 2.5 cm in width. When the ribs are annular, the seal may be located between two ribs.
A coupling sleeve may be provided as an independent unit or it may be provided by an expanded or belled end of one tube which fits over the end of another tube. In either case difficulties arise in accurate fit and sealing. Moreover, when the coupling sleeve is a belled end of one tube, the degree of belling has to be very large in order to fit over the ribs of the other tube. Further problems arise when it is desired to couple ribbed tube and plain walled tube together. It may be seen that, if ribbed tube of large outside diameter is to be joined to plain walled or other tube of small outside diameter, then there is a very large gap to be sealed between the two tubes. Generally, coupling between plain walled tube and ribbed tube is not carried out because of the difficulties involved. However, where it cannot be avoided, it has been found necessary to use independent coupling sleeves for the purpose. One reason for this is that bells provided in the ends of tubes to fit over ends of adjacent tubes must be sufficiently large to fit over ribbed tube. Thus, the gap presented between plain walled tube and the large coupling bell at the end of ribbed tube is too large to be sealed by conventional sealing means.
Ribbed tube of the type having substantially raised ribs is usually made by means of apparatus of the travelling mold tunnel type. A tubular parison of plastics material is extruded from an extrusion nozzle into a travelling mold tunnel over a forming plug. The forming plug defines the inner tube surface and the travelling mold tunnel defines the outer tube surface. Thus, the parison is forced into the cavity between the plug and the tubular tunnel which moves axially over the plug. The tubular tunnel has a mold surface to form the ribs or other configuration on the final tube. There are various means of providing such a travelling mold tunnel but this is often comprised by two tracks of mold blocks which come together in cooperating pairs to form a tunnel on a forwardly moving run parallel and coaxial with the extrusion nozzle.
It is known to introduce at least one pair of mold blocks, known as cuff blocks, adapted to mold a cuff of different outer surface of the tube into the mechanism of the travelling mold tunnel so that such different surface will be cyclically introduced on the surface of the molded tube according to the length of the runs of mold blocks. Of course such differing pairs of mold blocks may be inserted into the mold train at whatever intervals are desired. Thus, more than one such pair may be present in the runs.
For example, European patent application No.
REFERENCES:
patent: 4362187 (1982-12-01), Harris et al.
patent: 4735444 (1988-04-01), Skipper
patent: 4865362 (1989-09-01), Holden
patent: 4913473 (1990-04-01), Bonnema et al.
patent: 5071173 (1991-12-01), Hegler et al.
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