Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Perforation by differential fluid pressure; or smoothing,...
Patent
1997-05-14
1999-04-27
Silbaugh, Jan H.
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Perforation by differential fluid pressure; or smoothing,...
264573, 264154, 83 53, 83177, B29C 4322
Patent
active
058978283
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing duckbill valves, and more particularly to a method of splitting such valves.
Duckbill valves are non-return valves which have a generally tubular body portion, from which two opposed lips extend. The opposed lips contact each other at the ends away from the tubular body. When the fluid pressure at the tubular end of the valve exceeds that outside the lips, the opposed lips open, allowing fluid to flow forwards through the valve. When the fluid pressure is greater outside the lips than inside the tubular body, the lips are pressed tightly in contact with one another, by the fluid pressure, and so prevent fluid from flowing backwards through the valve.
Cross-linked polymer duckbill valves are formed by compression transfer moulding and the polymer is cross-linked in the mould with the opposed lips integrally formed with each other, being joined by a land. The cross linking of the polymer results in an excessive cycle time.
DESCRIPTION OF THE PRIOR ART
A number of methods are known for separating the opposed lips of such moulded valves. One method is to use a laser to ablate the land between the two lips. The problem with this method is that the laser removes material and creates a permanent gap between the opposed lips. The valve is therefore liable by leak in the backwards direction.
Another method is to shear the land between the two lips. Using this method, a chisel point is inserted through the tubular body of the valve, and contacts the inside of the land area between the two lips. The outside end of the lips is supported on a rubber pad. By applying pressure to the chisel point, the cross-linked polymer material is compressed between the chisel point and pad. If the pressure is applied rapidly enough, the material shears with the creation of a brittle fracture split to separate the two lips. Although the resulting split may not be flat, for cross-linked polymers, there is an exact male-female match, and therefore a good seal can be achieved with no leakage in the backwards direction. A problem with this method is that the pad needs frequent replacement as it is cut and damaged by the action of the chisel point.
Recently, it has been proposed to manufacture duckbill valves from thermoplastic elastomer (TPE) For such valves, the shearing method of splitting is unsatisfactory. Due to the elastic nature of TPE, a brittle fracture is not obtained with a chisel point. Instead, the material tears, and accordingly there is not an exact correspondence between the opposed lips. This results in the valves leaking in the backwards direction at low pressure.
SUMMARY OF THE PRESENT INVENTION
According to a first aspect of the present invention, a method of forming a duckbill valve includes the steps of moulding a valve with its lips joined by a land and subjecting the inside of the valve to a fluid pressure, to split the lips of the valve.
By applying fluid pressure to the inside of the valve, the land joining the lips balloons and bursts thereby separating the lips in such a way that the opposed faces are an exact male-female match. The surface characteristics of the lips so formed suggest once again that the lips are separated by a brittle fracture.
Preferably, substantially all the outer surface of the valve other than the outside of the lips is supported during splitting. By supporting the outside of the valve, it is ensured that only the land between the two lips splits and that the valve does not split at any other point, for example through its side.
Although the duckbill valve may be made of a cross-linked polymer valve, it is preferred that the valve is made from TPE, and more preferably the valve is made of styrene-ethylene-butylene-styrene block copolymer (SEBS).
The fluid pressure may be a blast of air, or other gas or liquid. It is preferred that the fluid is inert so that it does not react with the valves, and is free from bacteria which may remain on the valve.
According to a second aspect of the present inve
REFERENCES:
patent: 2032923 (1936-03-01), Eldridge
patent: 3226527 (1965-12-01), Harding
patent: 3257026 (1966-06-01), Taylor
patent: 3266355 (1966-08-01), Williamson
patent: 3805649 (1974-04-01), Hester
patent: 5261459 (1993-11-01), Atkinson et al.
patent: 5620639 (1997-04-01), Stevens et al.
International Search Report, Dec. 8, 1995.
Mondszein Karl
Rosens Erwin Anton
Sillince Mark Erich
Heinekin Technical Services, B.V.
Lawson Mardon Plastics
Lee Edmund H.
Silbaugh Jan H.
Whitbread PLC
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