Mechanical duty rubber bellows

Details Mechanical duty rubber bellows Mechanical duty rubber bellows

1998-10-13

2001-05-29

Sandy, Robert J. (Department: 3626)

Seal for a joint or juncture

Seal between fixed parts or static contact against...

Contact seal for other than internal combustion engine, or...

C277S636000

Reexamination Certificate

active

06237922

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to mechanical duty bellows employed as dynamic pressure seals where a positive seal without leakage is made between moving parts.
BACKGROUND
A bellows as a dynamic or movable pressure seal is often employed for sealing a reciprocating plunger or similar device where one end of the bellows is fixed and the other attached to the moving plunger. A bellows is selected because it is leak-proof and a long stroke may be had by simply providing a sufficient number of convolutions. The flexing of the bellows is accomplished by a bending of the bellows material at the convolutions. This bending action is characteristic of all prior types of bellows.
Prior types of bellows intended for such dynamic use are usually made from metal, either stretch formed from a metal tube or brazed-up from metal diaphragms. These bellows are of limited flexural life due to the bending of the metal at the convolutions which generates unpredictable stresses and leads to early fatigue cracking. Metal bellows are thus limited to low frequency operation or occasional use. A further disadvantage with metal bellows is their sensitivity to vibration which can cause premature fatigue cracking.
Another type of bellows is made from rubber, either molded in one piece or made up from separate rubber diaphragms sewn together. However this type of rubber bellows is intended for use as a dust cover and the like and is not suitable for pressure service.
Details of the design and application of both prior types of bellows can be found in the manufacturer's literature. An excellent listing of manufacturers of all types of bellows is given in the current publication of;
The Thomas Register of American Manufacturers
Five Penn Plaza, New York N.Y. 10001 USA
Published annually
There is a need for a long stroke positive pressure seal which can be operated at high cycle rates for extended periods. Up to now the usual solution for high-speed reciprocating service has been to employ a sliding seal such as a rod sealed by packing or pre-formed rings. Sliding seals always permit some leakage and are thus not positive sealing. Also they have the disadvantage of requiring lubrication which in some applications is objectionable.
THE INVENTION
I have found that by constructing a bellows from a number of annular rubber diaphragms of comparatively thick cross-section alternately bonded to a series of outer and inner metal hoops, a dynamic seal having a long service life results. The metal hoops limit the rubber diaphragms to simple shear loading only during flexure of the bellows and since the stresses for rubber in simple shear are predictable, it is possible to calculate suitable dimensions for the diaphragms to control shear stresses within acceptable levels and a long stroke positive pressure seal having an extended service life at high reciprocating speeds is obtained.
It is to be understood that the expression, simple shear, is taken as meaning a shear action without bending or stretching of diaphragm. This occurs where the shear strain is moderate as more fully explained hereinafter.


REFERENCES:
patent: 3241844 (1966-03-01), Morley
patent: 4469467 (1984-09-01), Odill et al.
patent: 4587145 (1986-05-01), Kanao
patent: 5087493 (1992-02-01), Wang

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