Seal for a joint or juncture – Seal between relatively movable parts – Circumferential contact seal for other than piston
Reexamination Certificate
1999-04-19
2001-02-20
Melius, Terry Lee (Department: 3628)
Seal for a joint or juncture
Seal between relatively movable parts
Circumferential contact seal for other than piston
C277S560000
Reexamination Certificate
active
06189894
ABSTRACT:
TECHNICAL FIELD
The present invention relates to hydraulic sealing devices and more particularly to an improved packing member or seal for forming a seal between a cylinder and a moveable shaft extending through the cylinder.
BACKGROUND OF THE INVENTION
It is common practice to form a seal between the wall of an opening and a shaft or other cylindrical member extending through the opening by positioning a packing member between the wall of the opening and the outer surface of the member. Packing members are typically annular bodies having a generally V-shaped or truncated V-shaped cross-section. Packing members are, in many cases, formed from an elastomeric material such as rubber or plastic. Such packing members are disclosed in U.S. Pat. No. 5,509,670 issued Apr. 23, 1996, and 5,704,615, issued Jan. 6, 1998, the disclosures of which are incorporated by reference herein for all purposes.
The operation of a device such as a hydraulic cylinder typically involves both static and dynamic forces generated by the friction between the packing member and the cylinder shaft. Static friction must be overcome during the initial actuation of the cylinder whereas dynamic friction is encountered during continued movement of the shaft. The amount of friction between the shaft and the packing member is determined by a number of factors including the amount of surface area of the packing member in contact with the shaft. Preferably, the amount of friction between the shaft and the packing member is minimized while maintaining an effective seal. The amount of force required to overcome static friction and initially move the shaft is typically greater than the force required to overcome dynamic friction after the shaft has started moving. Since the amount of force required to overcome static friction is greater than the amount of force needed to overcome dynamic friction, static friction is an important consideration in the selection and design of packing members. Moreover, during the operation of a hydraulic cylinder, a large difference between the force required to overcome static friction and the force required to overcome dynamic friction may result in the cylinder jerking or “stuttering” during operation. Large hydraulic and mechanical stresses can be generated when a hydraulic cylinder jerks in such a manner, stresses that may damage or cause excessive wear of system components, for example, hydraulic valves, fittings and the hydraulic pump supplying pressurized fluid to the cylinder. Consequently, it is desirable not only that the friction between a packing member and a slidable member passing through the packing member be minimized, but also that the difference in the amount of force required to overcome static versus dynamic friction be minimized.
It is also important that a packing member or seal be formed from a readily available, economically feasible material. One such material is urethane. Some types of urethane have many desirable properties including increased resistance to abrasion and wear as compared to other plastics and elastomers. Urethane is also generally more resistance to cuts and tears than other plastics or elastomers, tends to non-brittle at higher hardness, resisting fracture during shock and impact loading, and maintains dimensional stability over a wide range of temperatures. One drawback to the use of urethane to form packing members or hydraulic seals is the tendency to stick during operation. Thus, it is desirable to reduce the amount of contact between the seal and the cylinder. However, adequate support must also be provided to the sealing edge of the packing or seal, and reducing the size of the contact area alone does not completely address the problem.
SUMMARY OF THE INVENTION
The present invention provides a packing member with an improved geometric configuration that results in reduced friction while simultaneously providing the sealing edge of the member with adequate structural support. The improved geometry of the member also provides reduced a static/dynamic load ratio.
In one embodiment, the packing member includes: (1) an annular body defining a central opening and an annular axis, said annular body having an upper sealing portion and a lower support portion; (2) the annular body further defining a groove extending into said upper sealing portion, the groove having an outer, outwardly inclined wall, an inner, inwardly inclined wall and a bottom wall; (3) the upper sealing portion of the annular body including radially extending inner and outer sealing lips formed adjacent to at least a portion of the groove, the outer sealing lip extending axially beyond the inner sealing lip; (4) the inner sealing lip including a first lower inwardly inclined surface and a second lower inwardly inclined surface, the second lower inwardly inclined surface being inwardly inclined at an angle greater than the first lower inwardly inclined surface; (5) the inner sealing lip further also including upper outwardly inclined surface, the upper outwardly inclined surface intersecting the second lower inwardly inclined surface, the intersection of the second lower inwardly inclined surface with the upper outwardly inclined surface forming an inner sealing edge which defines a first plane; and (6) an upper sealing lip surface, the upper surface defining a second plane, said inner sealing lip being further defined by the inner, inwardly inclined wall of the groove. The packing member also includes a lower generally cylindrical support portion, the lower support section having an annular inner support wall, an annular outer support wall, and a bottom wall. The intersection of the annular inner support wall and the first lower outwardly inclined surface of the inner sealing lip defines a fifth plane, and the intersection of the first lower inwardly inclined surface of the inner sealing lip and the second lower inwardly inclined surface of the inner sealing lip defines a sixth plane. The annular inner support wall and annular outer support wall define substantially concentric parallel inner and outer cylinders. The packing member thus forms an annular support gusset defined by the inner cylinder, first lower inwardly inclined surface of the inner sealing lip, and the sixth plane. The annular gusset extends around at least a portion of the packing member and supports at least a portion of the inner sealing lip extending above the sixth plane.
The geometry of the packing member is particularly applicable to the manufacture of seals from a urethane composition having a Shore A hardness of from about 90 to about 100, providing reduced friction due at least in part to the support provided to the inner sealing edge by the annular gusset.
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UTEX Industries, Inc. brochure on Utex “KF” Design Ram Seals, from “Other Quality Products Availa
Intellectual Property Law, P.C.
Jorgenson Edward I.
Melius Terry Lee
Meyers Philip G.
Miller William L.
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