Seal for a joint or juncture – Seal between relatively movable parts – Piston ring or piston ring expander or seat therefor
Reexamination Certificate
1997-12-12
2001-11-27
Mah, Chuck Y. (Department: 3626)
Seal for a joint or juncture
Seal between relatively movable parts
Piston ring or piston ring expander or seat therefor
C277S435000, C277S437000
Reexamination Certificate
active
06322080
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a sealing arrangement comprising a one-piece sealing ring with a parting joint and compensating clearance and cover ring surrounding or enclosing the sealing ring in the peripheral direction.
2. Description of the Prior Art
Sealing arrangements for a body of circular cross-section such as a piston rod are known, in particular for piston compressors. Dry running piston compressors are machines which require no foreign lubrication in the compression part. Such compressors have fixed sealing elements past which a piston rod is moved. The seal elements are usually arranged one after the other in series and form in this manner a so-called packing. A packing of this type with sealing arrangements and sealing rings is known from CH 439 897. Sealing rings are subject to wear at the sealing surface which lies against the piston rod. In order to maintain the sealing function over longer periods of time, the known sealing ring has wear compensation wherein the sealing ring is split up into three sealing ring elements with partial joints extending parallel to a tangent with respect to the piston rod and with radial joints forming a compensatory ring gap. A hose spring peripherally surrounding the sealing ring exerts a preload on the sealing ring elements towards the piston rod. This known sealing arrangement has the disadvantage that the sealing ring has a large number of partial joints, which impair the sealing function. In order to seal off these joints, a cover ring lying in contact in the axial direction is arranged adjacent to the sealing ring. Such a sealing arrangement has the disadvantage that it has a relatively long extent in the axial direction. A known problem of such sealing arrangements at piston rods is the frictional heat which arises. Dissipation of the heat of friction via the seal elements themselves is possible only with difficulty, since the seal elements are usually made of plastic and act thermally almost as insulators. The greatest portion of the heat of friction is thus led off in a clearly less efficient manner by the piston rod. The heat of friction which arises is thus largely responsible for high wear, among other things, when sealing rings of plastic are used. Thus, a complicated and expensive cooling of the packing containing the sealing arrangement is often required.
SUMMARY OF THE INVENTION
It is the object of the present invention to overcome the disadvantages of known sealing arrangements.
The sealing arrangement in accordance with the invention for a piston rod with a circular cross-section thus comprises a one-piece sealing ring with a ring gap and compensatory clearance as well as a cover ring surrounding or enclosing the sealing ring in the peripheral direction, with the sealing ring having a section at least at one end which, together with the other end of the sealing ring, forms an overlapping ring gap, and with the sealing ring having a wall thickness decreasing towards the parting joint or ring gap respectively.
An advantage of the sealing arrangement in accordance with the invention is to be seen in that the overlapping ring gap in the axial direction produces a high degree of gas-tightness. The surrounding or enclosing cover ring assists the sealing action and exerts in addition a bias load acting on the sealing ring towards the piston rod. The surrounding or enclosing cover ring seals the overlapping parting joint in the radial direction.
Suitable materials for the sealing ring are plastics for dry running applications such as filled polymers with a matrix of polytetrafluoroethylene (PTFE) or a mixture of mechanically solid, high-temperature-resistant and wear-resistant polymers, which are also designated as “high-temperature polymers”, such as poly(ether ether ketone) (PEEK), poly(ether ketone) (PEK) polyimide (PI), poly(phenylene sulphide) (PPS), polybenzimidazole (PBI), polyamideimide (PAI) or also epoxy resin. The high-temperature polymers are not capable of dry running in their pure form and hence require additional solid lubricants such as carbon, graphite, molybdenum sulphide, PTFE etc. Such high-temperature polymers are then designated as “modified”.
An advantage of the sealing arrangement in accordance with the invention is to be seen in the fact that a sealing ring manufactured of a high-temperature polymer can, in particular, be used.
The term “high-temperature” polymer serves as a collective term in connection with the use of sealing elements in piston compressors for plastics which are distinguished from the customary filled PTFE materials by the following properties:
High-temperature polymers have a high mechanical stability even at the high temperatures that are usual in dry running.
High-temperature polymers have no cold flow properties, so even finely shaped sealing rings remain form-stable and, in particular, require no additional support ring when used in a packing even at high pressures.
High-temperature polymers have a substantially higher module of elasticity, which leads to greater stiffness for larger ring diameters of a sealing ring.
With high-temperature polymers, sealing rings can be manufactured which, in comparison with filled PTFE, have substantially smaller diameters and nevertheless a substantially higher mechanical loadability, so that such sealing rings made of high-temperature polymers are suitable, in particular, for use at high compression end pressures.
A previous disadvantage in the use of high-temperature polymers was to be seen in the fact that the poor ability to adopt to a specific shape made it difficult to achieve complete contact of the sealing ring over the entire periphery of a piston rod, so that leaks resulted.
The sealing ring in accordance with the present invention has the advantage that the sealing ring has a radial wall thickness which decreases towards the parting joint or the ring gap respectively, which means that the sealing ring is made somewhat thinner and thus softer in bending in the region of the overlapping ring gap. By virtue of this design, a sealing ring consisting of high-temperature polymers has good shape matching ability.
The sealing ring in accordance with the invention is, in particular, suitable for dry running ring piston compressors, with the sealing ring preferably consisting of a modified high-temperature polymer with so-called self-lubrication properties. A sealing ring of this type can be manufactured as a very narrow ring so that, on the one hand, the piston rod better transmits the heat via radiation heat to the packing and, on the other hand, a smaller frictional surface exists between the sealing ring and the piston rod, which reduces the heating up. In this manner, an excessive heating up of the piston rod can be prevented, which has the additional advantage that the sealing ring is subject to reduced wear.
The sealing arrangement in accordance with the present invention has a high imperviousness so that only slight leakage occurs through the sealing arrangement, and the leakage takes place mainly between the piston rod and the sealing surface of the sealing ring. During this, a gas bearing arises between the piston rod and the sealing surface, which reduces the production of heat and thus, in addition, the heating of the piston rod as well as the wear on the sealing ring.
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patent: 1369075 (1921-02-01), Ballman
patent: 1391845 (1921-09-01), Moratta
patent: 1488052 (1924-03-01), McFarlane
patent: 1538107 (1925-05-01), Giller
patent: 2064527 (1936-12-01), Ericsson
patent: 3057630 (1962-09-01), Snned
patent: 3305241 (1967-02-01), Hart
patent: 3942806 (1976-03-01), Edlund
patent: 439 897 (1967-12-01), None
patent: 7318583 (1975-07-01), None
patent: 4201246C2 (1993-12-01), None
patent: 2 678 039 (1992-12-01), None
patent: 278564 (1927-10-01), None
Mah Chuck Y.
Maschinenfabrik Sulzer-Burckhardt AG
Peavey Enodi
Townsend and Townsend / and Crew LLP
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