Seal for a joint or juncture – Seal between relatively movable parts – Relatively rotatable radially extending sealing face member
Patent
1988-01-14
1989-12-26
Stinson, Frankie L.
Seal for a joint or juncture
Seal between relatively movable parts
Relatively rotatable radially extending sealing face member
277 92, 277173, 277177, F16J 1532
Patent
active
048893498
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a sealing arrangement consisting of a sealing means, a first machine part (for example, a sealing housing or piston) separating a space of higher pressure from a space of lower pressure and forming, to receive the sealing means, an annular space which is limited, towards the space of lower pressure, by an end face supporting the sealing means, and of a second machine part (for example, a cylinder or rod) forming an opposing surface interacting with the sealing means and movable in rotation and/or axially, the sealing means, which encloses a gap together with the opposing surface, comprising a sealing ring made of flexible material, which, on a tubular sealing-ring part, forms a sealing edge projecting relative to the opposing surface, a supporting part, which supports the tubular sealing-ring part on the side of higher pressure, and a tension ring made of elastic material, which touches the tubular sealing-ring part and is subjected to the higher pressure and which rests against the end face of the annular space.
In sealing means, a high specific frictional capacity related to the sliding sealing surface, which occurs in the sealing gap between the sliding sealing surfaces, can be converted into heat under the influence of high pressure to be sealed off and at a high peripheral speed of the shaft forming the opposing surface. If as little leakage as possible is to be ensured, the width of the sealing gap must be of the order of magnitude of the roughness of the surfaces of the sealing ring and of the shaft which form the gap. Mixed friction usually occurs here. In a sealing ring made of low-wear plastic based on polytetrafluoroethylene, a coefficient of friction of approximately 0.05 must be expected under high surface pressure and with mixed friction. Because the curve of the pressure drop in the sealing gap cannot be defined where mixed friction is concerned, a shaft seal subject to radial pressure must be designed so that the sealing-surface pressure is at least as high as the pressure to be sealed off. Under these conditions, for example, even at a pressure of only 5 MPa and with a shaft diameter of 80 mm and a rotational speed of 1500 revolutions per minute, a specific frictional capacity of at least 150 Watts per square centimeter of the sealing surface is obtained. As a comparison, the specific heating capacity of an electrical cooking plate amounts to only approximately 8 Watts per square centimeter. The elimination of the frictional heat is therefore an important object.
However, in conventional shaft seals with a sealing edge of small axial extent, which is subjected to radial pressure, the actual frictional capacity is usually even substantially higher than the value calculated above, because, since there is an insufficient hydrostatic relief of the sealing edge, the sealing-surface pressure is generally substantially higher than the pressure to be sealed off and is therefore too high in sealing terms. The result of this is that such shaft seals with plastic sealing rings cannot be used under the operation conditions assumed above, because of the danger of overheating of the sealing surfaces.
Furthermore, with conventional sealing rings used for sealing off higher pressures, there is excessive flattening of the sealing edge and consequently an undesirable enlargement of the sealing surface because of too high a radial force, with the result that, for this reason too, an extremely high frictional capacity is obtained, at the same time with unfavorable conditions for heat elimination. The generation of heat in the sealing gap therefore often causes the failure of shaft seals and limits the range of use in terms of pressure and peripheral speed.
In the known sealing arrangement described in the introduction (DE-C-3,217,118, especially FIGS. 1 and 5), the fraction of the sealing-surface pressure originating from the pressure to be sealed off is kept small because the sealing edge is arranged near the low-pressure end of the tubular sealing ring and the latter is supported, r
REFERENCES:
patent: 3384382 (1968-05-01), Rink
patent: 3443814 (1969-05-01), Dahlheimer
patent: 4053166 (1977-10-01), Domkowski
patent: 4243233 (1981-01-01), Arai
patent: 4268045 (1981-05-01), Traub
patent: 4723782 (1988-02-01), Muller
Martin Merkel GmbH & Co KG
Stinson Frankie L.
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