Seal for a joint or juncture – Seal between relatively movable parts – Relatively rotatable radially extending sealing face member
Patent
1987-01-27
1988-09-27
Ward, Robert S.
Seal for a joint or juncture
Seal between relatively movable parts
Relatively rotatable radially extending sealing face member
277 12, 277 15, 277 22, 277 88, 366 84, F16J 1536, F16J 1540, B01J 1920, B29B 748
Patent
active
047736542
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a shaft seal assembly, in particular for an apparatus for continuous processing of very viscous media, in particular for producing high molecular weight polymers, for example for the condensation of polyester, having at least two parallel shafts, each carrying processing tools, and with which shafts feed and removal devices for the product being processed and one reaction chamber that can be subjected to a vacuum are associated, the vacuum chamber being defined on at least one side by a housing portion which has ducting devices for the shafts that can be coupled with a distributor gear driving them and located on the outside, wherein the reaction chamber, in the vicinity of the shaft ducting devices, is sealed off via sealing means including at least one slide ring seal from an external sealing- or confining-liquid chamber surrounding the shaft ends and containing a confining or sealing liquid.
In apparatuses of this kind, also known as reactors, but also as in multiple-shaft mixers or kneaders for plastics production, in which for degassing purposes a reaction chamber subjected to a vacuum is provided, the problem of sealing between the reactor interior and the atmosphere in the vicinity of the shaft ducts arises. Sealing is difficult because in many of these reaction operations a vacuum is used, and in the condensation of polyester a pronounced vacuum, to the extent of 0.1 Torr, is used.
In the shaft ducts of such apparatus, it is known to use special slide ring seals and to provide containing-liquid chambers, which are filled with a suitable confining liquid, such as cooled thermal oil, and are subjected to a vacuum. For reasons having to do with service life, slide ring seals having sliding surfaces of silicon carbide are used.
Because slide ring seals have to be able to "breathe" somewhat, for functional reasons, because of the axially resiliently loaded sealing ring, it is unavoidable in practice that confining fluid will be aspirated into the reaction chamber. In many cases, however, this is undesirable or impermissible.
It is therefore the object of the invention to devise a shaft seal assembly for such reactors or for apparatuses subjected to comparable conditions, which assures satisfactory sealing of a housing interior, in this case in particular, a reaction chamber subjected to a vacuum, with respect to the atmosphere, with a long service life and easy maintenance, while at the same time the entry of confining liquid or other undesirable contaminants into the sealed housing interior is reliably precluded.
For attaining this object, the shaft seal assembly as described above is characterized in accordance with the invention in that on the side oriented toward the reaction chamber, adjoining the sealing means, each shaft is surrounded by a cushion of inert gas, which has a higher pressure than the confining fluid, and is defined such that it is sealed off from the reaction chamber by housing portions surrounding the shafts over a portion of their length as well as by the product being processed which surrounds the shafts and is under pressure.
Because of its higher pressure, the cushion of inert gas prevents the entry of confining liquid via the sealing means and via optionally provided shaft radial bearings into the sealed-off chamber.
Because the inert gas cushion is itself sealed off, along the shafts toward the sealed-off chamber--with the exception of the housing portions intermittently surrounding the shafts--by means of the product being processed, which is under pressure, on this side of the inert gas cushion its own sealing devices, subjected to wear and for example such as slide ring seals or the like, are not required. At the same time, the inert gas cushion prevents the vacuum from the reaction chamber from reaching the sealing means and becoming operative there. Small quantities of inert gas entrained into the reaction chamber during operation are harmless; they are aspirated out by the vacuum pumps and the like subjecting the reaction chamber to the vacuum.
REFERENCES:
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patent: 4500093 (1985-02-01), Kapich
Meyer, "End Face Seal", Maschinostroenie, 1978, p. 228.
Slide Seal for Chemical Reaction Stirrring Vessels by Dipl. Ing. H. Schnarkowski-Chemie-Ing. Techn. vol. 36, 1964, pp. 1134-1136.
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