Coating apparatus – Immersion or work-confined pool type – With means for moving work through – into or out of pool
Reexamination Certificate
2000-11-17
2003-04-29
Lamb, Brenda A. (Department: 1734)
Coating apparatus
Immersion or work-confined pool type
With means for moving work through, into or out of pool
C118S419000
Reexamination Certificate
active
06554904
ABSTRACT:
The present invention concerns a roller arrangement for a product to be coated in a molten metal bath, having a roller which rotates in the metal bath and is retained at the ends rotatably on support arms by way of rolling bearings, the rolling bearings being arranged in bearing housings sealed with respect to the metal bath.
In hot galvanizing, tinning, or aluminizing, one or more rollers, bearing-mounted at both ends, are immersed into a metal bath in order to guide therein the strip that is to be coated. Plain bearings have hitherto predominantly been used to support the rollers in the metal bath. These bearings, completely immersed in the metal bath, have the disadvantage of short service lives, since high temperatures, friction, and attack by the liquid metal cause severe wear on the bearing surfaces. The wear results in rough running or even brief seizing of the roller. The reason for the rough running or seizing of the roller is friction at the roller journal, which scores into the bearing shell as the diameter is reduced. Solid particles and surface damage in the contact region accelerate this process.
U.S. Pat. No. 5,571,328 and EP 0 524 851 A1 disclose plain bearings that use ceramic plates in a wedge-shaped arrangement as the outer bearing shell. This is intended to prevent the roller journal from scoring into the bearing shell. Wear-related surface damage and particle deposits on the bearing journal nevertheless subject the ceramic plates to impacts, and can cause premature bearing failure.
DE Patent 43 07 282 A1 discloses a further roller arrangement in which the buoyancy of an air-filled roller in the metal bath is used to reduce load. Rolling bearings whose rolling elements rotate in the liquid metal are provided to support the roller. A disadvantage of this embodiment, however, is the fact that as a result of wear and dissolution effects in the metal bath, internal bearing clearance increases and dimensional accuracy is lost.
The publication “Antriebstechnik” 34 (1995) No. 7 furthermore describes a rolling bearing for use in a molten zinc bath which is embodied as a solid ceramic bearing. A disadvantage of this embodiment, however, is the fact that during service in molten metal, solid particles can penetrate into the raceways, and subject the ceramic bearing to impacts as they are rolled over. In addition, the ceramic can suffer damage due to impacts or thermal shock while being installed or removed.
To solve this problem, DE Unexamined Patent Application 39 40 890 A1 proposes to place the bearings in closed bearing housings that are sealed with respect to the molten bath. Sealing is accomplished by way of a conical sleeve that is retained displaceably on a shaft and is pressed by a spring element against a conical trough secured to the bearing housing. During operation, friction associated with abrasion occurs between the rotating roller and the stationary portion of the conical seal, so that the arrangement can become leaky after extended operation.
It is therefore the object of the invention to develop a roller arrangement of the kind cited initially in such a way that even in extended operation, complete sealing of the bearing housing with respect to the metal bath can be guaranteed.
According to the present invention, this object is achieved substantially in that, in order to seal the bearing housing with respect to the roller, sealing surfaces extending transversely to the roller axis are configured on a radially projecting shoulder of the roller and on the bearing housing, and are pressed against one another or against an interposed seal element. The result of this configuration is that molten metal from the metal bath must pass between the sealing surfaces of the roller shoulder and bearing housing in order to get into the interior of the bearing housing. The gap formed between the sealing surfaces can be very well sealed by axially acting contact pressure, however, so that any penetration of molten metal into the bearing housing can be reliably prevented even during extended operation.
According to an embodiment of the invention, provision is made for the radial shoulder to be provided on the end portion of the roller engaging into the bearing housing, i.e. sealing occurs on the inner side of the bearing housing. In this case a gas conduit preferably opens into the bearing housing in order to deliver gas to the bearing housing and generate a positive pressure, and by way of the positive pressure to push the radial roller shoulder toward the sealing surface of the bearing housing. With this configuration, generation of the contact force in the region of the sealing surfaces is achieved by the fact that the internal pressure acting in all directions attempts to push the roller journal out of the bearing housing against the hydrostatic pressure of the metal bath. This force can be calculated as the product of the difference between the internal pressure and the hydrostatic pressure times the cross-sectional area of the roller journal in the passthrough region. This pneumatic contact force has the advantage of not requiring any additional installation space, and guarantees that the sealing surfaces touch one another and that the roller journal remains axially in position. Wear in the region of the sealing surfaces results in axial shifting of the roller journal. The running surfaces of the bearing must correspondingly allow axial displacement of the roller journal.
If the internal pressure is greater than the hydrostatic pressure in the molten metal, it constitutes an additional safety feature. The reason is that if leaks occur in the region of the sealing surfaces, for example as a result of wear, the result of the internal pressure is that molten metal does not enter, but rather gas emerges, at a volume flow that is kept low by the fact that the annular gap between roller and bearing housing is narrow.
According to a development, provision is made for there to be arranged, between the sealing surfaces of the roller shoulder and bearing housing, an annular disk made of seal material that is pressed via the roller shoulder against the sealing surfaces on the bearing housing. This embodiment has the advantage that the annular disk can be configured as a wear-and-tear part, and can easily be replaced as necessary. The annular disk can be joined to the roller so that it co-rotates with the roller. In this case wear occurs only between the annular disk and the bearing housing. Alternatively, it is possible to join the annular disk to the bearing housing, so that the annular disk is stationary and wear thus occurs only between the annular disk and roller shoulder. According to a preferred embodiment, however, the annular disk is coupled, for example by way of driver pins, to the cage of a rolling bearing, the result being that it co-rotates during operation and a uniform load thus occurs on the two sealing surfaces.
The annular disk is preferably made of ceramic, which has the advantage that it is inert with respect to the molten metal. The friction between the very low-roughness ceramic surface and the seal participant is largely wear-free. The scuffing that is possible in the case of contact between two metal surfaces can thus be eliminated.
In an alternative embodiment of the invention, provision is made for the sealing surfaces of the roller shoulder and bearing housing to be provided on both sides of the annular gap formed between the bearing housing and roller, and for a seal element to be provided that is simultaneously pressed against both sealing surfaces and seals the annular gap, the seal element being coupled to the rolling bearing cage so that during operation, the seal element rotates both with respect to the roller journal and with respect to the bearing housing. With this embodiment, therefore, the sealing surfaces on the bearing housing and roller are not pressed against one another as in the embodiments described above, but rather the two sealing surfaces each seal the annular gap on one side (radially inward and radially outward) by their c
Gimpel Matthias
Siegmann Eckhard
Lamb Brenda A.
Liniak, Rerenato & White, LLC
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