Bearing system for pot roller

Abstract

The bearing system is configured to be used between a roller journal and a support frame in a molten metal electroplating line of a steel strip. The system includes a sleeve configured to be attached to the journal and a bearing assembly having a bush that rotatably supports the sleeve. The sleeve is made of solid cemented carbide. An elastically compressible layer couples the sleeve to the journal such that the sleeve and the journal are mechanically coupled to rotate together.

Description

Cross - Reference to Related Applications

[0001] This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application No. 63 / 351,245, filed on June 10, 2022, which is currently pending. The disclosure of this application is incorporated herein by reference in its entirety.

Technical Field

[0002] This disclosure relates to an article for use in coating a substrate with a molten metal, i.e., a bearing assembly for use in an immersion roller that transports a steel strip through a molten metal bath.

Background Art

[0003] Coating a steel strip with a metal or alloy improves corrosion resistance and increases the value of the steel strip. Coated steel is widely used in many applications, including construction, household appliances, and automobiles. Common coatings include zinc (galvanized), zinc 95 / aluminum 5 (galfan), aluminum 55 / zinc 45 (galvalume), and pure aluminum (aluminum plated).

Summary of the Invention

Problems to be Solved by the Invention

[0004] The most economical way to apply this metal coating is via a hot dip coating line. As shown in FIG. 1, a steel strip 10 is fed through a protective shroud or snout 40 into a molten metal bath 20 held in a pot 30, then redirected by a sink roller 50 and passed between two small stabilizing rollers 60 before exiting the bath 20. A gas knife 70 just above the bath surface removes excess molten material for a uniform coating.

[0005] The productivity of the coating line is highly dependent on continuous operation, and interruptions are costly. One of the main causes of undesirable maintenance stops is the failure of the synchronizer bearings.

[0006] A type of bearing system well - suited for pot rollers is the sleeve bearing. US8047718 describes a sleeve bearing for a roller in a molten plating line, and the sleeve bearing includes a sleeve fixed to the shaft of the roller and a bearing housing having a bush fixed inside to support the sleeve.

[0007] Figure 2 shows a pot synchronizer roller 50 with a bearing system according to the prior art. The bearing system includes a sleeve 100 that fits onto a journal 90 and a bearing assembly that is attached to a support frame 80 and mounted around the sleeve 100. The bearing assembly consists of a bearing housing 110 and a bush 120 having a bush surface 130 configured to slidably engage the outer surface 140 of the sleeve 100. Preferably, the sleeve 100 includes a lip 150.

[0008] During assembly, the sleeve 100 is pressed onto the journal 90, and then a retaining ring 160 is slid over the sleeve 100 and welded to the journal 90. The retaining ring 160 engages the lip 150 to prevent the sleeve 100 from moving laterally relative to the journal 90.

[0009] In such a pot roller bearing system, the sleeve 100 rotates within the bearing housing 110 with the inner surface 130 of the bush in sliding contact with the outer surface 140 of the sleeve. These sliding surfaces come into contact with molten metal and are lubricated. Since the molten metal is at a high temperature and highly corrosive, sleeves and / or bushes made from standard bearing materials exhibit rapid wear and early failure.

[0010] As shown in FIG. 1, the sink roller 50 is used to apply tension to the strip 10 when the strip 10 changes direction so as to exit the pot 30. The sink roller 50 is the most stressed, and the sink roller bearing has the highest failure rate.

[0011] The master's thesis submitted to the University of West Virginia by Venkatesh Parthasarathy in 2003 and titled "Long-Term Performance of Pot Hardware in Continuous Galvanizing Lines" contains the following content, namely, "Generally, the materials used for bearing sleeves are Stellite 6, CF3M (cast version 316 stainless steel) with tungsten carbide laser cladding, Tribaloy T-800, Tribaloy T-400, and Metaullic 2012 and 2020. These bearing sleeves operate with maximum efficiency when moving against an appropriate bush material. Typical bearing sleeve and bush assemblies used in production lines are Stellite 6 sleeves and semi-circular Stellite 6 bushes, CF3M with tungsten carbide laser cladding and SiAlON ceramic, Tribaloy T-800 sleeves and semi-circular Tribaloy T-800 bushes, or Metaullic 2012 sleeves and Metallic(sic) 2012 self-aligning bushes." (page 4)

[0012] US6037287, titled "Laser Clad Pot Roll Sleeves and Bushings for Galvanizing Baths" by Praxair S.T. Technology, describes that tungsten carbide is desirable as a wear-resistant material on the outer surface of the sleeve. In the said patent, several known processes are compared for applying a coating such as tungsten carbide. These processes include overlay welding, spray fusion process, and transferred plasma arc. According to the said patent, since the coating thickness is limited to several millimeters and the coating wears out relatively quickly during use, none of these processes could apply a coating of sufficient thickness for use on pot roller sleeves. The said patent describes a wear-resistant coating for journals, journal sleeves, and bushings of rolls immersed in a molten metal coating bath having a tungsten carbide composite material applied through laser melting, also known as laser cladding.

[0013] The use of sleeves made of 316L stainless steel with a corrosion- and wear-resistant overlay containing tungsten carbide particles applied by laser cladding to move against bushing products such as advanced ceramic materials sold under the brand name "WEARGUARD" by McDanel Advanced Ceramic Technologies has been found to reduce wear and save costs by extending the movement of the pot roll. However, the coating thickness achievable using laser cladding is also relatively thin and wears or peels off from the journal.

[0014] As described in the prior art, sleeves of wear-resistant materials have been attached to the synchronizer journal by shrink fitting, also known as press fitting. When a sleeve having a stainless steel coated with tungsten carbide is mounted on a stainless steel journal, the sleeve can be shrink fit and / or welded to the journal.

[0015] Another wear-resistant material, silicon nitride, has been used to form solid journal sleeves. Since the coefficient of thermal expansion of silicon nitride is much smaller than that of stainless steel, great care must be taken to form an interference spring that does not generate an unacceptable level of stress inside the silicon nitride sleeve during operation at high temperatures. In US5252130, Hitachi describes mounting a ceramic member in the form of a cylinder on the outer periphery of a stainless steel roller shaft journal by using an intermediate member that functions as a stress buffer. The intermediate layer is composed of a metal that has a low yield point and can thereby plastically deform elastically at a stress lower than the fracture strength of the ceramic. Cited examples of metals useful as the intermediate member include Ti, Au, Ag, Al, Pd, Cu, Ni, austenitic stainless steel, or ferritic stainless steel.

[0016] The use of a metal as the intermediate layer causes unique problems. In particular, during the initial start-up of the line, the intermediate layer must fill the gap between the journal and the sleeve to prevent the molten coating material from entering the gap. At the operating temperature, the intermediate metal layer must accommodate the thermal expansion difference between the sleeve and the journal. Copper, cited as a preferred material for the intermediate layer, cannot be used to fill the entire gap during cold times because it has no compressibility and applies excessive stress to the sleeve at the operating temperature. The patent contemplates removing a portion of the copper to allow it to expand to buffer the stress.

[0017] A material that has been proven to be superior to silicon nitride for use as a pot roller bearing sleeve is cemented tungsten carbide, a cermet which is generally a ceramic / metal composite material produced by mixing tungsten carbide powder in the range of 70% to 97% of the total weight with a binder metal, usually cobalt or nickel, compressing the material in a mold, and then sintering it. The term "cemented" means that tungsten carbide particles are trapped in a metal binder material and both are "cemented" together, forming a metallic bond between the tungsten carbide particles and the binder (such as WC-Co, WC-Ni) during the sintering process. Cemented tungsten carbide has resistance to all forms of wear (including sliding wear, erosion, corrosion / wear, and intermetallic wear), exhibits a relatively high degree of toughness and high compressive strength, withstands deflection, and retains its hardness value at high temperatures. Compared to cobalt-based alloys with high hardness and wear resistance used in bearing systems for continuous metal coating lines, cemented tungsten carbide can also better withstand higher temperatures of molten aluminum and corrosion problems associated with coating strips with gallium or aluminum.

[0018] As described in Plexair's U.S. Patent US603728, a very effective pot roller bearing assembly combines a journal sleeve having a wear surface of tungsten carbide composite material that contacts a silicon nitride bush. The limiting factor of this assembly is the thickness of the tungsten carbide coating. If the thickness of the tungsten carbide layer can be increased, a longer bearing life can be achieved. The hard tungsten carbide coating also has a tendency to peel from the associated metal substrate as a result of fatigue cracks at the discontinuous interface between the coating and the metal substrate in the coating under high load conditions such as those in high-tension lines processing heavier gauge strips.

[0019] The sleeve can be composed of solid carbide tungsten carbide. The use of a cemented carbide sleeve also allows for a very significant reduction in the metal consolidation stage compared to manufacturing methods compatible with coating methods such as laser cladding. Lowering the consolidation stage increases the hardness, wear resistance, and corrosion resistance of the carbide, which is particularly important in immersion coatings of aluminum or aluminum-containing alloys because of the higher operating temperatures and increased corrosivity. The relative ease with which the level of the consolidation stage can be changed in a solid carbide tungsten carbide sleeve allows for the optimization of the relative mass loss when the sleeve and a ceramic bush (e.g., silicon nitride) slide into contact with each other as a result of wear and / or chemical wear.

[0020] Since the carbide tungsten carbide sleeve is somewhat brittle and has a significantly lower coefficient of thermal expansion than stainless steel, it is not practical to shrink-fit such a sleeve directly into a stainless steel journal because the sleeve has a high tendency to fail from hoop stress. In such solid tungsten carbide sleeves, sealing the gap during cold conditions and buffering stress at the operating temperature cannot be reliably achieved using copper or other metals cited in US6037287.

[0021] What is needed is a bearing system for a synchronizer bearing comprising a sleeve having a thick wear-resistant surface of carbide tungsten carbide. Particularly advantageous is such a bearing system incorporating a journal sleeve of a material such as solid carbide tungsten carbide.

Means for Solving the Problem

[0022] A bearing system for use between a roller journal and a support frame in a molten metal dip coating line for a steel strip, the bearing system comprising a wear sleeve attached to the journal and a bearing assembly having a bush for rotatably supporting the sleeve, the sleeve being made of solid cemented tungsten carbide, and an elastically compressible layer coupling the sleeve to the journal such that the sleeve and the journal are mechanically connected to rotate together, the journal sleeve being adapted to rotate within the bearing assembly, the bearing assembly having a ceramic bush component disposed to contact the outer surface of the sleeve, and the combination of a particular bush and sleeve being selected to wear at a relative rate that maximizes the runtime of the bearing system in a particular mechanical and chemical environment of use.

[0023] In one aspect, a bearing system for use between a roller journal and a support frame in a molten metal dip coating line for a steel strip, the bearing system comprising a sleeve configured to be attached to the journal and a bearing assembly having a bush for rotatably supporting the sleeve, the bearing assembly having the sleeve made of solid cemented carbide, and an elastically compressible layer coupling the sleeve to the journal such that the sleeve and the journal are mechanically connected to rotate together.

[0024] Details of one or more variations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features and advantages of the subject matter described in this specification will be apparent from the description and drawings, and from the claims.

Brief Description of the Drawings

[0025] The accompanying drawings, which are incorporated in and constitute a part of this specification.

[0026]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

DETAILED DESCRIPTION OF THE INVENTION

[0027] Before further describing the present subject matter, it is to be understood that the present subject matter described herein is not limited to the particular embodiments described, and as such, can naturally vary. Also, it is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present subject matter belongs.

[0028] The prior art bearing system of FIG. 2 is suitable for use with a sleeve 100 made of metal, such as a stainless steel sleeve 100 coated with a wear-resistant layer such as tungsten carbide. However, for a sleeve 100 made entirely of hard tungsten carbide, due to the difference in thermal expansion, the bearing system of FIG. 2 is not practical. In particular, a journal 90, which is generally made of stainless steel, has a significantly higher coefficient of thermal expansion than a sleeve 100 made of hard tungsten carbide. When attempting a standard shrink or slip fit, during heating, the journal 90 will increase in diameter much more than the sleeve 100, and the outer surface 170 of the journal 90 will press against the inner surface 180 of the sleeve 100, generating stress on the inner surface 180. Since hard tungsten carbide is inherently somewhat brittle, this internal circumferential stress, i.e., hoop stress, will cause cracks in the sleeve 100 and cause the bearing system to fail.

[0029] "The Carbide Guide," published by General Carbide, does not recommend shrink fitting a tungsten carbide sleeve onto a steel journal as follows.

[0030] "Shrink Guide Lines - Carbide Cylinder Attached to the Outside of a Steel Ring: Normally, tungsten carbide should not be subjected to tensile stress, and thus a carbide sleeve shrunk onto a steel shaft would seem to be doomed to failure. However, sometimes when it is necessary to do so, it may succeed. In these cases, a set of stress calculations must be performed. By reversing the subscripts 'c' and's', the Lame's equation can be used. Additional stresses must also be considered. Operating above room temperature rapidly increases the tensile stress in the inner diameter (I.D.) of the carbide and leads to premature failure. When shrinking carbide onto the outside of steel, the designer should exercise extreme caution and use only the minimum interference necessary.

[0031] In summary, when it is necessary to shrink-fit a carbide sleeve onto the outside of a steel shaft, all operating conditions and stresses must be considered. 」, 「Carbide Guide」, pages 4-15.

[0032] Attaching a carbide sleeve to a stainless steel journal according to the bearing assembly of FIG. 2 for use in a molten metal coating line causes several significant problems. First, in order to account for the higher thermal expansion of the journal 90, a large gap at room temperature is required between the outer surface 170 of the journal 90 and the inner surface 180 of the sleeve 100. At startup, preheating of the bearing assembly may not be sufficient to completely close this gap before the synchronizer is immersed in the molten metal. Ingress of molten metal into the gap leads to rapid failure of the bearing assembly. Second, the retaining ring 160 expands more than the lip 150, reducing the retaining force on the lip 150. Third, the sleeve 100 is positioned radially in the center of the journal 90 and must be connected to the journal 90 to rotate with the journal 90 during operation. Unless a mechanical connection such as welding is used, the inner surface 180 of the sleeve 100 must grip the outer surface 170 of the journal 90 for the sleeve 10 to rotate with the journal 90 within the bearing assembly 80. However, increasing the amount of interference fit to the level required for rotational connection between the sleeve 100 and the journal 90 subjects the outer surface 170 of the journal 90 to excessive stress, causing cracks and failures in the sleeve 100.

[0033] Figure 3 illustrates an improved synchronizer 50 to which a bearing system according to the present disclosure is attached. The bearing system includes a sleeve 200 mounted on a journal 90 and a bearing assembly attached to a support frame 190 and mounted around the sleeve 200. Since the sleeve 200 is a cylindrical body having an open end and a cap end that caps the end of the journal 90, it can also be called an end cap. In this regard, the open end of the sleeve provides an opening to an internal cavity or chamber in which the journal 90 is disposed. The bearing assembly is composed of a bearing housing 210 and a bush 220 having a bush surface 230 configured to slide and engage with the outer surface 240 of the sleeve 200. The sleeve 200 preferably includes a lip 250. The bearing system also includes a retaining ring 260. A compressible material 270 is disposed between the outer surface 280 of the journal 90 and the inner surface 290 of the sleeve 200. The compressible material can be disposed along a part or the whole of the region between the outer surface 280 of the journal 90 and the inner surface 290 of the sleeve 200.

[0034] The bearing system also includes an inflatable gasket 300 disposed between the lip 250 and the retaining ring 260.

[0035] In the bearing system of the present disclosure, the retaining ring 260 is disposed to mechanically engage with the lip 250 of the sleeve 200 before the retaining ring 260 is attached to the journal 90 by welding or the like. One configuration and method for this mechanical engagement are shown in FIGS. 4 and 5, where the lip 250 has a flat surface 330 and the retaining ring 260 includes a key 340. During assembly, the sleeve 200 is pressed against the journal 90, and then the inflatable gasket 300 and the retaining ring 260 are slid onto the sleeve 200. The key 340 of the retaining ring 260 is position-adjusted with the flat surface 330 of the lip 250 so that the retaining ring 260 is non-rotatably engaged with the sleeve 200 before the retaining ring 260 is welded to the journal 90.

[0036] During preheating, the journal 90 and the retaining ring 260, both made of stainless steel, expand more than the sleeve 200 and the lip 250, which are preferably made of ultra-hard tungsten carbide or similar wear-resistant materials such as ceramics, carbides, cermets. The expandable gasket 300 prevents the formation of a gap between the retaining ring 260 and the lip 250, firmly presses the sleeve 200 against the journal 90, and expands when heated to prevent molten metal from entering between the retaining ring 260 and the lip 250.

[0037] Also during preheating, the journal 90 expands radially more than the sleeve 200, compresses the compressible material 270, acts to position the journal 90 radially centered within the sleeve 200, and acts as a stress buffer to prevent excessive stress on the inner surface 290 of the sleeve 200.

[0038] The compressible material 270 must be able to withstand the service load and thermal cycles without excessive deformation. That is, the compressible material 270 must elastically deform when heated to the operating temperature and must recover some of its original size upon cooling when the bearing assembly 190 is taken out of service for maintenance or an unscheduled line stop.

[0039] In one embodiment, the journal 90 and the retaining ring 260 are made of stainless steel (e.g., 316L) or carbon steel (e.g., E52100) by bath chemistry, and the sleeve 200 is made of cemented carbide such as tungsten carbide, titanium carbide, tantalum carbide or a mixture thereof, or a similar metal, ceramic or cermet material containing cobalt, and / or nickel and molybdenum. In one embodiment, the compressible material 270 preferably consists of compressible graphite such as Graphoil. Other materials suitable for use as the compressible material 270 include expandable products containing graphite and / or vermiculite. In one embodiment, the sleeve is made of a cemented carbide containing between about 70% and 94% carbide.

[0040] The expandable material 300 can be a material that maintains an expanded state at the elevated operating temperature of the bearing assembly, such as a perlite-based material. Other materials suitable for use as the expandable material 300 include mineral or refractory ceramic fiber-based materials containing vermiculite or expanded graphite.

[0041] FIG. 6 shows a perspective view of another embodiment of the bearing system. The sleeve 200 is formed of a cylindrical body that is open at both ends and has an internal cavity sized to receive the journal 90. An annular first lock ring 605 is connected to the first end of the sleeve 200, and an annular second lock ring 610 is connected to the second opposite end of the sleeve 200. The rings 605 and 610 each have a key that engages a corresponding key slot of the sleeve 200 to lock the sleeve 200 in place. In the assembled state, the ring 610 is adjacent to the roller 50. The gasket 205 can be disposed in the gap or region between each lock ring 605 / 610 and the sleeve 200. The gasket(s) 205 can be made of an expandable material.

[0042] This specification contains many specific details, but these should not be construed as limitations on the scope of the claimed invention or what may be claimed. Rather, they should be construed as descriptions of features specific to particular embodiments. The specific features described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, the various features described in the context of a single embodiment can also be implemented separately in multiple embodiments or in any suitable sub-combination. Furthermore, features are described above as acting in a particular combination and may initially be claimed as such, but one or more features from the claimed combination may in some cases be deleted from the combination, and the claimed combination may be directed to a sub-combination or a variation of a sub-combination. Similarly, operations are depicted in the drawings in a particular order, but this should not be understood as requiring that such operations be performed in the particular order shown or in a sequential order to achieve the desired result, or that all of the operations shown be performed. Only some examples and embodiments are disclosed. Variations, modifications, and enhancements to the described examples and embodiments, as well as other embodiments, can be made based on what is disclosed.

Claims

1. A bearing system for use between a roller journal and a support frame in a molten metal electroplating line of a steel strip, comprising: a sleeve configured to be attached to the journal; a bearing assembly having a bush for rotatably supporting the sleeve, wherein the sleeve is made of cemented carbide; an elastically compressible layer that couples the sleeve to the journal such that the sleeve and the journal are mechanically coupled to rotate together; the bearing system.

2. The bush is disposed around the journal sleeve. The bearing system according to claim 1.

3. The sleeve fits onto the journal such that the journal is rotatably disposed within the sleeve. The bearing system according to claim 1.

4. The sleeve has a lip. The bearing system according to claim 1.

5. The bearing system according to claim 4, further comprising a retaining ring that mechanically engages the lip of the sleeve. The bearing system according to claim 4.

6. The lip of the sleeve forms a flat surface, and the retaining ring has at least one key that engages the flat surface. The bearing system according to claim 5.

7. The at least one key positions the retaining ring relative to the flat surface of the lip such that the retaining ring is non-rotatably engaged with the sleeve. The bearing system according to claim 6.

8. The compressible material is disposed between the outer surface of the journal and the inner surface of the sleeve. The bearing system according to claim 1.

9. The roller journal is attached to a roller. The bearing system according to claim 1.

10. An expandable gasket is disposed between the retaining ring and the lip. The bearing system according to claim 5.

11. The retaining ring is fixed to the journal via the lip of the sleeve. The bearing system according to claim 5.

12. Both the journal and the retaining ring expand more than the sleeve and the lip when heated. The bearing system according to claim 5.

13. Both the sleeve and the lip are made of ultra-hard tungsten carbide, ceramic, carbide or cermet. The bearing system according to claim 12.

14. The inflatable gasket prevents the formation of a gap between the retaining ring and the lip, thereby caulking the sleeve against the journal to prevent the intrusion of molten metal between the retaining ring and the lip, and expands when heated. The bearing system according to claim 10.

15. The journal and the retaining ring are made of stainless steel, and the sleeve is made of solid ultra-hard tungsten carbide. The bearing system according to claim 1.

16. The sleeve is made of tungsten carbide strengthened with cobalt, carbide or cermet material. The bearing system according to claim 15.

17. The sleeve is configured to rotate within the bush. The bearing system according to claim 1.

18. The sleeve has an outer surface, and the bearing assembly has a ceramic bush component arranged to contact the outer surface of the sleeve. The bearing system according to claim 17.

19. The compressible material has compressible graphite. The bearing system according to claim 1.

20. The compressible material has an expanding material including graphite or vermiculite. The bearing system according to claim 1.

21. The sleeve has a wear-resistant material. The bearing system according to claim 1.

22. The sleeve contains 70% to 94% carbide. The bearing system according to claim 1.

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