WO2009000303A1

WO2009000303A1 - Flinger for a seal assembly

Info

Publication number: WO2009000303A1
Application number: PCT/EP2007/005890
Authority: WO
Inventors: Xiao Bo Zhou; Ronaldus Johannes Brakel
Original assignee: Ab Skf
Priority date: 2007-06-22
Filing date: 2007-06-22
Publication date: 2008-12-31

Abstract

The present invention relates to seal assembly comprising a flinger and an elastomeric sealing lip, wherein the flinger comprises a cylindrical portion and a flange portion extending radially outwards therefrom, and wherein the cylindrical portion is formed from a steel material having on a surface thereof a black oxide layer, which surface engages with a portion of the elastomeric sealing lip.

Description

Flinqer for a Seal Assembly

TECHNICAL FIELD

The present invention relates to a seal assembly for a railway axle bearing and is more particularly directed to the f linger component of such an assembly that serves as the running surface in engagement with the sealing element.

BACKGROUND

Radial seal assemblies are widely applied to seal an annular gap between relatively rotatable components; for example, the gap between a revolving shaft or axle and the housing bore of a rolling element bearing. The seals serve to retain lubricant within the bearing cavity and to exclude the entry of contaminants. Both of these aspects are important for proper running of the bearing and the prevention of early failure. A typical radial seal comprises an outer casing to which a sealing lip is bonded. Elastomeric materials, such as nitrile rubber, may be used for the sealing lip. The outer casing seals statically against the housing bore. The sealing lip provides dynamic sealing during rotational conditions (and static sealing during stationary conditions). Thus, to prevent excessive wear of the sealing lip and premature loss of sealing function, the running surface in engagement with the sealing lip needs to be smooth and wear resistant. For easy maintenance and replacement, seal assemblies for axle bearings are generally mounted as a unit. The seal assembly can then further comprise a wear ring to serve as the running surface in contact with the sealing lip.

In hostile operating conditions, the wear ring will often incorporate a radial flange. The component is then referred to as a flinger, and additionally acts to dynamically repel contaminants like grit and moisture. Seal assemblies for railway axle bearings, which must exclude grit, muddy water and other contaminants, often incorporate a flinger.

A flinger needs to possess several properties. These include good wear resistance and low surface roughness. Moreover, it is important that the friction torque generated at the contact surface between the flinger and the sealing lip is sufficiently low. Friction generates heat, and high temperatures will accelerate the ageing of the seal, leading to premature loss of sealing function. Thermal transfer occurs from the seal to the bearing, and high temperatures are detrimental to bearing life. Large fluctuations in temperature are also detrimental to bearing life. It is a standard railway safety procedure to measure the temperature of a journal box. So-called hotbox detectors are placed at intervals along a railway track, and the measurements taken include the temperature at either side of a journal box and/or the temperature at the inboard and outboard side of an axle bearing. If an excessive temperature difference is measured, an alarm is triggered and the train will have to stop for servicing. Consequently, a flinger that produces a stable friction torque in running contact with the sealing lip is important, as this leads to stable heat generation. A low temperature at e.g. the inboard side of a sealed axle bearing and a high temperature at the outboard side might trigger such an alarm. In the case of a flinger for the seal assembly of a railway axle bearing, a further important property is that a stable friction torque is generated both in clockwise and counter clockwise rotation of the axle.

A variety of flingers are known. Some are made of stainless steel, which is an expensive material. Moreover, if the flinger has a relatively complex geometry, the better formabilty of low-carbon steel may make the application of low-carbon steel more desirable. However, to obtain the necessary wear resistance and corrosion resistance, a flinger made from a low-carbon steel will typically need to undergo a surface treatment, for example zinc plating or nickel plating. These processes change the dimensions of the treated component, which complicates the manufacturing process. In the case of a flinger with a relatively complex geometry, a further potential disadvantage of these plating processes is non-uniform deposition of the metal layer. To counteract the aforementioned two difficulties, a conversion coating process, such as electroless nickel plating or zinc anodization, is sometimes applied. Both of these processes are expensive, however.

An example of a relatively inexpensive conversion coating process is zinc phosphating. A seal assembly for an axlebox bearing is known which comprises a flinger that is made of zinc-phosphated low carbon steel. The phosphating process delivers the necessary corrosion and wear resistance, but also increases the surface roughness of the material. The present invention aims to address at least some of the problems associated with the prior art and to provide an improved seal assembly and flinger.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a seal assembly comprising a flinger and an elastomeric sealing lip, wherein the flinger comprises a cylindrical portion and a flange portion extending radially outwards therefrom, and wherein the cylindrical portion is formed from a steel material having on at least a surface thereof a black oxide layer, which surface engages with a portion of the elastomeric sealing lip.

The present invention will now be further described. In the following passages different aspects/embodiments of the invention are defined in more detail. Each aspect/embodiment so defined may be combined with any other aspect/embodiment or aspects/embodiments unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

The flinger will typically be formed from a low-carbon sheet steel, such as AISI 1010 (0.08 - 0.13 wt% C, 0.3 - 0.6 wt% Mn) or a low alloy steel, such as AISI 1330 (0.28 - 0.33 wt% C, 0.16 - 0.19 wt% Mn, 0.15 - 0.35 wt% Si).

The sealing lip will typically be formed from a nitrile rubber. A silicone rubber may also be used.

The black oxide layer will typically consist of or comprise magnetite (Fe₃O₄). This layer may be formed by conventional means in the art, for example, by hot or cold blackening, to form a black oxide conversion coating. In a hot blackening process, the back oxide conversion coating may be formed by exposing the flinger to an alkaline aqueous salt solution (for example caustic soda and/or sodium nitrite) at a temperature of from 130 to 17O⁰C, preferably 140 to 160⁰C. Prior to exposure to the salt solution, the flinger is preferably cleaned and rinsed. The flinger can then be immersed in a bath of the salt solution, or the salt solution can be sprayed or brushed on. The duration of exposure depends on the coating thickness required. A typical value for the thickness of the black oxide coating is from 0.5 to 2 microns, preferably approximately 1 micron. After the chemical black oxidation, the flinger is preferably rinsed to get rid of any remnants from the salt solution.

The seal assembly according to the present invention comprises at least one elastomeric sealing lip. The lip engages with the steel flinger, which is provided on its running surface with a black oxide coating. It has surprisingly been found that the black oxidized flinger generates stable friction torque in running contact with the elastomeric sealing lip.

More particularly, tests conducted with a seal assembly incorporating a black oxidized flinger according to the present invention demonstrate that the stable friction torque is generated in both a forward and reverse direction of rotation. The stable friction torque in both directions corresponds to a stable seal temperature and flinger temperature in both directions of rotation. These stable running conditions delay the ageing of the elastomeric seal and increase the reliability of the seal. A bearing which is sealed by an assembly comprising the flinger according to the present invention is, moreover, subject to less temperature variations, which is beneficial for improved service life and longer maintenance intervals. In addition, the advantageous surface hardness of the steel is also retained, and the flinger exhibits improved wear resistance.

In an advantageous further development of the invention, a layer of an organic sealant is applied on top of the black oxide surface layer. The organic sealant preferably comprises an oil-based composition. The sealant preferably contains one or more corrosion inhibitors and optionally one or more waxes. The sealant improves the corrosion resistance of the flinger, while at the same time preserving the advantageous wear and friction characteristics obtained from the black oxidation process. The sealant is preferably applied to the black oxide coating as an oil-in-water emulsion. This has the advantage that the emulsion can easily be applied and readily wets the surface and fills any pores in the black oxide coating. It has been found that the emulsion works best at a concentration of 5 to 25 % (by volume) oil-in-water, preferably 15 to 25%, more preferably approximately 20%. The sealant may be applied by immersing the flinger in the emulsion, or the emulsion can be sprayed or brushed on. To facilitate drying, the emulsion may be applied at an emulsion temperature of around 150 -160⁰C.

A lubricant or grease is often applied between the sealing lip and the running surface, to further reduce friction, and the sealant, if present, should be compatible with the lubricant. One example of a grease that may be used is a multipurpose grease comprising a mineral oil base fluid thickened with a lithium complex soap thickener.

A particularly preferred sealant for use in the present invention is a water soluble (emulsifiable) formulation.

The present invention also provides a rolling element bearing comprising a seal assembly as herein described. The rolling element bearing may be a railway axle bearing, such as a double-row tapered roller bearing. Rolling element bearings are well known in the art.

The present invention also provides a method of producing a flinger component for a seal assembly as herein described, the method comprising the steps of: (i) providing a flinger component formed from a steel material; and (ii) forming a black oxide surface layer on at least a portion of the flinger.

The method may further comprise:

(iii) depositing a layer of an organic sealant on top of the black oxide surface layer. The sealant is preferably as herein described and is preferably applied to the surface as a water-in-oil emulsion.

It will be appreciated that the method may comprise an initial cleaning step and optionally a pre-rinsing step prior to the formation of the black oxide conversion coating. Similarly, it will be appreciated that the method may comprise a rinse step after the formation of the conversion coating and/or after the deposition of the seal layer.

The method may further comprise the step of forming a seal assembly by providing a combination of the flinger and an elastomeric sealing lip, the black oxide surface layer on the flinger facing the sealing lip. A lubricant or grease may be provided between the lip and flinger.

The present invention also provides a flinger for a seal assembly as herein described, wherein the flinger comprises a cylindrical portion and a flanged portion extending radially outwards therefrom, and wherein the cylindrical portion is formed from a steel material having a black oxide surface layer.

One preferred application of a flinger according to the present invention is as part of a seal assembly for a railway axle bearing. The assembly may be a cartridge-type (unitized) seal assembly or a semi-unitized seal assembly. In this latter case, the flinger and sealing element are separable, allowing both to be replaced if necessary. Thus, a flinger according to the invention can also be a loose replacement part.

The stable friction torque that is generated in both directions of rotation makes the flinger according to the present invention particularly advantageous for the seal assemblies of railway axle bearings. The flinger is not restricted to railway applications, however, and can also form part of a seal assembly for a truck axle bearing, for example, or for any bearing arrangement mounted on a shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail for explanatory, and in no sense limiting, purposes, with reference to the following figures, in which:

Figure 1a - 1 b illustrate an application of a seal assembly that incorporates a flinger according to the invention, and an enlarged view of the seal assembly,

Figure 2a - 2f illustrate graphs of seal torque, seal temperature and flinger temperature.

DETAILED DESCRIPTION

Figure 1a illustrates an example application of a seal assembly according to the invention. The seal assembly 100 functions to provide a seal between a bore of a housing and a rotating member. In this example, the housing is an outer ring 104 of a double-row tapered roller bearing 102 and the rotating member is a shoulder of an inner ring 106 of the bearing. The bearing 102 is sealed at an inboard side A and an outboard side B with reference to a radial centerline 108.

With reference to figure 1 b, the seal assembly 100 can comprise a sheet metal casing 110 to which an elastomeric sealing element 112 is bonded. The elastomeric sealing element 112 has at least one radial sealing lip 114. The seal assembly further comprises a flinger 116, which has a cylindrical portion 118 and a first radial flange 120 that extends outwardly at an axially outward side of the cylindrical portion. The flinger 116 may be made from sheet steel that is formed by stamping, and the inside diameter of the cylindrical portion provides an interference fit onto the rotating member. The assembly in the illustrated example is a unitized seal assembly, and the flinger further comprises a second radial flange 122 at an axially inward side of the cylindrical portion 118. Other embodiments are possible that do not include the second radial flange, to enable the inventive flinger to be used in semi-unitized seal assemblies. A suitable grease 124 is provided between the sealing lip 114 and the cylindrical portion 1 18.

The flinger 116 rotates as the inner ring 106 of the bearing 102 rotates, and the outer diameter of the cylindrical portion 118 is in running contact with the radial sealing lip 114. This generates friction torque, which in turn generates heat. Excessive heat may lead to lubricant breakdown and to premature ageing of the elastomeric seal. Ageing of the sea! is a main contributor to loss of interference between the seal and its running surface, and occurs more quickly at higher temperatures. Thermal transfer occurs from the seal to the bearing and high temperatures are also detrimental to bearing life. Moreover, large temperature differentials across a bearing are detrimental to its life. A railway axle bearing is sealed at an inboard side and an outboard side. It is therefore beneficial if the heat generated at either side remains stable.

To increase seal reliability and bearing life, the flinger 116 should generate stable friction torque during rotational contact with the sealing lip 114. In the case of a seal assembly mounted on a railway axle bearing, it is also advantageous if stable friction torque is generated in both clockwise and counter clockwise rotation. This is achieved according to the present invention by providing at least the surface of the steel flinger that engages with the sealing lip with a conversion coating of black oxide.

The black oxide layer will typically consist of or comprise magnetite (Fe₃O₄). This layer may be formed by conventional means in the art. One method that may be applied is a hot blackening process to form a black oxide conversion coating. In a hot blackening process, the back oxide conversion coating may be formed by exposing the flinger to an alkaline aqueous salt solution (for example caustic soda and/or sodium nitrite) at a temperature of from 130 to 170⁰C, preferably 140 to 160⁰C. Prior to exposure to the salt solution, the flinger is preferably cleaned and rinsed. The flinger can then be immersed in a bath of the salt solution, or the salt solution can be sprayed or brushed on. The duration of exposure depends on the coating thickness required. A typical value for the thickness of the black oxide coating is from 0.5 to 2 microns, preferably approximately 1 micron. After the chemical black oxidation, the flinger is preferably rinsed to get rid of any remnants from the salt solution.

In an advantageous further development of the inventive flinger, a layer of an organic sealant is applied on top of the black oxide surface layer. The organic sealant preferably comprises an oil-based composition and preferably contains one or more corrosion inhibitors and optionally one or more waxes. The sealant improves the corrosion resistance of the flinger, while at the same time preserving the advantageous wear and friction characteristics obtained from the black oxidation process. The sealant is preferably applied to the black oxide coating as an oil-in-water emulsion.

To confirm the advantageous friction characteristics obtained from the black oxidation process, tests were conducted on seal assemblies comprising a steel flinger with a black oxide surface layer in dynamic engagement with an elastomeric sealing lip. Friction torque, seal temperature and flinger temperature were measured. The tests were conducted on a suitable test rig comprising a frame and a driven spindle. The seal is fixed to the test rig frame and the flinger is mounted on the driven spindle, on an adapter having the same diameter as the inner ring of a railway axle bearing. The spindle is equipped with a dynamometer to measure seal torque over time. A first thermocouple is affixed to the elastomeric sealing element 112. A second thermocouple is affixed to the f irst radial flange 120 of the f linger, as close as possible to the contact area of the sealing Iip114. During the tests, the driven spindle is run at 900 rpm, which is a typical speed for the testing of railway seals. The test involves rotating the spindle (and flinger) in a clockwise direction at the specified speed for a duration of 220 minutes. Rotation is then interrupted for a duration of 10 minutes. The spindle is then rotated in a counter clockwise direction at the specified speed for a duration of 220 minutes. The cycle is repeated for e.g. 120 hours.

This test was performed with a nitrile rubber seal of a type commonly used to seal railway bearings. The flinger used was a black oxidized steel flinger according to the invention. The contact area between seal lip and flinger was lubricated with a multipurpose grease. The results are shown in figures 2a, 2c and 2e, where the x-axis 200 represents test duration in hours and where the y-axis 202 in figure 2a represents torque in Nm and the y-axis 204 in figures 2c and 2e represents temperature in degrees Celsius.

Figure 2a illustrates a graph of seal torque 206. Figure 2c illustrates a graph of seal temperature 208. Figure 2e illustrates a graph of flinger temperature 210.

As can be seen from figure 2a, the torque remains substantially constant duπng rotational conditions and the average value generated in both directions of rotation is approximately the same. As a result, the temperature of the seal and the flinger remains stable during rotational conditions in both directions of rotation. The peak temperature values that repeatedly occur, after the cooling down period during stationary conditions, display little variation, as can be seen from figures 2c and 2e.

By contrast, figures 2b, 2d and 2f respectively illustrate graphs of seal torque 206, seal temperature 208 and flinger temperature 210, which values were obtained from a second test using a second seal assembly. The second test was performed under identical test conditions; the same seal type was used and the same grease was used to lubricate the contact between the sealing lip and the surface of the flinger. The only difference in the second test was that the steel flinger had no coating of black oxide. The greater fluctuations in seal torque 206, seal temperature 208 and flinger temperature 210 are apparent from figures 2b, 2d and 2f.

Consequently, it can be seen that a black oxidized steel flinger according to the present invention has advantageous properties, even in the absence of an organic sealant on top of the black oxide layer.

It should be understood that the invention is not restricted to the above-described embodiments, but may be varied within the scope of the following claims.

REFERENCE NUMERALS

Figure 1a - 1b illustrate an application of a seal assembly according to the invention, and an enlarged view of the seal assembly,

100 seal assembly,

102 double-row tapered roller bearing,

104 outer ring,

106 inner ring,

108 centreline,

110 casing,

112 elastomeric sealing element,

114 sealing lip,

116 fiinger,

118 cylindrical portion,

120, 122 radial flange

124 lubricant

A inboard side

B outboard side.

Figure 2a - 2f illustrate graphs of seal torque, seal temperature and fiinger temperature,

200 x-axis: test duration in hours,

202 y-axis: torque in Nm,

204 y-axis: temperature in degrees Celsius,

206 seal torque, 208 seal temperature,

210 fiinger temperature.

Claims

CLAIMS:

1. A seal assembly comprising a flinger and an elastomeric sealing lip, wherein the flinger comprises a cylindrical portion and a flange portion extending radially outwards therefrom, and wherein the cylindrical portion is formed from a steel material having on at least a surface thereof a black oxide layer, which surface engages with a portion of the elastomeric sealing lip.

2. A seal assembly as claimed in claim 1 , wherein the black oxide layer is or comprises magnetite (Fe₃O₄).

3. A seal assembly as claimed in claim 1 or claim 2, wherein a layer of an organic sealant is present on top of the black oxide surface layer.

4. A seal assembly as claimed in claim 3, wherein the sealant comprises an oil-based composition.

5. A seal assembly as claimed in claim 3 or claim 4. wherein the sealant comprises one or more corrosion inhibitors.

6. A seal assembly as claimed in any one of claims 3 to 5, wherein the sealant comprises one or more waxes.

7. A seal assembly as claimed in any one of the preceding claims, wherein a lubricant is provided between the sealing lip and the cylindrical portion.

8. A seal assembly as claimed in any one of the preceding claims, wherein the seal assembly is a unitized assembly.

9. A seal assembly as claimed in any one of claims 1 to 7, wherein the seal assembly is a semi-unitized assembly.

10. A rolling element bearing comprising a seal assembly as defined in any one of claims 1 to 9.

11. A rolling element bearing as claimed in claim 10, wherein the rolling element bearing is a railway axle bearing.

12. A method of producing a flinger component for a seal assembly, the method comprising the steps of:

(i) providing a flinger component formed from a steel material; and (ii) forming a black oxide surface layer on at least a portion of the flinger.

13. A method as claimed in claim 12, wherein the flinger comprises a cylindrical portion and a flange portion extending radially outwards therefrom, and wherein the black oxide surface layer is formed on the cylindrical portion.

14. A method as claimed in claim 12 or claim 13, further comprising the step of: (iii) depositing a layer of an organic sealant on top of the black oxide surface layer.

15. A method as claimed in claim 14, wherein the organic sealant comprises an oil- based composition.

16. A method as claimed in claim 14 or claim 15, wherein the sealant comprises one or more corrosion inhibitors.

17 A method as claimed in any one of claims 14 to 16, wherein the sealant comprises one or more waxes.

18. A method as claimed in any one of claims 14 to 17, wherein the sealant is deposited on the surface as a water-in-oil emulsion.

19. A flinger for a seal assembly, wherein the flinger comprises a cylindrical portion and a flanged portion extending radially outwards therefrom, and wherein the cylindrical portion is formed from a steel material having a black oxide surface layer, which cylindrical portion constitutes a running surface for engagement with an elastomeric sealing lip.

20. A flinger as claimed in claim 19, wherein the black oxide surface layer is or comprises magnetite (Fe₃O₄).

21. A flinger as claimed in claim 19 or claim 20, wherein a layer of an organic sealant is present on top of the black oxide surface layer.

22. A flinger as claimed in claim 21 , wherein the sealant comprises an oil-based composition.

23. A flinger as claimed in claim 21 or claim 22, wherein the sealant comprises one or more corrosion inhibitors.

24. A flinger as claimed in any one of claims 21 to 23, wherein the sealant comprises one or more waxes.