Oleophilic bearing with surface-modified part made of stainless rolling bearing steel

Abstract

In order to make a bearing, such as a roller bearing, insensitive to a lack of maintenance lubrication or irregular maintenance lubrication while at the same time retaining its mechanical performance, at least one bearing part of the bearing is provided at least partially with an oleophilic adhesion promoter layer. The adhesion promoter layer binds a lubricant layer of the bearing to the bearing part provided with the adhesion promoter layer. The adhesion promoter layer is bonded to an elemental-iron-free surface of a bearing part body. The removal of free iron from the bearing part body surface is carried out with nitric acid, chromate solution and/or citric acid. The treated bearing part has an oleophilic anti-corrosion adhesion promoter layer. The bearing may be used in pressure-operated devices, in particular in turbine handpieces used by dentists, because the loss of the lubricant layer during operation of the device was particularly high.

Claims

1. A bearing, comprising: an inner ring; an outer ring which is rotatable relative to the inner ring; wherein the inner ring has an inner ring body made of stainless steel and the outer ring has an outer ring body made of stainless steel; wherein a lubricant layer is formed on at least part of either an inner ring surface between the inner ring and the outer ring and/or an outer ring surface between the inner ring and the outer ring; and wherein at least part of either surface of the inner ring body and/or of the outer ring body is elemental-iron-free and is bonded to an oleophilic adhesion promoter layer.

2. The bearing as claimed in claim 1, wherein the bearing is in the form of a rolling bearing.

3. The bearing as claimed in claim 2, wherein the bearing is in the form of a deep groove ball bearing or an angular contact bearing, wherein the bearing comprises a plurality of balls and a cage for guiding the balls.

4. The bearing as claimed in claim 3, wherein at least one ball has a ball body having at least part of a surface of the ball of which is elemental-iron-free, wherein the surface of the ball has an oleophilic adhesion promoter layer.

5. The bearing as claimed in claim 3, wherein the inner ring, the outer ring and/or the ball has on its surface a functional group of alcohols and phenols which is bonded to the oleophilic adhesion promoter layer.

6. The bearing as claimed in claim 1, wherein the oleophilic adhesion promoter layer has a silicon-carbon-oxygen-hydrogen bond.

7. A method for producing a bearing, the bearing comprising an inner ring, an outer ring which is rotatable relative to the inner ring, and a plurality of balls between the inner and outer rings, wherein the inner ring has an inner ring body made of stainless steel, wherein the outer ring has an outer ring body made of stainless steel, wherein each ball of the plurality of balls have ball bodies made of stainless steel, wherein a lubricant layer is formed on at least part of either an inner ring surface between the inner ring and the outer ring, an outer ring surface between the inner ring and the outer ring, and/or a surface of the plurality of balls, and wherein at least part of either surface of the inner ring body, the outer ring body and/or the ball bodies is elemental-iron-free and is bonded to an oleophilic adhesion promoter layer, the method comprising the steps of: (1) removing elemental iron from at least part of either surface of the inner ring body, of the outer ring body and/or of the ball bodies; (3) applying an oleophilic adhesion promoter layer to at least part of either surface of the inner ring, the outer ring and/or the plurality of balls.

8. The method as claimed in claim 7, wherein the elemental iron is removed in method step 1 with citric acid, nitric acid and/or a chromate solution.

9. The method as claimed in claim 8, including a second (2) method step between method steps (1) and (3) the elemental-iron-free surface of the inner ring body, of the outer ring body and/or of the ball bodies are coated with a functional group of alcohols and phenols.

10. The method as claimed in claim 9, including in a fourth (4) method step wherein the inner ring is mounted in the outer ring.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawing:

(2) FIG. 1 is a cutaway view of a dental turbine handpiece;

(3) FIG. 2 is a highly diagrammatic detailed view from FIG. 1;

(4) FIG. 3a shows a roughness measurement of the raceway of an inner ring body prior to the removal of elemental iron; and

(5) FIG. 3b shows a roughness measurement of the raceway of the inner ring body from FIG. 3a after the removal of elemental iron.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) FIG. 1 shows a turbine handpiece 1 used by dentists in cross-section. It has a housing 10 in which a rotor shaft 12 is arranged. A rotor 16 is arranged on the rotor shaft 12, which is connected to a tool 14. The tool 14 can be in the form of a drilling tool, a grinding tool or the like.

(7) The rotor shaft 12 is supported by a first bearing 18a according to the invention in the form of a rolling bearing and a second bearing 18b according to the invention, which is likewise in the form of a rolling bearing. The rotor 16 is driven by compressed air, which is guided to the rotor 16 by an air supply channel 20. The compressed air is conveyed away via an air outlet channel 22.

(8) The bearings 18a, 18b cannot be provided with grinding covers (sealing disks), since these would lead to high friction torques in the bearings 18a, 18b, so that the idle speeds of up to 500,000 min.sup.1 required by dental customers could not be achieved. The idle speed is the maximum speed of the rotor shaft 12 which is established when no external loads are acting on the tool 14. During dental treatment, axial and radial forces are transmitted to the drilling tool 14, so that the speed of the rotor shaft 12 in the load phase of the turbine handpiece 1 falls significantly. The bearings 18a, 18b used can therefore not be sealed but only covered.

(9) However, such a cover disk has the disadvantage in rolling bearings according to the prior art that there is a gap between the inner ring and the cover disk of the rolling bearing, through which the lubricant layer used in the rolling bearings can pass to the outside. In dental turbine bearings, the effect of the loss of lubricant is enhanced by the fact that supplied compressed air is able to escape to the outside not only via the air outlet channel but also through the rolling bearings. This leads overall to the lubricant layer being transported away and thus to a situation of inadequate lubrication in the rolling bearings. The typical consequence in the prior art is that the bearing parts of the rolling bearings, in particular the inner ring, outer ring, balls and cage thereof, move in the mixed or boundary friction region. This in turn leads to abrasive wear of the bearing parts of the rolling bearings and consequently to the premature failure thereof.

(10) In order to remedy this problem, the bearings 18a, 18b according to the invention are provided with a lubricant coating which interacts with functionalized surfaces of the bearing parts and is thus not carried off, or is carried off only slightly, by the compressed air flowing through the bearings 18a, 18b. This results in a significantly longer lifetime of the bearings 18a, 18b, even if they are not re-lubricated or are re-lubricated only irregularly.

(11) FIG. 2 shows an enlarged detail 24 from FIG. 1 in highly diagrammatic form. The detail 24 shows a first bearing part in the form of an outer ring 26 of stainless rolling bearing steel. The first bearing part is chosen in the form of an outer ring 26 merely by way of example for reasons of representation. In a further preferred embodiment, the first bearing part is an inner ring.

(12) An outer ring body 27 of the outer ring 26 has a surface 28 which has been wet-chemically treated with nitric acid and dichromate solution. The treatment depthindicated in FIG. 2 by the broken line 30is only a few nanometers. A hydroxyl group layer 32 has been deposited on the treated and subsequently cleaned surface 28 by means of an H.sub.2O plasma. The hydroxyl group layer 32 serves to anchor an oleophilic adhesion promoter layer 34. The adhesion promoter layer has a silicon-carbon-oxygen-hydrogen bond. The adhesion promoter layer 34 binds a lubricant layer 36. The lubricant layer 36 is represented in FIG. 2 by grease molecules, wherein the variables R.sup.1, R.sup.2 and R.sup.3 serve as representatives of alkyl or alkenyl radicals having a usually uneven number of carbon atoms. Alternatively or in addition to the grease molecules, the lubricant layer can comprise molecules of an oil.

(13) Opposite the first bearing part there is a second bearing part in the form of a ball 38. The second bearing part is represented as a ball with a small radius merely by way of example. The second bearing part 38 can also be an inner ring. The ball 38 has a ball body 39 made of stainless rolling bearing steel. The ball body 39 has, analogously to the outer ring 26, a modified surface 40, a hydroxyl group layer 42 and an adhesion promoter layer 44. The adhesion promoter layer 44 also binds the lubricant layer 36. The lubricant layer 36 can as a result be retained securely between the first bearing part in the form of an outer ring 26 and the second bearing part in the form of a ball 38.

(14) FIG. 3a shows a roughness measurement of a surface of the raceway of an inner ring body of a bearing according to the invention prior to modification with nitric acid and dichromate solution. The bearing surface of the inner ring body has a mean roughness index of Ra=0.0339 m.

(15) FIG. 3b shows a roughness measurement of a surface of the raceway of the inner ring body according to FIG. 3a after modification with nitric acid and dichromate solution. The bearing surface of the inner ring body now has a mean roughness index of Ra=0.0346 m. A comparison of the two measurements according to FIG. 3a and FIG. 3b shows that the mean roughness has not increased significantly as a result of the surface modification. The surface modification is accordingly not an etching process but rather a treatment method for selectively removing elemental iron from the surface of the bearing part body.

(16) In summary, the invention relates to the lubrication of a bearing, in particular of a rolling bearing. In order to make the bearing insensitive to a lack of maintenance lubrication or irregular maintenance lubrication while at the same time retaining its mechanical performance, at least one bearing part of the bearing is provided at least partially with an oleophilic adhesion promoter layer. The adhesion promoter layer binds a lubricant layer of the bearing to the bearing part provided with the adhesion promoter layer. The adhesion promoter layer is bonded to an elemental-iron-free surface of a bearing part body. The removal of free iron from the bearing part body surface is carried out preferably with nitric acid, chromate solution and/or citric acid. Overall, the treated bearing part has an oleophilic anti-corrosion adhesion promoter layer. The bearing according to the invention distinguishes itself especially when used in pressure-operated devices, in particular in turbine handpieces used by dentists, since the loss of the lubricant layer during operation of the device was hitherto particularly high here.