GB2116589A - Making sintered steel bearings - Google Patents

Abstract

In a method of manufacturing a bearing element, a quantity of annealed bearing steel powder is compacted in a die to a form similar to, but oversize from, the required element, the compact is vacuum sintered to greater than 99% full density and, after annealing, is cold formed to the required dimensions of the element.

Description

SPECIFICATION Manufacture of bearing elements from powder This invention relates to the manufacture of bearing elements from bearing steel powder. A typical bearing steel powder is known as EN3 1 and has a composition as follows: C Si MN Cr S P Min. 0.90 0.10 0.30 1.00 Max. 1.20 0.35 0.75 1.60 0.050 0.050 It is known to use EN3 1 powder produced by a water atomisation process in the manufacture of bearing elements. The known process comprises annealing the powder, compacting it in a die to form a compact which is similar to, but oversize from, the required finished article, sintering the compact to considerably less than full density and, thereafter hot forging the compact to size.

An object of the present invention is to improve on this known process.

According to the present invention, in the manufacture of a bearing element, a quantity of annealed bearing steel powder is compacted in a die to form similar to, but oversize from, the required element, the compact is vacuum sintered to greater than 99% of full density and is subsequently annealed and cold formed to the required dimensions of the element.

The process of the invention produces a bearing element which is substantially fully dense.

Up to 0.5% of molybdenum may be added to the bearing steel powder.

In a typical example, EN3 1 bearing steel powder, produced by water atomisation of liquid bearing steel, is annealed, conveniently by the process disclosed in our co-pending application No. 8201 699.

The annealed powder is cold compacted in a die to form a compact similar to, but oversize from, the required bearing element. The compact may take the form of a hollow cylinder, say 50 mm in diameter and 20 mm in length. The compact is then placed under vacuum and its temperature is raised to a sintering temperature and held at that temperature for about one hour. At the end of this temperature treatment, the compact has been sintered to greater than 99% full density. An annealing stage follows.

The compact is then reduced to the required dimensions of the bearing element by a cold forming stage. This stage may be cold worked, but is conveniently a rolling technique known as FORMFLO which enables a roller to be rolled around the inner periphery of a hollow cylinder while the cylinder is free to roll in a die so that both the inner and outer surfaces of the hollow cylinder are shaped simultaneously.

In a specific example, a steel powder, conforming to the above specification with a carbon content of 0.90% in the atomised condition and with the addition of 0.5% of molybdenum, was sintered to a fully dense condition, i.e. greater than 99%, in vacuum at 1 4250C. After sintering, the carbon content was 0.70%. By increasing the carbon content to 1. 15% prior to sintering, it was found that full density was obtained at a sintering temperature of 1 3700C and the final carbon content was 0.93%.

Claims

1. A method of manufacturing a bearing element in which a quantity of annealed bearing steel powder is compacted in a die to form similar to, but oversize from, the required element, the compact is vacuum sintered to greater than 99% of full density and is subsequently annealed and cold formed to the required dimensions of the element.

2. A method as claimed in claim 1, in which up to 5% of molybdenum is added to the powder prior to compaction.

3. A method as claimed in claim 1 or 2, in which the powder prior to compaction contains 0.9% carbon.

4. A method as claimed in claim 1 or 2, in which the powder prior to compaction contains 1.15% carbon.

5. A method of manufacturing a bearing element as claimed in claim 1 and substantially as hereinbefore described.

New claims or amendments to claims filed on 31 .11 83 New or amended claims 1. a method of manufacturing a bearing element in which a quantity of annealed bearing steel powder is compacted in a die to form a similar to, but oversize from, the required element, the compact is vacuum sintered to greater than 99% of fully density and is subsequently annealed and cold formed to the required dimensions of the element.

2. A method as claimed in claim 1, in which up to 0.5% of molybdenum is added to the powder prior to compaction.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Manufacture of bearing elements from powder This invention relates to the manufacture of bearing elements from bearing steel powder. A typical bearing steel powder is known as EN3 1 and has a composition as follows: C Si MN Cr S P Min. 0.90 0.10 0.30 1.00 Max. 1.20 0.35 0.75 1.60 0.050 0.050 It is known to use EN3 1 powder produced by a water atomisation process in the manufacture of bearing elements. The known process comprises annealing the powder, compacting it in a die to form a compact which is similar to, but oversize from, the required finished article, sintering the compact to considerably less than full density and, thereafter hot forging the compact to size. An object of the present invention is to improve on this known process. According to the present invention, in the manufacture of a bearing element, a quantity of annealed bearing steel powder is compacted in a die to form similar to, but oversize from, the required element, the compact is vacuum sintered to greater than 99% of full density and is subsequently annealed and cold formed to the required dimensions of the element. The process of the invention produces a bearing element which is substantially fully dense. Up to 0.5% of molybdenum may be added to the bearing steel powder. In a typical example, EN3 1 bearing steel powder, produced by water atomisation of liquid bearing steel, is annealed, conveniently by the process disclosed in our co-pending application No. 8201 699. The annealed powder is cold compacted in a die to form a compact similar to, but oversize from, the required bearing element. The compact may take the form of a hollow cylinder, say 50 mm in diameter and 20 mm in length. The compact is then placed under vacuum and its temperature is raised to a sintering temperature and held at that temperature for about one hour. At the end of this temperature treatment, the compact has been sintered to greater than 99% full density. An annealing stage follows. The compact is then reduced to the required dimensions of the bearing element by a cold forming stage. This stage may be cold worked, but is conveniently a rolling technique known as FORMFLO which enables a roller to be rolled around the inner periphery of a hollow cylinder while the cylinder is free to roll in a die so that both the inner and outer surfaces of the hollow cylinder are shaped simultaneously. In a specific example, a steel powder, conforming to the above specification with a carbon content of 0.90% in the atomised condition and with the addition of 0.5% of molybdenum, was sintered to a fully dense condition, i.e. greater than 99%, in vacuum at 1 4250C. After sintering, the carbon content was 0.70%. By increasing the carbon content to 1. 15% prior to sintering, it was found that full density was obtained at a sintering temperature of 1 3700C and the final carbon content was 0.93%. Claims

1. A method of manufacturing a bearing element in which a quantity of annealed bearing steel powder is compacted in a die to form similar to, but oversize from, the required element, the compact is vacuum sintered to greater than 99% of full density and is subsequently annealed and cold formed to the required dimensions of the element.

2. A method as claimed in claim 1, in which up to 5% of molybdenum is added to the powder prior to compaction.

3. A method as claimed in claim 1 or 2, in which the powder prior to compaction contains 0.9% carbon.

4. A method of manufacturing a bearing element as claimed in claim 1 and substantially as hereinbefore described.

4. A method as claimed in claim 1 or 2, in which the powder prior to compaction contains 1.15% carbon.

5. A method of manufacturing a bearing element as claimed in claim 1 and substantially as hereinbefore described.

New claims or amendments to claims filed on 31 .11 83 New or amended claims

1. a method of manufacturing a bearing element in which a quantity of annealed bearing steel powder is compacted in a die to form a similar to, but oversize from, the required element, the compact is vacuum sintered to greater than 99% of fully density and is subsequently annealed and cold formed to the required dimensions of the element.

2. A method as claimed in claim 1, in which up to 0.5% of molybdenum is added to the powder prior to compaction.

3. A method as claimed in claim 1 or 2, in which the powder prior to compaction contains 1.15% carbon.