GB1561788A - Piston rings - Google Patents

Description

(54) PISTON RINGS (71) We HEPWORTH & GRANDAGE LIMITED, a British Company of St. John's Works, Bradford BD4 8TU, Yorkshire, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to piston rings.

It is known to electroplate piston rings with substantially pure chromium, and to spray piston rings with substantially pure chromium or molybdenum.

According to the present invention, there is provided a cast iron or steel piston ring having on its outer peripheral surface a coating of a chromium-based alloy containing 10-40% iron.

Preferably the alloy consists of 75% chromium and 25% iron. The percentages are given by weight.

The cast iron or steel piston ring may be formed on its outer peripheral surface with a shallow annular groove to receive the coating, the shoulders of the groove being triangular in cross-section.

Two embodiments of the invention will now be described by way of example with reference to the accompanying drawings, of which: Figure 1 shows a cross-section through one embodiment of a cast iron or steel piston ring provided with a wear resistant coating in accordance with the invention, and Figure 2 is a similar view of a second embodiment.

Referring to Figure 1, a cast iron or steel piston ring 1 is formed with a shallow annular groove 2 on its outer peripheral surface, which in operation engages the wall of the cylinder. The shoulders 3 of the groove are of triangular formation in crosssection, rather than rectangular, so that the minimum area of cast iron or steel comes into contact with the cylinder wall.

After suitable preparation, the groove is sprayed with an alloy of 75% chromium 25% iron by means of a plasma gun, filling the groove as shown at 4. The plasma spray is surrounded by a shield of inert gas, e.g. argon or nitrogen, in a manner per se known. After spraying, the annular surface is ground to the required finish.

Referring to Figure 2, an alternative form of piston ring has the coating 5 of chromium iron alloy sprayed on the cylindrical peripheral surface 6 instead of being provided with the groove 2. The peripheral surface is then finish-ground.

Piston rings in accordance with the invention have been found to have excellent resistance to wear and to scuffing; and moreover the microscopic porosity in the coating which results from its application by spraying is believed to help in the retention of lubricating oil, thereby improving lubrication between the piston ring and the cooperating cylinder.

WHAT WE CLAIM IS: - 1. A cast iron or steel piston ring having on its outer peripheral surface a coating consisting only of chromium-based alloy containing 10-40% iron.

2. A piston ring as claimed in claim 1 wherein the coating consists of an alloy of 75% chromium and 25% iron.

3. A piston ring as claimed in claim 1 or claim 2 formed on its outer peripheral surface with a shallow annular groove which is filled with the coating.

4. A piston ring as claimed in claim 3 wherein the groove is provided by forming the outer peripheral surface of the ring with shoulders which are triangular in cross-section, the apioes being at the outer diameter, whereby the minimum area of the cast iron or steel of the piston ring may contact the wall of a cooperating cylinder.

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

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. (54) PISTON RINGS (71) We HEPWORTH & GRANDAGE LIMITED, a British Company of St. John's Works, Bradford BD4 8TU, Yorkshire, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to piston rings. It is known to electroplate piston rings with substantially pure chromium, and to spray piston rings with substantially pure chromium or molybdenum. According to the present invention, there is provided a cast iron or steel piston ring having on its outer peripheral surface a coating of a chromium-based alloy containing 10-40% iron. Preferably the alloy consists of 75% chromium and 25% iron. The percentages are given by weight. The cast iron or steel piston ring may be formed on its outer peripheral surface with a shallow annular groove to receive the coating, the shoulders of the groove being triangular in cross-section. Two embodiments of the invention will now be described by way of example with reference to the accompanying drawings, of which: Figure 1 shows a cross-section through one embodiment of a cast iron or steel piston ring provided with a wear resistant coating in accordance with the invention, and Figure 2 is a similar view of a second embodiment. Referring to Figure 1, a cast iron or steel piston ring 1 is formed with a shallow annular groove 2 on its outer peripheral surface, which in operation engages the wall of the cylinder. The shoulders 3 of the groove are of triangular formation in crosssection, rather than rectangular, so that the minimum area of cast iron or steel comes into contact with the cylinder wall. After suitable preparation, the groove is sprayed with an alloy of 75% chromium 25% iron by means of a plasma gun, filling the groove as shown at 4. The plasma spray is surrounded by a shield of inert gas, e.g. argon or nitrogen, in a manner per se known. After spraying, the annular surface is ground to the required finish. Referring to Figure 2, an alternative form of piston ring has the coating 5 of chromium iron alloy sprayed on the cylindrical peripheral surface 6 instead of being provided with the groove 2. The peripheral surface is then finish-ground. Piston rings in accordance with the invention have been found to have excellent resistance to wear and to scuffing; and moreover the microscopic porosity in the coating which results from its application by spraying is believed to help in the retention of lubricating oil, thereby improving lubrication between the piston ring and the cooperating cylinder. WHAT WE CLAIM IS: -

1. A cast iron or steel piston ring having on its outer peripheral surface a coating consisting only of chromium-based alloy containing 10-40% iron.

2. A piston ring as claimed in claim 1 wherein the coating consists of an alloy of 75% chromium and 25% iron.

3. A piston ring as claimed in claim 1 or claim 2 formed on its outer peripheral surface with a shallow annular groove which is filled with the coating.

4. A piston ring as claimed in claim 3 wherein the groove is provided by forming the outer peripheral surface of the ring with shoulders which are triangular in cross-section, the apioes being at the outer diameter, whereby the minimum area of the cast iron or steel of the piston ring may contact the wall of a cooperating cylinder.

5. A piston ring as claimed in any preceding claim wherein the coating is sprayed by a plasma gun.

6. A piston ring substantially as above described with reference to and as illustrated in Figure 1 or Figure 2 of the accompanying drawings.