GB2079790A

GB2079790A - Sprayed coatings including iron and chromium; piston rings

Info

Publication number: GB2079790A
Application number: GB8119639A
Authority: GB
Original assignee: SOMERTON RAYNER MICHAEL; Nippon Piston Ring Co Ltd
Current assignee: SOMERTON RAYNER MICHAEL; Nippon Piston Ring Co Ltd
Priority date: 1980-07-01
Filing date: 1981-06-25
Publication date: 1982-01-27
Also published as: JPS5716160A; DE3125997C2; GB2079790B; JPH0143022B2; DE3125997A1

Abstract

A sliding member, such as a piston ring 1, having an improved wear resistance for use in an internal combustion engine is provided on its sliding surface with a spray coated layer 3 of an alloy powder containing 8 to 53%, more preferably 15 to 50% by weight, of chromium and 0.8 to 8.0%, more preferably 1.5 to 5.5% by weight, of carbon, the balance being iron. <IMAGE>

Description

SPECIFICATION A sliding member for use in an internal combustion egine The present invention relates to a sliding member for use in an internal combustion engine.

A number of recent requirements, including a higher output, a higher speed of rotation and strictor control of environmental pollution by exhaust gas, have imposed increasingly severe operating conditions on internal combustion engines. Accordingly, all the sliding members in an internal combustion engine are required to have an improved wear resistance which can withstand such more severe operating conditions.

There are generally known two types of method for improving the wear resistance of a sliding member. One of these involves plating, such as chromium plating or composite nickel plating, the member, while the other relies on spray coating of molybdenum or a mixture of various components. Neither of these methods are, however, sufficiently effective to provide a high degree of wear resistance to satisfy the above-mentioned recent requirements.

Accordingly, it is an object of the invention to provide a sliding member having an improved degree of wear resistance.

Accordingly, the invention resides in a sliding member for use in an internal combustion engine wherein said sliding member has a sliding surface provided with a spray coated layer of an alloy powder containing 8 to 53% by weight of chromium and 0.8 to 8.0% by weight of carbon, the balance being iron.

In the accompanying drawings, Figure 1 is a cross-sectional view of a piston ring used in an internal combustion engine and constructed according to one example of invention and; Figure 2 is a graph showing the results of wear resistance tests comparing sliding members according to the invention with conventional sliding members.

Referring to Fig. 1, there is shown therein a piston ring 1 having an outer peripheral surface 11 in which a groove 2 is formed.

Provided in the groove 2 is a spray coated layer 3 which is composed of an alloy powder containing 8 to 53% by weight of chromium and 0.8 to 8.0% by weight of carbon, the balance being iron and which provides an improved degree of wear resistance.

It is found that if the chromium content in the alloy powder of the layer 3 is less than 8% by weight, it is impossible to achieve the intended wear resistance since it is then impossible to obtain a sufficiently high level of hardness required for satisfactory wear resistance. If, on the other hand, the upper limit of 53% is exceeded, the spray coated layer 3 acquires an undesirably high level of hardness since excessively large quantities of very hard chromium oxide and carbide are formed. Although the wear resistance of the sliding member would then be greatly increased, disadvantageously it may cause wear on the material with which it is in sliding contact.

Therefore, the chromium content should be kept within the range of 8 to 53%, and more preferably, 1 4 to 50% by weight.

Although the carbon content depends on chromium content, a carbon content less than 0.8% by weight fails to form a sufficiently large quantity of chromium carbide to make the spray coated layer sufficiently hard to provide satisfactory wear resistance. If the upper limit of 8% is exceeded, however, excessive precipitation of carbide occurs in the material to be coated, resulting in the formation of a spray coated layer having an unnecessarily and undesirably high lever of hardness. Although the wear resistance of the sliding member would then be greatly increased, disadvantageously it may cause wear on the material with which it is in sliding contact. Moreover the spray coated layer becomes so brittle that it may easily peel off the base material. Therefore, the carbon content should be kept within the range of 0.8 to 8.0% and more preferably 1.5 to 5.5% by weight.

The sliding member of the invention which is spray coated with an alloy powder composed of specific amounts of chromium, carbon and iron as hereinabove described, exhibitis outstanding wear resistance, apparently because very hard chromium carbide and oxide are uniformly distributed in the base material.

The sliding member of the invention also exhibits outstanding performance when used in an engine of the exhaust gas recirculation (EGR) type, or any other type in which exhaust gas control is taken into consideration.

A particularly serious problem when an engine of the EGR type experiences is the corrosive and abrasive wear which the exhaust gas causes. However, the sliding member of the invention is resistant to corrosion since it contains chromium, which is itself resistant to corrosion. It is also resistant to abrasive wear since the voids in the spray coated layer trap uncombusted carbon particles which cause abrasive wear and prevent them from accumulating in the clearance between the engine cylinder and the piston ring.

Comparative wear resistance tests were conducted to verify the superiority of the sliding member of the invention. The results of these tests will now be described.

Test samples each measuring 15mum by 20mm by 7mm were prepared from ductile cast iron. Each of the alloy powders shown in Table 1 was spray coated on the sliding surface of one of the samples using a plasma to form a spray coated layer having a thickness of 0.2mm. Table 1 shows the samples of this invention.

Table 1 C Cr Balance Hardness HV wt% wt% Sample 1 1.2 40 Fe 750 Sample 2 2.5 15 Fe 620 Sample 3 5.0 45 Fe 980 Sample 4 2.5 25 Fe 640 For comparison purposes, there was prepared another sample (sample 5) having a sliding surface on which a 0.2mm thick spray coated layer composed solely of molybdenum was formed using a plasma. Sample 5 had a hardness of HV 800.

Each of samples 1 to 5 thus prepared was mounted as a stationary member in a rotary wear testing machine. The stationary member was pressed against the top of a disc-shaped sample formed from cast iron containing 3.2% carbon, 2.0% of silicon and 0.8% of manganese, the balance being iron, and having a hardness of HRB 98. The disc-shaped sample was rotated while a lubricant was continuously supplied to the contacting surface of the stationary member and the discshaped sample. The tests were conducted under the following conditions, and the amount of wear was determined on each of samples 1 to 5.

Test Conditions Quantity of lubricant: 0.2 liter/min.

Lubricant: SAE30 Load: 20 kg/cm2 Sliding velocity: 5 m/sec.

Overall distance of movement: 300 km The results are shown in Fig. 2. As is evident therefrom, the sliding members of the invention showed only about half the amount of wear observed with the prior art sample having a spray coated layer of molybdenum.

Claims

1. A sliding member for use in an internal combustion engine, wherein said sliding member has a sliding surface provided with a spray coated layer of an alloy powder containing 8 to 53% by weight of chromium and 0.8 to 8.0% by weight of carbon, the balance being iron.

2. A sliding member as claimed in claim 1, wherein said alloy powder contains 1 5 to 50% by weight of chromium and 1.5 to 5.5% by weight of carbon, the balance being iron.

3. A sliding member as claimed in claim 1, for use in an internal combustion engine substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.