GB1562455A - Process for friction surface of tubular metalli articles such as liners and cylinders - Google Patents

Description

(54) A PROCESS FOR IMPROVING THE FRICTION SURFACE OF TUBULAR METALLIC ARTICLES SUCH AS LINERS AND CYLINDERS (71) I, JUAN RETOLAZA IBARGUENGOITIA, of Ribera de Zorrozaurre, 10-12 Bilbao, Spain, a citizen of Spain, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a new process for obtaining a wear resistant, anti-friction surface on tubular metallic articles such as liners and cylinders.

More precisely it refers to a process capable of reducing the internal friction on the surface of liners or cylinders in internal combustion engines to provide a longer ser- vice life with the minimum amount of wear for both the liner and the piston assembly by means of an electrolytic or other hard chromium coating produced under special conditions.

It is known that a smooth hard chromium coating does not provide the ideal surface for lubrication purposes in the case of liners and cylinders and several methods are already known for producing a hard chromium surface capable of retaining the lubricating oil. These chromium coatings are usually called porous chromium. However, most of the processes used to obtain porous chromium have their drawbacks in that the pores are located in the chrome itself and thus their depth is limited by the thickness of the chromium coat. If the pores should reach the base metal it would then be left unprotected and it would be prone to possible corrosion by the engine exhaust gases; also this would endanger the adherence of the chromium to the base material.Consequently if the pores have to be shallower than the thickness of the chromium coat, it means that at some time during the normal life of the liner or cylinder, the wear will exceed the depth of the pores and the piston assembly will then rub on a flat dense chromium surface. This is a situation which the porous chromium was intended to prevent.

In the past efforts have been made to solve this problem by machining or knurling the internal surface of the liner's base material prior to plating so as to present an engraved or dented surface produced by mechanical means. By using a knurling roller, the base material is engraved with pockets of pyramid shape along spiral lines, with each pocket separated from its neighbouring pocket by one or several millimetres, and each pocket being anything from one half to several millimetres deep. The sur face when so prepared and subsequently chromium plated presents a surface with chromium coated pockets or recesses which would remain even when the chromium on the frictional surface had been worn off.

The great disadvantage of this process is that it involves a costly precision mechanical operation; also the chromium is dense and flat between the pockets and covers several square millimetres, which is an excessive area of flat and dense hard chromium, because of the danger of scuffing to the piston assembly.

In accordance with the present invention, which is intended to avoid the above mentioned disadvantages, a process for providing an oil retaining surface on a tubular metallic article such as a liner or cylinder for an internal combustion engine, comprises the hard chromium plating of a base material surface which has been previously roughened by steel shot blasting.

The shot blasting operation is preferably performed using more or less conventional shot blasting equipment by rotating the tubular article around its own axis while a nozzle projecting the steel shot moves longitudinally along the same axis. Alternatively, the relative rotational and axial movement of the article and the nozzle may be caused by rotating the nozzle around its axis and moving the tubular article along the same axis.

Alternatively, both the nozzle and the article may be rotated around, and moved along their common axis.

Thus the whole surface of the liner or cylinder is treated, or if required, only part of the surface is subjected to the shot blasting treatment, as it may be beneficial to reduce or increase the effect in some areas depending upon requirements.

The use of steel shot with a grain size in the range shot number SAE S70 to S170 for the blasting leavers burrs around the edges of the pockets or recesses. These burrs are then removed by honing with an abrasive tool with a grain size (approximately the nominal size in ten-thousandths of an inch) in the range 200 to 500 in a flexible agglomerate which prepares the surface sufficiently smooth for chrome plating and completely free from burrs. The pockets or recesses will vary in wldth and depth, from less than one hundredth of a millimetre possibly to several tenths of a millimetre.

The distance between the pores or pockets will not be greater than t a millimetre.

The liner thus prepared and treated is then hard chromium plated in a conventional manner to the required thickness. The liner or cylinder is then finished by honing followed by a lapping or blasting operation which assists in the initial running-in.

The lapping is performed by using a powdered abrasive suspended in oil and rubbed against the liner or cylinder wall with the aid of a cast iron mandrel. The blasting is carried out by a conventional method similar to that described for the initial steel shot blasting, but using aluminium oxide powder or some similar abrasive medium.

By reference to the enclosed schematic drawing the various steps of the process can be followed: In this drawing: Figure 1 shows schematically a longitudinal section of the liner or cylinder where "A" is the external face and the chain dashed line "C" represents the internal surface of the liner before the steel shot blasting operation and "B" shows the same surface after being deformed by the blasting.

In Figure 2 line "D" represents the surface after the honing which has removed the peaks and the burrs created by the blasting operation.

In Figure 3 line "El" represents the chromium coating over the surface "D", and in Figure 4 there is shown the chromium surface "E2" after the honing and subsequent lapping or blasting operations.

WHAT I CLAIM IS:- 1. A process for providing an oil retaining surface on a tubular metallic article such as a liner or cylinder for an internal combustion engine which comprises the hard chromium plating of a base material surface which has been previously roughened by steel shot blasting.

2. A process as set forth in claim 1 wherein the surface to be chrome plated is subjected to blasting with steel shot of grain size in the range shot number SAE S70 to S170 whilst causing relative movement between the article and a shot blasting member along and around the axis of the tubular article.

3. A process as claimed in claim 1 or 2, wherein the shot blasting operation is performed only on part of the surface of the article.

4. A process as claimed in any of claims 1, 2 and 3, wherein the article after steel shot blasting and prior to chromium plating is subjected to a de-burring operation such as by honing or polishing with abrasive powder which has an approximate grain size in the range 200 to 500 then-thousandths of an inch in a flexible agglomerant which produces a surface roughness adequate for the finish required, the imprints of the steel shot blasting having a width and depth which can vary from less than one hundredth of a millimetre to several tenths of a millimetre as required, and the distance between imprint and imprint being not greater than half a millimetre.

5. A process as claimed in any of claims 1 to 4, wherein the metallic surface so treated is chromium plated by a conventional method with hard chromium to an adequate thickness to produce the required size and correct tolerances and is finished by honing followed by lapping or blasting with abrasives as required.

6. A process for providing an oil retaining surface on a tubular metallic article substantially as hereinbefore described by reference to the accompanying drawings.

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

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. Thus the whole surface of the liner or cylinder is treated, or if required, only part of the surface is subjected to the shot blasting treatment, as it may be beneficial to reduce or increase the effect in some areas depending upon requirements. The use of steel shot with a grain size in the range shot number SAE S70 to S170 for the blasting leavers burrs around the edges of the pockets or recesses. These burrs are then removed by honing with an abrasive tool with a grain size (approximately the nominal size in ten-thousandths of an inch) in the range 200 to 500 in a flexible agglomerate which prepares the surface sufficiently smooth for chrome plating and completely free from burrs. The pockets or recesses will vary in wldth and depth, from less than one hundredth of a millimetre possibly to several tenths of a millimetre. The distance between the pores or pockets will not be greater than t a millimetre. The liner thus prepared and treated is then hard chromium plated in a conventional manner to the required thickness. The liner or cylinder is then finished by honing followed by a lapping or blasting operation which assists in the initial running-in. The lapping is performed by using a powdered abrasive suspended in oil and rubbed against the liner or cylinder wall with the aid of a cast iron mandrel. The blasting is carried out by a conventional method similar to that described for the initial steel shot blasting, but using aluminium oxide powder or some similar abrasive medium. By reference to the enclosed schematic drawing the various steps of the process can be followed: In this drawing: Figure 1 shows schematically a longitudinal section of the liner or cylinder where "A" is the external face and the chain dashed line "C" represents the internal surface of the liner before the steel shot blasting operation and "B" shows the same surface after being deformed by the blasting. In Figure 2 line "D" represents the surface after the honing which has removed the peaks and the burrs created by the blasting operation. In Figure 3 line "El" represents the chromium coating over the surface "D", and in Figure 4 there is shown the chromium surface "E2" after the honing and subsequent lapping or blasting operations. WHAT I CLAIM IS:-

1. A process for providing an oil retaining surface on a tubular metallic article such as a liner or cylinder for an internal combustion engine which comprises the hard chromium plating of a base material surface which has been previously roughened by steel shot blasting.

2. A process as set forth in claim 1 wherein the surface to be chrome plated is subjected to blasting with steel shot of grain size in the range shot number SAE S70 to S170 whilst causing relative movement between the article and a shot blasting member along and around the axis of the tubular article.

3. A process as claimed in claim 1 or 2, wherein the shot blasting operation is performed only on part of the surface of the article.

4. A process as claimed in any of claims 1, 2 and 3, wherein the article after steel shot blasting and prior to chromium plating is subjected to a de-burring operation such as by honing or polishing with abrasive powder which has an approximate grain size in the range 200 to 500 then-thousandths of an inch in a flexible agglomerant which produces a surface roughness adequate for the finish required, the imprints of the steel shot blasting having a width and depth which can vary from less than one hundredth of a millimetre to several tenths of a millimetre as required, and the distance between imprint and imprint being not greater than half a millimetre.

5. A process as claimed in any of claims 1 to 4, wherein the metallic surface so treated is chromium plated by a conventional method with hard chromium to an adequate thickness to produce the required size and correct tolerances and is finished by honing followed by lapping or blasting with abrasives as required.

6. A process for providing an oil retaining surface on a tubular metallic article substantially as hereinbefore described by reference to the accompanying drawings.