GB2177027A

GB2177027A - Repair of worn crankshafts

Info

Publication number: GB2177027A
Application number: GB08611006A
Authority: GB
Inventors: John Lomas; John Howell
Original assignee: FLORA INTERNATIONAL Ltd
Current assignee: FLORA INTERNATIONAL Ltd
Priority date: 1985-05-04
Filing date: 1986-05-06
Publication date: 1987-01-14
Also published as: GB8611006D0

Abstract

The repair involves the steps of depositing material on the worn portion by a metal spraying operation, machining the material deposited by the metal spraying operation to a diameter less than that which is ultimately desired, and building up a surface coating on the machine portion by an electro-deposition process, to provide a hard, smooth surface, with optimal final machining or polishing. The electrodeposition can comprise 1 to 3 layers.

Description

SPECIFICATION Crankshaft reclaimation Description of invention This invention is concerned with improvements relating to the reclaimation of crankshafts, particularly but not exclusively crankshafts designed for relatively highspeed operation.

Crankshafts designed for reiatively highspeed rotation are typically forged from open-hearth carbon steel, and the surface of the crankshaft is hardened by a carburising operation. Difficulty is encountered particularly when the journal of the crankshaft becomes worn, since once the hardened surface is destroyed wearing takes place more rapidly.

When spare parts may reliably be obtained in high volume markets, such as motor vehicles, it is common practice to scrap a worn crankshaft and replace it with a new one. However this process is wasteful and expensive, especially where larger crankshafts are involved. In addition, under certain circumstances replacement crankshafts may be difficult to obtain.

A conventional method of repairing a worn crankshaft is to build up the worn journal with strips of weld material, and to machine down to the required diameter. Great care must be taken to ensure a smooth surface to the machined journal, and even then it is not possible to obtain performance characteristics which approach those of the original crankshaft.

In addition to the above limitations, build up of the journal with strips of weld material is both difficult and time consuming to accomplish, and the heating of the journal of the shaft may cause stresses to appear in the shaft when it is subsequently cooled.

According to this invention there is provided a method of reclaiming a worn crankshaft involving the steps: a) depositing metal on the worn portion by a metal spraying operation; b) machining the re-built portion to a diameter less than the desired final diameter; c) building up a surface coating on the machined portion by an electro-deposition process.

Preferably the portion of the crankshaft to be treated is first subjected to a surface treatment operation, such as grit blasting, to provide a surface which provides good receptivity to the sprayed metal. It will however be appreciated that the worn portion may first be machined to provide a better surface if this is desirable or necessary.

The metal spraying operation may involve process in which metal is carried towards the work on a flame, such as by the use of a gas (acetylene) pistol, or a plasma torch, or in which metal is reduced to molten state by an electric arc and impelled towards the work on a jet of gas. Thus, metal may be deposited on the crankshaft without applying to the crankshaft any undue heat, avoiding subsequent stress problems.

By the use of a metal spraying operation, metal of acceptable quality may reliably be deposited on a worn portion of the crankshaft to a desired depth, allowing the crankshaft to be machined back to a diameter, typically 0.002 to 0.020 inches (0.05 mm to 0.5) less than the desired diameter, more typically 0.005 to 0.010 inches (0.125 mm to 0.25).

Advantageously the electro-deposition is carred out using an electrode, preferably carrying electrolytic material, which is moved across the surface of the shaft during deposition. Thus, conveniently a concave, part-cylindrical electrode is used, advantageously as anode, which is wrapped with absorbent material on which the electrolyte is carried.

Advantageously the material applied by the electro-deposition operation comprises nickel/cobalt or chromium, advantageously to provide a coating having a hardness in the range 40 to 60 rockwell.

If desired the electro-deposition coating may be machined or polished subsequent to its application.

By the use of this invention a worn crankshaft may be built up with metal which is both strongely adhered to the crankshaft, and which has a hard smooth layer proving a shell-like sealing outer surface.

Advantageously the electro-deposition process involves the application to the machine shaft of at least one layer additional to that providing the outer layer, and preferably two additional layers.

A first of said layers comprise a thin flash coating of a material comprising nickel or molybdenum, such as nickel alumimum or molybdenum, to seal the machined metal and which provides a suitable base material.

A second of said layers may comprise or by constituted by copper, serving two functions, the first to provide a stress-relieving layer to the flash coating, the second to provide a "marker" layer. In this manner the need for further treatment may be determined, by checking the sump oil for the presence of copper, without the need to disassemble the engine.

Advantageously the outer layer is a chrome steel, or a nickel/cobalt steel.

Where a surface coating of 0.005 inches is to be applied to the machine shaft, typically the layers will be in the following proportions: a) initial flash coating-0.0005 inches (0.0125 mm); b) marker layer-0.001 inches (0.025 mm); c) outer layer 0.0035 inches (0.0875 mm).

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, or a class or group of substances or compositions, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

In this manner an otherwise scrap crankshaft may readily be refurbished to a high standard with a high expectency of an extensive period of continued use, including circumstances where the journal within which the crankshaft runs comprises alu minium or an aluminium alloy.

Claims

1. A method or reclaiming a worn crankshaft involving the steps: a) depositing metal on the worn portion by a metal spraying operation; b) machining the re-built portion to a diameter less than the desired diameter; c) building up a surface coating on the machined portion by an electro-deposition process.

2. A method according to Claim 1 wherein the portion of a crankshaft to be treated is first subjected to a surface treatment operation, such as by grit blasting, or machining, to provide a surface which provides good receptivity to the sprayed material.

3. A method according to one of Claims 1 and 2 wherein the metal spraying operation involves a process in which metal is carried towards the work on a flame.

4. A method according to one of Claims 1 and 2 wherein the metal spraying operation involves a process in which metal is reduced to molten state by an electric arc and carried towards the workpiece on a jet of gas.

5. A method according to any one of the preceding claims wherein the shaft is machined to a diameter less than the desired final diameter within the range 0.002 inches to 0.02 inches less than the desired diameter.

6. A method according to Claim 5 wherein the range is 0.005 to 0.01 inches.

7. A method according to any one of the preceding claims wherein the electro-deposition process is carried out using an electrode which is moved across the surface of the shaft during deposition.

8. A method according to Claim 7 wherein the electrode is concave, part-cylindrical, and comprises absorbent material on which electrolyte is carried.

9. A method according to Claim 8 wherein the part-cylindrical electrode is utilised as anode.

10. A method according to any one of the preceding claims wherein the material applied by the electrode-deposition process comprises nickel/cobalt or chromium.

11. A method according to any one of preceding claims wherein the electro-deposition process involves the application to the machine shaft of at least one layer additional to that providing the outer layer.

12. A method according to Claim 11 wherein said additional layer comprises a thin flash coating of a material comprising nickel or molybdenum.

13. A method according to one of Claims 11 and 12 wherein the electro-deposition process involves the application to the machine shaft of two layers additional to that providing the outer layer.

14. A method according to Claim 13 wherein the second additional layer comprises or is constituted by cooper.

15. A method according to any one of Claims 11 to 14 wherein a surface coating of between 0.005 inches and 0.009 inches is to be applied to the machine shaft, comprising the following layers: a) an initial flash coating of between 0.0005 inches and 0.001 inches; b) a central marker layer of between 0.0005 inches and 0.001 inches; c) an outer layer of between 0.0035 inches and 0.007 inches.

16. A method of reclaiming a worn crankshaft, when carried out substantially as hereinbefore described.