GB2192642A - Electro deposition - Google Patents

Abstract

A process and apparatus is described for the electro-deposition of an overlay alloy onto a bearing alloy surface (14). The process comprises the steps of cleaning the surface, providing relative motion between the surface to be plated and a porous pad (52) in contact with said surface, providing a flow of plating solution to the porous pad and said surface whilst applying a voltage difference between said surface which is cathodic during overlay deposition and an anode (51) connected to the porous pad. An example of the deposition of a tin-based overlay alloy containing cobalt is described.

Description

GB2192642A 1 SPECIFICATION zincate layer in hot oil has been observed. Tin

and zinc is known to comprise a corrosion Process and apparatus for the deposition of couple which has resulted in the complete de bearing alloys lamination of the overlay from the zincated 70 aluminium alloy.

The present invention relates to alloys suitable A process has now been discovered which for bearing applications and particularly to a permits the direct plating of overlay onto the process and apparatus suitable for depositing aluminium of aluminium alloy bearing surface such alloys. without the need for intervening zincate and Where overlays have been applied to bear- 75 other interlayers.

ings by electroplating techniques they have According to a first aspect of the present conventionally been applied by plating in well- invention a process for the electro-deposition known plating vats or baths with the bearings of an overlay onto an alloy surface comprises being totally immersed in the plating solution. the steps of cleaning the surface, providing Particular problems arise in the deposition of 80 relative motion between the surface to be overlay alloys on aluminium alloys as distinct plated and a porous pad in contact with said from other bearing alloys such as those surface, providing a flow of plating solution to based, for example, on copper. the porous pad and said surface whilst apply Most plating of overlays comprising, for ing a voltage difference between said surface example, lead or tin-based alloys has been 85 which is cathodic during overlay deposition carried out either in fluoroborate plating baths and an anode connected to the porous pad.

which are highly acidic in nature or in other, The method is generally known as brush also highly acidic, plating solutions. Such plat- plating but has in the past only been used for ing methods involve a lengthy series of pro- the plating of selected areas of a component cess steps. Firstly the bearing surface must be 90 or for localised repairs and not for the pro cleaned and provided with what is normally vision of a uniform thickness of overlay on the known as a zincate layer to inhibit reoxidation surface of an aluminium or chromium alloy of the cleaned aluminium alloy surface and to bearing.

promote adhesion of the subsequent interla- Relative velocity between anode and surface yer. An inteflayer, often of nickel, copper or 95 being plated preferably lies within the range an alloy based on one of these metals is 0.05 to 2 m.sec-1 and more preferably in the plated on top of the zincate layer. The primary range 0.1 to 1 m.sec.-'.

purpose of the interlayer is to protect the zin- The porous pad may comprise a covering cate layer from corrosive attack by the fluoro- on the anode.

borate or other acidic plating solution from 100 The method has proved to show unexpec which the overlay alloy is to be deposited. ted benefits in the plating of overlays onto This plating sequence brings with it its own aluminium-based bearing alloys. It has been specific problems. The principal problem of unexpectedly found possible to deposit over these relates to the interlayer. There is evi- lays directly onto the aluminium alloy substrate dence to suggest that the presence of the 105 without the need for pre- treatments such as interlayer tends to render a bearing more seiz- zincating and, therefore, without the need for ure-prone when the co-operating shaft wears interlayers such as nickel etc. Furthermore the through the overlay. A further problem also method of the present invention reduces the related to the interlayer concerns the change number of cleaning stages to two instead of in alloy composition of the deposited overlay. 110 six as in a conventional plating bath method.

Where, for example, lead-10% tin is plated This latter benefit clearly has important conse onto a nickel interlayer a diffusion effect at quences on the size and cost of the plating engine operating temperatures tends to cause plant required and also on the actual process depletion of tin in the overlay by reaction with ing costs.

the nickel. The effect of tin depletion is to 115 According to a second aspect of the pre render the overlay more prone to corrosion. sent invention apparatus for the electro-dem The overall effect of the presence of th e inter- position of an overlay onto the surface of a layer is to render the bearing alloy system bearing comprises means for holding one or unstable over its operational life perhaps even more bearings, an anode, a porous material shortening the operational life of the bearing. 120 interposed between the surface and the an Other less acidic plating systems do exist ode, the porous material contacting the sur- but are very much more expensive; in some face of the bearing to be plated, drive means cases the cost of the overlay plating solutions to,provide relative movement between the may be very high and not commercially viable. surface of the bearing to be plated and the Therefore, such plating solutions may be dis- 125 anode, means to render the bearing surface missed on the basis of cost alone. It has been cathodic with respect to the anode and means found, however, that even where such expen- for supplying plating solution electrolyte to the sive solutions are used the long term integrity cathodic and anodic surfaces.

between the overlay and the zincate layer is In one embodiment of apparatus according questionable as corrosion between overlay and 130 to the present invention the bearings may be 2 GB2192642A 2 held in cylindrical pairs and rotated about their reservoirs 42 pumped at a controlled rate by axis. peristaltic pumps 43 through conduits 44.

The electrolyte may be supplied to the out- Used solutions are returned to reservoirs 42 side of the porous material or may be sup- from the collector troughs 40 via drain condu plied by passing through the material from the 70 its 45, pumps 46 and refrigeration units 47.

inside, for example, via the anode itself. Solutions are supplied via the conduits 44 to The anode may be cylindrical and mounted a cylindrical plating brush 50 which comprises on a swinging arm which biasses the anode a central core 51 of graphite forming the an against the Iearing surface to be plated. ode the graphite being covered with a sleeve It has been found that when plating rela- 75 52 of Selvyt cloth (trade mark). The anode tively soft alloys of the kind often employed may also comprise nonreactive metals such for bearing overlays that a soft, porous textile as, for example, platinum. The brush 50 is material is preferable. An example of such a mounted on a swinging arm 53 which is pi suitable type of material is that sold under the voted on a shaft 54 held in a support pillar trade name of Selvyt cloth. 80 55. Connected to the swinging arm 53 and In order that the invention may be more brush 50 via the pivot shaft 54 is a motor fully understood some examples will now be and clutch unit 56 adapted to move the brush described with reference to the accompanying 50 through an arc to bring it into contact with drawings of which: the bore of the bearings 14 to be plated at a Figure 1 shows a schematic part sectioned 85 controlled load. The wash tanks 11 and 12 view of apparatus accordng to the present in- have lower collector troughs 60 and upper vention set up to brush plate pairs of half splash guards 61. The troughs 60 have drain bearings; conduits 62 connected to a manifold 63 to Figure 2 shows a part, sectioned side view take away waste water. Clean wash water is through one of the plating tanks of Fig. 1 and 90 supplied from a pump 64 via a manifold 65 to its associated apparatus; conduits 66. Water is allowed to access the Figure 3 which shows a schematically gen- bearings 14 through conduits 67 by operation eral arrangement of the bearings to be plated of solenoid valves 68. Suitable electrical con and the plating electrodes etc. tacts 70 are provided to make the bearing 39 Referring now to the drawings and where 95 surface cathodic. A known power supply-71 the same features are denoted by common is also provided to control both voltage, our reference numerals. rent and time; the power supply 71 also has - The apparatus comprises a clean and etch the facility to change polarity of the elec tank denoted generally at 10, wash tanks de- trodes.

noted generally at 11 and 12 and a brush 100 Operation of the above apparatus will now plating tank denoted generally at 13. Bearings be described in relation to the deposition of a to be plated 14 are held in a jig 15 which is tin-cobalt overlay onto an aluminium-20 wt% mounted on a plate 16 which is itself fixed to tin-1 wt% copper bearing alloy. Bearings 14 a shaft 17 of a motor 18. The motor 18 is of 53mm dia and 30mm length and compris mounted on threaded shafts 19 which are 105 ing a steel backing having the stated alumi adapted to move the motor 18 and bearing jig nium alloy thereon were degreased in trichlo in a direction parallel to the axis of the roethylene and loaded into the jig 15 in three motor shaft 17. The threaded shafts 19 are sets of two pairs effectively forming a cylindri themselves part of a gantry 20 having cal tube of bearings. The jig 15 was then grooved wheels 21 which co-o perate with 110 assembled onto the plate 16 of the motor 18.

rails 22 which support the gantry 20 for With the mounting block 30/motor 18 at the transverse motion with respect to the row of furthest extent of its travel to the left on the tanks 10, 11, 12 and 13. The gantry 20 is threaded shafts 19 the gantry 20 was tra moved along the rails 22 by a chain drive 23 versed along the rails 22 until the jig and which is conrolled by sprockets driven by an 115 bearings were opposite tank 10. The bearings electric motor (not shown) having known con- 14 were then advanced into the clean and trol means (not shown). The motor 18 is etch tank 10 to allow penetration of the brush moved parallel to the direotion of the shaft 17 50 into the jig 15. The bearings were then by means of the threaded shafts 19 which co- rotated at 120 rev./min. with the bearings an operate with threaded holes in a mounting 120 odic at 9 volts whilst 10% hydrochloric acid block 30. The motor is moved by rotation of was pumped into the region where the bear the shafts 19 which are driven. by pulleys 31 ing surface and Selvyt cloth contacted. This and 32 linked by a toothed belt 33, the ptjlley was continued for 2 minutes at a current of 32 being driven by an electric motor 34 hav- about 8 amps. The polarity of the bearings ing- known control means (not shown). The 125 was then reversed to cathodic and the pro clean and etch tank 10 and the plating tank cess repeated for a further 2 minutes under 13 and their associated systems comprise the same conditions.

lower collector troughs 40 and upper splash The bearings were then withdrawn from the guards 41. Clean and etch or plating solutions tank 10 and the gantry 20 advanced to the are supplied to the tanks 10 and 13 from 130wash tank 11 where they were rinsed with 3 GB2192642A 3 clean water with the bearings rotating at 40 be applied to many other overlay metals and rev./min. The bearings were then advanced to alloy systems, examples of which may include the plating tank 13 where they were plated Pb-Sn, Pb-Sn-Cu, Pb-Sb, Sn-Sb, Sn-Ni, with a Sn-Co overlay. The plating solution Sn-Cd, Sn, Sn-Cu, Pb, Pb-1n, Sn-in, Sn used comprised 50 gm/lit stannous sulphate, 70 Sb-Cu, Cd-Ni.

gm/lit cobalt sulphate, 50 gm/lit sodium

Claims (1)

1. heptonate and the pH was adjusted to 2 by CLAIMS means of acetic acid. The

   jig and bearings 1. A process for the electro- deposition of were rotated at 120 rev./min. with a plating an overlay onto an alloy surface the process solution flow of approximately 0.2cm3-1 sec. 75 comprising the steps of cleaning the surface, and a brush pressure of approximately 20 providing relative motion between the surface 9M/CM-2. The bearings were cathodic at a to be plated and a porous pad in contact with potential of about 15v with an initial current the surface, providing a flow of plating solu flow of 8A rising to about 16A. The bearings tion to the porous pad and the surface whilst were plated for a time sufficient to deposit 80 applying a voltage difference between the sur between 20 and 25 urn of overlay. The bear- face which is cathodic during overlay deposi ings were then rinsed in tank 12 and dried. tion and an anode connected to the porous The resulting overlay possessed an average pad.

   of 8% Co in the Sn matrix. 2. A process as claimed in Claim 1 The resulting plated bearings were tested in 85 wherein the alloy surface is an aluminium al a known -Sapphire- testing machine whih loy.

   measures the fatigue rating of the overlay. 3. A process as claimed in Claim 1 or r, The testing schedule comprised the following Claim 2 wherein plating solution is supplied procedure and conditions: through the porous pad.

   Shaft speed 2800 rev./min. 90 4. A process as claimed in any one pre Initial load 62 MPa ceding claim wherein the plating solution is Load increased after 20 hours at each load by supplied via the anode.

   7 MPa until failure 5. A process as claimed in any one pre Oil temperature WC ceding claim wherein the velocity of relative Sinusoidal load pattern 95 motion between the alloy surface and said po Test results of 97, 103, 103, 90 and 90 rous pad lies in the range from 0. 05 to MPa were obtained on the bearings produced 2m.sec.-'.

   by the method described. 6. A process as claimed in any one pre Further bearings were produced with an ad- ceding claim wherein the velocity lies in the ditional surface treatment of a zincate layer on 100 range from 0.1 to lm. sec.-'.

   the aluminium alloy but without an additional 7. A process as claimed in any one pre interlayer. Fatigue test results on the---Sap-ceding claim wherein the alloy surface to be phire- machine gave ratings of 62, 62 and 76 plated is substantially cylindrical.

   MPa demonstrating an adverse effect of the 8. A process as claimed in any one pre- zincate layer. 105 ceding claim wherein the overlay comprises tin For the purposes of comparison the same and cobalt.

   AI-20Sn-lCu alloy overlay plated with a 9. A process as claimed in any one pre- known Pb-10Sn overlay by a known conven- ceding claim wherein the surface to be plated tional immersion plating method in a fluorobo- is the surface of a bearing alloy.

   rate-type bath with zincate and nickel interlay- 110 10. A process as claimed in Claim 9 ers gives a fatigue rating typically in the re- wherein the bearing alloy is in flat strip form.

   gion of 70 MPa on a -Sapphire- test rig. 11. A process as claimed in Claim 9 In the above the bearings are themselves wherein the bearing alloy is in cylindrical or rotated, however, it will be appreciated that semi-cylindrical bearing form.

   the anode may be rotated instead or in addi- 115 12. Appratus for the electro-deposition of tion. an overlay onto the surface of a bearing corn The electrolyte may be supplied into the prises means for holding one or more bear plated surface and anode gap or via the anode ings, an anode, a porous material interposed itself. between the bearing surface and the anode It is envisaged that the method of the pre- 120 the porous material contacting the surface of sent invention could be applied to the plating the bearing to be plated, drive means to pro of continuous strip with overlay. The overlay vide relative movement between the surface coated strip may then be processed into bear- of the bearing to be plated and the anode ings by known techniques. Such a process means to render the bearing surface cathodic may alleviate one of the most serious 125 with respect to the anode and means for sup drawbacks of the plating of bearings which is plying plating solution electrolyte to the catho the labour intensive and, therefore, costly step dic and anodic surfaces.

   of jigging and dejigging bearings before and 13. Apparatus as claimed in Claim 12 after plating. wherein the porous material is a covering over The method of the present invention may 130 the anode.

   4 GB2192642A 4 14. Apparatus as claimed in either Claim 12 or Claim 13 wherein the material si a soft textile material.

   15. Apparatus as claimed in any one of Claims 12 to 14 wherein the anode is cylindrical.

   16. Apparatus as claimed in any one of Claims 12 to 15 wherein the bearings are held in cylindrical pairs and are rotated about their axes by drive means.

   17 ' A process substantially as hereinbefore described with reference to the accompanying specification and,drawings.

   18. Apparatus. substantially as hereinbefore described with reference to the accompanying specification and drawings.

   Published 1988 at The Patent Office, State House, 66171 High Holborn, London WC 1 R 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.