WO2000008232A1

WO2000008232A1 - Method of treating a bearing surface

Info

Publication number: WO2000008232A1
Application number: PCT/GB1999/002438
Authority: WO
Inventors: Martin Robert Bowers
Original assignee: Laystall Engineering Company Limited
Priority date: 1998-08-08
Filing date: 1999-08-09
Publication date: 2000-02-17
Also published as: GB9918592D0; AU5428499A; GB9817237D0; GB2340775B; GB2340775A

Abstract

A method of treating a bearing surface (12) of a component (10) formed from a base material is described. The method comprises the steps of bringing the surface (12) into proximity with rollers (14, 16), the rollers and surface are then moved relative to each other with a contact force in the range 0.25 to 20 Newtons per mm of roller contact width, and particles of a material having a hardness higher than that of the base material are introduced between the rollers and the surface such that at least some of the hard particles are forced into the base material of the surface by the rollers.

Description

Title: Method of treating a bearing surface.

Description of Invention

The invention relates to the treatment of bearing surfaces.

The treatment of bearing surfaces to provide surfaces with greater wear resistance is well known. In particular, it is well known to bore and lap metal surfaces making use of an abrasive powder composed of hard grains or grit particles, such as silicon carbide particles. Further, it is well known that wear properties can be improved if such particles are embedded into surfaces. Details of the apphcation of this technique to cylindrical bearing surfaces are provided in our prior Patent No. GB 1,372,171, and in respect of cylindrical and swept bearing surfaces in our prior Patent No. GB 1,574,141. However, the methods described in these earlier patents suffer from a number of disadvantages, for example:

(a) large amounts of the abrasive powder and carrying media are wasted during the production process;

(b) the tooling used in the embedding process is in essence a consumable adding further to process cost, and

(c) the process is difficult to automate due to a high level of manual intervention.

According to the present invention there is provided a method of treating a surface of a component formed from a base material, the method comprising the steps of bringing the surface into proximity with rollers, moving the rollers and surface relative to each other with a contact force in the range 0.25 to 20 Newtons per mm of roller contact width, and introducing particles of a material with a hardness higher than that of the base material between the rollers and the surface, such that at least some of the particles are forced into the material of the surface by the rollers.

The invention provides a number of advantages. First, considerably less abrasive powder carrying media is used. This itself provides a reduction in processing cost but it also leads to reduced post process cleaning after treatment, providing further reduction in cost. Second, the force apphed to the rollers introduces a degree of residual stress into the base material surface and this enhances particle retention. Third, highly localised areas may be treated on a surface providing improved wear characteristics only where required, eliminating the need to treat areas not required provides further cost savings. Fourth, durable tooling is used with considerably longer life than the type used on the previous methods. Fifth, the process may be readily automated and used in production line manufacturing, with obvious advantages. Sixth, relatively soft materials, such as aluminium and aluminium alloys, can be treated without scoring or damaging the surface which is a problem when using the previous methods. Finally, non cylindrical surfaces may be treated, giving a much wider range of apphcations for this method.

For convenience the particles of a material with a hardness higher than that of the base material will simply referred to as "hard particles" in this specification.

The hard particles may be introduced between the rollers and the surface in a slurry applied to the surface. Alternatively, the hard particles may be introduced by adhering them to the surface using a light adhesive.

In a further alternative the hard particles may be adhered to a tape using a light adhesive, and the tape passed around at least one of the rollers. The tape may be provided in the form of a cassette.

In yet a further alternative a mask may be manufactured to conform to the surface to be treated and the hard particles adhered to the surface of the mask, the mask then being brought into proximity with the surface, between the surface and the rollers.

Preferably the surface is rolled more than once such that the hard particles are fully embedded in the material.

The method may comprise the further steps of removing excess hard particles and repeating the rotating of the rollers and surface relative to each other with a contact force in the range 0.25 to 20 Newtons per mm of roller contact width, such that the hard particles previously forced into the surface material are forced further into the material and the material closes around them.

The method may comprise a further step of subsequently using an abrasive to produce the desired surface finish and to remove any loose hard particles from the surface.

Preferably the hard particles are silicon carbide.

The surface may be an internal cylindrical surface with a longitudinal axis and the rollers may have longitudinal areas arranged to be parallel with the longitudinal axis of the surface.

Methods of putting the invention into effect will now be described, by way of example only, with reference to the accompanying drawings in which:

FIGURE 1 schematically illustrates the application of the method to an internal cylindrical surface;

FIGURE 2 illustrates in cross-section the method of the invention in operation;

FIGURE 3 illustrates a roller arrangement appropriate for slurry or other direct methods of introduction of hard particles;

FIGURES 4 and 5 illustrate roller arrangements appropriate for alternative methods of introduction of hard particles.

Referring now to the Figures, a component 10 of a base material bears an internal cylindrical surface 12 to be treated, in order to improve its wear characteristics. Two rollers 14,16, are provided for implementation of the treatment method. The rollers 14,16, are supported by rods 18,20, such that their longitudinal axes are parallel with the longitudinal axis of the component 10. The rollers 14,16, can be inserted into the component 10 and biased in opposite directions as shown by the arrows 22,24, such that they come into contact with the internal cylindrical surface 12 with a contact force in the range 0.25 to 20 Newtons per mm of roller contact width dependant on the base material being treated, the contact force being controllable. The bias is applied to the rollers by any appropriate method, such as hydraulically, pneumatically, or mechanically.

In this case, the component 10 is rotated, as shown by arrow 26, although alternatively or additionally, the rollers 14,16, may be rotated in order to provide relative rotation of the rollers with respect to the internal cylindrical surface 12. As the rotation occurs, particles P of material having a hardness higher than that of the base material, which for simplicity will be referred to as hard particles, for example silicon carbide, are introduced between the rollers 14,16, and the surface 12 such that the hard particles P are forced into the base material of the surface 12, as illustrated in Figure 2. The rotation is continued until the whole surface 12, or that portion of it being treated, has been rolled more than once, and preferably a number of times, such that the hard particles P are fully embedded in the material.

The extent of the embedding or impregnation of the hard particles into the base material being treated may be determined by one or more of the following methods, as appropriate for the base material being treated and the hard particles being embedded: a) SEM X-ray mapping (assuming hard particles have distinctive chemical composition to base material); b) optical Microscopy; c) destructive cross sectioning, or d) Beta particle diff action.

The contact force between the rollers 14,16, and the cylindrical surface 12 is closely controlled in order to introduce a degree of residual stress into the base material of the surface being treated, as this enhances hard particle retention.

In most cases, the method involves further steps as follows. Any excess and loose hard particles are removed from the component 10 and rollers 14,16, and further rolling, as described above, is undertaken with the same range of contact forces but without the introduction of further hard particles. This ensures that the hard particles introduced into the material of the surface 12 are pressed further into the surface and the base material is closed tightly over or around them. Depending on the component 10 being treated, a further final operation to hone the surface using abrasives to achieve the desired surface finish, and to remove any loose hard particles may be undertaken. This is particularly suitable for example when a cylinder bore is being treated.

There are a number of options for the manner of introduction of the hard particles between the surface 12 and the rollers 14,16, each having different benefits and particular instances where it is applicable.

The first option for introducing the hard particles, is to mix them with a carrier fluid to form a slurry which preferably has an even and predetermined concentration of hard particles. The slurry is applied to the cylindrical surface 12 of the component 10 before rolling, or may be fed at a controlled rate in front of the rollers 14,16, dependent on the format of the component 10 to be treated. For this method of introduction, rollers of the form illustrated in Figure 2 are appropriate.

The next method of introduction of the hard particles again uses rollers of the configuration illustrated in Figure 2. In this case, the hard particles are fixed with a light adhesive, in a controlled manner and density, to the portion of the surface 12 to be treated. Any excess is removed after the rolling operation, using an appropriate solvent for the adhesive if necessary.

The third manner of introduction of the hard particles uses apparatus as illustrated in Figure 3. The hard particles are fixed in a controlled manner and density by a light adhesive to a tape 30, which is preferably provided in a cassette 32. The tape is then fed over one or more of the rollers 14,15,16, which in turn presses the tape 30 against the surface 12 to be treated. This results in the hard particles being pressed into the base material of the surface 12 and hence being removed from the tape 30. The remaining roller or rollers 14,15,16, then press the hard particles into the base material, ensuring that the base material closes over them as required. This particular option provides the benefit that few excess hard particles are introduced. This thus reduces the problems which can result from excess hard particles which fail to be washed off intricate components with many holes and pockets, such as for example cylinder blocks.

The fourth option uses rollers as illustrated in Figure 4. In this case, a mask 40 is made especially to conform to the surface 12 to be treated and the hard particles are fixed to the appropriate face or faces of it, 42, in a predetermined pattern and density according to the treatment required. The mask 40 is then placed in proximity with the area of the surface 12 to be treated and the rolling process is carried out. Following the rolling, the mask 40 may be removed before a possible second rolling operation is conducted to complete the submerging of the particles into the material of the surface 12.

In general, the method of treatment may be undertaken by rotating the component 10 with respect to the rollers 14,15,16, and/or the rollers 14,15,16, with respect to the component 10, in order to provide the relative motion.

Whilst the method is described above with reference to the use of two or three rollers, additional rollers may be used if desired. The rollers may treat a portion of the surface the width of the rollers, or the rollers may be moved axially with respect to the component 10 in order that a larger area of the surface is treated.

The examples given above relate to the processing of internal cylindrical surfaces. However, the method of the invention is suitable for the treatment of most surface geometries and is not limited to the treatment of cylindrical surfaces.

The features disclosed in the foregoing description 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.

Claims

1. A method of treating a surface of a component formed from a base material comprising the steps of bringing the surface into proximity with rollers moving the rollers and surface relative to each other with a contact force of 0.25 to 60 Newtons per mm of roller contact width, and introducing particles of a material with a hardness higher than that of the base material between the rollers and the surface such that at least some of the hard particles are forced into the base material of the surface by the rollers.

2. A method according to claim 1 wherein the hard particles are introduced between the rollers and the surface in a slurry applied to the surface.

3. A method according to claim 2 wherein the slurry is introduced just in front of the rollers as they move.

4. A method according to claim 1 wherein the hard particles are introduced by adhering them to the surface using a light adhesive.

5. A method according to claim 1 wherein the hard particles are introduced by adhering them to a tape using a light adhesive, and passing the tape around at least one of the rollers such that the hard particles are between the surface and the tape.

6. A method according to claim 5 wherein the tape is provided in the form of a cassette.

7. A method according to claim 1 wherein the hard particles are introduced by manufacturing a mask which conforms to the surface to be treated and adhering the hard particles to the surface of the mask, and bringing the mask into proximity with the surface such that the hard particles are between the mask and the surface.

8. A method according to any preceding claim wherein the surface being treated is rolled more than once such that the hard particles are fully embedded within the base material of the surface.

9. A method according to any preceding claim wherein it comprises the further steps of removing any excess hard particles from the surface and the rollers and again moving the rollers and the surface relative to each other with a contact force of 0.25 to 20 Newtons per mm of roller contact width such that the hard particles are forced further into the base material of the surface and the base material closes around them.

10. A method according to claim 10 wherein it comprises a further step of subsequently using an abrasive to produce the desired finish on the surface and to remove any loose hard particles from the surface.

11. A method according to any preceding claim wherein the hard particles are silicon carbide.

12. A method according to any preceding claim wherein the surface is an internal cylindrical surface having a longitudinal axis and the rollers have longitudinal axes arranged to be parallel with the longitudinal axis of the surface.

13. A method of treating a surface substantially as hereinbefore described with reference to the accompanying figures.

14. Any novel feature or novel combination of features as herein defined and or shown in the accompanying drawings.