GB2290042A - Coating surfaces - Google Patents

Abstract

The surface of a metallic workpiece 1 is coated with a metallic material by rubbing a body 3 of the metallic coating material against a surface of the workpiece 1 with sufficient force and at a frequency which causes frictional heating to soften the materials such that the coating material adheres to the workpiece surface. The motion of the body 3 is rectilinear and reciprocal or orbital and the workpiece is moved relatively preferably in a direction perpendicular to the linear component of reciprocal movement. Apparatus for performing this method employs counterweights reciprocated counter to the movement of the body 3.

Description

COATING SURFACES This invention relates to the coating of surfaces.

It has been proposed to coat a surface of a metallic body with a metallic coating by providing a cylindrical rod of metallic coating material, rotating that rod rapidly about its cylinder-axis while pressing a circular end face of the rod against the surface to be coated so that sufficient frictional heat is generated to soften or melt the coating material adjacent to that end face, and causing relative translational movement between the rod and the surface to be coated so that softened or melted material from the rod which adheres to the surface, forms a continuous coating on the surface.

While that method operates satisfactorily it does have a number of limitations. In particular, use of the method results in the production of a coating in the shape of a strip of a width substantially equal to the diameter of the rod, the ends of the strip being of semi-circular shape. It has provided difficult or impossible to form a reliable welded joint between separately formed strips when a second strip is formed alongside a first strip.

In practice, therefore, the maximum width of a continuous strip of metallurgically continuous coating is limited to the diameter of the largest rod that can be used.

The present invention aims to provide a method which enables those difficulties to be overcome or at least reduced.

From one aspect the present invention consists in a method of coating a surface of a metallic body with a metallic coating, comprising the steps of providing a workpiece of metallic coating material, causing relative reciprocatory or orbital movement between the workpiece and the body while pressing together the body and the workpiece so that frictional engagement between an operative end face of the workpiece and a face of the body which is to be coated and which abuts that operative end face causes the generation of heat resulting in the softening or melting of the workpiece adjacent to that operative end face, and causing relative translational movement between the workpiece and the surface to be coated so that softened or melted material from the workpiece, which adheres to that surface, forms on it a coating.

From another aspect the present invention consists in a metallic body with a surface having a metallic coating applied to it by the method outlined in the last preceding paragraph.

The term relative reciprocatory movement is used herein to denote movement such that, in the absence of any accompanying relative translational movement, each point on one of the moving components repeatedly travels to and fro along a notional line on the other component. In carrying out the present invention the relative reciprocatory movement is preferably rectilinear. The term relative orbital movement is used herein to denote movement such that, in the absence of any accompanying relative translational movement, each point on one of the moving components repeatedly travels around a notional circle, ellipse or other closed path on the other component. An orbital movement may be generated by combining two synchronised reciprocatory movements which are caused to occur in directions transverse to each other.When relative reciprocatory or relative orbital movement occurs between two components there is normally no bodily rotation of one component relative to the other, although in some cases there may be some relative oscillatory, angular movement between the components.

In carrying out the invention it is preferred to cause the workpiece to perform reciprocatory or orbital movement and to cause the body to undertake translational movement relative to the workpiece, the rate of that translational movement normally being very much less than the rate at which the workpiece moves.

In one preferred method the operative end face of the workpiece is of elongated shape, the workpiece being so disposed that the relative translational movement take place in a direction transverse to the major dimension of that end face. In a particularly preferred method the workpiece is reciprocated rectilinearly in a direction parallel with the major dimension of the end face, while the body is caused to perform translational movement in a direction at right angles to the direction of reciprocation. In an alternative method there is an assemblage of workpiece, each individual workpiece being in the form of a rod or wire. The assemblage is preferably such that operative end faces of the workpiece are relatively close together so that material from the individual workpieces merges together to form a common coating.The workpiece may be arranged to provide an assemblage of elongated shape, the body being caused to perform translational movement in a direction transverse to the major dimension of the assemblage.

With either of these kinds of arrangements the width of the strip of coating material that is applied to the workpiece is substantially equal to the major dimension of the end face of the workpiece or of the assemblage, and a workpiece or assemblage with a relatively long and narrow end face can be used if a wide strip of coating material is required. When the workpiece employed has a relatively long and narrow end face, the area of that end face is relatively small; in particular it is much smaller than the area of the circular end face of a rotary rod of a size that would be required if a strip of similar width were to be produced by means of the method of coating that was previously proposed and that is described above.Similarly the total area of the end faces of an assemblage of workpieces of the kind described is relatively small, so that it can be much smaller than the circular end face of a single rotary rod. This can represent a major advantage of the present invention for the following reasons. To achieve satisfactory coating of any one material on any other it is normally necessary for the applied pressure to have a certain minimum value. In using the present invention to form a strip of any particular width, the area can be made much smaller than that of a circular rod so that the force required to achieve the desired pressure is correspondingly reduced. For example an eight-fold reduction in area and in force can often be achieved.

That reduction in force also leads to a reduction in the force needed to cause relative translation between the workpiece and the body. Further the energy requirements required for the coating are also considerably reduced.

In using the method the present invention each component area of the end face of a workpiece or an assemblage of workpieces moves at the same rate (or at substantially the same rate relative) to the body to be coated. In consequence, heat is generated substantially uniformly over the whole of the face or over each individual face, and softening or melting occurs evenly. This is in marked contrast to what occurs when a single rod of relatively large diameter is rotated to generate heat by friction, for then there is virtually no relative movement near the centre of rotation and substantially no rise in temperature at the centre.However, the rate of relative movement increases progressively from the centre to the periphery of the circular end face of the rod, so there is a corresponding increase in the rate of production of heat and a corresponding increase in temperature towards the periphery. Another advantage of using the invention is that the ends of a strip of coating material applied to a body can be substantially rectilinear instead of being semi-circular.

The method in accordance with the present invention constitutes a form of friction welding, and the method may be carried out with the aid of known kind of friction-welding apparatus or with the aid of apparatus similar to known kinds of friction-welding apparatus. As is already known, it is highly desirable for a friction-welding machine of the kind adapted to generate reciprocatory or orbital motion to be dynamically balanced, that is for the machine to be such that reciprocatory or orbital movement by one component, such as that to which a workpiece is attached, is balanced at each stage of its movement by corresponding movement of a counterweight in the opposite direction, and the component and counterweight are linked by means biasing them to a neutral position, so that there is little or no resultant reciprocatory or orbital load applied to a stationary part of the apparatus.A friction-welding machine that is dynamically balanced in this way is described and illustrated in the complete specification of British Patent No 1 414 454 of Allwood, Searle and Timney (Holdings) Limited. Now a difficulty tends to arise if a machine of that kind is used for carrying out a method in accordance with the present invention in that the machine becomes progressively unbalanced as material from the workpiece becomes transferred to the body being coated and the mass of the workpiece consequently becomes less.In order to avoid or reduce that problem, a method in accordance with the present invention is preferably carried out with the aid of apparatus in two parts: a first part which generates a reciprocatory or orbital movement and is dynamically balanced, and a second part which is driven by the first part and which carries or is adapted to carry a workpiece, the second part also being dynamically balanced or being capable of being dynamically balanced and additionally being provided with adjustment means operative, while the apparatus is in use, to enable dynamic balance to be retained or substantially retained as the mass of the workpiece is progressively reduced. The adjustment means may operate automatically.

In the accompanying drawings: Figure 1 is a schematic perspective view of a workpiece and a body being coated by a method in accordance with the present invention, Figure 2 is a schematic view of apparatus that can be used in carrying out the method illustrated in Figure 1, Figure 3 is a schematic section along the line 3-3 of Figure 1, Figure 4 is a schematic underneath view, to a larger scale of a carrier and wires that may be employed in place of certain components shown in Figure 2, and Figure 5 is a schematic side view, to a larger scale, of part of a beam included in Figure 1 but modified to illustrate an alternative form of drive means.

In Figure 1 a metallic body 1 of rectangular shape is being coated with a strip of metallic coating 2 derived from a metallic workpiece 3. A relatively long and narrow end face of the workpiece 3 engages the surface of the body 1, and the workpiece is reciprocated rapidly to and fro in a direction parallel with the longer dimension of the end face, as indicated by the arrow 4. The body is restrained (by means that is not shown) against movement in the direction in which the workpiece moves.

The workpiece is pressed against the body so that frictional heat is generated which is sufficient to soften or melt the workpiece and cause it to adhere to the surface of the body. As this occurs the body 1 is caused to undertake translational movement in a direction at right angles to the reciprocatory movement of the workpiece, as indicated by the arrow 5.

The apparatus shown in Figure 2 comprises a first part 6 and a second part 7. The first part 6 generates reciprocatory movement and is dynamically balanced. It comprises a beam 8 which is mounted for longitudinal reciprocation between guide bearings (not shown). At one end of the beam 8 is a pair of rocking bars 9. One end of each bar is connected to the beam by a pivoted link 10. Central parts of the rocking bars are pivoted at 11 to the frame of the apparatus, which remains stationary when the apparatus is in use. The other end of each rocking bar is connected to one end of an associated counterweight 12 by a pivoted link 13. Thus the arrangement is such that when the beam 8 moves lengthwise in either direction the two counterweights 12 move in the other direction.Each counterweight is also connected to the beam by means of a plurality of leaf-springs 14, the ends of which are firmly anchored to the counterweight and the beam in the manner of a cantilever so that in use, when the beam and counterweight move in opposite directions (as they are constrained to do by the associated coupling link 9), the springs 14 flex. In a convenient construction, part of the beam 8 and part of each counterweight 12 comprises a stack of components held together by a bolt or bolts extending longitudinally through aligned holes in those components. The stack comprises metal plates and end portions of the leaf-springs 14, a metal plate being disposed between each spring and the next. If it is considered necessary to insert an additional spring this can be effected by removing some plates and replacing them by the end portions of the spring.Conversely, if a spring is removed its end portions can be replaced by plates.

In use the beam 8 is caused to reciprocate at its natural frequency, which is determined by the mass of the moving parts and the strength of the leaf springs. The natural frequency is substantially independent of the amplitude of movement of the beam. Any suitable drive means may be employed for reciprocating the beam. The drive means may be such that the amplitude can be varied to and from zero and may incorporate apparatus of the kind that is the subject of British Patent No 1 385 471 of Allwood, Searle and Timney (Holdings) Limited.

The second part 7 of the apparatus is shown in conjunction with the body 1 and the workpiece 3. The workpiece is coupled to the beam 8 by any suitable means, this being indicated by the chain-dotted line 15, so that the workpiece and beam reciprocate in unison. A bar 16 overlies the workpiece and moves in unison with it. End portions of the bar are anchored to the upper ends of flexible rods 17, the lower ends of which are similarly anchored to end portions of a plate 18. The plate is restrained against reciprocatory movement, of the kind undertaken in use by the workpiece 3 and the bar 16, but is so mounted as to be capable of vertical movement. In use the plate 18 is pressed downwards by an hydraulic ram 19 acting between the plate and a base 20 which is fixed relative to the frame of the apparatus and remains stationary.Thus, in use, the ram 19 exerts a downward force on the plate 18, and the plate exerts a downward force on the rods 17. The bar 16 is pulled downwards by the rods 17 and pushes the workpiece 3 downwards onto the body 1. The bar 16 reciprocates in unison with the workpiece 3, but the plate 18 does not reciprocate. The relative movement between the bar 16 and the plate 18 is accommodated by flexure of the rods 17, which act in a manner similar to rods described in and illustrated in the complete specification of the aforementioned British Patent No 1 414 454.

A counterweight 21 is provided to enable the second part 7 of the apparatus to be dynamically balanced. End portions of a coupling-link 22 are pivoted to the bar 16 and to the counterweight 21 at 23 and 24 respectively. A vertical slot 25 in the coupling link 22 accommodates a pin 26, which is fixed relative to the frame of the apparatus and therefore remains stationary. The ends of leaf-springs 27 are firmly anchored to the bar 16 and the counterweight 21 in the same way that the leaf-springs 14 are anchored to the beam 8 and the counterweights 13.

When the apparatus is in use and the workpiece 3 and bar 16 are caused to reciprocate, the counterweight 21 also reciprocates but always moves in a direction opposite to that in which the bar 16 moves. Initially, any movement of the bar is mirrored by an equal but opposite movement of the counterweight. As the workpiece is progressively consumed, however, the bar 16 shifts gradually downwards, and the coupling link 22, counterweight 21 and leaf-springs 27 shift with it. As the pin 26 remains unmoved it occupies a position progressively nearer the upper end of the slot 25. Consequently, continued reciprocatory movement of the workpiece and bar causes movement of the counterweight that is complementary but of progressively reduced amplitude.The reduction in the amplitude of the reciprocatory movement of the counterweight compensates for the progressive reduction in the mass of the workpiece 3. In this way it is possible to arrange for the second part 7 of the apparatus to remain dynamically balanced throughout the coating operation.

It will be understood that as the workpiece 3 reciprocates the body 1 is gradually and continuously moved in a direction at right angles to the main plane of the workpiece 3. In view of the relatively large force applied by the ram 19, a considerable force is required to move the body 1; and the reaction to that force is largely borne by the workpiece 3. In order to locate the workpiece against lateral movement as a result of the movement of the body 1 it is desirable to provide restraining means. One preferred form of restraining means is shown schematically in Figure 3. The restraining means comprises a backing plate 28 against which the workpiece 3 bears, the backing plate being connected by flexible rods 29 to a beam 30.In use the backing plate reciprocates in unison with the workpiece but the beam 30 is restrained against reciprocation so that the relative movement between the backing plate and the beam is accommodated by the flexing of the rods 29, in a manner similar to that in which the rods 17 accommodate relative movement between the bar 16 and the plate 18.

However, there is an additional movement that must be allowed for, namely the downward movement of the workpiece 3 as material is removed from its lower end face. As explained above, the bar 16, rods 17 and plate 18 move downwards in unison with the workpiece. If desired the backing plate 28, flexible rods 29 and beam 30 may also move downwards in unison with the workpiece.

To this end the beam may be mounted in a vertically extending slide (not shown), fixed relative to the frame of the apparatus, the beam being moved downwards in unison with the workpiece. When this arrangement is adopted the backing plate 28 may be fixed to the bar 16.

While movement of the backing plate in unison with the workpiece may in some instances be entirely satisfactory, difficulties may arise from the fact that in use there is a progressive decrease in the height of that part of the workpiece 3 which is unsupported, between the body 1 and the backing plate 28. This variation tends to give rise to changes in the rate of flow of heat from the site where the heat is frictionally generated, with the result that the temperature distribution in the neighbourhood of the weld may vary unacceptably. To avoid problems of that kind it may therefore be desirable, at least in some instances, to anchor the beam 30 in such a manner that it does not move relative to the frame of the apparatus, and to restrain also the backing plate 28 against vertical movement.It is then necessary for the workpiece 3 to slide gradually downwards over the backing plate, though relative reciprocating movement is avoided, as before, by the flexing of the rods 29.

In a modified construction these and other difficulties can be at least largely avoided. This construction is illustrated schematically in Figure 4 which is a view from below of a carrier 31 which is mounted in place of both the workpiece 3 and the backing plate 28, end portions of the carrier being connected to flexible rods 29 and the carrier as a whole being coupled to the beam 8 so as to be caused to reciprocate to and fro. End portions of the carrier are also connected to flexible rods 17, but the lower ends of the rods are connected to a part of the frame of the apparatus. Thus, in use the carrier is constrained to reciprocate in unison with the beam and is prevented by the flexible rods 17 and 29 from undertaking any other form of movement relative to the frame of the apparatus.

Vertical holes extend through the carrier 31, and wires 32, which are made from coating material and which constitute an assemblage of workpieces, are passed through the holes so that end portions thereof project a short distance and end faces thereof engage the body 1 to be coated. A downward force is applied to each wire so that the pressure on the end face of each wire is substantially the same as that exerted on the operative end face of the workpiece 3 in the embodiment shown in Figures 1 and 3. The downward force can be applied in any suitable manner. For example, where the wires 32 are relatively short and stout each wire may be urged downwards by an individual hydraulic ram mounted above the carrier. In some instances several wires may be urged downwards by a common ram. In an alternative arrangement a part of each wire above the carrier passes between pressure rollers and is gripped tightly by them.

A torque is applied to the rollers to urge downwards the wire that is between them. Here again it may be possible to arrange for several wires to be urged downwards by the same pair of rollers. An advantage of this latter arrangement is that the wires can be of any desired length. In each of the arrangements outlined above the pressure means, for urging the wires downwards, is preferably mounted on a fixed, non-reciprocating part of the apparatus and a length of each wire extending between the pressure means and an upper part of the carrier flexes in use as the carrier reciprocates.

Although the word wire is used to describe the workpieces used in this form of the apparatus it must be understood that the workpieces may be relatively thick and relatively stiff and may thus resemble rods. One advantage of using wires is that suitable coating materials may well be obtainable in the form of wires of an appropriate diameter whereas it may well be more difficult to obtain from stock, or even to have specially manufactured, workpieces to the necessary dimensions for use in apparatus of the kind shown in Figures 1 to 3.

In use, the projecting end parts of the wires 32 come into frictional engagement with the body 1 and are softened or melted so that material from the wires adheres to the body. Lateral movement of the body causes a coating of material from the wires to be formed on the body. The holes in the carrier are sufficiently close together for a continuous, unbroken coating to be formed.

In each of the forms of apparatus described above the drive means is of the kind described in an earlier patent specification and is preferably such that the amplitude of reciprocation is increased progressively from zero when the apparatus is started up. An alternative form of drive means is illustrated in Figure 5. The beam 8, part of which is shown in the Figure, runs between fixed bearing blocks 33. A transverse slot 34 is formed in an enlarged portion 35 of the beam. A block 36 is slidable in the slot 34 and is formed with a central hole. An eccentric driving member 37 is rotatable in that hole and constitutes a central portion of a shaft 38, the axis of the driving member being parallel with the axis of the shaft but spaced a short distance from it so that the driving member is eccentric with respect to the shaft.

Portions of the shaft 38 immediately adjacent to the driving member are mounted for rotation in bearings (not shown) that are fixed relative to the frame of the apparatus. End portions of the shaft project outwards beyond the bearings and one carries a pulley (not shown) for engagement by a belt which also passes over a pulley on the spindle of a driving motor, while the other carries an eccentric disc (not shown) so disposed that the centre of gravity of the whole rotatable assembly lies on the axis of the shaft. Rotation of the assembly, by the motor and belt, causes the desired reciprocation of the beam.

The beam reciprocates with constant amplitude. In order to enable reciprocation to be carried out by a motor of reasonable power stressing means (not shown) is provided and is operative to displace the beam 8 and counterweights 12 from an initial, neutral position in which the leaf-springs 14 are unstressed, to an end position in which the beam and counterweights are at the ends of their paths of travel and the leaf-springs are stressed to their maximum extent. This can be effected by rotating the shaft 38 through 90" by means of a pawl and ratchet-wheel mechanism powered by hydraulic rams.

When the shaft 38 is then driven by the motor the pawl and ratchet-wheel mechanism is automatically disconnected and this shaft rotates with increasing speed until the operating speed is reached at which the apparatus is fully balanced. Until that occurs, however, more energy is required from the motor than is necessary at the operating speed, when all that the motor does is to overcome frictional forces and the like. The apparatus is of course fully lubricated; the block 36, for example, is lubricated by squeeze-film lubrication.

The methods and apparatus described above can be used to coat a body made of one metal with a coating of the same metal or with a coating of a different metal. The coating may serve to replace metal that has been removed from the body by wear or by corrosion, or it may serve to add a protective layer.

Suitable values of dimensions, loads and amplitudes can best be determined by simple experiment, but it can be said that in a typical apparatus of the kind illustrated in Figures 2, 3 and 5 the amplitude of the reciprocatory movement of the beam and the workpiece is about 8 mm, and the force exerted by the ram 19 is about 8 tons (8128 kg).

Claims (11)

1A method of coating a surface of a metallic body with a metallic coating, comprising the steps of providing a workpiece of metallic coating material, causing relative reciprocatory or orbital movement between the workpiece and the body while pressing together the body and the workpiece so that frictional engagement between an operative end face of the workpiece and a face of the body which is to be coated and which abuts that operative end face causes the generation of heat resulting in the softening or melting of the workpiece adjacent to that operative end face, and causing relative translational movement between the workpiece and the surface to be coated so that softened or melted material from the workpiece, which adheres to that surface, forms on it a coating.

2 A method as claimed in claim 1 wherein the relative reciprocatory movement is preferably rectilinear.

3 A method as claimed in claim 1 or claim 2 including the further step to cause the workpiece to perform reciprocatory or orbital movement and to cause the body to undertake translational movement relative to the workpiece, the rate of that translational movement normally being very much less than the rate at which the workpiece moves.

4 A method as claimed in any preceding claim wherein the operative end face of the workpiece is of elongated shape, the workpiece being so disposed that the relative translational movement take place in a direction transverse to the major dimension of that end face.

5 A method as claimed in claim 4 including the further step that the workpiece is reciprocated rectilinearly in a direction parallel with the major dimension of the end face, while the body is caused to perform translational movement in a direction at right angles to the direction of reciprocation.

6 A method as claimed in any preceding claim there is an assemblage of workpiece, each individual workpiece being in the form of a rod or wire, the assemblage is such that operative end faces of the workpiece are relatively close together so that material from the individual workpieces merges together to form a common coating.

7 A method as claimed in claim 1 wherein the workpieces are arranged to provide an assemblage of elongated shape, the body being caused to perform translational movement in a direction transverse to the major dimension of the assemblage.

8 A method as claimed in any preceding claim wherein each component area of the end face of a workpiece or an assemblage of workpieces moves at substantially the same rate relative to the body to be coated.

9 A method of coating a surface substantially as described hereinbefore with reference to the accompanying drawings.

10 Apparatus for performing the method as claimed in any preceding claim comprising a machine of the kind adapted to generate reciprocatory or orbital motion, reciprocatory or orbital movement by one component, such as that to which a workpiece is attached, being balanced at each stage of its movement by corresponding movement of a counterweight in the opposite direction, and the component and counterweight are linked by means biasing them to a neutral position, so that there is little or no resultant reciprocatory or orbital load applied to a stationary part of the apparatus.

11 Apparatus for performing a method of coating a surface substantially as described hereinbefore with reference to the accompanying drawings.