IMPROVED ALUMINIUM PRODUCTS AND ARTICLES

Abstract: A downhole tool or other product (P) made essentially of aluminium base material is provided with a hard-faced surface comprised by geometric elements or rough particles (2a) of hard material. Filler material (3) serving to secure the elements/particles to the surface is applied by gas-shielded metal arc welding (e.g. TIG welding) in pulsed mode, so as to fill in the spaces between the elements/particles. In this way, substantial hard-facing can be applied to aluminium articles, where conventional hitherto only steel articles have been susceptible to substantial hard-facing.

Description: IMPROVED ALUMINIUM PRODUCTS AND ARTICLES The present invention relates to improved aluminium products or articles and especially to such products as improved to resist abrasion and cutting. The invention is especially but not exclusively concerned with aluminium tools as used in the oil industry. Aluminium, both as pure aluminium and as an alloy, is used as a material in a very wide variety of products. Aluminium is light, enjoys good workability and casting characteristics and these are features attractive for use in the manufacture of many products. Aluminium also has a relatively low melting point and a high thermal (and electrical) conductivity property, the latter also being a valuable feature for certain products. Aluminium now finds use for tools in the oil industry. Many of the above characteristics of aluminium are attractive for this use, but a particularly attractive feature resides in the fact that aluminium is non-magnetic. Many operations, for example downhole in the oil industry require monitoring via electrical test and checking equipment and the operation of such equipment can be seriously jeopardised by the proximity of a magnetic metal e.g. many steels: hence the benefit of aluminium. Aluminium too can be also be drilled through when the tool has reached its final position, which is desirable in certain drilling and casing operations. However aluminium does not enjoy naturally good resistance to abrasion and cutting, with the result there has been shying clear of aluminium for environments of an abrasive nature. This characteristic therefore, as will be appreciated is a disadvantage for a downhole oil tool. Various techniques are available for treating aluminium to make it more suitable for many environments, usually techniques of a mechanical or coating (paint) form. Hard chromium plating is possible for aluminium and this will provide a certain hard-facing for resistance to abrasion. Plating of aluminium however does require specialised treatment processes, reducing the widespread use of this treatment of aluminium. It is also known to embed tungsten granules in an aluminium tool surface by firing them at high speed against the surface. This only provides a relatively thin facing, suitable for drilling in sand, for example, but not in rock formations of a more challenging nature. Hard-facing of a more substantial nature is commonly applied to steel tools, using tungsten carbide inserts as one example. Such techniques have not been considered applicable to aluminium however. It is an object of the present invention to provide aluminium products effectively adapted for use in an abrasive environment, and also to a method of making such a product. Therefore according to one aspect of the present invention a product made of aluminium base material is provided with a hard-faced surface comprised by elements or particles of hard material on the surface, and filler material serving to secure the elements /particles to the surface. In particular the filler material can fill in the spaces between the elements /particles. The phrase "aluminium base material" will be understood to include alloys of aluminium, which will generally include a proportion of other elements such as Silicon (Si) and Magnesium (Mg), according to the desired properties of the material. The hard material can be tungsten or particularly tungsten carbide. It may comprise crushed particles, or the elements may be in the form of more regular solid elements such as trapezoids. The filler material is preferably applied by a gas shielded fusion (welding) process, and especially gas metal arc welding (GMAW) process. GMAW in this context is understood to include both inert and active gas types (known as MIG or TIG and MAG welding respectively) . A pulsed current mode of operation is preferred. The filler material preferably comprises an aluminium based filler and in particular can comprise 5% silicon aluminium filler or 5% magnesium, together with other minor constituents. According to a second aspect of the present invention a method of hard- facing a surface of an aluminium product comprises the steps of (a) applying elements or particles of hard material to the surface and (b) applying filler material to the surface by melting so as to secure the elements /particles to the surface. By this means, the inventor has found that substantial hard-facing can be provided without substantial distortion of the underlying aluminium base material. Preferably as a first step the elements/particles are applied to the surface and subsequently secured to the surface by a second step comprising the application of the filler material to the surface such that the filler material fills in the spaces between the elements/particles. Again, the melting can be by a GMAW, and in particular MIG (or TIG) welding of a pulsed form is preferred. The filling material can be a 5% silicon aluminium wire form filler, although other comparable fillers are possible, and the gas shielded fusion process can include a high purity argon gas shield used in a pulse mode gas metal arc welding process. The best filler may depend on the type of base material, according to content of Si, Mg etc. The hard element can be of tungsten material, with the element preferably of button or trapezoidal form, or alternatively crushed tungsten carbide particles may be used. As a preliminary step the elements (trapezoids) may be minimally held in place on the surface e.g. by spot welding prior to the application of the filler material for securement of the elements. The present invention is also an aluminium product provided with hard- facing by the above method of the second inventive aspect. Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings wherein: Fig 1. Shows in plan part of a surface of an aluminium product hard-faced in accordance with the present invention; Figs 2 & 3 show two possibilities of the side view of the product of Fig 1, and Fig 4 shows in side view a hard-facing operation of an aluminium product in accordance with the present invention. Referring to Figs 1 to 3, a surface 1 of an aluminium product P, for example a downhole tool as used in the oil industry, is hard-faced by the application of hard elements 2 in the form of tungsten trapezoids, with filler material (shown hatched) applied to the surface 1 to secure the trapezoids 2 in place. In particular and after any contamination is removed from the surface 1 (and the filler), in the hard-facing operation the tungsten tapezoids 2 are firstly applied to the surface 1 in an appropriately spaced manner (per Fig. 1), then the filler material 3 is applied to the surface 1 by a fusion process to fill in the spaces between the trapezoids 2 and to secure the trapezoids to the aluminium surface 1. The fusion process is essentially a welding process. Welding of aluminium presents certain difficulties, not least of all due to the tendency for the formation of an oxide film on the aluminium work surface. Consequently an inert gas shielded welding process (e.g. MIG welding) is selected for the application of the filler material 3 to the surface 1 , as this is believed best to overcome these difficulties. Also, careful selection of the filler material is made. Thus a filler wire of aluminium with a suitable silicon content (e.g. about 5%) is chosen in this example and applied with a high purity argon shield in a pulse mode gas metal arc welding (G.M.A.W.) process. G.M.A.W. processes are established in the welding art so will not be described in detail here. The hard-facing layer can be applied with (or ground to) an appropriate thickness (T). The trapezoids 2 may be minimally held in place, especially when on a curved surface (Fig 3), by a preliminary step, for example by spot welds 4, prior to securement by the filler material 3 on the surface 1. In the example of Fig 4, hard elements of particle (granule) form are employed in place of the trapezoids. These particles may comprise for example crushed tungsten carbide. Thus as shown, the hard-facing operation using particles can involve directing the particles (2A) say from a hopper 5 onto the aluminium surface 1 with a follow up G.M.A.W. process to apply the suitable filling 3 (using a filling material as above described) securing the particles 2A on the surface. In this operation, the product (work piece) and the weld gun/hopper are caused to move relative to each other. The hard-facing can be ground back after filling, to achieve desired dimensions. Other hard materials may of course be suitable. Diamond inserts are known, for example, including ones where the diamond is carried on a tungsten carbide button or trapezoid. A groove or trench (such as trench 6 shown dashed) may be formed in the base material to receive the particles, which is then filled with the filler material. The crushed carbide can of course be applied simply by hand, in stages if need be. The product P may be of pure aluminium, but the invention is also applicable to products made of aluminium alloys, including for example magnesium and/ or silicon. The base material for different applications will vary between these different compositions according to the desired properties of the material, as is well known. As a rule, the composition of the filler will correspond approximately to that of the base material, to avoid "hot cracking". Examples of suitable filler are Oerlikon Alufil 5Si (which has approximately 5%wt silicon), Alufil 5Mg (approximately 5%wt magnesium) and Alufil 99.5 (99.5% pure aluminium). Depending on the spacing desired, wire of 0.8mm to 1.2mm diameter may be appropriate, with feed rates of 10-15 metres per minute being typical. The nature of aluminium brings a risk that the hard elements may sink into the base material through over-heating. The parameter known in the art as interpass temperature should normally be around 150°C, but this can be achieved quickly because the elements are small. Normally in Al-Al welding one would pre-heat the parent material to 100°-120°C to assist flow, but to avoid overheating the present technique can be performed without pre-heating. One may also allow cooling by stopping and starting in any given area. Larger pieces will dissipate heat more quickly, mitigating the problem. Although the exact welding apparatus may not be critical, MIG welding in pulse mode is believed to be particularly suitable for achieving good flow without overheating. TIG (inert gas-tungsten arc welding) welding, which is commonly used in AC mode for aluminium production, has a "cleaning" action by which the hard granules will "float" to the surface of the filler. This is not desirable, especially when the product is to be ground down to a specific size. Other types of welding such as MAG, where the gas is not purely an inert gas, may also be used. MIG and MAG are types of GMAW that can be operated in pulsed mode.

Claims: CLAIMS 1. A product primarily of aluminium including a hard-faced surface comprised by elements of hard material on the surface, and filler material serving to secure the elements to the surface. 2. A product as claimed in claim 1 wherein the filler material substantially fills the spaces between the elements, to the height of said elements. 3. A product as claimed in claim 1 or 2 wherein the hard material comprises tungsten carbide. 4. A product as claimed in claim 1, 2 or 3 wherein the hard material comprises irregular particles. 5. A product as claimed in any preceding claim wherein the hard material comprises regular solid elements such as trapezoids. 6. A product as claimed in any preceding claim wherein the filler material is aluminium-based. 7. A product as claimed in claim 6 wherein the compositions of said base and filler materials each include between one and ten percent silicon by weight. 8. A product as claimed in claim 6 or 7 wherein the compositions of said base and filler materials each include between one and ten percent magnesium by weight. 9. A product as claimed in any preceding claim wherein the filler material is melted and applied by a gas shielded arc welding process. 10. A method _ of hard- facing a surface of an aluminium article comprising the steps of (a) applying elements of hard material to the surface of an article made of an aluminium base material and (b) applying filler material to the surface by melting so as to secure the elements /particles to the surface of the article. 11. A method as claimed in claim 10 wherein the elements are applied to the surface and subsequently secured to the surface by a second step comprising the application of the filler material. 12. A method as claimed in claim 10 or 11 wherein the filler material is applied so as substantially to fill the spaces between the elements, to the height of said elements. 13. A method as claimed in claim 10, 11 or 12 wherein the hard material comprises tungsten carbide. 14. A method as claimed in claim 10, 1 1, 12 or 13 wherein the hard material comprises irregular particles. 15. A method as claimed in any of claims 10 to 13 wherein the hard material comprises regular solid elements such as trapezoids. 16. A method as claimed in any of claims 10 to 15 wherein the filler material is aluminium-based filler. 17. A method as claimed in claim 16 wherein the compositions of said base and filler materials each include between one and ten percent silicon by weight. 18. A method as claimed in claim 16 or 17 wherein the compositions of said base and filler materials each include between one and ten percent magnesium by weight. 19. A method as claimed in any of claims 10 to 18 claim wherein the filler material is melted and applied by a gas shielded arc welding process. 20. A method as claimed in claim 19 wherein a pulsed welding current is used. 21. A method as claimed in claim 19 or 20, wherein the gas shielding is by an inert gas such as argon.

Inventors: MURRAY BRIAN GEORGE, MURRAY, BRIAN, GEORGE
Applicants: BGM PATENTS LTD, MURRAY BRIAN GEORGE, BGM (PATENTS) LIMITED, MURRAY, BRIAN, GEORGE
Application year: 2000
Main classification: B23K9
IPC codes: B23K9