Substrate facing method, body and kit

Details Substrate facing method, body and kit Substrate facing method, body and kit

2000-02-18

2002-04-09

Dunn, Tom (Department: 1725)

Electric heating

Metal heating

For deposition welding

C219S093000, C219S117100

Reexamination Certificate

active

06369344

ABSTRACT:

This invention relates to a method of facing a substrate, a facing body for facing a substrate and a kit for facing a substrate. The method, body and kit ensure or obtain an improved degree of adhesion between the substrate and the facing body, which may be done, for example, to improve the wear resistance of faced surfaces, and in a convenient and easily employed way.
It is known to apply hard facing materials to surfaces of components, tools and implements which may be subject to wear in order to improve their wear resistant or cutting properties. An example of a hard facing material is tungsten carbide, which, in a known process, is positioned on a metal surface and then fixed in place by means typically of brazing, or soldering onto the surface. Usually, the tungsten carbide is in the form of small regular shaped blocks, often referred to as tips or inserts.
WO-A-9527588 discloses a method for facing a substrate, for example, a stabiliser for a drill string, using such tungsten carbide blocks of rectangular shape having sides of about 13 mm×5 mm and thicknesses of 3 mm. The entire contents of WO-A-9527588 are incorporated by reference herein for all purposes.
In WO-A-9527588, the following steps in a method of facing a substrate are described:
a) Tungsten carbide blocks are first treated by spraying, on a contact surface thereof, a layer of nickel alloy of about 0.25 mm thick.
b) The tungsten carbide blocks are then placed, with their sprayed faces being directed towards the substrate, in holes in a perforated mat of rubber. The holes are shaped so that the blocks form an interference fit therein. Typically the mat is of rectangular shape with sides 10 cm by 15 cm and a thickness of 3 mm. The mat conventionally comprises from 10 to 1,000 holes for the reception of the tungsten carbide blocks.
c) The flexible mat is then positioned upon the surface of the substrate, for example, a stabiliser, fishing tool or any other surface, whereupon it substantially conforms to the shape thereof whilst at the same time retaining each of the tungsten carbide blocks in a predetermined location.
d) The blocks are then each welded to the substrate using an electrical welding machine, the machine being set to apply a voltage of 75 volts and a current of 5000 amps to produce a weld joint or connection.
e) After the blocks have been welded to the substrate surface, the mat is removed, the substrate is heated to a temperature of between 80° C. and 150° C. (preferably about 125° C.) and sprayed with a nickel alloy to a thickness of 0.25 mm. The purpose of this is to reduce susceptibility to oxidation during subsequent processing.
f) The substrate is then further heated to a temperature of between 200° C. and 400° C. (preferably about 250° C.) and the entire surface is again sprayed with a nickel alloy until a layer of thickness about 3.5 mm has been built up; during spraying the temperature of the area around each block is raised to between 1050° C. and 1150° C. so that the alloy fuses.
The faces of the tungsten carbide blocks which contact the substrate, (hereinafter known as contact faces thereof), are substantially planar and make only a single point contact with the substrate if the substrate is curved. It will be appreciated that a substantially triangular void will be formed between the contact face and the substrate. This substantially triangular shaped void is filled with molten metal during the fusing process.
Furthermore, when using relatively large inserts, or when working with a flat substrate, the quality of the weld is unreliable due to the large areas of contact between the insert and the substrate and therefore the variable current density at the contact points and hence the temperature generated by resistance heating. In addition, the braze thickness is inconsistent.
Moreover, it has been facing that arcing can sometimes occur between those portions of the contact face and the substrate which have sufficient proximity to one another but which are not in contact with one another. This in turn reduces the quality of the weld as the welding current is distributed over a larger than desirable area.
Furthermore, step a) above is required in order to ensure that there is brazing material between the contact face of each block and the substrate, while step b) can be awkward and time consuming.
It is an object of the present invention to mitigate the problems of the prior art.
Accordingly, the present invention provides a method of facing a substrate comprising the steps of:
a) applying a plurality of facing bodies to a carrier in a pattern corresponding to the desired pattern of the bodies of the faced substrate, the carrier having holes positioned substantially centrally with respect to each body and each body having, on a contact face thereof to be fixed to said substrate, raised weld elements which serve to locate said contact face substantially parallel and spaced from the substrate;
b) applying the carrier to the substrate with said contact faces of the bodies facing the substrate;
c) electrically welding each body to the substrate by applying a welding tip to the body exposed through said hole, said weld elements ensuring that a gap remains between said contact face and substrate after welding; and
d) brazing said bodies to said substrate so that brazing material flows between said bodies and the substrate.
Preferably, said bodies have a first face opposite said contact face, which first face is adhered to one side of said carrier. In which case, preferably, the method further comprises the step of:
e) before step d) above, peeling the carrier from the first faces of the bodies, step a) above including the step adhering with the releasable adhesive. Preferably, said carrier is paper. Alternatively, said carrier may be burnt off before step d).
Alternatively, said carrier may comprise a perforated rubber mat, said bodies being pressed into and retained by respective perforations which correspond in size and shape with the bodies.
The method preferably further comprises the step of:
f) before step d) above, but after step e) if applicable, heating the bodies and the substrate to a temperature of between 80° C. and 150° C. (preferably about 125° C.) and spraying with a stabiliser to inhibit oxidation. Said stabiliser may comprise a nickel alloy or a fluxing agent, and may be about 0.25 mm thick.
The method preferably further comprises the steps of:
g) after step f) above, further heating the bodies on the substrate to a temperature of between 200° C. and 400° C. (preferably about 250° C.) and spraying with braze material, preferably a nickel alloy; and wherein step d) above comprises fusing the alloy at a temperature of between 1050° C. and 1150° C.
Such a method has numerous advantages. An improved current path is created by the raised weld elements which reproducibly determines the contact between the bodies and the substrate. This consequently improves and makes more consistent the weld of the body to the substrate. Moreover, a consistent gap is left between the contact face and the substrate after welding so that the braze is drawn under the bodies by capillary action and the amount of braze is balanced. That is to say, with a flat substrate, the braze will reliably be of even thickness.
Moreover, because a gap is reliably produced for the braze material to be introduced under the bodies, step a) of the prior art method mentioned above can be eliminated. As a result, the carrier can be made of paper or card and the bodies can be adhered thereto as a first step in an automated process. On the other hand, the bodies could still be supplied loose for insertion in a rubber mat, as described in WO-A-9527588.
Accordingly, a second aspect of the present invention provides a facing body suitable for facing a fishing tool or drill string stabiliser for use in oil and gas industry drilling, comprising a body having a contact face and a working face opposite the contact face, wherein the contact face comprises spaced raised weld elements which serve to locate said contact face subst

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