Method for applying material to a substrate

DETAILED DESCRIPTION I claim: 1.
A process for brazing refractory particles onto a substrate, which process comprises applying to the substrate a brazing material, a particulate refractory material to be brazed onto the substrate and a binder composition; and connecting the substrate to a source of an electric current to cause the current to flow through the substrate whereby the substrate is heated to sufficient temperature to cause the brazing material to fuse.
2.
A process as claimed in claim 1 wherein after brazing the refractory material onto the substrate the substrate is re-heated to cause thermal tempering thereof by passing an electric current through the substrate.
3.
A process as claimed in claim 1 wherein the particulate refractory material is selected from the carbides, nitrides, borides and silicides of nickel and tungsten and has a mass median particle size in the range 0.
01 to 1.
5 mms.
4.
A process as claimed in claim 1 wherein the brazing material is selected from a cobalt-based and a nickel-based alloy.
5.
A process as claimed in claim 1 wherein the binder composition comprises a material selected from a volatile material and a thermally decomposable material which is substantially eliminated from the coating on the substrate during the brazing process.
6.
A process as claimed in claim 5 wherein the binder comprises an acrylic polymer.
7.
A process as claimed in claim 1 wherein the coated substrate is heated by passing a current of from 50 to 250 amps at a voltage of 10 to 50 volts AC or DC through it.
8.
A process as claimed in claim 1 wherein the coated substrate is heated in a protective atmosphere or under vacuum.
9.
A process as claimed in claim 8 wherein the protective atmosphere is provided at least in part by the products of volatilisation and/or decomposition of the binder composition.
10.
A process as claimed in claim 1 wherein the overall coating applied to the substrate comprises 5 to 10 parts of tungsten carbide refractory grit, 1 to 2 parts of a cobalt or nickel based brazing powder, from 2 to 5 parts of the binder and, optionally, from 1 to 2 parts of a flux, all parts being by dry weight