The Lafitte process was first heard of in 1905.3 It may be described as the handy application of a patent fluxing sheet between parts to be welded, and can only be used for joining iron and steel. The flux is sold as a plate, size 4 by 8 inches and about 1/16 inch thick. This plate is composed of a preparation of calcined borax and iron filings, molded over a sheet of wire gauze. The gauze is about 15 meshes to the inch length.

1 Calculated from weight of thermit powder.

2 Calculated from weight of test bar.

3 Iron Age, May 11, 1905.

The iron of the wire is low-carbon (0.08 per cent, by color determination1).

The pieces to be welded are brought to the welding heat and forced together with a Lafitte plate between the contacts. As with all smith-welding, one of the contact surfaces should be decidedly convex, so that the point of it is first brought to bear on about the middle of the other contact surface. As the two surfaces are forced together, with the plate between, the borax melts and flows out, fluxing both surfaces as it flows. The iron gauze, which is inside the plate, is also partly melted and welds itself in place on both surfaces. It is likely that the strength of the Lafitte weld is as much due to the binding action of this low-carbon iron wire as it is to the complete fluxing of the borax. If properly done, the weld should be flawless. It is not necessary to use more of the plate than will cover both surfaces. The plate can be cut with ordinary shears.

From tests made it is claimed that the Lafitte weld is as strong as the metal, in case soft steel is welded; but that in high-carbon steel there is a slight lowering of the elongation and tensile strength (due no doubt to the reheating of a specially treated product).

In all but one of these tests the tensile strength is greater for the Lafitte weld than for the body of the stock, which may indicate that an upset of metal was crowded into the weld by the pressure of welding; while with cast steel the quality of the metal might be improved by the pressure.

Hard Steel Test Mn, 1.35; C, 0.45; S, 0.045; P, 0.083; Si, 0.08

1 Specially analyzed.

Test by the French Government1 - (Toulon Arsenal)

The Lafitte method may suggest itself for stock welds, such as the joining of axle parts and in chain making; in other words, in instances of multiple welding, where the pressure machinery is handy. It is most used in France and Germany.