This has long been a favorite alloy for forming bearings for the journals of shafts, etc. The large proportion of tin which it contains renders it essentially anti-friction, while the copper and antimony render it hard enough for light work. When the bearings have to carry a great weight, however, the Babbitt metal is too soft, and yields under the pressure. To keep it in place and give it strength enough, the inventor uses cast-iron boxes having one or more recesses or cups for the reception of the soft metal, which is not only east in place, but so managed that it shall be literally brazed or soldered to the more rigid cast-iron. The following are the directions given by the inventor for preparing and using this metal: -
"In the first place, I melt four pounds of copper; and when melted, add by degrees twelve pounds best quality Banca tin; then add eight pounds regulus of antimony; and then twelve pounds more of tin, while the composition is in a melted state.
"After the copper is melted, and four or five pounds of tin have been added, the heat should be lowered to a dull red heat, in order to prevent oxidation; then add the remainder of the metal, as above named.
"In melting the composition, it is better to keep a small quantity of powdered charcoal in the pot, on the surface of the metal.
"1 make the above composition in the first place, which I call hardening; then, as I want to use for lining-work, I take one pound of the hardening and melt with two pounds Banca tin, which produces the lining-metal I now use, which I consider the best I have ever used. So that the proportions for lining-metal is four pounds copper, eight regulus of antimony, and ninety-six pounds tin.
"The object I have in first preparing the hardening, as above mentioned, is economy; for when the whole is melted together, I find there is a great waste of metal, as the hardening is melted at a much less degree of heat than the copper and antimony separately.
"I find, in my practice, that in melting the lining-metal, or tin for tinning the boxes, there is some oxidation on the surface of the metal, which should be skimmed off. This oxide I save, and, when I get a quantity, put it into a black-lead crucible, add about one tenth in bulk of pounded charcoal, expose it to a smart red heat, which brings it back again to metal fit for use.
"The box or article to be lined, having been cast with a recess for soft metal, is to be nicely fitted to a former, which is made the same shape as the bearing, except being a hair larger than the bearing.
"Drill a hole in the box for the reception of the metal, say half or three quarters of an inch, according to the size of the box. The box having been thus prepared, coat over the part not to be tinned with a clay wash; wet the part to be tinned with alcohol, and sprinkle on sal ammoniac, ground as fine as common table salt. Heat the box till a fume arises from the sal ammoniac, and immerse it in a kettle of Banca tin melted, care being taken not to heat it so that it oxidizes.
"After the box is tinned, should it have a colored appearance, sprinkle a little sal ammoniac, which will make it of a bright silver color, and cool it gradually in water; then take the former, to which the box has been fitted, and coat it over with a thin clay wash, and warm it so that it will be perfectly dry; heat the box until the tin begins to melt; lay it on the former and pour in the metal, which should not be so hot as to oxidize, giving the metal a head, so that as it shrinks up it will fill up. After it is sufficiently cool take it off the former and scour the box, so that there may be no sand or dirt on it, which would injure the bearing.
"A shorter method may be adopted when the work is light enough to handle quickly, viz., when the box is prepared for tinning it may be immersed in the lining-metal instead of the tin, brushed lightly in order to remove the sal ammoniac from the surface, placed immediately on the former, and lined with the same heat."