716. Q.—­What is the composition of the brass used for engine bearings?

A.—­The brass bearings of an engine are composed principally of copper and tin.  A very good brass for steam engine bearings consists of old copper 112 lbs., tin 12-1/2 lbs., zinc 2 or 3 oz.; and if new tile copper be used, there should be 13 lbs. of tin instead of 12-1/2 lbs.  A tough brass for engine work consists of 1-1/2 lb. tin, 1-1/2 lb. zinc, and 10 lbs. copper; a brass for heavy bearings, 2-1/2 oz. tin, 1/2 oz. zinc, and 1 lb. copper.  There is a great difference in the length of time brasses wear, as made by different manufacturers; but the difference arises as much from a different quantity of surface, as from a varying composition of the metal.  Brasses should always be made strong and thick, as when thin they collapse upon the bearing and increase the friction and the wear.

717. Q.—­How is Babbitt’s metal for lining the bushes of machinery compounded?

A.—­Babbitt’s patent lining metal for bushes has been largely employed in the bushes of locomotive axles and other machinery:  it is composed of 1 lb. of copper, 1 lb. regulus of antimony, and 10 lbs. of tin, or other similar proportions, the presence of tin being the only material condition.  The copper is first melted, then the antimony is added, with a small proportion of tin-charcoal being strewed over the surface of the metal in the crucible to prevent oxidation.  The bush or article to be lined, having been cast with a recess for the soft metal, is to be fitted to an iron mould, formed of the shape and size of the bearing or journal, allowing a little in size for the shrinkage.  Drill a hole for the reception of the soft metal, say 1/2 to 3/4 inch diameter, wash the parts not to be tinned with a clay wash to prevent the adhesion of the tin, wet the part to be tinned with alcohol, and sprinkle fine sal-ammoniac upon it; heat the article until fumes arise from the ammonia, and immerse it in a kettle of Banca tin, care being taken to prevent oxidation.  When sufficiently tinned, the bush should be soaked in water, to take off any particles of ammonia that may remain upon it, as the ammonia would cause the metal to blow.  Wash with pipe clay, and dry; then heat the bush to the melting point of tin, wipe it clean, and pour in the metal, giving it sufficient head as it cools; the bush should then be scoured with fine sand, to take off any dirt that may remain upon it, and it is then fit for use.  This metal wears for a longer time than ordinary gun metal, and its use is attended with very little friction.  If the bearing heats, however, from the stopping of the oil hole or otherwise, the metal will be melted out.  A metallic grease, containing particles of tin in the state of an impalpable powder, would probably be preferable to the lining of metal just described.

718. Q.—­Can you state the composition of any other alloys that are used in engine work?