LUBRICATING MINIATURE current literature BEARINGS Extreme Environment Seals. Research was At Stockholm, recently, the F.A.I. world cham performed on the development and evaluation of pionship control-line team race was won for composite materials suitable for use as static and Britain with an aircraft equipped with an Eta 15 Mk . dynamic seals at temperatures ranging from I I engine, built by Eta Instruments Ltd., and cryogenic to 1,500°F. and at pressures up to believed to be the most powerful engine in its class 5,000 lb/sq.in. Whilst it is pointed out that in the world. This is a 2.5 c.c. diesel engine. With metallic composite materials are not intended to an engine of such a diminutive size operating with be used where conventional materials are applicable 15,000 and 20,000 r.p.m. the method utilised to they can be used to solve problems brought about support the crankshaft is obviously of great import by the space age. It was reported that stainless ance; it must be rigidly held and yet subjected to steel skeletons impregnated with indium made the minimum rotational constraint. Two Hoff good static seals at —320°F. and that such compo mann miniature ball bearings are used to locate sitions as babbitt-molybdenum (40% concentration) the crankshaft and are mounted at either end of an and babbitt-stainless steel (40% concentration) extended one-piece aluminium alloy housing that is were also found to have merit for this application. bolted directly on to the front of the aluminium pressure diecast crankcase. A Hoffmann N6358 Various composite materials were evaluated as ball bearing (⅝-in. o.d.) is fitted at the front and a potential high temperature static seal materials. Hoffmann S1 V2 (¾-in. o.d.) at the rear of the A two-inch disc made of silver-molybdenum (40% housing. The counter-balanced forged steel crank concentration) retained gas pressure from zero to shaft has a main shaft 0.25 in. o.d. 5,000 lb/sq.in. at 1,200°F. despite repeated tem perature and pressure cycling. An O-ring 6½ in. o.d. and 3/16 in. dia. cross-section, machined from silver-molybdenum (30% concentration) was evaluated at temperatures up t o 955°F. A mixture of sodium and potassium nitrate, which has a liquid range of 300 to 1,000°F. was used to heat the O-ring, which sealed air and nitrogen. The evaluation showed that the O-ring can be employed as a high temperature seal although its full potential was not realised because of irregularities on the surface of the O-ring. To ensure that the bores of the bearings are In a programme t o develop a hydraulic system t o accurately aligned they are assembled in the front operate at about 4,000 lb/sq.in. and 1,000°F. a housing simultaneously with the aid of a special number of seal configurations were fabricated and hand-operated fixture equipped with two reference evaluated in a full-scale rig using a reciprocating spigots which locate in the bores of the bearings. piston rod. Stainless steel-silver indium and Correct lubrication is very important. This is molybdenum-silver composites were used to applied in the form of castor oil which is contained fabricate wedge-shape and other rod seals. After in the fuel. Fuel consists of 45 % paraffin, 30% one of the seals had been subjected to about ether, 22 % castor oil and 3 % amyl nitrate. 115,000 reciprocation cycles and five thermal cycles at 900 to 1,000°F. without leaking, it was This two-stroke diesel engine has a swept volume of 2.484 c.c. and weighs 6.3 oz. developing 0.4 h.p. concluded that the performance was superior to at 16,800 r.p.m. The corresponding power/weight that of seals from other sources which developed ratio is 1.0 b.h.p./lb. and specific output is 161 excessive leakage before 15,000 cycles. (Leon L. b.h.p./litre. Smith, II T Research Institute, Lubrication Engineer ing, March, 1964). Approximately 4,000 Eta engines are built every year and about 60% are exported. Besides pro viding power for model aircraft, engines u p to 5 c.c. are installed in model racing cars, hydroplanes and Boundary Lubrication of Chrome Steel. This model boats. It is interesting to note that Mr. K. short note states that the use of iodine-anisole or Bedford, designer of the Eta engines, currently iodine-anisole-turbine oil as boundary lubricants holds the European speed record for 5 c.c. model for chrome steel, rather than turbine oil alone, racing cars. resulted in a reduction of the coefficient of friction The illustrations show the Eta 2.5 c.c. engine on and a marked decrease in wear. (R. S. Owens and R. W. Roberts, Wear, Nov./Dec, 1964). the right and the 5 c.c. unit on the left. 20 SCIENTIFIC LUBRICATION , May. 1965
Industrial Lubrication and Tribology – Emerald Publishing
Published: May 1, 1965
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