Machinery's Handbook, 31st Edition
2324 GEAR MATERIALS Good castings made of this alloy should have the following minimum physical charac teristics: Ultimate strength, 30,000 pounds per square inch; yield point, 12,000 pounds per square inch; elongation in 2 inches, 10 percent. These alloys, especially No. 65, are adapted to chilling for hardness and refinement of grain. No. 65 is to be preferred for use with worms of great hardness and fine accuracy. No. 63 is to be preferred for use with unhardened worms. Gear Bushings: For bronze bushings for gears, SAE No. 64 is recommended of the fol lowing analysis: copper, 78.5 to 81.5; tin, 9 to 11; lead, 9 to 11; phosphorus, 0.05 to 0.25; zinc (max), 0.75; other impurities (max), 0.25 percent. Good castings of this alloy should have the following minimum physical characteristics: Ultimate strength, 25,000 pounds per square inch; yield point, 12,000 pounds per square inch; elongation in 2 inches, 8 percent. Flanges for Composition Pinions: For brass flanges for composition pinions ASTM B30-32T, and SAE No. 40 are recommended. This is a good cast red brass of sufficient strength and hardness to take its share of load and wear when the design is such that the flanges mesh with the mating gear. The composition is as follows: copper, 83 to 86; tin, 4.5 to 5.5; lead, 4.5 to 5.5; zinc, 4.5 to 5.5; iron (max) 0.35; antimony (max), 0.25 percent; aluminum, none. Good castings made from this alloy should have the following minimum physical characteristics: ultimate strength, 27,000 pounds per square inch; yield point, 12,000 pounds per square inch; elongation in 2 inches, 16 percent. Materials for Worm Gearing.— The Hamilton Gear & Machine Co. conducted an exten sive series of tests on a variety of materials that might be used for worm gears, to ascertain which material is the most suitable. According to these tests chill-cast nickel-phosphor- bronze ranks first in resistance to wear and deformation. This bronze is composed of approximately 87.5 percent copper, 11 percent tin, 1.5 percent nickel, with from 0.1 to 0.2 percent phosphorus. The worms used in these tests were made from SAE-2315, 3 1 ∕ 2 percent nickel steel, case-hardened, ground, and polished. The Shore scleroscope hard- ness of the worms was between 80 and 90. This nickel alloy steel was adopted after numer- ous tests of a variety of steels, because it provided the necessary strength, together with the degree of hardness required. The material that showed up second best in these tests was a No. 65 SAE bronze. Navy bronze (88-10-2) containing 2 percent zinc, with no phosphorus, and not chilled, per formed satisfactorily at speeds of 600 revolutions per minute, but was not sufficiently strong at lower speeds. Red brass (85-5-5) proved slightly better at from 1500 to 1800 revolutions per minute, but would bend at lower speeds, before it would show actual wear. Non-Metallic Gearing.— Non-metallic or composition gearing is used primarily where quietness of operation at high speed is the first consideration. Non-metallic materials are also applied very generally to timing gears and numerous other classes of gearing. Raw hide was used originally for non-metallic gears, but other materials have been introduced that have important advantages. These later materials are sold by different firms under various trade names, such as Micarta, Textolite, Formica, Dilecto, Spauldite, Phenolite, Fibroc, Fabroil, Synthane, Celoron, etc. Most of these gear materials consist of layers of canvas or other material that is impregnated with plastics and forced together under hydraulic pressure, which, in conjunction with the application of heat, forms a dense rigid mass. Although phenol resin gears in general are resilient, they are self-supporting and require no side plates or shrouds unless subjected to a heavy starting torque. The phenol resinoid element protects these gears from vermin and rodents. The non-metallic gear materials referred to are generally assumed to have the power- transmitting capacity of cast iron. Although the tensile strength may be considerably less than that of cast iron, the resiliency of these materials enables them to withstand
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