Machinery's Handbook, 31st Edition
Transmission Roller Chains 2637 The smaller sprockets of a drive are usually made of steel. With this material the body of the sprocket can be heat treated to produce toughness for shock resistance, and the tooth surfaces can be hardened to resist wear. Stainless steel or bronze may be used for corrosion resistance, and Formica, nylon or other suitable plastic materials for special applications. Roller Chain Drive Ratings.— In 1961, under auspices of The American Sprocket Chain Manufacturers Association (now called American Chain Association), a joint research program was begun to study pin-bushing interaction at high speeds and to gain further data on the phenomenon of chain joint galling among other research areas. These studies have shown that a separating film of lubricant is formed in chain joints in a manner similar to that found in journal bearings. These developments appear in ANSI/ASME B29.1-2011 (R2016), and are contained in Table 9. The ratings shown in Table 9 are below the galling range. The horsepower ratings in Table 9 apply to lubricated, single-pitch, single-strand roller chains, both ANSI Standard and Heavy series. To obtain ratings of multiple-strand chains, a multiple-strand factor is applied. The ratings in Table 9 are based upon: 1) a service factor of 1; 2) a chain length of approx- imately 100 pitches; 3) use of recommended lubrication methods; and 4) a drive arrange- ment where two aligned sprockets are mounted on parallel shafts in a horizontal plane. Under these conditions, approximately 15,000 hours of service life at full load operation may be expected. Table 15. Roller Chain Drive Service Factors
Type of Input Power Electric Motor or Turbine
Type of Driven Load Smooth
Internal Combustion Engine with Hydraulic Drive
Internal Combustion Engine with Mechanical Drive
1.0 1.2 1.4
1.0 1.3 1.5
1.2 1.4
Moderate Shock Heavy Shock
1.7 Substantial increases in rated speed loads can be utilized, as when a service life of less than 15,000 hours is satisfactory, or when full load operation is encountered only during a portion of the required service life. Chain manufacturers should be consulted for assis- tance with any special application requirements. The horsepower ratings shown in Table 9 relate to the speed of the smaller sprocket and drive selections are made on this basis, whether the drive is speed reducing or speed increasing. Drives with more than two sprockets, idlers, composite duty cycles, or other unusual conditions often require special consideration. Where quietness or extra smooth operation are of special importance, small-pitch chain operating over large diameter sprockets will minimize noise and vibration. When making drive selection, consideration is given to the loads imposed on the chain by the type of input power and the type of equipment to be driven. Service factors are used to compensate for these loads and the required horsepower rating of the chain is deter- mined by the following formula: Required hp TableRating Multiple Strand Factor hp tobe Transmitted Service Factor # = − Service Factors: The service factors in Table 15 are for normal chain loading. For un- usual or extremely severe operating conditions not shown in this table, it is desirable to use larger service factors. Multiple-Strand Factors: The horsepower ratings for multiple-strand chains equal sin gle-strand ratings multiplied by these factors:for two strands, a factor of 1.7; for three strands, 2.5; and and for four strands, 3.3.
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online