Gear unit selection is made by comparing actual transmitted loads with catalogue ratings. However, it is important to realise that catalogue ratings are based on a standard set of loading conditions, which inevitably change for different applications. Therefore, a service factor must be used to calculate a theoretical transmitted load, or equivalent load,before comparing with catalogue ratings. Equivalent load = actual load x service factor.
Mechanical Ratings and Service Factors
Mechanical ratings measure capacity in terms of life and/or strength, assuming 10 hours per day continuous running under uniform load conditions, when lubricated with an approved oil and working at a maximum oil temperature of 100°C, For normal application lubricant equivalent to ISO VG 320 should be used. See publication G/105 for details. When a unit transmits less than catalogue rating its life Is increased, If the running time Is more than 10 hours per day,a service factor from Table 1 ensures selection of a unit which transmits less than catalogue rating, its life therefore is increased consistent with the increased daily running time. If this increased life is not required, the service factor need not be used. Similarly the use of a service factor for less than 10 hours per day gives a reduced life consistent with the reduced daily running time. Catalogue ratings allow 100% overload at starting, braking or momentarily during operation, upto 10 times per day. The unit selected must therefore have a catalogue rating equal to, or greater than half the maximum overload. If the unit is subjected to sustained overloads or to shock loads, these must be reflected in the chosen service factor if overloads can be calculated or estimated then the actual loads should be used instead of a factor. When detailed operating conditions are not available Table 3, page 4 gives a guide to the load characteristics of many varied applications, and should be used to determine appropriate service factors from table 1.