BS ISO 6336-6:2019 pdf free.Calculation of load capacity of spur and helical gears.
Variable loads resulting from a working process, starting process or from operation at or near a critical speed will cause varying stresses at the gear teeth of a drive system. The magnitude and frequency of these loads depend upon the driven machine(s), the driver(s) or motor(s) and the dynamic mass elastic properties of the system.
These variable loads (stresses) may be determined by such procedures as
— experimental measurement of the operating loads at the machine in question,
— estimation of the spectrum, if this is known, for a similar machine with a similar operating mode, and
— calculation, using known external excitation and a mass elastic simulation of the drive system, preferably followed by experimental testing to validate the calculation.
To obtain the load spectra for fatigue damage calculation, the range of the measured (or calculated) loads is divided into bins or classes. Each bin contains the number of load occurrences recorded in its load range. A widely-used number of bins is 64. These bins can be of an equal size, but it is usually better to use larger bin sizes at the lower loads and smaller bin sizes at the upper loads in the range. In this way, the most damaging loads may be limited to fewer calculated stress cycles and the resulting design is more accurate regarding the effective load. It is recommended that a zero-load bin be included so that the total time used to rate the gears matches the design operating life. For consistency, the usual presentation method is to have the highest torque associated with the lowest numbered bins, such that the most damaging conditions appear towards the top of any table.
The cycle count for the load class corresponding to the load value for the highest loaded tooth is incremented at every load repetition. Table 3 shows as an example of how the torque classes defined in Table 4 can be applied to specific torque levels and correlated numbers of cycles.BS ISO 6336-6 pdf download.