Zhaowei Machinery & Electronics Co., Ltd.

How to Choose Gear Motor Safety Factors

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When selecting gear motors, the safety factor refers to the coefficient of the gear motor (generally >1; the capacity of gear motor > motor capacity) , which is determined based on the factors including service condition and driven machine, in order to achieve a surplus of rated mechanical energy and thermal energy in the gear motor. Factors influencing include running time and load (also known as loading conditions) are also considered.  

motor safety factor

One of the basic requirements for gear motor safety factors is ensuring that the gear has a suitable bearing capacity. At present, for the bearing capacity of the tooth surface, root and bonding, although there is a standard calculation method, it is probably still difficult to complete the gear transmission design for engineering and technical personnel who have little experience in this area. This is because there are so many factors (commonly shown as coefficients or parameters) and some of them are contradictory and influence each other. In the calculation for the bearing capacity of gear motor devices, it is important to choose the appropriate safety factor. This is because a safety factor that’s too high will increase the outer dimension and weight of the transmission device, increasing the manufacturing cost in the end. If the safety factor is too low, it may lead to unexpected failure and danger. An appropriate safety factor should be at a reasonable manufacturing cost and meet given reliability requirements.  

Minimum safety factor for gear contact and bending fatigue strength:

High reliability (failure rate ≤ 1/10000) 1.50 ~ 1.60, 2.00

Relatively high reliability (failure rate ≤ 1/1000) 1.25-1.30, 1.60

General reliability (failure rate ≤ 1/100) 1.00 ~ 1.10, 1.25

Low reliability (failure rate ≤  1/10) 0.85, 1.00

Key points of selecting the safety factors of the gear motor:

  1. Expected discreteness of machining accuracy and material quality of all structural elements. 
  2. Consequences caused by damage and failure of gear. For example, the consequences caused by tooth bending and fracture are generally more serious than those caused by surface fatigue of the gear (pitting), especially in situations related to personal safety, such as the use of cranes, elevators, etc.
  3. Reliability of data related to assembly, installation, and usage conditions.
  4. Reliability of the calculation method.

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