CAN-DO: Understanding & Maximizing Product Life

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om_tech_support_JT
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CAN-DO: Understanding & Maximizing Product Life

Postby om_tech_support_JT » Mon Apr 09, 2012 12:19 pm

Q: I have a medical device that I will be introducing to the general market with your gear motors installed. Long product life is important to me and my customers. Can you explain which factors affect life, and what things should I do to maximize life from your products?

A: Most of our RoHS-compliant products are also rated for twice the expected life as conventional motors. For example, our V-series AC gearmotors are rated for 10,000 hours of operation as well as quiet operation and high torque output. Besides selecting the right product, there are numerous factors that affect longevity of our products.

<Factors>
Factors of motor and gearhead life can be classified into 3 categories. The 1st category is the environmental factor. Environmental factors may include water, dust, and/or the ambient temperature. Using products with proper protection ratings for the application environment is critical. Oriental Motor offers different IP ratings for our motors and gearheads for various environments such as IP67, IP54, or IP20. The 2nd category is the operational factor. Operational factors may include the amount of load, the type of load (such as uniform load, light impact load, or medium impact load), the operating speed, the duty cycle, as well as installation mis-alignments that may create excess overhung load and thrust load. It is important to use a product for its designed purpose and stay within the specifications provided. The 3rd category is the maintenance factor depending on the maintenance needs of the specific type of motor and gearhead. Oriental Motor’s motors and gearheads are maintenance-free.

Both environmental and maintenance factors are self-explanatory. Therefore, we will be focusing on operational factors in our discussion.

<The Motor>
The motor life can be affected by a number of factors, such as deterioration of insulation, wear of mechanical parts and deterioration of bearing that all affect the function of motor. However, in most cases the life of a motor is determined by the bearings. The bearing life is represented in terms of grease life and bearing mechanical life;

1) Grease life is affected by grease deterioration due to heat
2) Mechanical life is affected by rolling fatigue

The motor life is estimated based on the grease life, since the bearing life is more affected by grease deterioration due to heat than the load applied to the bearing. As it shown on the following equation, the temperature is the most determinant of grease life, meaning that grease life is significantly affected by temperature. The motor life is almost doubled the time when the temperature is reduced by 15 (Celsius).

Logt=6.12-1.4×(n/Nmax)-(0.018-0.006×(n/Nmax))×T
Where t:Bearing life time (hour)
n:Bearing rotating speed (r/min)
Nmax:Bearing permissible rotating speed (r/min)
However, when (n/Nmax)>0.25、we use (n/Nmax)=0.25
T:Bearing Temperature is assumed Motor surface temperature+10 (Celsius)

<Gearhead>
The gearhead life is reached when power can no longer be transmitted because the bearing mechanical life has ended. Therefore, the actual life of a gearhead varies depending on the load, how the load is applied, and the operating speed. Oriental Motor defines life under certain conditions as "rated life," based on which the life under actual operation is calculated according to load conditions and other factors. The tooth surface of Oriental Motor's gearheads is lubricated by a grease lubrication mechanism. Oiling is not required.

● Rated Life
Oriental Motor defines the rated life as the life of a gearhead under the following operating conditions:
[Conditions]
Torque : Permissible torque
Load type : Uniform load
Input speed : Reference input speed
Overhung load : Permissible overhung load
Thrust load : Permissible thrust load

● Rated Life
Lifetime under actual conditions of use is calculated based on the operating speed, load and load type, using the following formula.
The calculated lifetime represents the actual driven hours.
L (Lifetime) = L1 × K1 / [(K2)3 × f] × Tf
Where L1: Rated lifetime [hrs.] depending on the gearhead type
K1: Speed coefficient
K1 = Reference input speed / Actual input speed
K2: Load factor
K2 = Operating torque / Permissible torque
Tf: Temperature factor. Refer to chart.

For more details about product life, please click on the following link:
http://www.orientalmotor.com/products/p ... h_life.pdf

To summarize, here are things you can do to help prolong life:

1. Select a long-life rated product.
2. Make sure you have the right IP protection rating on your products to handle your specific environment.
3. Stay within specifications.
4. Lower operating temperature = longer life.
5. Keep load conditions uniform if possible. Minimize shock loads.
6. Avoid excessive overhung and thrust loads.
7. Operate at lower speeds.
8. Use brushless motor systems. Brushless motors are more efficient than AC motors and run cooler.
9. Use safety factor for torque and speed.

Please contact our knowledgeable technical support group if you have any questions.

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