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Magnetic Degaussing: Why it is Critical for Electric Motor Repair?

05/04/2021

2021-03-degaussing a shaft for electric motor repairOne of the extra steps we can perform at HECO when performing repairs, maintenance, or rebuilds on your electric motors is magnetic degaussing. While some may feel this step is unnecessary, experience has taught us that it can help prolong the life of your bearings and your motor!

Why Magnetic Degaussing of Motor Components is Important

You may be wondering why magnetism is an issue -- are motors all about electromagnetism and currents? It's true that AC electric motors experience magnetic induction via an electromagnetic field in the motor windings. However, we're talking about a different type of magnetism: one that can damage your motor instead of make it turn.

The type of magnetism that is a source of concern would be, for example, placing a metal screwdriver against the end of the motor shaft and having it remain in place when you remove your hand. That is the kind of magnetism that causes problems. More specifically, magnetized components parts can result in bearings that appear to have been subjected to shaft circulating currents and static discharge -- and these can cause serious damage to motor bearings.

How HECO Performs Magnetic Degaussing

At HECO, we use a Gauss meter to measure the magnetic level of the various components within your electric motor. We then record those values in gauss units. For reference, a typical refrigerator magnet measures at about 100 gauss while a powerful electromagnet (like you would find in an MRI machine) could be around 15,000 gauss.

The individual gauss values are then mapped out on a diagram that shows the key components in your motor out to document what we found and help determine if any parts need degaussing (i.e., demagnetized). If a component is above a certain gauss level, then we recommend degaussing.

The degaussing is accomplished by using a demagnetizing unit. If, for example, the part that needs to be degaussed is a shaft, wires from the demagnetizing unit will be wrapped around the shaft. The demagnetizing unit will perform what is called a downcycle, which uses full wave DC to eliminate any residual magnetism that is present. Then the auto degauss will reverse polarity to gradually reduce the magnetic field. When the processes are complete, the component is checked again using the Gauss meter to ensure the magnetism level is acceptable.

What Happens When Magnetic Degaussing Isn't Performed

When degaussing isn't performed, you run the danger of damage to your bearings. Shaft circulating currents can discharge and cause electrical damage to the surface of bearings. This damage takes the form of fluting, ball bearings with a frosted appearance due to surface damage, and electrical pitting caused by welding of two surfaces together. And it only takes a small amount of magnetism to cause these kinds of problems.

This surface damage to bearings will accelerate their natural wear, which means you'll have to replace them more often -- and that can get expensive. Damaged bearings will also adversely affect motor performance and lead to a catastrophic failure. Depending on how and where those damaged bearings are, they can cause damage to other moving parts within your electric motor.

Conclusion

At HECO, we are committed to the highest quality repair practices for the electric motors you are responsible for. That's why we include magnetic degaussing as a crucial step in our process. The components in your motor will be checked for problematic levels magnetism and will be degaussed before you receive them back from us. This prevents issues with shaft circulating currents and static discharge that can reduce the useful life of your motor bearings lead to damage to your motors.

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