Posted on
Your machine is down and you pull out a faulty servomotor and send it out for repair. The diagnosis is quick, there is coolant or oil in your motor and it needs to be rebuilt. Your motor had a seal on the shaft, sealed plugs, and gaskets between all of the exposed parts. How did your servo motor fill with oil?
There are a number of common routes liquids can take to get into your motor. Oil and coolant are killers of servomotors, so you need to know these routes in order to prevent liquid intrusion from happening again.
Where’s the Leak?
Shaft Seal:
- Reusing old seals reduces their effectiveness.
- Replace seal after scheduled maintenance.
- Replace seal after every repair.
Environmentally Sealed Plugs:
- Pins get loose over time.
- Always replace worn plugs.
Servo Motor Connectors:
- Liquid enters between motor & connectors.
- Liquid in gap wear out plus & connectors.
- Mate connectors to matching connectors.
- Seal both sides of mated connectors.
Stators Made of Stacked Laminations:
- Liquid will leak through stack.
- Metal casing around stator prevents leaks.
- Casing is not usually present.
- Seal laminations with two part epoxy.
Direct Spray of Coolant or Oil:
- Check for sprays.
- Modify motor to limit exposure.
- Modify cabling to limit exposure.
How To Keep Coolant and Oil Out:
Replace Shaft Seal When the Motor Is Worked on
Routine maintenance? Replace the seal. Changing bearings? Replace the seal. It is common for maintenance personal to reuse old seals versus replacing with new ones due to time constraints, budget, or laziness.
Even Environmentally Sealed Plugs Leak over Time
Replace worn plugs especially if there are loose pins that liquid could get around.
Servo Motor Connectors Need to be Mated
Even sealed connectors need to be mated with matching sealed cable connectors to ensure proper protection. Unsealed cable connectors will allow contaminants into gap between motor and cable connectors. As no seal is perfect, this unnecessary exposure to the plug surface will lessen the time it takes for contaminants to infiltrate the connector.
Stacked Laminations Allow Liquid to Leak through
AC servo motors have a stator that is made up of stacked laminations which will allow liquid to slowly leak through them. Some brands, such as Yaskawa, put a thin metal case around the stator to prevent liquid intrusion. Many other manufacturers such as Fanuc do not and just paint over the laminations. We have found that sealing the laminations with a two part epoxy paint significantly reduces the chance of contamination through the laminations.
Avoid Direct Spray on Servo by Oil or Coolant
Make sure that your servo is not being directly sprayed by oil or coolant. If it is not possible, there are many custom solutions out there to modify the motor or cabling to limit exposure.
In Summary...
These are some general tips on preventing liquid intrusion into your servo motor. If your servo motor is flooded and you need help, send it in to us and we will repair your servo and work with you to find a way to prevent flooding in the future.
