Question about bearings

[Greenman]

Can I replace an open race bearing with a sealed one in a table saw? The open race bearing loaded up with sawdust and surprise surprise, locked up and trashed the motor housing. I ordered a sealed bearing for it, but there appears to be some friction at the seal. I'm wondering if that seal might melt and lock up the bearing and trash yet another motor housing.

 

[boomerang]

I believe you'll be fine. If it was in an application where it was running at high rpm for long periods of time with little or no cooling you might have an issue but those seals can handle high heat. There is lubrication inside the bearing which lubricates the seal as well as the bearing. If the seal overheats, it will not melt, it will harden. You'll lose the sealing properties but the bearing will still be shielded from the sawdust to an exponentially greater degree than what was in there originally. Most electric motors have internal fans for cooling and the housing for the bearing acts as a heat sink.

There is a lot of information in the article below and that can be detrimental but the following paragraphs I think are key to your query.

http://www.machinedesign.com/mechanical-drives/lowdown-sealed-bearing-speed-limits

"The contact-type seal bearing provides maximum protection against all contaminants. It gives the best protection against dust, water, and other contaminants because the seal lip contacts the inner ring, separating and protecting the rolling elements from the external environment. The pressure of the rubber lip against the seal groove wall maintains seal effectiveness. However, this also reduces bearing speed capacity and increases torque. It also results in sliding friction between the seal lip and inner ring, which generates heat.

To prevent overheating, premature wear, and seal-lip seizure, it is important to keep an oil film between the seal lip and groove. A film is developed in the groove when the bearing is initially put into service and grease is pushed against the seal by the rotation of the rolling elements and retainer. Because contact seals are also usually made from nitrile rubber with steel inserts, operating temperature limits speed capacity. If the seal’s maximum temperature is exceeded, the seal material will lose elasticity and harden, causing it to wear quickly, which reduces its sealing capability. The maximum continuous operating temperature recommended for a typical nitrile rubber contact seal is 100 C."

After all that, there is a reason Bosch put in the type of bearing it put in which is I know what is going through your head. The average Joe, unless he's very well versed on bearings and their applications is not going to be able to answer your question with full certainty. But I think you'll be fine.

 

[PottedMeat]

open race bearing loaded up with sawdust

thats a weird place to find an open bearing. did you replace it off what you found or is it a bosch part number? there probably was one, just disintegrated long ago

 

[Greenman]

thats a weird place to find an open bearing. did you replace it off what you found or is it a bosch part number? there probably was one, just disintegrated long ago

The Bosch bearing is open, and their replacement bearing is open as well. I have a sealed one that I'm going to use.

 

[Greenman]

I believe you'll be fine. If it was in an application where it was running at high rpm for long periods of time with little or no cooling you might have an issue but those seals can handle high heat. There is lubrication inside the bearing which lubricates the seal as well as the bearing. If the seal overheats, it will not melt, it will harden. You'll lose the sealing properties but the bearing will still be shielded from the sawdust to an exponentially greater degree than what was in there originally. Most electric motors have internal fans for cooling and the housing for the bearing acts as a heat sink.

There is a lot of information in the article below and that can be detrimental but the following paragraphs I think are key to your query.

http://www.machinedesign.com/mechanical-drives/lowdown-sealed-bearing-speed-limits

"The contact-type seal bearing provides maximum protection against all contaminants. It gives the best protection against dust, water, and other contaminants because the seal lip contacts the inner ring, separating and protecting the rolling elements from the external environment. The pressure of the rubber lip against the seal groove wall maintains seal effectiveness. However, this also reduces bearing speed capacity and increases torque. It also results in sliding friction between the seal lip and inner ring, which generates heat.

To prevent overheating, premature wear, and seal-lip seizure, it is important to keep an oil film between the seal lip and groove. A film is developed in the groove when the bearing is initially put into service and grease is pushed against the seal by the rotation of the rolling elements and retainer. Because contact seals are also usually made from nitrile rubber with steel inserts, operating temperature limits speed capacity. If the seal’s maximum temperature is exceeded, the seal material will lose elasticity and harden, causing it to wear quickly, which reduces its sealing capability. The maximum continuous operating temperature recommended for a typical nitrile rubber contact seal is 100 C."

After all that, there is a reason Bosch put in the type of bearing it put in which is I know what is going through your head. The average Joe, unless he's very well versed on bearings and their applications is not going to be able to answer your question with full certainty. But I think you'll be fine.

Thanks for the info. I'll install the sealed bearing.
Looking around a little bit, I discovered that Bosch has admitted that there have been a lot of failures with that bearing. I'm surprised it lasted as long as it did. The housing it's mounted in is ventilated in such a way that dusty air is pulled through the bearing. I wouldn't have thought it would last a week after looking at the setup.

 

[Greenman]

Just to bring this to a conclusion, I received the new bearing (sealed), the new motor housing, (the old bearing spun in the plastic housing when it locked up, chewed out a lot of the plastic) and a set of new brushes. Just put it together and it works. Saved me about $550.