bearings for 350F?

stephen thomas · Aug 30, 2021

I'm building an oven which includes a squirrel cage blower fan.
The fan is well down in the hot section and (is intended) to distribute hot air from the duct-enclosed elements out into the box. Operating temp is 325 - 350 F. Max temp is 500F.

This thing won't be used often, but the bearings need to be "reliable" in the sense of not seizing up. They can be pretty loose tolerance, there's nothing else critical about locating the blower shaft, max 1200 rpm. Only one bearing will be down just above the hot chamber separated by a 26 ga sheet. The other will be above the insulation, out in ambient air.

I have browsed the catalogs for high temp bearings, they are overkill.
Cheap is the modus for this part.
Other than "try-it-and-see" does anyone have experience using clapped out loose (sloppy) ball bearings for a hot app like that? Needs to work well a couple hours at a time, for maybe 50 hrs total. The rest is bonus.

Any preference for (non-graphite, non-exotic) plain sleeve bearings?

Thanks!
smt

DDoug · Aug 30, 2021

What do the furnace exhauster blowers use ?

Those are everywhere now, and even on gas water heaters too.
115 Volt AC Jakel 119278-00 PP-355 Draft Inducer Blower | AC Centrifugal Blowers | Blowers & Fans | Electrical | www.surpluscenter.com

gbent · Aug 30, 2021

Can you bleed off and duct some non-heated air to keep the bearing cool? Furnaces and other move the air before it gets warm.

Joe Gwinn · Aug 30, 2021

I bet the cheapest will be whatever is used for the hot-side fan in convection ovens used in home kitchens, such as those made by the Bosch group, like Thermador. Or GE, I bet. Probably a commodity part.

Milland · Aug 30, 2021

There's a range of cheap fully-ceramic ball bearings available from Ebay, when used with stainless "tolerance rings" (the wavy sheet metal gap fillers) to avoid excessive stress on ID and OD, they should be fairly reliable for this sort of application to well over 350F (zirconia ceramics can be used to 1000C).

6004-2RS Full Ceramic Bearing ZrO2 Ball Bearing 20x42x12mm Zirconia Oxide | eBay

http://www.usatolerancerings.com/uploads/PDFs/USA Tolerance Rings_Catalogue_Rev.08-28-13_A.pdf

stephen thomas · Aug 30, 2021

What do the furnace exhauster blowers use ?

Those are everywhere now, and even on gas water heaters too.

I bet the cheapest will be whatever is used for the hot-side fan in convection ovens used in home kitchens, such as those made by the Bosch group, like Thermador. Or GE, I bet. Probably a commodity part.

I was hoping someone knew a good example of same ^^^^^^^

None to tear apart here, too little info online. Though many of you have better google-foo than i do.

6004-2RS Full Ceramic Bearing ZrO2 Ball Bearing 20x42x12mm Zirconia Oxide | eBay

http://www.usatolerancerings.com/uploads/PDFs/USA Tolerance Rings_Catalogue_Rev.08-28-13_A.pdf

This is great!
I did not know about either product though must have seen the tolerance rings.
Thanks much.

smt<--- just got back last nite from a week with friends on Highland Lake, outside Hillsboro.

Milland · Aug 30, 2021

stephen thomas said:
smt<--- just got back last nite from a week with friends on Highland Lake, outside Hillsboro.

Did the skeeters getcha? Dang things have been pestering me even inside the building...

stephen thomas · Aug 30, 2021

skeeters were worse than i remember previous years, but tolerable.
At least the temps were often 10 -15 deg less than we returned to in Elmira, most days.

smt

Scottl · Aug 30, 2021

Non-sealed bearings. Wash out the existing grease and use a high temperature grease to repack.

Rickyb · Aug 30, 2021

Stephen, bearing tempering temp is somewhere around 350°. At that temp or higher the bearings will continue to temper, getting softer and softer. Insulation or ceramics is your answer.

crossthread · Aug 30, 2021

Any chance that bronze bearings with the proper high temperature grease would work. Not sure just throwing it out there for discussion.

strokersix · Aug 30, 2021

Or Teflon bushings perhaps? Just a thought. Teflon is good for high temps and as low friction bearing but not sure about both simultaneously.

Phil in Montana · Aug 30, 2021

Just change your location of the bearings to a lower temp, nothing wrong with a larger shaft with a 8 inch stick out, its done all the time. My oven has been going 35 years on the first set of bearings...Phil

Joe Gwinn · Aug 30, 2021

Phil in Montana said:
Just change your location of the bearings to a lower temp, nothing wrong with a larger shaft with a 8 inch stick out, its done all the time. My oven has been going 35 years on the first set of bearings...Phil

Yeah. I just finished looking at a few repair videos for convection domestic ovens. The hot end has no bearings. The motor bearings are it, and there is a long shaft sticking through the oven-wall insulation, with a fan blade at the far end, in the hot zone.

Commercial bakers ovens also can have fans, and may have hot-end bearings, likely of graphite running dry. Well, I looked at a few, and they also have no hot bearing. The message seems to be to avoid the hot-end bearing if at all possible.

EmGo · Aug 30, 2021

Joe Gwinn said:
Yeah. I just finished looking at a few repair videos for convection domestic ovens. The hot end has no bearings.

Yabbut .... the ceramics are cheap, I bet most stuff you see today was designed before they were available, would't take much to get a couple and give them a test. If it fits his design better, why not ?

Milland · Aug 30, 2021

strokersix said:
Or Teflon bushings perhaps? Just a thought. Teflon is good for high temps and as low friction bearing but not sure about both simultaneously.

I try to keep Teflon out of areas that get upwards of 400F. Over 500F some PTFE's can start decomposing, and the gasses can be hazardous.

Polytetrafluoroethylene - Wikipedia

Peter from Holland · Aug 31, 2021

Milland said:
I try to keep Teflon out of areas that get upwards of 400F. Over 500F some PTFE's can start decomposing, and the gasses can be hazardous.

Polytetrafluoroethylene - Wikipedia

Smoking and machining teflon is a good one

Peter

stephen thomas · Aug 31, 2021

Thanks for all the ideas and information.
Learned some things that could be useful,googling some of the links & responses.
Waiting to hear back from Accurate to see if they care to add any (cheap) suggestions.

I am glad to learn how accessible and relatively inexpensive ceramic bearings can be, and about the fact that tolerance rings are a commodity item.

However, it looks like the path is going to be move the bearing supports back 2" - 4" into or out past the insulation, have a 6" - 8" shaft extension, and use cheap common bearings. I built the fan rotor (squirrel cage) by cutting down a much longer original. So will set it up on my ex-Hardinge factory balance wheels and make sure it is not too far out of balance.

Thanks!
smt

Tony Quiring · Aug 31, 2021

Is there a material to make the shaft that has poor heat transfer?

Depending on heat cycle the shaft may still transfer heat to bearings.

Smaller diameter maybe?

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crossthread · Aug 31, 2021

Maybe castellate the shaft to act as a series of fins to sink the heat.

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