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nc5a
01-13-2016, 01:34 AM
I searched this forum and PM for ideas on an induction bearing heaters and didn't find anything that supported or disproved my idea, so here goes.

I'm in the process of rebuilding 1 of the 7 machine tools I recently purchased and needed to replace bearings in a 10 HP lathe drive motor. I've used the hot pan of oil, and a torch but for the past 30 years I've used a commercial induction bearing heater at work. But now that I'm retired I don't have access to the nice induction bearing heater from work so I decided to build one.

As I searched for parts to build one I got to thinking of a faster cheaper way to build or buy an induction heater that would heat bearings fast and easy. Which led me to thinking about an induction cooking surface. I found nothing on the internet about using an induction cooking surface to heat bearings but knowing the basics of how induction heating works I figured it would work. Maybe not as fast or convenient as a commercial induction heater but work just the same.

So I bought an induction cooking plate for $55 and put it to the test heating the bearings for the motor. WOW! I was very impressed with the results. The bearing ID is roughly 1.5" and the OD is roughly 3". The instructions say minimum pan size is 5" so I was concerned that a 3" bearing wouldn't heat up so I placed a 6" ring around it first and set the plate for 212 deg F. And in 2 minutes and 45 seconds the bearing was 192 deg F according to my IR gun, what a discovery. Next I took the ring away and heated one of the old bearings in the center of the plate at 212 deg F and had basically the same result 188 deg F in 2 minutes 45 sec.

So if you're looking for an induction bearing heater that you can also cook lunch on get an induction hot plate, I think you'll be impressed.

Ron

http://i738.photobucket.com/albums/xx25/roman52/4-IMG_2676_zps6ea5gcli.jpg (http://s738.photobucket.com/user/roman52/media/4-IMG_2676_zps6ea5gcli.jpg.html)

http://i738.photobucket.com/albums/xx25/roman52/6-IMG_2678_zps3segdrpw.jpg (http://s738.photobucket.com/user/roman52/media/6-IMG_2678_zps3segdrpw.jpg.html)

http://i738.photobucket.com/albums/xx25/roman52/8-IMG_2680_zpsgcuijhfb.jpg (http://s738.photobucket.com/user/roman52/media/8-IMG_2680_zpsgcuijhfb.jpg.html)

http://i738.photobucket.com/albums/xx25/roman52/3-IMG_2675_zps2hie9evf.jpg (http://s738.photobucket.com/user/roman52/media/3-IMG_2675_zps2hie9evf.jpg.html)

Magicniner
01-13-2016, 03:24 AM
Great Idea!
It would be interesting to see what was possible with a thin ceramic insulator under the item to be heated and an insulating cover,

- Nick

nc5a
01-13-2016, 03:42 AM
The rule for induction heating this way is the surface has to be magnetic so introducing a ceramic insulator under the bearing would prevent the hot plate from turning on. Also, in my opinion an insulated cover isn't necessary, the heating take place very fast with this type of heater and in general you only need around 200 deg F or 150 to 160 deg F delta T.

Noitoen
01-13-2016, 04:02 AM
I had a regular induction heater for bearings, the type you stick the bearing on a magnetic core and at the end of the heating cycle, there was a small automatic demagnetizing cycle that insured that the bearing was not magnetized. You should check if the cooled bearing is not magnetic and attract magnetic debris.

Boostinjdm
01-13-2016, 10:33 AM
What about smaller bearings. Maybe down to 1/2" ID.

10KPete
01-13-2016, 10:42 AM
Hey, that's great Ron!! Thanks for sharing your find and 'research' Now if you could just get one to go to heat treat
temps.......:rolleyes:

Pete

lakeside53
01-13-2016, 11:45 AM
Nice. Good idea. I'm going to get one!

I use a typical convection microwave - with NO microwave! Works well (170F-450F) for bearings, baking paint and heat treat tempering. Often you need to heat the female part (like a housing) and in my case , almost always Almag castings. As mentioned above, induction doesn't help unless it's steel/iron etc.

Willy
01-13-2016, 12:54 PM
Yes great idea and I can vouch for the fact it works very well.
I picked up a new induction "hot plate" two years ago on Ebay for $30 shipped. It was listed as having a blemish but all I could find was a small crack in a decorative molding.
Very fast and the nice thing is you have the option of presetting the desired temp.

Magicniner
01-13-2016, 01:19 PM
The rule for induction heating this way is the surface has to be magnetic so introducing a ceramic insulator under the bearing would prevent the hot plate from turning on.

I did say thin, in my opinion magnetic sensing of the item to be heated and it's size could still work through a thin insulator.


Also, in my opinion an insulated cover isn't necessary, the heating take place very fast with this type of heater and in general you only need around 200 deg F or 150 to 160 deg F delta T.

For heating bearings no opinion is necessary as clearly demonstrated by the OP.
Achieving higher temperatures could expand the potential uses in the workshop considerably though,

- Nick

ironmonger
01-13-2016, 01:23 PM
I would only add that a thin insulating ceramic layer would have no effect on the magnetic field. The coil is not at the immediate surface of the hot plate, so adding a little more would be fine, although the surface of the heating plate is not a great conductor of heat in the first place. There might be little to gain, especially at the low temperature's that you are using.

I use a medium frequency induction heater for bending and forging. The principles are the same, but different frequencies have different effects. My coils (http://courtiron.com/images/PICT0128.JPG) are wrapped in an insulating material. More trouble is often caused by having the heated material to close to the coil than farther away. I my applications, a coil has a ID of roughly twice the dia. of the stock being heated.

CCWKen
01-13-2016, 02:44 PM
I get by with a $1 incandescent light bulb. I set the bearing right on the bulb. Probably takes a little longer than induction heating but I don't notice while I'm getting ready to drop the bearing on. In a few minutes, it's ready.

ikdor
01-13-2016, 05:29 PM
Just out of curiosity, how does the induction heater know the temperature of the bearing? I'm impressed.
Lacking a decent thermal contact it would almost be forced to track the change in inductance from the change of the specific resistance of the target material due to temperature rise. But I doubt this would work outside of a lab environment and even then only if you don't move the target.
Or does it just assume the top surface is the same temperature as the bearing and accept the lack of accuracy? I'm confused as my induction heater has a glass surface but this material looks different.

Igor

J Tiers
01-13-2016, 09:04 PM
That ferrous only deal...... it seems not quite to be about ferrous, but a combination of things which ferrous material tends to combine nicely. Some cooktops can in fact use copper, or at least aluminum bottoms, but not quite as efficiently.

Ferrous has a combo of features.... It carries the magnetic flux, and limits the depth of conduction *at the induction frequency*, despite being a high resistivity material, which would normally deepen the skin depth.

The better conductivity of aluminum and copper still has enough skin depth that they do not heat as well at the typical operating frequency. Obviously not a problem for this application, as nearly all bearings are ferrous material.

Illinoyance
01-13-2016, 09:21 PM
Actuallu the material just needs to be a decent conductor of electricity. It acts like a shorted turn on a transformer. Induced current causes the heating.

Rich Carlstedt
01-13-2016, 09:28 PM
Ron, good idea !.

I have been using my "Demagnetizer " for years for heating bearings.
Its a large old commercial unit about 6 inch in Diameter with a 2 1/2 Hole and 2 1/2" thick
After 15 seconds, the bearing starts to get pretty warm

Rich

J Tiers
01-14-2016, 12:23 AM
Actuallu the material just needs to be a decent conductor of electricity. It acts like a shorted turn on a transformer. Induced current causes the heating.

Problem is if it is a GOOD conductor, it has low losses. There is a fixed turns ratio, "N" to 1, with "N" being what the drive coil has, and the "1" being kinda sorta 1, since it is all about eddy currents.

So, there is a reasonably fixed ratio of currents, and so with a limited primary current (the drive is current limited) the secondary current is also limited. If the max current in the "secondary" does not get it very hot according to I^2 * R, then it reflects a bad power factor to the primary, and does not do much cooking. The secondary reactance is larger than the resistance.

The primary wants to see a good resistor as the load, so the effective inductance of the secondary should have an impedance no higher than the resistance. The better the conductivity of the pot, the worse the cooking power. You can use a sheet of steel as a heater under an unsuitable pot. Dunno how efficient that is, sounds more like a regular electric stove.

nc5a
01-14-2016, 01:14 AM
I had a regular induction heater for bearings, the type you stick the bearing on a magnetic core and at the end of the heating cycle, there was a small automatic demagnetizing cycle that insured that the bearing was not magnetized. You should check if the cooled bearing is not magnetic and attract magnetic debris.

Good point Noitoen. I knew about the magnetizing and demagnetizing offered with commercial induction bearing heaters but I didn't consider it with the induction heat plate. So I went back to the shop and heated one of the old bearings with the induction heat plate and sure enough it was slightly magnetic when heated to 200 deg F and removed from the induction table. The magnetizing was so slight that you had to really pay attention and have a sensitive feel when checking. Once the bearing cooled the magnetizing affect was virtually gone.

I didn't understand why it disappeared so I heated the bearing again, let it cool and checked for magnetizing. This time it was still slightly magnetized. Touching the bearing with a small magnet caused the magnetic properties to dissipate.

I also wound 10 turns of #18 wire around the magnetized bearing and hit it with a 9 volt dc battery alternating polarity to cover my bases but the magnetism was still there.

Anyone have an idea how to demagnetize the bearing before putting it on the shaft?

LibbyHillBrewer
01-14-2016, 01:16 AM
If I may interject with a sideline question: I've been following this thread all day and I guess I lack experience with bearings. Why heat them up and won't heating damage the lubrication that comes embedded in the bearing?

Sent from my SAMSUNG-SM-G900A using Tapatalk

nc5a
01-14-2016, 01:36 AM
The bearing is heated to expand the ID so it will slide on a shaft machined for an interference fit. It prevents damage to bearings and the shafts. I've been told that most factory lubed bearings can handle 200 to 250 deg F without damage so I limit the temperature to the low 200's

lakeside53
01-14-2016, 01:46 AM
If they have seals... go a bit lower unless you know the max temperature rating. Shields are fine to 275F or more if the grease stays in.

RichR
01-14-2016, 02:40 AM
Anyone have an idea how to demagnetize the bearing before putting it on the shaft?

To demagnetize something you want to expose it to an AC magnetic field and move it away from the field. You could try leaving
the induction heater on and lift the bearing away from it.

im#2
01-14-2016, 02:57 AM
well you guys are working too hard again- wallyworld has a turbo heater in the toaster section that beats that thing all to hell and you can warm your sandwiches or what ever in it too. 35.00 or so and ive had one for several years and its work beautifully, bearing almost spot on for heat and it wont over doo them if you get sidetracked time wise.

LibbyHillBrewer
01-14-2016, 03:04 PM
Thanks for clearing that up fellows. Much appreciated

Sent from my SAMSUNG-SM-G900A using Tapatalk

jdunmyer
01-14-2016, 07:43 PM
I'm with CCWKen, just use a light bulb. A larger bearing can take a while, so this isn't for production type jobs, but for the occasional bearing, it works well. If the bearing is large, as in several inches I.D., placing a piece of cardboard or something on top to hold in the heat helps a lot. I don't use a thermometer, just touch the bearing now and then, and when it's too hot to keep my hand on, use a rag or glove, pick it up and install it.

Note: the new LED or CFL bulbs won't work, you have to have one of those old, now-illegal types.

old mart
01-19-2016, 08:41 AM
My old firm designed and built a crankshaft machining centre for the Ford Motor Company engine plant in Wales. The four cylinder cranks were finish machined and deburred ready for final grinding. Part of the process was to shrink fit a gear onto the crank. the gear was heated inside a water cooled induction coil and robotically fitted. Fine adjustment of the time/power of the induction was needed to keep the temperature within pre determined parameters.

Black_Moons
01-19-2016, 10:54 AM
I must be weird. I just use a $20 heat gun and an IR spot thermometer to heat my bearings.

Maybe one day i'll get one of them fancy digital heat guns with temperature settings. But id likely still just use it at 'very hot' and keep checking the bearing to see if its up to temperature.

For castings I just use a propane torch and IR thermometer.

_Paul_
01-19-2016, 02:15 PM
I must be weird. I just use a $20 heat gun and an IR spot thermometer to heat my bearings.

BM that's not weird at all, I must confess to being really low tech by balancing any offending bearing on the end of an upward facing 100w filament bulb then have a cup of tea by which time it's normally "cooked" enough to do the job.

Paul