Inductive Heating

Thread Starter

Subzero27

Joined Jul 7, 2020
3
Hello,

I am trying to build a inductive bearing heater. The idea is that when a circular metal bearing is placed on a transformer core ( on tbe secondary side ) it will create a short circuit and heat up.

So basically instead of the primary winding there will be the bearing attached. I guess many companies make bearing heaters based in this concept. Here is a video -

What I want to understand is my theory correct and if so what should be the ideal rating of such a transformer?

Thanks
 

jpanhalt

Joined Jan 18, 2008
10,221
Welcome to AAC.

A brief search showed Bessey units between 1870 W (approximately, 17 A, 110 V) to 9000 W (15 A , 600 V). It may vary with the size of the bearing. What voltage do you have available?
 

jpanhalt

Joined Jan 18, 2008
10,221
The Bessey unit for 240 V is 30 A. I suspect something in the 15 A to 20 A range would work and be easier to build but slower.
 

shortbus

Joined Sep 30, 2009
7,926
I'm betting that the heater is more than just a transformer primary at mains frequency. Just a guess (didn't look to Google) that it is a high frequency DC voltage on the primary.
 

MaxHeadRoom

Joined Jul 18, 2013
21,403
I would have thought the more common method of hydraulic press-on would be simpler etc, as they still do to press locomotive wheels onto the axle, to prevent tearing, a linseed oil is used.
White lead was once used, but has since been banned due to the health hazard.
These presses operated at many tons pressure successfully.
For bearings a much lower pressure would be required.
Max.
 

shortbus

Joined Sep 30, 2009
7,926
I had some time so read a little about them, I was wrong and you are right. But using an alternating DC square wave would I think heat them up faster. But then I tend to think of an induction heater as like a ZVS induction heater.
 

MaxHeadRoom

Joined Jul 18, 2013
21,403
All of the HF heating systems I have worked on have been mainly HF 450khz and up, , the only LF (120Hz) was for heating a Large iron ingot all the way through.
Any thing you just need skin heating, requires H.F. of some kind.
Heating throughout requires a progressively higher freq.
Max.
 

jpanhalt

Joined Jan 18, 2008
10,221
I also did a little reading on it and agree with @shortbus #8. Induction heating seems to focus on using higher frequencies and taking advantage of skin effect for controlling depth of heating. Bearing heating seems to focus on heating the whole mass of the bearing to lower temperatures -- well below the temperatures at which material properties change. Only one vendor stated that it utilized high frequency "technology," but there was no further description.

The difference seems to be that the bearing acts as a single turn secondary. It has a core. Whereas in induction heating, say for surface hardening, the item is put inside a coil. It has no core, nor is it a closed loop necessarily.
 

MaxHeadRoom

Joined Jul 18, 2013
21,403
All of the various industrial ones I have worked on have had a single turn work coil, in some cases it may appear to be an open/non-closed loop, but is just an extension of a continuous single loop secondary to the primary coil.
The one exception for more than one turn was the L.F. 100lb ingot heating, which was heated all the way through.
Max.
 

jpanhalt

Joined Jan 18, 2008
10,221
All of the various industrial ones I have worked on have had a single turn work coil, in some cases it may appear to be an open/non-closed loop, but is just an extension of a continuous single loop secondary to the primary coil.
The one exception for more than one turn was the L.F. 100lb ingot heating, which was heated all the way through.
Max.
Were those heaters for large roller/ball bearings? By large, I mean in excess of 10 kg.
 

MaxHeadRoom

Joined Jul 18, 2013
21,403
I have not had the opportunity to work on bearing heaters, but studying the video I would expect low frequency to be applied for that application, the inner ring is heated all the way through to only 110°C, so not that a high heat demand.
As already mentioned, the 60hz/120hz heater I worked on was intended for 100lb ingots heated to red hot level all the way through.
Max.
 
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