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highyields
Senior Contributor

I had to heat a gear to a blue color to get it off,

There is a gear on my combine gear box that is "heated" in oil to 350 degrees to get it on the shaft, but to get the gear off my parts gear box they told me to use a torch, well by the time the gear finally game it got hot enough that it started to turn blueish color,  I cooled it off slowly, but that it got soft, or brittle??   I hate to but everything together then have it go to hell right away.   The dealer told me they use a torch and reuse the gears, they have  rosebud torch head, I just had a regular one,  the ruined gear i just heated a little bit and it came right off, course since I wanted to use this gear, it didn't work that slick. 

 

So did I ruin my gear??  

 

 

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5 Replies
BA Deere
Honored Advisor

Re: I had to heat a gear to a blue color to get it off,

I think so, you shouldn`t heat something like a ring gear anyway over 400º or it hurts the orginal heat treatment. If you use the old gear and it chips off you might make more problems, a new one might be cheaper in the long run.  I`m no expert, just my 2¢.

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jdmfarmxs
Friend

Re: I had to heat a gear to a blue color to get it off,

Steel will turn blue about 900 degrees.  That is the temperature that is used to relieve the stress in heat treated items.  You should not have made it brittle at that temperature.  It is possible some of the hardness could have been removed.  Check it with a file.  The other possibility is that it was case hardened.  Just the surface is hard.  That process introduces higher levels of carbon in the skin of the material improving wear characteristics.  Heating to blue would not have removed this.  As I said before a file will tell you.

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highyields
Senior Contributor

Re: I had to heat a gear to a blue color to get it off,

Thanks for the info

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Nebrfarmr
Veteran Advisor

Re: I had to heat a gear to a blue color to get it off,

Before you re-use it, be sure that blue is the only color you see.

When I was in school, I learned there are a whole rainbow of colors, which show how hot the steel is/got.  While Blue is not hot enough to cause much in terms of brittleness, especially if allowed to cool slowly, look for other colors, as well.

I can't remember the whole spectrum, but I know we made home-made chisels out of stuff like old harrow teeth and the like, and with a cold chisel, you wanted to harden it to where it was just turning a 'straw' color (before quenching) for maximum hardness without being brittle (after hardening with a quench when red hot).

Now, I am by all means no expert, but if you let it cool gradually, I would say you didn't get it brittle, but I do have a couple other concerns.

1) you may have actually 'softened' it a bit, which may or may not cause problems

 

2) if you heated the area of the gear in the center near the shaft more than the rest of the gear, it is possible you stressed the gear, by uneven heating.  By heating only the center, you will cause just the middle of the gear to expand, but the cooler outer part will not want to swell, causing a stress on the gear.  As it cools, it can (but probably won't) cause the gear to be more likely to chip.  If you didn't heat it up past what it takes to turn blue, I doubt it was stressed enough to make that a problem, but the more likely problem is that now the center hole of the gear is a slightly different size than it once was, changing the press-fit to the shaft.

I was taught to heat the entire gear evenly, while having cold damp rags on the shaft, to get the gear to 'loosen' as much as possible, while still keeping the proper press-fit (or interference-fit) to the joint. 

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highyields
Senior Contributor

Re: I had to heat a gear to a blue color to get it off,

It was blue color, My Dad knows one of the local blacksmith, he thought to we might have gotten it a little softer, he said if you know what kinda steel it was you could heat it to the critical temperature then quench it in oil.  I was a little bit to scared to try that, since I didn't know really what kinda steel was in the gear. 

The reason the darn gear was so hard to get off was that the key was rusty, course I didn't now that ahead of time, but its amazing what rust will hold.  

 

We used the damp rag method,  I am a little concerned with the softness of the gear, if that will cause premature wear of the gear? 

I'm going to find out.  

 

 

 

Thanks for the information 

I appreciated it

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