Will This Furnace Work For Heat Treating?

[David Kirtley]

Well, I don't see any reason not to. We have one of the fancy 3D metal printers that does that with argon, although in a much more sophisticated way. It goes through several cycles of drawing down a vacuum and filling with argon until the oxygen sensors read low enough values. They really don't want the powdered metals to burn.

It will behave differently than a reduction atmosphere though as it will not have a lot of free carbon. Probably not a substantive difference though.

 

[Flammable_Solid]

I am wondering about using Argon injection to create an inert atmosphere in this little furnace. I have a TIG welder and 150 CF Argon bottle. I normally TIG weld with a 15 to 20 CFH flow rate. Would it be possible to use this setup with the furnace? There are no heating elements on the back wall of the furnace. Seems like I could drill a hole through the back, insert a pipe, and inject the Argon. Might this work? What would be an appropriate flow rate? Below is a picture of the injection kit Paragon sells for another one of their furnaces.

Bob

View attachment 83961

We do this on a daily basis at work. I think your kiln should have a vent in the top, so it shouldn't leak out the front door too much. Argon will displace oxygen, so probably a few cubic feet per hour should be fine. You can set up something that will oxidize in there (like clean piece of copper), heat it up with the flow going, cool it, then see how/if it oxidized.

 

[frostheave]

Well, I don't see any reason not to. We have one of the fancy 3D metal printers that does that with argon, although in a much more sophisticated way. It goes through several cycles of drawing down a vacuum and filling with argon until the oxygen sensors read low enough values. They really don't want the powdered metals to burn.

It will behave differently than a reduction atmosphere though as it will not have a lot of free carbon. Probably not a substantive difference though.

Thanks David. I think I'll give it a try.

Bob

 

[frostheave]

We do this on a daily basis at work. I think your kiln should have a vent in the top, so it shouldn't leak out the front door too much. Argon will displace oxygen, so probably a few cubic feet per hour should be fine. You can set up something that will oxidize in there (like clean piece of copper), heat it up with the flow going, cool it, then see how/if it oxidized.

Thanks for the info Flammable. The furnace does have a vent with a plug on the top. The vent hole into the furnace is about 3/4" in diameter. Sorry for all the questions , but here are a few more:

1) At what temp should I heat the copper and for how long?

2) Should the furnace be shut off and and let the copper cool inside?

Thanks

 

[Flammable_Solid]

Copper melts at 1984F. Take it up to 1200F, shut the furnace off, and cool it from there. Cool it to room temperature with the argon flowing.

Also, use a thermocouple (Type K should be fine) to determine the working zone of your furnace. The internal temperature will vary more than you think, especially near the door.

 

[frostheave]

Copper melts at 1984F. Take it up to 1200F, shut the furnace off, and cool it from there. Cool it to room temperature with the argon flowing.

Also, use a thermocouple (Type K should be fine) to determine the working zone of your furnace. The internal temperature will vary more than you think, especially near the door.

All right, I'll give it a try. The black dot in the middle of the furnace, in the pic below, is the existing thermocouple. So, are you saying the interior temperature varies a lot depending on where it is measured? Is it better to position the work towards the rear? Thanks.

Bob

 

[pdentrem]

At work we have a larger version of that style of box. http://www.brownells.com/gunsmith-t...extra-large-heat-treat-furnace-prod13791.aspx

Internal size of about 22x22x13". Takes a long time to heat up due all the thermal mass involved. I have it on a timer so that starts on the early morning before we get in. I replaced the analog controls with Watlow PWM controllers. Added 2 thermal couples, one for the main control and the second for over heat protection.

Yes the temperature will vary based upon position. Every one is different. Difficult to test without a bit of work and charting it all on paper. Using a temperature probe that you can bend a bit to reach at a minimum of 8 zones, 27 zones is better. Divide the space into 2 layers of 4, 3 layers of 9. Another way would be to use Temperature indicating paint on some test pieces and use some method to support them in the various zones.

As for protecting the heating elements from an early death, use a ramping program that does not run at 100% for any long length of time. PWM is a very good way to control the power going to the elements. We use a S&M Engineering belt annealler, we start it off at 1000 F, which it reaches fairly quickly. During the work week we leave it at 1000 24hrs as an idle temp. Naturally this would not work for you. A touch expensive. We go from there to what ever temp is required for the job. It is the 100% power setting that kills the elements. They will get stressed and burn out near the joints where the exterior wiring meets the elements. The other place they burn is if there is a sharp bend.

As for gas we use Nitrogen 5.0 or crack Ammonia for a 4/1 Nitrogen/Hydrogen mixture. Argon gets expensive in our case.
Pierre

 

[Flammable_Solid]

Pierre is spot on. In our electric furnaces you are only putting heat in at the side walls and you also have little to no convection moving the heated atmosphere around. The areas that do not have heating elements in them are only heated by radiation from the heating elements, so they don't contribute to the heat input. As good as refractories are, it is still the equivalent of having a hole in the bottom of a bucket.

Most likely, the center of your working zone will be about 2/3 of the way back and only extend about 2" in front of that.

 

[frostheave]

At work we have a larger version of that style of box. http://www.brownells.com/gunsmith-t...extra-large-heat-treat-furnace-prod13791.aspx

Internal size of about 22x22x13". Takes a long time to heat up due all the thermal mass involved. I have it on a timer so that starts on the early morning before we get in. I replaced the analog controls with Watlow PWM controllers. Added 2 thermal couples, one for the main control and the second for over heat protection.

Yes the temperature will vary based upon position. Every one is different. Difficult to test without a bit of work and charting it all on paper. Using a temperature probe that you can bend a bit to reach at a minimum of 8 zones, 27 zones is better. Divide the space into 2 layers of 4, 3 layers of 9. Another way would be to use Temperature indicating paint on some test pieces and use some method to support them in the various zones.

As for protecting the heating elements from an early death, use a ramping program that does not run at 100% for any long length of time. PWM is a very good way to control the power going to the elements. We use a S&M Engineering belt annealler, we start it off at 1000 F, which it reaches fairly quickly. During the work week we leave it at 1000 24hrs as an idle temp. Naturally this would not work for you. A touch expensive. We go from there to what ever temp is required for the job. It is the 100% power setting that kills the elements. They will get stressed and burn out near the joints where the exterior wiring meets the elements. The other place they burn is if there is a sharp bend.

As for gas we use Nitrogen 5.0 or crack Ammonia for a 4/1 Nitrogen/Hydrogen mixture. Argon gets expensive in our case.
Pierre

Lots of good info. Thanks Pierre. I will definitely refrain from using 100% ramp speed. I am really surprised about the varying temperatures. I just assumed it would be relatively consistent everywhere inside the furnace. Maybe one day I'll try mapping the temperature zones in mine.

Bob

 

[frostheave]

Pierre is spot on. In our electric furnaces you are only putting heat in at the side walls and you also have little to no convection moving the heated atmosphere around. The areas that do not have heating elements in them are only heated by radiation from the heating elements, so they don't contribute to the heat input. As good as refractories are, it is still the equivalent of having a hole in the bottom of a bucket.

Most likely, the center of your working zone will be about 2/3 of the way back and only extend about 2" in front of that.

Thanks Flammable. Sounds like I better stay away from the door. Just out of curiosity, say I was heat treating a 1-2-3 block. Would there be any good reason to put the block in the furnace at ambient temperature, then ramp the temp up to the set point, let it soak, then remove it? I.E. does the work HAVE to go into a hot furnace, or can it go in a cold furnace and heat up as the furnace does? Thanks.

Bob