Too many knives in oven?

Matt Rochester

Matt Rochester

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Nov 28, 2014
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Is there any such thing? I am limited on time for heat treating since it takes all day with tempering so I try to make it count. How many do y'all do at once. It's all air hardening so I'm just plate quenching.
 
If you're talking about putting hardened blades into an oven for tempering, this is more of a physics question. The more blades you have (the more mass) means that it will take longer for each blade to reach the desired temperature compared to when you only have a few. Now, since blades are typically thin (even at the thickest parts of their cross sections) there shouldn't be much of a noticeable difference.

If you're not talking about tempering, could you be more specific as to what you are doing?
 
I have an Evenheat and the most I put in is 6 pieces at a time. Either 6 fixed blades or 3 blade and 3 springs for slip joints.
The main reason is my quench plates are only 12" X 12" and that's all that will fit on them at once.
 
I try to keep it to 5-6 blades at a time. I may do a few Austinizing cycles, but then temper all the blades together. I'll austinize and quench 5 blades, and then start over and do another 5.
 
I usually do 6 or so if its oil quench stuff. If I'm plate quenching, then it's a question how many will your plate allow.
 
I usually do no more than two or three at a time, but the main thing is that you don't want them piled up so much that any of them are laying right next to the heating elements. If they're too close, you risk overheating. The temps of the coils are going to be higher than that of the space around the thermocouple.
 
I plate quench them one at a time and usually do 6-7 at a time. I never thought about them being too close to the elements. I do check the hardness of each knife and all of them have came out within a point of each other so I'm assuming that I haven't been overheating them? I have heard of guys making a shield but I haven't tried it since I didn't think it was an issue. Am I wrong?
 
I would imagine if your oven has been soaking at temp for a while, and the elements are no longer going full blast for longer periods of time, you'll probably be ok. That said, I still like to keep things at least a couple inches away if I can help it. Maybe I'm being over paranoid. :D
 
I usually do 6 -8 at a time . I have 2 sets of plates and 2 knives fit in 1 set of plates for quenching , plus I freeze the plates .
 
My rack holds 4 knives. That is the max I will do. If I were doing small neck knives I could probably put 2 to a packet if it would still fit the plates which would double the amount.
 
For tempering, I put as many as I can fit. For hardening, I have put as many as 16 in my 220v oven, but I have better results with smaller batches.

Lets suppose I have 16 knives to harden. Scenario A is - I put them all in at once. The oven takes a long time to heat up. Now I start sequentially quenching - let's say I can quench a knife every 3 minutes. Let's say every 4th knife, I need to leave the oven closed for a few minutes to let the temperature catch up. The last few knives in this batch of 16 will have sat in the oven for quite some time, and the decarb/pitting is substantial.

Scenario B is - I put 8 in, heat, and sequentially quench. Then I put the remaining 8 in and repeat. Because the oven heats faster, I find this to be no slower than scenario A, and the decarb/pitting is less severe.

If you are air quenching and/or using foil then the factors I mention here may not be a problem.
 
You can use foil and plate quench in the foil.
The kiln must provide enough room to have space around the blades and space between blades and sides of the kiln. Less space is needed for tempering .
Blades should have a rack to place them edge up . Set up your proceedure to be able to quickly remove each blade in the quenching stage.
 
Thanks for all the answers. I normally do 7 at a time as I have 7 slots. This last time I slid 2 extra ones in. We will see how they turned out!
 
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