Heat treat oven woes, brick issue?

[Drew Riley]

Just to toss this out here, but higher temp rated bricks don’t insulate as well as lower temp bricks. A brick rated for 3000F generally won’t insulate as well as one rated for 2300F.
As for wet bricks, I’d think that a couple of firings should take care of that, and you’d no doubt see steam coming from somewhere.

 

[ren01228]

I’m putting my money on the bricks. Density does not tell everything. Thermal conductivity is what matters which is usually associated density but it’s not always the case. The real k23 bricks should feel like a heavy foam. You can easily snap the brick in half with your hands. If one Accidentally falls on the ground it usually will bust up into 3 or more chunks.

Thanks for the input. Either way I definitely regret buying them from facebook marketplace at this point. The guy had told me someone was coming later that day to pick up 200 bricks... hopefully they worked out for them.

The higher rated brick I have used had much smaller pores, but there might well be other bricks available. Judging from the picture, I think it is more likely that they are 2,300F bricks and got rained on before you picked them up. Can you call the person you bought them from and find out how long they had been sitting on the pallet in the open? I doubt the PID is at fault. Either the brick is the wrong kind, or it is full of water.

Can you run the oven without the enclosure? Or at least take the top off? If you have only run it a few times and it was enclosed, you may not have driven off the moisture. If the bricks indeed contain moisture, it may just condense on the sheet metal and drip right back onto your bricks. How hot did the sheet metal get?

You could also do a separate test and just weigh a brick and bake it in the oven for a few hours and then weigh again. Repeat until the weight does not change anymore.

Before I built the case I ran it for probably 4-5 hours total at around 550C. Do you think this would be sufficient to dry them out? Regardless I'll bake a brick and see if there are any changes. The sheet metal gets HOT after about an hour I'd say. I let it cool for a while and tried to move it with a rubber glove on and it melted it right away.

I'm questioning the brick/insulation factor also. My oven is k-23 brick lined with a outer 1/2" cement backer board shell in a angle iron frame. Ive had my oven at 1900* plus and I can place my hand on the outer shell with little discomfort.

Hmm thanks for the input. Mine gets really hot fairly quick, and that's only running at 750C max temp.

Just to toss this out here, but higher temp rated bricks don’t insulate as well as lower temp bricks. A brick rated for 3000F generally won’t insulate as well as one rated for 2300F.
As for wet bricks, I’d think that a couple of firings should take care of that, and you’d no doubt see steam coming from somewhere.

Was not aware of that, thanks. It ran for a few hours total without the case up to 550-600C and I didn't see any steam.

 

[Hubert S.]

Before I built the case I ran it for probably 4-5 hours total at around 550C. Do you think this would be sufficient to dry them out? Regardless I'll bake a brick and see if there are any changes. The sheet metal gets HOT after about an hour I'd say. I let it cool for a while and tried to move it with a rubber glove on and it melted it right away.

I tested a small piece of my brick today, it weighed 52g. I soaked it for a minute and then blotted it dry with a towel. It had absorbed 39g of water. I cooked it in the tempering oven at 375F for a couple of hours and weighed it again. It was just over 52g, so almost all the water was gone. So yes, if you ran it for 4-5 hours without enclosure, you probably got rid of most of the water if there was any.

I'm not sure if this has been asked before, but did you verify your thermocouple is reading accurately? Did you verify that the PID controller is set to type 'K' thermocouple input and not type 'J'?

 

[ren01228]

Threw one of my spare bricks in the oven for a couple hours as well, didn’t change the weight so they are dry. And yep quadruple checked I selected “K” type.

When directly wiring the elements how would I read the temperature? You need a separate thermocouple reader/meter I’m assuming since the PID won’t have power?

At this point I’m likely just going to pick up some new bricks from a reputable source and see what happens. The hard part for me was the case and wiring, so not too big a deal. I’ll update this thread to let everyone know how it goes. Really appreciate all the help!

 

[Jax knives]

When directly wiring the elements how would I read the temperature? You need a separate thermocouple reader/meter I’m assuming since the PID won’t have power?!

I'm assuming your pid is already powered from a fuse. Just move the 120 vlt power wire from the line side of the SSR to the load side of the SSR. For simpler terms put both 120 volt power wires on the SSR on the same terminal.You have just jumpered the SSR.

if it helps my oven is a 4"x6"x18" chamber, k-23 lined at 3500 watts and gets to 1500* between 12- 15 mins.

 

[PEU]

When I made my oven (https://www.bladeforums.com/threads/heat-treatment-oven-wip-peu.1314585/) I used the wrong bricks, they were rated for much higher temperature than needed, the result was they absorbed a lot of the generated heat, so carbon steel temperatures are easily reachable, but stainless took ages.

The solution was to change the bricks to Morgan Thermal Ceramics K23, the texture is like chalk with pores and they are light. The original ones where almost 50% heavier.

My build has no cement, just interlocking bricks, and also have an outside perimeter chamber lined with ceramic blanket

The oven works great with these since then

Pablo

 

[Cushing H.]

Threw one of my spare bricks in the oven for a couple hours as well, didn’t change the weight so they are dry. And yep quadruple checked I selected “K” type.

When directly wiring the elements how would I read the temperature? You need a separate thermocouple reader/meter I’m assuming since the PID won’t have power?

At this point I’m likely just going to pick up some new bricks from a reputable source and see what happens. The hard part for me was the case and wiring, so not too big a deal. I’ll update this thread to let everyone know how it goes. Really appreciate all the help!

What JAX said. Keep the PID powered and use it to read temperature, and “jumper” the output side of the SSR like jax said.

BE CAREFUL .. in doing this you will disable some safety interlocks, and that exposed element will be Energized and stay that way as soon as The oven is plugged in...

 

[ren01228]

Ah I understand now, thanks for the explanation Jax and Cushing. Gonna try that out as a last ditch effort and if it doesn’t work new bricks it is!

And PEU that oven looks very nice, thanks for the input.

 

[scott kozub]

It's possible the temperature readings are off. Have you tried verifying with something other than the PID?

Salt melts melts at 801C. Easier still would be to toss a piece of carbon steel in there and see if you can get it to non magnetic. I doubt this is the issue but its an easy check.

Also, there's no possibility of a short across the coils is there? When you check the resistance did you check it at the leads in the oven? A short should be easy to see when you open teh oven and see a black section of coil. Like other said, make sure you check everything else before buying new bricks but this does sound like a brick issue unfortunately.

 

[ren01228]

Finally got it working properly and did a couple blades in 52100 today! Grain test came out good so looking forward to testing them out. The bricks I had were not even similar to the K-23’s.

I’m sure that contributed to it obviously, but I’m also embarrassed to admit I may have had the thermocouple connected wrong the whole time as well. I was under the impression that if it was hooked up wrong it would just read the opposite way, so you just swap the wire at the head of the TC and problem solved (NOPE).

I didn’t think it mattered what TC wire I used as pos or neg, but it does!!! When I initially hooked all the wiring up again I had them connected reversed to the PID (neg to pos and vise versa). The heating had slowed down and was struggling to climb a bit around “800C” I think, I opened it up and the TC tip and elements looked WAY hotter, a real bright orange color. This is what made me realize something else was up, since I knew it wasn’t the bricks this time around . I read a thread on here that gave some great information about TC’s but wasn’t able to find it again to share here. Still don’t completely understand TC’s and wiring stuff in general but I sure know more than when I started.

Anyways thanks a ton to everyone for the help! Feels good to finally get it working.

 

[Stacy E. Apelt - Bladesmith]

I was pretty positive the wiring of the TC was the issue. Glad it worked out.