Question about newly built HT oven.

[Wuatt]

Howdy everyone, I have a quick question about the time it takes the HT oven I recently built to get from room temp to 1500F.
I recently finished building my new HT oven, and the general look was inspired from the one that Red Beard Ops recently built (With certain tweaks I made throughout the build to better suit what I wanted and liked).

Due to wiring the oven in a similar fashion other than a few tweaks, I was expecting similar results (38min from room temp to 1500F I believe is what he got). But I ended up being blown away when my oven hit 1500F from room temp in just 16 minutes and change. So blown away that I let it sit for several hours with the door open to bring it down to room temp before trying again in order to make sure it wasn't a fluke. The second run from room temp to 1500F took just over 13 minutes, which (from my understanding of heat treat ovens) is exceptionally fast.

I thought maybe it was a faulty reading off the thermocouple, so I threw a piece of 01-Tool Steel I had kicking around in for 5-10 minutes or so and when it came out it was non magnetic (Not a perfect test, but ballpark accurate), so I know the reading wasn't faulty, an the oven really was 1500F, or at least close to it.

So my questions are, Is this really far outside the normal speed for heating up?, Is this speed dangerous in any way? and what may have caused this vast difference in performance with relatively minor differences between my oven and the one it was based off.

If anyone has a tough time believing this I don't blame them, and I can do another run to 1500F and record it with a timer if needed.

Thanks in advance everyone!

 

[A.McPherson]

What tweeks did you make?

 

[Ken H>]

What size is the oven? How many watts? What is the voltage and amp draw when heating? No way to comment on anything without that info.

Also, what type of insulation? 16 minutes to 1500F - WOW, that is impressive.

 

[Wuatt]

What tweeks did you make?

I carved the bricks for the back of the oven so that they sit into the oven (Like the door bricks). I changed some of the electrical work, so my total coil resistance was 17.5Ohms instead of 17.8Ohms. I used breakers instead of fuses. I used 2" Ceramic fiber blanket to coat the oven bricks instead of 1" (Which resulted in an *extremely* tight fit between the frame and oven body). And a bunch of other really small tweaks that were mostly for aesthetics and wouldn't effect heating in any way

 

[Wuatt]

What size is the oven? How many watts? What is the voltage and amp draw when heating? No way to comment on anything without that info.

Also, what type of insulation? 16 minutes to 1500F - WOW, that is impressive.

The oven is 18" long 7" wide and 6" tall. Its around 3600w + or - a bit. I'm not sure of the voltage draw when heating, but the amperage draw peaked at 17, but averaged about 14.5 while running (It's on a 240v 20a outlet, and I measured the voltage coming out of the outlet at 248v)

I used 2.5 x 4.5 x 9.0" K23 fire bricks that I was told were "Top of the line bricks" (Pretty sure it was just a salesman being a salesman since he couldn't tell me exactly what made them different from regular K23 bricks) and a very tightly packed a layer of 2" Ceramic fiber blanket insulation around the entire outside of the oven.

One other thing that may or may not be of note is that no-matter what I try, if I set the oven temp to 500F the coils will turn on for a very short period of time (Maybe a minute or so? not too too sure) and the oven will just keep climbing straight past till about 625F - 660F before VERY slowly inching its way back down to 500F and holding (It took at least as long if not longer to get from 660F to 500F than from room temp to 1500F).

Any advice I can get would be awesome, I'm almost worried to use it too much because I don't know if heating up that quickly will damage anything.

Thanks!

[Edit to correct oven size, I wrote 6.5" wide, it should have been 7" wide]

 

[Britt_Askew]

My oven will get to 1475 in 9 minutes and 1975 in just under 30. and holds temp +-1 degree since I did an autotune.
Bricks are dry/ no mortar and I use no blanket. Oven is 7.5 wide x 6 tall x 18 deep.
I built mine from plans found here a long time ago, bolts going thru the back of oven and the wire was just wrapped around the bolt and 2 washers and a nut squeezing the wire and for a bunch of years havnt had a problem with elements doing high carbon blades but recently switched to stainless and got fustrated, with the higher temps 10 blades and the element would break, 10 blades and brake, 10 blades and break, 1 blade and brake then I watched the Red Beard oven video and ordered some of the ceramic blocks like he used and have HT'd over 150 blades since without a problem , If you see this Thanks Red Beard Ops !

 

[Nick-D]

My oven is much the same heating time wise. A combo of small chamber, decent I sulation seal and good power elements mean it cracks up pretty quick.

The problems overshooting at low temps will be pid settings related, the settings to hold temp at 1500 are very different than at 500.

 

[Wuatt]

I ran a test this afternoon and the oven hit 1500 in 13:20 and 1975 in about 28 minutes and reached 2000 in 29:20.

I'm super stoked to start working with stainless steel! Anyone have recommendations for what stainless to try first?

 

[12345678910]

One other thing that may or may not be of note is that no-matter what I try, if I set the oven temp to 500F the coils will turn on for a very short period of time (Maybe a minute or so? not too too sure) and the oven will just keep climbing straight past till about 625F - 660F before VERY slowly inching its way back down to 500F and holding (It took at least as long if not longer to get from 660F to 500F than from room temp to 1500F).

Any advice I can get would be awesome, I'm almost worried to use it too much because I don't know if heating up that quickly will damage anything.

Thanks!

[Edit to correct oven size, I wrote 6.5" wide, it should have been 7" wide]

The controller needs to "learn" it will get better.

But it really makes sense to let the oven settle out at temp before using it.

 

[Ken H>]

I really envy ya'll with those fast heating ovens. I've got an EvenHeat 18" that's around 3KW and about 6.5"X10"X18" and it takes over an hour to heat up to 1975°F. Most of my work has been in SS so don't really remember 1500°F time as I'm just starting with carbon steel.