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Author Topic: homebuilt PID control Kiln!!  (Read 3671 times)
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Joe Calton
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« on: April 30, 2013, 07:08:12 PM »





http://pic100.picturetrail.com/VOL602/13504682/24155286/406478525.jpg

http://pic100.picturetrail.com/VOL602/13504682/24155286/406478526.jpg

Here she is, my new Kiln! this should really help with some of the steps in my heat treat, as well as let me throw away the bucket of wood ashes for annealing!

Ive had her running for about a week now, and she is wonderfull!! to anneal blades, I now put the blades in, close the door. hit the go baby go button, and she will take them from room temp, to 988 over the course of one hour, hold them there for 2 hours, and then shut herself off, and then cool down to room temp over the next 8 hours or so. NO MORE WOOD ASHES FOR JOE!!!

next post will have the parts and hopefully where I got them and what they cost
   

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Joe Calton
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« Reply #1 on: April 30, 2013, 07:33:43 PM »

I got the soft firebricks from hightempinc on ebay they are listed as K23 bricks. 12 of them were $67.10 shipped, I got 24

the PID and thermocouple and SSR's were from auberins 

http://www.auberins.com/index.php?main_page=product_info&cPath=20_3&products_id=22

http://www.auberins.com/index.php?main_page=product_info&cPath=1&products_id=4

http://www.auberins.com/index.php?main_page=product_info&cPath=2_30&products_id=30

the kanthal for the heating element came from

http://kruegerpottery.com/kanthal-a-1-wire-13-gauge.html


The rest of the parts were some scrap steel for the frame, a couple of 220 20 amp on off switches and some boxes from home depot and my scrap piles.

She seems to be learning the heat chamber pretty well, and will keep a set temp +/- 4 degrees at 1000 degrees

the toughest part was the programing instructions for the PID,


Total cost, was right at $425 and a day to put it together!
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larnotlars
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« Reply #2 on: April 30, 2013, 10:33:35 PM »

I'm jealous!

I would be tempted except for the second to last line... programming the PID?

Does it involve sacrificing livestock? Contracts in blood?

Honestly, what is involved... I used to program back when computers ran on BASIC...
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Daniel Rohde (D-Vision)
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« Reply #3 on: May 01, 2013, 09:40:14 AM »

incredible Joe very nice!!!
of course I have a few questions Roll Eyes
How big is it?
how big is the camber?
How hot can it go?
what do you use it for?(my guess is annealing(there was no hint on that one) and tempering right?)
again very nice! Shocked
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Joe Calton
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« Reply #4 on: May 01, 2013, 08:15:10 PM »

lar, it seems pretty simple to get a program going or to change it now, it just took awhile of reading and rereading the instructions. its not as user friendly as a lot of things. but the program I use is pretty simple. this controller can run a 30 step program. and I know it can do a lot more than what I know how to tell it to do, but Im getting along with it now, and will learn more about it the more I use it. but it is very impressive for the $70 or so that it cost!

Dvison,it is roughly 9x11x28" outside dimensions, and 4.5x4x22" inside. I would have built it bigger, but I was limited by the place I had picked out in the shop for it. most of my blades are under 22" OAL anyways, although I do like to make them bigger sometimes!

it sounds kinda small, but the other day I had 8 leafspring choppers from OAL of 14" up to 22", plus 2 stock removal flat stock 52100, one forged flat stock 52100 edc type test blades, 2 1095 neck knives, 4 1095 forged edcs, for a total of 17 blades in it at one time. the kiln doesn't care how many blades are in it at one time. and it was so nice to load them and hit the go button and forget about it!

I thought I had built it to go to 2300, but when I looked up the thermocouple I used to post the link, I used one that was rated at 2000 max. that's an easy fix if I ever need to go all the way to 2300, the bricks and the heating element can surely take it there, I went way overkill on the heating element, so that it would last a long time, and as always, more power is more better!

I built it 1st for annealing. that was one step in my heat treat that was lacking, and was a big variable. I mean, how do you tell if steel is 1000 degrees? its still magnetic, what color is 1000? so to do the subcritical anneals by eye, Id just go to nonmagnetic the first anneal, then a bright red the second, and then a dull red the third. plus I was tired of fooling with wood ashes.

2nd- it is way more accurate than my toaster for the tempers, so ill start using it instead

those 2 were the reasons that I built it. of course now that I have it, I can run all sorts of tests, and maybe try some stainless for kitchen knives

my big reason for posting it, was to show that you can build your own equipment at a huge cost savings when starting out, and when adding to the shop with a little time and research. I saw where paragon wanted around $1500 for a kiln this size. now mine is not a paragon, its ugly, unpainted, doesn't have a gas valve, and im sure a host of other things. but I built the thing, if it breaks, I can fix it. and it cost a 3rd of the paragon. and with that $1000 that I did not spend on the kiln, Ill build a nice new sword lenth forge that runs on propane to forge, and 220 volts to anneal and temper with a slide out element tray and removable controls, and still have money left over.
« Last Edit: May 01, 2013, 08:23:47 PM by Joe Calton » Logged

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Daniel Rohde (D-Vision)
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« Reply #5 on: May 02, 2013, 05:45:48 AM »

how accurate is it temperature wise?
how do you know it's at the right temp?(if you don't a machinist told me you can get temp sticks that are like chalk and melt at different temps)
is there a way of knowing if it was totally annealed?
Thanks for the reply(and a long one at that) Wink
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Joe Calton
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« Reply #6 on: May 02, 2013, 08:29:30 AM »

you know that's a good question, I don't know how to calibrate it. I will have to find that out. Thanks!!

I will calibrate it to the temper temps by the steel itself in the edge flex tests, but I don't know how to calibrate it at the higher temps.

you can tell if the blades are fully annealed by how easy it is to work the steel. drilling holes, grinding, ect...
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mreich
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« Reply #7 on: May 02, 2013, 09:33:07 AM »

The only other calibration that I can think of, is simply figuring out what temperature you need to set for the blades to get to critical or non-magnetic.

I have a regular Evenheat kiln, but I had to figure out that on my oven, 1460*F is non-magnetic for 52100, and go from there.

I don't expect anyone else's numbers to match mine, but I don't think the numbers are important. If 52100 is non-magnetic at 1360*F by your magnet, that is the number that counts.
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« Reply #8 on: May 02, 2013, 10:01:03 AM »

this is what I fond from a brief search for temp sticks I think you can get them higher though.
http://www.nissenmarkers.com/catalog/Category/Temperature-Indicating-Sticks
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wnelson aka. dedox
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« Reply #9 on: May 02, 2013, 11:19:12 AM »

here are the temperature telling sticks that Carter talks about, http://www.tempil.com/products/tempilstik-original/ and they go from 100 to 2000F
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« Reply #10 on: August 17, 2013, 03:50:31 AM »

My wife has a kiln she uses for ceramics, but it just has Hi Med Lo settings, I wish I had the know how to add a PID controller to it.
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mreich
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« Reply #11 on: August 17, 2013, 05:37:08 PM »

I think I just noticed something, Joe.

Do you just put a handful of blades in there?

I've found that it's pretty important to orientate my blades just right in my kiln. If I don't arrange them in the rack in an arrowhead formation, the ones close to the elements get way warmer than the ones in the middle.

It's easy to see the color difference, especially when I'm bringing them just to critical, then pulling them out right away. I use my kiln for the most accuracy on post forging quenches and normalizations.

I'm even careful of the order of the blades in the kiln. The ones on the outside go to the middle, and the ones on the right go on the left on the next heat.

I'm certainly not trying to take anything away from your oven, but I'm sure it makes a difference on short heats.
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Joe Calton
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« Reply #12 on: August 19, 2013, 07:15:36 AM »

mreich,  good eye!

 that pic was taken right after I built the kiln, and I was annealing those choppers at 990. I have since decided to put them in the kiln edge down as the heating element is about halfway up the wall of the chamber, that way the edges are close to the thermocouple, and they are out of line of direct heat from the element.

when I do annealing, I just pack as many as I can get in there at once that I have ready for annealing. when I am using the kiln for the heat prior to the quench, I do 2 at once, edge down, in the center of the kiln, and may drop down to one at a time on the next batch of kitchen knives I do. kitchen knives are the only thing I heat for the quench in the kiln, everything else gets heated in the forge, as I have more control and can heat just the edge.

I have thought about grabbing some 1/8" or thereabouts steel to make baffles for the sides of the kiln chamber to keep the direct heat from the elements away from the blades, but have not gotten to it yet.


also, every time I do a heat cycle in the kiln, it is over one hour. except the heat for the quench, when I bring the kiln up to temp first, then place the blades in, let them come up to temp for 10 minutes or so, then pull them out. so when the blades are getting heated over the 60 minutes, the element is fired in very short bursts of about 5-10 seconds each. I was in a hurry one day, and set the kiln to go from ambient to my hardening temp in 20 minutes to save some time, and melted down one of the SSR's, so now there is a second reason to take it slow!
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mreich
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« Reply #13 on: August 19, 2013, 07:35:08 AM »

Right on, Joe!

I'm glad you noticed that too, as it reaffirms my suspicions of the limitations of kilns.

Still, great work on making your own kiln! You did save a bunch of money, and that seems like a pretty advanced project!
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Joe Calton
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« Reply #14 on: August 19, 2013, 03:39:28 PM »

Thanks man!

Wait until I get the new modular propane forge/ electric kiln in one finished. you may just fall in love and make one for yourself!
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