Newbie used kiln rebuild.

[Wiremonkey]

Hello all.  New to this forum.   Been getting a lot of good info from here.  I do a lot of fabrication work and have access to a clay 3D printer but no easy way to fire things so decided to get a kiln.   After looking at new ones and finding out what kind of lead times there are to get one I started looking for a used one.  Slim pickings there too.  I found one that needed work for $50.   Went to pick it up and saw how the guy was just bouncing it around on a dolly I knew it was going to be a fair amount of work.  So talked him down to $40 and drove off with it. 

I ended up with a Cress FX-23-B.   Seems like it was made in 2009.   Cone 10 kiln.   Lots of bricks broken, floor cracked pretty bad, pan rusted out, elements broken, kiln sitter tube broke and missing some pieces, thumbwheel seized and lots of rusty screws.  Also, my place has 208 so had to change the element voltage.   Cress was a big help in getting me parts.   Because I went to 208 a lot of the wiring had to be upgraded to handle the new amperage.  Luckily I live by an aerospace surplus store that sells new high heat cable by the pound.  Wire is the cheap part.   Also made a new metal floor from stainless to replace the rusted one from a scrap I had.  

I'm going to build a controller using a Arduino and an SSR.   I do a lot of high voltage dimmer repair in theaters so have lots of new high amp SSRs.   Even have a rugged high temp arduino from another job.  I ended up gutting the kiln sitter and timer wheels and will build an enclosure on top of the existing one as there is no chimney on this one.   I work with industrial automation as well so will build in safety contactors.   I thought about getting a PID controller but I really don't like the weird menu structures.  This arduino version will be a spreadsheet of firing schedules that will live on an SD card that I can select from.  

In the end this is going to be about $1000 kiln.  I know that's not cheap but know I know this thing inside and out.    After reading a lot of posts seem people just toss these when the bricks get bad.  I probably made a mistake but it's an interesting journey to rebuild one.  

I do have a question about the bricks.  Is it ok to mix new and old?  I did a lead test and found none on there.   I attached some pictures.  One shows how bad the bricks were and one shows the new Bricks.  I reused 11 of the 40 bricks.  

Sorry if this is all rambling.  I'm bad at introductions.

[neilestrick]

Looks good. No problem mixing old and new brick. Most people toss them when that many bricks are beat up  because it usually coincides with the bricks being very old and getting weak and crumbly. And if they're paying a repair person to do the work it gets really expensive to do a rebuild that extensive. At some point it's more cost effective to get a new kiln with updated controls. Doing it yourself it's a worthwhile investment. Nice work.

[Wiremonkey]

Thank you Neil.   Sometimes there is no turning back once you start.  One thing I couldn't find info on is how tight the stainless jacket should be.   Was pretty loose when I opened so wasn't sure how much to tighten it back.  Do you need to keep room for expansion?   Also, if there is no chimney to hold the mushroom ceramic insulators is it ok to flip them over so the wider side is against the brick to stabilize it more?  

[neilestrick]

1 hour ago, Wiremonkey said:

Do you need to keep room for expansion?

No, get it tight.

1 hour ago, Wiremonkey said:

Also, if there is no chimney to hold the mushroom ceramic insulators is it ok to flip them over so the wider side is against the brick to stabilize it more?  

Do you mean the insulators that go over the element pigtails? If the stem is broken off, I would replace the insulator, as the stem is what keeps the pigtail from contacting the metal jacket.

[Wiremonkey]

Yes.   Those insulators.  They aren't broken but this kiln didn't have the extra piece of bent sheet metal with the holes where those insulators go.  They were just pushed up against the brick.  Seemed a bit wobbly.  Was thinking of flipping the insulator over to make it more sturdy.  Since I'm going to put a new enclosure on top of the original housing I figured it would act as the chimney to keep some of the heat away from the electronics.   

Haven't figured out why this interface rotates some pictures. 

[Mark C.]

Its ok that they are  against the bricks-do not rotate them. You will find the wire pigtails stick out just enough to hold them in place. The metal jackets always has those holes which give them some space .

You can see them in the 4th photo down on my rebuilb a few years ago here

 

[Wiremonkey]

That's an awesome rebuild.  I guess what I'm trying to figure out is that this kiln doesn't have that extra piece of sheet metal that the insulators rest on.   The part I marked A in your image.  I have only the B side of this. 

 

 

[neilestrick]

If your pigtails are centered in the holes and coming through the brick perpendicular to the brick, then you could turn the insulators around. But depending on how the brick are grooved, they may come through at an angle, or may not be perfectly centered. If that's the case, I would enlarge the hole in the brick slightly so that the stem of the  insulator goes into the brick a bit to keep the pigtail from contacting the jacket.

[Wiremonkey]

That makes sense.  I have to drill out the holes for the pigtails so will try and make them as perpendicular as possible.  Thanks again for the help. 

[Mark C.]

The A and B image did not post-but I get that you need to drill out the bricks a little to fit insulators

[Wiremonkey]

What temp does the exterior of kilns usually get?   Would a paint that can handle 650 deg F be ok for the control box?

[neilestrick]

2 minutes ago, Wiremonkey said:

What temp does the exterior of kilns usually get?   Would a paint that can handle 650 deg F be ok for the control box?

That should work for the control box. @Mark C. what kind of paint did you use on your Skutt rebuild?

[Mark C.]

I used high heat engine paint. I got the old paint off with  wire wheels (assorted sizes) and the new paint is holding up very well. Engine paint has limited color selection as the only draw back. I have used silver high heat paint for 4 decades with great results as well.

In terms of the A and B photo -skutt uses a metal hold off piece of metal that the box is screwed to to keep it cooler-its a simple good design.Every manufacture has a different approach to this heat issue

[Wiremonkey]

Than makes sense.  I have a can of 2k Ford Blue engine paint.   Will see how that goes.   

I think that extra piece of metal is on the newer Cress kilns.   Not this one though.  I'm going to keep the original control box as a heat shield and add a smaller one on the front of it.   

[neilestrick]

3 minutes ago, Wiremonkey said:

I'm going to keep the original control box as a heat shield and add a smaller one on the front of it.   

That's a great way to do it. Keep all the important stuff in the outer box and everything will stay cooler. Relays will last a lot longer.

[Bill Kielb]

On 9/25/2021 at 10:50 AM, Wiremonkey said:

I'm going to keep the original control box as a heat shield and add a smaller one on the front of it.   

Just a suggestion, if you limit the size of the attachment points of your control box  you will reduce how much heat is conducted.  Anything that limits the contact area and creates a space for air is very effective at reducing the conductance. If your control box has a continuous attachment tab on both sides, stand-off with washer or dimple in the metal is old school very effective and simple. Additionally the Element plane / control plane shield  or separation is  fairly standard now.  Usually perforated top and bottom to allow air to rise and vent naturally. Also very effective.

[Wiremonkey]

Thanks for those tips.  Makes sense to dimple the metal to detach it from the other box.     Here are some progress pictures of what I'm doing.  I'm removing the control box from the relay box so I can hold it and not have to crouch down.  The secondary box is a bit bigger as I wanted to add a fan to cool the relay, contactor and power supply.  Top and bottom of the secondary box is vented top and bottom.  

[Bill Kielb]

Looks nice. If you have not already done so, the  fan  traditionally would be at bottom (to get the coolest air) blowing in to pressurize as practical to maximize heat transfer. Passive cooling is usually desired for maintenance and longevity but the fan ought to do a nice job. Looks nice and tidy. Is the controller a pid module (off the shelf temperature controller)?

[Wiremonkey]

Thanks Bill.  The fan is actually at the bottom. This site seems to rotate picture for some reason.   I use these fans in installations and one has been running 5 years 24/7 in not great environments.  Just have to blow them off once and a while.  
 

The pid controller is a custom arduino configuration in an off the shelf enclosure.  I use a lot of PID controllers for motors and just find them aggravating.   The cool thing about this control design is I can lay out my firing schedules in a spread sheet, put them on an industrial micro SD and pop it in the controller.  No millions of cryptic 3 digit codes that make no sense.  Plus I can program what safety features I want or what feedback I want to see.  

[Hulk]

When we cleaned dusty control boxes (and PCs) out on the floor at the steel mill, we then fitted them with fans that blow into the box, with a oiled foam carburetor air filter (like one used to see on motorbikes) on the outside - then there's periodically cleaning the filter instead of the box filling up with metal dust, and side benefit, the fan lasts longer. A typical callout was overheat shutdown due to power supply fan locked up - full of dust.

[neilestrick]

I've got a fan in the control box of my big kiln with SSR's. It's a freestanding box next to the kiln, but the radiant heat from the kiln still heats it up quite a bit. I think fans are a smart way to do it since kilns rooms are typically pretty warm, and the area immediately around a kiln is pretty warm regardless of how well the room is vented. I put an SSR in the wall mounted control box of my baby test kiln, but on that one I mounted the heat sink with the cooling fins on the outside of the box so I wouldn't need a fan. However, when I have the two big kilns running at the same time as the baby kiln I've noticed that the cooling fins run considerably hotter, so I aim a box fan at the controller at those times. I'm going to add a cooling fan into that control box so I don't have to use the box fan.

[Wiremonkey]

Hi all.  Thanks for all the great tips.  Really helped.   

I've got it all put together and fired it up.  Just wanted to burn off the element film so didn't go too high.  Nothing blew up though!  Was a heck of a project to sort out.  Know way more about kilns now than I thought I would.   Made some weird decisions on design that made it all a little bulkier than I thought it would be but will be fine once its placed.  I have an automotive heat shield between the original box and new box but want to add some heat batting.  Is the ceramic stuff the way to go?  

[neilestrick]

8 hours ago, Wiremonkey said:

I have an automotive heat shield between the original box and new box but want to add some heat batting.  Is the ceramic stuff the way to go?  

Ceramic fiber would be overkill for between the two boxes, and it's not at all durable or safe to work with. Most kilns just have a 1/2" thick fiberglass type insulation to protect the electronics. Plus with that big cooling fan it's probably not all that necessary anyway.