Kiln Corrosion vent and elements

[JBT]

I’m having a little bit of a problem with heavy corrosion in my down draft vent and I’m also having to replace my heating elements at a faster rate then I should.

I have an L&L Equad production Kiln

I first fired it August 11^th and had replace the heating elements after 45 firings or so in the begging of October.  Firing to cone 6 for glaze and 06 for bisque

I sometimes open the kiln a little on the early side around 400 F (I know this is not best use but could this cause corrosion)

My down draft vent has corrosion through out the venting system and in the motor and exhaust

So I’m really trying to figure out what I’m using that causing this corrosion.

My first though is Aluminum Hydrate powder. I use it both to prevent glaze from sticking and to allow slide on my larger pieces 15 to 26 in wide. I find it reduces the risk of cracking. I know that silica sand can be used in it place to prevent cracking.

I generally dry piece well and do a long preheat. Especially when large pieces are in the kiln.

I use a Standard’s #182 White Stoneware C/10: I know white clay can sometimes be corrosive in pug mills

I can also go into more detail about recipes if anyone thinks that might be part of the problem

Thank you all and happy 2023

JB

[neilestrick]

What firing schedule are you using?

Are you firing a lot of really flat pieces and packing the kiln with a lot of shelves?

How did you determine that you needed new elements after 45 firings? That's a ridiculously short time for that model.

Where is the kiln located?

Are the vent holes in the floor of the kiln clogged?

Alumina hydrate won't affect anything.

Corrosion in the vent is normal. You're pulling all those fumes out of the kiln and they mix with the moisture also coming out of the kiln and it creates a fairly corrosive  environment. You should still get a few hundred firings from your vent motor before it needs replacing, though.

Side note, 182 is not a good clay for cone 6 functional work. It will be under fired at cone 6. If you're doing functional work, consider using #630 instead, which will fully vitrify at cone 6 and is very similar.

[JBT]

thanks neilestrick!

at this point I don't have too many flat piece but was going to be getting more shelves because my large plates are pretty popular right now. 

I do have piece that take up most of the my 10 cubic foot kiln. usually firing  2 to 4 layers in my 36 in tall kiln.

the element broke which is why i replaced it. probably could of gotten more out if it but was careless in cleaning the elements/element holders.

my vent system has corroded so much their is a hole in it along where a heat band from the lid hits it . Its 18 in from kiln. I was going to take apart the motor once my current firing is finished and cool to see what the damage is.  I think Im probably around 70 or 80 firings I'll have to check.

as far as i can tell the vent is not clogged.

 

yea I know the cone 10 clay is not great for cone 6 firings but I wanted to be able to fire my work in community gas firings and wood firings that fire to cone 10. I think moving forward I'll switch to more appropriate clay.

[neilestrick]

6 hours ago, JBT said:

the element broke which is why i replaced it. probably could of gotten more out if it but was careless in cleaning the elements/element holders.

So you only replaced the one element? Sometimes and element will randomly break if it gets crud on it, or if there's a flaw in the wire or some unknown reason. It happens. That doesn't meant that all the elements are worn out, though. You should be getting anywhere from 200-300+ firings from the elements on that kiln.

On the box that connects to the bottom of the kiln, how far open is the little slider? The hole it covers should be 1/2 open. If you've got it too closed off then you won't be mixing enough room air to dilute the air from the kiln, and you'll be starving the vent for air.

The flexible duct coming out of the vent motor won't necessarily last all that long. They get eaten up pretty fast. They start to become brittle and weak, at which point if you bump it you can poke a hole in it pretty easily. To make it last longer you can use rigid metal duct, or a rubberized/plastic hose that can handle the heat. The Orton kiln vent comes with a rubberized hose of some sort.

What firing schedule are you using?

[JBT]

I replaced all of the elements. Perhaps i should have only replaced the one :).

the slider was all the way open. I adjusted to 1/2 open.

do you think  this Industrial Duct Hose, 3"x25ft would work?  https://www.zoro.com/hi-tech-duravent-industrial-duct-hose-3x25ft-2001-0300-1025/i/G1869697/

thank you so much, neilestrick you have been a huge help so far!!

Cheers

JB

[neilestrick]

You'll need to see what the max temp rating of the hose is. I wouldn't use anything rated under 250F. Check out McMaster Carr or Grainger if you don't need 25 feet of hose.