New Rohde Kiln Lid Gap And Cooling Down Rate

[agafdesign]

I've just purchased a brand new Rohde TE 75 MCC with the ZWR 75 extra ring. Got off to a rocky start because the TC 304 controller supplied with it was faulty but now got a replacement.

 

Two days ago I did the first firing so the kiln was empty (100 C per hour up to 1050C - held for one hour) and not sure about a couple of things:

 

Lid Gap

I've read here:

http://community.ceramicartsdaily.org/topic/2278-kiln-issues/

That a gap between the lid and body is normal at high temperatures but ....

 - Should I still expect such a gap on a brand new kiln?

 - What is the point having a ventalation pipe if all the fumes will come out of this gap anyway?

My gap was not at the hinge end or by the front clip.

 

Cool Down Rate

The kiln heated up perfectly according to the programme. After the hour at 1050C it switched off (there are no options on this controller to set the cool down rate). In the first 5ish minutes it cooled 80C. After about 20 minutes it was down some 200C. Is that kind of cool down rate normal?

 

I've read this:

http://community.ceramicartsdaily.org/topic/4969-how-fast-is-your-kiln-heating-up-and-cooling-down/

which seems to suggest a much slower rate but then it could be a different kiln or it could be because my kiln was empty ... ?

 

Any thoughts would be very helpful.

[Arnold Howard]

The lid of even a new top-loading kiln will have a gap. It is normal. But a large gap (about 1/4" -- 6mm) indicates that the lid cannot "float" to compensate for expansion of the firebrick firing chamber. The bricks expand when they get hot. How wide is the gap under the lid when the kiln is hot?

 

The cooling rate of your kiln seems to be fast.

 

Sincerely,

 

Arnold Howard

Paragon Industries, L.P., Mesquite, Texas USA

ahoward@paragonweb.com / www.paragonweb.com

[neilestrick]

I respectfully disagree with Arnold. I think that cooling rate is not too unusual for an empty kiln. The ware is what really holds the heat in. The bricks will hold a certain amount of heat, more more so at the lower end of the firing, not at peak temp. If the lid gap is quite large, that could be contributing to the fast cool down.

[agafdesign]

@Arnold - thanks for that. I would say at the peak temperature the widest gap could be 5mm but very hard to measure because of the heat!

 

I'm wondering ... there is a clip on the front to stop someone accidently opening the kiln. I had this closed and in that area, and around the hinges at the back, there was no gap. But should I leave some play in the clip which would allow the lid to lift here. That way it might float more easily and evenly with a smaller gap all the way round?

 

Still going back to the other puzzle - why have a ventalation pipe (which I have out the side) if fumes will come out of this gap anyway??? Can't get my head round that.

[agafdesign]

@neilestrick

 

Thanks for the feedback. I guess the only thing to do is monitor the cool down rate when the Kiln is full. I plan to do a bisque firing later this week....

[neilestrick]

Your vent should still work. All lids gap at least a little. Try firing without the clip and see what happens.

[Chantay]

I don't know where you live, but at 10 degrees Fahrenheit this morn I decided not to fight the weather and postpone firing my kiln for two days till warmer. I imagine external temp can affect cool down. I have anew kiln and older one. My new kiln shows a gap at the lid when firing, old one not so much.

[agafdesign]

Thanks all.

 

When fully loaded on a bisque fire it took 18 hours to go from 960 degrees to 100 degrees C and so that seems more normal. The floating lid still gets me though!