[joy72]

I have a Cress Kiln model # B-23-H. Firing green wear everything works great. When I do the final glaze firing, the lid on my kiln seams to warp open slightly. I am trying to obtain cone 6 firing. Cone 5 (witness cone) is the only one that bent. It took about 6 hours to fire the green wear and I had the kiln on for 12 hours for the final firing. My question is what is wrong with my lid? The kiln is level and the lid sits level when it is closed and not being fired. Did I just buy a dud? Is is a used kiln in good shape. Any suggestions? ~ Joy

[neilestrick]

This is perfectly normal. As the kiln heats up, the bricks expand and the lid lifts. Typically the gap opens up in the front because the back is held in place by the hinge. The newer hinge systems used by L&L and Skutt (and possibly others) have the hing pin running through an elongated hole, which allows the hinge side of the lid to also move up and down, keeping the lid level as it expands.

The kiln not reaching cone 6 is probably not related to the lid, unless your cone was right up near the lid. The sitter probably needs adjustment, or just put a higher cone in the sitter.

[joy72]

neilestrick, on 12 May 2012 - 09:55 AM, said:

This is perfectly normal. As the kiln heats up, the bricks expand and the lid lifts. Typically the gap opens up in the front because the back is held in place by the hinge. The newer hinge systems used by L&L and Skutt (and possibly others) have the hing pin running through an elongated hole, which allows the hinge side of the lid to also move up and down, keeping the lid level as it expands.

The kiln not reaching cone 6 is probably not related to the lid, unless your cone was right up near the lid. The sitter probably needs adjustment, or just put a higher cone in the sitter.

Thanks for the reply. I did install a new cone sitter (the ceramic part with the rod and holder) so it is probably not adjusted correctly. Any helpful hints on how to adjust it? (I am very new to this) ~ Joy

[Marcia Selsor]

Yes it is normal. I place an extra inch of ceramic blanket on my electric glaze firings as well as spray the lid interior side with ITC ceramic coating for added insulation. But the bricks expand when heated to the higher temps and cause the visual gap you describe. As Neil says some kiln companies have improved the hinge design.
Marcia

[neilestrick]

How to adjust sitter HERE.

[joy72]

Marcia Selsor, on 12 May 2012 - 10:32 AM, said:

Yes it is normal. I place an extra inch of ceramic blanket on my electric glaze firings as well as spray the lid interior side with ITC ceramic coating for added insulation. But the bricks expand when heated to the higher temps and cause the visual gap you describe. As Neil says some kiln companies have improved the hinge design.
Marcia

Thanks for the tips, I have never heard of ceramic blanket before.

[joy72]

neilestrick, on 12 May 2012 - 10:57 AM, said:

How to adjust sitter HERE.

Great help! Thank you, I love your blog ~ your pottery is stunning.

[neilestrick]

joy72, on 12 May 2012 - 12:26 PM, said:

neilestrick, on 12 May 2012 - 10:57 AM, said:

How to adjust sitter HERE.

Great help! Thank you, I love your blog ~ your pottery is stunning.

Thanks! Happy to help!

[Arnold Howard]

joy72, on 12 May 2012 - 10:34 AM, said:

I have a Cress Kiln model # B-23-H. Firing green wear everything works great. When I do the final glaze firing, the lid on my kiln seams to warp open slightly.

As others have said, a slight gap between the lid and kiln body is normal. You will see light under the lid due to that gap. However, something is wrong if the lid rises in the front.

A gap forms under the lid because the center of the lid bows inward slightly as it gets hot. This happens because the outer surface of the lid is cooler than the inner surface, so the lid expands more on the hot inner surface.

If the lid actually rises in the front, the hinge may be bent. The hinge should have play in it to allow it to remain flat against the kiln. Without the play, the lid can rise 1/4" or more at the front.

Sincerely,

Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
ahoward@paragonweb.com / www.paragonweb.com

[joy72]

Arnold Howard, on 14 May 2012 - 06:03 AM, said:

joy72, on 12 May 2012 - 10:34 AM, said:

I have a Cress Kiln model # B-23-H. Firing green wear everything works great. When I do the final glaze firing, the lid on my kiln seams to warp open slightly.

As others have said, a slight gap between the lid and kiln body is normal. You will see light under the lid due to that gap. However, something is wrong if the lid rises in the front.

A gap forms under the lid because the center of the lid bows inward slightly as it gets hot. This happens because the outer surface of the lid is cooler than the inner surface, so the lid expands more on the hot inner surface.

If the lid actually rises in the front, the hinge may be bent. The hinge should have play in it to allow it to remain flat against the kiln. Without the play, the lid can rise 1/4" or more at the front.

Sincerely,

Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
ahoward@paragonweb.com / www.paragonweb.com

Arnold, There is more then a 1/4" gap up to 1/2". I will check the hinge, I am suspecting that may be the problem. I am not sure if it is an adjustable type of hinge or not. Does a draft play a part in the lid staying flat? I have my kiln in my garage with just natural airflow (garage door open a foot and the back door open about a foot also). I am so very grateful for finding this community~ what a great support for budding artists.
Thank you
J.Joy White

[yedrow]

Unless mentioned, we use square cones instead of the sloped triangular based cones to get a more accurate firing. At home doing ^6 I use a ^7 in the sitter and watch large cones through the peep-hole. I don't particularly trust a kiln-sitter.

[Arnold Howard]

joy72, on 14 May 2012 - 08:53 AM, said:

Arnold, There is more then a 1/4" gap up to 1/2". I will check the hinge, I am suspecting that may be the problem. I am not sure if it is an adjustable type of hinge or not. Does a draft play a part in the lid staying flat? I have my kiln in my garage with just natural airflow (garage door open a foot and the back door open about a foot also).

Joy, a draft from the garage should not affect the lid.

When the kiln is at room temperature, lift the back of the lid near the hinge. Does it have play? A bent hinge can bind the lid and prevent it from "floating" as the kiln gets hot. A bent hinge is easy to fix. Straighten it with pliers. Do not place a brick on the lid to prevent the lid from rising.

As the firebricks expand, the kiln will grow a little in height. This will cause the lid to pull down at the hinge just enough to raise the lid at the front. That is the purpose of the play in the hinge.

Sincerely,

Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
ahoward@paragonweb.com / www.paragonweb.com