Kiln Ventilation - faster firing?

[Paul Tarlow]

I know that kiln ventilation systems are promoted as speeding ceramic firings.

Does the greater evenity they provide allow faster cooling with glass?

- Paul

[Bob]

Hi Paul,

I have an Orton Kiln Vent on each of my two kilns. They draw a small amount of air downwards through holes in the lid of the kiln. SO the kiln can be kept closed during the firing. Orton states in their literature that the vent improves evenivity. I am not sure. I have noticed darker regions on the surface of glass when it starts to glow incandescently. I believe these are cooler spots that are caused by downward drafts. The darker spot is always in the same relative position on the kiln shelf. On the rare occasion I have had pieces thermally shock with the crack going through the area where the darker spot is located.

So what do I do about it? I only run the venting system during the initial heating through the brittle zone ( I turn it off at about 800F). I don't use it for cool down. I run the vent through a dimmer switch to slow the fan speed down.

These are just observations... I may be totally out to lunch on this. But I don't think that the venting improves evenivity for glass kilns.

Cheers,

Bob

[charlie holden]

I have Orton vents on my kilns and I think they help with evenivity. I was worried about the potential problem of cold air being pulled in and directed at the glass, as Bob has talked about, so I installed the inlet vents in the walls of my kilns. The air is pulled in horizontally about an inch below the ceiling, and is directed across the kiln and at the elements hanging on the ceiling. The air is pulled out the floor of the kiln.

The amount of air pulled through is not enough to even things out when the elements are on full blast. I have three thermocouples at various hieghts in a broad, wide, shallow kiln. The ceiling elements definitely heat the upper thermocouples faster and hotter than the lower ones. So I still have to rely on element spacing across the ceiling for evenivity across the surface of broad pieces.

It is during soaks that venting pays off. Both slump soaks and anneal soaks are very even top to bottom when air is circulating. I have found this to be critical when doing dropouts.

The other great advantage is that fumes get pushed through to the outside. Very little smell of smoke when burning off binders and the like. If you don't need to pull off fumes, Henry Halem has a system of circulating air in his casting kilns that uses positive pressure forcing air into a manifold that runs along the bottom of the kiln. See his website: glassnotes.com

Bob, you might be able to suspend a ceramic disk below your inlet holes to redirect the air away from your glass.

[charlie]

So what do I do about it? I only run the venting system during the initial heating through the brittle zone ( I turn it off at about 800F). I don't use it for cool down. I run the vent through a dimmer switch to slow the fan speed down.

you probably already know this, but a lot of motors aren't designed to run through dimmers. doing so can burn them up.

[Cynthia]

I have Orton vents on my kilns and I think they help with evenivity. I was worried about the potential problem of cold air being pulled in and directed at the glass, as Bob has talked about, so I installed the inlet vents in the walls of my kilns. The air is pulled in horizontally about an inch below the ceiling, and is directed across the kiln and at the elements hanging on the ceiling. The air is pulled out the floor of the kiln.

The other great advantage is that fumes get pushed through to the outside. Very little smell of smoke when burning off binders and the like. If you don't need to pull off fumes, Henry Halem has a system of circulating air in his casting kilns that uses positive pressure forcing air into a manifold that runs along the bottom of the kiln. See his website: glassnotes.com.

I also use the Orton venting on both of my kilns. In the Jen-Ken 21" shelf, brick kiln, side and top elements, it is effective for venting fumes only. Evenivity isn't really an issue in this kiln and venting doesn't noticeably speed up cooling. the inlet holes are placed in the lid near the center, with outlet holes in the floor in a similar position. This works well for venting fumes, but not for any other purposes in my experiences. I haven't experienced the cold spots from air coming in with either kiln. They are all different.

In my Denver which is a larger 30" x 60" x 15" deep fiber kiln, the inlet holes are drilled one per side about an inch below the top edge with outlet holes drilled in the center of the floor (both vents are plate mounted to thd bottom of the kilns). The elements on this kiln are in the lid only, and it has cool perimeters. Once I installed the vent on the Denver, I did see improvement with the cool perimeters, but it wasn't a fix. Also, not a noticeable difference in the rate of cooling the kiln.

I use the vent up to 1000 F to vent out fumes from organics, lusters, glues...not for even heating or rapid firing. Doesn't really help significantly with those issues.

[Bob]

So what do I do about it? I only run the venting system during the initial heating through the brittle zone ( I turn it off at about 800F). I don't use it for cool down. I run the vent through a dimmer switch to slow the fan speed down.

you probably already know this, but a lot of motors aren't designed to run through dimmers. doing so can burn them up.

Actually charlie I didn't. Thanks for the tip. I've been doing it for about 6 years so I guess these motors are OK. Good idea about the ceramic disc. Thanks

Cheers,

Bob

[Brian and Jenny Blanthorn]

I know that kiln ventilation systems are promoted as speeding ceramic firings.

Does the greater evenity they provide allow faster cooling with glass?

- Paul

Was something on this over craftweb a while ago

As U R awaire there is 2 different cooling

Above aneal n after

After realy is a problem of thermal shock

I could C a system where air could B drawn allong pipes on the kiln thereby preheated then introduced in2 the kiln