How thick can porcelain be before kiln firing makes it unreliable?

It's been a while since I worked with this medium, but I'll try to convey some knowledge that may be helpfull.

Depending on the consistency of the slurry being poured will directly affect the dried results in it's "green" condition. Depending on how many times you fire the particular piece will also affect it's final size. Each time the piece will shrink more and more.

If you are looking for an exact finished size you will need experiment with the consistency of the slurry, the temperature it is fired at and how many times.

We normally would let large pieces slowly cool down within the kiln for 2 days to avoid shattering or cracking. The kiln door would be locked during this entire time.

Good Luck! Maybe someone else will have a better reference to go by.

Thanks for the response!

Shrinkage is not a concern. Nothing else has to fit this part once it's made. In addition, there are several machining actions to be performed that will prepare the geometry of the disk for subsequent post processes.

I am concerned mostly with the strength of the part during the firing the process and afterwards.

I know from my own experience that cooling heated parts too rapidly creates residual stresses internally and that those trapped stresses can cause subsequent failure even when external loads are light.

My ignorance in working with porcelain is what's showing here. The experience of most of the pottery people I've spoken to is limited to earthenware: the more generic clay based substrates common to making pottery.

I am still in the process of designing the geometry of the mold from which the prototype part will be formed. I can still change the wall thicknesses to suit the recommendations I receive.

The budget for this experiment is very modest. Since development funds are limited I would like to insure that the prototype comes out of the kiln in sufficiently good shape to justify further investment of time and money .

Thanks for the support.

BTW, is the bike in your avatar yours? Slick!

L.J.

Wish I did own the bike in the avatar. It has glass wheels. Looks like it's moving when it's parked.

Normally you can figure roughly 7 to 10% shrinkage but depending on the formula it can be 15 to 20%. Once you decide on the type and composition of the slurry you would need a test fire with your original specs and then compare the results. Vertical and horizontal shrinkage is also different but not by that much. You may want to start with the extra 10 % when poured and see how close you are when firing is complete.

Hi,

why porcelaine, why not alumina, zirconia ....?

Why not buy (Coors in the US, TKF in Germany, many others also)

Easiest way if alumina is acceptable: buy a ceramic bonded (alumina, white) grinding disc of desired shape. Machine to desired shape. Fill porosity with dental cement if required.

Firing is a time consuming and costly process.

Have success

RHABE

dear l.j.

i'm an artist who works in porcelain. i have found that, depending on the porcelain body and your immediate climate/environment, the "vessel" walls that contain your honeycomb feature [that IS the wall you're referring to, correct?] can be roughly up to twice the thickness as your honeycomb walls [.25"] and not give you too much problem during the drying/firing. it's best that the drying be slow and long [two to three weeks, depending on climate]. to accomplish this, keep the piece covered at all times with 5 - 10 minute phases of uncovering once or twice per day. rotate the piece one quarter turn per day. turn piece over every other day. this drying phase is as important, or even more so, than the firing phase. so go slow.

do not make the outer walls alot thicker or thinner than your honeycomb. that throws the shrinkage off. one dries faster than the other thus shrinks faster thus warps or cracks.

good luck.

bdehnert

Hi Bdehnert!

Thank You!

I understand what you said and very much appreciate your taking the time to help.

The outer wall (the perimeter) will be the same thickness as the walls that make up the honeycombs.

It may take some time to make the prototype and then fire it. As soon as I have something to report, one way or another, I will activate this string.

To Bdehnert and all of you that supported this inquiry, thanks!

L. J.