Kilnformed Container

[Paul McNulty]

Hydrostatic pressure of a 24" column of glass works out to 2.17 psi.
Although the compressive strength for Vermiculite board is close to 150 PSI & its Modulus of Rupture is 36. This is equivalent to a 2 pound point load breaking a 1" x1" bar over a 12" span for a 3 point bend test. Although it is strong in compression - its low tensile and flexural strength require that casting vessels be engineered in such a way that they cannot flex (or be in tension) when loaded.

[NancyB]

In the video, the annealing time is computed by multiplying the box thickness by 4 and following the annealing cycle for that thickness. Can you tell me where the factor of 4 comes from?

Thanks.

[NancyB]

So, it's been almost a year since I posed the above question. Any thoughts?

[ejgiebel]

I use the time of day plan with my electric company (I get charged a lower rate during lower demand periods, which includes the weekends) and I am assuming that the 8 hour hold at 200 degrees is to fully dry the investment block so as not to get steam bubbles. I am hoping I can do that ramp to 200 and hold for 8 hours as a separate step prior to adding the glass and sides, and then just ramp from room temp at 100 degrees an hour until I get to bubble soak at 1225.

Just trying to fit this into the 9pm Friday to 5am Monday window for lower cost electric. Once it gets down to 250 degrees, it won't need much power to keep the ramp down at 41 degrees an hour. Oh, and I live in the desert, so the investment block isn't going to pick up a lot of moisture from the air if there is any concern about that.

[mksanders2020]

How does one make the kiln formed container using billet instead of strips?

[marykaynitchie]

I think that you can cut the right amount of billets by weight and stack the pieces over the core. The glass should flow to the sides, and form the walls and bottom of the box.

Mary Kay

[Lschnellinger]

How thin can I got on the walls of the container? I’m thinking I can make it as thin as I can cut strips, so 1/4”?

Also, on the firing schedule - I would think the slow drop from process temp to annealing temp would risk devit in that range. With open-face casting, we drop AFAP from process temp to 1225 and do an anti-sucker hold, before dropping 50 dph to 900. Seems like that should work for this process as well, right?

I’d also like to repeat the above question from Ed: why not pre-dry the investment mold separately from the firing?

Thanks much for any help.

[marykaynitchie]

The slow drop is there for a reason--the form of a box is much more challenging to anneal than most open-faced molds. We are not sure how thin you can go with this process, but if you try it and find out, please let us know!

Mary Kay