Monday, March 25, 2013

Further Test on Stainless Steel Foil Box

by Janet Alexander
Technical Advisor

In my March 1 blog I found a way to make a stainless steel box from foil I can easily purchase at Grainger.  
In my test, the sterling silver fired perfectly and the box didn't flake. I had someone email me that she had purchased some foil online and that after six firings the foil fell apart. So, I did some more testing on my box.

Its still strong
I fired it at 1500 degrees F for 30 minutes with carbon in it. It never fell apart but it did have some minute flaking after the 8-9th time. It is still strong and the lid still is flexible at the center bend I made for opening. But hey, for the price of $28, I can make a heck of a lot of boxes in different sizes to accommodate what I want to fire without flaking for the first several firings.

But look at the flakes. . .   I didn't even notice them until they started building up on the kiln floor.
Tiny Flaking

I tested a little further and fired the box at 1650degrees F for one hour. No problem. Even though the suggested maximum temperature for this foil
(321) is for 1600 degrees, it worked fine. Now, that's not to say that I recommend firing it at a hotter temperature than what the manufacture suggests. I am sure that over time it will degenerate at that temperature and intermittent heating.

The chart on the left shows that this foil is good for intermittent use up to 1600 F and 1700 F for continuous use. The difference in these two uses is attributable to the cooling down of the metal. As it cools, the metal contracts. As it heats, it expands. This process causes the scaling or wear to occur from the stress of heating and cooling - and this happens more quickly with shorter, more frequent firings.

A lesson I'd like to reiterate here is to always follow the manufacture's suggested use if you want to have an expected outcome. If you deviate from that, then test first.

In the meantime have fun claying around!


karenchrist said...

We rely on our pyrometer to tell us the temperature in our kiln, then we are shocked when something strange happens. When I got a bunch of bronze nuggets out of my kiln I found that my pyrometers reading was 200 degrees off and I couldn't depend on the reading it was giving me. With glass I was firing visually but the clay cannot be done that way.

Janet Alexander said...

Very true Karen!
Thank you for your comment!