Unexpected Result During Fire Resistance Test (final Test)

Introduction: Unexpected Result During Fire Resistance Test (final Test)

That’s the second part of refractories test. After that test I will choose the best material for my new metal melting furnace project. This particular experiment consists of 2 smaller tests

Step 1: Proportions for the First Test

During the first test, I made such mixtures:

1. Fire clay – 100%;

2. Fire clay – 40%; Grog – 40%; Graphite dust – 20%

3. Fire clay – 40%; Grog – 50%; Graphite dust – 10%

4. Fire clay 40%; Grog – 50%; Graphite dust – 5%; Mineral wool – 5%

5. Fire clay – 40% Grog – 40%; Graphite dust – 10%; Alabaster – 10%

6. Alabaster – 50%; Sand – 50%;

7. Cement – 50%; Sand – 50%

Step 2: Drying Into the Oven

I put samples into the oven to dry them:

- 5 hours +50 C° (122F°);

- 2 hours +100+180 C° (212-356 F°);

- 2 hours +250 C° (482 F°).

Step 3: After the Oven Drying

All samples survived except one. Sample #6 (Alabaster/Sand – 50/50%) was damaged during the air drying.

Step 4: Testing With a Torch

First part of the test was with gasoline torch. During it samples didn’t get any damages.

Step 5: Testing in the Melting Furnace

Second part of the test in the smelting furnace was much more destructive. The process took about an hour. In my opinion, the temperature was more than 1200 C° (2192 F°). All samples were damaged. Only the sample #3 got minor damages. Therefore, in this test it’s the best result.

Nevertheless, the sample #7 (cement/sand – 50/50%) was damaged but held the shape. Therefore, I wanted to make one more test where cement could be one of the main ingredients.

Step 6: Second Test Samples

During the second test, I made samples:

1. Cement – 50%; Sand – 25%; Grog – 25%;

2. Cement – 50%; Fire clay – 25%; Grog – 25%;

3. Cement – 40%; Sand – 17.5%; Grog – 15; Fire clay – 27.5%;

4. Cement – 22.5%; Sand – 27.5%; Grog – 22.5%; Fire clay – 27.5%;

5. Cement – 22.5%; Sand – 22.5%; Grog – 22.5%; Fire clay – 27.5%; Graphite dust -5%

All steps of the process were the same as in the first experiment.

Step 7: Melting

Finally, in the smelting furnace samples started melting. I think that the problem is the sand and the cement.

Step 8: Final Results

I used the river sand and not the silica sand. Silica sand as I now sustain much higher temperatures than river sand.

I’ve made a decision to use fire clay/grog/graphite dust (40/50/10%) in my new furnace.

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    6 years ago

    Well in mine I use 50% plaster of paris and 50 % perlite or the same with vermiculite added in so theres another 3 ingredients to test .You have your work cut out for you now . Better to read up , follow established routes then branch off I think


    Reply 6 years ago

    Thanks for you receipt. Could you share how much vermiculite did you add?

    Of course theory is important and I read about some working formulas. My idea was to use ingredients which are easy to find. Such things as perlite and vermiculite are not sell in next door shop and even in supermarkets in my country. The stuff you mentioned could be bought only through the Internet or in some exclusive shops. My idea was to use widespread materials. I will definitely write if my final formula is bad and doesn't work in the furnace during real melting.

    P.S. The only thing which is not widespread is graphite dust but it's produced near my town, so it wasn't hard to buy it :)


    Reply 6 years ago

    perlite and vermiculite can both be found pretty darn easy, even in small towns. you just have to know where to look.

    The gardening center of even a tiny hardware store should have 5lb bags of both. ANY greenhouse type store will have both, and almost any building center will at least have perlite.

    Just be aware that it will make a lighter product with better insulating qualities, but it will NOT raise the temperature resistance of your formula.

    Personally, I use an almost 50/50 mixture of kaolin and kyanite, and then add 'busted crucible and firebrick grog" to the mix. Regular grog is too variable for my taste. I have successfully melted small batched of iron using my recipe. You do need to fire the vessel(like any other high temperature ceramic vessel) before putting it into service. And before each use, I thoroughly dry it next to the glory hole, so that any absorbed moisture from the evening before doesn't explode my precious clay metal melters.

    If you intend to do iron though, best off just getting a good graphite crucible or 4. For aluminium, a small, deep cast iron pot with a clay wash works as well or better than ceramic crucibles. Bronze requires the same basic set up as iron.

    Just my two cents.


    Reply 6 years ago

    Thank you Ironsmitter. Your information is very interesting and useful.
    You're right, I didn't check greenhouse type stores. That's a good idea. About
    other stores... Types of products which are sold can be different because of
    the country. Yes, of course, now we have globalization and the world became
    smaller but some goods can not be used or at least widespread in a particular
    region except some common basic products. Now, I use only handmade steel crucibles for aluminum as well as brass
    melting. I will definitely need a graphite crucible
    when I try to melt iron. Thanks again
    for your tips.


    6 years ago

    Challenge assumptions and accepted practice, dare to discover for yourself by being scientific, all are traits of the successful in life.

    You will go far! ☺


    Reply 6 years ago

    Thanks Hank. I really appreciate you words. :)