Monday, December 8, 2014

Serious Progress on the Foundry Furnace

I intended to be this far along after last weekend but being ill last weekend changed those plans.  I was able to make some serious progress on it this weekend.

Friday morning before work, I finished cutting the top to allow for a smaller, hinged lid so that I don't have to remove/open the entire lid to put scraps inside.

After work I went to TechShop to bend up some handles and MIG weld them to the top as well as a hinge for the smaller lid.  I found a cool old wingnut and bolt in the community scrap bin that I used for a handle for the smaller lid.

Here the lid is cleaned up a little with a wire brush in the angle grinder.  No reason really, just piddling around.

I then shot the top and bottom with some high temp BBQ grill paint in a rattle can.  I didn't put a lot of effort in the paint job as it's mainly just to keep the rust under control.

Sunday morning, I got up and started on it again.  I put the 1-1/2" sheet metal screws in the previously drilled holes.  Recall, these will hopefully help to give the cement something to bite into on the walls and lid.  Then, I got to work putting the forms together.

I wasn't able to find "real" refractory cement locally.  There are quite a few home brew recipes on the Internet but I decided to go with my own blend.  I used 3 parts perlite to 1 part QUICKRETE #1102 Mortar Mix by volume.  The mortar mix was suggested by an employee of the hardware store who mentioned that a lot of people use it for outdoor pizza ovens and barbeque grills.  I checked the MSDS from QUICKRETE and it has a melting point ">2700 degrees F".  I never was able to find much in the way of expansion/contraction rates but hopefully it will work for my purpose.

I mixed the two ingredients thoroughly.  Dry at first and then added just enough water to give it an oatmeal-like texture.  I realize that isn't the best example, people like there oatmeal different ways.  In general, I think most people make oatmeal too runny.  I like my oatmeal just moist enough where it sticks together but not so wet that you can pour liquid out of it.  I mixed the mortar/perlite in the same manner: it would hold together when squeezed but no water dripped out.

The next hour or so was spent putting in a few inches of the mix at a time, tamping it evenly to remove any air, and repeating.  Initially, I mixed up about 4 gallons which I thought would be more then enough but this only ended up being 2/3 of what I needed.  I made another quick batch and then finished with some to spare.  I used the leftovers to make a small coffee can furnace and also threw the rest in some of the plastic bowls I used for measuring.

Unfortunately, it's chilly and damp here so now I am concerned about how long it will take for the mix to dry out sufficiently to use the furnace.

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