Improper Use of Forge

[Clayton M.]

I built a forge that I had intended to do some brass smelting with. I finished it two weeks ago and last night I smelted my first chunk of brass. After I was done I noticed four cracks on the outside of the forge (this a brick forge with 4 inch thick fire bricks as the walls and floor of the forge) and the center seam line of the ceiling bricks is cracked. 

 

Is this because of the heat of the fire needed to melt brass, or is it something else? The bricks that formed the ceiling suffered no damage other than the cracked mortar it was the exterior walls that cracked. Those wall are about 8 inches thick, before I made this forge I could put my bare hand on the firebricks and it would only be warm to the touch. 

 

I did use portland cement to mortar the exterior wall together but I used Heat Stop to mortar the bricks exposed the forge fire. 

Have I caused enough damage to my forge to consider it a problem. 

 

If it will help I'll upload pictures detailing the extent of the damage.

[jacobd]

If I remember correct most fire bricks are rated between 2300-3100 Fahrenheit. If you bought US stove or a firebrick that may be the problem. I'm curious myself. I'm waiting for a veteran to chime in.

[Clayton M.]

The bricks that make up the outer wall as well as the ceiling are regular paver bricks that you can get at Home Depot for $0.50. The large fire bricks I have I doubt you can buy them. Their dimensions are 4" thick by 9" inches tall by 8.5" wide. I've six "little" bricks that are good for 2200 degrees F. The pavers in the ceiling didn't have a problem with the heat it was the mortar, which is rated for well above 2000 degrees F. That were I'm lost. I did several preheating fires in the forge, five in a weeks time and then I let it sit for a week before using to melt the brass.

[Steve Sells]

You can not smelt an alloy.  2,000F is not high enough.  Maybe if you back up, and read to learn more, figure out what you are doing, you may figure out what went wrong.  Hard to carry on a conversation when you start in the middle.

[ThomasPowers]

smelting is to take ore and make metal from it.  You wanted to melt brass.

 

Masonry does not deal well with expansion and contraction during heating and cooling cycles.  It is often expected that things will crack and so you design it so that cracking doesn't cause issues until it gets so bad that you need to do a reline. Doing a reline is an expected maintenance on a furnace.  Good design and construction makes is to it's not a common requirement...

 

Not knowing how you designed and built yours it would be hard to tell how critical the cracking is.  Pictures are mandatory!

[Clayton M.]

I'm sorry about that, the terminology is quite all there yet in my head. I mis-spoke, I meant melting but wrote smelting. I will get pictures up today after school and I will explain how i put it together so everyone has a better understanding. Sorry about the confusion.


I'm not sure if it is understood that it isn't just the interior of the forge that has cracked. The exterior wall has cracked in four places, if I remember correctly. The pictures will explain better than I can.

[ThomasPowers]

if you want monolithic sections to remain monolithic you need to build in expansion joints designed to let things expand and contract without breaking.

 

As the interior layer heats and expands what is the cooler outside layer going to do?  As to criticality it depends on the design...

[Clayton M.]

if you want monolithic sections to remain monolithic you need to build in expansion joints designed to let things expand and contract without breaking.

 

As the interior layer heats and expands what is the cooler outside layer going to do?  As to criticality it depends on the design...

 

I remember my dad doing that when we put tile down on our main floor. He used some special kind of caulking for the grout where three big sections came together. I just looked it up and there are several kinds of caulking that withstands temps well over 2000 degrees F, but not for very long. I will see if I can get a hold of some to try it out. 

 

Anyways, here are the pictures of my forge. I do have more if these pictures don't help enough. I did notice that the cracks occurred along the center joint (image 3372), and in image 3382 the crack splits off from the center joint and up the joint.

 

Hope this helps.

[Clayton M.]

Sorry about the sideways picture on the end. Use your imagination and turn it to the left. It was upright before I uploaded it and so I don't' know what went wrong.

[Charles R. Stevens]

My experiance is with hornos and ovens, but lets see if any of this applies.

Tho good old soft red clay brick has been used for centuries it realy dosnt like high temp. It spalds, melts and such. Hard red brick isnt any better, and is designed for cement mortor (cement is hard wile lime is soft).

The soft yelowish tan "fire brick" does heat much better, but it will still deteriate at high tempetures.  So the usual plan is to use fire brick, cut and stacked in such a way that it will be stable with out morter. "Fire cement" may be used but one must have very tight and small joints, and the expension and contraction will crack the morter, and aventualy the brick, so it is important that it is self suporting with out the morter.

Now the outer shell is usualy conventenal masonry (red hard brick with cement morter) with a gap between the inner and outer shells. This can be left open, but is usualy filed with a lose, heat resistant material, such as sand, vemiculite or perlite. This isolates the outer shell from the expansion and contraction if the iner shell.

As i said, my experiance is not with melting fernaces.

[Cary Brief]

I did not read every post but did not hear about your fuel.  As far as Portland cement, from my knowledge  this is not normally used in furnace construction 

[Frosty]

I did not read every post but did not hear about your fuel.  As far as Portland cement, from my knowledge  this is not normally used in furnace construction 

As I recall the discussion was about propane forge construction. The OP was by a person guessing at how to build one and folk trying to help him make HIS ideas work. I think this thread died a natural death when the OP did a little reading in the gas forge section.

Just read the gas forge construction section if you want to build a gas forge. I'm doing a demo tomorrow and am going to use a brick pile forge. My shop forge or new forge are a little intimidating to folk who just want to give smithing a try without investing a BUNCH on tools and equipment.

I used to take my shop forge but in reality if you were to have one like it built for you it's cost several grand. My new smaller portable gasser would run in the $400.+ range. Folk can see experimenting with a new craft if the forge costs $30 - 50 in fire brick and about $10 15 for the burner, $25 for the regulator, $15 - 20 for a gauge, heck the hose is the most expensive single part of the build.

For under $100.00 a person can have a propane forge that will melt steel if you wish.

Getting fancy with mortars, cast refractories as hard inner liners on ceramic refractory blanked forges, etc. etc. is fun for the tinkerers but a major stumbling block for beginners. Keep it simple.

Frosty The Lucky.