Clamping Soft Fire Brick?

[kraythe]

I am trying to update my forge configuration and I have designed a side mounted ribbon burner that uses a soft fire brick for the flare protection. The jets are 3/8" ID steel tubes and the design is a pressurized plenum burner. What I want to do is mount the burner on one side of the forge which will be rectangular. The base will be made of soft fire brick with hard fire brick on top for the internal floor to be sacrificial for borax (I do a lot of cable welding). The idea for the sides is that they would be soft fire brick painted with ITC-100 on the hot face. So think of a square floor of 8 fire bricks and sides with the firebricks sitting flat with the internal edges as hot faces.

 

What I want to do is make a roof for this forge that consists of soft fire bricks set on edge so that the 4.5" is the thickness of the roof, the 2.5" by 9" side is the hot face (with itc-100 coating) and the bricks are stacked to form the roof. The problem is I have to support the bricks or they will fall like a house of cards. I thought of drilling the bricks with a half inch threaded rod that would pass dirctly through thecenter of each brick and would have flat clamps on both sides that would allow them to be held clamped together (sort of like a vice)

 

What I am concerned about is expansion and contraction of the bricks under heat. Soft firebricks are pretty soft and can be easily broken by hand. If they expand while clamped and when heated to glowing, they could come apart quite spectacularly. At the same time I would rather not use hard firebrick because the insulating properties are not as good and the thermal mass of those bricks is quite high.

 

So does anyone have experience with clamping soft fire bricks and if so, what were the challenges you faced, if any?

 

Thanks in advance.

[swedefiddle]

If you drill the soft brick it will break. Rub two bricks together at an angle, you can make them wedge shape, like a cathedral arch.

 

I would use refractory cement over regular brick, for the ceiling. Make it upside down to let the slurry dry and not fall. Use some ni-cad wire (used for the heating element in a clothes dryer that someone is throwing out), the ni-cad wire will help support the refractory and will not burn.

 

Try not to over-think the mission. I have used the same regular fire bricks for a long time without breaking. I have many pieces of hi-temp fire brick. :D :D

 

Neil

[kraythe]

If you drill the soft brick it will break. Rub two bricks together at an angle, you can make them wedge shape, like a cathedral arch.
 
Neil

I have drilled soft brick with success using a drill press driven by hand with a hole saw as a bit.

I don't want to cast the roof because the thermal cycling will crack the roof without a doubt.

[HWHII]

I would suggest making a rack to hold them out of 316L stainless. Lets say you use a 3/8" x 1 1/2" flat bar or thicker it would last along time. The stainless will hold up in the heat of your forge.

[timgunn1962]

I have pinned soft bricks together with stainless steel TIG rod. It's the easiest way I have found to bridge the roof of a quick-and-dirty softbrick forge.

 

If you grind the end of the rod down to a D-bit; take off half the the rod for the first half inch or so, you can drill a hole almost the full length of the rod through several bricks and either snip off the protruding ends once it's through, or withdraw the "drill" and fit another rod. I tend to use 2.4mm rod (3/32") because it's what I have. 

 

I started by using hardened drill-rod for the D-bits, then got lazy and used unhardened drill-rod, then got bone idle and just used the welding rod itself. Hardened drillrod lasts longer, but the welding rod is easy and cheap. It helps to start the hole with a normal drill bit, or I sometimes drill a hole through a scrap of wood and hold it against the brick to give me a straight start.

[AndrewOC]

Hi kraythe,

try looking up;

Blacksmith-shop Equipment, Light Forging, Heavy Forging, Drop-hammer and Machine Forging, Angle and Plate Smithing, Spring Smithing, Motor-vehicle Smithing and Vicing, Coach Smithing and Repairs, Tool Smithing, Hardening and Tempering, Treatment of Low-carbon Steel, Special Smithwork

It is an ICS Library text.

This seems to be on 'Google Books', though my work server doesn't let me check.  In it I am sure there is a picture of a furnace roof clam/p which holds bricks in an arch and provides a lifting eye.

 

AndrewOC

[Dave Hammer]

Watch the following video.... 

It will show you one way to make your top.

 

Video was removed by source

[kraythe]

The problem is I have seen lots of forge construction vids of similar nature but what I really wanted to know is hw it worked out over the long term, not just how to put it together.

[AndrewOC]

Very neat idea from Dave.

Flat roofs tend to be high maintainance, though.  See at 25:10 to 25:18 how there is starting to be some sag in the roof, just something to keep aware of.

In theory an arched roof may settle in and compensate for this... sorry I don't know exact furnace examples (check out old brick kilns and iron smelters and their arches, i 'spose).

A.

[Dave Hammer]

I purposefully do not clamp the roof bricks too tight.  If you do, the bricks will break.  It's kind of a balancing act.  I very much like the idea of putting them on edge, rather than flat.  There is no doubt the structure will be stronger.  It may take a set of threaded rod on each side (and maybe not).  Also, when you handle these structures, be gentle with them.

 

The more you handle soft brick, the more likely they will be damaged.  I only use this type of forge when my Super C forge is not large enough for my current project. 

[prburner]

If you go with the threaded rod clamping method, put an old automotive valve spring between the clamping bar and each tightening nut on the threaded rod.  As the bricks expand, the springs compress. As they cool the springs keep the roof tight.  

 

This is how we made flat roofs for pottery kilns back in the day.  Lasted longer than any other method we tried.

[matthew2riches]

It is ok to drill soft firebrick.

 

[timgunn1962]

I drill soft firebrick with a holesaw, no problem.

 

Depth of cut is usually limited to about 1 1/2" with a standard holesaw, so it tends to be a case of drill as deep as you can, then break out the core and repeat if you are doing a full brick at 3" thickness. 

 

I often use a smaller holesaw once I've started a big hole, and take out 3 or 4 smaller cores with perhaps a 20mm holesaw, knock off any remaning  nibs and take another bite with the big one. It's only really needed for the bigger holes (3" hole for a 2" burner, which uses 2 1/2" NB pipe for the retention cup). Once you've got the hole started, it will guide on the OD.

 

If you can get to both sides, it's easier to run a pilot hole through with a longish drilbitl and use a holesaw from both sides.

 

Depending on the soft brick, it can ruin the holesaw. JM23 or K23 is nice and soft. Some of the others are harder and will quickly render the holesaw useless for anything else, LW23GRD are the toughest on tools that I've found in the UK.

[AndrewOC]

Found the roof clamp picture.

 

 

 

Drop forging, Angle smithing, Spring making.... ICS Reference Library, c.1911, section 67, page 32-33.

 

enjoy,

AndrewOC

[knots]

Insulating fire brick:  I have drilled them, sawn them to special shapes on a table saw,  used them restrained, and used them loose. Using them loose seems to be the thing that they like the least , other than being dropped.

 

If you think about it,  thermal cycling on a brittle insulating material is a major cause of failure.  That is because, in the case of a forge, the inside is at forging heat while the outside is at maybe a few hundred degrees.  Thermal expansion is therefore greater on the inside than the out side.  This would cause the brick to bend and eventually crack.  Putting them in compressionis probably one of the few things that can be done to help stabilize them.   I like the valve spring idea because the coefficient of expansion of the steel compression rods is probably greater than that of the insulating fire brick.  The springs would asure that a reasonable amount of compression be maintained when the forge is in and out of use.

 

However, why not use refractory insulation board for the roof.   Make up a heavy gage metal pan. Use nichrome wire and ceramic buttons to secure a couple of layers of insulating board in the pan.  Coat it with ITC and away you go.  Light and easy to remove for maintenance, as well as highly efficient .   Seems like the coating would protect the board from the corrosive atmosphere of welding.   

[kraythe]

I wanted to get away from cast jobless. I have done a ton of forge building and burner building but u just find that the bricks are the easiest to build, maintain and configure. You can have it small and flat one day and taller and cooler the next day.

The valve springs might work. I think I would want to spread the load out so I wouldn't use a plain nut but rather a piece of bar stock against the side of the bricks. Arched roofs are an interesting idea but my blown ribbon burner wouldn't dovetail with that well if the bricks are on edge.