My method for casting ribbon burners

[Ted Ewert]

I've posted most of this material in one spot or another, but I thought a consolidated thread might be helpful.

I like to use acrylic for forms in casting since cement won't readily stick to it. It's fairly cheap in small quantities, machines easily and is structurally rigid enough for this purpose. I use 3/16" sheet for the outer forms, although slightly thinner will work too. I buy scraps at my local Tap plastic shop for a dollar each, although I don't know if other locations have the same policy. 

For the holes I use solid round rod. I would not recommend tubing since it will shatter easily if you need to grab it with pliers (explained later). 

I also pour mine a little differently. This can be done in several different ways depending on your needs. I have been using a piece of 2" wide x 3/16" thick flat stock for my base. This gives me a good structure to clamp the forms around, and I don't want my burner to be the same size as my plenum. I then epoxy this steel base to the plenum to both attach and seal it. Some will wince at the mention of using epoxy, but in my case the plenum does not get hot and JB weld works just fine. If you have any reservations about heat, just cast it directly on to the plenum, which is the preferable method anyway.

Whatever method of forming you use, holes in the pattern of your choosing must be drilled first. You then need to use some form of anchor to attach the casting to the plenum. I use several bolts which are threaded into the base. These, as I found out the hard way, will prevent your cement from seperating from the base. 

At this point I stick my rods into the holes. Acrylic rod is not dimensionally precise, so you'll get some tight fits and some loose fits. For the tight fits I put a little oil on the tip of the rod and lightly tap it into place. It just has to be in the hole enough to not move around when the cement is added, and you're going to have to pull it out, so don't pound it in too much. Also, don't worry about getting all the rods aligned perfectly. You can adjust them after the cement is poured in. You also want them to be an inch or so longer than the top of your form so you can have something to grab on to when you remove them. 

At this point you're ready to pour. I use an old baking pan with a sheet of wax paper in it to pour on. The wax paper makes for easy clean up since things get messy.

I mix my cement a little on the wet side which makes this process a whole lot easier. I work the cement in with a thin piece of steel flat stock. The clear forms make it easy to see if you have any gaps in your cement. When you get it all filled in you can then adjust the rods to your satisfaction.

Let it set for about 12 hours, then remove the rods. Leave the outer forms on for this step as it supports the still semi-soft cement. I grab the rods with a pair of pliers and give them a twist to loosen them first (this can take a little muscle on the tight ones). Once it's loose, keep twisting back and forth as you slowly and gently pull it straight out of the hole. Once you get it out of the steel base it usually slides out pretty easily. 

As you can see in the picture, I have used 4 tubes instead of solid rods. If you grab these with the pliers as they are they will shatter. I had to insert a steel rod in the middle of each one to prevent this before extracting them. That's why I recommend solid rods. 

I like to leave the forms on for at least 24 hours. At that point the cement is set up enough to resist crumbling along the edges. Once the forms are removed, you can sand the edges with some 100 grit sandpaper to smooth things out. I have also used the belt sander at this point to flatten the top and to take a little off here and there if it doesn't fit. If you use the belt sander, feed it in slowly and make sure the casting is well supported underneath. 

Like regular concrete or mortar, make sure you keep it damp for a few days while it cures.

Questions and comments are welcome.

 

Ted

 

 

[ianinsa]

Ted thanks for posting this! the perspex seems like a grand plan , personally i haven't ever had issues with crayons providing you drill them out! a doddle with a cordless once the refractory has cured fully.

Ian