Don't Blow 'Um Up
Or Wack 'Um With A Hammer Page
There is another area we have yet to cover as a real trouble spot to the longevity of the burner heads. This is in the area of physical abuse. The most classic is the case of binding the head in the burner port...crack! The casting is 4" in diameter and the burner port is supposed to be 4.5" in diameter. This gives a little slack and allows for some slight movement (reference to fig. 5), but if they are both 4," the slightest movement breaks the head.
Not surprisingly, many people loose their burner heads during a big studio move where the plumber guy applies the hammer to the pipe work to loosen it up a tad, and "whack!" If you pound on the pipe work five feet away the shock still follows the metal all the way to the burner head and plop, on the floor it goes in a couple of big pieces‒ don't hammer the pipe work.
Another great area is with vibration caused by the door of the glory hole or furnace opening and closing with an air valve constantly hitting or shaking the unit or with powerful vibration from the air blower system. Constant, hard vibration will eventually shake even a good burner head to pieces.
You see, the physical strength of the burner head is not that great. It is probably twice as strong as a soft brick. I did a lot of experimenting trying to strengthen the physical mass, that's easy. I could make it hard as a rock. But the harder I got it the less well it withstood the thermal changes. For example, the material used for crucibles is hard as hell, but we very gingerly raise the furnace temperature going up and down so we don't crack 'um. Face it, the major threat to a burner head is the thermal stress it must go through each day in it's cycle, not the plumber with the hammer. So I made a mix which would take some physical abuse but which was stronger under thermal abuse. I have experimented with a lot of different things but have returned to the original formula for every burner I have ever sold.
While we are on the subject of physical abuse, occasionally I get a customer who will literally blow up a burner, like an old fashioned pipe-bomb. Well, it's more like a gas cannon. In my youth we'd celebrate appropriate holidays by shooting off an acetylene and oxygen filled drive shaft housing plugged with a Life magazine. Boom! Instant confetti. At a hundred thirty-five dollars a pop it looses its humor. So what's happening to cause the explosion?
When a gas/air mix burns it expands rapidly, as much as seven times in volume. If the expansion happens in a closed space, like in the mixer section behind the burner head, we get an explosion. Earlier, I talked about how any burner system will have a pop-back point on the low end. This is true. If you turn down any system low enough it will pop back,... boom! It usually is a small boom but what if there's a lot of pipe work of large sizes behind the head? Then we have a large explosion. It is a matter of physics. I recommend that a system have no more than two feet of 1-1/2" black iron pipe between the mixer and the burner head. Any more piping and it is almost guaranteed that at some point you will blow the head right up. It may be the first time you light it.
Well that's about it for the exciting stuff. No more explosions. But there is one more caution in the physical abuse section. It is very important to mount the burner system by the iron pipe work behind the head. Use a regular clamp or a "U" bolt and attach it to the frame of the furnace. This provides support for all the weight of the burner/head/mixer, etc.. It is especially important not to rest the totality of this weight onto the head and expect it to hold upunscathed. It might hold up for a short while but to be so cavalier is asking for trouble.
To summarize, if you build a burner port along the guidelines suggested, and use a turndown schedule that keeps the heat out of the head, we eliminate nearly all the bumps in the road. |