sskalko

A problem with using a solid steel or cast iron block for a ribbon burner is heat transfer. As the furnace interior warms up, heat is transferred through the hot faces on the inside of the furnace to the exterior faces where it is dissipated to the environment. Refractory materials in general slow this transfer of heat such that: 1. Enough heat is kept inside the furnace to allow it to reach forging temperatures. 2. Only a small amount of heat travels through the hot face wall to the furnace's exterior and this small amount of heat can be easily dissipated by the surrounding air; keeping the exterior of the furnace relatively cool. Now replace a section of the hot face wall with a modestly sized ribbon burner block. This block is going to absorb heat, this heat is going to travel through the block until it reaches the plenum on the other side. The biggest thing cooling the ribbon burner is the flow of air through the block into the furnace. With a refractory the flow of heat through the ribbon burner can be offset by the air flow. However, steel and cast iron have much better heat transfer than refractory and this means the air flow alone will not be enough to keep the plenum side of the burner below the ignition temperature of the propane/air mixture on the plenum side. The result will be a detonation and fire on the wrong side of the burner. How do I know this? My first ribbon burner forge experienced a fire on the wrong side of the burner when operated incorrectly (by me). The burner in question was made out of a hard refractory cement The forge was being being run very hot to do some forging welding for about half an hour. When the welding was done I turned down the air/gas flow to reach a normal hot working temperature. About five minutes later I heard a loud boom and then had fire coming out of places it shouldn't have. No one was hurt and but the blower fan was trashed from the detonation. The problem was the heat stored in the burner's refractory during the high temperature run. As long as the higher temperature was balanced by high air flow things were fine, but with high temperature and low air you get fire in the wrong place. My new ribbon burner has a water block build into the plenum side of the burner to prevent this. Steve

Nautilair has some 12 VDC combustion blowers. www.ametektip.com They are good fans, they have variable speed control and are designed for combustion applications. They are pricey though and can be difficult to source.

I use compression fittings quite a bit at work and home. I have some tips for making leak tight connections. 1. Seat the ferrules on the tubing using a spare fitting before making your final connection. When the ferrules are tightened on the tubing for the first time they deform the tubing and lock into place. By using a spare fitting mounted in a vise to lock the ferrules you can ensure that the tubing is fully inserted into the fitting and squared up properly. 2. Don't over tighten the fittings. Over tightening the fittings can deform the tubing and ferrules to the point where their sealing surface is distorted. Finger tighten the nut and then turn with a wrench about a turn and a quarter. 3. Avoid bends close to the fittings. The tubing is distorted close to the bend and might not allow the ferrules to seat properly. Depending on what you used to bend the tubing and the size the tubing this can vary. Hope this helps. Steve

I am looking for some help with a forge issue of a non-technical nature. I am a member of a Twin Cities (Minneapolis and St. Paul) makers space aptly named the Twin Cities Makers. Our landlord is relucant to allow us to have a forge which is a shame because our shop has a 4" natural gas header. I am looking for some help from members of this community that have had to deal with fire code and insurance liabilty associated with having a natural gas forge. I have looked at the NPFA code for non-listed appliance and understand that I will need to have a safety shutoff valve. In my case this will be a fail close solenoid valve from McMaster-Carr that is specifically listed for this purpose. The forge will also have an air flow switch on the blower discharge to close the safety valve on lose of power to the blower. It will also have a "fire eye" to close the safety valve on lose of flame. Since building forges rather than buying a UL listed forge seems to be very common, I assume there is some experience in this community in dealing with fire marshalls and insurance companies. Anyone who could offer any help and advise when dealing with fire inspectors and insurance agent with regards to a homemade natural gas forge would be much appriciated.