PROPANE: The Pleasure of 'Pane
In the world of hobby foundry work, there are basically three viable foundry fuels available for the foundry man: Charcoal, Waste Oil and Propane. Each fuel has its advantages and disadvantages in foundry furnace operation, but one option may just be “perfect”.
Charcoal: Simple, Accessible, Effective:
Like many, I started my foray into foundry work with a Gingery-style charcoal-fueled furnace based on the very low apparent cost and simplicity of the required equipment.
Indeed, a charcoal foundry is very forgiving, relatively inexpensive (particularly during barbecue season), and requires almost no special equipment to get started. On the “down” side, charcoal can be a real pain to get lit in a furnace, it produces a fair amount of smoke early in the burn and LOTS of ash, it can produce quite a bit of sparks (which tends to freak out the neighbors), and while cheaper, pound-for-pound than other fuels, the consumption rate is rather high if you plan to melt more than a few pounds of metal at a time. Also, charcoal furnaces tend to be physically larger than propane or oil-fired furnaces due to the fact that the charcoal must be in very close contact with the crucible to melt efficiently and quite a bit of material is required to generate the required heat to melt a comparable charge.
Waste Oil: Inexpensive, but “Waste” for a Reason:
A second alternative fuel source for the hobby foundry is waste oil. This can be almost anything from used cooking oil to recycled engine oil. Basically, if the oil is flammable and can be atomized, it stands a good chance at being a viable fuel in an oil-fired furnace. Another plus is that in some areas, the cost of waste oil may be absolutely free! Sometimes, local restaurants and mom-and-pop oil change shops are willing to let loose of reasonable quantities of used oil simply for the asking. Of course, this brings to light one of the most distinct disadvantages of waste oil, and that is storage. Generally speaking, you will consume may gallons of waste oil in melting metals and the safe and convenient storage of this much oil has, and continues to be, a major turn-off to moving toward waste oil burners in my foundry furnace designs.
While the cost benefit of waste oil burners is significant, and the relative easy of burner construction is also a plus, the negatives far outweigh the positives in my opinion. Waste oil burners tend to be pretty finicky and downright messy most of the time. Waste oil burners tend to be quite a bit larger than propane burners as well, making efficient space utilization more of a challenge. Waste oil burners require a significant “pilot” flame to start and can be notoriously difficult to heat up to “burn temperature”. Often, you will spend a considerable amount of time getting the burner to stay lit and if the flame goes out, you find yourself with an oily mess inside your furnace that you must clean up before continuing. Compounding the problem is the fact that many homebuilt waste oil burners produce a lot of smoke during operation if the burner design is not pretty highly refined and functioning properly. For me, the question is very simple: Do you want to be in the waste oil burner design hobby or do you want to melt metal?!
Propane: The Perfect Foundry Fuel?:
First, let me attempt to curb the controversy by stating that propane is NOT the perfect foundry fuel! However, in the environment that the hobby foundry is used, it just might be the closest thing to “perfect” that we have available.
Compared to charcoal and waste oil fuels, propane is hands-down the most expensive fuel of the three per pound. Additionally, some fairly specialized equipment is needed to safely and efficiently use propane as a foundry fuel. However, with the modern high-efficiency burner designs available and a little “bargain hunting” search engine maneuvers; the cost-per-pound of propane usage can be significantly reduced to the point that the apparent advantages of charcoal and waste oil begin to diminish substantially.
Propane has many advantages as a foundry fuel in comparison to charcoal and waste oil. Perhaps most obvious is the fact that there is almost no preparation required to use propane. It’s pretty much ready to go when you are. Provided you have a sufficient supply on hand, melting metal using propane can be achieved in a few short minutes in many cases. Storage of propane is also quite convenient as well. I use a 40-pound tank for most of my foundry work and I can get it filled all year for around a buck per pound or sometimes less. Propane burns totally clean, leaving no residue in your furnace, on your crucibles, in your melt and no smoke to alarm the neighbors or the boss (a.k.a., the ‘lil missus). Another benefit is that propane furnaces are comparatively very easy to light and once they are started, they are remarkably easy to keep at melting temp for successive melts.
Propane Burners & Equipment
If you choose, as I did, to use propane as the fuel of choice in your foundry furnace, you will be faced with either purchasing or building a propane burner. As you might expect, there are commercial burners available that will do the job, but I am NOT going to tell you where to get them! What the hell good would that be?! This sight is about doing things yourself, with your hands, and your brain pan. It’s all about education and Imagineering! Really, did you expect anything less?
However, if facilities and/or skills prevent you from fabricating your own burner, by all means make an effort to support a fellow hobby foundry enthusiast with your purchase. Rex Price manufactures some of the nicest naturally aspirated propane foundry burners you will ever find at a price that is more than reasonable. Understand that, with proper care, a propane foundry burner should last you a lifetime, so don’t skimp. You can visit Rex’s site here at www.hybridburners.com. Tell him we sent you.
If you have a reasonable amount of mechanical ability (nothing extraordinary required), I would recommend construction your own high-efficiency propane burner from scratch. However, before you do, consider Michael Porter’s book “Gas Burners for Forges, Furnaces & Kilns” and absolute must-read. I built the burner for my “Hell Boy” furnace based on Mike’s 1-inch Furnace Burner design and I continue to be amazed at the efficiency and ease of use this burner provides. Even if you don’t choose to build your own burner, consider this book a necessary part of your foundry library. You won’t regret the purchase.
Fortunately, the remaining “special” equipment (e.g., propane storage tank, high-pressure adjustable regulator, hose & fittings) you will require can be obtained quite easily. I have found Tractor Supply Company to have a pretty good price on 40-pound tanks. Of course, these are quite popular and can be had at virtually all propane vendors and welding supply houses in your area. The regulator, hose and fittings are somewhat more challenging to obtain. Fortunately, Larry Zoeller at Zoeller Forge offers the parts needed in one place. Bought my regulator, fittings and hose from Larry and the quality and service is excellent, the price is right and the parts are perfectly suite to the purpose of foundry furnace burner operation.
Propane Furnace Burner Problems? Don’t be Fooled!:
Since about 1998, propane tanks have been required to incorporate an “overfill protection device” or OPD. An OPD is a safety device designed to prevent overfilling of a propane cylinder. Essentially, an OPD is a float valve inside the tank that closes when the propane level reaches about 80% of “full.” It also incorporates a check-valve device that stops gas flow when the tank is disconnected. The easy way to tell if your propane tank is equipped with an OPD is to look at the valve hand wheel. All OPDs have a triangular shaped hand wheel on the valve. All tanks with “non-triangular” hand wheels do not have an OPD.
Generally, the OPD is nothing to worry about. However, there are times when you may find yourself trying to troubleshoot a foundry furnace burner that is difficult to start, has low heat output or “chugs” during operation. This “chugging” is often accompanied by a flame that burns inside the burner tube rather than burning cleanly at the nozzle exit inside the furnace chamber.
Unfortunately, many foundrymen begin to suspect the burner as the culprit when in fact, the problem may be the propane supply tank itself. More accurately, the OPD valve on the propane tank could be the cause of the burner “problem.”
Some (I think most) OPD valves have a sort of “check-valve” feature that is designed to restrict gas flow if the tank is turned all the way on. The device is basically an “excess flow device” that is designed to shut off the gas flow if, for example, the hose gets cut or ruptured. Given that a foundry furnace burner has a comparatively high gas flow demand than most propane-fuel appliances, this check valve can activate prematurely without much notice. If your furnace burner is having any of the aforementioned difficulties, try closing the tank valve ¼ - ½ turn from the fully open position and try lighting the burner again. Oddly enough, opening the valve to about 80% of wide-open seems to keep the frost that develops on the outside of the tank somewhat in check as well.
While this technique tends to solve most of the fuel delivery problems to the burner, there are times when this may not solve the burner issues previously described. I have had opportunities where I could not prevent my burner from “chugging” even after performing the valve adjustment procedure described above. Given that my burner is a “known” design that historically works very well, I was confident, following a brief technical inspection, that there was nothing mechanically wrong with my burner. In this case, I dialed my delivery pressure down to about 5psi and closed the choke to the lighting position. After lighting the burner and establishing a stable, relatively low velocity flame, I set the choke to produce a slightly “rich” flame setting and let the burner run for about 10 minutes. After this short warm-up period, I slowly increased my gas pressure to the desired setting and reset the choke to achieve the desired burn and set off to melting metal. Why did this make a difference, you ask? Well, I can’t say for sure, but I suspect that it has something to do with the filling method employed by the propane vendor.
Technically speaking, propane tanks should be filled by weight, not volume. However, that requires a bit of math skill to subtract the tare weight of the tank from the total weight to determine how much propane can be added to the tank to fill it and most propane refilling jocks don’t care for the effort. However, with the advent of the OPD to propane tanks, the process of properly filling a propane tank was given another shot in the cojones by allowing the refilling person to rely on the OPD itself to tell him when the tank is “full.” Basically, many propane vendors simply open the valve and hit the transfer pump and pay no attention at all to the amount of propane going in to the tank. Instead, they wait and listen for the OPD to close and then shut off the pump. The danger in this procedure is that the pump could, in theory, overcome some of the seating force of the OPD and overfill the tank by some unknown amount. This practice forces the OPD to seat very tightly at the top of its travel and could limit the gas flow for a significant period of time during the first use of the tank after refill. If this theory holds true, it could take several minutes of burn time to consume enough of the extra fuel to restore the vapor space at the top of the tank to allow the OPD to unseat itself enough to allow proper gas flow. That is why I have used my “slow burn” procedure described above before jumping to conclusions about a burner problem. The other thing that really gets me is that this “OPD-dependent filling method” has resulted in a policy that almost all propane vendors employ, and that is to charge a flat fee to refill a propane tank no matter what may be left in the tank! In other words, unless you run your tank absolutely empty ever time, you will pay for any residual propane left in the tank again when you have your tank refilled! So, if you have a tank that still has 4 pounds of propane left in it and take it to get it filled, many propane vendors will charge you for 20 pounds of propane even though they only add 16 pound of gas to fill it. All of this, because a few people don’t want to do a little simple math. Sigh…….