Troubleshooting Your New Forge or Burner

Let me begin with a few things to look for if your burner(s) is not operating in the manor you think it should, or if the flame does not match the image on my page. Perform all your burner adjusting and tuning outside of the forge. Some things to look for if the burner is not working properly should include an inspection of the tiny jet opening for rough edges on the inside or outside, metal chips or other obstruction in the jet hole, wrong sized jet, or a miss-aligned jet opening. It must be aimed directly down the center-line axis of the burner tube and be smooth with no obstructions. Check that your jet is not mounted so close to the burner tube throat that it is obstructing or limiting the intake of air, a possibility with some straight sided bell fittings. Be sure you used a 1/8" diameter jet pipe, and not anything larger, because it will obstruct the intake air flow if too large. Check that the burner bell intake opening is the proper size, depending on the method of jet tube mounting you elected to least 1-1/4" (1-1/2" or even up to 2" is better) diameter if set screw locking is used, and 1-1/2" diameter (1-3/4" to 2" is better) if you lock the jet by screwing a short nipple section down on top of preferred method. I am operating burners with the minimum sized bell openings, as stated in the last sentence, and they function well for me, but this is a marginal set of dimensions. Bigger is better to reduce drag and the lowering of the amount of intake air. Sometimes there are very rough edges, or a rim protruding down into the burner tube throat right at the opening. This can be from the threading machine and/or the pipe cutter used to cut the nipple off the pipe stock. Remove any constricting rim or rough projections in the throat with a round file. Also use a long round file to smooth and clean the interior of the burner tube, same for the jet tube prior to mounting it. Be sure the flare, or straight nozzle, is adjusted correctly in conformance with the tuning instructions. Also remove any projections or flange from the nozzle end of the burner tube.

I strongly encourage the use of "Tweco Tips" on any burner design you choose to follow. They will go a long way to improve the performance of your burner. And, speaking of tips, a tip on how to easily align your jet to the center-line axis of the burner tube was suggested to me recently. Simply hook the gas jet pipe to your water hose, and the jet of water can easily be adjusted for dead center, especially if you use the Tweco tip for your jet. The soft copper can be bent easily to obtain perfect alignment.

Congratulations on finishing the construction of your new forge. I have put together a few thoughts, comments, and observations, about getting the most out of your forge, or troubleshooting it. The forge and its burners operate together as a system, and it is a complex one that can be affected by many different factors. If your forge is not reaching the temperatures you think it should be you may find some help here. I can't cover all the possible factors that may contribute to problems in forge operation, nor do I know or understand them all, but I have run into a number of things which will have an impact on the operation of a forge, and I will relate some of them here.

I should make a comment about the completeness of the information on my "Forge and Burner Design Page". I did not write the page to be a set of plans for any particular forge design. However, if you study all the text descriptions, and the images, there is enough detail to allow you to duplicate my forges, virtually to the weld and screw. You need to study the information closely however. I just finished helping a fellow find the reason his burners were running too rich, even though they were build "exactly" like mine. We discussed them for several weeks via e-mail until I prevailed upon him to send me some images. As soon as I saw the image of his burner I knew the problem. His jet tubes were very large diameter pipe which blocked a large portion of the intake air flow to the burner throat. Please study the details closely. If you discover that your burner is not built "exactly" like mine, you probably have found the problem. Once you understand the basics of how the burner works you will know what you can change and what not to. In this instance, he may use a smaller jet tube, but not a larger one. There isn't much you can change on these burners without changing how they operate, and mostly in a negative direction.

One of the most common complaints I receive concerns not being able to achieve welding heat. The naturally aspirated burner is easily capable of reaching welding heat, and above, but it is easy to "defeat" your burners if you create any "back-pressure" in your forge chamber. The burner operates by creating a low pressure in the throat of the burner bell when the high velocity gas stream injects down the throat of the burner. The low pressure sucks in air to mix with the gas stream creating a "balanced" mixture for burning in the nozzle and forge chamber. The low pressure is a very weak one, and if you bottle up the gasses in the chamber by restricting the exhaust opening area in your forge chamber, you will reduce the amount of air being sucked in, but not the amount of gas being injected. You will then see a lot of blue flame emitted from the front and rear, if you have a rear opening in the forge, which you should. The chamber will be running cool, and very fuel rich. The gasses will seek the oxygen outside the forge and you will see a secondary burn at the opening to the forge, especially in dim light. There will normally be some light yellow flames, but there should not be any blue flames emitted from the forge. The blue flames should not reach any further from the burner than the floor of the forge at maximum, normally less.

If you have a back-pressure problem, the first thing to do is open up your forge exhaust opening and see if that helps. Open up both the front and rear openings, and that may require increasing the gap between the movable back wall and the walls of the forge chamber, if you have a movable back wall installed. It should have about 3/4" of clearance all around its circumference for gasses to pass through. BTW, there is about 7 times more gas exiting a forge than injected into it due to the expansion of the gasses upon heating. This should tell you how important exhaust area is.

If you are running more than one burner, shut off all but one burner and see if the forge operates properly. If the blue flames are gone, move up the movable back wall and try working with the forge and doing a forge weld. If you have the heat necessary then you are having back pressure problems due to the large increase in gas volume into the forge when running multiple burners. This points back to exhaust opening area problems. You can have too many burners for a given chamber volume, but I do not know what that ratio is. This is not as big an issue with the Mongo series of burners because of their much greater entrainment ratio and resulting greater suction.

I would like to add a few words about forge welding in a gas forge. Just because you can't weld doesn't mean you don't have the temperatures necessary for welding. If you are not experienced in gas forge welding you may simply not understand the technique to do a weld. Welding is not easy for the beginner. Here are a few tips.

   1. Make sure the metal is properly prepared for a weld. This means, in part, it needs to be very clean. There should be no scale or other surface coatings on the metal. File it clean on both surfaces where the weld will join. Look in the books for further information regarding scarfing, and other preparations, or ask someone who is experienced in forge welding.

   2. When the iron first gets red, flux it lightly, and continue the heat. Then flux it again when it reaches a yellow heat.

   3. When the flux starts to gently "boil" on the surface of the iron, turn the iron so that all sides reach welding heat, as indicated by the bubbling flux. Also, allow enough time for the heat to "soak" into the center of the section. If the center of the iron is not hot it will not weld. How long you will need to soak it will be determined by the thickness of the iron, and your experience.

   4. When the entire section to be welded is at an even bright yellow glow, and the flux is bubbling evenly all over the weld area, you are ready to do the weld.

   5. Withdraw the iron from the forge and very quickly remove the excess flux by giving it a quick shake, or a tap on the edge of the anvil, and then hit it with the hammer gently to "stick" the weld. In the beginning you may want to dispense with the shaking or tapping off of excess flux in order to prevent the iron from losing its heat. Just hit it directly the moment you get it on the anvil. Be aware it will spray a lot of molten flux, so be careful...wear eye protection. Once the weld has stuck you can proceed to hammer with greater force and refine it.  If it breaks apart you are hitting it too hard....try it again. This operation is easier to say than to do. You must withdraw the iron, shake off the flux, position it on the anvil, and strike your blow, all with one very quick smooth movement. Any delay at all will cause the metal to lose its heat and the weld to fail.

   6. You will have to take a number of welding heats to complete the weld, fluxing each time you heat. You may want to remove excess gummy dirty flux with a wire brush between heats on occasion,  and then flux again with clean flux before returning it to the fire. Parts of the iron that will not be actually welded, but will be reaching high heat will scale in the welding process. To prevent this, simply flux this area too, and then when the work is done and the iron is still at a low red heat, plunge it into the quench tank to blast off most of the remaining flux.

   7. A gas forge will not magically turn you into a forge welder, but it is much easier and cleaner than forge welding in coal. If your forge is reaching temperatures high enough to boil the flux, the problem is probably not in the forge, but in your technique. The one exception to this would be if your burners are improperly jetted, or the choke incorrectly adjusted, resulting in an oxidizing atmosphere in your forge. Having a jet opening that is too small will lead to this situation. If the jet opening drill size number (the bigger the number the smaller the hole) is larger than a #60 or #62 this may be a problem. One additional consideration is the iron you are using. Some kinds of steel will not weld due to the addition of lead or other metals in the alloy to improve its machining properties. This is called "free machining steel", and it is not weldable in the forge. You can't recognize it in the scrap pile, nor on the grinder, so be aware of this possibility. I recently tried to demo a forge weld to a fellow, only to grab a piece of free machining steel. After my third failure to weld it I realized I had free machining steel. I then used another piece of iron to successfully demo the weld and save face.   :-)

If you have modified anything in the design of the burner or forge, without knowing what you are doing, you may not reach the high temperatures you want. If you know what you are doing, by all means change and experiment, but if you don't, you would be well advised to build the burner and forge exactly as shown in my drawings, descriptions, and images. That includes the kind of insulation, its thickness, and the ITC-100 lining. I would even suggest you add an additional layer of Kaowool over what I have shown. You would be better off by doing so. If I were to build another big 4 burner forge I would increase its shell diameter to 14" and add an additional layer of Kaowool.

By all means do add a choke to your burner. It will add low-end capability that will not be available without it. Also be very sure you have gone through he burner tuning process that I have described elsewhere. If your burner will not perform well in open air it will not perform well in the forge, especially during light up.

A blown forge can increase the controllability of the burner, but if a blown forge is operating at a perfectly balanced fuel/air mixture, and a non blown forge is operating at a perfectly balanced fuel/air mixture, both at the same gas pressures, the results in the forge chamber should be identical. The blower will provide you with an additional control factor, but what you gain is not necessarily worth the additional investment in resources, increase in complexity, and loss of freedom to operate in the absence of electricity. A naturally aspirated burner with a choke can very closely duplicate all the operating parameters of a blown burner except at extreme low or high pressures. At low pressures the naturally aspirated burner will simply not create enough vacuum to draw in the necessary air and will begin to "huff" as it starts getting an oscillating burn back into the burner tube. A slight increase in gas pressure, or possibly closing the choke, will solve this.

In either kind of forge, experience and knowledge are necessary for success. It is easy to run an oxidizing environment in either kind of forge, and easy to go to the opposite extreme as well. Don't blame your forge until you are positive that the problem is not in your technique of operation. A certain amount of understanding is necessary on your part in order to operate these tools efficiently. If you have a knowledgeable smith in your area enlist his help in the beginning.

If your propane tank is far removed from your forge, if your regulator(s) do not match the parameters of the Fisher regulator I described (BBQ regulators will not work), if your gas lines are of small diameter, these all could be a factor in your forge operating differently than I describe. You will need to explore these factors on your own. I use industrial quality fittings and hardware throughout my system, and if you elect to use cheap lightweight low capacity hardware from the local hardware store, that too will impact your results. Please do not burden me with problems caused by such external factors. In building tools you pretty much get what you pay for. Many times taking shortcuts to save money will impact the results you get. I can't solve those problems for you.

One subject that is well worth covering regards burner chokes. If you want to obtain the best low end performance from your burner, you must have a good choke installed on it. The choke needs to be able to completely close off the intake air if you wish to be able to get the burner operating down in the ounces range of gas pressure. I can obtain an output with my Micromongo burner that is about equal to a candle flame output while maintaining complete flame stability and neutrality. Please see the link above for more choke information.

Here is one very important last comment. Due to the difference in background experience we each have, your perceived mental image derived from my descriptions will vary from mine. You may describe the flames coming out of my forge very differently than I do. This is a problem that is not easy to overcome, and has caused occasional problems when I have tried to help people in the past. In a recent case we determined that the forge in question was in fact operating at a very high and acceptable temperature, but my descriptions didn't seem to match what the owner felt he was seeing. He was achieving welding temperatures and above, but could see "blue flames" at the mouth of his forge when running multiple burners. Sometimes I just don't have an answer for such "problems", if indeed they are problems. Perhaps he has a little back pressure problem, perhaps not. At some point you have to bite the bullet and take charge of the situation and decide if there really is a problem. I can't do that for you from a distance. If your forge is economical, easily forge welds, heats your iron for general forging well, and is adjustable within a reasonable range, then it is probably a pretty good forge and may need no further tuning or modification. Please consider this before contacting me to help troubleshoot your forge.

Thank you.    :-)


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Author: Ron Reil

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Golden Age Forge

15 Jan 01