Cast and Forge Posted February 18, 2020 Share Posted February 18, 2020 Hey forum, My first ribbon burner forge gone through some action the last weeks. I experienced backfiring of the burner for the first time and it scared the heck out of me. I ran the burner between 0 and 0.1 bar of propane. After the backfiring I experimented a little bit and found that the burner wont backfire if I dont use below 0.2 bar of pressure for several houres of forging. I noticed that the outlet ports in the burner block starts glowing right at the face after some time (see picture 1). After about 3 to 4 houres of forging at 0.2 bar I noticed that the a single flame burned inside of one burner port. (Picture 2, right side, last port). In fear of backfire I shut off the gas. Is there anything I can do to prevent the flame from burning inside of the single port? Is it even a problem? I want to run the forge at a craft faire and backfiring wouldnt be that nice for the audience I think. Thanks in advance! Quote Link to comment Share on other sites More sharing options...
Latticino Posted February 19, 2020 Share Posted February 19, 2020 Natural aspirated or forced air burner? Actual position of burner at top of forge? Any changes in back pressure by use of doors? In my mind multiport burners are quite sensative to quantity, diameter and length of outlets as well as material of manufacture. Ideally you want very short outlets so cooling effect of incoming air gas mixture is closest to face. I suspect that if you need to run at that low a pressure you should have more and smaller outlets, and the location of the outlet that starts burning back indicates insufficient baffle in the block mixing chamber. Before making a new burner, you might consider turning your forge 90 deg to side fire and painting the burner face with IR reflective material like plistix or metrocoat. Good luck Quote Link to comment Share on other sites More sharing options...
Ted Ewert Posted February 19, 2020 Share Posted February 19, 2020 It will only backfire if the rate of burn (flame front) exceeds the exit velocity of the gas. An easy fix is to plug up a few of your burner outlets with some wool. That should increase the gas velocity through the other ports. Quote Link to comment Share on other sites More sharing options...
Latticino Posted February 19, 2020 Share Posted February 19, 2020 Agreed with a couple of reservations (see below), though this also has the downside in reducing the potential maximum heat output of the burner assembly at high fire. You are also assuming that when blocking off an outlet port you will get the same quantity of air/gas mixture flowing out of the burner block. It isn't quite that simple, especially with a NA burner. An increase in velocity at the outlet will also increase the backpressure in the system that the inducer sees. If I remember my fluid dynamics, the friction loss in the outlet is related to the square of the fluid velocity, so a small change in velocity will result in a larger change in friction. Practically that can limit the effectiveness of the change you propose for a NA burner (and also makes it potentially more difficult to tune NA burners with multiport outlets). That is another good reason for shorter outlet lengths, as the total friction is also a direct function of the length. The other issue is a concern about the burner surface temperature reaching the ignition point for the fuel/air mixture by way of radiant heat transfer. I'm sure any gas forge operator has experienced relighting their forge without using an outside source of flame if it is "hot enough" after a temporary shutdown. You really don't want the burner block to get "hot enough". Quote Link to comment Share on other sites More sharing options...
Cast and Forge Posted February 19, 2020 Author Share Posted February 19, 2020 Thanks for your answers so far! Its a burner with a 600m3/h blower, speed controlled and with a ball valve for fine tuning the air. The burner comes in from the top of the forge. The burner ports are 8mm in diameter, formed by plastic straws. The inside was nearly like a mirror when i pulled them out of the block after casting. The material of the block is a medium desity refractory with stainless steel needles inside to act as reinforcement, rated for 1400 °C Any idea where I can find ITC100 in europe? Pottery stores got some kiln wash but its never stated for which temperatures its rated. Quote Link to comment Share on other sites More sharing options...
Latticino Posted February 19, 2020 Share Posted February 19, 2020 With a blown system I would definitely look into adjusting the number of outlets, as Ted suggested. Of course you will lose high fire capacity, which is probably why the old Johnson multioutlet forges used to have slide gates that closed off burner ports that weren't in use (if I recall correctly, it has been 40 years since I've seen one in use) Quote Link to comment Share on other sites More sharing options...
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