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| NeoTechs newbie melting endevours. ;) |
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| NeoTech:
So i thought i would make a new thread instead of soiling my "question" thread of bargain buying crucibles.. So to sum it up, i made a furnace, with a propane burner and i did some cooking of that furnace yesterday and today i made some ingots.. The ingot mold is two pieces of L formed steel welded into the shape of two V's with a wall.. i made them stand up a bit from the ground, it helped when i needed to pry the ingot out of them.. Anyway.. 2 pistons and some valve cover i had lying around.. Ended up like this. ;) Now trouble shooting.. My propane burner is of the jet burner type with a small nossle for the gas flow.. This works great when its cold.. When it has run for a while and it got "distbured" a wind gust came and well blow on it.. What happened the damn thing starts pulsing or dieseling.. anyway sounds alot.. And.. the temperature is dropping alot.. from 730-740C to around 650-680C.. So the first batch i did. no problem at all, the aluminium melted well and it got hot enough to poor without problem.. The second run i did.. well slag formed alot more, unmelted parts needed to be stirred out in the melt.. And the third run was the same.. The two last runs had the annoying pulse jet sound.. It dont go away unless i choke out all the air intake and it just becomes a big sooty flame.. Even if i lower or raise the gas flow it wont stop.. it just sounds more or less.. This is a tad bit annoying.. and confusing.. Any suggestions of corrections on the burner? Is it not enough airflow that causes it when it gets hot? The only air intake it has is through the burner tube.. I have fitted a piece of steel to the burner tube so it centers in the inlet tube on the furnace.. its quite - snug.. i wonder if it would be a problem or not? I recon the air should come in through the burner not around/outside of it. |
| Meldonmech:
Hi NeoTech, Have you any pics, or drawings of your burner, this would make it much easier to diagnose the problem. Cheers David |
| vtsteam:
How big a propane tank are you using? Is it getting very cold? Or alternatively, is the nozzle getting too hot? It's a time dependent problem, so those are two things that change over time. |
| NeoTech:
It seems like the tank was getting cold when the "pulsing" started.. In combination with not that much of gas left in the tank it seems like it got starved.. The tank is 6kg propane tank (P6). But i was gonna do a 4th run (got alot of pistons to melt) and it never even could manage 400C.. so it just toppled off at 380C and started falling back. the refractory didnt go all read. And quite fast after just a couple of minutes it started to pulse. I tried to reset it by choking out the air and let a flame form and then reintroduce air, but it just wouldnt play along.. A friend of mine suggested the tank has gotten to cold for the remaining gas to keep pressure.. And so we took temp on the tank it had fallen from 24C to 19C rapidly. I will go and exchange my P6 aluminium tube for a P11 (11kg) Carbon fibre tube in the morning - its lighter to carry anyway.. And this is the design of the burner. - it just a 0.8 mig tip on a slab of steel fitted to a 21/32 fitting so i can use the handle, and a tube is snuggly presed onto it.. The tube itself has a centering ring on the air intake of the furnace and a steel tube as a choke. (nothing fancy) |
| MetalCaster:
My propane burner is similar, and it can be a bit finicky some times. On a windy day, I put something on either side of it to block the wind. My burner is very sensitive to the choke setting. Occasionally, and for some unknown reason, it starts the pulse-jet thing, which is combustion occuring inside the burner tube (not where you want it to happen). I have to turn off the burner, pull it from the furnace, and relight it. The pulse-jet is bad since it will overheat the burner tube and can cause problems. |
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