sqdqo Posted April 11, 2011 Share Posted April 11, 2011 A little advice if you would. I don't know much about steel and built a wood fired maple sap evaporator with fire brick lined block sides and rear. The top and front are 1/4" plate. The outside dimensions are 56"L x 48"W. It served my purpose but I was surprised at how much it warped as it got hot. I have a 23"x37" hole in the top that the evaporator pan sits over and the flame contacts the bottom of the pan. In the 48" width at first it probably warped 2" vertically and had a diagonal warp of about 6". I bolted 1-1/2" x 1/8" angle on both sides and the rear and one piece of angle across the width of the opening in front of the 6" flue pipe opening. It calmed the warping down some but I am surprised at the strength of the warp, it even bends the angle iron. The front has a barrel stove door and doesn't warp. What weight plate steel would I have to use to keep it from warping? Can a person have a piece of cast iron made? Would it be affordable? Any other ideas would be appreciated. Quote Link to comment Share on other sites More sharing options...
Fe-Wood Posted April 11, 2011 Share Posted April 11, 2011 A few pictures would be an enormous help. warping as you may know is caused by uneven expansion/contraction of the material, any material. If you can line it with a refractor of some sort that may help. Does it cause any functionality problems? Quote Link to comment Share on other sites More sharing options...
clinton Posted April 11, 2011 Share Posted April 11, 2011 Ya steel will do that- making a connection that can move would help- like a slip joint, sandwich two pieces of angle that will accept the plate but be loose enough to slide, this would allow the whole side to move instead of a localized area. It may still warp depending on how well insulated it is and how hot your fire is. A free standing cast iron stove maybe a good option, you can find them cheap and even free sometimes, just modify it to suit your needs Quote Link to comment Share on other sites More sharing options...
fciron Posted April 11, 2011 Share Posted April 11, 2011 If I understand your description properly, you have a brick fire-box with an opening that is smaller than the pan you are heating. To me this suggests that you're producing a lot of heat and it's being directed at the center of your pan. As the center of the pan heats it will expand, the edges of the pan are not getting as much heat and are not expanding to the same degree, so they are squeezing the center of the pan. That's why it's buckling. (Uneven expansion, as Fe-Wood said.) If your pan fit was the same size as the opening in your firebox, then it would heat more evenly. Trying to go to heavier plate could get ridiculous, because all of your time would be spent heating the plate, rather than evaporating sap. Which brings me to this: the evaporators I've seen (an entire two) have been lighter sheet metal affairs on open frames. The sap is evaporated below the boiling point, so the fire is kept low and the temperatures involved weren't high enough to cause warping. It's possible that in trying to heat the 1/4" plate you're building a bigger fire than you need for the evaporation process and thus over-heating the plate. I am not sure about that analysis, I will check my firefox books later. Quote Link to comment Share on other sites More sharing options...
fciron Posted April 11, 2011 Share Posted April 11, 2011 Well, I found a sorghum boiler in one of the foxfire books. It seems it does get boiled, but the pan in the photos was quite light. It appeared to be a sheet-metal-lined wood frame. That would seem to confirm my memory that evaporators are lightly built. I just reread your first post and see that the 1/4 plate is part of your firebox, not your pan. Whoops. The process of warpage is still as I described. It seems to me that the surest fix would be to bring in the firebrick lining so that the pan rests on the bricks rather than the warping iron. Quote Link to comment Share on other sites More sharing options...
sqdqo Posted April 11, 2011 Author Share Posted April 11, 2011 I guess I didn't explain as well as I should have. The 1/4" is the top of the brick lined fire box. this is the part that warps so much. The actual evaporator pan is made out of 16ga stainless. It does not warp. the plate warps enough that it puts a strong pitch to the pan and therefore creates a pitch in the pan with most of the boiling sap at one end. Quote Link to comment Share on other sites More sharing options...
fciron Posted April 12, 2011 Share Posted April 12, 2011 Why does the firebox need a top other than the evaporator pan itself? I suspect the pan heats more evenly because it is full of liquid and that it doesn't get much above the boiling temperature of the liquid. (I suspect for syrup it's well above 212 degrees Fahrenheit.) The pan also has sides which help to stiffen it. Quote Link to comment Share on other sites More sharing options...
Fosterob Posted April 12, 2011 Share Posted April 12, 2011 If you made a frame out of something more substantial than 1/8 angle you should be fine. Angle is no good in any size to resist twisting and 1/8 might be strong enough to keep wet cardboard from sagging. I would use 2x2x1/4 wall tube to frame your opening. Tube is great for this kind of thing. Anything you put will probably warp due to more heat on one side though. Firebricks on the inside of the top to protect the plate? Rob Quote Link to comment Share on other sites More sharing options...
knots Posted April 12, 2011 Share Posted April 12, 2011 What is the volume/weight of fluid contained in the evaportator ? Steel looses strength as it is heated. If you are heating a large volume /weight of fluid the you may be experiencing this failure because the heated steel does not have the strength to support the load of the evaporator. How hot does the plate get ? Does it ever reach red heat ? I assume that this evaporator runs for long periods of time when in service. Quote Link to comment Share on other sites More sharing options...
arftist Posted April 12, 2011 Share Posted April 12, 2011 The main problem is the frame strength as Rob said. 1 1/2" x 1/8" angle is very light. In this aplication it is useless. Quote Link to comment Share on other sites More sharing options...
Judson Yaggy Posted April 13, 2011 Share Posted April 13, 2011 For those of you that are unfamiliar with the process, evaporators run HOT. If you are not boiling your sap as hard and fast as you can you are wasting fuel and time. It takes around 45 gallons of sap to produce a gallon of syrup, that's a lot of steam to make and get rid of. As far as I know all the commercial wood fired models have blowers to really heat things up. They also have linings of both firebrick and what looks like spun ceramic insulation like the Kaowool we use in our gas forges, and cast iron parts to reduce warpage. I'm sure you could forge with the fire inside of them if you wanted a forge with doors down at floor level. SQDQO- Where are you located? Perhaps we could put you onto a local metalworker for more advice. Quote Link to comment Share on other sites More sharing options...
IRON FIST RICH Posted April 13, 2011 Share Posted April 13, 2011 i also make maple syrup and my arch is made out of sheet metal sides and 1/4 inch angle iron, but i have 1 inch arch board insulation and full 2x4x9 inch fire brick and usually after a 8 hour boil the sides are just getting to hot to touch RICH there is a site that deals with maple syrup and all related items. if you need it let me know (not sure what the forum rules are about posting other websites) Quote Link to comment Share on other sites More sharing options...
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