Steam Hood Fabrication

[ibby458]

Since we're still in the deep freeze here, I'mm finding time to start my steam hood. I've got the 26 ga. stainless all cut to my plans, and hope to start bending metal tomorrow. (After I go over and check out Fred's new hood)

The condensate channel around the edge is 1 inch wide, and 2 inches tall. The only way I could figure out to join the corners of the channels is to cut them at 45 degrees where they meet , and solder on L strips in the bottom and sides to seal them up.

Is there a better way?

[hookhill]

Ibby,
Going to be doing the same thing next week out of aluminum. Not sure how easy it is to solder aluminum. If you are making your hood out of stainless I think cutting the joints to a 45 and then soldering would work. I was thinking of overlapping the joints and then using some silicone. Good luck. The weather is perfect for these types of indoor projects!

[super sappy]

Hook hill- If you look at my pics you will see what I came up with.I could not get the aluminum solder to work.Sooo- got some Alum u channel from Home Depot and mitered the corners of the water channel. I used a Stainless wire brush to clean the joint then I used a brazing rod (Bernzomatic) for alum. The joints were easy and did not leak.I was real suprised to see how strong they were.The thing works great.-Super sappy

[ibby458]

Silicone is my backup plan. I've soldered some stainless that was easier than tin, and others that the solder just beaded up and rolled off. I don't remember (or even if I ever knew) just what formulation this 26 gauge is. I bought it cheap off eBay a year ago. It's not a polished, shiney stainless, but it won't corrode, which is the main thing.

As I thought about it, I figured out how to cut the corners so they overlap. I have a bunch of 1/8 x 1/8 stainless pop rivets, so I can rivet it for some extra strength.

[ontario guy]

you will need special flux to solder stainless. Once you have that it is the same as soldering copper.... Good luck.

Mark

[maple flats]

I find soldering with an elec soldering iron better than a torch by far for SS. If you need one do a search online, they are available, and yes, you need flux made for SS.

[ibby458]

I have the special stainless flux - actually a liquid, not a paste. It works great on 304 stainless, but 309 & 316 just makes the solder bead up and roll off.

Fred gave me a stick of special brazing rod for stainless. We'll give that a try if the solder fails.

[mapleman3]

As far as aluminum, I just built most of my hood in the past 2 days, I just need to make the pan and u channels, I have a product I got online called dura fix.. awesom stuff for joining aluminum... just heat with a propane torrch and start adding the alum. rod and you get a nice joint.. hard as steel and safe too, no lead no flux.
http://durafix.com/index.html

[ibby458]

The main body of the hood is all assembled. My first discovery is that freshly cut stainless is SHARP. Hap to put gloves on to keep the blood off the hood.

My stainless pop rivets were actually 3/16 boat rivets with closed ends. Perfect for the job, but even the Hulk on steroids couldn't have popped them! After 3, my arms were like rubber, so I switched to aluminum rivets. Much easier!

Going to build/install a set of stiffeners today. That 26 gauge is nice, but pretty flimsey. With any luck, I'll get that done and get the doors cut out and the Lexan installed. THEN - the preheater!

[Sugarmaker]

Ibby,
Yes the stainless pop rivet in 3/16 are a challenge. About like a 22 going off when it finally lets go. I used many on the hoods and fought every one with a hand pop rivet tool.
Sounds like you are well on your way!

Regards,
Chris

[maple flats]

You need a 2 handed long handled pop rivet tool. I have used one in my old furnace business, they work way easier, I got it at an auto body repair supply store, not overly expensive. The only thing easier would be pneumatic.

[ibby458]

I'll definately check out the two handed tool, and even possibly a pneumatic if the budget allows. I'm sure this isn't the last hood I'll ever make, and I want it as easy as possible.

Installed U channel stiffeners yesterday. Also found that many of the aluminum rivets were loose. Drilled them out, improved the fit and reriveted. The metal sheets had been shipped/stored in a roll, and it stayed curved after bending, So I wasn't able to hold the stiffeners in place tight enough to rivet. I have a bunch of 1/4 x 3/4 Stainless truss head bolts, so we bolted the stiffeners in place. THAT pulled it flat!

THe door holes are all cut out, reinforced and the sharp spots filed smooth. Gotta put on the doors today, and solder the drip chanels. THEN - the preheater tomorrow. At 10 below zero this morning, it don't look like I need to rush much!

[maple flats]

I was in the furnace business before I sold out over 7 years ago. You should take your sheet stock and roll it opposite to the curl just enough to allow it to flatten and once it is flattened, put the cross braking in it (creating a very slight crease from one corner to the opposite corner). Design the cross braking so both lines of the x go the same direction and so that the slight bow resulting bows out and not inward (in other words do not flip the sheet, just rotate it). This will make it quieter in use if some serious activity is happening inside because the larger flat sides will not flex back and forth which is sometimes possible but usually not (the oil canning effect). Then put the final bends to fabricate the shape you want. This will remove most of any curl and it also makes the sheet stiffer or less flexable after fabricating. If you look at any professionally made furnace plenum or larger duct work you will see an example of cross braking. When you do it only bend enough to put a slight crease across it. By the way, 26ga SS is likely the best to use for this, strong enough but not too heavy and besibes that 24 or heavier is much harder to get a shape to hold unless you have a commercial weight brake such as found in a tin shop (probably at labout 1000# for an 8 footer and re-enforced against flexing while making a bend) However even with a real solid brake you still do not get the exact same angle the full length of the brake because the ends of the sheet bend easier than the center because it has no adjacent metal to help resist bending like the center does. You just bend so that the center is correct and then gently pull back at the ends while still in the brake to match. A trim brake for siding will work but you need to take more time to get a constant angle along the bend and you will need 26 or even 28ga for workability, yes 28 is heavy enough for a hood but 26 would be sturdier and likely best. Once you have assembled the hood you can not add the cross braking any way that I know of. Good luck.
Dave

[ibby458]

Thanks for the advice! I've seen cross braking before, but my brake is only 4' and my flue pan is 5 1/2', so I had to make it in two pieces and seam it in the middle. That would make it tricky to cross brake. I could have done it without the seam, and taken it to a friends to break, but it would have used quite a lot more stainless, with more waste. Even so - If I ever build another, I'm going to do it the way you advised. That seam bugs me, even though I camoflaged it quite well. i will CERTAINLY roll the sheet against the curl to flatten it. Fighting that curl gave me heartburn.

I soldered all the seams in the drip channel, and the corners, and installed a 3/4" copper drain fitting. I saw a marking that this is 304 stainless, and it soldered like a dream! I have a few spots where the fit was not ideal and they leak, but nothing a dab of silicone won't seal.

The doors are all installed. I used 1/4" lexan so I could see thru them (Plus I already had some). I overlapped the sides of the holes as much as I could, but there's still gaps where that DARN curl pulls the metal away from the door. The only plan I could come up with to seal it is to grease the lexan with vasoline around the edges, put a thick bead of silicone on the metal around the doors, and gently close them so they form a perfect seal. Hope that works!

I got all the fin tube and pipe in the shop to start the preheater today. Since it's all used, I got a bottle brush that will go in there with enough drill extensions so I can spin the brush while scrubbing it with soapy water. Rinse the heck out of it, let it dry and start soldering!

[maple flats]

You can cross break even if it does not go from corner to corner, just do it 2 times with an overlap if needed. I do not think you want to seal with vaselene because it would melt and get in the syrup. It melts at less than 200 degrees I believe. Do not worry about minor leaks, they will likely suck air in not push steam out as long as you have a decent draft on the hood.

[ibby458]

I was going to wash off the Vasoline after the silicone hardened. It's only to keep the silicone from sticking to the Lexan during curing. The seams and drips that will get siliconed are all in the drip channel area or the outside of the hood. I don't see anything dripping into the pan.

I'm going to solder up the preheater today. When I laid it out on the bench, I put a wood chunk under opposite corners so it's twisted a bit. That leaves the inlet end at the very lowest point and the outlet at the very highest. There's a drain valve on the inlet side and now every drop should drain out. With the outlet being the high point, every air bubble should rapidly make it's way to the vent.

I should get that done early enough so I can start hanging it and the drip pan in the hood. I reinforced the top, and hung some 1/2" stainless all thread down from each corner. SS angle goes between them for the heater to sit on, and another set for the drip pan. With the all thread, I can change the angles it sits by raising and lowering the nuts under the angle.

[ibby458]

Post Season Performance Report.

The hood worked well in that it directed most of the steam thru the preheater and out the pipe. I also discovered several interesting facts.

Silicone is rated to around 500 degrees, and the product does indeed stay intact at steam hood temperatures. However, it loses all adhesion well below that. All my sealed spots pulled away and fell off. I'm glad I soldered the drip channel seams!

Lexan doors do not fall apart at 200 degrees, but they do swell and warp. No way could they seal tight. Also - you can't see thru them anyway, so I should have just used Stainless.

25' of 3/4 finned tubing will preheat sap to 190+ degrees in a 200 degree hood, UNTIL you get 'er cooking good and the flow thru the preheater gets up over 1 gallon/minute. On the days I REALLY get it ripping, 145-160 was the best I could do consistently. Still a lot better than 36 degree sap entering!

Even with leaky seams etc., the hood stayed 200 or a bit hotter. (My thermoter only goes to 200). If it drops below that, I haven't been firing it right.

THe constant drizzle of hot water is a lot more useful than I ever thought. That feature alone made it worth doing.