Thread: burner for steam bending.

Originally Posted by malb

Jake, you haven't given a lot of info on what you want to steam, and how many of them at a time. .

sorry, I'm not really sure yet to be quite honest.

I'm building chairs part time. Need to bend bows etc. Mostly one piece at a time. Though occationally be nice to bend say half a dozern small spindles at once.

There is a settie I'd like to make that has a bow near 100inches long. (about 2.5m?) Should fit into a box 4inch square.

So say a box 6inch square and 100inches long should cover all my needs. Thinking maybe could have trap door sort of arrangements, that allows me to shorten the box for shorter bends (too clever maybe)

I'm just going to make one up and just see how it goes with the kettle, fingers crossed its all I need.

What I'd love confirmation on mostly though is,,,,

since from what I've read, maintaining 100degrees is the most important thing.

Can I use that entirely as a guide. eg If I make a long box, and stick the thermometer in the end and I'm still getting that 100degrees is all well ? Do I need to worry about flow rates etc. something I might be missing. Spose I'll find out anyhow with an experiment or two.

Thanks for all the ideas btw so far.

Assuming you're using green wood, then if you're seeing steam at the low end of the box, you'll be OK. It's the heat that counts and if there's steam, there's heat.

Originally Posted by apricotripper

Quick question..... thinking of having a stab at steam bending using an old cook top I found. Its missing the gas tank. Read heaps on steam bending already.

Trying to get as much heat as possible. Got the impression that different burner heads generate more heat than others.

Wanna to try and nail it the first time, as you do uno.

Is this burner head good enough do you think? Or should I go buy something that will generate more heat ?

Any particular propane bottle I should go for ?

ta.

I built a timber boat some years ago and came up with a wonderful steamer. I had to bend chines and stringers over 6 metres long, so it had to be BIG. Here's my solution: For the heat source, a 20 litre kero tin. For the steaming chamber, I found a 6 metre long piece of galvanised downpipe, but these days I'd be looking for an old woodfire flu, so you could change length from one metre up to 2 kilometres.

Here's the deal: Cut a hole in the kerosene tin as close to the top as you can, the diametre of the pipe you are using (use the pipe as a template). Then simply insert it and bung it with silicon. Of course, this is not something that you want to move round, so once you've got your position right, then assemble it.

I then got old carpet scraps and gaffer tapes them to the pipe to retain the heat along its length. I cut an old 44 gallon drum in half longitudinally, placed a couple of bricks on either side to support the can over the fire, and then created a whopper of a fire in it. (At this point it's also good to have a bunch of potatoes, rubbed with salt and olive oil and wrapped in aluminium foil to chuck into the coals as well. Your apparatus is likely to draw neighbours and interested onlookers.)

Fill the can halfway or so with water and throw the potatoes into the fire. Sit back. When the thing gets going, you'll know it. For best results, I tied rope round the end of my pieces of wood so that I could shove them down the guts of the pipe and then be able to retrieve them. Stick a towel in the end to bottle up the steam while they are in there. Of course, it will depend upon how thick the timber is that you are steaming, but for 19mm stuff, about 20 minutes should do.

A tip: Have absolutely everything you need in position for clamping! You will have about 20 or 30 seconds to work with when you pull the wood out. No more!

Just for fun, I took a 2 metre long piece of pine, 18mm thick and steamed it a good long time and managed to actually create a circle with it. Some timbers steam better than others, and I have a book which tells you about its steaming properties. If you need some guidance for a particular species, please feel free to send a PM.

Happy steaming, potato eating, and boat-building!
Michael

ta for the ideas. see what happens.

I found a plastic high pressure pipe. 100mm diameter. 8mm thick walls I'm going to use for a bigger steam box next week.

When i was at college in the UK we had two sections of 300mm dia galvanised pipes standing about 5 ft tall with a kettle element in the bottom and a plywood lid on top with a hook underneath where the timber hung from.I have since made one over here ,same principal but out of an old pool filter.

thanks for the idea.

I've got myself setup now though. Getting good results from a fast boil electric kettle. Stick with that until it fails.

if it don't work on timber Jake it might be ok for cooking dim sims

Originally Posted by echnidna

if it don't work on timber Jake it might be ok for cooking dim sims

yep. or getting high.

just throw a thoroughly washed out 20L thinners drum into an enclosed BBQ,

Apricotripper, please forgive me for stating the obvious. Steam does not get any hotter with more heat. As long as you can direct the steam to where you want it your burner should be perfectly adequate.

Steam does get hotter under pressure.

ta. I didn't really know that. quite new to this stuff. The thermometer stuck in my steamer reads 128degrees though...does that mean its reading the temp of the water around the insides of the steamer ?

G'day
assuming 128degC not degF, and your thermometer is accurate (test by dipping into boiling water) 3 other possibilities

First - More likely measuring the air temp in between droplets of water vapour.

second - there is quite a lot of pressure in there - 2 or 3 atmospheres at least at a guess - the maths is too fiendishly complicated for my addled brain http://en.wikipedia.org/wiki/Boiling_point.
If so, this would be a Bad Thing unless it is a well-designed pressure vessel.

3rd possibility from vague recollections of steam theory from marine gingerbeering intro course nearly 30 yrs ago... please someone correct me if I got this wrong !!

Water vapour /steam evaporates at 100deg C. This state is called "wet steam" - big droplets of water vapour. Additional heat dosn't increase the temperature of the steam - rather it is absorbed into breaking down large water vapour droplets into
smaller ones, until most are broken down to single molecules of H2O. Once that
occurs, the steam is said to be "dry". Dry steam increases temperature freely with
additional heat applied.

As your little steamer should only be producing enough heat to generate wet steam, and you are unlikely to be pressurising your steamer to maybe 300KPa, it is most likely a dodgy thermometer or option 1.

cheers
AJ

Yes, AJ's correct in that you need a pressure vessel to generate enough "containment" to increase the temperature of steam.

The steam only needs to be at the boiling point, which makes the wood pliable. If you could apply considerable pressure, like in an autoclave, then you could speed up the process, but you'd still want the temperature about at boiling as to not damage the cellular structure off the wood.