Heating a Press 1

[mcfridge]

Hey guys,

I had another post on how I'm building a press for making skis/snowboards (

http://www.eng-tips.com/viewthread.cfm?qid=138318

).

If you go to this page

http://www.grafsnowboards.com/pressidx.htm

and go to either the 6th or 7th picture down, you can see how it basically looks. I want to heat the press somehow to speed up the curing times. These guys did this using a heat blanket:

http://www.skibuilders.com/articles/heatedpress.shtml

I wanted to use something different (i.e. some sort of heated fluid & piping) but everything I've came up with has been too expensive. I need it to be fairly cheap, get the temp up to somewhere around 170-180F and hold it for about an hour, and be able to withstand spressure between 40-80 psi. Does anyone have any other ideas I might be able to try?

 

[IRstuff]

Why not a strip heater?

TTFN

 

[GenB]

Only steam will give you steady heat,
to keep the temp you will need at least 50psi sat. steam,
I do not think you will find a cheaper fix.
to calc, the steam needed, you calc the area and convert to radiation sq-ft of. to lbs/steam per hour to btuh to kWh.-
then you decide if a gas/oil fired or electric steamer will be needed. the press will have to widstand 100psi pressure (WAWP-steam), carbon or s.s. will be a good pressure material.
genblr

 

[mcfridge]

Thanks for the responses guys.

GenB, could you elaborate a bit? What would you use to generate the steam? I looked into small boilers & even HW heaters and they cost too much. The press is made with steel I-beam so I'm not too worried about the extra pressure from the steam.

Also, would you use some sort of piping, or how would you transfer the steam? Right now, I am using firehose as the "bladder", which I fill with air from a compressor, which pushes down on a track of bars to get the pressure evenly distributed. Would I be able to fill the bladder with steam (probably have to switch to a different material) and get any heat transfer?

 

[MikeHalloran]

Make platens with liquid channels.

Get an engine and a radiator from a junkyard.

Route the engine's coolant through the platens and the radiator.

Run the engine when you need heat.

Change the engine's thermostat to control the temperature.



Mike Halloran
Pembroke Pines, FL, USA

 

[dalcazar]

this is a challenge I must say..

I would probably avoid any liquid heating under the press itself, using steam in your bladder sounds like a good idea, but remember you'll need to get the water out of it after each use. Additionally you'd have heat conduction resistance thru the square aluminum tubing, and a lot of the heat would be lost in the inner spaces due to convection. If you can fill those spaces with a liquid you'll increase your efficiency greatly.

What you could also do is run a steam line thru the tubing itself to provide heat in there instead of in the bladder, that way you avoid putting water in the bladder and you can insulate between the bladder and the tubing to improve your efficiency a bit more, I'm sure the fire hose will take the external temperature.

however you still need to keep the price down, and with these alternatives mentioned you still need to make the steam, and as far as investment goes I really don't see a viable cheap alternative to the electric blanket. Your energy costs will be higher to generate steam (heat to above 212 degrees and evaporate) than to heat to 180 degrees electrically and keep it there. You might as well go that way and invest a little in keeping your heat losses down by insulating between the heating pad and your aluminum tubing.

 

[mcfridge]

MH,

I had actually considered doing something like that, but I didn't know what kind of temperatures I could get and if it was feasible or not.

dalcazar,

Thanks for that answer. I figured that going with the heat blanket would be cheapest, but I guess I wanted to try to come up with something different that what had already been used.

 

[GenB]

Steam boiler. How much is too much?
you have to calculate the needed lbs/hr steam then shop for a steam boiler

http://www.steamequip.com

has smzll boilers- I see the page is down now but you can check later.
if small boiler needed: electric can be the answer and if more than 4 HP (140lb/hr) gas fired will be most economical.

to rid of water within the chamber you need a steam trap at the bottom drain location of the enclossure,
with a steam boiler yo do not need an accumulator.
to cnect to a moving plattens, you will need flex teflon/ss hoses which are std and safe to use in lower pressure
steam systems: 50-150psi pressure.
genblr

 

[MintJulep]

I'm with IRStuff. Simple electric resistence strip or cartridge heater. Depending on the mass of your press, and the level of control needed, either simple on/off proportional control or SCR-PID.

Watlow, Chromalux, Omega and others will happily sell you what you need.

 

[MikeHalloran]

Steam gives you uniform temperature, _on the surface where it's condensing_. It would work better if your press opened horizontally, so the condensing surfaces (aluminum tubes) would be vertical, and the condensate could fall out unobstructed.

I don't think it would work very well in the firehose bladders, which are not easily drained. Also, using steam to pressurize the firehoses removes your ability to set the pressure and temperature independently.

Assuming you choose to heat the aluminum tubes, you only need a single (large) connection to each tube to do it with steam, but steam hose is pretty stiff. To heat the tubes with engine coolant, you'd need two smaller more flexible hoses per tube.

Electric heat has some advantages; you can have different zones set to different temperatures, and common controllers can implement ramped temperature cycles, which are useful for some kinds of resin. You can get electric heaters in silicone blankets, which can be nearly in contact with the resin. And the required electric cables won't get in the way as much as a bunch of pressurized hoses.

You did ask for cheap, too. Junkyard engines are cheap. In many places, whole cars with usable engines are even cheaper.



Mike Halloran
Pembroke Pines, FL, USA