A Heated Vacuum Press: Anybody Have One?

[John TenEyck]

I have a lot of panels to veneer in the near future. I want to use Weldwood Plastic Resin Glue. At 70 deg it requires 14 hours to cure, at 140 deg. 30 minutes. You see where I'm going here. I've tried an electric blanket over the top but the temp. rise was minimal. I've also used halogen lights, and that does work, but I would need a lot more to adequately cover my 2 x 5 foot panels and I'm concerned about the fire risk left unattended. So, does anyone have a heated vacuum press? I'm thinking of two options. One is to embed copper tubing under the Melamine base platen and pump hot water through it from a small electric water heater. The other option is some sort of electric heating mat underneath with thermostatic control. Typical under floor electric heaters, however, do not appear to have enough watt density to raise the temp. up close to 140 F. Anyone been down this road and have some advise? Thanks much.

John

[richard poitras]

My thoughts are foam under the system and electric blanket with insulation on top. I don’t see how you can’t get the temp you are after with the right amount of insulation. Good luck.

[Loren Woirhaye]

I think you're headed down a road of disappointment.

I hope you're making money on these panels. I'd recommend getting a 1/2" plate of aluminum to heat as your platten and welding up a veneer press frame. Use pneumatics if you want to get technical, but veneer press screws aren't too costly and are foolproof. You can put insulators in between the platten and the screws to reduce heating of the handles. 80-20 might work but steel is stiffer and cheaper and will definitely work. Depending on tolerances (this is probably pretty unforgiving) you may want to hire it out to a welding shop with a big surface plate or whatever they use to make flat frames. The aluminum caul will flex a bit but the frame underneath had best be free of anything but minor distortion.

[James Conrad]

While I am quite familiar with using PRG's I've never tried to cure it at high temperatures. Which makes me wonder if there are any ill effects on the glue in doing so, such as does the fast cure cause it to be more brittle and possibly fail. Cutting the cure time from 14 hours to 30 minutes is a pretty big change.

What about making an enclosure out of rigid XPS foam? You might be able to then heat the space with some incandescent light bulbs with a dimmer switch, use a digital kitchen probe thermo to watch the temp...

[Peter Quinn]

Outsource to a veneer company. I was subbing for a guy with a heated hydraulic press, 7-9 minute cycle for a permanent cure. Very very flat panels. Pretty sure you could almost fry an egg on those platens, something close to 150 degrees. I can't imagine how you would achieve that on both sides of a panel in a vacuum press. They make silicone heating blankets that will achieve a pretty good temperature, but they are pretty expensive, worth googling if its worth the investment to you. Perhaps they could be included in the platens, not sure how you get the electrical feed into the bag? We have a local veneer outfit that we sub to for laying up bulk speciality panels, its a good value versus paying for the specialized press, training, maintaining, etc.


eg: http://www.watlow.com/products/heaters/flexible-silicone-heaters.cfm

[Mel Fulks]

The closest thing I've done is stack up pieces with plastic between them ,put weight on stack, and leave over night.

[Kevin Jenness]

Absent a major investment in equipment or outsourcing, it might pay to investigate other adhesives. I think Unibond 800 will cure in 4-6 hours at 70 F, so you could get 3 layups in a long day.. There are pvas like Unibond One that offer a relatively stiff glueline and cure in a couple hours that might be worth consideration. The electric blanket effect can be enhanced by covering it with a quilt and using it to preheat the platen while you are prepping your layups. You could enhance that with an electric space heater under your (enclosed base) press table You might also look at using two or more presses driven by a single pump and controlled by a manifold, if you have the space. Your hydronic heating idea could work, though I have not seen it done. Commercial heated presses are expensive for good reason.

[Bob Michaels]

What about making an enclosure out of rigid XPS foam? You might be able to then heat the space with some incandescent light bulbs with a dimmer switch, use a digital kitchen probe thermo to watch the temp...

I built a kiln to dry roughed out bowls from the lathe. kiln cabinet is roughly 24" x 30" x 5' long with a hinged top, 2" styrofoam liner, light bulb at one end with 4" round air intake hole and a 4" duct booster fan diagonally across to draw the hot air across the cabinet. I was up to over 100 deg with a 100 w bulb. Not my invention...read about it here & on web sites. Just a possibility...easy & cheap to build but not sure it would do the job, maybe (2) 100 watt bulbs. If interested I'd be happy to take photos.

[Jamie Buxton]

What works for me is a couple shipping blankets under the vacuum bag, a couple electric blankets on top of the bag, and a couple more shipping blankets on top. It gets quite toasty in there. Give it a half hour to warm up.

You might consider other adhesives. If you want to stay with urea-formaldehyde, Unibond 800 cures faster -- 5 hours at 65 degrees, 3 hours at 75 degrees, and 2 hours at 85 degrees. Or epoxy, which is also a non-creeping glue. West System's 105/205 epoxy cures in 3-4 hours at 70 degrees. It also will cure at 40 degrees, which no urea-formaldehyde will do. Okay, it takes a long time, but it does cure.

[John TenEyck]

Thanks for the comments everyone. I didn't know Unibond 800 cures so much quicker than PRG, so that in itself is a major step forward. Outsourcing is out of the question; no one I know of to do it and not enough margin to consider it. I can't use PVA type glues as my veneer is shop sawn and much thicker than commercial stuff. I had gaps open up at the seams on two consecutive projects using Better Bond. Feedback from the source I purchased it from told me it is unsuitable for 1/16" thick veneer. Wish they had made that fact known in their literature/website. Epoxy isn't something I like to use because it's a mess to work with, at least for me.

I have a home built dehumidification kiln powered by 3, 100 Watt light bulbs, which takes a pretty big load of wood (250 BF) up to 110 F with no problem. So the idea of an insulated box is feasible and I may use that approach. But the comment about added insulation over a couple of electric blankets sounds like an even easier idea, so I'm going to go run some tests to see how hot I can get a couple of platens. I'll let you know how it goes.

Thanks.

John

[Jamie Buxton]

... But the comment about added insulation over a couple of electric blankets sounds like an even easier idea, so I'm going to go run some tests to see how hot I can get a couple of platens. ...

A couple of platens? I don't use a top platen. The top platen will get in the way of heat trying to go to the glue.

[Mel Fulks]

John, since you are doing tests anyway try the stack method. The Weldwood has a unique ability to pull itself down ,it was demonstrated to me long ago and I have used it a number of times. Glue must be thin enough to DRIP off a stick ,NOT STREAM,and applied to both surfaces. I have even tested it by covering work with with a 1/4 inch piece of plywood ,using spring clamp around edges ,and putting a small weight in the middle. Even using that test the veneer pulled down.

[John TenEyck]

You're right Jamie, I don't use a top platen either.

John

[John TenEyck]

Mel, what do you mean by "pull itself down"? Sorry, but I have no clue what that means. If it's related to pressure and bonding, that is independent of the time required for the glue to set and harden, which is temperature dependent.

John

[Loren Woirhaye]

I use Titebond 2 Extend. It's rated for RF gluing and hot press use. I use it on a Hess edgebanding press and it will cure the glue in a couple of minutes. The heater gets hot enough for spit to dance on it and that's what works for solid wood. I've glued up to 3/4" thick edging with the press. There is a second strip heater so the banding is already pre-heated when it goes on the press.

I'd be concerned about a silicone rubber heating blanket damaging the vacuum bag at the temperatures my press cures glue at. Really an aluminum or steel platten at 1/2" thick gets pretty heavy on its own. I have some 1/2" steel plattens on a case clamp, about 24x30" and they are 80 or more lbs each I think.

[Mel Fulks]

I just mean that when thin and on both surfaces it has an attraction to itself that can over come even light seemingly inadequate pressure. When veneers are being used and room temp is not much over 70 degrees you have time to stack up a good number of pieces before weighting the pile. It works best with good flat substrates,of course. I do realize that you have a vacuum set up ,I just thought this stack method might help handle the volume. It is counterintuitive but with the Weldwood glue it works. I've tried the same thing with PVA glues and it doesn't work,and as acknowledged by others thinning PVA can cause problems.

[Harry Hagan]

What about contraction when the veneer cools? A 70º differential could cause problems; especially if the expansion rates between the veneer and substrate aren’t the same.

[Mel Fulks]

I have used it only as described . That's why any change such as addition of heated platen ,etc should be tested. Where there are pieces of equal size it works very well. If it can't be used by John for current job it might be handy for someone who does not have a vacuum set up.

[John TenEyck]

THanks Mel. I don't anticipate an issue related to assembly time. I would mix and apply the glue at room temp.; heating would only occur once the work is placed inside the vacuum press.

John

[John TenEyck]

PVA glues creep. It's acceptable with thin, commercial veneer but can be and was a problem with thicker, shop sawn veneer. Not a option.

John

[John TenEyck]

OK, I think this just got a lot easier, thanks to Jamie. I checked the Unibond 800 tech data and, sure enough, it sets in 1 hour @ 90 F. Weldwood PRG requires 5 hours at 90 F. A simple test with just a single, doubled over electric heating blanket on top of my vacuum table (sitting on top of a piece of foam insulation) shows I can get at least 100 F. So if I make a stack of foam board, electric blanket, platen, veneer and substrate, vacuum table, electric blanket, insulating blanket, I should be good to go.

Thanks everyone. I'll post something when I actually get to work on this project which is going to be a couple of months away.

John

[jerry cousins]

i use unibond in a vacuum bag - both sides wrapped in an electric blanket with a heavy top cover - i heat the platens & bag while i prepping the piece - maybe an hour. i have done both single pieces and 3 layers stacked - cures within 2.5 hours. my unibond mix is 4 to 1 by volume.
i can then remove it from the bag and start an other press. although i don't actually begin to work the piece until at least another 4 or 5 hours.
jerry