Veneering questions

[Woodmonkey]

If i use an electric blanket over my bag press, how much will this reduce the pressing time if using cascamite?
Also is there some kind of valve I can install in the system so that once the pump has sucked the air out I can turn it off, I currently have to leave it running or it will allow air back in.

 

[marcros]

a check valve (aka a non return valve) should do the job. I dont know about the electric blanket question.

 

[RobinBHM]

For Borden one-shot UF:

10degc 18hours
15deg 8 hours
20 deg 3hours
25 deg 2hours
30 deg 1 hour
50 deg 4.5mins
60 deg 3.5 min

thats assuming pressing veneer onto mdf using a heated platten press it will take longer if the veneered side is face down in your press as the heat has to get through the board.

google: borden one shot for the pdf on info on borden one shot H powder resin UF glue

 

[custard]

I've asked myself the same questions Woodmonkey but never really answered them satisfactorily. I once worked in a workshop that used industrial heating blankets with vac pressing and it was a huge advantage, but when I looked at getting similar blankets for my own workshop I concluded they're too expensive to justify. Airpress recently released a heating mat range, but it's interesting to note that they're only for pu bags,

http://www.airpress.co.uk/115-bheater-matsb/

Regarding the timing issue, I suspect that Cascamite is actually slower setting than Robin's chart would suggest, I don't know this for a fact but I've fair bit of experience with Cascamite plus liquid UF with both slow and fast hardeners, and that's my strong suspicion based on practical experience.

Regarding a non return valve, some vac press units operate intermittently when the pressure drops, my Airpress unit doesn't, I wish it did but I don't think there's an easy solution. A non return valve on its own wouldn't work as there'll always be some system leakage, so you'd need something that sensed the pressure drop and then topped up the vacuum.

Bottom line is that I use UF glues regularly, but for vac pressing I always try to use PVA in the first instance, as I've so far been unable to find any alternative to running the system constantly for 12 hours or so. Consequently I tend to do vac press veneering and laminating with UF as the first job in the morning, and in the winter crank up the woodburner to the max. All a bit of a faff but I haven't found a better method which is why I'll be following this thread with interest!

 

[Woodmonkey]

So you think a standard household electric blanket is not worth the bother custard?

Or something like this:
http://www.warmfloor24.co.uk/warmfloor2 ... oC54Xw_wcB

 

[custard]

So you think a standard household electric blanket is not worth the bother custard?

Or something like this:
http://www.warmfloor24.co.uk/warmfloor2 ... oC54Xw_wcB

I simply don't know, but before putting my work and equipment at risk I'd like to better understand why there's such a whopping price difference between commercial heating mats and cheaper domestic alternatives!

 

[Beau]

Regarding a non return valve, some vac press units operate intermittently when the pressure drops, my Airpress unit doesn't, I wish it did but I don't think there's an easy solution. A non return valve on its own wouldn't work as there'll always be some system leakage, so you'd need something that sensed the pressure drop and then topped up the vacuum.

Custard. Not entirely true. I have a vacuum bag that runs off a venturi powered by a compressor. It takes a bit of work but I can get the bag to completely seal and there is a stop valve on the inlet or should I say outlet.

Sorry OP not very experienced with cascamite.

 

[Chrispy]

Another thing to bring into the equation is the effect of the vacuum on the adhesive, and the adhesive on the vacuum, water boils at 0d Celsius if you can get a vacuum of 29" of Hg so even with less of a vacuum from your pump bring the temp up to 18 or 20 and you should be pulling steam through the pump as well as air to maintain the pressure drop. This I think will speed up the PVA setting but not sure that the same would be the case with UF.

 

[custard]

Regarding a non return valve, some vac press units operate intermittently when the pressure drops, my Airpress unit doesn't, I wish it did but I don't think there's an easy solution. A non return valve on its own wouldn't work as there'll always be some system leakage, so you'd need something that sensed the pressure drop and then topped up the vacuum.

Custard. Not entirely true. I have a vacuum bag that runs off a venturi powered by a compressor. It takes a bit of work but I can get the bag to completely seal and there is a stop valve on the inlet or should I say outlet.

Sorry OP not very experienced with cascamite.

You make a good point, that may also be true with my Airpress...just I've never trusted the bags, connectors, and pipes enough to risk it! The way I look at it is that vac bag pressing works right at the very edge of minimum acceptable gluing pressures, so I try and avoid risks where ever possible. That doesn't make me right, I've no particular technical expertise when it comes to vac bag pressing beyond simple practical experience!

 

[Beau]

No I never entirely trust it and normally glue in the morning so can check it during the day but usually can get a complete seal. Having a 3HP compressor running as the alternative does focus the mind

 

[Sawyer]

I currently have to leave it running or it will allow air back in.

Clears that one up then! Finding the same annoying trait with my own bag press, I'd wondered if it was a duffer. Apparently not.
I often use cauls or animal glue instead to avoid the irritation and expense of running the pump for hours on end.

 

[Woodmonkey]

I think I will get an electric blanket and do some testing...

 

[ComfortablyNumb]

cascamite cures in around 10 minutes in a heated press that's set to 80 degrees Celsius. You don't get full bond strength till quite a while after that though, at least until material has cooled. I'm not a fan of hot pressing as unless both veneers or laminates are identical the boards warp