I have been producing doors for sometime now and have been using a standard PVA for all aspects of production. Now i have started using 3mm thick veneers as i cut myself in house, and am having a few issues.
1. Usually when pressing harder woods
like Maple i cant find the happy medium with heat and time pressed. Seems if i press at to hot temp. the veneer curls on the edges causing what setting of the glue that has happened to release. Wood is too strong. If i turn the heat down then i need to press for long lengths of time and may as well cold press.
2. Mostly in these winter months i have had a few issues with cracked/split veneers ones doors get to customers. I chalked the first couple issues up to very cold dry temps and wood loosing a ton of moisture. I am still seeing the odd split here and there though so maybe thinking the glue is somehow a culprit
construction of components is pretty straight forward:
Commercial 32 lb particle board core capped with min. 3/4" x 1-1/4" solid wood strips. calibrated thickness then hot pressed with 3mm wood veneers on both sides. Finish component is roughly 5" x 98" x 1-3/8"
I don't want to venture into mixing catalysts and have really toxic stuff around you have to wear respirators and such anytime its open but at the same time i want quick production presses like you should get from a hot press.
Any particular reason you are using 3mm thick veneer, other than to cut in-house? I can't imagine it is cheaper to cut 3mm veneer in-house than purchase 0.6 mm veneer from a veneer face manufacturer. In the case of veneer and especially the adhesion thereof, thicker is not necessarily better.
It takes a lot longer time for heat to penetrate 3mm of Maple to the glue-line than 0.6 mm. That is certainly part of your adhesion problem and also part of the reason for veneer cracking and checking. You don't want to leave any wood, and especially Maple, under heat for longer than necessary. All you are doing is drying it out, not getting a better bond. The pressure (shrinkage) exerted by the veneer drying out are greater than the adhesive and process are capable of controlling.
Not sure where you got the idea that catalysts are highly toxic and you need to wear a respirator when around catalyzed glue. I haven't seen that in any door plant I have ever worked at. (I wouldn't drink the stuff, but no reason to put on a hazardous waste suit either.) And pre-catalyzed PVA adhesives are available if you want to get away from mixing.
I see some major flaws in your materials and processes. Personally, I think you need to re-think the whole thing and look to thinner veneer and catalyzed adhesives. Any good adhesive manufacturer will be more than willing to advise you on their products and how to use them.
Thanks for your input, i was thinking urea resin glue i believe when i was righting that post sorry, we went 3mm on our veneers for a few reasons. 1) Customers always asking for thicker veneers like their eng. hardwood 2) We can produce ourselves in house for same cost as buying from producers and have a huge variety now, if i can get my hands on the wood i can now produce engineered doors from it.3) it stream lines my production through all species including MDF.4) It keeps my employees busy. Do engineered hardwood manufacturers not lay roughly 3mm veneers on their "plywood" sub-straight?
Gene where are you?
I think the moisture in the glue is readily absorbed into the maple, it expands before the glue sets. After the glue has set the maple equalizes its moisture content and tries to shrink. It is thick enough to start acting like a board rather than a veneer. Snap, crackle, pop! If you absolutely have to have 3mm use a glue w/o water. Epoxy?, sure to make a mess & expensive.
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