Veneer pressing time
Necessary waiting period between hot-pressing and further processing of panels. November 18, 2002
Question
When hot pressing custom veneer panels, how long should the panel rest after pressing before processing it further (i.e. cutting to size or sanding)?
Forum Responses
It is best to wait 24 hours. This will provide time for complete glue cure. The panels retain quite a bit of heat post press. They need time to return to ambient temperature. If you stack them without sticking them, this heat takes a long time to dissipate.
You can speed this up by doing the following:
1. Stick the panels after exiting the press.
2. Position some fans to blow through the panels
This will carry off heat relatively quickly and allow subsequent sizing and rework in a shorter time period.
I agree with the above to a point. Are you talking about sheet veneer or raw flitch veneer? It makes a difference. At our facility in Miami, Florida, we press sheet veneer in a hot press with PVA Adhesive. After pressing the panels, they are dead stacked from the time they are pressed until the next working day. Then delivered to the customer. This time can be 24 hours or as little as 15 hours.
Locke Wilde, forum technical advisor
From the original questioner:
We press raw flitch veneer only with PVA adhesive. Typically we lay the panels on a flat cart and sticker the panels so they can dissipate heat evenly. When you say dead stacked, do you mean no stickering and flat stacking?
Yes, but I am talking about pressing sheet veneer to panels, not raw veneer.
Locke Wilde, forum technical advisor
If your press has enough pressure and heat, try a Urea glue. You can get a sample from Jeff at Custom Pak Adhesives. It is a hard glue line when it's out of the press. You can machine right away. You do have to watch the cooling/warpage factor. (It's always better to dead stack and mach, when cool). Also, we would not do finish sanding the day we press a panel. But for rapid production, Urea is great.
It also depends on what core material. The above works for flk and mdf. We also do a lot of 5-ply with lumber core and we always dead stack that for several days to one week if possible to avoid warpage.
Some good ideas:
* Even glue spread. 4 to 7 mils depending on open time, temperature, and type of glue. Cross linking PVA made for hot pressing is far superior to Urea resin, in my opinion.
* Cover platens with heavy canvas and then Mylar to help reduce blows or blisters.
* Stack flat with no stickers overnight.
