Repairing Dents in Heated Veneer Press Platens
Repairs and workarounds may help (a full replacement would be costly). March 28, 2012
Question
We have a heated hydraulic press which has damage to the platens. Is there any cure for this other than changing the platens? In particular, any resin that could be put into the press to fill the deformed areas, or some form of rubber matting that could take up the differences?
Forum Responses
(Veneer Forum)
From contributor R:
Two options: replace the platens or take them out and have them re-surfaced. I have been working with both hot oil heated and electric heated platens for many years and have found that once the platens have been damaged, there is no easy fix for them other than the two ways I suggested.
From contributor I:
I have dealt with this problem for quite a while. Depending on the level of damage, we have successfully used a heavy felt or neoprene fabric to overcome some of the irregularities. We have also sandwiched particularly important pieces between two sheets of 1" MDF or something similar. The second suggestion effectively turns it into a cold press, but if you aren't in a hurry we have made it work. If you are running high volume through this press, the only real option would be to replace or resurface. If you aren't and just need a solution every once in a while, we have had success using the above methods.
From contributor C:
What are the platens made of? What type of heat method do they use? And how out of whack are they?
From the original questioner:
They are aluminum and electronically heated. They are out by around 0.75mm we think. We have been advised a silicone rubber mat might help.
From contributor C:
That's quite a bit. If the silicone rubber does not do it, you can get a metal compound to level the dent (it is a dent, right?) and then put a new sheet of aluminum over it. How did this happen? The worst story I have heard is someone closing a press with a staple gun in it!
From contributor L:
The rubber mat should work. I have used one for mahogany crotch with much better results than a solid platen. The best rubber for a cold press I have used is gum rubber. I thought it might be too soft but seems to work better than a harder rubber.
From John Van Brussel, forum technical advisor:
I have heard of customers using Bondo (car body filler) with success. We also sell a press pad which can help make up for small deviations in platen tolerance. Because of the construction of the platens the aluminum may be damaged but there is also a special particleboard under the aluminum sandwich construction which may have a dent in it as well.
If you use rubber or silicone blankets, be careful because they may transfer to the veneer surface and affect the finish.
From contributor R:
Here's my experience with a 5x10 aluminum platen electrically heated press. It was a Hofer H5000. It was a good press overall, but we overused it for what it was designed for, light to medium press production (about 100 panels per week). It was used solely for blue print matched paneling.
We were rookies and during the learning process we managed to press a multitude of things - panels, razor blades, putty knives, etc. Some of the small dents, if they tend to be towards the outside of the press, you can get around by shifting your panels around and using filler boards where it's damaged. We had a low spot in the middle of the press, almost a valley. We separated the platen from the 1 1/2" particleboard. If you have a similar situation, this is relatively easy, and shim with yorkite in the area of the valley to push it down.
We also added a feel-good measure that seemed to work for a while - painter's canvas, which allowed the heat to penetrate and do its job, but it also took up some of the low spots and gave us a flatter surface. This worked but lasted about 3 months, and several changes of the canvas. The canvas isn't cheap. New platens at the time were around 10,000 dollars, so this wasn't an option. But continually making quick fixes costs money, and lost production time costs money. Is that better than just biting the bullet and (I know it's hard right now) fixing it right?
From contributor D:
No, there is no filler for this that I have ever had success with in over 20 years of repairing this type of platen. Bondo will not work because it cannot transfer the heat adequately enough to give you quality results. A defect of .75mm may be eliminated by reseating the platens according to the manufacturer's specifications. However as pointed out, the insulation material may have to be changed as whatever caused the damage may have also damaged the insulation material. The press pad will work but it's very expensive and I have tried it in the past. It takes too long, in my opinion, to transfer the heat through this material. Your options are as follows.
1) Try to reseat the platens.
2) If this does not work you can use 2mm smooth silicone material. The silicone is 40-60 duro and should take it out but you cannot allow the silicone to touch the veneer and must place Mylar between the veneer and the silicone.
3) Natural rubber membrane will work at temperatures below 90 C in the same fashion as above but don't exceed 90 C.
4) Replace the platens.
The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).
Comment from contributor A:
The advice about filling and sheeting with another aluminum sheet was good. I have not heard of using Bondo but I have used Metalux. It is a cold casting product which can be used for repairing engine castings. There are two types, aluminum and steel. Both transfer the heat and act like their respective metals in terms of heat and both are non-permeable to oil.
