Shopping for a Hot Veneer Press
My questions at this point are as follows:
1. Will 90 work for me? Why or why not?
2. What are the advantages and disadvantages of aluminum face platens and mylar?
3. We are getting more and more NAF/LEED work. What is a compliant adhesive recommendation that allows fastest turnaround from press to machine for laminate. Same for veneer. (Veneer will be sheet stock typically on paper).
I am an independent press tech located in Charlotte, NC. There are different answers to this question. It varies from person to person. The main thing is the press pressure depends upon the glue you are planning to use. Certain glues can work at the lower pressure, and others can only work at a higher pressure. What is going to be your main core material? MDF, PB, or ply?
If you mainly plan to run MDF and PB, then you don't require a filler glue or need to compress the material as it is already flat. If you plan to run ply, you can have problems of an uneven surface. This can cause you problems if there is a big variance. As this won't bond unless you either compress the wood to apply pressure everywhere or you use a glue that can act as a filler. There are many things to consider on aluminum or steel. Steel is usually oil heated and can reach a higher temperature than aluminum platens. Most aluminum platens are electrically heated and glued together. If they get too hot they will separate. Oil platens can get hotter, but can be more expensive. Both can be damaged easily and any debris on your board, can damage a platen. Some manufacturers use oil on their electrically heated platens. This is more to distribute the heat evenly across the platen. This won't help it reach a higher temperature, but will result in a more even heat distribution across the platen, which is better.
Mylar is great to use to cover your platens and easier to clean. You can clean the mylar or replace it and don't have to worry about scratching it. If you are working straight on the steel, you have to be weary of scratching/damaging the platen. This can be very expensive to repair or replace. There are many companies out there that can help you with the glue. I have to have my own glue brand, but there are plenty of companies out there to help you with glue. It really depends upon the press you get and what material you will mainly run.
In regards to your pressure question, the higher pressure is always betters. It will help better with ply. But again, it is really dependent upon the glue you use and the glue requirements.
Our company is a major supplier of hot presses to the woodworking industry. There is no need to be biased in answering your questions. There are many good suppliers of PVA adhesives in the market. This family of adhesive is typically LEED compliant and perfectly suited to hot pressing both HPL and veneers. Thickness calibration of the core or faces should not be a problem with the type of materials you are thinking to use, with the possible exception of imported plywood cores.
I believe you will find that most PVA glue manufacturers will recommend a laminating pressure range of 30 psi to 85 psi for these applications. I find that 40 to 50 psi is the most you would use for HPL, while veneer can tolerate more. With backed veneer, 50 psi a good laminating pressure. A 90 metric ton press produces a maximum of 43 psi laminating pressure on a 48" x 96" panel, while a 120 metric ton press will produce 57 psi. A good glue bond requires intimate contact of the face and core material over the whole surface. Pressure compresses the two materials together to accomplish this. The pressures used in this process are insufficient to compress any of the face or core materials you will be using. That being said, 43 psi vs 57 psi is something, but will not make a major difference.
You will see more calibration issues with plywood cores - the additional pressure will be a benefit in these cases. Core calibration is not much of an issue when pressing stock sheets of material - one sheet at a time. The issue arises when pressing cut to size components - multiple pieces in each press load. Parts with tapers laid side by side - the thin side of the panel my not get sufficient pressure if it is sitting beside the thick edge of the next panel. In the end, careful loading of the press will have the greatest effect on the pressure distribution.
There are three families of heating platens available in the market - solid steel platens that has been drilled for circulation of a heating fluid - laminated or fabricated aluminum or steel platens heated with water or hot oil and made by sandwiching a closed circuit tube structure between two face plates - and third, 10 mm thick aluminum platens heated directly by electrical resistances. Solid steel platens provide the ultimate heat characteristic in terms of uniformity in temperature and heat transfer to the glue line and produce the fastest cycle times, but they are more expensive and require more heating power. Laminated/fabricated platens are a good solution for smaller shops where production rates are low. This type of platen will deliver excellent quality, but with 30% longer cycle times than with solid steel platens - their price and power requirements are lower. Electric heated aluminum platens have very fast heat up times, but offer the lowest productivity rates, the least temperature uniformity, and are expensive to replace when they fail - and they will eventually.
There is no downside to mylar platen covers. The cost to replace them is nominal. They provide a very smooth surface over the platen to prevent scratching of HPL surfaces and glue is easily cleaned off of Mylar. Aluminum platens without mylar covers typically require a release agent to be applied to them to prevent glue from sticking to them.
From contributor C:
I've been in this industry-going on 30 plus years! No longer do any pressing, but when I did, the Joos press was the machine of choice. I but out panels now from a supplier using a Joos press! You would do yourself a favor and call the real experts at Joos and find out why Joos is recognized as the best in the business. Do your homework and you won't have regrets long term. As the saying goes: "when you buy quality, you cry only once". Best of luck and don't buy yourself a couple tons of scrap iron.
From Contributor L:
Can anyone explain the differences in hot and cold presses?
There is not too much difference between the two types of presses when you compare them on their construction. A heated press will either have a platen that is drilled for heating, or they will have a heated platen attached to a steel plate. A cold press just has a steel plate for pressing on the material. If you have a heated press, you have to insulate the cylinders from the platen with insulation or added steel to keep the heat away. This heat can degrade the seals on the cylinders quicker.
Both presses can reach identical pressures. The biggest different is the glue. Most cold presses, especially air bag presses only reach 50 PSI. The glue used requires longer time in the press and is designed to achieve a bond at 50 PSI or less. If you are cold pressing, you can press a stack of material on average of 45 minutes per stack, depending upon glue. If you are hot pressing, you can press a single panel from 45 seconds (I have run one at 25 seconds before) per panel. These will give you a higher cycle rate.
Depending upon your production, you can achieve a higher production rate with a hot press. You can also have a higher temperature resistance with your panel as the glue is heat activated. But again, it depends upon the glue you use. I ran a hot press that was pressing veneer onto plywood and they were producing a panel every 18 seconds. This was with a full automatic production line. To achieve this with a cold press, it is possible. But you need multiple presses and to create a high stack of panels. Some large manufacturers have multiple opening hot presses, but these can be expensive.
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