Originally published: May 20, 2009
This post is in honor of Craig's years of dedication to the industry we all love.
My name is Craig Thomas, Project Manager for Daubert Chemical Co., and I have worked with companies helping them with the thermoforming process for 20 years. Mark Viers and I have known each other for years as friends and associates while we both serviced the thermoforming market from different sides of the supply chain. So when Mark called me and asked if I had any tips for companies that spray membrane press adhesive I agreed to share some tips for common questions that have come up over the years from companies that spray PUD (polyurethane dispersion) for thermoforming.
Good spay techniques are essential to producing a quality pressed product.
What equipment should I use?
To achieve a smooth even spray I always recommend a HVLP gun, using a .050” to, 065” tip, with a pressure pot system. A cup gun is OK for small jobs but for extended use a pressure pot. You kind buy a pressure pot as small as 2 quarts.
What should I do if my guns continues to clog up are drip when I release the trigger?
These adhesives are sheer sensitive which means that if the adhesive is subjected to forcing the adhesive through a gun at high fluid pressure it will tend to “ball up” or string causing clogging at the tip. Clean the gun and hose thoroughly. Make sure your needle is open to the point that you have full trigger. Now set your pressures at 15 to 20 psi for the fluid side of your gun and the atomization (air) pressure at 50 to 60 psi. These settings will allow the adhesive to flow through you equipment with the least amount of sheer. An easy way to see if your fluid pressure is corrct is to pinch the air supply to the gun closed and pull the trigger. The adhesive will come out in a stream without atomization air. The stream should come out 2 to 3 ft like a garden hose. If you pressure is too high the stream will look a garden hose with a pressure nozzle. Also, if you have a filter on your pik-up tube in the pot, I recommend you remove that and strain your adhesive while putting it into the pot.
Now you know why I recommend a pressure pot system. So you can make these important improvements.
Can I stack my part when spraying?
Yes, as long as they are the same size. This will save glue due to less overspray.
What is the best way to spray my parts?
You need to spray the edges with 2 or 3 goods coat to insure enough adhesive remained on the surface and did not dive-in to the routed edge of the board. You do not need to let the adhesive dry between coats. Now you can spray the top surface with 1 even coat. It is very important to hold the gun perpendicular (90 degrees) to the part while spaying.
What is the correct dry time for the adhesive?
You need to “rack” the parts for drying and rack from top to bottom so not to knock any debris on the wet glue from stacking parts above the previous sprayed parts. The parts should be dry to the touch in 15 minutes and ready to press. The higher the humidity in the shop the longer it take to dry.
Those are answers to some of the most common questions I have received over the years. There were many more but because of time and the possibility of boring you to death, I will stop here
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