Reprinted with permission from MLS Machinery, Inc.
Glue spreaders are used to apply glue to either one side of a board or panel or to both sides at the same time. They can also be used to apply glue to a veneer that will be laminated onto a board, or to apply glue onto layers of veneer to build up sheets of plywood. It puts on a pre-determined amount of glue which is very thin. Once the panel is glued a veneer or high pressure laminate is attached. High pressure laminates are products like Formica used for counter tops or kitchen doors. As an example a counter top is a piece of particle board or composite board which has a rounded front, Formica is applied on the top after the panel has gone through a glue spreader. In door manufacturing where the part is visible from both sides glue will be applied on both sides and then high pressure laminate will be attached to both sides, from here the part will go into a press or to post forming, both of which are discussed under separate categories.
Glue spreaders come in various widths and normally have very low horse power. The widths can be as low as 6" wide for applications such as clamp carriers where glue is only applied onto one long but narrow edge before it gets attached to the next piece before going into the clamp carrier. They can go all the way up to 72" wide or wider depending on how wide the panel is that will require glue. Glue spreaders come in two roll or four roll systems, two rolls normally being used to glue one side at a time, four rolls do both sides at the same time.
Normally the rollers that actually apply the glue onto the panel are rubber. On a four roll glue system there are two rubber rollers one on the top and one on the bottom, the other two rollers would normally be chromed and are called doctor (as in medical doctor) rollers. The doctor roll is spaced very close to the rubber roll that actually comes into contact with the panel, however the doctor roll is used to determine the thickness of the glue that is actually going to go onto the panel. It can be raised to allow more glue or can be spaced very close to the rubber roll to minimize the amount of glue. Any excess squeeze of the glue would go into a pan at the bottom of the glue spreader and will be re-circulated through the pump to be used again. In some cases, some companies do not use a chrome doctor roll and might only use two rubber rollers. This would be the difference between a four roll and a two roll glue spreader. In some cases certain manufacturers might use a ceramic or rubber doctor roll. Before glue is applied to a panel or part it is advisable to first go through a panel cleaner to clean the panel before the glue is applied because residue of sawdust or small particles might adhere once glued and once laminates such as Formica or veneer are applied the bumps would show through, which is called telegraphing.
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