Reprinted with permission from MLS Machinery, Inc.
Presses, as discussed under previous categories, are available in either hot or cold. Presses can be either fully automatic through feed presses, or manual style presses. Presses can come in various sizes, the most common being 4x8 or 5x10. Standard presses are normally 4x8, 4x9, 4x10, 5x8, 5x9, 5x10, and 5x12, the most common being 4x8 or 5x10. Hot presses have a heated platten that can be heated by either electric, hot water (steam) or oil. A manual press is similar to an ironing press for shirts. The panel to be pressed would be inserted between the plattens manually. The reason for pressing is to get a smooth finish when applying a laminate or veneer to the pre-glued substrate (example particle board). The heat allows for quicker curing time so the part can be sent to other operations quicker. Electric is the most expensive press to run; oil and steam heated plattens require a separate boiler system to keep the water or oil hot. Some presses are tremendously large machines taking up entire buildings; as an example, in the manufacture of particle board these press lines could be 200-500 ' long in total with fully automated loading and unloading systems.
The normal manual press that we see in most shops has cylinders that either come from the top down pushing the plattens together, or from the bottom up. Presses can have numerous daylights (openings); therefore a multiple daylight press, for example a six daylight press, would have six openings and seven plattens, in this case the machine could press six panels at a time. In most cold presses, cylinders could either be opened or closed by air or hydraulics. Some cold presses have a very large daylight (opening), example 30-60", whereas in the multiple daylight press, the daylights (openings) are only three to four inches. In these cold presses with 40" daylight, multiple panels can be pressed at the same time. This would normally be for low glue curing speed which can be a couple of hours. For companies that have large production in cold pressing, they would normally have a number of these types of presses side by side. In this type of press, which is manual, the operator will determine how long the platten must stay closed.
Through feed presses are mainly hot presses and are for high production such as in the manufacture of particle board or the production of full panels that are laminated with either veneer, high pressure laminates or sometimes paper or vinyl that will eventually be cut up for furniture parts.
Most of the presses discussed so far are for the production of flat panels. There are presses called membrane presses which allow the application of a laminate to a non-flat product. As an example, a door that has been routed and has grooves in the surface can have a laminate attached on top of it which can be either a special veneer or vinyl. The membrane press pushes the laminate into the pre-routed grooves and crevices using a rubber type platten that is either oil or air filled and heated in some manner. This membrane, under pressure, will find its way into all these nooks and crannies at the same time, pushing the veneer or vinyl into these contours. These types of presses can be manual or again fully automated feed through presses. The rubber membrane platten will stay closed for a pre-determined time, depending on the material. Many items today are made with this type of press; for example, in the auto industry, some dashboards of motor vehicles as well as household doors that have shapes in the surface or certain post formed doors. This system is quite fast and very effective.
High frequency presses are presses that use very high voltage to press items together. These presses are used in numerous situations but all work basically the same way. These machines could be used instead of clamp carriers to attach pieces of wood side by side or for normal pressing, that is to press and form parts at the same time. A high frequency press actually cooks the glue so drying the part is done in a very short period as opposed to a clamp carrier where you have to wait until the part has gone the full rotation and comes back to the operator. In this case the part is fed through the press, sometimes automatically. The press has side and top pressure such as the flattener in a clamp carrier. The pressure, using hydraulically or air operated cylinders, pushes the part from both sides and top, and exerts high voltage or frequency which in turn "cooks" the glue almost immediately and therefore dries the part in approximately one-half a minute. The part is warm to the touch after going through the press because it actually does cook the glue.
These presses are also used in the manufacture of, for example, leather or office chairs, the leather upholstery is applied over the chair seat and back that has been pressed and curved in a high frequency press. The seats and backs are manufactured through a glue spreader applying one flat piece of veneer on top of another until the required thickness is reached. The part is placed in a mould in such a press while it is still wet with glue and the mould would form the wood into the shape of the mould under this incredible high frequency electrical current. This current will go through the platens of the press which are the moulds themselves, the part will dry almost instantaneously and within one and one-half minutes a curved piece of plywood that will eventually become a chair front or back will be ready for upholstery. These machines are more expensive than clamp carriers and that is one reason why clamp carriers are still used.
Many people do not like using high frequency presses because they are rumored to have caused cancer, which has never really been proven. One other application is where a very heavy edge of, for example solid wood, is attached to the edge of a panel, as opposed to using an edgebander as edgebanders have limitations on how thick a piece can be edged. When making doors for government specifications such as hospitals, etc. these doors are specked to be made out of particle board with a solid edging all around the door which can be anywhere up to 3” thick. These strips will be attached to all four sides of the particle board sometimes by high frequency presses called rim banders similarly to that discussed above.
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