Machine for the application of thin layers of material (veneer, paper, foil, HPL) on panel materials with the help of pressurized and heated plates.
The machine frame is usually made of solid steel beams, which have been welded together in a shape of a box. In the space between the four lower beams usually the pressure pump of the hydraulic system is placed. The pressure table with the heated plates lies within the machine frame. There is a distinction between two different kinds of veneer presses cylinders: the downstroke press and the upstroke press. A downstroke press will move the abovelying cylinders towards the belowlying pressing plates; the upstroke press moves the belowlying cylinders towards the abovelying pressing platens. Interlinked toothed rack guides compensate the pressure difference in the hydraulic system and make sure that a precised closing of the plates is achieved.
Pressing surfaces and heating plates
Basic structure of a pressing table with aluminum heating plates:
The evenness of the pressing surface determines amongst others the quality of the workpiece surface and of the gluing performance. Uneven plates, remains of glue on the surfaces, scratches, irregular spread of the heat within the pressing surfaces are all possible causes for bad results in a glueing process. There are also other factors for this which do not have a correlation with the press, such as the quality and the choice of the glue, and the surface of the workpieces/materials.
Because heat stimulates a constant and quick drying process of the glue the most common kind of pressing surfaces are heating plates.
Common measures of plates
In order to protect the pressing surfaces in a long-run and to simplify the process of cleaning, plastic foils which are glue-resistent can be spread over the pressing surfaces. (see picture) Through fed presses with automatic feeding will use these foils also for the transportation of the workpiece through the press.
Generation of the pressing pressure
Safety equipments (selection)
Emergency Stop Line
Approximately 50 cm above the ground runs an emergency stop line all around the machine, which in a case of operation (pulling or pressing) immediately interrups the closing process of the press. (see picture Ott-press)
Table safety system
Under the lower pressing plate runs an emergency stop line all around the machine or there is a sensible contact strip, which if activated immediately stops the opening process of the press.
Protection of the jamming of the press plates after wrong use
Alternative terms for veneer presses:
Typical question of a used press buyer: 'Are the plates still allright? "
Generally there needs to be a distinction, what application the second hand press should be used for. The highest quality level is a pressing of very fine and thin foils or veneers on big surfaces. Other applications that have lower demands for the quality of the plates are the work with thicker veneer or with solid wood, especially there is a further treatment of the surfaces after the press. In other words: not every scratch in the plates means that they need to be exchanged.
Optical test (unprecise)
Cracks, visible bumps or damages, remains of glue, ...
Oil droplet test (more accurate)
By a pipette, oil droplets are placed onto the lower plate in a semetrical order, so that are the closing of the platens will squash the droplets and create round circles. If these have a constant order it is a good sign for the quality of the plate, even if very high quality standards are needed.
With paper and glue on the real workpiece