DE10128290B4 - Short-cycle press for tempering wood-based panels - Google Patents

Abstract

Short-cycle press (1) for tempering wood-based panels such as chipboard, fiber, or similar wood-based panels by coating with resin impregnated papers to decorative panels using pressure and heat, comprising a press frame with arranged therein by means of pressure cylinder (4) movable press plate (3) and a lower fixed press plate (2), which are designed to be unheated and uncoolable, being attached to the press plates (2 and 3) with the interposition of press pads Preßbleche (9), wherein the required heat to the pressed material (10) by means of a surface heating ( 8) formed electrical resistance heater on one or both Preßbleche (9) can be introduced, wherein the surface heating (8) consists of an elastic resin layer (11, 15) embedded therein with electrically conductive synthetic resin composition and wherein between the surface heating (8) and the press plates ( 2, 3) each have an insulating layer (7) is attached t.

Description

The invention relates to a short-cycle press for tempering wood-based panels according to the preamble of patent claim 1.

Short-cycle presses for the coating of wood-based panels with melamine-resin or phenolic-impregnated paper have experienced an enormous increase in performance in recent years, which was mainly characterized by the ever faster curing papers. Today, modern high-speed systems run up to 180 cycles per hour, about twice as fast as they did 10 years ago. Along with this development, however, the demands on the short-cycle presses have grown and not only in terms of speed. The fast-setting films or papers have become increasingly sensitive. Even the slightest pressure or temperature differences on the plate surface can be recognized as shades and are thus committee or second choice.

A possible cycle press, from which the invention proceeds, is in DE 26 15 898 A1 described.

When designing the short-cycle presses, the required stiffnesses of the press frames and the press plates are carefully calculated and the arrangement of the impression cylinders determined. In addition, in known embodiments, plungers are used below the impression cylinder, which cause a kind of multipoint support and thus have a more uniform application of force with improved pressure distribution result. Such a designed short-cycle press is from the DE 197 18 795 A1 known. Theoretically, the stiffness of the press racks and the heated press plates could be arbitrarily increased and thus the deflections and deformations would converge to zero and result in an absolutely uniform pressure distribution on the wood-based panel. In addition to the purely economic aspects, but an additional effect that sets this path limits. Since the coating is carried out by hot pressing, the press plates must be heated to operating temperatures of 150 ° to 200 ° Celsius. Since heat is removed from the press plates by the wood-based panels and the laminate, a certain temperature profile arises in the press panels. At the pressing surface prevails the lowest temperature which rises steadily towards Heizkanalbohrung. All materials are subjected to a thermal change in length or volume. As they cool, they contract and expand when heated. If, within a workpiece, regions with different temperatures prevail, the material molecules in the individual regions want to expand or contract according to their temperature, but are partly hindered in this. This means that, for example, the slightly colder press surface is under tensile stresses, since the rest of the press plate does not want to contract to the same degree.

As a result of thermal expansion obstructions, the entire press plate curves. In this case, the press plate deforms concave. This leads to undesirable overpressures on the edge of the plate, which brings the disadvantages described above. To compensate for these thermal deformations have been known for some time Gegenheizungssysteme. For this purpose, in the case of short-cycle presses, a second channel system is introduced into the press plates, close below the side facing away from the product. Theoretically, the press plate on the counter heating side energy must be withdrawn to obtain a plane-parallel press plate. Despite years of use of counter-heating systems in different variants of the temperature control and arrangement of the heating channels of the main heating and counter-heating had to be found that with a counter-heating, the thermal deformation and its effects on the pressure distribution on the pressed material improved, but can not be eliminated to full satisfaction ,

From the DE 100 53 764 A1 goes out an investment in which the arrangement of a plurality of Kurzhubzylindern, the pressure distribution on the pressed material is improved and also made controllable. This embodiment of the short-cycle presses represent a significant improvement over previous short-cycle presses with counterheating, which has even faster response times and thus allows improved control loops. Nevertheless, especially in the outermost edges of the pressed material effects of the thermal deformation of the press plate continue to be visible. These phenomena are also due to the fact that the thermal state of the heating plates in a clock-bound press is not in an equilibrium state, but constantly changes. At the beginning of the pressing phase, a large amount of heat energy is initially removed from the press plates. The temperature gradient and thus the thermal deformation become correspondingly large. With increasing pressing time decreases the heat loss and ultimately the thermal deformation.

During emptying and loading of the press, the heat loss goes to zero. Nevertheless, a measurable concave deformation remains, since the inertia of the mass, the temperature profile can not be compensated so quickly. However, if production stops, the temperature profile will equalize and may even reverse depending on the level of thermal losses on the back of the press plates and thus produce a convex state of deformation of the press plates. If the production then continues again, it comes to a different pressure distribution in the first pressings as in continuous operation, which can lead to committee.

To improve the pressure distribution on the pressed material so-called press pad are also installed in the short-cycle presses between the press plates and the structuring press plates. Due to the elasticity of these press pads in addition to the thermal deformations of the press plates especially also thickness tolerances of the wood-based panel are compensated. The disadvantage here is that the Preßpolster are poor thermal conductivity and deteriorate the heat transfer from the press plate to Preßgut and thus cause an extension of the pressing time. In addition, the press pads are subject to high wear and must be changed regularly, resulting in not inconsiderable maintenance costs.

Another problem with today's short-cycle presses is the long heating and cooling times. After a longer standstill, for example during a maintenance shift, the press plates must first be brought to operating temperature. Due to the large mass of the press plates, the heating process takes about 3 to 4 hours. Conversely, during repair work, the press plates must first be cooled before the press is accessible. To lower an operating temperature of typically 190 ° Celsius to a tolerable 100 ° to 120 ° Celsius, so many hours are required. This again leads to a reduction in the availability of the system.

The invention has for its object to provide a short-cycle press of the type described, in which the above-mentioned disadvantages do not occur due to the heating, a rapid cyclic heating of the remuneration films is made possible with the adhesive and a uniform pressure application is given to the surfaces of the material to be pressed.

This object is achieved by a short-cycle press with the features of claim 1.

The solution found is now based on a completely new approach, by which the above-mentioned disadvantages are largely eliminated. In the short-cycle press according to the invention, the press plates are not heated as before. The press plates serve only as a static component for flat distribution of the force exerted by the pressing cylinder pressing force on the entire pressing surface. In order to largely eliminate the heating of the press plates, the press plates are covered on the side facing the pressed material with an insulating layer, which can be designed as insulating. To generate the required Preßwärme only an immediate heating of the press plates is provided. For this purpose, electrically heated thin-walled surface heaters are provided, which rest directly on the press plate or the press plates. The surface heaters consist of an elastic synthetic resin, preferably made of silicone resin, with possibly inserted fabric inserts as reinforcement and form an electrically conductive synthetic resin layer (polymer), wherein in the Kunsthartschicht an electrically conductive resistance mass is mixed, or embedded in the elastic resin resistance wires in skeleton construction ,

The former has the advantage that the heat generation takes place uniformly over the entire pressing surface and only very small temperature differences occur at the pressing surface, which are far better controlled and controllable than heated press plates by means Heizkanalbohrungen. By a corresponding adjustment of the elasticity and the strength of the synthetic resin, the trained surface heating can also take over the function of a press pad. By this construction, the stored heat is drastically reduced. The heating and heating times are thereby reduced to a minimum. Since the heat is generated very close to the pressed material, there are hardly any temperature fluctuations between the individual phases of the pressing process. Even with an empty short-cycle press, it no longer comes to the unwanted increase in the surface temperature at the pressing surface.

As a result, a consistent product quality can be maintained during startup operation as well as in continuous operation. It is crucial that in this system, the pressure distribution can now be set uniformly and very stable on the material to be pressed. There is no significant thermal deformation due to the heat loss during the pressing process more. Slight temperature differences between the top and bottom of the press plates, as they can occur due to the slight heat conduction through the insulation, are easily compensated by the Kurzhubzylinderanordnungen acting with pressure pieces on the lower pressure plate.

When using electrically conductive polymer as surface heating, the electrical flux is perpendicular to the surface. The contact can be made single-sided or two-sided. In both cases, the press plate can be used as an electrical pole. Thus, only on the side facing away from the surface heating a second pole is to be attached. For this purpose, thin steel, copper or aluminum foils can be glued to the surface heating. In one-sided contacting, both terminals / poles are connected to the split steel or aluminum foil. The current flows from the film perpendicular through the conductive polymer and Preßpolster as Gegenpol and from there spatially offset also vertically through the polymer to the film with the negative contact. The steel, copper or aluminum foil can be designed to be two or even multiply divided and then quasi electrically connected in parallel. To exclude a risk to persons, the use of low voltage is provided.

Another advantage of the invention is to be mentioned that the manufacturing costs decrease significantly. Electric surface heating systems are inexpensive components. By eliminating the heating system of the press plates, eliminating the channel bores with closure strips, the supply lines for the medium and the heating system for the medium.

Further advantageous measures and embodiments of the subject matter of the invention will become apparent from the dependent claims and the following description with the drawing.

Show it:

1 the short-cycle press according to the invention in front view according to the invention,

2 an embodiment of the surface heating according to the invention in plan view,

3 a second embodiment of the surface heating and

4 a third version of the surface heating.

The short-cycle press 1 persists 1 from the formed in the form of a window frame web plates 6 , at the top of the window directly on the web plates 6 arranged impression cylinder 4 and with them raised and lowered upper pressure plate 3 as well as in the window on the web plates 6 arranged stationary lower press plate 2 , The impression cylinder 4 are provided in two rows along the longitudinal center axis and consist of cylinders and pistons which exert their force on the upper press plate 3 and thus on the layered pressed material 10 transfer. For optimal and controllable pressure distribution on the material to be pressed 10 are between the lower press plate 2 and the web plates 6 Kurzhubzylinderkolbeneinheiten 5 arranged, either directly on the faces of the web plates 6 or in sections of the web plates 6 are arranged centrally and vertically. The short-stroke cylinder piston units 5 form an outer frame on the lower press plate 2 ,

In the middle press area, is the lower press plate 2 over plungers 16 , on the vertical and centric arranged web plates 6 supported.

According to the invention are between the non-heatable and coolable press plates 2 and 3 electric surface heating 8th directly on the press plates 9 provided resting. So that the heat generated only in the direction pressed material 10 acts are sufficiently thick insulating 7 between the surface heating systems 8th and the press plates 2 and or 3 appropriate. To 2 is the surface heating 8th from an elastic synthetic resin layer 11 with inserted and embedded resistance wire 12 as well as the electrical connections 13 , According to the first embodiment of claim 1, the surface heating 8th from an elastic synthetic resin layer 15 , which by mixing an electrically conductive resistance mass and by means of a metal foil 14 with connection 13 and the opposite press plate 9 is heated as a negative pole.

4 shows yet another embodiment of the synthetic resin layer 15 with several metal foils 14 and connections 13 on the opposite surface to the press plate 9 ,

LIST OF REFERENCE NUMBERS

1

Short-cycle press

2

lower press plate

3

upper press plate

4

pressure cylinder

5

Kurzhubzylinderkolbeneinheit

6

web plate

7

Insulating layer / insulation

8th

panel heating

9

Press plates top / bottom

10

Layer packet / compressed material

11

Resin layer

12

resistance wire

13

connections

14

Foil made of steel, aluminum or copper

15

Synthetic resin layer + resistance mass

16

plungers

Claims (6)

Short cycle press ( 1 ) for tempering wood-based panels such as chipboard, fiber, or similar wood-based panels by coating with resin-impregnated papers to decor panels using pressure and heat, comprising a press frame with arranged upper by means of pressure cylinder ( 4 ) movable press plate ( 3 ) and a lower fixed press plate ( 2 ), which are designed to be unheated and uncoolable, wherein on the press plates ( 2 and 3 ) with the interposition of press pads press plates ( 9 ) are mounted, with the required heat to the pressed material ( 10 ) by means of a surface heating ( 8th ) trained electrical Resistance heating device via one or both press plates ( 9 ) can be introduced, wherein the surface heating ( 8th ) made of an elastic synthetic resin layer ( 11 . 15 ) is embedded therein with electrically conductive synthetic resin composition and wherein between the surface heating ( 8th ) and the press plates ( 2 . 3 ) each have an insulating layer ( 7 ) is attached. Short-cycle press according to Claim 1, characterized in that the electrically conductive synthetic resin layer ( 11 . 15 ) consists of a suitable synthetic resin such as silicone resin and is designed as a press pad elastic. Short-cycle press according to claim 1 or 2, characterized in that the electrically conductive synthetic resin layer ( 11 . 15 ) on one or both sides of films ( 14 ) made of aluminum, steel or copper. Short cycle press according to one or more of claims 1 to 3, characterized in that the surface heating ( 8th ) from in the elastic resin layer ( 11 . 15 ) embedded resistance wires ( 12 ) in skeleton construction or an electrically conductive resistance mass. Short-cycle press according to one or more of Claims 1 to 4, characterized in that the surface heating ( 8th ) is designed operable with low voltage. Short-cycle press according to one or more of Claims 1 to 5, characterized in that the plane parallelism or the pressure distribution of the lower press plate ( 2 ) via short-stroke cylinder piston units ( 5 ) is controllable.

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