DE2230220A1 - USE OF METAL FIBER FLEECE AS PRESSURE PAD IN HEATING PRESSES - Google Patents

Description

Th. Goldschmidt AG, Essen

Use of metal fiber fleeces as pressure pads in heating presses

It is known that when pressing on carrier webs or curable foils impregnated with curable synthetic resins Wood-based panels, preferably in hydraulic heating presses, press cushions are used for pressure compensation. The press pad is located between the heating plate of the press and the press plate, which is the heat treatment plate impresses the surface structure. The press pad is used for. Pressure equalization during the pressing process and reduces the Wear of the high-quality press plate. Differences in pressure arise from unevenness in the heating plate, in the press plate and / or in the material to be pressed. The press pads, which are used in multi-level or single-level presses, exist preferably made of cotton and / or asbestos fabrics. These pads have a good pressure equalizing effect. A disadvantage however, is their low thermal conductivity.

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When coating is in the pressed material, for. B. in the chipboard to be coated, heat dissipated by the heating plate must be tracked over the press pad and the press plate. Due to the low thermal conductivity of the cotton asbestos fabric cushion, the temperature on the press plate drops because not so much Heat can be tracked as is absorbed by the pressed material.

Metal mesh has also been used to equalize pressure. Although these have better thermal conductivity, but a much worse cushioning effect than the cotton asbestos fabric.

When using cotton asbestos fabrics as a press pad, it is therefore necessary that relatively long pressing times or higher temperatures of the heating press must be provided for proper curing of the synthetic resin to reach. The temperature of the heating press is preferably increased in order to achieve as many pressing cycles as possible. This is particularly true when pressing in single-day, short-cycle presses. However, the temperature increases relatively narrow limits.

More recently, the so-called short cycle method has been used increasing importance. This is the curing process

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the synthetic resin surfaces are carried out in a continuously hot single-daylight press, while the cooling of the Material to be pressed takes place outside the press. Press plates and press pads are therefore firmly mounted in the press.

To carry out the short-cycle process, the wood-based panels cut to size and the Synthetic resin films collapsed on the loader; By means of a belt tray, the material to be pressed is fed into the heated press and deposited there, whereupon the tape tray returns to its starting position. Immediately afterwards the press closes and the resin hardens under heat and pressure in the press. After the curing time has ended, the The press is opened and the hot prefabricated board is moved out of the press with a transport device.

If the press plate temperatures are too high, the synthetic resin film condenses on the press when it is loaded lower hot press plate. prematurely without pressure, so that defective surfaces arise.

The invention is based on the object of finding a press pad, which the heat transfer of the heating press favors the press plate under pressure, so that the heating press is set to lower temperatures

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can be heated and on the other hand, after opening the press, the heat transfer through the press pad is reduced again so that the press plate its temperature
reduced, so that a premature hardening of the deposited synthetic resin films when reloading is avoided. After closing the press, however, the temperature of the press plate should rise again quickly. According to the invention, this is achieved in that a compressible metal fiber fleece is used as the press pad, which after pressure relief assumes at least approximately the original thickness of the press pad.

When the press is closed, the metal fiber fleece is compressed and conducts heat well. When opening the
Press takes the metal fiber fleece at least approximately
back to the original thickness so that air can flow between the metal fibers. This lowers the temperature and the thermal conductivity in the decompressed metal fiber fleece.

To increase the mechanical strength of the press pad according to the invention, it is possible to use the
To provide metal fiber fleece with stitching. These
Measure is particularly recommended when the

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Cushions are not permanently installed in the press , but are extended after each press game with the material to be pressed, as z. B. is the case in multi-stage presses.

To prove the technical effect, reference is made to the attached Figures 1 and 2, the diagrammatically the temperature profile on the press plate was measured. Figure 1 shows the temperature profile when using a cotton asbestos pad at a heating plate temperature of 185 C. In the open press the Temperature at first, and then under pressure by heat transfer to the pressed material to a temperature to drop below 135 ° C. The material to be pressed is then pressed for 75 seconds under 20 kp / cm pressure, with a The temperature rises to around 143 C. After the press has been emptied, the temperature of the press plate rises continue on.

In Figure 2, the temperature profile is shown when using the method according to the invention, it should be noted that the hot plate temperature

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is only 175 C, i.e. 10 C lower. In the open press, the temperature falls as a result of the poor heat conduction of the press pad. If the press is now loaded and brought to pressure, is using the same pressure as in the 1st attempt after 45 seconds of pressing time Temperature of approx. 149 C reached, while using the cotton asbestos pad after 45 seconds Pressing time only a temperature of about 139 C has been reached. After the depressurization and the When the press is emptied, the temperature of the press plate drops as a result of the expansion of the metal fiber fleece and the associated poor thermal conductivity.

The comparison of the two diagrams shows that when the metal fiber fleece according to the invention is used it is possible to shorten the pressing time considerably at lower heating plate temperatures without Having to accept qualitative losses in the tempered material. This results in the press cycles considerably shortened and the economic utilization of the presses increased considerably.

To form a metal fiber fleece suitably metal fibers are used, their stretch-309884/0668

limit is high, ie. Metal fibers, which Do not permanently deform plastically under pressure, but return to within after pressure relief return the fleece to its original starting position. From this requirement the choice of the material required for this results. A steel wool fleece is preferred a weight of about 1000 g / m, the metal fibers of the fleece are 30 to 70 u thick.

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Claims (2)

Claims 1.J Process for pressing carrier webs impregnated with curable synthetic resins or curable plastic films onto the surface of wood-based panels in heating. press, with a press pad being inserted between the press tool and the press plate / characterized in that a compressible metal fiber fleece is used as the press pad
is used, which after pressure relief at least approximately assumes the original pressure pad thickness again. 2. The method according to claim 1, characterized in that the compressible metal fiber fleece with stitching seams
is fixed. 3098 * 34/0668 Blank page