Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
  • B27M—WORKING OF WOOD NOT PROVIDED FOR IN SUBCLASSES B27B - B27L; MANUFACTURE OF SPECIFIC WOODEN ARTICLES
  • B27M1/00—Working of wood not provided for in subclasses B27B - B27L, e.g. by stretching
  • B27M1/06—Working of wood not provided for in subclasses B27B - B27L, e.g. by stretching by burning or charring, e.g. cutting with hot wire
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
  • H01T19/00—Devices providing for corona discharge

Definitions

• the invention relates to a method for modifying a wooden surface, wherein an electrode is arranged opposite the wooden surface to be modified and wherein an alternating high voltage is applied to the electrode in order to cause a discharge between the wooden surface and the electrode under atmospheric pressure.
• the corona discharge has a rough structure of the conductive plasma in cross section of the air gap between the electrode plates.
• the electrode plates are provided with perforated polyethylene shields. The perforations then each correspond to a discharge path between the two electrode plates.
• the known method leads to a relatively uneven modification of the surface to be modified due to the effects of the plasma. This is particularly true when a wood surface is actually treated with the known method, since wood typically has an inhomogeneous structure, so that its dielectric properties are not distributed uniformly over the wood surface to be modified. As a result, this means that some areas of the wooden surface are subjected to a significantly greater modification than others.
• the invention is therefore based on the object of demonstrating a method of the type described at the outset with which the wood surface to be modified can be modified uniformly and which can also be carried out in large time and at reasonable costs even with large wood surfaces.
• This object is achieved in that a dielectric layer is arranged between the electrode and the wooden surface to be modified and that the alternating high voltage is applied at a frequency of more than 600 Hz.
• the first feature of the new method results in a dielectrically impeded discharge which acts on the wood surface to be modified.
• a dielectrically impeded discharge is principally distinguished by a significantly finer distribution of the plasma, ie the actual discharge areas over the entire cross section covered by the discharge.
• the alternating high voltage with the frequency of more than 600 Hz also contributes to the fine distribution of the plasma.
• the energy input is of the order of 1 kWh per m 2 of wood surface and can therefore be assessed as relatively low.
• the new method can not only be used to improve the adhesion of various coatings on the wooden surface, which already includes the coating with glue and thus the gluing or gluing over the wooden surface.
• the modification of the wooden surface can also be carried out as a finishing step for the wooden surface without the wooden surface subsequently being coated. This includes, for example, the removal of loose or damaged parts of the wooden surface, as is desired after sawing or when restoring wooden workpieces.
• the wood surface can also be preserved by the method according to the invention.
• the atmosphere in which the discharge between the wooden surface and the electrode is generated be called, modified from normal air by the addition of certain gases. This applies in particular if these gases are to be stored in the wooden surface to be modified.
• the desired gas mixtures can simply be blown into the zone of the discharge, since this takes place under atmospheric pressure.
• the new method does not subject the wooden surface to thermal stress.
• the gas temperature in the area of the discharge does not rise appreciably above room temperature.
• a piece of wood that has the wooden surface to be modified can be grounded as a counter electrode to the electrode. This means that in addition to the piece of wood that has the wooden surface to be modified, only a single additional electrode is required to carry out the new method. The conduction properties of wood are sufficient for the formation of the counter electrode.
• a piece of wood having the modifying wooden surface can, however, also be arranged on a flat counter-electrode arranged parallel to the flat electrode.
• the piece of wood acts like a second dielectric layer in front of the counter electrode. This means that the dielectric properties of the wood dominate over its conductivity.
• a piece of wood having the wooden surface to be modified is conveyed on a conveyor belt made of dielectric material via a flat counter electrode arranged parallel to the flat electrode.
• the two electrodes ie the electrode arranged opposite the wooden surface to be modified and the counter electrode, stand still, and the piece of wood is transported between them.
• the conveyor belt for the piece of wood also serves as a dielectric layer in front of the counter electrode.
• the surface of the electrode facing the wooden surface to be modified is selected to be small compared to the surface of the wooden surface to be modified, even strongly contoured wooden surfaces can be scanned under defined discharge conditions in order to carry out the desired modification of the wooden surface.
• the area of the electrode is preferably dimensioned relative to the area of the wooden surface to be modified such that the wooden surface to be modified covers at least 90% of the cross-sectional area of the discharge.
• the discharge power is used as completely as possible for the desired modification of the wooden surface. As little as possible of the discharge power should, in addition to the wooden surface to be modified, i. H. be consumed directly between the electrode and a counter electrode.
• the alternating high voltage in the new method is preferably at a frequency of more than 5 kHz, i. H. preferably applied from 10 to 3000 kHz.
• the alternating high voltage is composed of individual high voltage pulses, the spacing of which is greater than their duration.
• the distance between the individual high-voltage pulses of a frequency in Correspond to the range from 10 to 20 kHz, while the duration of the individual high-voltage pulses has frequency components in the range of over 500 kHz.
• the alternating high voltage with alternating polarity is applied to the electrode in the new method, the build-up of charges is prevented both on the dielectric layer in front of the electrode and on the wooden surface to be modified.
• the distance of the electrode with the dielectric layer from the wooden surface to be modified is typically between 1 to 25 mm in the new method. That said, this distance is not critical. However, it goes without saying that the size of the alternating high voltage must be increased with increasing distance. Typical values for the alternating high voltage are 30 to 50 kV for individual high voltage pulses. In the case of a sinusoidal high voltage, the frequency of which can also be in a range above 100 kHz, for example between 100 and 3000 kHz, the alternating high voltage is typically 10 to 15 kV.
• Figure 1 shows a first basic arrangement for performing the new method
• Figure 2 shows a second basic arrangement for performing the new method.
• Figure 1 shows a flat, ie plate-shaped electrode 1 and an equally flat, ie plate-shaped counter electrode 2, which are arranged parallel to each other.
• a conveyor belt 4 made of dielectric material 5 runs over the counter electrode 2.
• a piece of wood 6 is placed on the conveyor belt 4.
• the counter electrode 2 is connected to the earth 9, the electrode 1 is connected to a high-voltage power supply 10.
• the high-voltage power supply 10 is based on semiconductor technology. It is commercially available and has a good efficiency of 80 to 90% as well as comparatively low purchase costs.
• an alternating high voltage is applied to the electrode 1, which causes a dielectrically impeded discharge 11 between the dielectric layer 3 and the wooden surface 7 under atmospheric pressure.
• the distribution of the plasma 12 in the region of the dielectric discharge 11 is, on the one hand, due to the fact that the electrical discharge 11 is dielectrically impeded and, on the other hand, due to the fact that the high alternating voltage which is applied to the electrode 1 is at least of the order of magnitude of 1 kHz, so homogeneous that there is a uniform action on the wooden surface 7 of the piece of wood 6.
• the electrode 1 is only small with respect to its surface facing the wooden surface 7, and it is completely surrounded by the dielectric layer 3.
• the electrode 1 is intended to be moved parallel to the wooden surface 7, which is indicated by arrows 13 to 15.
• the wooden surface 7 is scanned with the electrode 1 in order to modify it uniformly in all areas despite the pronounced contour 16 present here.
• the structure of FIG. 2 differs from that of FIG. 1 in that no separate counterelectrode 2 with a dielectric material 5 arranged in front of it is arranged. Rather, the piece of wood 6 is here directly connected to the earth 9 and thus also assumes the function of the counter electrode 2 and the dielectric material 5 according to FIG. 1.
• the distance 8 according to Figures 1 and 2 can be 1 to 25 mm. Typically it is in the range of a few Millimeters.
• the following information for alternating high voltages, with which the new method has been successfully tested, relates to this.
• the first case it is a sinusoidal alternating high voltage of 10 to 15 kV with a frequency between 100 kHz and 3 MHz.
• a thin layer of wood can be removed from the wood surface 7 to be modified, the structure of which has been destroyed by prior mechanical processing and which therefore has only a loose bond to the solid wood.
• Such a mechanical processing is to be understood as a sawing process, for example, by which the wooden surface 7 to be modified was created.
• pores between the wooden fibers are also opened by the method according to the invention.
• the thin wooden layer damaged by the mechanical pretreatment is removed from the wooden surface 7 and the physical one and chemical surface properties are changed so that a better connection of glue and solid wood and thus a higher adhesive strength is achieved.
• a toothing (galvanizing) of the pieces of wood is still required. Due to the modification of the wooden surfaces 7 according to the invention, a higher adhesive strength can be achieved here, so that, depending on the load, the teeth of the wooden pieces can be dispensed with.
• a previous planing step can be dispensed with before the glueing of wood.
• the new process removes a thin layer of wood, the structure of which was destroyed by previous mechanical processing and which therefore only has a loose bond to the solid wood.
• the pores between the wood fibers are opened so that coatings, such as paints, are better anchored.
• reactive gases can be introduced between the electrodes 1, 2, so that the wood is coated out of the plasma 12 or is subjected to a chemical reaction.
• the coatings applied in this way or the reactions caused in this way can already represent the final treatment of the wooden surface 7 to be modified.
• the wetting capacity can be influenced by the modification of the wooden surface 7 according to the invention. Pulsed discharge can also cause densification of the wooden surface 7. From a density of 1.4 g / cm 3 , for example, water absorption over the wooden surface 7 can be largely prevented. This results in a very environmentally friendly method of wood preservation. Bleach
• the method according to the invention is to be modified such that oxygen is introduced into the region of the dielectric barrier discharge.
• the discharge then generates atomic oxygen and ozone, which are used to bleach out the undesirable wood components.
• This bleaching effect can also be achieved by generating ultraviolet light in the dielectric barrier discharge.
• care can be taken to ensure that oxidation of the wood surface itself does not occur.

Landscapes

• Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Physics & Mathematics (AREA)
• Plasma & Fusion (AREA)
• Mechanical Engineering (AREA)
• Wood Science & Technology (AREA)
• Forests & Forestry (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Chemical And Physical Treatments For Wood And The Like (AREA)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)

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• 1999
  • 1999-12-01 DE DE19957775A patent/DE19957775C1/de not_active Expired - Fee Related
• 2000
  • 2000-11-09 EP EP00993244A patent/EP1233854B1/de not_active Expired - Lifetime
  • 2000-11-09 DE DE50004948T patent/DE50004948D1/de not_active Expired - Lifetime
  • 2000-11-09 JP JP2001541662A patent/JP2003515460A/ja active Pending
  • 2000-11-09 HU HU0302096A patent/HU226188B1/hu not_active IP Right Cessation
  • 2000-11-09 US US10/148,505 patent/US6818102B1/en not_active Expired - Fee Related
  • 2000-11-09 PL PL00355633A patent/PL195614B1/pl not_active IP Right Cessation
  • 2000-11-09 AT AT00993244T patent/ATE257063T1/de active
  • 2000-11-09 CZ CZ20021908A patent/CZ297731B6/cs not_active IP Right Cessation
  • 2000-11-09 AU AU54375/01A patent/AU5437501A/en not_active Abandoned
  • 2000-11-09 CA CA002393952A patent/CA2393952C/en not_active Expired - Fee Related
  • 2000-11-09 WO PCT/EP2000/011083 patent/WO2001039944A1/de not_active Ceased

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