The present invention concerns production of wood veneer especially for furniture production.

Veneer is commonly used for decorative and construction purposes in different types of furniture but also for other products. It is beneficial if the veneer could be pro- duced in a good quality at a reasonable cost.

In the production of veneer a number of process steps are normally performed. Logs of selected sorts of wood are first selected. With the logs held at a desired condition a number of boards are cut from the log, which boards may be given a desired condition regarding moisture ratio. The boards are planed and scanned for any defect parts. Undesired defect parts are cut away. The boards are then joined together to give boards of a suitable length for the beam to be formed. After that the boards, having suitable lengths, are glued and pressed on top of each other to give a beam. The beam is then heated to about 40°C to about 70°C in order to be able to slice veneers from the beam. The temperature used depends on the tree species and temperatures outside the above range may be used sometimes. For instance for birch 30°C sufficed in one test. The veneer is sliced by means of veneer knife equipment.

According to one aspect of the present invention the wood of the boards and the beams are kept at a relatively constant moisture ratio, below the fibre saturation point (FSP) during the entire process of making veneer. Below the fibre saturation point the water is bound in the cell walls and other parts of the wood. Above the fibre saturation point there is free water in the cell cavities of the wood. Keeping the wood below the FSP and at a relatively constant moisture ratio gives a number of advantages. If the moisture ratio is not held relatively constant the wood may shrink or swell, risking that the boards and/or beams are deformed. The free water contains organic and inorganic nutrients (calcium, potassium, phosphorus, sulphur, iron, magnesium, sugar etc), which in combination with a high moisture ratio and glue may lead to colour deviation at the glue joint itself or in the area adjacent the glue joint. Such an influence is to be avoided and therefore all free water should be removed from the wood. The remaining, bound water is needed to transfer heat to the inner parts of the log and plasticize the lignin, resins and starch in the wood. Getting rid of the free water and have even and balanced moisture (between sapwood and heartwood) will take 5 to 10 days. However for some sorts of wood, such as oak, it will take longer time.

FSP differs between different species and also if measured in the heartwood or in the sapwood. For the species that are intended to use it is known that the FSP may vary between a moisture content of 22 and 35%. To be on the safe side the process according to the present invention is run at a moisture ratio clearly below the FSP. In one embodiment the process is run at an FSP below 20%.

In the process of the present invention boards are conditioned to be well under the FSP. The wood is then kept well below the FSP during the entire process of pro- ducing the veneer. To keep the wood well below the FSP the entire process is run in a controlled environment, i.e. in controlled temperature and relative humidity of the processing plant or at least in key areas of the processing plant. As the wood is hygroscopic the problem is normally not to hinder moisture from entering the wood. On the contrary in processing plants having a temperature of 20°C and an air humidity of 50% the wood will be dried towards a moisture ratio of 8-9%. Thus, moisture must be added, if needed to avoid drying up. It is achieved by means of air humidifiers. In the processing plant humidity spreaders may be used to avoid drying.

The boards are planed and/or fine sanded to have a desired thickness. The planed boards are then scanned, both on the surface and in depth, depending on the thickness of the boards to evaluate the quality. If defects are found the defective parts are repaired, cut out or the entire board is discarded. A possible repair may be done by means of drilling and plugging. The planed boards are then joined to form boards of suitable length for forming a desired beam. In one example the boards are glued to each other by means of finger joints. A person skilled in the art realises that the boards may be joined by any type of joint.

The boards, for instance joined by finger joints, are planed and/or sanded to get a fresh and smooth surface for glue used for bonding the boards and forming beams. The boards are then placed in a proper order to get a desired look of the formed beams. In some beams one or more of the boards may have a different thickness than the rest of the boards. The boards, applied with glue to each other, are then put in a press. The pressing time and pressure used depend on the type of glue and press used. In connection with placing the boards forming a beam in the press a holder may be attached to the beam. The holder is used when placing the formed beam in the veneer knife equipment. In other embodiments no holder is used. The beams are normally produced in rather long lengths and are then cut in lengths optimal for the form of veneer needed for the end product. Depending on the intended use of the veneer, beams of relatively short length are produced in some embodiments, normally in the lengths wanted for the further process steps. Each beam is then completely sealed, in order to keep the moisture content, to hinder that further moisture is introduced in the wood of the beam and to manage the next process step. The sealing may be accomplished by means of plastic, as discussed further below. Also, other means of sealing may be used.

To slice veneer from the beam, the beam is heated to a temperature from about 40°C to about 70°C, depending on the specific properties of the spices. If the beam is not heated sufficiently the wood is not plasticized, which means that veneers cannot be cut in a proper way. Heating above 70°C increases the energy and time needed, which should be avoided, a further purpose being to hinder movements in the wood. The time of heating depends on the sort of wood used and the thickness of the beam. In the process of the present invention the temperature and moisture content of the wood is constantly monitored during the heating. In one embodiment wireless measuring instruments are used to measure temperature and moisture.

The heating of the beams is made according to one of several different methods.

In one method the beams are heated in a closed space by means of steam and relevant moisture, which in this case is steam at about 40°C to 70°C and a relative air humidity of about 97%. This method is known as steaming. In one embodiment the plastic or other seal was kept on the beams during the steaming.

In an alternative method the beam is heated by being placed in a water bath at about 40°C to 70°C. To hinder penetration of moisture the beam is enclosed by plastic. The plastic may have the form of a bag, from which bag some air is pumped out to reduce the pressure. The plastic is welded at any open end to totally enclose the beam. In another embodiment a strip of plastic is wound around the beam to enclose it. In one embodiment a plastic of 150 g/m ² is used. In other embodiments plastic below 150 g/m ² is used.

In still a further alternative method the beam is placed in a microwave oven and is heated to about 40°C to 70°C. In order to hinder drying up of the beam, also in this method the beam is normally enclosed by plastic. The plastic used in this method may be the same as used according to the previous method. The enclosing using plastic will also assist in giving an even heating of the beams. Using a microwave oven will reduce the energy and time needed to heat the beam to the desired about 40°C to 70°C.

In all of the above described methods the sealing of the beam may be done by means of glue, lacquer, oil, grease etc., in stead of plastic. In one example the beam is placed in a bath of acrylic lacquer, glue or silicone fluid. In one further example the same glue is used both for gluing the boards together to form the beam and to seal the beam.

As movements of the wood, shrinking caused by evaporation of the water in the cells (around the micelles), only take place if the bound water evaporates or if water - in the case of dried wood - penetrates the cell walls, expanding the volume of the wood, and causes cracks, it is beneficial if this water is kept inside the wood for as long time as possible. The process is run below FSP, which means that some shrinking has taken place in the boards before they are glued together forming beams. The cells of the wood are hygroscopic (i.e. may take up moisture), and therefore a swelling of the fibres and the wood will take place if placed in a water bath without sealing. This is to be avoided as it causes deformation of the wood and beam. Thus, the beams are enclosed by plastic or by any other means to keep it waterproof, when the desired moisture balance of the wood is reached, or the beams are steamed in a controlled climate.

The beam is held heated at about 40°C to 70°C until reaching the veneer knife equipment. In connection with placing the beam at the veneer knife equipment, any plastic is removed from the beam. Normally the plastic is removed manually. At the veneer knife equipment, veneer of a desired thickness is sliced from the beam. In one embodiment the sliced veneer is dried to a moisture content of about 10-12%. Depending on the veneer formed different temperatures may be used when drying the veneer.