From the production of solid wood panels and integrated materials, each manufacturer pays more attention to product quality than before. With the continuous improvement of the panelization process, product quality has also been greatly improved. However, due to the different production methods and process levels of each enterprise, solid wood panels or integrated materials, as the main raw materials for the production of solid wood products, have exposed some problems in production and finished products. The most prominent one is that if the production process conditions are not well controlled, warping is very likely to occur, and cracking may occur in severe cases. Even if the above problems do not occur in production, warping or cracking often occurs during user use.
How to solve this problem is a common concern of enterprise technicians and managers.
1 Solid wood plywood and integrated wood production process
Now the production of solid wood plywood and integrated wood varies according to the different equipment used. The general production process is:
1.1 Solid wood plywood production process
Drying sawn timber → material selection/workbench → cross-cutting/cross-cutting saw → double-sided planing/double-sided planing → longitudinal sectioning/multi-blade saw (single-blade saw) → board matching/workbench → glue coating/glue coating machine → plywood/plywood machine → moisture balance/drying kiln → sanding/sanding machine → inspection/workbench → solid wood plywood
1.2 Glued timber production
Dry sawn timber → material selection/workbench → cross-cutting/cross-cutting saw → double-sided planing/double-sided planing → longitudinal sectioning/multi-blade saw (single-blade saw) → cutting (defect removal)/cutting saw → milling gear/iron gear machine → gluing/gluing machine → extension/extension machine → four-sided planing/four-sided planing machine → (finger-joined timber) → finger-joined production line/automatic finger-joined machine board matching/workbench → gluing/gluing machine → boarding/boarding machine → moisture balance/drying kiln → sanding/planing machine → inspection/workbench → glued timber
2 Wood is dried and stored, and moisture content is strictly controlled
For wood used to produce solid wood plywood or glued timber, the drying standard must be strictly controlled to ensure that the moisture content of the wood in the entire pile is uniform. This is the primary factor to ensure that solid wood plywood or glued timber does not warp or crack.
2.1 Storage after wood drying
Drying of wood for solid wood plywood or integrated materials must strictly control its final moisture content, and at the same time ensure that the moisture content deviation of the wood in the whole kiln is controlled to the minimum range, that is, strictly control the drying benchmark of the moisture content balance stage in the later stage of wood drying. After the wood is dried and taken out of the kiln, it must be placed in the dry material shed for storage. The main purpose of storage: First, to further balance the moisture content in the wood. During the drying process of wood, the moisture content of the upper and lower parts, the inside and outside of the wood pile, and the inside and outside of each piece of wood are different. The appropriate time of storage can make the moisture content of the wood tend to be consistent. Second, it can release the stress in the wood. Because the change of moisture in the wood during the drying process leads to the change of size and volume in all directions of the wood, the wood will produce internal stress. Keeping the wood for a certain period of time can effectively reduce the internal stress. When the wood is used for solid wood products, especially furniture production after drying, the storage time should be no less than 1 month.
2.2 Strictly control the moisture content of solid wood narrow boards and finger-jointed materials
Before solid wood narrow boards or integrated materials are spliced, their final moisture content must be strictly controlled. Generally, the moisture content of solid wood for furniture is required to be 8-12%, but the specific moisture content depends on the equilibrium moisture content corresponding to the place where the product is used. When splicing solid wood narrow boards or finger-jointed materials, the moisture content deviation of adjacent narrow strips of spliced boards must be controlled within 2%; if possible, it is better to control it within 1%. To control the moisture content of spliced wood, it is mainly necessary to perform the correct moisture balance treatment in the late stage of wood drying. Otherwise, it is necessary to force moisture balance before splicing to ensure that the moisture content of the wood is consistent.
3 Splicing process conditions of solid wood splicing and integrated materials
3.1 Strictly control the specifications of solid wood narrow boards and finger-jointed materials
Solid wood narrow boards and finger-jointed materials can be spliced into boards of required width in different splicing structures. However, in production, flat splicing is still the main form. The width of solid wood narrow boards or finger-jointed materials should generally be controlled within 60mm, but this also depends on the thickness of solid wood plywood or integrated materials. If the thickness of solid wood plywood or integrated materials is less than 20mm, its width should be reduced; when the thickness is greater than 30mm, its width can be appropriately increased. When splicing, the chord and radial textures of adjacent narrow strips should be properly matched to avoid too many chordal strips.
3.2 Raw material processing for splicing
Solid wood narrow boards or finger-jointed materials should be surface processed by planer or precision trimming saw so that the roughness of the bonding surface is not greater than Rmax=200-300μm. The amount of glue applied depends on the surface finish of the bonding surface. Generally, the amount of glue applied should be controlled at 150-180g/m2. If the surface roughness is too large, the amount of glue applied will increase, and excessive glue will greatly reduce the bonding strength. This is mainly because the adhesive changes from liquid to solid during bonding, forming internal stress, which is exactly the opposite of the bonding state during bonding.
3.3 Reasonable splicing and gluing pressure
When solid wood narrow boards or finger-jointed materials are glued into solid wood plywood or integrated materials, periodic and continuous plywood machines are mainly used for pressure gluing. Generally, the gluing pressure depends on the hardness of the wood species, and the pressure in the gluing direction is usually 0.7-0.8MPa. In order to prevent the glued parts from warping or bulging during gluing, a certain pressure is often applied to the front side of the glued parts (the side of the gluing direction), and the pressure is generally 0.1-0.2MPa. The residual stress in the board after splicing needs to be released before subsequent mechanical processing can be carried out. The aging time depends on the specifications of the solid wood plywood or integrated materials, and the natural aging time is usually not less than 7 days and nights.
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