Pre-treatment of wood before bonding

1. Wood appearance control
In order to ensure good bonding strength of wood, the wood surface for bonding must be flat, smooth and free of contamination. When processing logs into various components, in order to ensure the strength of the overall bonding, the processing tools should be sharp to avoid tearing the substrate tissue on the bonded surface of the wood and worsening the cohesive strength.

2. Control of moisture content
General The moisture content of wood is 15 to 25% and cannot be used directly for gluing. High water content affects the infiltration and diffusion of non-water-soluble adhesives, reduces the concentration of water-soluble adhesives, and prevents the water in the adhesive from evaporating quickly. Hair, difficult to cure, low bonding strength. On the other hand, it contains a lot of water. During use after bonding, the water evaporates and shrinks, forming internal stress on the bonding interface and weakening the bonding strength.
If the moisture content of the wood is low, the porous wood will absorb part of the adhesive, forming countless tiny hooks and anchors, increasing the bonding strength; the water-containing adhesive will spread faster, and the volume shrinkage of the wood will be reduced during curing, and the bonding stress will be reduced. Reducing is beneficial to bonding. Therefore, the wood moisture content of the wood should be small, and the optimal moisture content for wood bonding is about 5 to 12%. If the moisture content exceeds this range, the wood should be air-dried or dried first, and the two bonding surfaces should be The moisture content of the wood should be consistent, otherwise large internal stress will occur after gluing, and sometimes even warp and deform the glued products.

3. Control of wood surface cleanliness
There should be no dust on the surface of the glued wood. If there is dust, it can be brushed off, sucked up with a vacuum cleaner or blown away with dry compressed air. The glued surface should be free of mold and mildew, and the texture should be as straight as possible.

4. Removal of oily substances on wood surface
Wood is easily contaminated by oil. Some wood itself contains oil. For example, the branches of pine trees contain a lot of oil. Therefore, the adhesive is not easy to soak in and the bonding strength is poor. Wood contaminated by oil should be washed with hot water or soapy water. Wash with the agent solution, then wash with clean water and dry. Oil stains can also be removed by washing with hot water with 5 to 6% sodium carbonate or sodium hydroxide. For branches with particularly large oil content, when the bonding strength requirements are high, the oil should be removed carefully, even Some sections with a diameter of less than 1 inch can be dug out and replaced with another piece. The glued wood that has been degreased should be cleaned with acetone, gasoline, etc. before gluing, and the gluing effect will be better.

5. Control of equilibrium moisture content in different regions
The size change of wood due to changes in humidity is significant. Therefore, in order to obtain the best gluing effect, the moisture content of the wood should be treated as much as possible to a balanced moisture content that is adapted to the local normal temperature before gluing. In this way, the internal stress caused by changes in humidity is minimized during use, and the bonded parts are not easily separated or deformed.
If the wood is glued under higher or lower humidity conditions, continuous dimensional changes will cause the glued parts to deform, and the increase in internal stress will cause the glue to separate. If wooden furniture from the hotter and humid southern areas of our country is transported to the drier northern areas, it will shrink and crack, and on the contrary, it will expand and deform.