I.Composite materialReasons for cracking
1、Cracking and deformation issues in composite materials are caused by substandard quality during production, specifically a lack of control over the moisture content of the wood.
2、After the wood has dried, do not use it immediately. Allow it to rest for a period before further processing. Before applying any adhesive, remove any rotten areas to prevent warping and cracking.
3. If the carpentry work is not up to standard, using pneumatic nail guns directly without pre-drilling will cause the panels to crack and deform.
II. How to prevent cracking in composite materials
1、Securing
Even in foreign countries, large-sized wood is often treated with wire or nails to control deformation and cracking, such as railway sleepers. In addition to tying, railway sleepers are also treated with chemical oil-based preservatives.
2、Reduce the size of individual timber pieces
Cut the wood into sufficiently small sizes to minimize the absolute difference in deformation between the wood's grain direction and radial direction, then join the pieces together, such as finger-jointed lumber, engineered lumber, and plywood.
3、Drying
Under controlled conditions to manage the drying rate of the composite material (ensuring a gradient of moisture content within the wood, both internally and externally, remains within a specific range), dry the wood to the moisture content level suitable for its intended environment. This ensures that the moisture content within the wood is in balance with the surrounding air humidity, effectively preventing both absorption and loss of moisture. Typically, freshly cut wood has a moisture content ranging from 35% to 60%, while finished solid wood products, flooring, and cabinets require a moisture content of 8% to 12%. For outdoor, weather-resistant wood, achieving a moisture content of 13% to 20% prior to installation is optimal.
4、Radial wood processing
"When cutting and processing engineered wood products, especially those with edge joining, aim to minimize the width of the wood grain direction. This reduces the absolute change in the wood grain direction, minimizing the difference in shrinkage between the two directions, and ultimately reduces the risk of cracking. This method is rarely used and is typically only applied when using high-quality materials. The main reasons for this are that it significantly reduces the yield of the wood, increases production costs, and is primarily suitable for panel materials.
5. Seal the wood surface
Applying paints and coatings to wood surfaces to seal the wood prevents moisture exchange between the wood and the external environment, thereby reducing cracking. This method is often used in conjunction with wood drying, such as in interior solid wood painted furniture. This significantly reduces the yield of timber, increases product costs, and is primarily suitable for panel-type wood. Interior furniture typically uses wood paint, while exterior weather-resistant wood uses weather-resistant wood paint.
6、Waterproofing Treatment
Apply a water-repellent substance, either as a single layer or a mixed system, to the surface of the composite panel, creating a relative interface between the wood surface and external water droplets. This helps to reduce the absorption of moisture by the wood to a certain extent, significantly reducing the yield of wood and increasing product costs. This type of treatment is primarily suitable for panel-type materials.
7、Filling wood gaps
Inject phenol resin or polyethylene glycol, or other organic materials, into the composite wood material to fill the "voids" within the wood, thereby preventing external moisture from entering and mitigating wood deformation and cracking to achieve dimensional stability. However, this method is costly and is typically used only for wood materials with specific requirements. This method increases product costs and is primarily suitable for panel-type materials.
8、Chemical Treatment
Methods such as heat treatment, acetylation, isocyanate treatment, and polymerization are used to stabilize wood, but these methods are expensive and prone to various defects, making large-scale application difficult. These methods are primarily used for wood in specialized applications. These methods increase product costs and are primarily suitable for panel-type materials.