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Persistent Disorder of solid Wood Furniture-face crack
Aug 15, 2018

   There are different reasons for the cracking of wood furniture. Generally divided into structural cracking and large plate surface cracking (face crack). Factories generally classify face cracks as coating defects and find causes for improvement in the painting process. In fact, in many cases, the root is also wood.

   Paint cracking refers to paint cracking or collapse along the direction of wood grain. If it has nothing to do with the direction of wood grain, it is generally a pure coating problem.

    Paint cracks found in the production line, but also out of the factory, cracking in the customer's home. Seasonally, summer is less common and occurs more frequently in winter. Geographically, there are fewer in the South and more in the North.

     After rubbing off the paint on the cracked surface of the wooden furniture, we found that the reason was the cracking of the wood below. This picture because the wood texture is exquisite, the face crack sees quite clearly. If the oak conduit is thick wood, the face is often mixed with the duct, it is difficult to identify with the naked eye.

   To solve the problem of surface crack of the wooden furniture, we must first start with the basic concept of wood cracking.

    Water in wood is divided into free water and bound water. Free water is the moisture in the wood conduit and between cells, which can move freely, and the combined water is the water in the cell. The moisture content of logs is about 60%, half of which is free water. When drying begins, the first thing to lose is free water, and the size and shape of the wood are unaffected. After natural drying to the fiber saturation point, the moisture content is about 25-30.The wood begins to lose the combined water, which brings about changes in the structure and size of the cell wall, which leads to the shrinkage of the wood size. With moisture content from 30% dry to 10%, the volume of wood shrinks by about 7% on average. .

    When the wood loses moisture, it will crack because the radial, chord, and axial (length) shrinkage rates are inconsistent. Cracking must be along the radial direction of the wood, from the center of the tree to the surface of the tree. Even if logs are cut into plates, the direction of cracking remains the same.

    Cell walls and ducts of wood are open structures. They lose water when wet and absorb water when dry. Surface cracks occur when excessive or rapid loss of water occurs. Even in the white embryo stage it is difficult to detect cracks, especially in oak. Such cracks can lead to defects in the back coating.

     In other words, the surface of the white embryo is mainly produced in the process of machining. The main causes are:

A. Workshop humidity is too low, especially in winter, often less than 20. Such a dry environment will accelerate the evaporation of water on the surface of the white embryo;

b. The white embryo is too long in the machining stage. Especially for factories with imperfect production management, lack of product progress tracking and early warning. The longer the white embryo is exposed to the air, the more likely it is to crack.

     All of the above problems have more mature solutions. Conditional factories, especially those in the north, can install spray devices in the workshop to keep the humidity in the workshop at a reasonable level and avoid excessive water loss of white embryos.

    Even if there is no condition to do the humidification pipeline, the semi-finished white embryo can be sealed by winding membrane after work every day to reduce the loss of moisture, which is also a simple and effective method.

     In terms of production mode, it is better to transform dispersed single machine operation into assembly line mode to improve production efficiency and shorten processing time. And make the duration more controllable, avoid forgotten orders or products in the workshop.

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