By Technical Department of Veriquality Inspection Service Source: Veriquality Inspection Service Co.,Ltd
Why need to control Moisture content for wooden furniture production?
If the moisture content in wood is not controlled adequately this can lead to significant after-market problems such as, dimensional changes due to material swelling or contraction, surface cracking, “sweating” - damaging paint or other coatings, and the formation of mould on untreated and painted surfaces.
1. It’s important that moisture control tolerances are established at the outset in the product specification. Factory QC systems should include the checking of the moisture content of incoming wooden materials as part of their IQC program. These checks should be repeated prior to or during inline inspections on the production line to ensure that moisture values have not moved out of tolerance during storage. A moisture check within a final inspection will confirm that the finished goods’ moisture values are within tolerance before they commence their shipping journey. There may be wide variations in temperature and humidity in transit so the correct baseline moisture value is very important.
2. A moisture test is very simple and the equipment (moisture meter) required inexpensive.
3. The most effective control is at the raw material selection and storage stage as it can be very difficult to correct or rework overly moist wooden products once finally assembled. The factories warehousing facilities are critical in this regard. Even the best timber or processed wood products can be damaged through excessive humidity or damp or exposure to high temperatures and sunlight during storage.
The acceptable moisture level in wood depends on the final use of the wood, the type and thickness of the wood, and the average relative humidity (RH) in the environment where the wood is to be used. Based on common guidelines or recommendations, the acceptable moisture level for wood objects used indoors is generally 6% to 8% for wood flooring, 6% to 9% furniture, and 9% to 14% for construction.
At least 75% of the wood manufacturing problems are moisture related.
That's why eliminating wood problems begins and ends with monitoring and controlling the moisture content (MC) in wood
As the moisture content in wood changes, wood expands or contracts, and this in turn causes a variety of problems. The moisture content of wood is measured as a ratio between the weight of the water in the wood and the weight of the wood itself. This ratio is stated as a percentage.
Because moisture causes the majority of problems in wood manufacturing and wood use, it is important to measure the MC of wood before, during, and after manufacturing.
Much of the process occurs at the factory level, or even before materials reach the factory. In many cases, lumber that comes into the plant for processing is already kiln dried. From there it undergoes a variety of steps, depending on the factory, to keep the moisture content in the wood below 12% or 13%.
All solid wood is purchased kiln dried. Due to the humid climate here in South China, the solid wood need to be re-dry before use. The manufacturer also need to set up the standard check points through the manufacturing process that monitor the moisture content and also utilize climate-controlled rooms to recondition parts as necessary and to use as storage before the next production process.”
This is important to know. For instance, if a woodworker brings home kiln-dried wood with a MC of 8% and then stores it in his garage, that wood could absorb another 6% or more of moisture.
To make certain the wood is properly dried, the most factories to uses a moisture meter before working on it.