The application of infrared moisture meters in the production process of particleboard!

Particle board is used by millions of people every day. It is a composite material that is cheaper and more uniform than solid wood. Even though it has a higher density than wood, it is still lighter and more brittle compared to other fiberboards like MDF (Medium Density Fiberboard) and OSB (Oriented Strand Board). Particle board is typically used for indoor applications such as furniture and cabinets because it expands and discolors when exposed to high humidity. It is also often sealed, painted, or covered with a veneer that has adhesive properties.

The moisture content of particle board is crucial at various stages of the manufacturing process. The moisture content determines the overall strength and durability of the board; the surface appearance and quality of the board are constrained by the distribution of moisture.

1. Summary of the Process

1. Peeling and Milling

The material for particle board is usually made from wood chips. The chips are brought in from outside. If the chips are prepared on-site, the logs are peeled, debarked, and screened before cleaning. Then, the clean wood chips are reduced in size in one or two stages, followed by further grinding to produce more "engineered" wood chips. Each particle reduction (grinding) process will produce a range of particle sizes. Fine particles are used for the surface layer, while coarser chips or particles are used for the core layer.

2. Drying and Mixing

After coming out of the chipper, the wood particles are moved to the drying and mixing area. A single-stage or multi-stage tubular drying system is typically used to reduce the moisture content of the particles to the desired level. The wood particles are then mixed with adhesives to bond them together. Melamine formaldehyde, urea, or phenol-formaldehyde resins are mixed in small rapid mixers or large slow-moving drums. Additional additives, such as flame retardants, can also be added at this processing stage. These adhesives and additives typically account for 4-10% of the weight of the finished board.

3. Forming and Pressing

This particle board mixture is then sent to a forming machine, with coarse particles in the core and fine particles on the surface, to form a uniformly distributed board blank with the target weight. The formed board blank is sent for pre-pressing and hot pressing, followed by finishing to create the final product, particle board.

4. Finishing Production Line and Packaging

After pressing, the boards are cooled, sanded, trimmed, and cut to final dimensions. The boards may also be painted or laminated. Finally, the finished products are packaged for shipment.

2. Quality Parameters and Measurement Points

Moisture, resin, and wax moisture measurements can be conducted simultaneously at multiple locations during the particle board production process using infrared moisture meters.

Moisture measurements can be taken on the raw wood chips (before they are crushed) to provide information about the dryer load and enable feedforward control of the dryer. The dry basis moisture range is typically between 45% and 150%.

After the dryer, moisture measurements can be taken at the outlet of the hammer mill for the crushed wood particles. The dry basis moisture range is typically 30-55%.

Then, on the pre-formed boards, the moisture range is 0 to 5%. An infrared moisture meter is usually installed within a range of 6 to 16 inches from the product, directly observing the wood chips and particles, or visible through a glass window. Sometimes, a probe sampler is used in conjunction with the infrared moisture meter to take readings in a chute where the fibers fall freely. The analog output of the infrared moisture meter is typically connected to a control device in the control room, allowing end users to monitor their process and record historical data.

Infrared moisture meters can also be applied in laboratories for rapid, accurate, and reliable sample testing.

3. Value and Quality Control

The incoming raw wood chips vary significantly in moisture content and composition. Different measurements at various locations during processing are important; they allow for automatic adjustments of temperature and/or processing speed to remove the appropriate amount of moisture, thus producing high-quality, consistent boards.