OSB Production Moisture Measurement
Did you know that Oriented Strand Boards (OSB) is replacing plywood as the material of choice for sheathing and flooring in most new homes built in North America? OSB is a material with good mechanical properties and low cost. It is also a more renewable product than plywood because it can be made from small, fast growing trees.
Moisture and temperature control is critical in the manufacturing of consistent, high-quality OSB. Temperature and its distribution influences the bonding of the wood strands. If temperature levels are too low, the resin will not bind sufficiently to the wood and delamination will occur. Over drying of the wood strands requires using more resin and wastes fuel, increasing costs, as well as adding the risk of flash fires.
OSB Manufacturing Process
Debarking & Stranding
Most OSB manufacturers use logs averaging 8 to 12” in diameter at breast height (DBH). Incoming logs are slashed, soaked and debarked, prior to being cut into strands ranging from 3.5 to 6” in length and 1” width. The green strands are then stored in wet bins waiting to be dried.
Drying, Screening & Blending
Since the moisture content of the wet strands ranges from 40 to 75%, they are dried to 5 to 10% moisture in a rotating single-pass or triple-pass dryer with an inlet temperature as high as 1250 degrees F. The dried strands are then screened and blended with a binder and wax, before entering the former where the strands are laid out as a continuous mat.
Forming Line & Pressing
Dried strands are classified into two sizes using various sizes of screen. Large strands are used for the bottom and top face layers of the OSB panel while the smaller strands are used for the core layer. Face and core layers are oriented opposite to each other and sequentially laid onto a conveyor belt as a mat. The overall mat thickness depends on the desired thickness and density of the finished panel. The mats are converted to panels under high pressure and temperatures within a press.
Finishing Line
Pressed panels are removed from the press line and conditioned on a rotating cooler prior to cutting them to final dimensions.
Quality Parameters and Measuring Points
Moisture, resin and wax measurements can be done simultaneously, at multiple locations within the OSB manufacturing process, using NIR Analyzers and RF Sensors from KPM Analytics.
Moisture of the green wood chips can be measured to calculate dryer load and to control the feed rate of the dryer. Without feed rate control the dryer can be easily overloaded.
After the dryer, moisture measurement can be done on the weigh belt before the blender. The measurements at this location are often used as an indicator of moisture level rather than an absolute moisture measurement, the aim being to narrow the final strand moisture content through tighter dryer control.
Installation Locations
The MCT460 Series NIR analyzers are integrated into key areas of a production process to continuously monitor incoming raw materials or control processes on the production line. Each option is designed to integrate seamlessly over belt conveyors, auger/screw conveyors, or bins & chutes to analyze moisture and other on-line constituents.
Measuring temperature at multiple locations with pyrometers and thermal imaging cameras from Process Sensors Corporation allows temperature and process speed to be adjusted automatically, ensuring that high quality, consistent panels are produced as efficiently as possible.
