Cement Wood Wool Board Production Process
There are generally four types of cement wood wool board production processes: semi-dry process, hot pressing process, three-layer orientation process, and flat pressing-steaming process. Currently, the semi-dry process is the most widely used method for producing cement wood wool board. This mature and reliable method is widely adopted, but it requires a long production cycle, numerous auxiliary equipment, and thickness tolerances, requiring sanding. However, this method currently has relatively systematic, standardized production equipment and reliable products, making it a popular production method worldwide. Furthermore, hot pressing for rapid curing of cement wood wool board is a hot topic of research, with numerous experts and scholars both domestically and internationally engaged in this area. However, this production process still has some challenges and has yet to be adopted by any manufacturer. The following is a brief introduction:
Semi-dry process
This production method is currently widely used in the Netherlands, Germany, France, Finland, Russia, Japan, and Switzerland. Its basic meaning is that cement and wood materials are added to the mixing mixer in addition to the amount of water required to ensure the hydration of cement, and as little water as possible is added to make the mixture of cement and wood wool board into a semi-dry state. Then, the semi-dry mixture is spread on the pad through the process of the paving machine, and the pad blanks are stacked on the mold car base with a locking mold through a stacking machine, stacked to 2 m high, and sent to the press through a conveying equipment for pressurization. Different pressures are applied to the slabs in the press depending on the type of use of the board. The general unit pressure is 2.5-3.0 MPa. It is pressed to the required thickness on the press and tightened with a locking device to maintain the pressure state to complete the consolidation of cement and wood materials. To shorten the curing time, the locked slabs are placed in a reinforced curing kiln at 60-80°C. Curing is generally required at 540-640°C/h for approximately 8 hours before removal from the molds. The boards are then naturally cured under insulated conditions for 5-7 days to dry at 70-110°C. The moisture content is controlled at 9% ± 4% to reduce shrinkage and improve dimensional stability. Trimming, shaping, and sanding are then performed to ensure the required dimensions and thickness.
The semi-dry production process is mature and reliable. Its development has made significant strides since the 1960s in terms of mechatronics, process control, accurate metering and thickness control, and improved assembly quality. It can produce boards 8-40 mm thick without the need for CO2 injection equipment. Complete equipment capable of producing 30,000-50,000 cubic meters of cement-based wood-wool board annually is 30%-50% less expensive than similar hot-pressing equipment.
The semi-dry process has limitations: 1. The production cycle is long. Even heat curing at 60-80°C requires 5-8 hours to achieve initial demolding strength, and there are strict requirements for the storage period of the wood material. 2. Additional production equipment is required, such as backing plates, corresponding backing plate return devices, cleaning devices, conveyor rollers, mold locking devices, curing and hardening kilns, and mold unloading and stacking equipment.
The resulting large production workshop area is an essential component of the semi-dry production process. 3. Panels produced using the semi-dry process exhibit significant thickness variations and require sanding.
Wood Wool → Mineralization Impregnation → Mixing → Laying and Forming → Pre-pressing → Pressing and Forming → Locking and Curing → Demolding → Secondary Curing → Trimming → Inspection
↑
Cement → Metering
Figure 1. Semi-dry Cement Wood Wool Board Process
Three-Layer Orientation
This production method involves uniformly arranging the wood materials horizontally in the core layer of the cement wood wool board and longitudinally in the surface layer. This resulting board offers greater dimensional stability and strength than hot pressing and semi-dry processes. This orientation is achieved on a specialized oriented laying machine. However, this type of wood material must be of a certain width, and flake-shaped wood chips are most suitable.
Flat Pressing-Pressure Steaming Method
For the flat pressing method, a certain amount of siliceous raw material must be added to the material composition. Quartz powder is the most effective silicon-rich material, but fly ash can also be used as an alternative. Fly ash should have a silica content of 50% or less and a loss on ignition of less than 8%. The other components of the flat-press-and-steam production process are essentially the same as the semi-dry process, differing in that the formwork is not a flat plate but rather a shaped formwork specified by the manufacturer. During the production process, the pressed and clamped slabs are cured in a curing kiln at 80°C for 12-16 hours. After demolding, they are then autoclaved at 172-185°C for approximately 20 hours to form a stable tobermorite gel with low shrinkage. This improves the dimensional stability of the cement wood wool board and its properties, such as water resistance and freeze-thaw resistance.