Medium density fiberboard technology
1, stock preparation
The first step in the production process of medium density fiberboard is the preparation of materials. The equipment mainly includes chippers, belt conveyors, screening machines, bucket elevators, and storage silos. MDF production raw materials are mainly wood fiber raw materials, which include small diameter wood, branch lintel, fuel wood, and processing residues. The ideal stock material is 60% ~ 70% of softwood materials, 30% ~ 40% of hardwood materials, and trees. Skin content should not exceed 5%.
2, the preparation of fiber
The preparation of fiber is mainly fiber separation, and it is the core link of MDF production process. Fiber separation equipment used wood chip silo (or preheated silo), small hopper, hot mill, paraffin melting and application devices, sizing metering device.
Fiber separation steps:
A: The hot mill transports the qualified wood chips into the wood chip bins. The wood chips are softened by cooking and then transported to the grinding chamber body through the hot mill to compress the wood chips. The wood chips with higher moisture content are squeezed out of moisture.
B: The paraffin wax is heated and melted by steam coils. The molten paraffin is injected into the wood chips in front of the mill body through the pump pipe. After the fibers are separated into fibers, the paraffin wax is distributed on the surface of the fiber more uniformly.
C: The sizing urea-formaldehyde resin passes through the device, and the adhesive pump is pumped into the double metering tank, and then enters the pump input discharging pipe to sizing the fiber. The fiber in the discharging pipe is in a high-speed flow state, and the glue is atomized. Spray evenly on the fiber surface. The curing agent can be added to the tank, and the formaldehyde trapping agent can be used for mixing.
MDF production process Drying process The main equipment consists of drying machine, drying pipe and cyclone separator, fiber conveying device, dry fiber silo and other components. The hot mill discharge pipe sucks the wet fiber of the drying pipe, and is in full contact with the hot air. The fiber is suspended in the air pipe and is transported by the airflow. The fiber runs in the air pipe for 4 to 5 seconds, quickly evaporating the moisture of the fiber to meet the requirements. Water content (8% ~ 12%).
Pavement molding is a very important process in the production process of medium density fiberboard. This process includes slab paving, pre-pressing, trimming, cross-section, etc. The requirements for the paving process are: uniform slab density, stable Consistent with the thickness, the slab weight control per unit area is continuously stable and consistent with a certain degree of compactness.
5, hot pressing
At present, the hot-pressing process for manufacturing medium-high density fiberboard in China is a batch-type multilayer hot-pressing process, and various process factors have an important influence on the performance of the MDF.
A: Hot-pressing temperature The choice of hot-pressing temperature depends mainly on the type and performance of the board, the type of adhesive and the production efficiency of the press. The temperature used depends mainly on the moisture content of raw materials, tree species, fibers, adhesive properties, and slabs. Thickness, heating time, pressure, and equipment conditions.
B: Hot-pressing pressure The hot-pressing pressure changes during the hot-pressing process. When the pressure is applied, the pressure gradually increases to reach the slab thickness requirement. That is, the pressure should be reduced, and the adhesive is cured, and the various bond strengths between the fibers are formed. The evaporation of water is mainly completed in the low pressure section, and the pressure in the low pressure section generally takes 0.6 ~ 1.3mpa.
C: hot pressing time The hot pressing time is mainly determined by the properties of the adhesive and the curing time, the fiber quality, the moisture content of the slab, the thickness, the hot pressing temperature, the pressure and other factors. The hot pressing time is generally required for a thickness of 1 mm. Time.
d: moisture content of slab In the hot pressing process, the effect of moisture in the slab is to increase the plasticity and thermal conductivity of the fiber, so the appropriate moisture content is guaranteed for the quality of the plate, generally controlled at about 10%, if too high Will make the table, the core density gradient increases, the bonding force between the core fiber is poor, the pressure steam, the steam is difficult to remove, resulting in blistering within the board, delamination, if the board will be loose, pre-curing Layer thickness, plate strength decreased.