Medium Density Fiberboard (MDF for short). 

Medium density fiberboard is a kind of artificial board made of wood fiber or other plant fibers, which is crushed, fiber separated, dried, applied with urea formaldehyde resin or other applicable adhesives, and then hot pressed. Its density is generally in the range of 500-880kg/m3, and its thickness is generally 5-30mm.

Histury.

Medium density fiberboard (MDF) is a product developed in the mid-1960s, and its output has developed rapidly in recent years. The reason is that it has excellent physical and mechanical properties, decorative properties and processing properties.

MDF Process

1. Material preparation

The first step of MDF production process is material preparation. The equipment mainly includes chipper, belt conveyor, screening machine, bucket elevator, storage bin, etc. The raw materials for MDF production are mainly wood fiber raw materials, including small diameter wood, branch wood, fuel wood, and processing residues. The ideal raw materials for MDF production are 60%~70% coniferous wood, 30%~40% hardwood, and the bark content should not exceed 5%.

2. Preparation of fibers

The preparation of fiber is mainly fiber separation, which is the core link of MDF production process. The equipment used for fiber separation includes wood chip silo (or preheating silo), small hopper, thermal mill, paraffin melting and application device, and sizing metering device.

Steps of fiber separation:

A: Hot grinding. The qualified wood chips are transported into the wood chip silo, and the wood chips are sent to the grinding chamber after being digested and softened. The wood chips are compressed by a hot mill to extrude water from the wood chips with high water content.

B: Waxing. The paraffin is heated and melted by the steam coil. The melted paraffin is pumped into the wood chip before entering the grinding chamber through the pump pipe. After being separated into fibers, the paraffin is evenly distributed on the fiber surface.

C: Sizing. The urea formaldehyde resin enters the double metering tank through the filter and glue pump, and then enters the pump into the discharge pipe for sizing. The fibers in the discharge pipe are in a high-speed flow state, and the glue solution is atomized and evenly sprayed on the fiber surface. Curing agent and formaldehyde capturing agent can be added into the glue tank for mixing.

3. Drying

The drying process of MDF production process is mainly composed of drying host, drying pipeline, cyclone separator, fiber conveyor, dry fiber silo, etc. The discharge pipe of the thermal mill sucks in the wet fiber of the drying pipe and fully contacts with the hot air. The fiber is suspended in the air duct and transported by the air flow. The fiber runs in the air duct for 4-5 seconds to quickly evaporate the moisture of the fiber and reach the required moisture content (8%~12%).

4. Forming

Paving and forming is a very important process in the production process of MDF. This process includes slab paving, pre pressing, edge trimming, cross section and other major parts. The requirements for the paving process are: slab density is uniform, stable, thickness is consistent, slab weight control on unit area is continuous, stable and consistent, with a certain degree of compactness.

5. Hot pressing

The hot pressing process for manufacturing medium and high density fiberboard in China is batch multilayer hot pressing process. Various process factors have important effects on the properties of MDF.

A: Hot pressing temperature. The selection of hot pressing temperature mainly depends on the type and performance of the board, the type of adhesive and the production efficiency of the press. The selection temperature mainly depends on the comprehensive factors of raw materials, tree species, fiber moisture content, adhesive properties, slab thickness, heating time, pressure and equipment conditions.

B: Hot pressing pressure. The hot pressing pressure changes during the hot pressing process. When pressing, the pressure gradually increases to meet the slab thickness requirements, that is, the pressure should be reduced. The curing of adhesives, the formation of various bonding forces between fibers, and the evaporation of water are mainly completed in the low-pressure section, which is generally 0.6~1.3Mpa.

C: Hot pressing time. The determination of hot pressing time is mainly related to the properties of adhesive, curing time, fiber quality, slab moisture content, thickness, hot pressing temperature, pressure and other factors. The hot pressing time is generally expressed as the time required for 1mm plate thickness.

D: Moisture content of slab. In the hot pressing process, the role of moisture in the slab is to increase the plasticity and thermal conductivity of the fiber. Therefore, an appropriate moisture content can ensure the quality of the slab, which is generally controlled at about 10%. If the moisture content is too high, the density gradient of the surface and core layers will increase, and the binding force between the core layers will be poor. When the pressure is reduced and the steam is exhausted, it is difficult to remove the water vapor, resulting in blistering and delamination in the slab. If the moisture content is too low, the slab surface will be soft, the thickness of the pre curing layer will be thick, and the strength of the slab will be reduced.