Relationship between thickness of plywood and pressure time pressure

Dry-heat cementing is carried out in the hot press. In the process of cementing, temperature, pressure and time are three important factors affecting the hot pressing process. They are interrelated and interrelated.The so-called hot pressure cycle means that the preformed slab is loaded into the hot press one by one or at the same time, the press closes, the pressure rises, and is kept under a certain pressure for a period of time, the pressure drops after the solidification of the rubber layer, the press opens and the slab is removed, thus completing a hot pressure cycle.During the whole hot pressing cycle, the adhesive fully contacts with the wood under the action of pressure, heating increases the slab temperature, redistributes moisture, compacts the wood, solidifies the rubber layer, removes steam when unloading pressure, and reduces the moisture content of the finished product to the specified value.General thermal cycle can be divided into three phases: the first phase of jujube booster stages, namely from plate to press all closed, the slab after load compressor under external pressure, near the hot platen rubber heat up quickly, then, in the phase of booster under the slab is not fully contact glue, so this phase if the bond strength of rubber curing was less than expected.Therefore, the period should be as short as possible.The second stage of jujube compression is the time from the closing of the press to the beginning of pressure relief.Such as platen temperature is 105-120 ℃, urea-formaldehyde resin plywood 30-50 seconds per millimeter thick, pressure for 1-1.2 MPa.The third stage is the pressure lowering stage, which can also be divided into three stages.In this stage, attention should be paid to controlling the pressure drop rate of the compressor. In the first stage, the pressure from the highest pressure falls to the equilibrium pressure of steam pressure and hot pressure plate pressure in the slab.When the two pressures are equal, that is, when they are at equilibrium pressure, they enter the second stage of depressurization.At this time, the inner layer of the slab bears a great deal of stress, which is caused by the contraction of the slab and the transformation of water in the slab into gas.Therefore, the steam should be discharged slowly at this stage.The third stage is the platen opening, for the multi-ply plywood to reduce unnecessary compression, the buck time can be carried out in advance.