Heating ways for plywood hot press

- Nov 16, 2020-

(1) Comparison of heating methods

The traditional heating method is steam heating and electric heating. Steam heating heats up quickly, but it needs to be equipped with a pressure boiler. The pipeline pressure is high, and the steam is easy to condense into water to form uneven surface temperature; electric heating has the characteristics of fast heating, high heating temperature, and simple control, but it consumes large power and works. The cost is high, and the resistance wire is not easy to replace when used in detail.

The advantages of heat conduction oil heating are: high heat capacity, uniform temperature, can be heated to a high temperature under normal pressure, low heat loss, can reduce production costs, its disadvantage is that the heating speed is slow, and temperature control is difficult. In the furniture industry, when the general hot pressing temperature is not high, the hot water circulation furnace can also be used to meet the requirements, and the fixed investment and work costs are very low.

(2) Function of hot pressing plate

The function of the hot pressing plate can be evaluated from several aspects, first is the use of the pressing plate material, and then the processing accuracy, which is the arrangement of the medium channels in the hot pressing plate.

The hot pressing plate is generally made of a whole piece of restricted steel plate processed by deep hole drilling, and is mainly used for oil heating and steam heating; the other is to use the aluminum plate on the outer surface after welding the pipeline, which is mainly used for electric heating. The use of a whole piece of steel plate can avoid oil leakage caused by poor sealing. At the same time, the rigidity and strength are high, but the hot-pressed plate is thicker; the latter, due to the general selection of thin plates, due to stress in welding and processing, requiring high processing accuracy.

The thin hot press plate is easy to preheat and temperature control, but the requirements for the processed parts are high. The uneven thickness of the workpiece will cause the deformation of the press plate and affect the subsequent processing quality; the thicker hot press plate is beneficial to increase the heat capacity and forward strength and rigidity. But it will increase the size of the press and consume more steel.

During manufacturing and processing, ensure that the flatness of the hot press plate and the upper and lower surfaces have satisfactory parallelism. The flatness tolerance of the hot press plate should be in the range of 0.1-0.18mm, and the parallelism tolerance should be in the range of 0.15-027mm. The roughness is 3.2 μm. The temperature difference across the entire width of the hot press plate should not exceed 2-3°C. If the temperature difference is too large, the moisture content will be uneven, the product is easy to warp, and the strength and appearance quality of the product will be affected.

The heating channels where the heating medium moves in the hot pressing plate are generally not valued by the furniture industry. The correct circuit planning should be based on the activity of the heating medium, the uniform heating of the plate surface, and the reduction of the leakage of the heating medium. Regarding the small press hot plate used in the furniture industry, the single-channel dual-circuit plan is generally used to meet the application requirements.

(3) Connection and sealing

The selection of suitable connection methods and sealing elements has important implications for heat transfer under high temperature and high pressure.

At that time, the connecting pipeline of the hot press plate was basically made of hoses, which made the connection very convenient. The domestic mainly used metal hoses, and some manufacturers chose imported Teflon hoses. Both methods can be used. With blue connection, the function of Teflon hose is better than that of metal hose. Asbestos rubber sheets are traditionally used as gasket materials. New materials such as polytetrafluoroethylene and coiled graphite are not particularly well sealed.