(1) Comparison of heating methods
The traditional heating methods are steam heating and electric heating. The steam heating is fast, but it needs to be equipped with a pressure boiler, the pipeline pressure is high, the steam is easy to condense into water, which causes uneven temperature on the surface of the board; electric heating has the characteristics of fast heating, high heating temperature, simple control, etc. The cost is high, and the shortcomings of the resistance wire are not easy to replace in the specific application.
The advantages of thermal 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, it is not easy to control the temperature. In the furniture industry, when the hot pressing temperature is generally not high, a hot water circulation furnace can also achieve satisfactory results, and the fixed investment and working costs are very low.
(2) Function of hot pressing plate
The function of the hot pressing plate can be evaluated from several aspects. The first is the application of the pressing plate material, then the accuracy of the processing, and the end is the placement of the medium channel in the hot pressing plate.
The hot-pressed plate is generally made of a whole constrained steel plate by deep-hole drilling. It is mainly used for oil heating and steam heating. The other method is to use an aluminum plate on the back surface of the welded pipeline, which is mainly used for electric heating. The use of a single steel plate can prevent oil leakage due to poor sealing. The rigidity and strength are high together, but the hot-pressed plate is thicker; the latter due to the general choice of thin plate method, due to stress during welding and processing, requires high processing accuracy.
The hot platen is thin and easy to preheat and control the temperature, but the requirements for the processed parts are high. The uneven thickness of the workpiece will cause the deformation of the platen and affect the subsequent processing quality; the thicker platen is conducive to increasing the heat capacity and forward strength and rigidity. But it will increase the size of the press and consume more steel.
When making and processing, it should be ensured that the flatness of the hot pressing plate and the upper and lower surfaces have sufficient parallelism. The roughness is 3.2 μm. The temperature difference across the entire width of the hot plate should not exceed 2-3 ° C. If the temperature difference is too large, the moisture content will be uneven, the product will be warped easily, and the strength and appearance quality of the product will be affected.
The heating channels of the hot medium in the hot pressing plate are generally not valued by those in the furniture industry. The correct circuit planning should be based on the principle of conducive to the movement of the heat medium, the uniform heating of the board surface, and the reduction of the heat medium leakage. Regarding the hot press plates of the small presses used in the furniture industry, the single-hole dual-circuit plan is generally used to satisfy the application requirements.
