The heating method affects the temperature selection, process control, and quality of the processed products when the hot press is used. The following hot press manufacturers give us a detailed description of the heating system of the hot press from the heating method, hot plate, connection and sealing.
(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, and the steam is easy to condense into the water to form the uneven temperature of the board surface; electric heating has the characteristics of fast temperature rise, high heating temperature, simple control, etc. The cost is high, and the defect of the resistance wire is not easy to replace when it is used in detail.
The advantages of heat conduction oil heating are: high heat capacity, uniform temperature, can be heated to a very high temperature under normal pressure, low heat loss, can reduce production costs, its shortcomings are slow heating speed, temperature control is not easy. In the furniture industry, when the hot pressing temperature requirements are not high, a hot water circulation furnace can also be used to meet the requirements, and the fixed investment and working costs are very low.
(2) Hot platen function
The function of the hot platen can be evaluated from several aspects. The first is the application of the platen material, then the accuracy of the processing, and the arrangement of the medium holes in the hot platen.
The hot-pressed plate is generally made of a whole restricted 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 after welding the pipeline. The use of a single steel plate can avoid 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 pressing plate 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 pressing plate and affect the subsequent processing quality. But it will increase the size of the press and consume more steel.
During manufacturing and processing, it should be ensured that the flatness of the hot platen and the upper and lower surfaces have satisfactory parallelism. The flatness tolerance of the hot platen should be in the range of 0.1-0.18mm, the parallelism tolerance should be in the range of 0.15-027mm, The roughness is 3.2 μm. The temperature difference should not exceed 2-3 ℃ throughout the entire width of the hot plate. 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 facilitating the movement of the heat medium, facilitating the uniform heating of the board surface, and reducing the leakage of the heat medium. Regarding the hot press plates of small presses used in the furniture industry, the single-hole dual-circuit plan is generally adopted 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 connection piping of the hot plate was basically dominated by hoses, which made the connection very convenient. The domestic mainly used metal hoses, and some manufacturers used imported Teflon hoses. Both methods can be used. Blue connection, Teflon hose is better than a metal hose. The gasket material is traditionally made of asbestos rubber sheet, and new materials such as PTFE, coiled graphite, etc., the sealing effect is more ambitious.