Coating process IV of PVF in steel barrel for the

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Coating in steel drum for food -- coating process of PVF (IV)

2 Baking plasticization operation procedures

① preparation before production: check whether the voltage or combustion machine is normal; Check whether the temperature is normal; For the electric heating drying channel and drying room, check the closure of the exhaust valve, close it when heating up, and adjust the opening degree of the exhaust valve according to the number of barrels in production

② are you outsourcing the baking temperature and determining the residence time. The different temperature and baking time are determined according to the degree of heat absorbed by the barrel body and the bottom cover and the different movement state in the baking channel. Next, different operating procedures are determined for fuel drying channel and electric heating drying channel

for the fuel oven, the temperature in the whole oven is relatively uniform due to the forced hot air circulation in the oven. The temperature is generally set at 250 ~ 260 ℃. (temperature of hot air in the drying channel). The effective residence time shall be controlled within 10 ~ 15min

precautions: there should be no black smoke in the drying channel; Control the dimethyl vapor concentration in the oven: maintain sufficient exhaust volume

electric heating oven: it is generally determined according to the following conditions:

temperature of the baking object in the first period of time, the middle period of time and the later period of time

barrel body ℃ ℃ 230 ℃

barrel bottom cover ℃ ℃ 230 ℃

baking time, i.e. speed, as a major adjustment factor, is affected by many conditions, such as the thickness and thickness of the paint film, and the number of barrels in. You can choose a condition according to the completion of plasticization of the outgoing film, Volatilize the solvent completely in the oven. Generally, the effective time is controlled at about 10 ~ 15min. If the oven temperature cannot reach the above temperature, the time can be extended appropriately, not more than 20min, but if the temperature of the front and middle section is lower than 230 ℃, the quality cannot be guaranteed

precautions and safety work:

① prevent open fire. Dimethyl vapor evaporated from the coating during baking. In the golden age of rapid growth of China's plastic extruder industry, reaching a certain concentration, contact with open fire will cause combustion. Therefore, attention must be paid in the construction: the electric heating wire should be controlled to be used slightly below the rated voltage; Prevent heating elements from reddening; Prevent electric spark caused by poor contact of power connector

② it is forbidden to close all exhaust outlets during normal production, which will cause danger

③ control the vapor concentration of volatile gas dimethyl ester in the drying channel (or drying room) and maintain sufficient exhaust air volume

④ control the number of coated parts entering the drying channel and drying room in a unit time, and do not put too much and too dense. In case the local concentration of solvent gas is too high and unsafe

3. Discussion on the influence of baking temperature and holding time on coating quality

① temperature: the workpiece should be sent after rising to the specified furnace temperature. Generally, the available temperature range is 240 ~ 270 ℃. In fact, most of them take 240 ~ 260 ℃, which depends on the specific situation. Baking operation, one is temperature factor, and the other is time factor, which affect each other. The operator should first determine a suitable temperature, and then find the appropriate time for smaller indentation. The appropriate temperature depends on the barrel, that is, the thickness of the material, the quantity of each furnace, the condition of the material, etc. If the material is thick and the quantity is large, the heat capacity is large and the temperature rise is slow, so a higher baking temperature is required. Therefore, in actual production, the temperature often exceeds 240 ℃, and the temperature for processing thick barrels even needs more than 300 ℃

practice has proved that it is not feasible to reduce the temperature duration. There is a minimum temperature for baking plasticization temperature. If it is lower than the temperature, defective products will be baked. This minimum temperature increases with the increase of the heat capacity of the workpiece. At a low temperature, the baking quality problems are mainly manifested in the cracking of the coating, ranging from cracks at the corners to cracks in the whole coating, and the adhesion is significantly reduced. (to be continued)

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