(1) Features of convection drying chamber
The convection drying equipment uses hot air as the heat carrier, and heats the heat evenly through convection, which is suitable for workpieces of various shapes, and the quality of the coating film is uniform;
This convection drying equipment uses hot air as a heat carrier to transfer heat to workpieces and coatings through convection. It has the following characteristics.
(1) Uniform heating, suitable for workpieces of various shapes, and uniform coating quality;
(2) The temperature range is large, suitable for drying and curing of various coatings;
(3) The equipment is easy to use and maintain;
(4) High enthusiasm, slow temperature rise and low thermal efficiency;
(5) The equipment is huge and the area of the middle ground is large;
(6) The coating film is prone to defects such as bubbles, pinholes, and wrinkles.
Since this type of equipment can uniformly cure the coating film on the surface of any shape workpiece, it is widely used.
(2) Composition of convection drying chamber
Convection drying equipment is mainly composed of chamber body, heating system, air curtain device and temperature control system. (See Figure 1_5_5).
The chamber body mainly plays the role of heat insulation, so the volume of the chamber body and the size of the door opening should be as small as possible, and the insulation layer of the guard plate should have sufficient thickness and be effectively sealed. For example, in a drying room at 150-200°C, when the temperature of the outer wall of the room is not higher than 40°C, the thickness of the stone-1-slag phase insulation layer is about 50-125mm, and the guard plate adopts the method of skeleton lap or panel lap joint. Carry out sealing (see Figure 1_5_6).
2. Heating system
The heating system consists of air ducts, air filters, air heaters and fans.
Convection drying adopts lower air supply and upper exhaust, the air duct includes suction duct and air supply duct, and the outdoor part is a round duct, and the indoor duct is rectangular. Each opening of the air supply pipe is equipped with a "lilJ plate", which is convenient for adjusting the balance of the air supply volume in the room. Since the heating section consumes a lot of heat, the air supply volume should also be larger, so the main air supply pipe inlet is located in the heat preservation section and the heating section. Correspondingly, an exhaust pipe is arranged on the upper part of the heating section and the opening density of the suction pipe is increased, and the high-concentration solvent vapor is discharged in time between the circulating fan and the heater.
The air filter keeps the air content below 0.5mg/m3 to prevent particles from appearing on the coating surface. Can be used in type fiber filter or viscous filled filter material filter.
There are several types of heaters, such as fuel oil, gas fired heaters, electric heaters and steam heaters. The steam heater is only used for low-temperature drying or moisture drying below 120°C. The electric heater has compact structure, high efficiency, and is easy to control, but additional power distribution facilities are required. Combustion heaters can be divided into direct type and indirect type. The direct heater is to mix the high-temperature gas produced by combustion with air and send it into the drying chamber to heat the coating. Its thermal efficiency is high, but the heat is not easy to control, and the hot air has poor clarity. It is only suitable for drying the primer. It is not declared to be used to bake the topcoat; the thermal efficiency of the joint heater is low, but the hot air is clear and the heat is easy to adjust, which can ensure the quality of the coating film after the topcoat is baked.
3. Air curtain device
For the straight-through continuous drying room, in order to reduce the escape of hot air from the opening at the west end, an independent air curtain device should be installed in the west, and the outlet wind speed is generally 10~20m/s. For workpieces coated with powder, an air curtain cannot be installed at the inlet to prevent the airflow from blowing off the powder particles on the surface of the workpiece. For bridge or II" type drying room, no air curtain device is required.
4. Temperature control system
The temperature control system mainly controls the temperature of the drying chamber to be constant by adjusting the heat output of the heater. The heat adjustment methods of heaters using different heat sources are different, but the systems all have multi-point temperature measurement and over-temperature alarm devices.
