For paint shop construction, curing furnace is a key unit. Paint film quality has a very important relationship with the temperature in curing furnace. The furnace heating methods are generally in two ways – hot air circulation & infrared radiation. Hot air circulation is also available as direct heating and indirect heating.
Direct heating method
There are two types of heat sources used for direct heating, electric heater and gas heater method.
The advantages of direct electric heater are extremely smooth temperature in the furnace and strong adaptability of workpieces – solid-state relay PID is used to adjust the temperature, temperature deviation in the furnace is small. The only disadvantage is its relatively slow temperature curve and installation power. Also, since it is heated by hot air circulation, the curing process is prone to secondary dust pollution. The furnace will take a big area construction.
In addition, infrared direct heating is widely used today – it is available as far infrared and high infrared:
Far infrared heating is already familiar to us. When the radiation spectrum of the far infrared heating body is the same as the absorption spectrum of the heated workpiece, the thermal efficiency is the highest, thus achieving energy saving.
The advantage of using far-infrared heating is that the radiation spectrum directly absorbed by the paint during the heating process so it will cure quickly. The furnace occupies a small area, but the furnace temperature uniformity by the far-infrared heating is not so smooth, so we always have to use a circulating fan stirring method to solve it.
The radiation spectrum of the heater during high-infrared heating is absorbed by the workpiece and the paint at the same time, so that the workpiece and the paint are heated at the same time, making the paint cure faster, thereby saving more energy. Most general high-infrared heating products are made of glass, which is easy to damage during installation. The life of high-infrared heaters is short, its working life is about 5,000 to 8,000 hours.
Gas Fired Heater
The advantages of gas-fired direct heating are fast heating speed, high conversion rate of heat energy, proportional control of furnace temperature control, and small temperature control deviation in the furnace. However, because the burner flame burns directly in the combustion chamber, the curing process is prone to secondary pollution of dust and waste gas. When designing, a high-temperature resistant filter should be installed in the heating chamber. In this way, the total pressure of the circulating fan should be considered larger when selecting the fan. In addition, the inner plate of the heating chamber must be made of high temperature resistance stainless steel. The cost of these two equipments is relatively increased and the furnace occupies a large area.
Indirect heating method
Indirect heating is also available in two ways: oil and gas. The characteristics of indirect combustion heating method are that there must be a heat exchange device, which is called a heat exchanger in this industry.
The flame burns in the furnace of the heat exchanger, so the material of heat exchanger should be selected as heat-resistant stainless steel (generally SUS310S material thickness cannot be less than 5mm).
Advantages of indirect heating method
Because the flame burns in heat exchanger, it will not cause secondary pollution of dust and exhaust gas during the curing process, the temperature is uniform, and the temperature control can adopt two-stage fire control and proportional regulation control. The control of temperature is more accurate.
The disadvantage of indirect heating method is that because it is heat exchanged through heat exchanger, the thermal efficiency is lower, the installation cost is relatively high and furnace construction take a larger area.
