Powder coating is a type of coating that is applied as a free-flowing, dry powder. Unlike conventional liquid paint which is delivered via an evaporating solvent, powder coating is typically applied electrostatically and then cured under heat or with ultraviolet light. The powder may be a thermoplastic or a thermoset polymer. It is usually used to create a hard finish that is tougher than conventional paint. Powder coating is mainly used for coating of metals, such as household appliances, aluminium extrusions, drum hardware, automobiles, and bicycle frames. Advancements in powder coating technology like UV curable powder coatings allow for other materials such as plastics, composites, carbon fiber, and MDF (medium-density fibreboard) to be powder coated due to the minimum heat and oven dwell time required to process these components. Powder coatings contain no solvents and release little or no amount of volatile organic compounds (VOC) into the atmosphere. Thus, there is no need for finishers to buy costly pollution control equipment. Companies can comply more easily and economically with environmental regulations, such as those issued by the U.S. Environmental Protection Agency. Powder coatings can produce much thicker coatings than conventional liquid coatings without running or sagging. Powder coated items generally have fewer appearance differences than liquid coated items between horizontally coated surfaces and vertically coated surfaces. A wide range of speciality effects are easily accomplished using powder coatings that would be impossible to achieve with other coating processes. Curing time is significantly faster with powder coatings compared to liquid coatings especially when using ultraviolet cured powder Coatings or advanced low bake thermosetting powders.
The automatic powder coating machine has several spraying methods, such as 1. Electrostatic spraying method: it is the most commonly used spraying method for powder automatic spraying equipment, mainly through the electrostatic field to make the electrostatic powder coating evenly fall on the surface of the workpiece to be sprayed, A uniform coating is then formed by leveling in a curing oven; 2. Electrostatic fluidized bed spraying method: The electrostatic fluidized bed spraying method is mainly by adding high-voltage electrodes to the interval of the porous plate at the bottom of the powder automatic spraying equipment and the container. Thus, a high-voltage electric field is formed between the piezo electrode and the workpiece, and the uniformity and adhesion of the coating thickness of the powder coating are greatly improved; 3. Electrostatic oscillating powder coating method: The electrostatic oscillating powder coating method used in powder coatng machine mainly converts the high-voltage point of direct current into a high-voltage electrostatic field, so that its periodic change produces electric field oscillation. And under the action of this oscillating electrostatic field, the powder coating will float.
Electrostatic powder coating gun is mainly composed of powder supply barrel, powder spray gun and controller. It is a special spray gun for electrostatic spraying of paints and powder coatings. It is both a paint atomizer and an electrostatic electrode generator. The powder needs to be charged to the workpiece to form an effective coating to protect and decorate the workpiece. Usually, a powder spray gun that can generate high-voltage static electricity is used as a production tool for powder coating. Such a type of spray gun will generate a high-voltage, low-current high-voltage electric field, and the powder particles will be negatively charged when they move in it, and then firmly adsorbed onto the workpiece to be coated. Such a process is often referred to as powder electrostatic spraying.
In electrostatic powder coating, the curing furnace is the key equipment. The quality of the paint film has a very important relationship with the temperature of the curing furnace. The heating method of the powder curing furnace can be divided into two categories: one is the hot air circulation type, The second type is the infrared radiation heating method. Hot air circulation heating can be divided into direct heating and indirect heating. There are two heat sources used for direct heating, electric heating spiral fin type and gas type direct heating. The advantages of the direct electric heating spiral fin type are uniform temperature in the furnace and strong adaptability of the workpiece: the solid state relay PID is used to adjust the temperature. The temperature deviation in the powder coating oven is small. The disadvantage is that the heating time is slow and the equipment power is large, and it is not fit for used as an industrial powder coating oven. Because it is heated by hot air circulation, the curing process is easy to cause secondary pollution of dust. The furnace occupies a large area. The advantages of the gas-fired direct heating method are fast heating speed, high heat energy conversion rate, proportional adjustment control for furnace temperature control, and small temperature control deviation in the warm furnace. Because the burner flame burns directly in the combustion chamber, the curing process is likely to cause secondary pollution of dust and exhaust gas, which is not suitable for use as a home powder coating oven. A high temperature resistant filter should be installed in the heating chamber, so that the full pressure of the circulating fan should be considered in the selection of the fan. In addition, the heating indoor plate must be made of stainless steel plate, the cost of these two equipment is relatively Increase, the furnace covers a large area.
