The purpose is to remove oil stains on the surface of plastic work - pieces. Because plastic products may be contaminated with oil during the processing, and these oil stains will affect the adhesion of the subsequent coating. Common degreasing methods include chemical degreasing and ultrasonic degreasing. Chemical degreasing uses alkaline or acidic solutions to react with oil stains to decompose and separate them from the work - piece surface. For example, a sodium hydroxide solution can effectively remove some animal and vegetable oils. Ultrasonic degreasing uses high - frequency vibrating ultrasonic waves in the degreasing solution to strip the oil stains from the work - piece surface. This method is more effective for plastic work - pieces with complex shapes.
Derusting Equipment (if there are rust marks)
Although plastic itself does not rust, if the plastic product is combined with metal parts or contaminated with metal impurities, derusting may be required. Common derusting methods include mechanical derusting (such as sandblasting) and chemical derusting. Sandblasting derusting uses the impact of high - speed sand flow to clean and roughen the substrate surface, so that the surface of the work - piece obtains a certain degree of cleanliness and different roughness. Chemical derusting mainly uses acid to react with rust. For example, a hydrochloric acid solution can be used to remove rust, and the reaction formula is .
Surface Conditioning Equipment
It is used to improve the microscopic state of the plastic work - piece surface and make it more conducive to the adhesion of the coating. The surface conditioner can increase the active points on the work - piece surface. For example, some surface conditioners containing titanium phosphate can form a uniform film on the work - piece surface, which is beneficial to the adsorption of the coating and lays a good foundation for the subsequent spraying.
Phosphating Equipment (Some plastics may require it)
Phosphating treatment forms a phosphate conversion film on the work - piece surface. For some special plastic - metal composite products, phosphating can improve their corrosion resistance and coating adhesion. The main component of the phosphating solution is zinc dihydrogen phosphate. Under certain temperature and acidity conditions, a phosphating film is formed on the work - piece surface through reaction. The reaction process is relatively complex. For example, the main steps of zinc - based phosphating reaction include metal dissolution, oxidization of accelerators, multi - stage dissociation of phosphate ions and phosphate precipitation and crystallization.
II. Spraying System
Spray Gun
This is the key equipment for spraying. There are various types of spray guns, such as air - spray guns, airless spray guns and electrostatic spray guns. The air - spray gun uses compressed air to atomize the coating and spray it onto the work - piece surface. Its advantage is that it is easy to operate and can achieve a more precise spraying effect, which is suitable for plastic products with high requirements for appearance quality. The airless spray gun pressurizes the coating through a high - pressure pump and atomizes and sprays it out instantly at the nozzle of the spray gun. The coating particles sprayed by this spray gun are finer and the coating is more uniform, and the spraying efficiency is also higher. The electrostatic spray gun uses the principle of electrostatic adsorption to make the coating particles charged and adsorbed onto the work - piece surface under the action of an electric field. Its advantage is that the coating utilization rate is high, especially suitable for plastic work - pieces with complex shapes, enabling the coating to be evenly attached to all corners.
Coating Supply System
It includes coating storage containers and delivery pipelines. The coating storage container needs to have good sealing performance to prevent the coating from volatilizing and deteriorating. The material of the delivery pipeline should be selected according to the properties of the coating. For example, for some organic solvent - based coatings, pipelines resistant to organic solvent corrosion should be used. At the same time, the coating supply system may also include a coating stirring device to ensure the uniformity of the coating composition, because some coatings may precipitate or stratify during storage.
Spray Booth
The spray booth provides a relatively closed environment for spraying operations. It can effectively collect the paint mist generated during the spraying process and prevent the paint mist from spreading to the surrounding environment. On the one hand, it protects the working environment and the health of operators, and on the other hand, it also improves the utilization rate of the coating. The spray booth is usually equipped with a ventilation system to extract the air containing paint mist, filter and purify it before discharging. Some advanced spray booths also have temperature and humidity adjustment functions, because temperature and humidity will affect the drying speed and spraying effect of the coating. Appropriate temperature and humidity conditions can make the coating adhere and dry better.
III. Drying and Curing System
Drying Equipment
It is mainly used to dry and cure the coating. Common drying equipment includes hot - air circulation ovens and infrared drying furnaces. The hot - air circulation oven heats the air and uses the circulation of hot air to dry the coating. It has good temperature uniformity and can make the coating on the entire work - piece surface dry evenly. The infrared drying furnace uses infrared radiation to heat the coating. Infrared rays can penetrate the coating surface, enabling the inside and surface of the coating to be heated simultaneously. The drying speed is relatively fast, and it is more suitable for some plastic - sprayed products with thick coatings or high requirements for drying speed.
Curing Equipment (For some special coatings)
Some plastic spraying requires the use of two - component coatings or thermosetting coatings. These coatings need to undergo a curing reaction to form a coating with good performance. The curing equipment can provide appropriate temperature, pressure and time conditions to complete the curing reaction. For example, some epoxy resin coatings need to be maintained at a certain temperature for a period of time to enable the epoxy group and the curing agent to undergo a cross - linking reaction to form a three - dimensional network - like cured coating, thereby improving the hardness, wear resistance and chemical corrosion resistance of the coating.
IV. Conveying System
Conveyor Chain
The conveyor chain is used to transport plastic work - pieces through the pretreatment system, spraying system and drying and curing system in sequence. It can set an appropriate conveying speed according to the requirements of the production process to ensure that each work - piece can be fully processed in each treatment link. The material of the conveyor chain should be selected according to the weight and shape of the work - piece. Generally, it should have sufficient strength and wear resistance, and its corrosion resistance should also be considered, because it may come into contact with some chemical solutions during pretreatment and spraying.
Suspension Device
The suspension device is the part that suspends the plastic work - piece on the conveyor chain. It should ensure the stability of the work - piece during transportation and enable the work - piece to be easily loaded and unloaded. For work - pieces with irregular shapes, the design of the suspension device is particularly important to ensure that each surface of the work - piece can be evenly sprayed during the spraying process.
V. Exhaust Gas Treatment System
Gas - collecting Equipment
It is mainly used to collect the exhaust gas generated during the spraying process and the drying process. These exhaust gases contain harmful substances such as organic solvents and paint mist particles. The gas - collecting equipment is usually installed at the exhaust ports of the spray booth and the drying equipment and collects the exhaust gas through pipelines and sends it to the exhaust gas treatment equipment.
Exhaust Gas Treatment Equipment
Common exhaust gas treatment methods include activated carbon adsorption, catalytic combustion and water spraying. Activated carbon adsorption uses the porous structure of activated carbon to adsorb the organic components in the exhaust gas. This method is suitable for treating low - concentration and large - volume exhaust gas. Catalytic combustion uses a catalyst to make the organic components in the exhaust gas burn and decompose at a lower temperature and convert them into harmless carbon dioxide and water. It is suitable for treating high - concentration and small - volume exhaust gas. Water spraying makes the exhaust gas fully contact with water, so that the paint mist particles and some water - soluble exhaust gases are absorbed by water, playing a role in preliminarily purifying the exhaust gas.
VI. Control System
Electrical Control System
It is used to control the operation of the entire plastic spraying line equipment. It can control the speed of the conveyor chain, the spraying parameters of the spray gun (such as spraying pressure, spraying volume, etc.), the temperature and time of the drying equipment, etc. The electrical control system usually consists of a control cabinet, sensors and actuators. The sensors can detect the running state of the equipment, the position of the work - piece and other information, and then feed this information back to the control cabinet. The control cabinet controls the operation of the equipment through actuators (such as motors, solenoid valves, etc.) according to the preset program and feedback information.
Quality Monitoring System
It is used to monitor the quality of plastic - sprayed products. It can detect the coating thickness and appearance quality (such as glossiness, color, etc.) of the work - piece. For example, a coating thickness gauge can be used to detect the coating thickness in real - time. When the coating thickness exceeds the preset range, the quality monitoring system can send an alarm to prompt the operator to make adjustments. At the same time, some advanced quality monitoring systems can also use machine vision technology to detect the appearance defects of the work - piece (such as sagging, orange peel, etc.) and improve the quality stability of
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