Cleaning is to remove oil, rust, dust, etc. on the workpiece by chemical or (and) physical methods to ensure that the workpiece obtains better coating adhesion and the smooth progress of production. Cleaning is an indispensable process before PVD coating, and it is also a process in PVD coating production. If there is a problem with cleaning, the coating production has to be delayed, the coating process may be interrupted, or the coating adhesion problem may cause customers Complaints and compensation, especially when the technical ability of the coating equipment is not high, the cleaning problem is more prone to the above risks.

Four factors affect the quality of cleaning, namely: cleaning time, chemical agents, mechanical action, and cleaning fluid temperature. These four factors also affect each other. The weakening of one factor can enhance the effect of the other three factors. to make up for it, and vice versa. Among these four factors, the minimization of cleaning time is also the goal pursued, which can improve the efficiency of cleaning. Shorten production time and lead time.

The main cleaning methods and steps should include chemical spraying, chemical immersion, ultrasonic cleaning, rinsing, and drying.

1) Chemical spray

The spray is very effective for cleaning, it can remove most of the oil and contaminants from the workpiece. Especially for workpieces with holes, it is more effective. The chemical agent sprayed on the workpiece will flow into the hole or the chemical agent will be directly sprayed into the hole to flush the inner wall of the hole. Therefore, when cleaning and loading the card, be sure to allow the workpiece to be sprayed. In addition, if the chemicals sprayed on the workpiece cannot flow away immediately, it will prevent fresh chemicals from continuing to clean the workpiece, and it will not be easy to dry in the subsequent drying steps. Therefore, when installing the card, ensure that it flows to the workpiece. The medicine on it can flow away naturally.

2) Chemical immersion and ultrasonic cleaning

Ultrasound is a sound wave with frequencies above 20 kHz beyond the range of human hearing. The propagation of ultrasonic waves depends on the elastic medium. When it propagates, the particles in the elastic medium oscillate, and the energy is transmitted through the medium in the direction of propagation of the ultrasonic waves. This kind of wave can be divided into longitudinal waves and transverse waves. In solids, both can be transmitted, while in gases and liquids, only longitudinal waves can be transmitted. Ultrasound can cause particle vibration, and the acceleration of particle vibration is proportional to the square of the ultrasonic frequency. Therefore, ultrasonic waves of several tens of kilohertz will generate a great force. When strong ultrasonic waves propagate in liquids, acoustic cavitation will be generated due to nonlinear effects. When the cavitation bubble is suddenly closed, the shock wave can generate thousands of atmospheric pressures around it, and the direct and repeated impact on the dirt layer, on the one hand, destroys the adsorption of the dirt and the surface of the cleaning part, and on the other hand, causes the dirt layer. break away from the surface of the cleaning parts and disperse them into the cleaning solution. The vibration of air bubbles can also scrub solid surfaces. Air bubbles can also "drill" into cracks to vibrate, causing dirt to fall off. For greasy dirt, due to ultrasonic cavitation, the two liquids are rapidly dispersed and emulsified at the interface. When the solid particles are wrapped by the oil dirt and adhere to the surface of the cleaning piece, the oil is emulsified and the solid particles fall off. In the process of vibration, the cavitation bubbles will cause the liquid itself to generate a circulating flow, which is the so-called acoustic flow. It can make the surface of the vibrating bubbles have a high-velocity gradient and viscous stress, and promote the destruction and shedding of the dirt on the surface of the cleaning parts. The high-speed microjet generated by ultrasonic cavitation on the surface of solid and liquid can remove or weaken the boundary dirt layer. , Corrode the solid surface, increase the stirring effect, accelerate the dissolution of soluble dirt, and strengthen the cleaning effect of chemical cleaning agents. In addition, the ultrasonic vibration causes a large vibration speed and acceleration of the particles in the cleaning solution, and also makes the dirt on the surface of the cleaning parts subject to frequent and intense impacts.

Because the ultrasonic wave will generate a low-pressure area and a high-pressure area during the transmission process, the cavitation phenomenon only occurs in the low-pressure area. Therefore, the workpiece to be cleaned needs to vibrate up and down in the ultrasonic wave, so that each area on the workpiece passes through the low-pressure area to obtain the cleaning effect of a "mini brush". The transmission speed of ultrasonic waves in water is 1500m/s. Assuming that the frequency of ultrasonic waves is 30,000Hz, the wavelength of ultrasonic waves used

λ=speed/frequency=1500/30000=0.05m=5cm

Therefore, if the ultrasonic wave of 30000Hz is used, the vibration distance of the workpiece should not be less than 5 cm. For other frequencies of ultrasound. The vibration distance can be calculated in the same way. In pure chemical immersion cleaning, the cleaning solution first dissolves the pollutants on the surface of the workpiece, and gradually penetrates and dissolves into the pollution layer. During this process, a layer of a dissolved saturated layer will gradually form on the surface of the workpiece. This saturated layer isolates the fresh chemical cleaning fluid from the deep contaminants, preventing the cleaning fluid from continuing to dissolve the deep contaminants. If this saturated layer cannot be destroyed and removed, the cleaning will stop. For relatively dirty workpieces, it is difficult to thoroughly clean the workpiece by pure immersion cleaning. Using the "micro brush" of ultrasonic waves, the dissolved saturated layer on the surface can be destroyed. The new chemical agent reaches the deeper pollution layer and continues to dissolve. The ultrasonic wave then continues to destroy the newly formed dissolved saturated layer. In this way, the cleaning continues. Go down until the workpiece is cleaned.

3) Rinse

The purpose of rinsing is to thoroughly clean the cleaning fluid or other dirt remaining on the workpiece so that the workpiece is cleaner before drying. Residues on workpieces will be difficult to clean after drying. In the industrial field. Usually, deionized water is used for rinsing, deionized water is used for rinsing instead of tap water. It can avoid impurities and pollutants in tap water remaining on the workpiece. However, deionized water is highly aggressive and can corrode the workpiece. Therefore, a certain amount of rust inhibitor must be added to deionized water before it can be used to rinse the workpiece. To prevent the workpiece from being rusted during the rinsing and drying process.

4) Drying

The cleaned workpieces are generally dried in an oven, which includes a box body, a drainage pipeline, a heating system, an exhaust system, and a temperature control system. The boiling and vaporizing temperature of the water is 100°C, so the baking temperature must be greater than 100°C, and it is recommended to be between 110°C and 130°C so that the water can be quickly evaporated and dried. After drying, the temperature of the workpiece is too high and it takes a long time to cool down.