Cleaning is the process of removing oil, rust, dust, and other contaminants from a workpiece through chemical or (and) physical methods to ensure good coating adhesion and smooth production. Cleaning is an essential process before PVD coating, and it is also the most important process in PVD coating production. If there is a problem with cleaning, the coating production will have to be delayed, the coating process may be interrupted, or there may be problems with coating adhesion, which can lead to customer complaints and compensation. Especially in the case of low technical talent of coating equipment, if there is a problem with cleaning, it is more likely to cause the above risks.

There are four factors that affect the quality of cleaning, namely: cleaning time, chemical agents, mechanical effects, and cleaning solution temperature. These four factors also affect each other. The weakening of one factor can be compensated for by enhancing the effects of the other three factors, and vice versa. Among these four elements, minimizing the cleaning time is also the goal sought, which can improve cleaning power, shorten production time and delivery cycle.

The primary methods and processes for cleaning should include: chemical spraying, chemical soaking and ultrasonic cleaning, rinsing, and drying.

1) Chemical spray

Spraying is very useful for cleaning, as it can remove most of the oil and pollutants on the workpiece. Especially for workpieces with holes, it is more useful as the chemical agent sprayed onto the workpiece will flow into the hole or be directly sprayed into the hole to flush the inner wall of the hole. So when cleaning and installing cards, it is necessary to ensure that all workpieces can be sprayed. Other than that, assuming that the chemical agents sprayed onto the workpiece cannot flow away immediately in a timely manner, it will hinder the continuous cleaning of the workpiece with fresh chemical agents, and it will also be difficult to dry in the subsequent drying process. Therefore, when installing the card, it is necessary to ensure that the chemical agents flowing onto the workpiece can naturally flow away.

2) Chemical immersion and ultrasonic cleaning

Ultrasonic waves are a type of sound wave that humans cannot feel, and they are also a type of mechanical wave. They form high-pressure and low-pressure zones (with pressure lower than atmospheric pressure) in liquids. Ultrasonic waves generate millions of cavitation effect bubbles in the low-pressure zone, which gradually increase and suddenly split inward when necessary, releasing huge energy and hitting the workpiece, thus playing a "micro brush" cleaning effect on the surface of the workpiece. The frequency of this "micro brush" is very high, and the ultrasonic frequency used for cleaning is between 20000 and 50000 hertz.

Due to the occurrence of low-pressure and high-pressure areas during the transmission process of ultrasound, and the phenomenon of cavitation only occurs in the low-pressure area. So the cleaned workpiece needs to vibrate up and down in ultrasound, so that each area on the workpiece passes through the low-pressure zone to achieve the cleaning effect of a "micro brush". The transmission speed of ultrasound in water is 1500m/s. Assuming the frequency of ultrasound crossing is 30000Hz, the wavelength of ultrasound crossing used is

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

So, if 30000Hz ultrasonic waves are used, the vertical vibration interval of the workpiece should not be less than 5 centimeters. For other frequencies of ultrasonic waves, the vibration interval can be calculated similarly. In pure chemical immersion cleaning, the cleaning solution primarily dissolves the pollutants on the surface of the workpiece and gradually penetrates and dissolves into the interior of the pollution layer. In this process, a fully dissolved layer is gradually formed on the surface of the workpiece. This fully dissolved layer isolates fresh chemical cleaning solution from deep pollutants, hindering the continuous dissolution of deep pollutants by the cleaning solution. Assuming that this fully dissolved layer cannot be damaged or removed, the cleaning will be interrupted. It is difficult to thoroughly clean dirty workpieces using pure immersion cleaning methods. The effect of using ultrasonic "micro brushes" can damage the dissolved and full layer on the surface. New chemical agents reach deeper pollution layers and continue to dissolve. Ultrasonic waves then continue to damage the newly formed dissolved and full layer. This cycle continues until the workpiece is cleaned thoroughly.

3) Rinse off

Rinsing is to thoroughly clean up any residual cleaning solution or other dirt on the workpiece, making it cleaner before drying. The residue on the workpiece will be difficult to clean up after drying. In the industrial field, deionized water is generally used for rinsing, using deionized water instead of tap water for rinsing. This can prevent impurities and pollutants in tap water from remaining on the workpiece. However, deionized water has strong corrosiveness and can cause corrosion to the workpiece. So, a certain amount of rust inhibitor must be added to deionized water in order to rinse the workpiece and prevent it from rusting during the rinsing and drying process.

4) Drying

The cleaned workpiece is usually placed in an oven for drying, which includes a box, drainage pipeline, heating system, exhaust system, and temperature control system. Eternal Joy Entertainment has a vaporization temperature of 100 ℃, so the baking temperature must be greater than 100 ℃, preferably between 110 ℃ and 130 ℃. This can quickly evaporate moisture and dry the workpiece without requiring a long period of cooling due to the high temperature of the workpiece after drying.

Article source: Jiangmen Ultrasonic Cleaning Machine http://www.kpzfcsb.com/