The coating technology of vacuum coating machine has been popularized in all aspects of our lives, including tableware, lamps, household appliances, showers, automobiles, digital products, knives, etc., including aircraft carriers. The coating technology is so widely used, and the number of talents in the industry is also gradually increasing, so what basic knowledge of the coating technology of the vacuum coating machine should be mastered when new people enter the vacuum industry? We have compiled some of them in the hope that they can help us:

Vacuum technology is a necessary technology to establish a physical environment lower than atmospheric pressure and carry out process manufacturing, physical measurement and scientific experiments in this environment. Vacuum technology mainly includes vacuum acquisition, vacuum measurement, vacuum leak detection and vacuum application. In the development of vacuum technology, these four aspects of technology are mutually reinforcing.
Vacuum refers to a given space of gas below atmospheric pressure, that is, a given space in which the number of gas molecules in each cubic centimeter space is about less than 250 billion. Vacuum is relative to atmospheric pressure, not that there is no matter in space. With the lowest pressure obtained by modern air extraction methods, hundreds of molecules still exist in every cubic centimeter of space. Gas rarefaction is an objective measurement of vacuum, and the most direct physical measurement is the number of gas molecules in unit volume. The smaller the molecular density of the gas, the lower the gas pressure, and the higher the vacuum. However, due to historical reasons, measuring vacuum is usually expressed by pressure. 1 Vacuum is usually measured in Pascal or Torr.

1： History
As far back as 1643, Italian physicist Torricelli found that there was atmosphere and atmospheric pressure in vacuum and natural space. When he filled a long glass tube with mercury, which was closed at one end, and stood upside down in the mercury tank, he found that the mercury level in the tube dropped until it was 76 cm away from the mercury level outside the tube. Torricelli believed that the space on the mercury surface of the glass tube was vacuum, and the 76 cm high mercury column was due to the atmospheric pressure.
In 1650, Otto von Grick of Germany made the piston vacuum pump. In 1654, he carried out the famous Madeborg hemispherical experiment in Madeborg: two copper hemispheres with a diameter of 14 inches (35.5 cm) were evacuated by a vacuum pump, and then two groups of eight horses pulled the copper ball in opposite directions, never separating the two hemispheres. This famous experiment once again proved that there is atmosphere in space, and the atmosphere has huge pressure. To commemorate Torricelli's important discoveries and contributions to science, the vacuum pressure unit used in the past was named after him.
In the middle and late 19th century, the success of the British Industrial Revolution promoted the development of productivity and scientific experiments, as well as the development of vacuum technology. In 1850 and 1865, the mercury column vacuum pump and mercury drop vacuum pump were successively invented, thus the incandescent bulb (1879), cathode ray tube (1879), dewar bottle (1893) and compression vacuum gauge (1874) were developed. The application of compression vacuum gauge makes it possible to measure low pressure for the first time.
At the beginning of the 20th century, the appearance of vacuum tubes promoted the development of vacuum technology to high vacuum. From 1935 to 1937, gas ballast vacuum pump, oil diffusion pump and cold cathode ionization meter were invented. These achievements and the Pilani vacuum gauge made in 1906 are still commonly used in most vacuum systems.
After 1940, vacuum applications were expanded to nuclear research (cyclotron and isotope separation), vacuum metallurgy, vacuum coating and freeze drying, and vacuum technology began to become an independent discipline. During the Second World War, the need for atomic physics experiments and the need for high-quality electronic vacuum devices for communications further promoted the development of vacuum technology.

2： Application field
(1) Vacuum environment on the earth
On the earth, it is usually to pump air into a specific enclosed space to obtain vacuum. The equipment used for pumping is called vacuum pump. The vacuum pump made earlier, with low pumping speed and low limit vacuum, is difficult to meet the needs of production and scientific experiments. Later, a series of vacuum pumps with different pumping mechanisms were made, and the pumping speed and limit vacuum were continuously improved. For example, the pumping rate of cryogenic pump can reach 60000 L/s, and the limit vacuum can reach the order of one hundred billionth of a Pa.

(2) Needed
In order to ensure that the vacuum system can reach and maintain the vacuum required by the work, in addition to the need to be equipped with a suitable vacuum pump with good air extraction performance, the vacuum system or its parts must also undergo strict leak detection to eliminate leaks that damage the vacuum. Low (coarse) vacuum, medium vacuum and high vacuum systems generally use air pressure for leak detection; For ultra-high vacuum systems, after the general leak detection method is used for rough inspection, leak detectors with high sensitivity, such as halogen leak detector and mass spectrometer leak detector, shall be used for leak detection.

(3) Application
With the development of vacuum acquisition technology, vacuum applications are increasingly expanding to all aspects of industry and scientific research. Vacuum application refers to the use of the physical environment of rarefied gas to complete certain specific tasks. Some use this environment to manufacture products or equipment, such as light bulbs, electron tubes and accelerators. These products are always kept vacuum during use; Others only take vacuum as a step in production, and the final product is used in atmospheric environment, such as vacuum coating, vacuum drying and vacuum impregnation.
Vacuum coating machine has a wide range of applications, mainly including low vacuum, medium vacuum, high vacuum and ultra-high vacuum applications. Low vacuum refers to the use of the pressure difference obtained by low (coarse) vacuum to clamp, lift and transport materials, as well as dust collection and filtration, such as vacuum cleaners and vacuum suction cups.
Medium vacuum is generally used to remove gas or water absorbed or dissolved in materials, manufacture light bulbs, vacuum metallurgy and thermal insulation. For example, if condensed milk is produced by vacuum concentration, the water in the milk can be evaporated without heating.
Vacuum metallurgy can protect active metals from oxidation during melting, casting and sintering, such as vacuum melting of active refractory metals such as tungsten, molybdenum, tantalum, niobium, titanium and zirconium; Vacuum steelmaking can avoid the burning of a few added elements at high temperatures and the infiltration of harmful gases and impurities, which can improve the quality of steel.
High vacuum can be used for thermal insulation, electrical insulation and avoiding the collision of molecular electrons and ions. The free path of molecules in high vacuum is larger than the linear size of the container, so high vacuum can be used in electron tubes, phototubes, cathode ray tubes, X-ray tubes, accelerators, mass spectrometers, electron microscopes and other devices to avoid collisions between molecules, electrons and ions. This feature can also be applied to vacuum coating for optical, electrical or plating decoration.
The energy transmission in outer space is similar to that in ultrahigh vacuum, so ultrahigh vacuum can be used for space simulation. Under ultra-high vacuum conditions, the formation of monolayer takes a long time (in hours), which can be used to study the surface characteristics, such as friction, adhesion and emission, before a surface is polluted by gas.