What Is a Vacuum Seal?
A vacuum seal is a sealing device that utilizes the properties of a liquid called magnetic fluid, which is attracted by a magnet.
The magnetic fluid is attracted to the magnet like iron sand while holding the fluid. The magnets in the vacuum seal hold the magnetic fluid, sealing the gap between the device and the joint. This prevents air, gases, and particulates from entering the sealed object, thereby maintaining a vacuum environment.
The holding force of the magnetic fluid is determined by the strength of the magnet (magnetic force), so the stronger the magnetic force, the greater the pressure resistance of the ring of magnetic fluid.
Use of Vacuum Seals
Vacuum seals are used to maintain quality when manufacturing products in which impurities, air, or moisture are strictly prohibited. Due to their high effectiveness in blocking fluid magnetism, they are often used in manufacturing industries with high vacuum, such as semiconductor, solar cell, or OLED panel manufacturing for smart phones.
Under these manufacturing conditions, vacuum seals have a very wide range of applications, as they are required to save energy and make manufacturing equipment more compact.
1. Semiconductors
In semiconductor manufacturing, vacuum seals are used in sputtering, CVD, and ion implantation equipment. These require a high-vacuum environment with vacuum seals to form uniform thin films and to control the electrical properties of semiconductors through ion implantation.
2. Solar Cells
They are also used in monocrystalline pulling equipment for the production of silicon ingots, which are indispensable for the manufacture of solar cells. Silicon ingots are vacuumed to prevent contamination from dust and dirt and oxidation by air during the manufacturing process. Vacuum seals are utilized to maintain a vacuum environment inside the equipment.
3. Organic EL
In OLED, vacuum seals are required for vacuum deposition to form thin films of OLED elements. In recent years, the demand for vacuum seals has increased as the demand for OLED has grown from LCDs.
Principle of Vacuum Seals
Vacuum seals use a liquid called magnetic fluid. A magnetic fluid consists of three components: magnetic nano-sized particles (magnetic particles), a surfactant, and a base liquid, such as water or oil.
Magnetic particles usually agglomerate with each other like magnets (spiking phenomenon), and surfactants are generally used to prevent this. Since surfactants have polarity, the same polarity repels each other. As a result, it is possible to create a stable magnetic fluid as a colloidal solution without agglomeration.
In addition to the magnetic fluid, the vacuum seal uses a permanent magnet and a rotating shaft. The vacuum seal has a mechanism that seals while rotating at high speed, but prevents contact between the rotating shaft and the magnetic pole material or permanent magnet. Since solids do not come into contact with each other like oil sheets, there is no need to worry about friction.
Structure of Vacuum Seals
A wide range of shaft shapes of seals are manufactured, from small products of a few millimeters to large products of several meters in scale. Vacuum seals consist of a rotating shaft and a pole piece with strong magnetism, and a magnetic field is generated in the gap between the two materials.
By guiding the magnetic fluid through the gap in this magnetic field, the magnetic fluid forms an O-ring and adheres closely to the pole piece, preventing intrusion from the outside.
Features of Vacuum Seal
Because of the contact between the rotating shaft and the fluid, the rotating shaft can be rotated as desired without abrasion. Furthermore, since the magnetic fluid seals the gap along the magnetic force lines, it does not flow out due to pressure differences, thus enabling the maintenance of a vacuum environment.
The greater the magnetic force, the higher the pressure resistance of the ring formed by the magnetic fluid. By forming the ring in several stages, a pressure-resistant vacuum seal is completed and can withstand greater pressures.
The inert nature of the magnetic fluid and its low vapor pressure also have a bearing on the life of the vacuum seal. The advantage of using a magnetic fluid that does not react easily is that it is resistant to deterioration and can be used for a long period.