1. Early Molecular Pump
In 1912, a German named W.Gaede invented the first molecular pump in the world, the diameter of its rotor is 50mm, and there are 8 slots in different sizes on rotors. The revolving speed is 12,000r/min, and the pumping speed is about 1.5L/ s. The working principle of this early pump is same as that of the modern molecular pump, but it is quickly eliminated due to lots of failure so it has not been popularized.
In 1926, M. Siegbahn developed a disk-type molecular pump in the university laboratory in Sweden. Its structure is similar to that of the modern drag-type molecular pump. The pump body has spiral grooves and the rotor is a disk. In 1939, LE BOLD produced two pumps with a diameter of 540mm. The dimensions of the groove are 22mm x 22mm on the inside and 22mm x 1mm on the outside. The revolving speed is 3,700r/min and the pumping speed is 73L/s.
The early molecular pumps are all traction type molecular pumps. With the disadvantages of large volumes, low pumping speeds, small gaps, and many faults, it is subject to many restrictions in application, and therefore it can only be used in some special fields and have not been popularized.
2. The Birth of Turbomolecular Pumps
In 1957, W. Becker of PFEIFFER GmbH in Germany invented a new molecular pump, named turbomolecular pump. Horizontal structure and the pump cavity is equipped with dynamic and static blade rows. The gas enters through the intake port at the center of the pump and flows through the suction channel to both sides of the pump body. The compressed air is discharged by the exhaust port after being compressed by the leaf array. The rotor of this turbomolecular pump is composed of 19 blade rows. As shown in Fig. 2, the diameter is 170mm, the revolving speed is 16,000r/min, and the pumping speed is 140L/s.
In 1966, SENCMA Corporation in France developed a 14 blade rows vertical turbomolecular pump, the rotor diameter is 286mm, revolving speed is 12,000r/min, and pumping speed is 650L/s, which creates the vertical turbomolecular pump pioneer.
There are many manufacturers of molecular pumps in Japan with strong ability to design and produce molecular pumps. In 1971, the Institute of Physical and Chemical Research of Japan successfully developed a 13 rotating blades row molecular pump and a 12 stationary vane rotor molecular pump, the rotor diameter is 300 mm and the revolving speed is12,000 r/min. In 1990, Japan's Osaka Vacuum Company first successfully developed a large-scale molecular pump with a pumping speed of 25,000 L/s.
At present, the basic structure of modern molecular pumps is horizontal and vertical. The horizontal molecular pump has the advantages of uniform force of the rotor, good bearing positioning force state, long service life, stationary rotor position during bearing replacement, and easy maintenance. But the assembly process of the vertical molecular pump is simpler than the horizontal molecular pump, so the development speed of the vertical molecular pump in recent years is very fast.
3. Modern Molecular Pump
Since the birth of the molecular pump, there has been a history of nearly one hundred years. With the continuous advancement of various science and technology, the molecular pump technology has also made many innovations and breakthroughs. The modern molecular pump is more intelligent, flexible, and efficient.
In recent years, with the rapid development of control theory and computer technology and applied to molecular pumps, the molecular pumps have been controlled by computer, and realized the remote control of pump. At the same time, based on information technology, the safety and monitoring systems have led to the development of molecular pumps in the direction of intelligence.
The pumping speed is the core parameter of the molecular pump. Increasing the rotational speed is one of the most direct methods to increase the pumping speed. With the development of the dynamic balancing technology, the molecular pump rotor can smoothly operate at ultra-high speed. And with the development of materials science, the material of the molecular pump rotor has also changed, it can be made of hard aluminum alloy, carbon fiber, titanium alloy and other high hardness materials, which further improved the rotational speed of the rotor.
In recent years, with the development of the semiconductor industry, the molecular pump is required to continuously exhaust a large amount gas in a high-pressure environment and ensure clean vacuum in many cases. The performance of traditional turbomolecular pumps in this environment has dropped a lot and it is difficult to guarantee the design results. In order to make the molecular pump adapt to the high pressure working environment, the traction molecular pump part is added on the original turbo molecular pump, and the turbo molecular pump and the trailing molecular pump are connected in series to form a composite molecular pump (as shown in Figure 3) with the advantages of both turbo molecular pump and the trailing molecular pump.
In addition, a number of new types molecular pumps have emerged in recent years, such as low-temperature molecular pumps that can efficiently extract water molecules, ceramic molecular pumps that can operate under strong magnetic fields and strong corrosion conditions, and magnetic suspension molecular pumps with advantages of contactless support, high-efficiency and high-life.