About our technologies

History of Rigaku’s magnetic fluid seals

Rigaku started producing magnetic fluid seals in 1978 when the company designed and developed as a shaft seal for the X-ray generator of internally manufactured X-ray diffractometer. In this unit, the magnetic fluid seal is used under demanding conditions such as high-speed rotation, high vacuum retention and water cooling.
By developing a unique magnetic circuit configuration, Rigaku successfully completed a rotary fluid seal that was able to withstand these severe operating conditions.

Rotating anode X-ray generator
Rigaku X-ray diffractometer

In the 1990s, to respond to the increase in demand of magnetic fluid seals for semiconductor manufacturing equipment, which is typically represented by CVD equipment, external sales of seal units became the main business.

Since 2001, we have unified our business into a magnetic fluid seal business. As a Rigaku Group company for the manufacture and sales of magnetic fluid seals, we have transactions with client companies not only in the field of semiconductor manufacturing equipment but also in a wide range of fields such as FPD equipment and analysis instruments.

Business results of Rigaku

Number of
client companies

Annual unit sales

Percentage of
custom-made products

We have been selling magnetic fluid seals for over 30 years, with our number of client companies reaching 1400 so far. Currently, we sell as many as 3500 seal units annually, and custom-made products dedicated to the use in customer’s equipment account for 60% of them.
With the experience and design capabilities obtained over the past 30 years, we manufacture and complete products according to the customer’s request.
Please see the Special-Order Products page below for details.

Manufacturing environment

Our manufacturing facilities are located on the premises of Rigaku Corporation in Akishima-shi, Tokyo, and we mainly manufacture products domestically.
Parts are cleaned thoroughly in a clean room before the assembly process, securing a cleanliness of products that is suitable even for precision electric and electronic equipment.

Magnetic circuit configuration unique to Rigaku magnetic fluid seals

In Rigaku magnetic fluid seals, independent multiple magnetic circuits are formed, by arranging the same pole of magnets to face each other across the pole piece whose tip is split in two. With the repulsion effect between the two adjacent magnetic fields, the magnetic flux focuses on the tips of the pole piece and the magnetic fluid is firmly held there. In this way, each stage of seal can withstand a higher pressure. This enables more compact-sized magnetic fluid seals.
Also, due to the magnetic circuit structure with high pressure resistance, the gap between the pole piece and the rotary shaft can be increased, which enables high-speed rotation and large diameter seal design.

Magnetic fluids for Rigaku

Magnetic fluids used in Rigaku’s magnetic fluid seal units can be divided into two major types: a type for general vacuum and another type for active gases.
The magnetic fluid type for general vacuum is mainly used for medium vacuum / inert gases and also suitable for high-speed rotation.
The magnetic fluid type for active gases can withstand the highly-reactive gases used for CVD and etching. Two grades are offered according to the difference in heat resisting temperature. The type for high-temperature active gas has a high heat resistance and is a clean magnetic fluid that can suppress the evaporation of base oil, even at high temperatures. We will offer a magnetic fluid that best suits your operating conditions.

The “vapor-temperature characteristics” graph is called a “vapor pressure curve”, showing the relation between the vapor pressure and the temperature of a magnetic fluid.
It indicates that the fluid evaporates less when the vapor pressure is lower, even at high temperature or high vacuum, and the amount of generated out gas that can cause contamination also decreases.

Vapor pressure – Temperature characteristics graph
Magnetic fluid for high-temperature active gas
Amount of out gas 180℃ 10 minutes 1wtppm or less
Vapor pressure [Pa] at 20℃ 6.1x10-14

Vapor pressure curve: Precaution

The vapor pressure curve above does not guarantee the operability and the service life of magnetic fluid seals.
The recommended operating pressure in the actual equipment should be more than one hundred times that of the saturation vapor pressure of magnetic fluid.

Example of use: When the temperature at the point for mounting the magnetic fluid seal is 100℃

  • It is recommended to use a magnetic fluid for active gas at a pressure higher than 10-3Pa.
  • It is recommended to use a magnetic fluid for high-temperature active gas at a pressure higher than 10-7Pa.
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