SEALING TECHNOLOGY
Magnetic fluids are currently used as vacuum seals where rotary motion is to be transmitted into the vacuum vessel and in a wide range of applications where an hermetic seal is a prime requirement.
MAGNETIC FLUID DESCRIPTION
Composition
|
Colloidal suspension of ferrite particles in polar or non-polar carrier liquids |
| Particle size |
Mean core particle size 10 nm |
| Viscosity |
1,000 - 25,000 cP at 27 deg. C.
|
| Temperature range: |
-40°C to 160°C depending on carrier liquid. |
| Density |
1.3 to 2.2 g/ml depending on fluid type. |
| Appearance |
Black liquid.
|
VAPOUR PRESSURE DATA FOR SEALING FLUID PRODUCTS
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PROCESS PARAMETERS
- Hermetic sealing from rough to high vacuums of 10-9 mbar or better
- Standard positive pressure capability of 2 bar, higher pressures optional
- Reactive gas compatible with appropriate magnetic fluid
- Wide speed range from indexing to many thousands of rev/min
- Low friction, slip-stick free rotation with high torque transmission
FEEDTHROUGH FEATURES
- Leak rate of 1E-12 standard cc helium/second
- Maintenance free, life of 3 years or longer depending on process
- Water-cooled for high temperature compatibility and cantilevered for aggressive processes
- Designs such as, module seals, cartridge seals or coaxial shaft seals are available
- Hollow shaft seals for passage of services, water, power or signals, into vacuum chamber
- Non-contaminating high reliability design
APPLICATION AREAS
Magnetic fluid seals have achieved global acceptance following extensive use in computer disk drives, vacuum processing, semiconductor and other industries.
SEMICONDUCTOR USAGE
Many semiconductor fabrication techniques use high vacuum equipment. Production equipment is usually single process. R&D and cluster tools often carry out single and multiple processes and a piece of equipment may use a variety of feedthroughs. Some perform simple tasks, such as rotation, whilst others perform multi-function roles, such as rotation and transportation of services in to the vacuum chamber.
INDUSTRIAL USAGE
The industrial use of magnetic fluid feedthroughs and seals falls into two categories:
- Industrial procedures that involve the use of high vacuum processing equipment
- Processing techniques that require a low friction, hermetic seal which excludes particulate or gases, not necessarily under vacuum.
SEAL FUNCTIONS
Provides rotary motion into a vacuum or process chamber or a load lock.
Hermetically seals the chamber and maintain vacuum and/or pressure integrity.
Introduces process gases and/or coolants in to the chamber or wafer support mechanisms.
Provides particulate exclusion seal in robotic wafer transport mechanisms or other sensitive areas.
Provides very low friction, smooth rotary motion with maximum torque transmission.
PROCESSES
- Ion implantation
- Ion beam and RF etching
- Epi deposition
- PVD (Physical Vapor Deposition – sputtering, electron beam gun)
- CVD (Chemical Vapor Deposition)
- MOCVD (Metal Organic Chemical Vapor Deposition)
APPLICATION AREAS
- Vacuum furnaces and heat treatment equipment
- Excimer and CO2 lasers
- Land and airborne surveillance, guidance and sensor systems
- X-ray rotating anode generators
- Gas unions for the manufacture of high efficiency lamps
- Fibre optic pre-form manufacture
Other areas that can benefit from this technology are:
- Environmental seals
- Aerospace & defence
- Laser systems