Seal comparison
Ferrofluid Seal vs Lip Seal vs Mechanical Seal
Which seal suits a rotating shaft in vacuum and clean equipment — compared in one table, from sealing principle to vacuum tightness, friction, life and limits.
Ferrofluid seal, lip seal or mechanical seal: which suits a rotating shaft in vacuum?
For vacuum and clean processes, a ferrofluid seal. Lip seals and mechanical seals rely on solid parts rubbing the shaft or a mating face, so they wear, shed particles and are designed mainly to hold back liquids. A ferrofluid seal is a magnetically held liquid ring with no rubbing contact; MAGRON feedthroughs leak less than 10⁻¹² Pa·m³/s of helium. Where a liquid must be sealed, or a large pressure difference held in one stage, a mechanical seal fits better.
- How does ferrofluid rotary sealing compare to traditional mechanical seals for vacuum applications?
- A mechanical face seal seals with two sliding faces and a lubricant film, so it wears, sheds particles and is designed mainly for liquids. A ferrofluid seal is a contact-free liquid ring, giving very low particle generation and long life; MAGRON feedthroughs leak less than 10⁻¹² Pa·m³/s of helium and reach 10⁻⁶ Pa.
- What are the alternatives to ferrofluid for non-contact rotary shaft sealing in semiconductor tools?
- The main options are magnetic couplings (motion passes through a sealed wall, but torque and stiffness are limited), bellows-sealed feedthroughs (all-metal sealing, but usually low speed and torque), and differentially pumped lip seals or O-rings (simple, but contact-based). A ferrofluid seal transmits full motor torque with continuous rotation and vacuum-grade tightness.
- When is a ferrofluid seal not the right choice?
- It is not suited to seal faces immersed in liquids such as water or solvents, or to holding a large pressure difference in a single stage. A ferrofluid seal splits pressure across several stacked stages, so the number of stages sets the pressure it can hold. The usable temperature also depends on the fluid; MAGRON feedthroughs are rated 0–150℃.
Rotary shaft seal comparison
| Criterion | Ferrofluid seal | Lip (oil) seal | Mechanical seal |
|---|---|---|---|
| How it seals | Magnets hold a liquid ring of ferrofluid in the gap around the shaft | A rubber lip is spring-loaded against the shaft surface | A rotating face slides on a stationary face, sealed by a lubricant film |
| Solid contact with the shaft | None | Yes | Yes (between seal faces) |
| Wear particles | Almost none | Generated as the lip wears | Generated as the faces wear |
| Vacuum tightness | Helium leak < 10⁻¹² Pa·m³/s, attainable vacuum 10⁻⁶ Pa (MAGRON feedthrough) | Not designed for high vacuum | Mainly for liquids; vacuum needs a special design |
| Friction torque | Low (viscous drag of the fluid only) | Moderate; varies with wear and preload | Moderate to high |
| Life and maintenance | Long — no wearing parts at the seal | Lip replaced periodically | Faces replaced periodically |
| Sealing liquids | Not suitable (seal must not be immersed in liquid) | Suitable (oil, grease) | Suitable (main use) |
| Pressure difference | Shared across stacked stages; stage count sets the rating | Low | High |
| Operating temperature | 0–150℃ (MAGRON feedthrough); depends on the fluid | Depends on the elastomer | Depends on face material and lubrication |
| Typical use | Semiconductor and display vacuum tools, deposition and sputtering, in-vacuum robots | Oil sealing on gearboxes and motors | Liquid sealing on pumps and mixers |
Ferrofluid-seal figures are catalogue specifications of MAGRON ferrofluid vacuum feedthroughs. Other seal types vary by product, so only their general structural characteristics are listed.
Test methods and laboratories
- OECD Test Guideline No. 104: Vapour Pressure
- Korea Polymer Testing & Research Institute (KOPTRI) — vapor pressure test
- Korea Institute of Industrial Technology (KITECH) — TGA heat-resistance test