Magnetic Mixers Applications
Ceramic Sliding Bearings for Magnetic Mixers
CERAMIC SLIDING BEARINGS
Key components of magnetic mixers are ceramic sliding bearings which are in direct contact with the mixed product and additionally are exposed to temperature changes and cleaning chemicals.
Usually the male bearing is made of zirconium oxide and the female bearing is made of silicon carbide. The static, robust male bearing is attached to the vessel's tank plate and the rotating female bearing is integrated and sealed with the mixing head. The inner bearing made of zirconium oxide has increased resistance to impacts and damage from sudden rotor settling or during assembly / disassembly of the mixer. The outer bearing made of silicon carbide provides superior abrasion resistance and low surface roughness.
Thanks to our extensive mechanical machining facility we can achieve high quality surfaces with minimal friction in the operating mode and with reduced breakage risk in dry run conditions.
Combination of zirconium oxide FZM and silicon carbide StarCeram© S
- Zirconium oxide (FZM) is used because of high impact resistance (high flexibility/low E-Modulus)
- Silicon carbide (SSiC) is used because of hardness and wear resistance
Why ceramics?
Ceramic bearings are one of the most critical parts in the mixer:
- Direct contact with the high value product (product lubricated)
- Exposure to cleaning chemicals and temperature cycling
Main advantages
- Corrosion and abrasion resistance against mixed media
- No grinding between metal parts
- Biocompatibility: complying with FDA rules and USP Class VI certification required for pharmaceutical and biotechnology industries
- Good thermo shock resistance CIP /SIP possible (clean in place / sterilization in place)
- Perfect finish and surface quality Ra < 0,5 μm
- No product residue or bacterial growth
- Low shear forces (particle generation below detectable levels)
- Minimalized drag force
- Emergency dry run possible
- Tight tolerances for perfect coupling between bearings (up to 5 μm)
- Simple design eliminates entrapments of product (no product stagnation between bearing surfaces)
- Easy maintenance - ceramic bearing parts can be replaced by users on site
Our strengths
- Long term proven quality in application
- One source for both ceramic materials
- High precision grinding technologies
- Metal-ceramic joints or threads in ceramics possible
Material properties
| Properties | Unit | StarCeram© S | Metal | ||
|---|---|---|---|---|---|
| Main components | - | ZrO2, MgO | SiC | Stainless steel | |
| Properties of microstructure | |||||
| Density | g/cm³ | ≥ 5.70 | 3.16 | 7.8 | |
| Open porosity | Vol. % | 0 | 0 | 0 | |
| Water absorption | % | 0 | 0 | - | |
| Average crystal size | μm | 50 | - | - | |
| Mechanical properties | |||||
| Hardness (DPH/HRC) | GPa | 10.7 | 23 | 61 | |
| Compressive strength | MPa | 2000 | - | 1700 | |
| Bending strength σm | MPa | 500 (DIN EN 843-1) | 450 | 2300 | |
| Modulus of elasticity (E-modulus) | GPa | 185 (static) | 440 | 210 | |
| Poisson ratio | - | 0.3 | 0.17 | 0.3 | |
| Fracture toughness KIc | MPa*m0.5 | 6.3 (SEVNB) | 2-3 | - | |
| Thermal properties | |||||
| Max. operating temperature | °C | 900 | 1400 | 120-280 | |
| Specific heat 20 °C | J/(kg*K) | 400 | 670 | 502 | |
| Thermal conductivity | W/(m*K) | 3 | 200 | 45 | |
| Thermal expansion coefficient 20-300 °C | 10-6/K | 10.6 | 4.4 | 12 | |
| Electrical properties | |||||
| Specific electrical resistance 20 °C | Ω•cm | 1010 | 108 | 10-6 | |
| Typical colour | - | yellow | black | - |
Examples
Female bearing made of silicon carbide StarCeram© SSiC, male bearing made of zirconium oxide FZM
Shrink fit ceramic in metal housing
Male bearing assembly on tank plate
Stirrers made of alumina