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

Eliminates risk of contamination from mechanical wear debris
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	FZM	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 (HV1)	GPa	10.7	23	7.2 (HV10)
Compressive strength	MPa	2000	> 2500	1700
Bending strength σ_m	MPa	500 (DIN EN 843-1)	450	500
Modulus of elasticity (E-modulus)	GPa	185 (static)	440	210
Poisson ratio	-	0.3	0.17	0.3
Fracture toughness K_Ic	MPa*m^0.5	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	-
Characteristic values may vary depending on shape of products and service conditions.

Examples

SSiC_female and male bearings_290x280.jpg — Female bearing made of silicon carbide StarCeram^© SSiC, male bearing made of zirconium oxide FZM

Shrink fit ceramic in metal housings_290x180.jpg — Shrink fit ceramic in metal housing

Male bearing assembly on tank plate_290x180.jpg — Male bearing assembly on tank plate

Stirrers made of Alumina_290x180px.jpg — Stirrers made of alumina

Near net shape forming method (F-Molding)

For stirrers elements Kyocera can produce complex shape elements using new near net shape forming method (F-Molding). In this method elements are casted directly to a parts shape without need of green machining before sintering. This way machining costs are reduced in comparison to other ceramic production methods.