Ceramic plungers and pistons reciprocate inside a bore, displacing fluid or transmitting motion. They are used where steel would score, corrode or wear the bore out.
Zirconia plungers are chosen for metering and dosing pumps where accuracy and seal life come first. The material takes a very fine polished finish, and its low friction against seal materials reduces both wear and drive power.
Yttria-stabilised zirconia is the toughest of the engineering oxides, with 8-10 MPa·m½ fracture toughness and flexural strength to 1200 MPa. It absorbs the impact and side loads that would crack alumina, and it carries the lowest thermal conductivity of the structural ceramics here.
Two limits apply. Continuous service above roughly 800-1000°C destabilises the metastable tetragonal phase, and moisture between 200 and 300°C can trigger low-temperature degradation, so stabiliser grade is matched to the duty.
Specifications
| Diameter | 5-80 mm |
| Length | up to 400 mm |
| Cylindricity | 0.005 mm |
| Diameter tolerance | ±0.005 mm ground |
| Surface finish | Ra 0.4 µm ground, Ra 0.2 µm polished |
| Straightness | 0.02 mm per 100 mm |
| End form | flat, domed, grooved or threaded |
Zirconia Properties
| Composition | Yttria-stabilised zirconia (Y-TZP) |
| Density | 6.00-6.05 g/cm³ |
| Vickers hardness | 1200-1350 HV |
| Flexural strength | 900-1200 MPa |
| Fracture toughness | 8-10 MPa·m½ |
| Max. service temperature | 800-1000°C |
| Thermal conductivity | 2-3 W/m·K |
| Thermal expansion (20-1000°C) | 10.0 ×10⁻⁶/K |
Machining and Tolerances
Plungers are centreless ground then lapped to size and finish. Surface finish matters more than the number suggests: a plunger polished to Ra 0.2 µm will outlast one at Ra 0.4 µm by a wide margin because it stops abrading the seal.
Where It Is Used
- High-pressure pump plungers in water jetting and dosing
- Metering pump pistons in chemical and pharmaceutical dosing
- Valve and dispensing pistons in filling equipment
- Pump components in HPLC and analytical instruments
- Wear pistons for slurry and abrasive fluid service
Frequently Asked Questions
What finish do you recommend for a seal running face?
Ra 0.2 µm polished, and smoother where the seal material allows it. Seals fail from abrasion long before the ceramic itself wears, so the best value in a plunger is usually the finish rather than the grade.
Can the plunger be joined to a metal drive?
Yes, and it is worth designing carefully. We recommend a compliant interface or a bonded joint that does not load the ceramic in tension, since ceramic carries compression far better than tension or bending.