Why investment casting
Impellers, bodies and trim parts get their hydraulic passages as cast, with a fine surface that supports efficiency and reduces machining to the sealing faces.
Components
- Impellers
- Diffusers
- Casings
- Valve bodies
- Discs
- Balls
- Seats and stems
Materials
CF8M / CF3M, duplex grades, CA6NM, bronzes, nickel alloys.
Frequently used alloys
| Grade | Type | Standard |
|---|---|---|
| CF8M | Mo-bearing austenitic stainless steel, cast 316 type 316 type | ASTM A351/A351M, A743/A743M |
| GX5CrNiMo19-11-2 (1.4408) | Mo-bearing austenitic stainless steel, cast 316 type 316 type | EN 10283 |
| CD3MN (4A) | 22Cr-5Ni-Mo-N duplex stainless steel 2205 type (Uranus® 45N, SAF 2205®) | ASTM A890/A890M, A995/A995M Gr. 4A |
| CA6NM | 13Cr-4Ni low-carbon martensitic stainless steel 13-4 type (F6NM) | ASTM A743/A743M, A487/A487M |
| CN7M | High-nickel austenitic alloy with Mo and Cu, cast Alloy 20 type Alloy 20 type (Carpenter 20Cb-3®, Durimet 20®) | ASTM A351/A351M, A743/A743M, A744/A744M |
Typical requirements
Hydraulic surfaces benefit from the as-cast finish and thin vanes; pressure tightness depends on sound feeding of flanges and junctions.
- Pressure tightness
- Smooth wetted surfaces
- Balanced, concentric geometry
Related engineering topics
Surface finish
Surface texture of investment castings: Ra and Rz, typical as-cast, blasted, ground and machined conditions, how to specify surface requirements and visual acceptance standards.
Non-destructive testing
NDT methods for investment castings: liquid penetrant, magnetic particle, radiographic and ultrasonic testing, computed tomography, leak testing, personnel qualification and acceptance levels.
Tolerances
Tolerancing of investment castings: ISO 8062-3 casting tolerance grades, VDG P 690, geometrical tolerances to ISO 1101, datum systems, machining allowance, shrinkage and distortion.