Characteristics of Volute Casting (Axial Flow Pump)
Volute casings typically present the following challenges:
Thin blades and complex curved surfaces: prone to cold laps, shrinkage cavities, and deformation
High precision requirements: guide vane profiles and installation positions directly affect hydraulic efficiency Sensitive to surface defects: porosity, slag inclusions, and pitting can induce hydraulic losses and vibration noise Blade roots and transition zones: susceptible to stress concentration and crack initiation
2) Material Selection (Common)
Materials commonly used for guide vane bodies are generally divided into three categories (specifically based on pump application and medium):
Cast steel: high impact resistance and strength, commonly used in high head and erosive conditions.
Stainless steel/duplex stainless steel castings: suitable for seawater or highly corrosive media.
Bronze/corrosion-resistant alloys (in certain regions/conditions): excellent wear and corrosion resistance, good vibration damping (if your application involves such materials).
Key point: The material of the guide vane body must balance corrosion resistance, erosion resistance, and machinability, while also considering the feasibility of heat treatment and welding processes.
3) Molding Process Routes (Two Mainstream Methods)
A. Sand Casting (e.g., shell molding, water glass sand, etc.)
Wide range of applications and relatively low cost.
Risk factors: thin sections and complex curved surfaces → insufficient feeding, cold joints, and shrinkage defects
Common approaches:
Segmented pouring / optimized riser system (to ensure adequate feeding to hot spots)
Use of more suitable mold sand properties (strength, permeability, coating)
Reinforcement measures in critical thin areas (such as ribs or localized feed gates, depending on structure)
B. Lost Foam Casting (EPC)
Often offers greater advantages for complex curved surfaces and thin-walled components.
Advantages: Easier to achieve cavity details, better blade surface finish
Risks: Impact from mold decomposition products, stricter requirements for pouring conditions
Common methods: Controlling dimensions before and after mold opening, pouring temperature/speed, cavity ventilation, and coating system
Actual selection depends on: your vane body size and weight, wall thickness, allowable cost, as well as target precision and surface roughness for subsequent machining
4) Risering/venting/pouring system considerations (determining defects)
The core of riser design for thin-walled impeller castings is:
Reduce cold shuts: Select the gate position appropriately to ensure thin sections are adequately fed with sufficiently hot metal.
Ensure proper feeding: Implement feed control and hot spot management near the thick-to-thin transition zone at the blade root.
Improve venting capability: Blade cavities are prone to air trapping—optimize vent channels and add localized vents as needed.
Avoid core erosion: Excessive gate velocity may lead to inclusions and core washout defects.
5) Post-processing and quality control (critical)
Axial flow pump guide vane bodies typically require at least:
Pour riser removal, sand cleaning and grinding (avoid rough handling that could damage the leading edge or transition zone of the blade)
Heat treatment/stress relief (depending on material and structure)
Non-destructive testing/inspection
Common methods: Ultrasonic Testing (UT), Radiographic Testing (RT) if necessary (based on material and standard)
Dimensions and appearance: Critical surfaces must not have excessive porosity or cracks Machining
The mating surface between the guide vane body and the hub/guide vane seat
Precision machining of profile/installation surfaces (commonly controlled using CMM or templates/inspection fixtures)
(Optional) Surface strengthening/coating: for corrosion or erosion-resistant conditions
6) Dimensional and hydraulic-related inspection items (recommended to focus on)
The final cast guide vane body must meet both assembly and hydraulic requirements; key inspection items typically include:
Guide vane profile/installation angle (installation angle, spacing, symmetry)
Root seat surface coaxiality/flatness (to prevent accumulation of assembly deviations)
Blade thickness and critical cross-sectional dimensions (deviations at thin-walled sections affect flow passages)
Leading edge/trailing edge contour (surface defects and burrs reduce performance)
Wall thickness and local flaws (non-destructive testing + appropriate thickness measurement)