Shot Blasting in Investment Casting

Shot blasting is a process that uses high-speed rotating impellers to propel steel shot or stainless steel shot to impact the surface of castings. It is one of the most common post-cleaning procedures in investment casting.

Core Functions of Shot Blasting for Investment Castings

1. Removal of Surface Contaminants (Basic Function)

Strip residual mould shell, refractory materials, oxide scales and sintered layers left on castings after shell removal in investment casting.

Clear burnt-on sand, flash and debris on gates and crevices.

2. Surface Strengthening (Key Function, not merely cleaning)

High-speed shot bombardment causes plastic deformation on the metal surface and generates a compressive stress layer. ✅ Improve fatigue strength, resistance to stress cracking and wear resistance of castings. ✅ Inhibit initiation of service cracks, suitable for loaded components (automotive parts, construction machinery, hardware structural parts).

3. Improvement of Surface Appearance

Eliminate rough casting surfaces, minor flow marks and pits.

Achieve uniform matte metallic finish.

Note: Shot blasting cannot significantly improve dimensional accuracy and cannot replace grinding or machining; it only optimizes surface roughness.Food Pump Casing

4. Auxiliary Inspection (Implicit Function)

After oxide scales are removed by shot blasting, visual inspection and non-destructive testing (Penetrant Testing PT, Magnetic Particle Testing MT) can be carried out conveniently, facilitating detection of tiny pores and cracks.

Application Fields for Investment Castings Requiring Shot Blasting

Automotive Components: Turbo housings, transmission parts, engine valve components, chassis structural castings

Construction Machinery & Hydraulic Parts: Valve bodies, pump housings, connectors, investment cast connecting rods

General Machinery: Gears, bearing housings, fixtures, transmission components

Hardware & Marine Industry: Marine valves, fasteners, lifting fittings

Aerospace Precision Castings: Stainless steel shot is generally adopted to strictly control dust and surface quality

Medical Equipment & Food Machinery Stainless Steel Castings: Clean stainless steel shot is selected.

Distinction between Easily Confirmed Processes

Shot Blasting: Shot ejected by impellers, high efficiency for mass production; performs both cleaning and strengthening.

Sand Blasting: Abrasives driven by compressed air with mild impact force, mostly for fine finishing and local treatment; hardly provides strengthening effect.

Supplementary Notes for Investment Casting Challenges

For thin-wall precision castings, blasting duration, blast power shall be properly controlled. Excessive blasting force may cause casting deformation, over-etching of surfaces and dimensional out-of-tolerance. Select proper abrasives according to material: steel shot for carbon steel castings; stainless steel shot is preferred for stainless steel castings to avoid surface iron contamination and subsequent rusting.