Issues of insufficient or uneven surface roughness after shot blasting
To address issues of insufficient or uneven surface roughness following shot blasting, the root cause lies in inconsistencies in blasting energy and coverage. The following outlines specific troubleshooting and adjustment measures.
1. Insufficient roughness (overall too smooth)
This condition reduces coating adhesion; solutions focus on three main areas:
1. Increase steel shot size: Shot that is too small lacks sufficient impact force. When high roughness is required, select shot larger than 1.0 mm (e.g., S330 or coarser).
2. Increase blast velocity: Check if the blast wheel speed has dropped, or adjust the flow control valve to increase the initial velocity of the shot.
3. Switch to high-hardness shot: Replace shot if it has become worn and rounded or if the hardness is too low (e.g., use cast steel shot with HRC 40–50).
4. Extend blasting time: Ensure complete coverage to avoid "under-blasting" caused by insufficient processing time.
II. Uneven roughness (inconsistent surface texture)
This manifests as areas of varying roughness—some rough, some smooth—on the same workpiece. Common causes and countermeasures include:
· Blast angle and blind spots: Adjust the blast wheel orientation so the shot strikes the surface at an angle of 30–70 degrees. If necessary, add more blast wheels or perform manual touch-up blasting.
· Workpiece masking/shadowing: Improve hanging methods or fixtures to ensure shot reaches all areas and to eliminate "shadow zones" where the workpiece blocks the blast.
· Uneven shot flow: Check the blast wheel feed hopper or control valve for blockages to ensure a stable supply of shot to each wheel.
· Equipment wear: Inspect and replace worn control cages and vanes; otherwise, the blast pattern will be disrupted, leading to localized insufficient energy.
III. Special cases and quick troubleshooting
· Spent/degraded shot: If the shot contains excessive fines (particle size <0.3 mm) or dust, activate the separator immediately or replace the shot.
· Vibration of thin-walled parts: Secure the workpiece more firmly to prevent vibration during blasting, which can cause uneven impact. Parameter adjustment guidelines:
· For a roughness of Ra 6.3–12.5 µm: S330 (1.0 mm) cast steel shot is recommended, with a velocity of 70–80 m/s.
· For a roughness of Ra 3.2–6.3 µm: S230 (0.7 mm) cast steel shot is recommended, with a velocity of 60–70 m/s.
It is advisable to first check the steel shot for wear and pulverization, as well as the control cage for wear; these two factors are the most common causes of uniformity issues. Would you like me to explain further how to check the control cage for wear?