What causes deep scratches and edge chipping on glass after white fused alumina blasting?

Glass is a brittle material with concentrated stress at its edges and corners. Deep scratches and chipping are caused by four major factors: white fused alumina selection, process parameters, equipment reclaiming system and the condition of glass substrate.

1. White Fused Alumina Related Causes

• Using excessively coarse grit sizes causes glass damage. Operators often apply coarse grades like 10#, 12# and 16# on qualified glass panels incorrectly.

  For architectural LOW-E glass rework, workers primarily use F80 and F100 white fused alumina, while F120 and F150 grades suit glass substrate pretreatment. Residual oversized particles from the white fused alumina screening process create deep scratches and edge chipping during blasting operations.

  Over-recycling white fused alumina produces sharp broken abrasive fragments. Exceeding the valid recycle cycles generates large amounts of sharp debris. Simply recycling the abrasive without removing fine powders allows these sharp fragments to circulate continuously and scratch the glass surface repeatedly.

  

2. Blasting Process Parameters

‑ Excessive blasting pressure: Pressure above 0.42 MPa brings excessive impact kinetic energy of abrasive particles.

Recommended pressure for F80 / F100 white fused alumina: 0.33‑0.42 MPa

Recommended pressure for F120 / F150 white fused alumina: 0.30‑0.38 MPa ‑ Too short nozzle‑to‑glass distance leads to concentrated impact force.

3. Problems of Blasting‑Booth Reclaiming Equipment

‑ Without air‑wash classifier, sharp fractured particles keep circulating inside the system and continuously scratch the substrate. ‑ Magnetic separator works normally while the classifier malfunctions. Only iron impurities are removed, yet sharp broken grit fragments remain. ‑ For coating‑glass blasting booth, both air‑wash classifier and magnetic separator are mandatory.

4. Intrinsic Factors of Glass Substrate

‑ Incoming glass already has micro‑chips or hidden cracks on edges. Blasting impact amplifies existing defects and shows up as post‑blasting chipping. ‑ Thin‑wall glass (3‑5 mm) has poor impact resistance, and is more susceptible to chipping than thick‑wall glass under identical blasting parameters.

Corrective Countermeasures

1. Select suitable grit grades: Use F80 / F100 white fused alumina for qualified LOW‑E coating stripping; choose F100 preferably for thin glass.
2. Reduce blasting pressure; maintain nozzle stand‑off at 25‑35 cm, adopt 30‑45° oblique blasting; avoid direct perpendicular impact on glass edges.
3. Inspect and repair air‑wash classifier; discharge sharp fine fractured particles timely. Stick to 5‑8 valid recycle cycles, mix 70 % used grit with 30 % new grit.
4. Inspect glass edges before blasting; sort out panels with inherent chipping or hidden cracks in advance.