Expansion Bolt Guide: Selection to Installation (Part 2)

5. Smart Selection: 3 Steps

• Step 1 – Load: Static → 50% safety factor; Dynamic (vibration) → 30% factor. Example: M8 bolt → 2.25 kN static / 1.35 kN dynamic capacity.

• Step 2 – Substrate: Concrete/brick → standard; Hollow/gypsum → hollow wall bolt; Steel → serrated type; Tile/glass → rubber cushion.

• Step 3 – Environment: Dry indoor → zinc-plated; Humid → hot-dip galvanized; Outdoor/corrosive → SS304; High temp → SS310S. Anti-loosening: static → spring washer; dynamic → spring washer + nylon lock nut.

6. Installation: Details Matter

• Preparation: Impact drill (≥500W for concrete), correct bit, brush. Substrate ≥C20 concrete or solid brick.

• Drilling: Hole dia = sleeve OD (e.g., M8 → 10 mm bit). Depth = bolt length – material thickness + 5 mm. Keep perpendicular; clean dust.

• Tightening: Assemble: bolt → flat washer → spring washer → fixture → sleeve. Hand-tighten then torque gradually. M6–M10 → tighten fully; M12+ → use torque wrench.

• Inspection: Shake test; 1.2x rated load for 5 minutes. Outdoor → apply anti-rust paint on head/nut.

7. Common Problems & Fixes

• Loosening: Weak substrate → switch to hollow wall bolt or steel plate. Wrong hole depth → re-drill. Low torque → re-tighten with torque wrench.

• Installation difficulty: Wrong bit → change bit. Hole tilted or debris → straighten, clean, or re-drill.

• Failure: Corrosion → replace with SS304. Fatigue → add bolts or upgrade grade. Never install near edge (<50 mm), under reversing loads, or for personnel/hazardous support.

8. Maintenance & Lifespan

• Inspect: Indoor static → every 6 months; outdoor/dynamic → monthly. Check looseness, rust, cracks, tilting.

• Anti-corrosion: Indoor → paint yearly. Outdoor → check coating every 6 months. SS304 in marine → rinse with fresh water.

• Action: Loose → unload, re-torque. Crack/severe rust → replace. Tilting fixture → realign, add bolts.

Expansion bolts are basic but critical. Master selection, installation, and maintenance to ensure safety and reliability.