Aggregate bin does not flow — bridges, rat-holes and wet sand
Symptom
The gate opens but nothing comes out, flow starts and stops, the sand bin stops every morning, or the bin's usable capacity shrinks.
Likely causes
- A bridge (arch) over the outlet, usually in the sand bin.
- A rat-hole that collapses and re-forms.
- Wet or dirty sand, overnight compaction, or frost.
- Build-up on the walls reducing the outlet.
- Oversize stones or lumps because the top grid is missing.
Most likely and cheapest to check first.
Checks
- Look from the top platform, wearing a harness. Never from inside.
- Check sand moisture and temperature.
- When the bin is low, inspect the walls for build-up.
- Check the vibrator runs only with the gate open.
Fix
- Run the vibrator in short bursts with the gate open.
- Use an air lance or a bar from the top platform, with a harness; strike the outside wall with a mallet.
- Drain sand before loading; cover stockpiles from rain; heat in winter.
- Clean the walls and fit a UHMW or rubber liner in the sand bin.
- Refit the top grid.
Stop the equipment if
Someone has to enter the bin. Empty it from below, lock out and work under a confined-space permit.
Parts you may need
Engulfment kills
A person standing on sand or gravel over an outlet can be pulled under in seconds when the material moves. Every clearing method here works from outside or from the top platform.
DANGERNever enter or stand on material in a bin. Only an empty, locked-out bin may be entered, under a confined-space permit with a second person outside.
FIELD TIPKeep each bin between half and full. Loading into the centre and not running bins empty reduces segregation and keeps the flow steady.
DANGERWould-be rescuers die too. Co-workers who enter a bin to dig someone out are engulfed in the same way. Rescue needs the same lockout, harness and standby as any entry: put it in the plant emergency plan, and post "CONFINED SPACE — ENGULFMENT HAZARD" at every access point.
⚠ Every check inside a machine starts with full lockout. Safety disclaimer