Paddle-to-liner gap too large or paddles touching
Symptom
Mix takes longer, a layer of concrete stays on the floor, stones wedge, or you hear scraping.
Likely causes
- Paddles worn, so the gap to the floor liner has grown above 5 mm.
- Paddle moved after a stone jam or after chipping hardened concrete.
- Paddle set too low after a change, so it touches the liner.
- High-silica aggregate or oversize stones wearing the paddles fast.
Most likely and cheapest to check first.
Checks
- Lock out the mixer (8-step procedure, section 1.2).
- Clean the paddle edge and the liner under it.
- Measure every paddle with a feeler gauge at its lowest point. Write each value on the paddle map.
- Turn the shafts by hand for one full turn and look for shiny contact marks.
Fix
- Loosen the paddle bolts, push the paddle down to a 3 mm gauge, retighten to torque.
- Replace paddles that can no longer reach 3 mm. Many are symmetrical and can be turned round once.
- After any change, turn one full revolution by hand, run one day, then retighten all new bolts daily for three days.
Stop the equipment if
Any paddle touches the liner, or any gap is above 8 mm.
Parts you may need
Why 3 mm matters
The gap between the paddle edge and the floor liner should be about 3 mm when new and stay in a 3–5 mm working range. With a larger gap, stones wedge between paddle and liner. That can stall the mixer, break a paddle or an arm and, in bad cases, damage the shaft and the motor. A large gap also leaves a layer of concrete on the floor that hardens and is hard to wash.
| Condition | Gap | Action |
|---|---|---|
| New or just adjusted | about 3 mm | — |
| Normal working range | 3–5 mm | Keep it here |
| Above 5 mm | — | Readjust at the next stop |
| Above 8 mm | — | Adjust or replace now |
| Paddle touches liner | 0 | Stop the mixer |
CAUTIONArms and paddles are cast iron. Hit them only with a plastic or copper hammer. A steel hammer can crack them.
FIELD TIPCheck whether your paddles are symmetrical before ordering new ones. Turning a worn paddle round can double its life.
COST OF NEGLECTA paddle costs little. A plant standing for a week waiting for one paddle loses its trucks and its customers.
FIELD TIPMeasure paddle and liner thickness every 2–3 months. Very abrasive aggregates (basalt, granite, slag) can halve paddle life. Uneven wear on one side of the mixer usually means off-centre loading or a paddle fitted at the wrong angle.
⚠ Every check inside a machine starts with full lockout. Safety disclaimer