I. Definitions

Stuck mixer: A condition where concrete remains in the mixing drum for an extended period without being discharged, causing it to set, seize the shaft and jam the mixing arms, thereby preventing the mixer from starting and operating normally.

II. First Steps for Emergency Shutdown

1. Immediately cut off the main unit’s power supply and control power, tag and lock the equipment, and strictly prohibit any forced start-up attempts.

2. Stop batching, feeding, water supply and the addition of admixtures; empty the batching hoppers.

3. Confirm that the mixer trucks have left the site and establish a cordoned-off area.

III. Case-by-Case Procedures

Case 1: Short downtime (≤30 minutes; concrete has not set and retains reasonable workability)

1. Open the main unit’s maintenance door and discharge port, and manually remove the surface layer of concrete

2. Operate the main unit in short, intermittent bursts, alternating between forward and reverse rotation, to loosen the concrete clinging to the shaft

3. Add an appropriate amount of clean water and retarder, then mix at low speed to soften the concrete

4. Once the material is fully loosened, drain the waste material from the main mixer and rinse thoroughly

5. Inspect the liner plates, mixing arms and blades for deformation or wear before resuming production

Scenario 2: Prolonged downtime (30–90 mins, concrete approaching initial setting)

1. Frequent intermittent operation is strictly prohibited to prevent motor burnout and gearbox shaft breakage

2. Remove the inspection hatches at both ends of the main mixer and the shaft end seal covers

3. Manually break up the hardened concrete clumps around the shaft layer by layer using steel chisels and pneumatic hammers

4. Clear material from the gaps between the mixing arms and the bottom of the tank, ensuring all moving parts are thoroughly loosened

5. Once cleaning is complete, fill the tank with water to soak and soften the residual mortar

6. After ensuring the shaft turns freely without binding, conduct a no-load test run

Situation 3: Severe machine stalling (≥90 min, initial setting and hardening have caused the machine to seize)

1. Disconnect all power supply; strictly prohibit any electrical start-up operations

2. Remove the main unit’s inspection cover and clear material over a large area

3. Use pneumatic or electric hammers to break up the hardened concrete in sections; strictly prohibit forcing the mixing shaft open

4. Clear clumps from the shaft sleeves, seals and gearbox connection points

5. Inspect for: bent mixing arms, broken blades, deformed main shaft, or abnormal noises from the gearbox

6. Replace any damaged components immediately and thoroughly clean the entire machine with high-pressure water

7. Ensure the shaft rotates freely by hand before conducting no-load and loaded test runs