In the previous article, we elaborated on the emergency solutions for a concrete mixing plant experiencing stalling. This article will focus on two aspects: preventive measures in the early stage and equipment maintenance after stalling occurs.

IV. Specialised Equipment Inspection

1. Electrical: Check for overheating in the main motor current, thermal relays, contactors and cables

2. Transmission: Gearbox oil temperature, gear oil level, couplings, and belt tension

3. Structure: Check for wear and deformation of the mixing shaft, mixing arms, blades, liners and wear blocks

4. Seals: Check shaft end seals and dust covers for slurry leakage or damage

5. Hydraulic / Pneumatic: Check whether the hydraulic and pneumatic cylinders for the discharge door are sticking

V. Disposal of Waste Material

1. Concrete left in the machine after shutdown must not be reused for on-site pouring under any circumstances.

2. Transport the material to the waste area for crushing, and use it for backfilling or as a sub-base for access roads.

3. Maintain a detailed record of waste material on site; unauthorised reuse is strictly prohibited.

VI. Procedures for Resuming Production and Trial Operation

1. Run the entire machine idle with clean water for 5–10 minutes to flush the system.

2. Run the machine empty for 3 cycles; ensure there are no unusual noises, jamming or abnormal vibrations

3. Conduct a test mix using low-strength mortar or clean water to flush the piping

4. For the first batch prior to full production, reduce the sand ratio and appropriately increase the admixture to test the system

5. Conduct on-site monitoring of the main unit’s current; normal production may only commence once the discharge status is confirmed as normal

VII. Preventive Control Measures

1. The dispatcher must confirm in advance that the mixer truck is in position; under no circumstances shall concrete be pumped if the truck is absent

2. Set an alarm for main unit material retention exceeding the time limit; an automatic prompt to unload or clean the machine shall be triggered upon exceeding the limit

3. In the event of a sudden power cut or equipment failure, immediately estimate the expected duration of material retention

4. During hot summer months, strictly control the standing time and add retarding agents as appropriate

5. Establish a handover procedure for retained material during shift changes to eliminate the risk of material left in the machine

6. It is strictly prohibited to leave the main unit on standby with material inside for extended periods

VIII. Safety Precautions

1. Material clearance must be carried out by at least two people, with a designated person monitoring the power supply.

2. When entering the interior of the main unit to work, the power must be switched off, the key removed, and a designated person must be on guard.

3. When using jackhammers or steel chisels, ensure personal protective equipment is worn to prevent injury from flying debris.

4. It is strictly prohibited to stand beneath the discharge chute or within the range of the rotating mixing arms whilst working.

5. Ensure adequate lighting is provided when clearing the machine at night.