The cargo crane does not slew. Troubleshooting

Greetings! Today we have a problem with the cargo crane, it won’t slew. In this case, there are no signals or alarms, the crane starts up, executes the commands “jib up, hook up” and “jib down, hook down,” but does not slew in any direction.

According to the instructions for the crane, you need to check the following circuit: Joystick - PLC - relay - Proportional Driver Unit - Proportional Valve.

Let's check the entire electrical circuit and figure out the reason for the improper operation of the cargo crane.

The command given by the operator using the joystick is received by the PLC module, processed, the intermediate relay prepares the circuit, then the command goes to the proportional driver, which sends a signal in milliamps to the proportional valve of the crane rotation hydraulic pump (two solenoids - right and left).

Slewing circut

I will not go into details of checking the entire circut, because you can read about this in the previous article, where the problem of the slow operation of the cargo crane was described and the remaining elements after the joystick were checked.

Here the problem turned out to be in the joystick, at the very beginning of the circuit. It did not give a signal to the PLC and, accordingly, further along the circuit.

Operation circuit diagram of joystick, driver and valves

The circuit diagram shows how the joystick works, using a potentiometer and microswitches it sends a command to the PLC, the 58K relay “informs” that the circuit is ready, and through the 42AMP driver it affects the proportional valves (right and left).

Command from joystick to valve

Because the circuit beyond the joystick visually did not work, then the problem had to be looked for in the joystick itself. After opening the joystick, one wire broke off, apparently due to poor soldering.

Repair of a joystick for slewing the crane

The wire was soldered into place, cargo crane was put into operation. For a more detailed study of the operation of the crane, I recommend the previous article.

Troubleshooting a cargo crane that does not slew (rotate) involves systematically checking various components and systems. Here’s a step-by-step guide to help diagnose and resolve the issue:

1. Check Power Supply

• Electrical Power: Ensure the crane is receiving the correct voltage and the power supply to the slewing motor is not interrupted.
• Hydraulic Power: If the crane uses hydraulics for slewing, check the hydraulic power supply, including pump operation and hydraulic fluid levels.

2. Control System

• Control Panel: Verify that the control panel and its indicators are functioning correctly.
• Joystick/Control Levers: Ensure the joystick or control levers for slewing are operational.
• Wiring and Connections: Inspect wiring, connectors, and terminals for any signs of damage, loose connections, or corrosion.

3. Motors and Drives

• Slewing Motor: Check if the slewing motor is functioning. Listen for any unusual sounds and feel for excessive heat, which could indicate a motor problem.
• Motor Starter/Contactor: Ensure the motor starter or contactor is not faulty.
• Motor Overload: Check if the motor overload protection has tripped and reset if necessary.

4. Hydraulic System (if applicable)

• Hydraulic Pump: Confirm the hydraulic pump is working correctly and providing adequate pressure.
• Hydraulic Valves: Inspect hydraulic control valves for proper operation. Check for blockages or malfunction.
• Hydraulic Hoses and Cylinders: Look for leaks, kinks, or damage to hoses and cylinders.

5. Mechanical Components

• Slewing Gear: Inspect the slewing gear and pinion for wear, damage, or misalignment.
• Bearings: Check the slewing ring bearings for proper lubrication and wear.
• Brake System: Ensure the slewing brake is not engaged or stuck. If it is, it may prevent slewing.

6. Sensors and Safety Systems

• Limit Switches: Verify that limit switches are not engaged or malfunctioning, which could be preventing slewing.
• Safety Interlocks: Check if any safety interlocks or emergency stop systems are activated.

7. Diagnostics and Error Codes

• Diagnostic Display: If the crane has a diagnostic display or onboard computer, check for any error codes or warning messages.
• Manuals and Documentation: Refer to the crane’s maintenance manual for specific troubleshooting steps and error code definitions.

8. Environmental Factors

• Weather Conditions: Ensure that extreme weather conditions, such as strong winds or cold temperatures, are not affecting the crane's operation.
• Obstructions: Check for any physical obstructions around the crane that might impede slewing.

9. Professional Assistance

• If the issue persists after performing these checks, contact a professional technician or the crane manufacturer’s support service for further diagnosis and repair.

By following these steps, you should be able to identify the cause of the slewing issue and take appropriate action to resolve it.

Crane model: DMC DDKC-3026-00 (Dongnam Marine Crane).

Also read other articles about DMC cargo cranes:

1. Problems with cargo cranes. Some problems with cargo cranes that occur on the ship
2. The crane hook goes up slowly. The cargo crane is not working. Troubleshooting
3. PLC failure. The cargo crane does not start. Troubleshooting
4. Motor Fault on the crane. Troubleshooting
5. The crane jib is luffing down under its own weight. Troubleshooting