Diagnosing Swing Drift and Abnormal Noise in the Tata Hitachi EX1200

[MikePhua]

The Tata Hitachi EX1200 and Its Swing System
The Tata Hitachi EX1200 is a large hydraulic mining excavator developed through a joint venture between Tata Motors and Hitachi Construction Machinery. Designed for high-production mining and heavy-duty excavation, the EX1200 features a powerful hydraulic system, a robust swing mechanism, and a high-capacity undercarriage. The swing system, responsible for rotating the upper structure of the machine, is powered by a hydraulic swing motor connected to a planetary swing drive and a large slew bearing.
The swing mechanism is engineered for precision and durability, but like all hydraulic systems, it is susceptible to wear, contamination, and control valve issues over time. One common symptom of degradation is swing drift—where the upper structure continues to rotate slightly after the operator releases the swing control.
Understanding Swing Drift and Its Causes
Swing drift is typically caused by internal leakage within the hydraulic circuit. When the swing joystick is released, the control valve should center and block flow to the swing motor, stopping rotation. If the swing continues to drift, it suggests that hydraulic oil is bypassing internal seals or valves.
Common causes include:

• Worn swing motor rotary group: Internal leakage in the motor allows oil to circulate even when the valve is closed.
  
• Leaking swing control valve: The spool may not seat properly due to wear or contamination, allowing oil to flow past the neutral position.
  
• Defective swing brake: The swing brake is a spring-applied, hydraulic-release mechanism that locks the swing gear when not in use. If the brake fails to engage fully, the upper structure may coast or vibrate after stopping.
  
• Air in the hydraulic system: Entrained air can cause delayed response and erratic movement.
  

In the EX1200, the swing brake is typically mounted on the swing motor and is activated by pilot pressure. If the pilot line is restricted or the brake piston is worn, the brake may not apply correctly.
Abnormal Noise and Vibration During Swing Stop
The presence of vibration and unusual noise when the swing stops suggests mechanical backlash or hydraulic shock. This can be caused by:

• Loose swing gear backlash: Excessive clearance between the swing pinion and ring gear can cause a clunk or jolt when the swing stops.
  
• Worn swing bearing: A damaged slew bearing can allow the upper structure to shift slightly, producing vibration.
  
• Hydraulic cavitation: If the swing motor is starved of oil or the return line is restricted, cavitation can occur, leading to noise and damage.
  
• Improper swing brake timing: If the brake engages too early or too late, it can cause a jarring stop.
  

A technician once described a similar issue on a mining site in Odisha, where the swing drift was traced to a cracked O-ring in the swing motor brake piston. The machine had been operating in high-heat conditions, which accelerated seal degradation.
Inspection and Troubleshooting Steps
To isolate the root cause, follow this diagnostic sequence:

• Check pilot pressure to the swing brake circuit. It should match factory specifications (typically 40–60 bar).
  
• Inspect the swing brake piston and spring for wear or binding.
  
• Test the swing motor for internal leakage using a flow meter.
  
• Remove and inspect the swing control valve spool for scoring or contamination.
  
• Measure backlash between the swing pinion and ring gear.
  
• Drain and filter hydraulic oil to check for metal particles or seal fragments.
  

Preventive Measures and Long-Term Solutions
To prevent recurrence:

• Replace hydraulic filters at recommended intervals.
  
• Use OEM-grade hydraulic oil with correct viscosity.
  
• Avoid abrupt swing stops that stress the brake and gear system.
  
• Periodically grease the swing bearing and inspect for play.
  
• Monitor swing brake timing during service calibration.
  

Conclusion
Swing drift and abnormal stopping behavior in the Tata Hitachi EX1200 are typically linked to internal hydraulic leakage, swing brake malfunction, or mechanical backlash. By systematically inspecting the swing motor, brake assembly, and control valve, technicians can restore precise swing control and eliminate vibration. With proper maintenance and timely seal replacement, the EX1200’s swing system can continue to deliver reliable performance in demanding mining environments.