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Common Faults of Three-Roll Plate Bending Machines

I. Rolling Quality Faults

Poor Cylindrical Roundness / Ovality: This is typically caused by parallelism deviations between the upper and lower rolls, or asymmetrical positioning of the side rolls, leading to uneven force distribution on the plate. To fix this, calibrate the roll shaft parallelism using a dial indicator, and use arc-shaped backing plates or ring fixtures for local correction.

Over-bending (Excessive Curvature): Press the emergency stop immediately, raise the upper roll by 2-3mm to relieve pressure, and slowly release the material stress by rolling back in 3 increments of 15° each. For subsequent operations, reserve a 0.8%-1.2% springback allowance.

Excessive Straight Margins at Ends: This is an inherent characteristic of symmetrical three-roll bending machines. It can be resolved by pre-bending the plate ends in advance, or by upgrading to asymmetrical or fully hydraulic models with pre-bending capabilities.

Plate Skewing / Misalignment During Rolling: The plate was not aligned parallel to the roll axis during loading. Readjust the plate's position to ensure the feeding direction is perfectly perpendicular to the roll axes.

II. Mechanical Faults

Excessive Temperature Rise in Bearing Housings: Caused by insufficient lubrication, bearing wear, or excessive load. Stop the machine to apply grease, check the bearing clearance, and strictly avoid overloading the equipment.

Severe Vibration / Abnormal Noise: Usually indicates damaged roll shaft bearings or excessive meshing clearance in the transmission gears. Stop the machine, disassemble the transmission box, replace worn bearings, and adjust the gear meshing clearance.

Roll Shaft Rotation Jamming: Caused by metal chips embedded in the roll surface, or jamming in the transmission chain/gears. Clean foreign objects from the roll surface, and inspect the transmission components for proper lubrication and wear.

Tilting Mechanism Malfunction: Occurs when the tilting mechanism is activated before the workpiece has completely cleared the upper roll. Strictly adhere to operating procedures; only operate the tilting beam after the workpiece has fully disengaged from the rolls.

III. Hydraulic System Faults

Insufficient System Pressure / Inability to Drive Load: Caused by internal leakage from a worn hydraulic pump, or a stuck relief valve failing to regulate pressure. Clean the relief valve, inspect the hydraulic pump for wear, and replace contaminated hydraulic oil and filters.

High Oil Temperature / Equipment Overheating: Caused by a blocked radiator or prolonged system overflow/pressure relief. Clean dirt and oil from the radiator, check the working status of the relief valve, and avoid prolonged full-load operation.

Hydraulic System Leakage: Caused by aged or damaged seals, or loose pipe fittings. Replace aged seals, tighten loose pipeline joints, and regularly check the hydraulic oil level.

Cylinder Crawling / Jerky Movements: Caused by air entrapped in the hydraulic system or aged seals. Perform an exhaust/bleeding operation on the system and replace the aged cylinder seals.

IV. Electrical Control Faults

System Fails to Return to Reference Point: Caused by a lost zero-position pulse signal or damaged position measuring components. Use an oscilloscope to check the zero-position pulse signal and replace the faulty measuring sensor.

System Alarms / Position Loop Hardware Faults: Caused by interference signals in the circuit. Connect filter capacitors in parallel in the corresponding circuit to eliminate interference, and check if the wiring shielding is intact.

Abnormal PLC Interface Signals: Interface signals do not match the standard values in the manual. Access the interrupt memory via the PLC to quickly locate the fault point by cross-referencing the interface manual.

Oil Pump Fails to Start / Entire Machine Inactive: Caused by an open circuit in the electrical control loop or a tripped thermal relay. Check the power supply circuit and the thermal relay status, reset the protective device, and restart the equipment.

V. Emergency Shutdown Faults

If any of the following situations occur, the power supply must be cut off immediately for inspection and maintenance. Operations can only resume after the hazard has been completely eliminated:

The temperature of the bearing housing exceeds 60°C, showing signs of overheating or emitting smoke.

White smoke is emitted during equipment operation.

The entire machine experiences severe, continuous vibration.

Noise levels suddenly increase significantly, accompanied by abnormal metallic impact sounds.