Case Study # 6
One of India’s largest fully integrated private sector steel plant on its western coast, has more than 150 cranes in steel plant service.
Cranes in the Steel Making Plant (Ladle Crane 350 T, with auxiliary crane 15T), and Plate Mill ranging from 20T- to 350T, crane wheels were suffering from shorter useful life, cracking, pitting and denting of track tread wheels cranes within 2-3 years of its service demanding repair, hard-facing or even replacement.
Evaluation, Assessment, Recommendation And Solution(s)
A plant visit was scheduled where on site crane wheel and axles were examined during operations at the steel making and plate mill at heights 30-40 m above the plant floor.
Both cast and forged crane wheel and axles were examined. Most of them were Chinese make, while some of the cranes were US, Europe makes as well.
A metallurgical failure analysis was performed on a set of carbon steel C45 gantry crane wheel following observation of excessive damage to the central tread surface, flange collar breakage, and cracking of wheel at track mating surfaces.
Rolling contact fatigue was considered as a possible failure mechanism due the presence of what appeared to be spalling. Metallurgical assessment and hardness testing of surface profiles revealed that portions (track width, collars and contacting ends), of wheel had not reached the specified hardness during heat treatment and non-uniform hardness was observed. It was determined that flame hardening was used which is not the correct heat treatment for the end application crane wheels, leaving the tread surface edges in a near normalized condition only.
Some wheels were cast while others were forged. Shafts were manufactured from forged C45 material mostly. Metallurgical defects were observed in wheels, non-uniform mechanical properties. The core of the wheel was not found in ductile condition, hence cracks from the radial diameter were found to be propagating to the centre of the wheel towards the shaft diameter and the hub region. Continual contact with the rail during the service allowed for plastic flow of the softer materials across the surface, resulting on observed damage and wheel-axle failures demanding frequent replacement. Refurbishing of the wheels, and hardfacing were added costs and increased downtime of the cranes when service was most required.
Acmecast developed four modules of alloy metallurgy for different cranes according to its service, application and duty requirements. C45, C55, En19, En24 crane wheels and axle shafts were manufacturing for various crane with crane wheel diameter ranging from 250 mm to 850 mm.
Complete virgin forged bar stock and wheel blanks were normalized, tempered, proof-machined, precision machined, while shafts were grinded to close tolerances post heat treatment. Proprietary heat treatment to wheels was applied that hardened and tempered the track width, collar and outer periphery of crane wheel to HRC 55-62, while keeping the rest of the wheel ductile.
The products performance exceeded the OEM product for more than 6-8 years, without asking repair maintenance, or hard-facing of track widths. Subsequently, we have supplied various solutions for crane spares, shafts, spindles and other mechanical spares to other divisions of the steel plant.