Metallurgical Crane Spec GB/T 28762-2012: Structure and Protection

GB/T 28762-2012 is the dedicated technical standard for the design and manufacturing of metallurgical cranes, issued and implemented in 2012. Metallurgical cranes operate in extremely demanding environments — intense heat radiation, molten metal splash, heavy dust, and frequent start-stop cycles — conditions that standard industrial cranes cannot handle. The standard mandates critical safety requirements for the metal structure's thermal insulation, high-temperature-resistant electrical systems, and dual braking on the hoisting mechanism, making it the fundamental reference for crane selection and use in the metallurgical industry.

Thermal Insulation Requirements for Metal Structures

The main girder, end carriages, and other structural components of metallurgical cranes must be protected against heat radiation. The standard specifies that a thermal insulation layer be installed on the underside of the main girder — the side facing the molten metal. This insulation layer may consist of high-temperature-resistant insulation boards (e.g., calcium silicate boards or ceramic fiber boards) or a composite structure of steel plate plus insulation wool. The insulation layer must be no less than 80 mm thick, with a protective facing of stainless steel or galvanized steel sheet. An air gap of at least 50 mm must be maintained between the main girder bottom plate and the insulation layer, creating a double-layer thermal barrier that minimizes heat transfer to the main girder web plate.

Thermal protection for the trolley frame and hoisting mechanism is even more critical, as these components sit closest to the hot metal ladle. The standard requires a full thermal insulation bottom plate on the trolley, made of stainless steel (1Cr18Ni9Ti or 304 stainless steel) with a minimum thickness of 6 mm. The hoisting rope must be a high-temperature-resistant type (silicone-coated or stainless steel wire rope), or alternatively, a heat shield must be fitted to protect the rope. The pulley block's heat shield must fully cover all pulleys to prevent molten metal splash from damaging bearings and rope grooves. Kelude Heavy Industry employs a three-layer thermal protection design in its metallurgical cranes — double insulation bottom plates with an air gap and a stainless steel outer facing — keeping the main girder bottom plate temperature below 120°C.

The standard also requires that the crane's work duty classification be no lower than A6. The hoisting mechanism must be equipped with a dual braking system — a service brake plus a safety brake. The safety brake engages automatically upon power loss, with a braking torque of no less than 1.5 times the rated hoisting torque. The hoist gearbox must use hardened tooth flank gears with a load-bearing capacity equivalent to AGMA Class 12 or higher. The fleet angle of the hoisting rope on the hoist drum must not exceed 3.5°, and the rope groove depth must be at least 0.4 times the wire rope diameter.

Electrical System and Protection Ratings

The electrical system of a metallurgical crane must meet higher protection ratings and withstand elevated temperatures. The standard specifies that electrical equipment — motors, control cabinets, resistor boxes, etc. — must have a protection rating of at least IP54 for indoor installations or IP55 for outdoor or semi-outdoor installations. Motor insulation must be Class H or better (rated for 180°C). If the internal temperature of the control cabinet exceeds 65°C, forced ventilation or air conditioning must be provided. Cables must be high-temperature-resistant, flame-retardant types rated for at least 125°C, and cable routing must avoid direct contact with hot surfaces.

Electrical safety design is the top priority for metallurgical cranes. The standard requires the hoisting mechanism to be equipped with encoder feedback for precise speed control and overspeed protection. The hoisting height limit switch must be configured as a dual system (mechanical plus electronic), with each limit switch operating independently — when one trips, the other remains in a standby alert state. A video monitoring system must be installed in the ladle travel area, allowing the operator to observe ladle positioning and pouring operations in real time from the operator cab. Each mechanism must feature fault self-diagnosis, displaying fault codes on the controller for rapid troubleshooting and maintenance.

The standard sets out detailed electrical safety protection requirements. Every metallurgical crane must be fitted with a main disconnect switch and emergency stop buttons distributed across the operator cab, floor operation points, and both sides of the crane bridge — no fewer than three in total. Earthing protection resistance must not exceed 4Ω, and each motor must have individual short-circuit and overload protection. The programmable logic controller (PLC) must be an industrial-grade unit with an operating temperature range of 0–60°C. The VFD carrier frequency must be automatically adjusted based on ambient temperature, with automatic derating during high-temperature periods to prevent overheating shutdowns.

Safety Devices and Interlock Protection

Metallurgical cranes must be equipped with a more comprehensive safety device system than standard cranes. The standard requires the hoisting mechanism to be fitted with an overload limiter, dual-configuration hoisting height limit switches, a lowering limit switch, an overspeed protection switch, and a slack rope protection switch. The crane travel mechanism must be equipped with travel limit switches, buffers, and an anti-collision device. The trolley travel mechanism must have travel limit switches and bidirectional buffers. For wind protection, an electric rail clamp must be installed and interlocked with an anemometer — an audible and visual alarm triggers when wind speed exceeds Force 6, and the rail clamp automatically engages to stop crane travel at Force 8 or above.

Interlock protection requirements: When the operator cab door is open, all crane mechanisms must be prevented from starting. After the main power supply is switched on, all mechanism controllers must be in the zero position before the crane can be started from the control station. Once the emergency stop button is pressed, the main contactor opens and latches, requiring a manual reset. When the overload limiter is activated, the hoisting mechanism is limited to lowering only — hoisting is disabled — and an audible and visual alarm is triggered simultaneously. The safety brake is interlocked with the service brake and the power supply: when the main power is disconnected, the safety brake applies automatically. Emergency lighting must be installed in the electrical room and operator cab, providing illumination for at least 30 minutes after a power failure.

Metallurgical Crane Technical Parameter Comparison Table

The comparison table below highlights the key differences in technical requirements between metallurgical cranes and standard cranes, helping equipment managers verify critical parameters during selection and acceptance.

Acceptance Testing and Factory Inspection

Before delivery, every metallurgical crane must pass a rigorous inspection and testing regimen. The standard specifies that each unit undergo a No-Load Test, a Rated Load Test (100% SWL), a Dynamic Load Test (at 1.1 times the rated load), and a Static Load Test (at 1.25 times the rated load). The hoisting mechanism is also subject to a brake slip distance test—after brake application under rated load, the load drop must not exceed 1/65 of the lifting distance achieved in one minute (approximately 0.46 mm/kN). The Safety Brake must independently assume braking duty if the service brake fails, with a brake slip distance not exceeding 1.5 times that of the service brake.

Verification of thermal insulation performance is another acceptance item unique to metallurgical cranes. The standard requires measuring the main girder bottom plate temperature under simulated thermal radiation conditions (heat flux density at the girder underside ≥ 5 kW/m²), and the temperature must not exceed the allowable limit. The high-temperature test for the electrical system involves running the Control Cabinet at an internal temperature of 65°C for 4 hours, during which no electrical component may overheat or malfunction. Every safety device must be individually function-tested—the actuation position and accuracy of Limit Switches, the alarm and cut-off points of the Overload Limiter, the clamping force and Response time of the Wind Protection Device / Rail Clamp, and the cut-off range and reset method of the emergency stop button. Only after all inspections are passed can the Factory Certificate and Type Test Report be issued.

FAQ: Metallurgical Crane Testing and Safety