EOT Crane Travel Mechanism Specs & Drive Configuration

GB/T 26472-2011, released and implemented in 2011, is the dedicated technical standard for the bridge travel mechanism of overhead cranes. As the drive system that moves the crane along the factory building rails, its performance directly determines the crane's positioning accuracy, operational stability, and load-bearing capacity. The standard is applicable to the design, manufacturing, and acceptance of crane travel mechanisms for electric overhead cranes. Kelude Heavy Industry designs and manufactures its crane travel mechanisms to this standard, uniformly adopting an individually driven configuration with variable-frequency speed control.

Crane Travel Mechanism Configurations

The standard specifies two types of crane travel mechanisms based on drive mode: centrally driven and individually driven. The centrally driven configuration uses a single motor to drive both sides of the crane bridge through a drive shaft and couplings. It is suitable for cranes with spans up to 16.5 m, offering the advantages of a simple structure, lower cost, and inherent mechanical synchronization. The individually driven configuration uses two motors, each driving one side of the crane bridge independently. This is the mainstream arrangement for medium- and large-span cranes, where each drive unit comprises a motor, a gearbox, and a brake.

When selecting a configuration, the span, lifting capacity, and work duty must be considered together. In centrally driven systems, the long drive shaft adds significant dead weight and deflection at larger spans, which can lead to vibration and torsional oscillation. Individually driven systems eliminate the long shaft but require synchronization control between the two motors. Traditional solutions use wound rotor motors with series resistance to achieve mechanical hard synchronization, while modern systems employ variable-frequency motors with VFDs for electrical soft synchronization—offering higher synchronization accuracy and smoother starting. In an individually driven setup, if one drive unit fails, the other can still operate at reduced speed for a short period, providing a degree of fault tolerance.

The standard also governs the arrangement and number of crane bridge wheels. Cranes with a lifting capacity of 32 t or less typically use a 4-wheel configuration—two driving wheels and two idler wheels. Cranes rated at 50 t and above must use an 8-wheel arrangement, with spreader beams (equalizing beams) ensuring uniform load distribution across all wheels. The number of driving wheels should account for 50% to 100% of the total wheel count, and no wheel slip is permitted between the driving wheels and the crane rail under full load. Wheel material is typically ZG55 or ZG50MnMo, with tread hardness of HB280–320 and a hardened layer depth of no less than 15 mm. Wheel flange height must be at least 25 mm, and flanges should be replaced when the inner-side wear amount exceeds 50% of the original thickness.

Long Travel Speed and Acceleration Requirements

The standard specifies long-travel speed ranges for different lifting capacities: 20–30 m/min for cranes up to 5 t, 20–40 m/min for 10–20 t, 15–30 m/min for 32–50 t, 10–25 m/min for 75–100 t, and 8–15 m/min for capacities above 100 t. Acceleration and deceleration times should be kept within 3 to 6 seconds. Jerk (rate of change of acceleration) must not exceed 0.5 m/s² to prevent excessive load swing. Higher lifting capacities call for slower travel speeds to keep braking distances within a safe range and to minimize the impact load on the metal structure.

Travel speed selection also depends on duty frequency and operating accuracy requirements. Cranes used in high-frequency operations (A6~A8) should be equipped with higher travel speeds to boost productivity, paired with a high-performance braking system and variable-frequency speed control. For applications demanding precise positioning—such as ladle crane alignment—slower speeds with micro-motion capability are preferred. The speed control ratio of the travel mechanism should generally be no less than 3:1; variable-frequency drive systems can achieve a wide range of 20:1 or more, meeting both high-speed travel and precise positioning requirements. With VFD systems, starting acceleration and braking deceleration can be set independently for actual operating conditions, enabling S-curve acceleration/deceleration profiles that minimize load swing.

Brake Configuration for Crane Travel

The crane travel mechanism shall be equipped with brakes. The standard specifies that in an individually driven configuration, each drive unit must have its own brake. Braking torque is selected at 1.5 to 2.0 times the rated torque under full load. Brakes are mounted on the high-speed shaft end of the gearbox (motor side), where braking torque is lower, response is faster, and the brake size is more compact. Brake actuators should be of the hydraulic push rod or electromagnetic type: hydraulic thrust brakes engage smoothly without impact, while electromagnetic brakes act quickly but with greater shock.

Brake installation and commissioning must meet the following requirements: the contact area between the brake wheel and brake shoes must be no less than 80% of the shoe area; brake shoe clearance must be uniform, with the difference between the two sides not exceeding 0.5 mm; and the brake spring working length must be adjusted per design requirements to keep braking torque within the specified range. Daily inspection of the brake includes checking brake shoe wear (replace when wear exceeds 50% of the original thickness), the surface condition of the brake wheel (turn or replace if cracks or grooves are found), and the hydraulic push rod oil level and stroke. Proper brake maintenance is critical to crane operating safety—brake failure is one of the most hazardous incidents in crane travel operation.

Crane Travel Mechanism Drive Configuration Comparison

The comparison table below highlights the key differences between centralized and individual drive configurations, offering design personnel a practical reference for drive selection.

Installation Tolerances and Crane Rail Requirements

The standard specifies installation tolerances for the crane travel mechanism. The permissible deviation for the center distance between the two crane runway rails is ±5 mm, and the rail elevation difference at the same cross-section must not exceed ±3 mm (or ±5 mm for large-span cranes). The diagonal deviation of the crane wheels must not exceed ±3 mm. Wheels on both sides shall be parallel, and all wheels on the same side shall be aligned in a straight line. The vertical skew of each wheel must not exceed 1/400, and the horizontal skew must not exceed 1/500. After installation, the drive wheels shall maintain uniform contact with the rail top surface, with a contact length of no less than 80% of the wheel width. At rail joints, the elevation difference shall not exceed 1 mm, and the gap shall not exceed 3 mm.

Maintenance of the crane rails and their fixing components is also a critical part of crane bridge travel mechanism management. The straightness, wear, and clamping plate tightness of the rails shall be checked during periodic inspections. Rails shall be replaced when the wear amount on the top surface exceeds 15% of the original rail height. The clamping plates must not loosen, and the tightening torque shall be checked quarterly. Reliable limit stops and buffers shall be installed at both ends of the crane runway rail. The buffer stroke must be sufficient to absorb the braking energy when the crane bridge impacts the stops at rated speed. For outdoor cranes, thermal expansion and contraction shall be considered by providing temperature expansion joints along the rail. These joints are typically spaced at 50–100 m intervals, with the joint width calculated based on the local temperature range.

Frequently Asked Questions