EOT Crane Trolley Travel Mechanism: Key Specs & Design

GB/T 26473-2011 is the dedicated technical standard for the trolley travel mechanism of overhead bridge cranes, and is used in conjunction with GB/T 26472, which covers the crane bridge travel mechanism. The trolley travel mechanism handles the lateral movement of the load across the bridge span, and its performance directly determines the crane's positioning accuracy and operational efficiency. The standard applies to the design, manufacturing, and acceptance of trolley travel mechanisms for electric overhead traveling (EOT) cranes. Kelude's trolley travel mechanisms feature variable-frequency speed control combined with horizontal guide rollers, delivering smooth operation and excellent resistance to rail gnawing.

Trolley Travel Mechanism Structure

The trolley travel mechanism consists of the trolley frame, wheel blocks, drive unit, and buffer stops. The trolley frame is a welded steel structural component that carries both the hoisting mechanism and the travel mechanism. It is typically fabricated from Q235B or Q355B steel plate, fully annealed to relieve residual welding stress, and then machined on the mounting surfaces. The standard specifies a series of seven standard trolley track gauges (center-to-center distance between rails): 1000mm, 1250mm, 1500mm, 1750mm, 2000mm, 2250mm, and 2500mm. The gauge should be selected based on rated lifting capacity — 5 to 10t trolleys use a 1000–1500mm gauge, 16 to 32t trolleys use 1500–2000mm, and 50 to 100t trolleys use 2000–2500mm. Choosing an incorrect gauge, whether too wide or too narrow, compromises trolley stability and leads to uneven wheel load distribution.

Trolley travel mechanisms typically use an individually driven configuration, with two motors each driving one side of the wheel set, synchronized electrically to ensure consistent travel on both sides. The trolley gearbox is usually a vertical shaft-mounted or horizontal reducer, installed on a dedicated reducer mounting bracket on the trolley frame. The trolley motor is either a conical-rotor brake motor or a variable-frequency asynchronous motor. The former has an integrated braking function and is well suited to frequent start-stop duty cycles; the latter, when paired with a frequency inverter, provides smooth speed control and reduces load sway. The drive shaft on a trolley is short and requires no intermediate support, but coupling alignment accuracy is critical — coaxiality deviation must not exceed 0.1mm.

Trolley wheels are available in two configurations: single-flanged and double-flanged. Single-flanged wheels are suitable for light-duty trolleys operating on rails with good straightness, while double-flanged wheels offer superior guidance and anti-derailment performance, making them the preferred choice for medium and large cranes. Wheel tread hardness must be no less than HB280, and tread diameter deviation must not exceed ±0.5% of the wheel diameter (D). After installation, wheels must maintain uniform contact along the full length of the rail; localized contact gaps must not exceed 200mm.

Trolley Travel Speed and Drive Configuration

The standard specifies trolley travel speeds as follows: 20–30 m/min for 5–10t trolleys, 15–25 m/min for 16–32t trolleys, and 10–20 m/min for trolleys rated above 50t. Trolley travel speed is typically higher than bridge travel speed because the trolley traverses a shorter distance (limited by the bridge span), so a faster speed is needed to maintain overall productivity. Acceleration time during start-up is generally kept within 2 to 4 seconds, and braking deceleration should be controlled within 0.3 to 0.5 m/s² to prevent excessive load swing during stops.

Drive motor power selection must account for trolley wheel load, running resistance, and acceleration force. Rated wheel load is calculated as (trolley dead weight + rated lifting capacity) / number of wheels. Running resistance includes wheel bearing friction and rolling resistance between the wheel tread and rail, typically estimated at 1.5% to 2.0% of the full-load wheel load. Acceleration force is calculated from the full-load mass and the required acceleration rate. Altitude and ambient temperature corrections should also be applied during motor selection — when operating above 1,000m altitude or in ambient temperatures exceeding 40°C, motor power should be appropriately derated. For trolleys with variable-frequency speed control, a 15% to 20% power margin is recommended.

Trolley Rail and Wheel Matching

The standard specifies that trolley rails should be light rails from the P series, with P24 or P38 being the most common choices. Rails must be securely mounted on the trolley runway beam, with an elastic pad (rubber or resin) placed between the rail base and the beam. The pad thickness should be 5 to 8mm and serves to dampen vibration and assist with rail leveling. Rail joints must be connected with fishplates, with a maximum height difference of 0.5mm at the joint and a maximum gap of 2mm. Rail clamp plates are typically spaced at 500 to 600mm intervals and must be tightened evenly to the torque values specified in the design drawings. Rail straightness must not exceed ±2mm over the full length. After installation, straightness should be verified using the wire-stretching method, measuring deviation at each segment and adjusting progressively to ensure uniform wheel contact along the entire rail.

For a 4-wheel trolley, the theoretical wheel load per wheel is (Q + G_trolley) / 4. For 8-wheel trolleys, a spreader beam (equalizing beam) is required to distribute the load evenly across all wheels. The spreader beam connects to the trolley frame via hinge pins, allowing it to pivot freely and maintain uniform wheel-to-rail contact even when the rail surface has minor irregularities. The spreader beam must be sufficiently rigid — maximum deflection under full wheel load must not exceed 1/500 of the beam span. Horizontal guide rollers are mounted on both sides of the trolley frame and contact the rail side faces, effectively preventing rail gnawing and skewing. The clearance between the guide rollers and the rail side should be set at 2 to 4mm — too small a gap accelerates flange wear, while too large a gap compromises anti-skew performance.

Trolley Travel Mechanism Parameter Comparison

The comparison table below summarizes trolley gauge, travel speed, and wheel configuration across different lifting capacity classes, providing a quick reference for selection and design.

Buffer Stops and Safety Devices

Trolley buffers shall be mounted at both ends of the main girder to absorb impact energy when the trolley reaches its extreme travel position. Buffers are available in three types: rubber, spring, and hydraulic. Rubber buffers offer a simple structure and low cost, making them suitable for trolleys with a travel speed of ≤30 m/min. Spring buffers provide a longer buffer stroke and higher energy absorption, making them ideal for medium-speed trolleys. Hydraulic buffers feature adjustable cushioning characteristics and no rebound, making them the preferred choice for high-speed applications or where smooth deceleration is critical. The buffer capacity shall be no less than the kinetic energy of the trolley striking at rated speed. Buffers must be securely mounted, with their centerline aligned in the same vertical plane as the trolley wheel centerline, within a tolerance of 3 mm.

Bumper stops (buffer stops) shall be provided at both ends of the trolley rail, with a height no less than one-third of the wheel diameter. The trolley travel limit switch shall be activated to cut off the power supply before the trolley buffer makes contact with the bumper stop. Travel limit switches shall be installed at both ends of the main girder and shall reliably actuate when the trolley is no less than 500 mm from the end limit position. After the limit switch is tripped, the trolley shall come to a stop no less than 200 mm from the buffer. Limit switches shall be inspected monthly to verify reliable operation. For outdoor cranes, the trolley shall also be equipped with a rain cover and rail sweeper to prevent water accumulation and debris from affecting safe trolley travel.

Trolley Operation FAQ