As indispensable material handling equipment in modern industrial production, the design of the trolley operating mechanism of a bridge crane directly impacts the performance and reliability of the entire machine. This article comprehensively designs the trolley operating mechanism of a 5T bridge crane, encompassing key aspects such as drive mode selection, motor and reducer selection calculation, wheel and track design, brake system configuration, and safety protection measures.
The trolley mechanism of a bridge crane is the crane’s transport mechanism, responsible for longitudinally moving the crane along the factory rails, thereby transporting heavy objects along the length of the workshop. As small to medium-sized lifting equipment, 5T bridge cranes are widely used in factory workshops, warehouses, and other places. The design of their trolley mechanism must balance efficiency, stability, and cost-effectiveness.
Based on industry standards and actual requirements, the basic design parameters for a 5T bridge crane trolley mechanism are as follows:
The 5T bridge crane trolley mechanism primarily consists of the following components:
The design must consider the following environmental conditions:
Bridge crane trolley travel mechanisms are divided into two types: centralized drive and separate drive. Each has its own characteristics and applicable applications. For 5T bridge cranes, the appropriate choice should be made based on specific requirements and budget.
A centralized drive system uses a single motor to drive the wheels on both sides via a drive shaft. Features of this drive system include:
Centralized drive systems are suitable for applications with smaller spans (generally less than 16.5m) and low operating speeds. For 5T cranes with limited spans and limited budgets, this solution may be considered.
Separate drive means that the driving wheels on each side are driven by independent motors, eliminating the need for a mechanical drive shaft connection. This drive method is commonly used in modern bridge cranes and features the following characteristics:
Separate drive is particularly suitable for long-span cranes. For 5T bridge cranes with spans exceeding 16.5m, separate drive is recommended. For example, the design example mentioned in page 4: “Trolley Travel Mechanism: Separate Drive Scheme, Using Four Wheels, Arranged Oppositely, and Separately Driven.”
After comprehensively comparing the characteristics of the two drive methods and considering typical 5T bridge crane application scenarios, this design recommends separate drive for the following reasons:
The typical separate drive layout is a “four-wheel, opposite-facing” arrangement, with two wheels on each side, one driving and the other driven. This arrangement offers excellent stability and traction performance.
The motor is the power source for the trolley mechanism. The proper selection of the motor directly impacts the crane’s performance and economic efficiency. The following details the motor selection and calculation process.
The main resistances the trolley mechanism must overcome include friction, slope resistance, and wind resistance (wind resistance is generally not considered for indoor cranes). For a 5T bridge crane trolley mechanism, friction resistance is the primary consideration. Friction Resistance Calculation:
Total friction resistance Ff can be calculated as follows:
Ff = β × (Q + G) × (2f + μd) / D [kN]
Where:
Substituting the values:
Ff = 1.8 × (49 + 147) × (2 × 0.0003 + 0.015 × 0.2) / 0.4 = 1.8 × 196 × (0.0006 + 0.003) / 0.4
= 1.8 × 196 × 0.0036 / 0.4
≈ 3.18 kN
Slope resistance:
Slope resistance is generally not considered for indoor cranes. Total operating resistance:
F = Ff = 3.18 kN (This differs from the “trolley operating resistance F = 8 kN” mentioned on page 8, depending on the lifting tonnage).
The motor static power Pj is calculated as follows:
Pj = F × v / (1000 × η) [kW]
Where:
Substituting the values:
Pj = 3.18 × 0.83 / (1000 × 0.85) ≈ 3.11 kW
To account for the inertia during crane startup, the motor power needs to be multiplied by the starting factor kd (range 1.2-1.5):
P = kd × Pj = 1.5 × 3.11 ≈ 4.66 kW
Based on the calculation results, after consulting the motor catalog, we selected the YZR series three-phase asynchronous motor for metallurgy and hoisting applications, specifically the YZR160M1-6. Its technical parameters are:
This motor meets the following requirements:
Table: Selection parameters of motors for trolley travel mechanisms
| Parameter name | Symbol | Unit | Numerical |
| Total running resistance | F | kN | 3.18 |
| Running speed | v | m/s | 0.83 |
| Static power | Pj | kW | 3.11 |
| Startup coefficient | kd | – | 1.5 |
| Required power | P | kW | 4.66 |
| Select motor model | – | – | YZR160M1-6 |
| Motor rated power | Pe | kW | 5.5 |
| Motor rated speed | ne | r/min | 930 |
The reducer is a key transmission component connecting the motor and wheels. Its function is to reduce the motor’s high speed to a low speed suitable for wheel rotation, while also increasing output torque.
The total gear ratio i of the trolley travel mechanism can be determined by the following formula:
i = n/nw
Where:
Thus, the total gear ratio is:
i = 930/39.6 ≈ 23.5
Based on the transmission ratio and input power requirements, a vertical reducer specifically designed for cranes, model ZSC-400, was selected. Its key parameters are:
This reducer utilizes a three-stage gear transmission. The gears are made of 20CrMnTi, carburized and quenched, with a tooth surface hardness of HRC 58-62 and an accuracy grade of 8-8-7.
When using the actual transmission ratio of 24.5, the actual operating speed is:
v’ = π × D × n / (60 × i) = 3.14 × 0.4 × 930 / (60 × 24.5) ≈ 0.79 m/s (47.6 m/min).
Compared to the design requirement of 50 m/min, the error is 4.8%, which is within the allowable ±5% range.
Couplings are required between the motor and reducer, and between the reducer and wheels. Selection based on shaft diameter and transmittable torque:
The following factors should be considered when selecting a coupling:
The wheel assembly is the actuating component of the trolley’s running mechanism, directly contacting the track and bearing the entire load. Its design directly impacts its running resistance and service life.
Based on the load characteristics and operating class of the 5T crane, the following wheel parameters are selected:
The maximum wheel pressure Pmax occurs when the fully loaded trolley is positioned on one end beam:
Pmax = (Q+G)/4 × k [kN]
Where:
Pmax = (49+147)/4 × 1.1 ≈ 53.9 kN
Based on the wheel pressure and operating speed, check the wheel load curve to confirm that a 400mm diameter wheel meets the requirements.
Based on the wheel load and operating level, select the QU70 crane-specific track:
The permissible wheel load for the QU70 track is 70kN (>53.9kN), meeting the operating requirements. During track installation, ensure the following:
The wheelset utilizes an angular bearing housing for easy installation and maintenance. The bearing housing houses 22216 spherical roller bearings with a dynamic load rating of 108 kN. The lifespan is calculated as follows:
L10 = (C/P)³×10⁶/(60×nw)
= (10⁶/53.9)³×10⁶/(60×39.6)
≈ 8.2×10⁴ hours
This is significantly longer than the required 4000 hours.
The braking system is a key component for ensuring safe crane operation and must ensure reliability and timely operation.
Based on the characteristics of the trolley operating mechanism, the YWZ5-315/23 electro-hydraulic drum brake was selected. Its main parameters are:
This brake offers the following advantages:
The required braking torque Mz is calculated as follows:
Mz = kz × Ff × D / (2 × i × η) [N·m]
Where:
Mz = 1.75 × 3180 × 0.4 / (2 × 24.5 × 0.85) ≈ 107 N·m
The selected brake’s minimum braking torque of 160 N·m is greater than 107 N·m, meeting the requirement.
The actual braking distance S can be estimated as:
S = v²/(2×a) [m]
Where:
Fb = 160×2×24.5×0.85/0.4 ≈ 16660 N
a = 16660/20000 ≈ 0.833 m/s²
S = 0.83²/(2×0.833) ≈ 0.41 m
Crane standards require that the braking distance S ≤ v²/(5000–6000) = 0.83²/5000–6000 ≈ 0.11–0.14 m. Obviously, a single brake cannot meet the requirements, so a dual-brake solution is required:
The total braking torque is 240 N·m. Recalculate the braking distance:
Fb = 240 × 2 × 24.5 × 0.85/0.4 ≈ 24990 N
a = 24990/20000 ≈ 1.25 m/s²
S = 0.83²/(2 × 1.25) ≈ 0.28 m
This still does not meet the requirements, so the following measures are required:
The final solution is to select two YWZ5-400/25 brakes (braking torque 250-315 N·m), for a total braking torque of 500 N·m:
Fb = 500×2×24.5×0.85/0.4 ≈ 52063 N
a = 52063/20000 ≈ 2.6 m/s²
S = 0.83²/(2×2.6) ≈ 0.13 m (meets the requirement)
To ensure safe crane operation, the trolley mechanism must be equipped with multiple safety protection devices.
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