Design scheme of trolley operating mechanism of 32/5t electric double-girder bridge crane

As an indispensable material handling device in modern industry, the design of the trolley operating mechanism of a bridge crane directly impacts overall machine performance and operating efficiency. This paper systematically designs the trolley operating mechanism of a 32/5t electric double-girder bridge crane, comprehensively analyzing the operating mechanism’s key parameters, structural components, drive mode, and control system. The design encompasses determining operating mechanism calculation conditions, selecting motors and reducers, designing the transmission system, selecting wheels and tracks, configuring the braking system, and verifying structural strength. Through theoretical calculations and verification, the operating mechanism meets the technical requirements of duty class M5, operating speed of 45m/min, and track gauge of 2500mm, while also ensuring smooth, safe, and economical operation.

Introduction

Research Background and Significance

A bridge crane, also known as an overhead crane or traveling crane, is a type of overhead crane with a bridge running on elevated tracks. It is widely used in factories, mines, and other locations for handling large parts and heavy equipment. As a medium-sized lifting equipment, the 32/5t electric double-girder bridge crane features a main and auxiliary hoist mechanism, capable of meeting lifting requirements of varying weights and playing a vital role in industrial production.

As a core component of a bridge crane, the performance of the trolley mechanism directly impacts the crane’s operating efficiency, positioning accuracy, and operational safety. An excellent trolley mechanism design should achieve smooth starting, accurate braking, and reliable operation, while also ensuring high energy efficiency and a long service life.

Design Task Overview

This design task involves the trolley mechanism for a 32/5t electric double-girder overhead crane. Key technical parameters are as follows:

• Lifting capacity: Main hook 32t / Auxiliary hook 5t
• Working class: M5
• Operating speed: 45m/min
• Track gauge: 2500mm
• Wheelbase: 2700mm (reference value)
• Trolley deadweight: Approximately 11.5t
• Lifting height: Main hook 16m / Auxiliary hook 18m

Overall Design of the Trolley Operating Mechanism

Structural Composition and Operating Principle

The trolley operating mechanism of a 32/5t electric double-girder overhead crane primarily consists of the following components:

1. Drive Unit: Includes the motor, reducer, brake, and coupling.
2. Traveling Mechanism: Includes the wheel assembly, wheel axle, and bearing assembly.
3. Transmission System: Includes the drive shaft, coupling, and open gears.
4. Frame Structure: The metal structure that supports and connects the various components.
5. Safety Devices: Includes buffers, limit switches, and derailment prevention devices.

Operating Principle: The motor transmits power to the reducer via the coupling. After deceleration and torque amplification, the power is distributed to the drive wheels on both sides via the drive shaft. Ultimately, friction between the wheels and the rails enables the trolley to move longitudinally along the bridge’s main girder rails.

Overall Layout

Based on the specifications and operational requirements of the 32/5t crane, the trolley mechanism utilizes a centralized drive system. The specific layout is as follows:

1. Drive Method: A centrally driven electric motor on one side is used, with a drive shaft providing synchronized rotation of the driving wheels on both sides.
2. Wheel Arrangement: A four-wheel structure, with two driving wheels and two driven wheels.
3. Braking System: A normally closed brake is installed on the high-speed shaft to ensure automatic braking in the event of a power outage.
4. Transmission Layout: Motor → Brake → Reducer → Drive Shaft → Wheel Assembly

Table: Selection list of main components of trolley running mechanism

Part Name	Selection requirements	Remark
Electric motor	YZR series metallurgical lifting special motor	Consider M5 working level
Reducer	ZQ series hardened tooth surface reducer	Gear ratio matching vehicle speed
Brakes	YWZ series hydraulic push rod brake	Adjustable braking torque
Wheel set	Double rim cast steel wheels	Diameter about Φ500mm
Couplings	Gear coupling	Compensation for installation errors

Trolley Operating Mechanism Design and Calculation

Calculation Condition Determination

Based on the design parameters and actual operating conditions, the following calculation conditions were determined:

1. Lifting capacity: Q = 32t (rated load of the main hook)
2. Trolley deadweight: Gxc = 11.5t
3. Working class: M5
4. Operating speed: v = 45m/min = 0.75m/s
5. Track model: QU70
6. Wheel diameter: D = 500mm
7. Mechanical efficiency: η = 0.9
8. Operating resistance coefficient: f = 0.008 (rolling bearing)
9. Slope resistance coefficient: α = 0.001
10. Wind pressure: q = 100N/m² (not considered for indoor operation)

Operating resistance calculation

The total resistance during trolley operation includes friction resistance, slope resistance, and wind resistance (negligible for indoor operation):

1. Friction resistance:
   • Ff = (Q + Gxc) × g × f = (32 + 11.5) × 1000 × 9.81 × 0.008 = 3414.12N
2. Slope resistance:
   • Fα = (Q + Gxc) × g × α = (32 + 11.5) × 1000 × 9.81 × 0.001 = 426.77N
3. Total static resistance:
   • Fj = Ff + Fα = 3414.12 + 426.77 = 3840.89N
4. Inertial resistance (startup):
   • Assuming start time tq = 4s, then acceleration a = v/tq = 0.75/4 = 0.1875m/s². Fg = (Q + Gxc) × a × 1.1 (accounting for rotating mass inertia) = (32 + 11.5) × 1000 × 0.1875 × 1.1 = 8971.88N
5. Total dynamic resistance:
   • Fd = Fj + Fg = 3840.89 + 8971.88 = 12812.77N

Motor Selection

1. Steady-state operating power:
   • Pj = (Fj × v)/(1000 × η) = (3840.89 × 0.75)/(1000 × 0.9) ≈ 3.2kW
2. Starting power requirement:
   • Pd = (Fd × v)/(1000 × η) = (12812.77 × 0.75)/(1000 × 0.9) ≈ 10.68kW

Based on the calculated power and the crane’s operating class (M5), a YZR160M1-6 motor is selected. Its technical parameters are:

• Rated power: 11kW
• Rated speed: 953 r/min
• Rotor moment of inertia: 0.32 kg·m²
• Overload capacity: 2.8 times

Reducer selection

1. Wheel speed:
   • n = v/(πD) = 0.75/(3.14 × 0.5) ≈ 0.478 r/s 28.66 r/min
2. Total transmission ratio:
   • i = nmotor/nwheel = 953/28.66 ≈ 33.26
   • Using the ZQ-350-V-3Z reducer with a nominal transmission ratio of i=31.5, the actual operating speed is adjusted to:
   • vactual = 0.75 × 31.5/33.26 ≈ 0.71 m/s ≈ 42.6 m/min
   • Meets the design requirement of 45 ± 10% m/min.

Slip Verification

To ensure no wheel slip during startup, the following conditions must be met:

• Fg ≤ φ × (Q + Gxc) × g × (driving wheel pressure / total wheel pressure)

Assuming φ = 0.12 (dry and clean track) and assuming the driving wheel pressure accounts for 50% of the total wheel pressure:

• Fg = 8971.88N
• φ × (Q + Gxc) × g × 0.5 = 0.12 × 43.5 × 1000 × 9.81 × 0.5 = 25619.1N
• 8971.88N < 25619.1N, meeting the no-slip condition.

Key Component Design and Verification

Wheel Assembly Design

Wheel Pressure Calculation:

Assuming uniform load distribution and four-wheel support, then:

• Maximum wheel pressure Pmax = (Q + Gxc) × g/4 × 1.1 (dynamic load factor) = (32 + 11.5) × 1000 × 9.81/4 × 1.1 ≈ 117.5 kN
• Select double-rim cast steel wheels with a diameter of Φ500 mm and QU70 track. The allowable wheel pressure of 150 kN > 117.5 kN meets the requirements.

Fatigue Strength Verification:

Contact stress calculated according to ISO standards:

• σH = 0.418 × √(Pmax × E/(b × R)), where b = 70 mm (rail top width), R = 250 mm (wheel radius), and E = 2.1 × 10⁵ MPa:
• σH = 0.418 × √(117.5 × 10³ × 2.1 × 10⁵ / (70 × 250)) ≈ 880 MPa

The allowable contact stress [σH] for cast steel wheels is 1000-1200 MPa, meeting fatigue strength requirements.

Drive Shaft Design

Torque Calculation:

Maximum torque transmitted by the drive shaft:

• T = 9550 × P/n × K = 9550 × 11/28.66 × 1.5 (impact coefficient) ≈ 5500 N·m

Shaft Diameter Design:

Preliminary estimate based on torsional strength:

• d ≥ (16T/(π[τ]))^(1/3) assuming [τ] = 45 MPa:
  • d ≥ (16 × 5500/(3.14 × 45 × 10⁶))^(1/3) ≈ 0.082m = 82mm

Taking into account factors such as the keyway, the shaft diameter is Φ90mm, and the material is 42CrMo, quenched and tempered.

Strength Verification:

Based on the combined bending and torsion verification, assuming a span of L = 1000mm, then:

• M = Pmax × L/4 = 117.5 × 1000/4 ≈ 29375N·mσe = √(M² + 0.75T²)/W ≤ [σ-1]W = πd³/32 = 3.14 × 90³/32 ≈ 71500mm³σe = √(29375² + 0.75 × 5500²)/71500 ≈ 41.5MPa < [σ-1] = 60MPa, thus meeting the strength requirement.

Coupling Selection

High-Speed Shaft Coupling:

• To connect the motor and reducer, select the GICL3 drum gear coupling. Its permissible torque of 1600 N·m (> 9550 × 11/953 = 110 N·m) meets the requirements.

Low-Speed Shaft Coupling:

To connect the reducer and drive shaft, select the GICL6 drum gear coupling. Its permissible torque of 6300 N·m (> 5500 N·m) meets the requirements.

Brake Selection

Based on braking torque requirements:

Tz ≥ Kz × Tj

Where Kz = 1.75 (M5 duty cycle), Tj = 9550 × P/n = 9550 × 11/953 ≈ 110 N·m

Tz ≥ 1.75 × 110 ≈ 192.5 N·m

The YWZ-300/45 hydraulic push rod brake with an adjustable braking torque of 200-400 N·m meets the requirements.

Structural Design

Trolley Frame Design

The trolley frame utilizes a box-beam structure, consisting of two main beams and several cross beams. Material: Q235B.

1. Main beam cross section: 400mm high, 300mm wide, 8mm web thickness, 12mm flange thickness.
2. Cross beam arrangement: End beams, drive unit support beams, and hoist mechanism support beams.
3. Connection method: Main beams and cross beams are welded, with post-weld annealing for stress relief.

Track installation design

1. Track fixing: QU70 tracks are secured with pressure plates. On the upper flange of the main beam, track gauge 2500mm.
2. Track joints: 45° bevel joints with a 3-5mm gap.
3. Track top elevation difference: ≤2mm (over the entire length).

Safety device design

1. Buffers: Polyurethane buffers are installed at both ends of the trolley, absorbing kinetic energy ≥5000J.
2. Limit switches: Two-stage limit switches: the first stage decelerates, the second stage cuts off power.
3. Derailment prevention device: Guard wheels are installed on the inside of the wheels to prevent derailment.
4. Windbreak: Not required for indoor use; rail clamps are required for outdoor use.

Control System Design

Electrical Control Solution

The trolley running mechanism utilizes variable frequency speed control to achieve smooth starting and precise stopping:

1. Control Devices: Frequency converter + PLC control, encoder for speed feedback
2. Speed Range: 1:10, Steady-State Speed Difference ≤3%
3. Protection Functions: Multiple protections, including overcurrent, overvoltage, undervoltage, overspeed, and limit switches

Speed Curve Planning

Optimized starting and braking speed curves to reduce shock:

1. Startup Time: 4 seconds, acceleration 0.1875 m/s²
2. Braking Time: 3 seconds, deceleration 0.25 m/s²
3. S-shaped Curve: S-shaped speed changes are used during acceleration and deceleration to reduce shock

3D Modeling and Engineering Drawings

Based on the above design, a complete set of engineering drawings was completed using CAD software, including:

1. Trolley running mechanism assembly drawing: Demonstrates the overall layout and assembly relationships
2. Component assembly drawings: Drive unit, wheel assembly, drive shaft, etc.
3. Parts drawings: Key components such as wheels, shafts, gear couplings, etc.
4. 3D Model: Used for interference checking and motion simulation

Table: List of main engineering drawings

Pattern Name	Map Sheet	Main content
Assembly drawing of trolley running mechanism	A0	Overall layout, main dimensions
Drive assembly drawing	A1	Motor, reducer, and brake assembly
Wheel assembly drawing	A2	Assembly relationship of wheels, bearings and shafts
Drive shaft parts drawing	A3	Shaft structure, dimensional tolerance, and technical requirements
Welding diagram of trolley frame	A1	Structural dimensions, welding symbols, and process requirements

Conclusion

This design completes the comprehensive design of the trolley operating mechanism for a 32/5t electric double-girder overhead crane. Through theoretical calculations and verification, the main conclusions are as follows:

1. The trolley operating mechanism utilizes a centralized drive system, using a YZR160M1-6 electric motor (11kW) and a ZQ-350 reducer. The operating speed is 42.6 m/min, meeting the design requirement of 45 ± 10% m/min.
2. Key components such as the wheel assembly (Φ500mm double-flange cast steel wheel), drive shaft (Φ90mm 42CrMo), and coupling have all passed strength verification and meet the fatigue life requirements for the M5 duty class.
3. The use of variable frequency speed control and S-shaped speed curve planning ensures smooth starting and braking, with a maximum acceleration of 0.1875 m/s² and a deceleration of 0.25 m/s², effectively reducing impact loads.
4. Safety devices, including buffers, limit switches, and anti-derailment devices, meet the safety requirements of crane design specifications.
5. The 3D model and engineering drawings fully convey the design intent and can be used for actual manufacturing and assembly.

This design comprehensively considers performance, safety, and economic factors, providing a reference for the design of similar crane trolley operating mechanisms. Future work will allow for further optimization of the lightweight design, exploration of new transmission methods and intelligent control strategies, and advancement of the operating mechanism’s technical capabilities.