Slewing Unit for Tower Cranes: Specifications and Selection Guide

Product Specifications

Technical details and manufacturing context for Slewing Unit

Definition

The slewing unit is a critical component of a tower crane that facilitates the horizontal rotation of the crane's upper works, including the jib (working arm) and counter-jib (counterweight arm). It is mounted between the stationary tower (mast) and the rotating superstructure (slewing platform), allowing the crane to swing loads through a full 360-degree circle. This precise rotational movement is essential for accurate load positioning on construction sites. The unit typically consists of a large-diameter slewing bearing (ball or roller bearing) that supports the rotating superstructure. A slewing drive mechanism, often comprising an electric motor, gear reducer (planetary or worm gear), and pinion, engages with a gear ring attached to the bearing. When activated, the motor drives the pinion, which rotates the entire upper structure around the fixed tower. Modern units often incorporate frequency-controlled drives for smooth, controlled acceleration and deceleration. The slewing unit must withstand significant axial, radial, and tilting loads, as indicated by parameters such as max axial load (500–1500 kN), max radial load (200–600 kN), and max tilting moment (500–2000 kN·m). The rated torque ranges from 100 to 500 kN·m, determining the maximum load the crane can rotate. Rotation speed is typically 0.1–0.8 r/min for safe load handling. The unit operates within a temperature range of -20 to 60 °C and requires hydraulic flow of 20–60 L/min if hydraulically driven. Protection class IP54–IP65 safeguards against dust and water jets. Materials include high-strength alloy steel, case-hardened bearing steel, and cast steel, with gear hardness specified as HRC 50–55. The mounting diameter ranges from 800 to 1600 mm, and the unit weight is 500–2000 kg. These values are reference ranges; verify model-specific specifications with the manufacturer.

Working Principle

The slewing unit operates by using a large-diameter slewing bearing to support the rotating superstructure. A drive mechanism, typically an electric motor with a gear reducer (planetary or worm) and a pinion, engages with a gear ring on the bearing. When the motor turns the pinion, it rotates the entire upper structure around the fixed tower. Frequency-controlled drives allow smooth acceleration and deceleration. The bearing handles axial, radial, and tilting loads, while the gear hardness ensures wear resistance. The unit's rotation speed is kept low (0.1–0.8 r/min) for precise load positioning.

Common Materials

High-strength alloy steel, Case-hardened bearing steel, Cast steel

Technical Parameters

Parameter	Typical range	Notes & selection driver
Rated Torque	100–500 kN·m	Determines the maximum load the crane can rotate.
Rotation Speed	0.1–0.8 r/min	Typical operating speed for safe load handling.
Slewing Angle	360 °	Full rotation capability.
Hydraulic Flow Rate	20–60 L/min	Required flow for the hydraulic motor.
Operating Temperature	-20–60 °C	Outside this range, seals may fail.
Protection Class	IP54–IP65	Protects against dust and water jets.IEC 60529
Material Grade	Q345B	High-strength structural steel for the housing.GB/T 1591
Gear Hardness	HRC 50–55	Ensures wear resistance and long life.ISO 6336
Weight	500–2000 kg	Affects crane counterweight requirements.
Mounting Diameter	800–1600 mm	Must match the tower top flange.
Max Axial Load	500–1500 kN	Vertical load capacity from the upper structure.
Max Radial Load	200–600 kN	Horizontal load capacity from wind and load swing.
Max Tilting Moment	500–2000 kN·m	Critical for stability under eccentric loads.

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Components / BOM

Slewing Bearing
Supports the rotating superstructure and facilitates smooth rotation with minimal friction.

Material: Case-hardened bearing steel
Slewing Motor
Provides the primary rotational power to drive the slewing mechanism.

Material: Copper windings, steel housing
Planetary Gear Reducer
Reduces the high-speed, low-torque output of the motor to low-speed, high-torque output suitable for rotating the crane.

Material: Alloy steel gears, cast iron housing
Pinion Gear Part
The final drive gear that meshes with the bearing's internal or external gear ring to transmit rotation.

Material: Hardened alloy steel
Frequency-Controlled Drives
Ramp the slew motor up and down so the load does not swing.

Industry Taxonomies & Aliases

Commonly used trade names and technical identifiers for Slewing Unit.

Applied To / Applications

This component is essential for the following industrial systems and equipment:

Tower Crane

View system integration details

Manufacturers of Slewing Unit

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Frequently Asked Questions

What is the function of a slewing unit in a tower crane?

The slewing unit enables the horizontal rotation of the crane's upper structure (jib and counter-jib) relative to the stationary tower, allowing 360-degree load positioning.

What are the key parameters to consider when selecting a slewing unit?

Key parameters include rated torque (100–500 kN·m), rotation speed (0.1–0.8 r/min), max axial load (500–1500 kN), max radial load (200–600 kN), max tilting moment (500–2000 kN·m), mounting diameter (800–1600 mm), and operating temperature (-20 to 60 °C). Always verify with the manufacturer.

What materials are commonly used in slewing units?

Common materials include high-strength alloy steel, case-hardened bearing steel, and cast steel. Gear hardness is specified as HRC 50–55 for wear resistance.

How does the slewing unit achieve smooth rotation?

Modern units often use frequency-controlled drives that provide controlled acceleration and deceleration, ensuring smooth and precise rotation. The gear reducer and pinion mechanism also contribute to stable movement.

Data Basis

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Preliminary Technical Classification

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pressure:	Not applicable (mechanical assembly)
other spec:	Max torque: 50-500 kNm (depending on model), Max axial load: 100-1000 kN, Max radial load: 50-500 kN
temperature:	-20°C to +50°C

Slewing Unit

Product Specifications

Industry Taxonomies & Aliases

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