JB/T 3668-2016 Multi-Point Underslung Crane Standard Guide
JB/T 3668-2016 "Multi-Point Suspension Cranes" is the product standard for multi-point suspension cranes. It specifies the classification, technical requirements, test methods, and inspection rules for multi-point (multi-support) suspension single-girder and double-girder cranes that operate on one or more suspension rails.
JB/T 3668-2016 is the product standard governing multi-point suspension cranes, defining their classification, technical requirements, test methods, and inspection rules. These cranes distribute the load across the factory structure through multiple suspension points, making them well-suited for material handling in workshops and warehouses with large spans and heavy lifting capacities.
Product Classification and Structure
JB/T 3668-2016 classifies multi-point suspension cranes by structure into: Double-girder multi-point suspension cranes — two suspension rails each support one main girder, held by multiple suspension units (≥4 points), with the electric hoist traveling along the main girders. Single-girder multi-point suspension cranes — one suspension rail supports a single main girder through multiple suspension units. The number of suspension points typically ranges from 2 to 8, determined by the span and rated lifting capacity.
The core component of a multi-point suspension system is the equalizing beam (spreader beam) — each suspension point is connected through the equalizing beam, which automatically rotates to redistribute the load to other suspension points when one point experiences excessive load, ensuring uniform force distribution. The standard requires the load difference between suspension points to be ≤±10%. The equalizing beam uses a box-type welded structure with a safety factor of ≥5.
Technical Requirements
Key technical requirements of the standard: The main girder deflection under rated load shall not exceed span/600. The wheel load difference between suspension points in a multi-point system shall be ≤±10% (automatically adjusted via the equalizing beam). Connection bolts between the suspension units and the runway beam shall be Grade 8.8 or 10.9 high-strength bolts. The rail installation straightness deviation shall be ≤2mm/2m. The elevation difference between rails shall be ≤5mm.
Additional requirements: The hoisting and travel mechanisms of the electric hoist shall comply with JB/T 9008.1 and JB/T 9008.2. The electrical control system shall include overload protection, short-circuit protection, and emergency stop functions. The work duty classification of the complete crane shall be determined per ISO 4301. Wind and anti-slip protection — multi-point suspension cranes used outdoors shall be equipped with rail clamps or anchor devices.
Runway and Factory Building Requirements
Multi-point suspension cranes impose special requirements on the factory structure: The maximum load at each connection point of the suspension rail must be within the design load-bearing capacity of the factory roof trusses. A load-bearing capacity verification of the roof trusses and columns must be performed before installation — with particular attention to local loads at connection points. The runway beam uses H-beam (sized based on span, wheel load, and suspension spacing), and the runway beam deflection shall not exceed span/800.
Rail installation requirements: The rail installation straightness deviation shall be ≤2mm/2m, with a cumulative deviation of ≤10mm over the full length. The vertical difference at rail joints shall be ≤1mm. The spacing between rail-to-truss connection points is typically 2–3m. Connection bolt torque shall be applied per the design requirements. Both ends of the rail shall be fitted with end stops and buffers. Kelude offers factory load-bearing capacity assessment and rail design services for multi-point suspension cranes.
Inspection and Maintenance
Factory Acceptance Test: No-load test, static load test (checking that the load difference between suspension points is ≤±10% at 1.25 times the rated load), and dynamic load test. Type tests are conducted every 5 years. In-service inspection — monthly checks for wear and loosening of suspension connection components and lubrication condition of the spherical plain bearings in the equalizing beam. Quarterly checks on the uniformity of load distribution across suspension points.
A comprehensive inspection is performed annually: static load test to verify main girder deflection and load equalization across suspension points, and non-destructive testing of welds and base metal on all load-bearing members. If the load difference exceeds ±15% during inspection, the equalizing beam shall be adjusted or worn spherical plain bearings replaced.
Rated Lifting Capacity
1~32t
Span Range
6~30m
Number of Suspension Points
2~8
Travel Speed
10~25m/min
Work Duty Classification
A3~A6
Rail Type
H-Beam or I-Beam
Kelude Heavy Industry: Overhead & Gantry Crane Solutions
Kelude Heavy Industry specializes in the design and manufacture of heavy-duty overhead cranes and gantry cranes. Our product range covers a wide spectrum of industrial lifting applications, from single-girder and double-girder overhead cranes to versatile gantry systems and specialized explosion-proof configurations. We deliver reliable, high-performance crane solutions tailored to the specific demands of modern manufacturing, logistics, and processing facilities.
Diverse Crane Types for Every Industrial Application
Our portfolio includes a comprehensive selection of crane types, each engineered to meet distinct operational requirements. Whether you need a compact solution for a light workshop or a high-capacity system for heavy steel processing, we offer a crane designed for the job. The table below outlines our primary crane categories and their typical applications.
| Crane Type | Typical Applications |
| Single-Girder Overhead Crane | Light to medium duty workshops, maintenance bays, and assembly lines. |
| Double-Girder Overhead Crane | Heavy-duty manufacturing, steel yards, and high-capacity lifting tasks. |
| Gantry Crane | Outdoor storage yards, precast concrete plants, and shipping terminals. |
| Explosion-Proof Crane | Hazardous environments such as chemical plants, paint shops, and oil & gas facilities. |
Key Features for Enhanced Performance and Safety
Our cranes are built with advanced features that prioritize operational efficiency, safety, and longevity. From precision control systems to robust mechanical components, every aspect is designed to deliver dependable performance in demanding industrial settings.
- High-Strength Steel Construction: Ensures durability and long service life even under continuous heavy use.
- Precise Speed Control: Offers smooth and accurate load positioning, enhancing productivity and safety.
- Multiple Safety Protections: Includes overload limiters, emergency stops, and travel limit switches to safeguard personnel and equipment.
- Low-Maintenance Design: Utilizes sealed bearings and self-lubricating components to minimize downtime.
- Customizable Configurations: Options for cab or pendant control, various lifting heights, and specialized end carriages to fit your facility.
Technical Specifications and Customization Options
We understand that every facility has unique requirements. Therefore, we offer extensive customization options for our cranes, including span, lifting height, and control systems. Our engineering team works closely with you to specify a crane that integrates seamlessly into your existing workflow. Below are some of the key technical parameters we can adapt to your needs.
| Parameter | Standard Range / Options |
| Lifting Capacity | From 1 ton to over 100 tons (custom capacities available) |
| Span | Up to 40 meters (131 feet) or more, depending on configuration |
| Lifting Height | Typically 6 to 18 meters (20 to 60 feet), customizable |
| Control Mode | Pendant station, wireless remote, or operator cab |
| Power Supply | Standard 3-phase AC power, voltage and frequency per your local grid |
Quality Assurance and International Standards Compliance
Kelude Heavy Industry is committed to delivering products that meet rigorous international quality and safety benchmarks. Our design and manufacturing processes adhere to recognized standards, ensuring reliable operation and regulatory compliance. We align our practices with global norms such as ISO 4301 for crane classification and ISO 12480 for safe use, reflecting our dedication to world-class quality.
All cranes undergo stringent testing and inspection procedures before delivery. This includes load testing, functional checks, and verification of safety devices. Our quality management system ensures traceability and consistency throughout the production process, providing you with a dependable and compliant lifting solution.
Frequently Asked Questions (FAQ)
Q: What is the typical lead time for a custom overhead crane?
A: Lead times vary depending on the complexity and specifications of the crane. Standard models can often be delivered within 4-6 weeks, while fully customized systems may require 8-12 weeks or more. We provide a detailed schedule upon project confirmation.
Q: Do you provide installation and commissioning services?
A: Yes, we offer professional installation and commissioning services. Our experienced technicians can supervise or fully manage the installation process to ensure your crane is set up correctly and safely, minimizing downtime.
Q: What kind of after-sales support and warranty do you offer?
A: We provide comprehensive after-sales support, including a standard warranty period and access to spare parts. Our service team is available for maintenance, troubleshooting, and technical consultations to ensure the long-term reliability of your equipment.
Q: Can you supply cranes for explosion-proof or hazardous areas?
A: Absolutely. We manufacture cranes specifically designed for hazardous environments, complying with relevant safety regulations. These cranes feature explosion-proof electrical components and specialized mechanical designs to operate safely in classified areas.
Q: How do I determine the right crane capacity for my application?
A: Determining the right capacity involves assessing the maximum load weight, duty cycle, and lifting frequency. Our engineering team can assist you in analyzing your requirements and recommend the most suitable crane class and capacity for optimal performance and longevity.
Q: Are your cranes compliant with international standards?
A: Yes, our cranes are designed and manufactured in accordance with major international standards, including ISO 4301 for classification and ISO 12480 for safe use. We can also adapt designs to meet specific local regulations or project requirements.
| Parameter | Multi-support Underslung Crane (Underhung Crane) | Standard Underslung Crane (Underhung Crane) |
|---|---|---|
| Number of suspension points | 2~8pcs | 2pcs |
| Maximum Span | ≤30m | ≤15m |
| Maximum lifting capacity | ≤32t | ≤16t |
| Wheel load Distribution | Uniformly distributed | Concentrated |
| Crane Rail Specification | Heavy-duty H-Beam | I-Beam |
| Factory buildingrequirements | Requires load calculation | Standard |
Underslung Crane FAQ: Multi-Point Systems Explained
Q: What is the difference between a multi-point underslung crane and a standard underslung crane?
A: A multi-point underslung crane distributes the load across the factory building structure through multiple suspension points (2–8), enabling larger spans (up to 30 m) and higher lifting capacities (up to 32 t). A standard underslung crane has only two suspension points, limiting it to spans of 15 m or less and lifting capacities up to 16 t. In multi-point systems, the suspension points are interconnected via equalizing beams to ensure uniform load distribution across all points.
Q: How does load equalization work in a multi-point system?
A: In a multi-point system, the suspension points are connected through equalizing beams (spreader beams) or spherical plain bearings. When one suspension point experiences a higher load, the equalizing beam automatically pivots to redistribute the excess load to the other suspension points. The standard requires that the load difference between any two suspension points not exceed ±10%. Equalizing beams must undergo strength verification with a safety factor of at least 5.
Q: What are the rail installation requirements for multi-point underslung cranes?
A: Crane rails should be H-beams selected based on span and wheel load. The straightness deviation of the rail installation must not exceed 2 mm per 2 m, with a maximum cumulative deviation of 10 mm across the full length. The elevation difference between individual rails in a multi-point track system must be kept within 5 mm. Rails are secured to the factory building structure using Grade 8.8 high-strength bolts, with no fewer than four bolts per connection point.
Q: What are the key maintenance inspection points for multi-point systems?
A: Monthly inspections should cover wear and loosening of suspension point connections, as well as the lubrication condition of the spherical plain bearings in the equalizing beams. Quarterly inspections verify that load distribution across suspension points remains uniform, which is done by measuring wheel loads at each point or detecting deformation in the suspension beams. An annual inspection checks all load-bearing components for cracks in weld seams and base metal.
