如何选择桥式起重机工作等级?

Selecting the correct overhead crane duty class is one of the most critical decisions before you purchase an 桥式起重机. Many buyers only focus on lifting capacity, span and lifting height, while ignoring duty classification. An undersized duty class leads to premature wear, frequent breakdowns and safety risks; an overspecified class wastes your budget.

Overhead crane duty class (also called working group or service class) follows ISO 4301-1 标准, graded from A1 to A8. It is determined by two core factors: total lifting cycles over design life and load spectrum (the percentage of full-load lifts). WEIHUA overhead cranes are designed strictly according to this classification system to fit different industrial workloads.

What is overhead crane duty class?

Duty class defines the designed working intensity of an 桥式起重机. It tells engineers how heavy and how often the crane will work throughout its service life.

• ◆ Utilization: total number of lifting cycles, 工作时间, shifts per day
• ◆ Load spectrum: how often you lift light, medium or near-rated maximum load

A1 stands for standby, very light intermittent use; A8 is for continuous severe heavy-duty service. Different duty classes decide the design of main beams, 提升机, 电机, 刹车, wheels and wire ropes.

笔记: Duty class is NOT equal to crane tonnage. Two 10-吨桥式起重机 can be A3 for maintenance and A6 for production line use, with completely different component configurations.

ISO A1–A8 overhead crane duty class quick reference

Crane duty class A1-A8 classification diagram

• ◆ A1–A3 Light Duty: Infrequent operation, mostly light loads, rare full-load lifting. Annual working hours ≤200. Typical use: 设备维护, power station standby crane, workshop installation.
• ◆ A4–A5 Medium Duty: Regular single-shift operation, mixed light and half loads, occasional full load. Annual working hours 200–600. Typical use: general machining workshop, 仓库, light assembly line. This is the most popular overhead crane class for standard factories.
• ◆ A6–A7 Heavy Duty: Multi-shift continuous production, frequent near-full-load lifts. Annual working hours 600–2000. Typical use: steel fabrication, 铸造厂, raw material handling, port and logistics yard.
• ◆ A8 Severe Duty: Non-stop heavy cycles, most lifts close to rated load, 24h continuous production. Typical use: metallurgical ladle handling, high-volume automated production lines.

Key factors to evaluate before selecting overhead crane duty class

Before confirming A1-A8 class, collect these site data:

• 1. Lifting frequency: average lifts per hour, working hours per shift, shifts per day, working days per year
• 2. Load spectrum: percentage of lifts at 0–30%, 30–70% and 70–100% of rated capacity
• 3. Design service life: expected service years and total lifecycle lifting cycles
• 4. Working environment: normal room, 高温, 灰尘, corrosive or metallurgical conditions
• 5. Movement requirement: frequent trolley and bridge travel, fast speed, continuous production tasks

Step-by-step process to select overhead crane duty class

步 1: Record real lifting cycles

Count average lifts per hour × working hours × shifts × working days, then multiply by target service life to get total cycles. Higher cycles mean higher duty class.

步 2: Calculate load spectrum

If most lifts are below half capacity, the load spectrum is light. If you regularly lift full or near-max load, you must upgrade the duty class.

步 3: Match cycles + load spectrum to ISO 4301 table

Combine the two values to get the preliminary A-class. 例如: moderate cycles + frequent half-load lifts usually falls to A5. High cycles + regular full loads requires A6 or above.

步 4: Add environment and safety margin

高温, 灰尘, impact load or critical safety applications require upgrading one duty class upward as a safety buffer.

步 5: Confirm with crane supplier

Send your working data to WEIHUA technical team. We will verify the duty class and recommend single girder or double girder overhead crane, matched hoist and control system.

Common mistakes when choosing overhead crane duty class

• 1. Choose low duty class just to cut cost for frequent production → fast component failure
• 2. Specify A7/A8 for occasional maintenance lifting → unnecessary high investment
• 3. Confuse CMAA service class with ISO A1-A8, causing mismatch in international procurement
• 4. Ignore trolley and bridge travel cycles, only count hoist lifting cycles

Why choose WEIHUA overhead cranes with correct duty class

WEIHUA designs overhead cranes strictly by ISO 4301 duty classification. Each component, including hoist, 减速器, brake and main girder, is sized for your confirmed A-class.

• ◆ Stable performance under matched workload
• ◆ Longer service life and lower maintenance cost
• ◆ Full compliance with global industrial safety codes
• ◆ Custom single girder, double girder and explosion-proof overhead crane solutions

常问问题

Q1: Can an A5 overhead crane run two shifts every day?

A5 fits regular single-shift work. Continuous two-shift heavy production usually requires A6.

Q2: What duty class overhead crane do I need for warehouse loading and unloading?

Most general warehouses adopt A4 or A5 overhead cranes.

Q3: Is FEM class the same as ISO A duty class?

They follow the same logic of utilization and load spectrum, with different naming systems. WEIHUA can provide both standard versions for your tender.

Final tips

How to select overhead crane duty class depends on your real workload rather than tonnage. Provide accurate lifting frequency and load distribution to your crane manufacturer, so you get an overhead crane that balances safety, durability and cost. Contact WEIHUA today to get professional duty class assessment and overhead crane quotation.