A Comprehensive Guide to Hoist and Crane Duty Class Classifications
In the realm of material handling equipment, the efficiency and reliability of cranes and hoists play a pivotal role in various industries. One crucial aspect that defines their performance is the duty cycle. Understanding the duty cycle and the corresponding duty classifications is essential for selecting the right equipment to meet specific operational requirements. This comprehensive guide delves into the intricacies of crane and hoist duty classifications, exploring the standards that govern them and the factors influencing their design and performance.
Understanding Duty Cycle and Its Significance
Picture a regular car engine. It’s built for daily use, not constant racing. The same principle applies to hoists and cranes. Duty cycle means how often and intensively you’ll use your equipment. This isn’t just about hours – it’s about the weight you’re lifting and how frequently you lift it.
The crucial factor is fulfilling the requirements of the intended use, irrespective of the hoist’s capacity. Acquiring a heavy-duty hoist and occasionally utilizing it for lifting lighter loads does not classify the hoist as light-duty.
The duty cycle refers to the ratio of a device’s working time to its total cycle time. In simpler terms, it indicates how frequently a device is expected to perform its lifting operation in each time frame.
The Formula for Calculating Operating Time for Electrically Operated Hoists
For Example: If the load is lifted at 100% of the safe working load for only 1/10 of the operating time, and the total plant operates for 24 hours per day, how many hours does the plant operate each day? Given that the average hook path is 3 meters, the hoisting speed is 8 meters per minute, and there are 12 cycles per hour.
Given data:
| Average hook path (m) | 3 |
| No. of cycle/hr. | 12 |
| Plant working time/day (in hrs) | 24 |
| Hoisting Speed (m/min.) | 8 |
Using the formula:
Operating time/Day = 3.60
With the operating time, load spectrum, and load lifted during operational hours in consideration, we can now ascertain the duty class. For instance, if the daily operating time is recorded as 3.60 hours, it falls within the range of ≤4 hours, potentially corresponding to 1 Am, 2m, 3m, or 4m class. A comprehensive explanation of the process for selecting these classes will be presented in subsequent sections of the blog.
Why does this matter? Choosing the wrong duty class for your needs is like using a sports car to move furniture. It might work initially, but you’ll likely face problems down the road:
Safety risks: Pushing equipment beyond its limits can lead to breakdowns and potential accidents.
Costly repairs: Overworking your hoist or crane means quicker wear and tear, leading to hefty repair bills or even replacements.
Slowdowns and delays: Using equipment that’s too weak for the job slows operations and reduces productivity.
Know about the top 6 key considerations for buying the best hoist and crane with this blog.
Different Types of Duty Class Classifications
Various international standards govern crane and hoist duty classifications, each with its own set of criteria and parameters. In India, the three primary standards that are commonly used are:
FEM Standards
Developed by the European Material Handling Federation, this standard is widely used in Europe and globally. It classifies hoists, trolleys and bridges based on load spectrum (light, medium, heavy, very heavy) and daily operating time.
Load Spectrum
Light: Occasional lifting of light loads with extended intervals between lifts. This entails lifting the full load only 10% of the time during operation.
Middle: Lifting of moderate loads at a consistent frequency with daily operation. This involves lifting the full load for approximately 17% of the operating time.
Heavy: Frequent lifting of substantial loads with an extended daily operation period. This means the full load is lifted for around 50% of the operating time.
Very Heavy: Continuous lifting of significant loads with prolonged daily operation. This implies the full load is lifted for approximately 90% of the operating time.
Notations Used:
1Dm/1Cm: Designed for standby or infrequent usage
1Bm: Tailored for light lifting applications
1Am: Ideal for light to medium lifting demands
2m: Suited for medium to heavy lifting requirements
3m: Engineered to handle heavy lifting conditions
4m/5m: Specifically built for severe lifting applications
From 1Am to 4m, the standard duty classes are utilized.
Now continuing the above-discussed example, having the understating of the light medium, a heavy or very heavy-duty requirements the class can be chosen.
| Load Spectrum | Average Operating Time /Working Day (Hours) | ||||
| L1 | Light | 2-4 | 4-8 | 8-16 | Over 16 |
| L2 | Medium | 1-2 | 2-4 | 4-8 | 8-16 |
| L3 | Heavy | 0.5-1 | 1 – 2 | 2-4 | 4-8 |
| L4 | Very Heavy | 0.25-0.5 | 0.5 – 1 | 1-2 | 2-4 |
| Duty Class | FEM | 1Am | 2m | 3m | 4m |
| ISO | M4 | M5 | M6 | M7 | |
Given the specified operating time/day of 3.60, it’s specified that the load is lifted at 100% of the safe working load for just 1/10 of the operating time. This indicates the need for a hoist designed for light-duty applications. Accordingly, a FEM 1Am class hoist is deemed suitable for this particular requirement.
ISO Standards
The International Organization for Standardization provides a comprehensive framework for crane duty classification. ISO standards consider factors like load capacity, load spectrum, and operating conditions to assign duty classifications, ranging from M2 (light) to M7 (very heavy).
M2: Utilized infrequently, with occasional usage
M3: Involves consistently handling low average loads, occasionally lifting the maximum load
M4: Involves managing medium average loads regularly, with occasional lifting of the maximum load
M5: Regularly handles medium and heavy loads
M6: Engages in traversing or dealing with other dead loads
M7: Involves regularly managing heavy loads
From M4 to M6, the standard duty classes are utilized
IS Standards
Issued by the Bureau of Indian Standards, this standard is specific to India and categorises hoists and cranes into five classes (I, II, III, IV, V) based on duty severity and operating time.
Classes:
I: Standby (minimal usage)
II: Light (occasional usage with light loads)
III: Medium (moderate usage with varying loads)
IV: Heavy (frequent usage with heavy loads)
V: Special (for specific and heavy lifting tasks)
A summary of the above three standards duty class is as follows:
| ISO – 4301 (For Cranes and Hoists) | IS – 3832 (CPB) / IS – 3938 (WRH)/ IS – 6547 (ECH) | FEM 1.001 – 2005 |
| M3 | Class I | 1Bm |
| M4 | 1Am | |
| M5 | Class II | 2m |
| M6 | 3m | |
| M7 | Class III | 4m |
| M8 | Class IV | 5m |
Other Common Standards
CMAA Standards: The CMAA (Crane Manufacturers Association of America) standards are predominantly utilized in North America. This set of standards offers a range of classifications from Class A, suitable for standby or infrequent use, to Class F, designed for continuous severe service.
ASME Standards: Sanctioned by the American Society of Mechanical Engineers and endorsed by the American National Standards Institute (ANSI), concentrate on categorizing lifting hoists into five duty classes. Ranging from H1 (suitable for standby, installation, or maintenance work) to H5 (designed for bulk material handling and continuous severe service), these standards ensure that cranes in the U.S. adhere to specific criteria.
These criteria include factors such as determining the maximum number of starts per hour, the maximum on-time minutes per hour, and the mean effective load. The application of this standard pertains to hoists marked with typical U.S. capacities.
Remember:
- These ranges are approximations and may vary slightly depending on the specific standard and its detailed definitions
- Consulting with a qualified engineer or equipment supplier is highly recommended to ensure you select the optimal duty class for your needs
- By understanding these various duty classification types, you can choose the right hoist or crane that delivers optimal performance, ensures safety, and maximizes your investment
Factors Affecting Duty Class Selection
Several key factors influence a hoist or crane’s duty classification:
Frequency of use: How often will you be using the equipment (hourly, daily, etc.)?
Average load: What is the typical weight you will be lifting?
Maximum load: What is the heaviest weight the equipment needs to handle?
Duty cycle time: How long will each lifting cycle last?
Environment: Will the equipment be used in harsh conditions (e.g., dust, extreme temperatures, etc)?
Type of lifting: Will the equipment be used for simple lifting or more complex operations (e.g., slewing, positioning)?
Considering these factors and consulting the relevant standards helps determine the duty class that best suits your specific needs.
Check out this blog to know the high cost of ignoring quality over price in buying hoists and cranes.
Key Takeaway:
When selecting a mechanical hoist, consider the number of working hours, velocity ratio, and operating pull. The table below offers a clear method for determining the appropriate duty class for a mechanical hoist.
| Mechanism Class | Running h/day |
| 1 | 0.5 |
| 2 | 1.5 |
| 3 | 3 |
| 4 | Over 6 |
The mechanical class in this context aligns with the standard duty classes previously discussed. The choice of the mechanical class depends on the hoist’s hourly operation time.
In conclusion, a thorough understanding of crane and hoist duty classifications is paramount for making informed decisions in material handling equipment procurement. The nuances of the duty cycle, coupled with adherence to international and regional standards, empower industries to select the right equipment for their unique operational requirements. By considering factors such as load capacity, frequency of use, work environment, duty cycle, and load spectrum, stakeholders can ensure the safety, performance, and longevity of their lifting equipment. As technology advances and industry needs evolve, staying abreast of the latest standards and best practices in duty classification remains imperative for a seamless and efficient material handling process.
At Bajaj Indef, our customers often trust us to identify the most suitable crane or hoist for their applications. You can explore our dedicated page to discover the perfect crane or hoist based on your required duty cycle and other specifications. Before finalizing any duty cycle decisions, feel free to reach out to our experts via email at [enquire@indef.com] or give us a call [+91 (22) 489-33303].
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