Chain blocks, also known as chain pulley blocks, are a type of lifting device that uses a chain to raise and lower loads. They provide mechanical advantage through a system of pulleys. When selecting and using chain blocks, it is important to consider the working load limits and safety factors to ensure safe and efficient lifting.
What Is A Safety Factor?
A safety factor is the ratio of breaking strength to working load limit. It indicates the block’s maximum load capacity relative to its forces under normal operation. Safety factors are incorporated into chain block design to account for dynamic loads, impact forces, wear and other unforeseen stresses.
Typical safety factors for chain blocks range from 3 to 5. This means the block has 3 to 5 times the capacity it is rated for under normal use. Regulatory bodies like OSHA require a minimum safety factor of 5 for most general purpose lifting equipment. However, specialized chain blocks can have lower safety factors depending on the application, such as chain pulley block 20 ton.
Working Load Limit (WLL)
The working load limit (WLL) refers to the maximum load a chain block is as designed to safely lift under normal operation. The WLL takes into account the safety factor incorporated into the block’s design and components. Chain blocks are typically rated with a specific WLL that is significantly lower than their ultimate breaking strength.
Under normal usage, the sum of all loads acting on a chain block should not exceed its stated WLL. Overloading chain blocks increases the risk of component failure and accidental release of the load. Always refer to the WLL mark or data plate when selecting the appropriate size chain block for a given lifting task.
Factors That Impact Safety
Several factors influence the safety factor and WLL of chain blocks:
- Pulley Size & Number – More/larger pulleys provide higher mechanical advantage but lower load capacity.
- Chain Grade – Higher grade chain with greater breaking strength allows for higher WLLs.
- Component Quality – Better material and construction techniques increase rated capacities.
- Certifications – Certified chain blocks by reputable standards organizations provide a defined WLL.
- Application – Specialized blocks for severe service have lower safety factors for cost efficiency.
Overview For The Safety Factors Of Chain Blocks
The safety factor and working load limit of chain blocks indicate their rated lifting capacity relative to their actual breaking strength. Safety factors of 3 to 5 times are common for general purpose chain blocks, providing a buffer for unforeseen loads and stresses.