How to Calculate SWL of Wire Rope Sling

The Safe Working Load (SWL) of a wire rope sling is an essential factor in lifting operations. It determines the maximum weight a sling can safely handle without risk of failure. Calculating SWL is simple, and this guide explains the formula in a way that everyone can understand.

Introduction 

The Safe Working Load (SWL) of a wire rope sling is the maximum weight it can safely lift without breaking. Knowing the SWL is important for safe lifting. This guide explains the formula in an easy way.

What is SWL (Safe Working Load)?

SWL refers to the maximum load a wire rope sling can safely carry under normal conditions. This value is calculated using the diameter of the rope and a safety factor, ensuring the sling operates within safe limits.

Formula to Calculate SWL of Wire Rope Sling

The standard formula for SWL of a wire rope sling is:

SWL = (D × D) ÷ 8 × SF

Where:

For a simple calculation, another commonly used formula is:

SWL = D × D × 8

Example Calculation of SWL

Let’s say you have a wire rope sling with a diameter of 10mm and a safety factor of 5.

Using the formula:

SWL = (10 × 10) ÷ 8 × 5

SWL = (100 ÷ 8) × 5

SWL = 12.5 × 5

SWL = 62.5 kg

So, the Safe Working Load (SWL) is 62.5 kg for this wire rope sling.

Wire Rope Slig SWL Calculator 

Factors Affecting SWL of Wire Rope Slings

Several factors can influence the SWL of a wire rope sling, including:

• Rope Diameter – Thicker ropes have a higher SWL.
• Rope Material – Steel ropes have higher SWL than fiber ropes.
• Safety Factor (SF) – Different applications may require a higher SF.
• Sling Angle – A wider angle reduces the effective SWL.
• Wear and Tear – Damaged ropes lower the SWL significantly.

SWL of Wire Rope Sling in Different Configurations

The SWL of a wire rope sling changes depending on the sling configuration used.

For example, if a single-leg sling has an SWL of 500 kg, a two-leg sling at a 90° angle can lift 700 kg.

Safety Tips for Lifting Operations

1. Check Manufacturer Guidelines – Always refer to the SWL chart provided.
2. Inspect the Wire Rope – Check for wear, broken strands, or corrosion.
3. Use Proper Sling Angles – Avoid sharp angles that reduce load capacity.
4. Never Exceed SWL – Overloading can cause sling failure.
5. Train Workers – Ensure personnel understand safe lifting techniques.

Conclusion

Calculating the SWL of a wire rope sling is simple using the formula SWL = (D × D) ÷ 8 × SF. By considering factors like rope diameter, safety factors, and sling angles, you can ensure safe lifting operations. Always follow safety guidelines and inspect slings regularly to prevent accidents.

FAQ's 

Frequently Asked Questions (FAQs) on Wire Rope Sling SWL

1. What is the safest angle for a wire rope sling?

The safest angle for a wire rope sling is 90 degrees (vertical lift), as it ensures maximum lifting capacity without additional stress on the sling. However, angles between 60° to 90° are generally considered safe.

2. What is the maximum capacity angle for a wire rope sling?

The maximum capacity is usually achieved at a 90° vertical lift. However, for multi-leg slings, the 120° angle provides a balance between increased capacity and safe load distribution. Exceeding 120° significantly reduces the SWL and increases the risk of failure.

3. How does the sling angle affect the SWL of a wire rope sling?

The sling angle directly affects the load capacity. As the angle increases (moves away from vertical), the effective SWL decreases. For example:

4. What happens if I exceed the safe working angle?

Exceeding the safe working angle puts excessive tension on the sling, reducing its effective SWL. It can cause the sling to break, slip, or fail, leading to serious accidents. Always refer to the SWL chart for correct angles and adjustments.

5. How do I calculate SWL for a multi-leg wire rope sling?

For multi-leg slings, use the SWL of a single-leg sling and multiply it by the load factor based on the sling angle. Example:

6. How often should wire rope slings be inspected?

Wire rope slings should be inspected before each use and regularly as per OSHA/ISO guidelines. A thorough inspection should check for broken strands, corrosion, wear, and deformation.

7. What is the best way to store wire rope slings?

Store wire rope slings in a dry, clean area, away from moisture, chemicals, and extreme temperatures. Keep them off the ground and coiled properly to avoid kinks and damage.

8. Can a damaged wire rope sling be repaired?

No, a damaged wire rope sling should never be repaired or reused. If any signs of wear, broken strands, or deformation appear, the sling must be replaced immediately to ensure safety.

9. Why do wire rope slings have a safety factor?

A safety factor (typically 5 or 6) is applied to compensate for unexpected loads, wear, and environmental conditions. It ensures that the sling operates safely even under slightly adverse conditions.

10. How do I choose the right wire rope sling for my lifting application?

Consider the following factors when choosing a wire rope sling: