Plum-shaped elastic pads (also known as coupling spiders, elastomeric inserts, or coupling cushions) are the heart of plum blossom couplings. They transmit torque while absorbing shock, dampening vibration, and compensating for misalignment. The ML Series polyurethane pads from Apex Coupling offer a durable, maintenance-free solution for a wide range of industrial applications.

This guide explains how ML Series elastic pads work, their key advantages, and how to select the right model for your application.

1. What Is a Plum-Shaped Elastic Pad?

A plum-shaped elastic pad (also called a quincunx cushion or ML coupling spider) is a polyurethane elastomer with a distinctive multi-petal (plum blossom) shape. It is installed between the two metal hubs of a plum blossom coupling. The pad’s lobes engage with the teeth of the coupling halves, transmitting torque through radial compression.

As the coupling rotates, the polyurethane element flexes to:

• Absorb vibration – Reduces noise and protects equipment

• Dampen shock – Absorbs impact loads to prevent damage

• Compensate misalignment – Accommodates angular, radial, and axial deviations

• Provide electrical insulation – Prevents stray currents

💡 The plum-shaped elastic pad is the wear component of the coupling – designed for easy and cost-effective replacement without removing the coupling hubs.

2. Key Advantages of ML Series Polyurethane Pads

3. ML vs MT – Understanding the Difference

The naming convention can be confusing. Here’s a simple breakdown:

💡 ML is the coupling, MT is the pad. When you need to replace the elastic element in an ML coupling, you are looking for an MT series pad. The ML Series pad is the standard elastomer for ML/LM (LM/LLM) plum blossom couplings.

Example: An ML5 coupling uses an MT5 elastic pad.

4. How to Select the Right ML Series Pad

Step 1: Identify Your Coupling Model

• Check the coupling nameplate or documentation for the ML model number (e.g., ML5, ML10).

• This determines the required pad size.

Step 2: Measure the Pad Dimensions (if replacing)

• Measure the outer diameter, inner diameter, and thickness of the old pad.

• Match these dimensions to the ML Series specification table.

Step 3: Consider Operating Conditions

• Temperature: ML Series operates -35°C to +80°C.

• Oil exposure: Polyurethane is oil-resistant and wear-resistant.

• Shock loads: Polyurethane provides excellent shock absorption.

Step 4: Consider Special Requirements

• Higher torque: Consider 98 Shore A hardness for increased torque capacity .

• Custom sizes: Non-standard dimensions are available on request.

5. Applications Where ML Series Pads Excel

6. Real‑World Example – Steel Mill Upgrade

A steel mill was experiencing frequent coupling failures on their rolling mill drives. The rubber pads were degrading due to oil contamination and high operating temperatures, requiring replacement every 2-3 months.

They switched to Apex Coupling ML Series polyurethane pads (ML8, 95 Shore A, high-strength PU). Results:

• Service life extended – polyurethane pads lasted 12+ months

• Oil degradation eliminated – polyurethane’s oil resistance

• High temperature tolerance – withstood operating temperatures up to 80°C

• Maintenance reduced – no lubrication required

• Downtime reduced – fewer replacements

7. Installation & Maintenance Tips

1. Inspect the pad – Check for cracks, wear, or deformation at planned maintenance intervals

2. Clean the hubs – Remove debris before installing a new pad

3. Install the pad – Insert the pad between the two coupling hubs – ensure proper engagement

4. No lubrication required – Pad is self-lubricating

5. Replace when worn – Don’t wait for complete failure

6. Easy replacement – Pad can be replaced without removing coupling hubs

8. Selection Checklist

• □ 

  Coupling model: ML1 to ML13 – match your coupling size

• □ 

  Material: Polyurethane – oil & wear resistant

• □ 

  Hardness: 95 Shore A (standard) or 98 Shore A (higher torque)

• □ 

  Torque: 25–12500 N·m – ensure it exceeds your requirement

• □ 

  Temperature: -35°C to +80°C – verify operating range

• □ 

  Oil resistance: Excellent – suitable for oil-exposed environments

• □ 

  Application: Rolling mills, cranes, petroleum equipment, pumps, conveyors

9. Conclusion

The ML Series polyurethane plum-shaped elastic pad from Apex Coupling offers superior performance compared to rubber pads – with excellent wear resistance, oil resistance, and long service life. With ML1 to ML13 sizes covering 25–12500 N·m torque capacity, there is a pad to suit every plum blossom coupling application.

👉 Need a plum-shaped elastic pad for your coupling? Contact us with your ML model and hardness requirements.