Among all ring die parameters, compression ratio is the most critical yet most confusing. Too high, and output drops; too low, and pellets fall apart. Here’s what you need to know to get it right.

1. What Is Compression Ratio?

Compression ratio = Effective hole length ÷ Hole diameter

It reflects the extrusion intensity on the material:

Higher ratio → denser, harder pellets

Lower ratio → higher output, but looser pellets

The goal is to find the right balance for your specific material and product requirements.

2. How to Calculate It

The “effective length” varies by hole type:

Example: Hole diameter 8mm, die thickness 66mm, relief hole 18mm


Effective length = 66 – 18 = 48mm

Compression ratio = 48 ÷ 8 = 1:6

3. Reference Ratios for Common Raw Materials

Important: These are empirical references only. Always verify through actual testing with your own material.

4. Moisture Content Matters

< 12% (dry): Lower compression ratio recommended to prevent excess fines

12% – 18%: Optimal range – select ratio by material type

> 18% (wet): Moderate-to-low ratio to avoid blocking

5. Three Common Mistakes

Copying others’ ratios blindly – different machines, speeds, and designs yield different results

Chasing max output with the lowest ratio – loose pellets create more fines and downstream losses

Assuming highest ratio = best quality – over-dense pellets crack easily and waste energy

6. A Simple Selection Process

（1）Identify your raw material and typical moisture range

（2）Use the reference table to pick a starting ratio

（3）Run a test batch – measure output, hardness, and fines

（4）Adjust up or down until both output and quality meet your needs

（5）Record the optimal ratio for future orders

Tip: If you process multiple materials, keep two ring dies with different ratios and swap as needed – one size rarely fits all.

About Us

We manufacture ring dies and complete pellet production lines. If you’re unsure about the right compression ratio for your material, send us your raw material details and target output. We can offer initial recommendations based on test data.

📧 Email: sylvia@woodymech.com