WELCOME TO SHANTOU

Knowledge

Machine maintenance

Company news

Industry news

Home page

Functions of Different Screw L/D Ratios for PP Sheet Extrusion

Time: 2026-04-29 15:21:19.406

Functions of Different Screw L/D Ratios for PP Sheet Extrusion

1. Definition

The L/D ratio means the ratio of screw effective length to screw outer diameter. It is the core parameter that determines plasticating capacity, melting time, mixing effect and production stability of PP sheet extruders.

2. Low L/D Ratio: 20:1 ~ 25:1

Main Functions & Characteristics

Short residence time of PP melt inside the barrel.
Low shear heat generation, less risk of PP thermal degradation and yellowing.
Simple plasticating process, suitable for general-grade PP homopolymer.
Limitations:

Insufficient melting capacity, poor mixing uniformity, easy to produce unmelted particles, crystal points and sheet surface streaks; unable to process modified PP, filled PP or high-speed production.

Application

Only for low-demand, low-output ordinary PP sheet.

3. Medium L/D Ratio: 28:1 ~ 32:1 (Most Widely Used for PP Sheet)

Main Functions & Characteristics

Sufficient conveying, melting and homogenization length for PP crystalline resin.
Balanced residence time and shear effect; complete plasticization without overheating.
Stable melt pressure and uniform melt temperature, ensuring consistent sheet thickness and flatness.
Good adaptability: suitable for PP homopolymer, PP copolymer and slightly modified PP.
Excellent compatibility with barrier screw and mixing elements.

Application

Standard configuration for conventional PP sheet extrusion, food packaging sheet, disposable plastic cup raw material sheet.

4. High L/D Ratio: 33:1 ~ 38:1

Main Functions & Characteristics

Longer melting and mixing section, strong dispersive and distributive mixing ability.
Enough time for adding and dispersing fillers, masterbatch, toughening agents and recycled PP materials.
High output capacity, adapt to high-speed & high-efficiency production.
Limitations:

Longer material residence time; excessive shear heat may cause PP degradation, molecular chain breakage and melt discoloration; higher energy consumption.

Application

Modified PP sheet, filled PP sheet, recycled material blended sheet, high-end thick PP sheet.

5. Ultra-high L/D Ratio: Above 40:1

Main Functions & Characteristics

Super strong mixing and devolatilization performance.
Can complete extrusion, mixing, degassing and volatile removal in one step.

Limitations

Easy over-shear, severe thermal aging of PP, strict requirement on temperature and speed control.

Application

Special functional PP sheet, high filling ratio modified material, special engineering PP sheet, rarely used in ordinary food-grade PP sheet production.