Extruder Operation and Control - Paulson Training

Summary

This video script explores the inner workings of an extruder, detailing how plastic raw material moves by gravity into the feed throat and is conveyed forward by a rotating screw through a heated barrel. The decreasing channel depth and shear heating from screw rotation melt the plastic. A screen pack and breaker plate filter contaminants, ensuring the melt is well mixed and at the correct temperature and pressure for extrusion.

Takeaways

• 🔧 The extruder's function is to process plastic raw material into a melt.
• 📉 The plastic travels by gravity from the hopper to the feed throat.
• 🔄 The rotating screw conveys the plastic forward through the heated barrel.
• 🔥 Shear heating, caused by compression and screw rotation, melts the plastic.
• 📍 The channel depth decreases along the screw, forcing the plastic through a smaller area.
• 🌡️ The barrel heating system works in conjunction with shear heating to melt the plastic.
• 🔍 A screen pack filters contaminants from the melt.
• 🏗️ The breaker plate supports the screen pack and allows the plastic to pass through.
• 📉 The screen pack is arranged with the coarsest screen next to the breaker plate for support.
• ⚙️ The screen pack consists of wire mesh filters, typically from 20 to 100 mesh.

Q & A

What is the function of the hopper in an extruder?

The hopper holds the plastic raw material and allows it to travel by gravity to the feed throat.

How does the rotating screw in an extruder contribute to the plastic's movement?

The rotating screw conveys the plastic forward through the heated barrel.

What is the purpose of the heated barrel in an extruder?

The heated barrel helps to melt the plastic as it is conveyed forward by the screw.

What is shear heating and how does it occur in an extruder?

Shear heating is the generation of heat caused by friction as the plastic is compressed and rotated along the screw.

Why does the channel depth decrease along the screw?

The channel depth decreases to force the plastic through a smaller area, which helps in melting it by increasing pressure and shear heating.

What is the ideal state of the plastic by the time it reaches the end of the screw?

By the time the plastic reaches the end of the screw, it should be well mixed, at a proper temperature, and at the necessary pressure for the die.

What is the role of the screen pack in an extruder?

The screen pack filters contaminants from the melt by forcing the plastic to flow through a set of wire mesh filters.

What does the term 'mesh' indicate in the context of screen packs?

The term 'mesh' indicates the number of wires per inch in the screen pack filters, typically ranging from 20 to 100 mesh.

What is the purpose of the breaker plate in an extruder?

The breaker plate is a sturdy metal plate with holes that supports the screen pack and allows the plastic to pass through.

Why is the order of screen mesh important in the screen pack?

The screen pack must be set with the coarsest screen next to the breaker plate so that each screen can support a finer one, preventing pressure differences from breaking the fine wires.

What can happen if the screen pack is not properly set up?

If the screen pack is not properly set up, it can contaminate the product, cause damage to the die, and lead to permanent damage.