Chapter 17
PLASTICS SYSTEMS
OBJECTIVES
After studying this chapter, the student will be able to:
▪ Describe a typical plastics plant equipment and operation.
▪ Review the granule storage and feed systems.
CHAPTER 17 REVIEW QUESTIONS
1. What is an extruder, and how does it work? Answer: An extruder is a complex device
composed of a heated jacket, a set of screws or screw, a heated die, large motor, gear box
2. Describe the sequence of events through a typical plastics plant. Answer: Granules are
transferred via an air system to the extruder feed tank. A pre-determined amount of
granules are dumped into the ribbon blender from the feed tank and blended with an
additive. This is metered into the homogenizer. Granules or powder is fed through a two
3. Describe how a granules feeder operates. Answer: The granules feeder conveys granules
from the feed tank to the Homogenizer . Granules leave the feed tank continuously when
the Extruder is in operation. They drop into a variable speed screw that leads to a scale.
4. What is a pelletizer? Answer: The Pelletizer’s rotating knives cut the strands of polymer
as they leave the die holes in the Extruder, producing pellets, the product of the Extruder
5. What is a pellet dryer and how does it work? Answer: The Dryer/Classifier System
removes pellet water from the pellets and classifies them according to size. There are
five different pieces of equipment in the Dryer/Classifier System.
• Scalping Box
6. Describe a screen pack. Answer: A screen pack is a polymer filtering device. It comes in
a variety of designs and shapes which range from circular, flat multi-layered screens to a
7. Describe a dry additive system. Answer: A dry additive system includes a series of
feeders, blenders and storage hoppers designed to mix and feed special chemical
8. Contrast the auxiliary, gearbox and main drive systems. Answer: The Main Drive System
has a 6000 horsepower AC electric motor. It turns the screws that melt and force the
polymer through the Extruder. This movement creates a mechanical energy which
contributes to the melting process. The system consists of the following:
• motor
• desch coupling
Auxiliary Motor System
The Auxiliary Drive Motor connects to the Main Drive through the Auxiliary Drive
Coupling. The Auxiliary Drive is designed to slow roll the screws. This will purge the
barrel of any polymer that remains in it. This purge is necessary because the barrel must
be empty, or almost empty, before the main drive will be allowed to start. The auxiliary
drive consists of a(n):
• motor -explosion proof, 100 hp; 460 volt; General Electric motor
• auxiliary drive coupling
• gear reducer.
Gear box
The Gearbox Lube Oil System is a force-fed, closed loop arrangement supplying oil to
the pinion shaft bearing assembly, thrust bearing assembly, all bearings and gear tooth
intermesh. The Gearbox Lube Oil System keeps the Extruder Gearbox cooled and
lubricated, thereby preventing damage to the gears. The Gear Box Pump is a 25 hp/1750
9. What is a melt divert valve? Answer: The melt divert valve is a large ball valve designed
10. Why do plastic granules need to be melted and extruded? Answer: The purpose of the
extruder is to melt the granule mixture, quickly quench it, and cut it into small pellets that
11. Explain how a classifier operates. Answer: The classifier is a vibrating tub with screens
in two stages that permit the desired size of pellets to pass through. Larger pellets or
12. What is a star feeder? Answer: A star feeder is a solids feeder connected to an air system
that is used to transfer plastic. When the slide valve is opened under a feed tank,
13. What is a pelletizer hub used for? Answer: The hub holds the blades that cut the pellets
14. What keeps the molten pellets from sticking together? Answer: The water quenches the
15. What are the four major sections of a polypropylene plant? Answer: Maintenance,