Extruder Flashcards
the equipment used to convert the solid plastic, usually in pellet form, into a melt.
extruder
is used for film and sheet, and is part of a blow molder for bottles.
extruder
is the granulated scrap from the conversion process
regrind
the screw if generally divided into three sections:
- the solids conveying section
- the compression or melting section
- the metering or pumping section
are usually circular in cross section, to avoid stagnant areas in the flow path
hoppers
a too-rapid decrease in diameter of the hopper can cause
bridging
hoppers can also be equipped with ______ to help in forcing plastic material into the throat of the extruder
augers
is often provided at the hopper and feed port, to prevent premature melting of the plastic, which can create blockages that interfere with a consistent rate of flow of the plastic into the extruder
cooling
responsible for conveying the plastic forward in the extruder
friction between the plastic and the barrel
This is the part of the extruder that determines the shape of the molten polymer as it exits the machine.
Die
True or False. The channel depth ratio in the feed section is greater than that in the metering section of the extruder.
True
True or False. Inside the barrel, the pellets should slip on the screw surface and stick to the inside barrel surface in order to be conveyed forward.
True
What do you call the machine that melts the polymer resins?
Extruder
True or False. Extruders by design can only have one hopper.
False
This is the part of the extruder that filters the molten polymer coming out.
Breaker Plate/Screen Pack
This is the body of the extruder which contains the screw.
Barrel
Which section in the extruder does the actual melting of the pellets take place?
Transition
This is the part of the extruder where pellets are placed.
Hopper
An extruder has the specs of 24:1. What does this mean?
The screw length is 24 times the barrel diameter
This part of the screw is responsible for delivering molten polymer at a desired and uniform rate to the shaping device.
metering section
The ratio of the depth of the channels in the feed section to the depth of the channels in the metering section
channel depth ratio
main function of the compression section of the screw
melting of the plastic
function to create back-flow and increased shearing to aid in the dispersion of the nonuniformity, and are typically located within the metering section of just after it
mixing devices
variety of mixing devices
pin, pineapple, Maddock and Dulmage designs
Extruder output is proportional to
the cube of the inside diameter of the barrel.
The ratio of the depth of the channels in the feed section to the depth of the channels in the metering section, called the
channel depth ratio
.Dies generally have at least _____ temperature control zone, independent of the extruder temperature settings, and may have several
one
Extruders generally contain _____ for filtering impurities out of the melt
screens
The amount of power required is affected by
the viscosity (resistance to flow) of the polymer and the back pressure generated by the die.
In this type of extruder, a vacuum is applied to the melt through a specially designed vent port on the side of the barrel
vented extruder
contain two screws.
-they can mix components much more effectively than single screw extruders, they are often used for mixing operations such as compounding in additives to make concentrates of color, antioxidant, etc.
Twin screw extruders
A rough guideline for crystalline plastics is to process them at about _____ above their melting point
50°C
For amorphous plastics, processing at ______ above the glass transition temperature provides a
rough guideline.
100°C
Plastics which are ______ should be processed at lower temperatures
heat-sensitive
_____ plastics should be processed at higher temperatures
highly viscous
usually consists of a rupture disk or a shear pin in the clamp which holds the die against the barrel of the extruder, as well as with an automatic shutoff if the pressure reaches a critical value
over-pressure safety device
materials with thickness of 0.003 in or less are considered
film
materials with thickness of ____ in or greater are considered sheet
0.010
is generally produced by downward extrusion
cast film
is typically used to pin the plastic against the first chill roll
air knife
can also be used to produce film and sheet with desired thicknesses and surface textures
calendering
In this process, the polymer melt is squeezed between pairs of co-rotating high precision rollers, followed by a series of chilling rolls.
calendering
For some operations, the chill roll method does not provide rapid enough cooling. In that case, ________ may be used for cooling and solidifying the plastic
a water-filled quench tank
There are two major approaches to minimizing the problem of gauge bands
- The oldest method is oscillating the film as it is wound, to produce some randomization of the thickness variations.
- The more modern approach uses sensors to monitor the thickness of the web on-line, using a scanning measuring head that travels across the film so that thickness can be measured along both the length and the width dimensions.
_____ ,stretching the film to produce some molecular realignment in the direction of the stretch, is often used to modify cast film properties
orientation
The film is referred to as “_____” if the orientation is equal in
the two directions
balanced
The film is referred to as “_____” if it is more highly oriented in one direction than in the other
unbalanced
A crystalline polymer must be oriented at a temperature _______, but high enough to provide some mobility to the molecules
below its melt temperature
the main components of a die include
inlet channel, manifold, approach or land, die lips
delivers the plastic from the extruder to the die
inlet channel
is designed to evenly distribute the melt within the die
manifold
carries the melt from the manifold to the die opening
approach or land
perform the final shaping of the melt as it exits the die
die lips
for cast film or sheet, the die opening is ______, producing a thin, wide exiting stream of plastic
slit-shaped
The most common die configuration for production of cast film and sheet is
coat-hanger die
is a continuous process in which the polymer is melted, the melt is forced through an annular die, and the resulting tube is inflated with air into a “bubble” and cooled
blown film extrusion
The principal polymers used in blown film production are
polyolefins
The properties of the film are determined by
the blow-up ratio and the speed
is the ratio between the diameter of the final tube of film and that of
the die
blow-up ratio
involves the extrusion and blowing of a tube of molten plastic in a downward direction
double bubble process
the double bubble process is most often applied to
PP film
introduced a triple-bubble process
Kuhne GmbH
uses infrared heat, rod heaters, and other annealing techniques in a “thermofixation” station to impart precise shrink rates to coextruded film
triple-bubble process
