EM2 KAP24 Produksjon, bearbeiding av polymerer

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EM2 KAP24 Produksjon, bearbeiding av polymerer

• Polymerisasjon (repetisjon)
• addisjonspolymerisasjon
• kondensasjonspolymerisasjon
• ko-polymerer
• flerfasesystemer

• Bearbeiding
• ekstrusjonsprosesser (extrusion)
• formblåsing (blow moulding)
• filmekstrusion (sheet and cast film extrusion)
• sprøytestøping (injection moulding)

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• Læremål
• Etter at dere har studert dette kapittelet skal
  dere kunne gjøre følgende
• 1. Beskrive addisjonspolymerisasjonen for
  polyetylen (PE), polystyren (PS) og
  polyvinylklorid (PVC).
• 2. Beskrive kondensasjonspolymerisasjonen for
  polyamid 6,6 (nylon 6,6).
• 3. Beskrive hvordan en kopolymer er oppbygget i
  termer av repeterende ledd.
• ABA (alternerende)
• ABBAABAABBBABA etc. (tilfeldig random)
• AAABBAAABBBAABB etc. (blokk)
• Podet (graft)
• 4. Beskrive hva man kan vinne med
  flerfasesystemer. Velg for eksempel slagfast
  polystyren (High Impact PolyStyrene HIPS).
• 5. Beskrive med enkle tegninger og med få
  setninger hvordan en ekstruder virker.
• 6. Beskrive med enkle tegninger og med få
  setninger hvordan så kalte ekstruderrelaterte
  prosesser som filmblåsing (blown film) og
  filmekstrusjon (sheet extrusion cast film)
  virker.
• 7. Beskrive hvordan sprøytestøpingsmaskinenen
  virker.

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Som en meget god kompletering til stoffet i
læreboka bør dere se på linkene neden.
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A typical single screw extuder. The electric
motor can be driven at a wide range of revs/min.
Today it is accomplished using variable speed DC
or AC drive systems. This particular machine is
equipped with screw cooling, vacuum venting for
processing moisture sensitive plastics such as PC
and PET. Not shown is subsequent process
machinery such as pipe-, blown film- and
sheet-extrusion dies and other processrelated
machinery. Examples of such special machinery is
presentet in the next slides.
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Prøv denne linken for å se litt mer om
profilekstrusjon og kabelmantling (wire coating)
Profil
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Blown film line with 3 extruders. This a 3-layer
film production. This a typical extruder related
process. The extruder is merely supplying the
meltet polymers at the right temperature and
output rate. The control system must give the the
matching bubble differential air pressure and the
haul off speed. Of course the total amount of
blown air must provide sufficient cooling. You
can see such a production in Trondheim and in
Levanger.
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The diameter of the bubble is controlled by the
balance between the internal pressure, the
ambient pressure and haul off traction. This an
example of a demanding process control system.
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A multilayer film die fed by 4 extruders.
A barrier layer is a diffusion barrier
Today with the requirements of low diffusion of
oxygen and moisture in packaging materials one
have to use multilayer films. One can consider a
modern diffusion less film consisting of strength
layers, barrier layers and adhesive layers. The
adhesive layers can bond to the strength layers
and barrier layers. Try to figure out wich one is
the adhesive layer. The polymer in the outer
layer is scratch and impact resistant. The inne
most layer has to be FDA -approved
(livsmiddelsgodkjent).
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Sheet extrusion line. There are three extruders
feeding a feed block. The feed block stacks the
melts from each extruder on top of each other and
the laminar flow beaviour of the melts will keep
them apart through the flow in the sheet die. The
result is that a multilayer sheet exits the die.
The final calibration of the thickness and
chilling is made in the 3-roll stack.
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Sheet or film extrusion die.
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INJECTION MOULDING
For thermoplastics, the injection molding machine
converts granular or pelleted raw plastic into
final molded parts via a melt, inject, pack, and
cool cycle. A typical injection molding machine
consists of the following major components, as
illustrated in Figure 1 below.
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Machine specification Clamping tonnage and shot
size are commonly used to quickly identify the
size of the injection molding machine for
thermoplastics. Other parameters include
injection rate, injection pressure, screw design,
mold thickness, and the distance between tie
bars. Machine function Injection molding
machines can be generally classified into three
categories, based on machine function
Auxiliary equipment The major equipment
auxiliary to an injection molding machine
includes resin dryers, materials-handling
equipment, granulators, mold-temperature
controllers and chillers, part-removal robots,
and part-handling equipment.
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Machine components Injection system The
injection system consists of a hopper, a
reciprocating screw and barrel assembly, and an
injection nozzle, as shown in Figure 1. This
system confines and transports the plastic as it
progresses through the feeding, compressing,
degassing, melting, injection, and packing
stages.
The hopper Thermoplastic material is supplied to
molders in the form of small pellets. The hopper
on the injection molding machine holds these
pellets. The pellets are gravity-fed from the
hopper through the hopper throat into the barrel
and screw assembly. The barrel As shown in
Figure 1, the barrel of the injection molding
machine supports the reciprocating plasticizing
screw. It is heated by the electric heater bands.
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The reciprocating screw The reciprocating screw
is used to compress, melt, and convey the
material. The reciprocating screw consists of
three zones (illustrated below) the
feeding zone the compressing (or
transition) zone the metering zone
While the outside diameter of the screw remains
constant, the depth of the flights on the
reciprocating screw decreases from the feed zone
to the beginning of the metering zone. These
flights compress the material against the inside
diameter of the barrel, which creates viscous
(shear) heat. This shear heat is mainly
responsible for melting the material. The heater
bands outside the barrel help maintain the
material in the molten state. Typically, a
molding machine can have three or more heater
bands or zones with different temperature
settings.
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The nozzle The nozzle connects the barrel to the
sprue bushing of the mold and forms a seal
between the barrel and the mold. The temperature
of the nozzle should be set to the material's
melt temperature or just below it, depending on
the recommendation of the material supplier. When
the barrel is in its full forward processing
position, the radius of the nozzle should nest
and seal in the concave radius in the sprue
bushing with a locating ring. During purging of
the barrel, the barrel backs out from the sprue,
so the purging compound can free fall from the
nozzle. These two barrel positions are
illustrated below.
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A mold system is an assembly of platens and
molding plates typically made of tool steel. The
mold system shapes theplastics inside the mold
cavity (or matrix of cavities) and ejects the
molded part(s). The stationary platen is attached
to the barrel side of the machine and is
connected to the moving platen by the tie bars.
The cavity plate is generally mounted on the
stationary platen and houses the injection
nozzle. The core plate moves with the moving
platen guided by the tie bars. Occasionally, the
cavity plate is mounted to the moving platen and
the core plate and a hydraulic knock-out
(ejector) system is mounted to the stationary
platen.
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Prøv denne linken for å se hvordan man lager
beholdere og plastflasker
Formblåsing