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Plastics Flashcards

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1
Q

what are some of the applications of plastic

A

construction
packaging
plastic lumber
automotive

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2
Q

what are the advantages of plastic processing

A

no further shaping is needed
less energy is required
painting is normally not required
handeling of product is simplified

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3
Q

disadvantages of plastics

A

low strength
low modulus of elasticity
limited useful thermal range
can degrade ehen subjected to radiation
fragile
dimensional instability
flammable
suceptible to chemical attack
may have associated health risk

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4
Q

advantages ofd the plastic material

A

high corrosion resistance
good insulating properties
good strength to weight ratio
ease of processing and reprocessing
capable of being rigid or flexible
can be transperant, translucent, or opaque

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5
Q

what are the 3 types of polymers

A

thermoplastics
thermosetting
elastomers

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6
Q

what are thermoplastics

A

they can be heated, cooled and reheated.
can be recycled
dont crosslink when heated

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7
Q

what are the 3 ways crosslinking is accomplished

A

tempurature
catalyst
mixing

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7
Q

what are thermosets

A

undergo curing when heated
crosslinking happens when heated
cannot be remelted

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8
Q

what are elastomers

A

caple of large elatic deformation

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8
Q

why are thermosets sometimes better then thermoplastics

A

more rigid
brittle
more resistant to common solvents
capable of higher surface tempuratures

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9
Q

what makes elastomers have the incrediable elatic properties

A

long molecules
dergree of cross linking is lower then thermosets

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10
Q

what are the 2 molecular structures for polymers

A

crystalline
amorphous

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11
Q

what is the properies of crystline steructure

A

not clear
opaque or translucent plastic
chains packed closely together

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12
Q

what is the properies of amprphous steructure

A

spagetthi type structure
clear plastics

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13
Q

what are the shaping processes for platics

A

injection molding
extrustion
compresstion molding
blow molding
rotational molding
calendering
composites

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14
Q

what is injection molding

A

a process wheere a heated polymer is forced into a cavity

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15
Q

injection molding facts

A

very similar to die casting
complex shapes possible
high tool cost
long lead time
economical for high volume production
typically for thermoplastics

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16
Q

what are the 3 units in the injection molding machine

A

injection unit
mold
clamping unit

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17
Q

how does the injectioln molding process work

A

1) mold is closed
2) melted plastic injected in cavity
3) screwback
4) mold opens and part is released

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18
Q

what are the 2 parts of the mold

A

cavity: internal design
core - external design

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19
Q

why are the 2 halves of the mold called the hot and cold sides

A

hot side- material is injected though this side
cold side- materials is cold and enjection system is only on this side

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20
Q

what is shrinkage

A

as the polymes cool they will shrink and the amount of shrinnkage is dependant on the type of plastic

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21
Q

what are the shrinkage factors

A

injection pressure
compaction time
molding tempurature
fillers tend to reduce shrinkare

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22
Q

what are the 4 common injection molding defects

A

short shott
flash
sink marks/voids
weld lines/knit lines

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23
what are the causes of short shot
not enough plastic to cold to slow to inject
24
what are the causes of flash
spaces is mold fhigh injection pressure melt tempurature to high mold wearing
25
what are the causes of sink marks
thick mold sections
26
what are the causes of weld lines
temp to low speed to love
27
what is a die
a tolol used to cut/form material into desired form/shape
28
what is extrusion of plastic
compression process in which flow of material is forced through a die
29
what are some applications of extrusion
pipes hose structural shapes sheet/film continuos filiment coated elctrical wire
30
what are the main components of the extruder
barrel screw die
31
what are some common die profiles
solid hollow wire/cable coating sheet/film filaments
32
what is viscoelasticty
the shape memory of the material
33
what is an example of a solid profile
rounds squares ireggular cross section
34
what happens when solid profiles are extruded
material is still soft after die to mnimize visoelasticy the die is made long
35
what is an example of a hollow profile
pipes hoses any cross section with a hole
36
what happens when hollow profiles are extruded
mandrel required to form internal shape
37
what happens when wire/ cable coating is extruded
pulled at high speed vaccum is drawn to promote adhesion
38
what is sheet/film made of
film- thermolplastics sheet- thermorming
39
what are some applicatoiooons of film
packaging pool covers liners for irregation
40
what are the processes for sheet/film
split die extrusion blown film extrustion calendaring
41
what is split die extrusion
conventional extrusion but uses narrow slit as die opening uniformity is sometimes a problem
42
what is blown film extrusion
combines extrusion to produce of thin film
43
what is the process of blown film extrusion
extrusion of tube tube is drawn to upward and expnded by air at the same time air pressure kept constant to keep thickness of film
43
what is the frost line
marks the position where solidification occurs.
44
what is calendaring
a process for producing sheet/film out of rubber or rubbery thermoplastics
45
what is the process of calendaring
feedstock is passed through the series of rolls to reduce thickness to desired games
46
calendaring facts
expensive equipment high productiomn rates has good surface finish and accuracy
47
what are applications of calendaring
pvc flooring shower curtians table cloths pool liners inflatable toys
48
what sis the comppression molding process
1) material is loaded 2) material is compressed and cured 4) part is ejected amd removed
49
what are the possible molding compounds availble
powders pellets liquid preform
49
compression molding facts
used with thermosets and elastomers used for rubber tires an dpmc parts marterial is preheated to shorten cycle times mold is heated to help cure the material
50
compression vs injection molding
compession: molds are simpliar injection: shorter cycle times and higher production rates
51
what are the common molding materials in compression molding
eppoxies urethanes elatomers phenolics melamine
52
applications for compression molding
electric plugs pot handles electrical sockets dinnerware plates
53
what is tranfer molding
very closely related to compression molding
54
what are the 2 different types of transfer molding
pot tranfer molding plunger transfer molding
55
what is the basic transfer molding process
1) material sis loded into chamber 2) pressure applied as polymer is pressed into cavity 3)part is ejected
56
pot vs plunger
pot: injected through vertical sprue channel plunger: injected through heated well
57
what is blow molding
a process where air pressure is used to inflate the soft plastic an important process for making really thin hollow parts
57
what is the process of blow molding
1) create tube (parson) 2) add heated parison into tube 3) clos the mold 4) add the compressed air into the mold 5) trim product and remove from mold
58
what are the 3 differnt blow molding procsses
injection extrusion stretch
59
what are the advantages of extrusion blow molding
reduces stresses has weight reduction properties reduction on waste reduced cooling times
60
whats is speciall about blow molding
only can be used with thermoplatics
61
what is rotaionial molding
a process that uses gravity inside a rotating mold to form a holllow shape its a simple but slow process
62
what polymers can be used in rotational molding
mainly for thermoplastics but can be used for elastomers and thermosets
63
what is the process of rotational molding
1. material is loaded into mold 2. mold is closed, heated, and rotated on 2 axies 3. plastic is colloed while still spinning 4. part is removed
64
what is thermoforming
flat thermoplastic film/sheet is heated or deformed into desired shape using mold
65
what is the process of vacumn thermoforming
1. plastic is heated 2. sooftened platic is placed over negitive mold 3.a vacumn effec draws the sheet into the cavitys 4. plastic hardens and shape is removed
66
postive vs negitive molds
positive- inerior matched the countour of the mold negive- the exterior will math the contour of the mold
67
what are the general design considerations for plastic
strength/stiffness impact resistance service tempuratures thermal expansion degradtion
68
what are the design considerations for extrusion
walol thickness hollow sections sharp corners shrinkage die swell
69
what are the design considerations in injection molding
economic quantities part complexity wall thickness corner radii and fillets ho;es shrinkage parting line location slides/side actions draft angles tolerances

Manufactoring (9 decks)

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