Injection Molding

Question 1

Volumetric contraction formula

Answer 1

1-(1- shrinkage, S )^3

Question 2

swell ratio formula {Dd, Dp, td, tp}

Answer 2

Rs=Dp/Dd=tp/td

Question 3

Dp means, td means

Answer 3

Dp: parison diameter
td: die wall thickness

Question 4

using volume cross sections, what’s Dm*tm equal to?

Answer 4

Dptp

Question 5

cavity dimension formula

Answer 5

Dc=Dp [1+ s + s**2]

Question 6

volume of pipe (hollow cylinder)

Answer 6

PI() * (Do3-Di3)/ 6

Question 7

polypropylene density from specific gravity of polypropylene and water density formula

Answer 7

p=g*p_water

Question 8

inner diameter in terms of outer diameter

Answer 8

Di=D0-2t (t: wall thickness)

Question 9

wall thickness in terms of diameters

Answer 9

t=(Do-Di)/2

Question 10

die diameter in terms of inner and outer die diameter

Answer 10

Dd=(Dd,o+Dd,i)/2

Question 11

The most important rubber product is which one of the following: (a) footwear, (b) conveyor
belts, (c) pneumatic tires, or (d) tennis balls? Explain why

Answer 11

(c)
crucial in automotive industry, provide necessary grip, traction and shock absorption for vehicles, important in terms of volume and economic impact

Question 12

Describe the following in terms of volume impact relative to highest volume impacted:

Pneumatic tires, Footwear, Conveyor Belts, Tennis balls

Answer 12

1) produced in huge quantities, various vehicles–cars, aircraft, bikes– millions of tires annually, largest rubber consumer
2) rubber used in soles, low rubber
3) essential in mining and manufacturing, rubber low
4) amount of rubber smallest

Question 13

Chemical name of the ingredient recovered from the latex of the rubber tree is

Answer 13

polyisoprene

Question 14

most important rubber additive, and why

Answer 14

carbon black, increases tensile strength, durability, heat resistance, abrasion resistance, protection against UV radiation

Question 15

how does carbon black improve abrasion resistance

Answer 15

boosts rubber’s ability to withstand wear and tear, essential for products encountering friction e.g. tires

Question 16

how does carbon black protect against UV radiation

Answer 16

carbon black particles absorb the UV, preventing it from penetrating rubber matrix, prevents rubber degrading when exposed to sunlight
carbon black dissipates heat generated by UV, reducing thermal stress on the rubber

Question 17

true or false:

carbon black can act as a mild antioxidant

Answer 17

true, it helps neutralize free radicals generated by UV exposure, reducing oxidative degradation of the rubber

Question 18

what’s the role of plasticizers in rubber manufacturing

Answer 18

-improves flexibility–reduces rigidity of rubber, making more flexible and easy to work with
-reduces glass transition temperature–plasticizers lower the Tg of rubber, improving performance at lower temps, making more pliable
-increases elasticity and elongation of rubber, improves durability–resistance to cracking, wear and tear–extending lifespan

Question 19

define rigidity

Answer 19

inability to be to bent/forced out of shape

Question 20

most important molding process in production of conventional rubber products, and why

Answer 20

compression molding
cost effective and suitable for variety of products

Question 21

briefly describe process of compression molding

Answer 21

placing set amount of raw rubber into mold cavity, compressing under heat and pressure to form desired shape

Question 22

purpose of calcium carbonate

Answer 22

used as a filler, to improve volume and reduce costs

Question 23

purpose of carbon black

Answer 23

reinforces rubber, improves strength and durability

Question 24

what’s vulcanization (purpose, process, application)

Answer 24

chemical process to enhance natural/syntehtic rubber properties [strength, heat/chemical resistance]

heating rubber with sulfur, sulfur atoms form cross links between long polymer chains of rubber

tires, seals, hoses, footwear

Question 25

impact of sulfur atoms forming corss links between long rubber polymer chains, in terms of material property

Answer 25

cross links allow rubber to stretch and return to original shape–more elastic, less likely to plastically deform under stress
this improves durability–can withstand repeated mechanical stress–longer lifespan

Question 26

As a result of cross-links in vulcanized rubber, the material can endure { 1 }, without melting or becoming {2} as a result of this additional {3}. The cross-linked {4}makes the rubber more resistance to {5}, {6} and other substances that cause {7}.

Answer 26

1: higher temperatures
2: brittle
3: stability
4: network
5, 6: chemicals, oils
7: degredation

Question 27

In vulcanization, sulfur is the { 1 }. The activator, { 2 } helps disperse the {3} and improve {4} of vulcanization. The other activator, { 5 }, works in conjunction with {2} to {6} the process.

Answer 27

1: primary vulcanizing agent
2: stearic acid
3: accelerators
4:efficiency
5: stearic acid
6: enhance

Question 28

How many minutes are required to cure (vulcanize) a modern passenger car tire: (a) 5, (b) 15,
(c) 25, or (d) 45?

Answer 28

(b)

Question 29

When is the tread pattern imprinted onto the circumference of the tire: (a) during preforming,
(b) while building the carcass, (c) during molding, or (d) during curing?

Answer 29

(c)

Question 30

Which of the following are not normally used in the processing of thermoplastic elastomers
(two correct answers): (a) blow molding, (b) compression molding, (c) extrusion, (d) injection
molding, or (e) vulcanization

Why?

Answer 30

(b) and (e)

compression molding–used in thermoset rubbers rather than TPE

vulcanization–chemical process fr thermoset rubbers, not TPEs, not suitable method for TPEs

Question 31

3 commonly used techniques in processing thermoplastic
elastonomers

Answer 31

extrusion, blow molding, injection molding

Question 32

most common polymer type in fiber-reinforced polymer
composites: (a) elastomers, (b) thermoplastics, or (c) thermosets

Why?

Answer 32

(c) thermosets

thermosets e.g. epoxy, have superior mechanical properties, chemical resistance and thermal stability

Question 33

high thermal stability means… Give an application

Answer 33

withstand high temps without losing mechanical properties e.g. thermosets don’t soften/melt upon heating, crucial for applications involving high thermal loads

Question 34

Most rubber products are properly classified into which of the following categories (three best
answers): (a) elastomer reinforced with carbon black, (b) fiber-reinforced composite, (c)
particle-reinforced composite, (d) polymer matrix composite, (e) pure elastomer, and (f) pure
polymer?

Answer 34

(a) elastomer, (c) particle-reinforced composite, (d) polymer matrix composite

Question 35

Elastomers reinforced with carbon black enhance rubbers mechanical properties, including {s…} and {d…}.
Particle reinforced composites; many rubber products are reinforced with particles e.g. {1} or {2} to improve performance.
Rubber products often fall into the category of { 3 }, as they consist of a { 4 } (the rubber, with various {5} and {6} to enhance properties.

Answer 35

strength
durability
1, 2: carbon black, silica
3: polymer matrix composite
4: polymer matrix
5, 6: fillers, reinforcements