Injection Molding Flashcards
Volumetric contraction formula
1-(1- shrinkage, S )^3
swell ratio formula {Dd, Dp, td, tp}
Rs=Dp/Dd=tp/td
Dp means, td means
Dp: parison diameter
td: die wall thickness
using volume cross sections, what’s Dm*tm equal to?
Dptp
cavity dimension formula
Dc=Dp [1+ s + s**2]
volume of pipe (hollow cylinder)
PI() * (Do3-Di3)/ 6
polypropylene density from specific gravity of polypropylene and water density formula
p=g*p_water
inner diameter in terms of outer diameter
Di=D0-2t (t: wall thickness)
wall thickness in terms of diameters
t=(Do-Di)/2
die diameter in terms of inner and outer die diameter
Dd=(Dd,o+Dd,i)/2
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
(c)
crucial in automotive industry, provide necessary grip, traction and shock absorption for vehicles, important in terms of volume and economic impact
Describe the following in terms of volume impact relative to highest volume impacted:
Pneumatic tires, Footwear, Conveyor Belts, Tennis balls
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
Chemical name of the ingredient recovered from the latex of the rubber tree is
polyisoprene
most important rubber additive, and why
carbon black, increases tensile strength, durability, heat resistance, abrasion resistance, protection against UV radiation
how does carbon black improve abrasion resistance
boosts rubber’s ability to withstand wear and tear, essential for products encountering friction e.g. tires
how does carbon black protect against UV radiation
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
true or false:
carbon black can act as a mild antioxidant
true, it helps neutralize free radicals generated by UV exposure, reducing oxidative degradation of the rubber
what’s the role of plasticizers in rubber manufacturing
-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
define rigidity
inability to be to bent/forced out of shape
most important molding process in production of conventional rubber products, and why
compression molding
cost effective and suitable for variety of products
briefly describe process of compression molding
placing set amount of raw rubber into mold cavity, compressing under heat and pressure to form desired shape
purpose of calcium carbonate
used as a filler, to improve volume and reduce costs
purpose of carbon black
reinforces rubber, improves strength and durability
what’s vulcanization (purpose, process, application)
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
impact of sulfur atoms forming corss links between long rubber polymer chains, in terms of material property
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
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}.
1: higher temperatures
2: brittle
3: stability
4: network
5, 6: chemicals, oils
7: degredation
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.
1: primary vulcanizing agent
2: stearic acid
3: accelerators
4:efficiency
5: stearic acid
6: enhance
How many minutes are required to cure (vulcanize) a modern passenger car tire: (a) 5, (b) 15,
(c) 25, or (d) 45?
(b)
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?
(c)
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?
(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
3 commonly used techniques in processing thermoplastic
elastonomers
extrusion, blow molding, injection molding
most common polymer type in fiber-reinforced polymer
composites: (a) elastomers, (b) thermoplastics, or (c) thermosets
Why?
(c) thermosets
thermosets e.g. epoxy, have superior mechanical properties, chemical resistance and thermal stability
high thermal stability means… Give an application
withstand high temps without losing mechanical properties e.g. thermosets don’t soften/melt upon heating, crucial for applications involving high thermal loads
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?
(a) elastomer, (c) particle-reinforced composite, (d) polymer matrix composite
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.
strength
durability
1, 2: carbon black, silica
3: polymer matrix composite
4: polymer matrix
5, 6: fillers, reinforcements
