Ch 9

what does carbon black do

increases tensile strength and resistance to abrasion (what is needed for tires) and tearing of the final rubber product, provides protection from ultraviolet radiation

what are the most common shaping processes for thermoplastic elastomers

injection molding and extrusion; generlaly more economical and faster than the traditional processes for rubbers that must be vulcanized

what are some extruded thermoplastic elastomer (TPE)

insulation coating for electrica wire, tubing for medical application, conveyor belts, sheet and film stock

how are thermoplastic elastomers processed

like thermoplastics but their applicatioons are those of an elastomer

why is only sulfur no longer used for vulcanization

long curing times; now various other chemicals are combined with smaller doses of sulfur to accelerate and strnegth the treatment (15 - 20 min)

are tires made with TPE

no

categories of fiber reinforced plastic shaping processes (FRP)

open mold processes, closed mold processes, filament winding, pultrusion, other

what is the best grade of rubber

pale crepe rubber involving two coagulation steps followed by warm air drying

what are some principal thermoset polymners

phenolics (particulate reinforcing phases), polyesters and epoxies (mostly FRPs)

how many corss links does soft rubber have

1 or 2 cross links per 1000 mers

what is the single most important reinforcing filler in rubber

carbon black, a collodial form of carbon obtained by thermal decomposition of hydrocarbons (soot)

what is rubber called when its at the stage of drying in the smokehouse

ribbed smoked sheet; it is then folded into large bales for shipment to the processor

how are fibers avaible in continous form as filaments

rovings (collections of untwisted continous strands), convenient form for handling

what is the typical L/D extruder range for rubber

10 to 15; this reduces risk of premature cross linking

recycled rubber added in some rubber products but usually __ %

10% or less

what is polyisoprene

C5H8 is the chemical substance that comprises natural rubber and its content in the emulsion is about 30%

what is the most familiar form of continou fiber

a cloth (fabric of woven yarns)

what is latex

a collodial dispersion of solid particles of the polymer polyisoprene in water

what are starting material for PMCs polymer matrix composites

a polymer and a reinforcing phase (these are processed separately before becoming phases in the composites)

what are china clays

additive in rubber, hydrous aluminum silicates reinforce less than carbon black but are used when the color black is not acceptable

rubber is always compounded with

additivites for vulvanization such as sulfur

where does natural rubber come from? syntehtic rubber?

argiculture; petroleum

how is rubber brought to rubber processors? why

as large bales instead of pellets or liquid resins; long tradition of handling NR in these unit loads

what is of most engineering interest for fibers

as the reiforcing phase in FRP

where do processing rubber into tires and other products occur

at processor (fabricator) plants, commonly known as rubber industry

what is open mold processes for FRP

based on FRP manual procedure for laying resins and fibers onto forms

how is raw rubber an agricultural indusrty

because latex, the starting ingredient, is grown on plantations in tropical climates

why is rubber usually black

because of high content of carbon black

what is the internal structure of the tirw

carcass (consist of multiple layers of rubber coated cords called plies); cords are strands of nylon, polyester, fiber glass, or steel, which provide inextensibility to reinforce the rubber in the carcass

what are some possible reinforcing agent materials

cermaics, metals, other polymers, or elements such as carbon or boron

what are other addivites in rubber

china clays, other polymers (styrene, PVC, and phenolics), antioxidants, fatigue and ozone protective chemicals, coloring pigments, plasticizers and softening oils, blowing agents in the production of foamed rubber, mold release compounds

why is shaping for composites generally less efficeint

composites are more complex than other materials, need to orient the reinforcing phase in FRPs (fiber reinforced plastic), composite processing technologies have not been the object of refinement ove ras many years as processes for other matierals

what does the processing of finished goods consist of

compounding, mixing, shaping, vulcanizing

what type of rubber molding process is the most important

compression because of its use in tired manf

what are principal molding processes for rubber

compression molding, transfer molding, injection molding

what is filament winding for FRP

continous filaments are dipped in liquid resin and wrapped around a rotating mandrel, producing a rigid, hollow, cylindrical shape

what are three tire constructions

diagonal ply, belted bias and radial ply

what is sometimes used to dry the rubber instead of a smokehouse

dried in hot air called air dried sheet; this is considered a better grade of rubber

what are the four basic shaping categories for rubber

extrusion, calednering, coating, molding and casting

what are possible geometries for reinforcing agents

fibers (just about eveyrthing coming out of industry is fibers), particles, and flakes

what is used to reinforced rubber belts to cause little or no extensibility

fibers commonly polyester or nylon; fabrics of these polymers are usually coated by calendering assembled together to obtain required number of plies and thickness and subsequently vulcanized by continous or batch heating processes

thermoplastic molding compounds include

fillers or reinforcing agents

rubber additives include

fillers that either enhance the rubber's mechanical properties (reinforxing fillers) or extend the rubber to reduce cost (non-reinforcing fillers)

what are common fiber reinforcing materisl

glass, carbon, and kevlar

how are molded parts for rubber footwear made

injection molding, compression molding, certain special molding techniques developed by the shoe industry

what does a reinforced hose tube consist of

inner tube (extruded of a rubber compounded for particular liquid that will flow trhough it), reinforcement layer (applied to inner tube as fabric or by spiraling knitting or braiding) outl layer (compounded for enviroment and applied by extrusion )

what is the shaping process of polymer matrix composites (PMCs)

many PMC shaping processes are slow and labor intensive; in general techniques for shpaing composites are less efficeint than othe rmaterisl

what are particles and flakes used in a lot

many plastic molding compound

are tires just rubber

no composites; has matrix and reinforcement

what are two basic types of hoses

plain hose (no reinforcement) is extruded tubing, reinforced tube

what is the difference between polymers and rubbers

polymers is delivered as pelets that metl and mold or as resin adn pour into mold but rubber comes in bail (blocks of rubber)

what are the three steps in tire production

preforming of components, building the carcass and adding rubber strips to form the sidewalls and treads, molding and curing the components into one integral piece; variations exist in processing depending on construction, tire size, and type of vehicle

how are most synethic rubbers made

produced from petroleum by the same polymerization tehcniques used to snythesize other polymers

what are the two basic steps in rubber goods production

production of the rubber itself and processing into finished goods

it is through compoudning that specific rubber is deisgned to satisfy a given application in terms of ____

properties, cost, and processability

what are some shaping processes for rubber and polymer matrix composites

rubber processing and shaping, manf of tires and other rubber products, PMC shaping processes and materials, open mold processes, closed mold processes, filament winding, pultrusion processes, other PMC shaping processes

where is natural rubber tapped from

rubber trees (hevae brasiliensis) as latex in southeast asia and other parts of the world

many of the production methods use for plastics are also applicable to ___ but

rubbers but rubber processing technology is different in certain respects and the rubber indistry is largely separate from the plastics industry

how does rubber extrusion work

screw extruders are generall used, the L/D of the extruder berrel is less than for thermoplastics, diw swells occur in rubber extudates (highly plastic polymer exhibits memory), rubber has not yet been vulcanized

what are some (thermoplastic polymer elastomer) TPE products

shoe siles, athletic footwear, and automotive components such as fender extensions and corner panels

what are some molded rubber products

shoes soles and heals, gaskets and seals, suction cups, and bottle stops; many foamed rubber parts are produced by moldind; also an important process in tire production

what is a woven roving

similar to cloth but it consists of untwisted filaments rather than yarns; can be produced with unequal numbers of strands in the two directionjs so that they posses greater strength in one direction

what is closed mold processes for FRP

similar to plastics molding

what is pultrusion for FRP shaping

similiar to extrusion only adapted to include continous fuber reinforcement

what kind of rubbers are used in the shoe industry? what is used for low production

solid and foamed; low volume production - manual methods are sometimes used to cut rubber from flat stock

is the shaping process for rubber simple

some products require several basic processes plus assembly work (ie tires)

what is a thermoplastic elastomer (TPE)

themoplastic polymer that posses the properties of a rubber

what are the most common matrix materials

thermosetting polymers

what is the rubber industry and goods made of rubber dominated by

tiress; tires are used in a larger number of autombiles, trucks, aircraft, and bicyeles

what is the preferred method to recover rubber

to recover rubber from latex involves coagulation (adding an acid such as formic acid, coagulation takes about 12 hours), the coagulum (now soft solid slabs) is then squeezed through rolls which drive out most of the water and reduce thicknes to about 3mm (1/8), the sheets are then draped over wooden frames and dried in smokehouses for several days

what is vulcanization

treatment that accomplishes cross-linking of elastomer molecules (add sulfur); makes rubber stiffer and stronger but retain extensibility; long chain molecules become joined at certain tie points which is reduces the ability to flow

what is yarn

twisted collection of filaments

what is calendaring

type of rubber shaping; rubber stock passed through a series of gaps of decreasing size by a stand of rotating rolls; rubber sheet thickness is slighlty greater than final roll gap due to die swell

what is kind of woven rovings are preferred in laminated FRP composites

unidirectional