Download Properties, Processing, and Applications of Rubber: A Comprehensive Study and more Study notes Design in PDF only on Docsity!
ME477 Kwon 1
SHAPING PROCESSES FOR
PLASTICS
- Properties of Polymer Melts
- Extrusion 3.Sheet and Film
- Fiber and Filament
- Coating Processes
- Injection Molding
- Compression &Transfer Molding
- Blow Molding & Rotational Molding
- Thermoforming
- Casting
- Polymer Form
- Design Consideration ME477 Kwon 2
Introduction
- Unlimited variety of part geometries
- Net Shape
- Less energy
- Lower temperature
- No finishing
ME477 Kwon 3
1 Properties of Polymer Melts
- Viscosity
- Newtonian fluid:
- Pseudoplastic fluid:
- Viscoelasticity
- Causes die swell
- Swell ratio,
- Mold Flow Index (MFI): A measure of flow and viscosity depending on temp. and shear rate
Dd
Dx d
x s (^) D r = D
γ
τ η &
=
η=coefficient of shear viscosity
( ) n
k γ
τ &
= γ&
τ
ME477 Kwon 4
2. Extrusion
- Shaping process for polymers metals & ceramics.
- A compression process – A material flows through a die orifice to provide long, continuous shaped material.
- Extrudate (extruded product) cut into desirable lengths.
- Equipment
- Internal Diameter (25-150mm)
- L/D ratio ranges from 10 to 30.
- The extruder screw rotates at about 60 rev/min.
- feed section
- compression section – transform to liquid
- metering section – the melt is homogenized and pressurized.
Qd = 0. 5 vd w
v d
Volume drag flow rate (m^3 /s):
A simple plate model
ME477 Kwon 5
An single-screw Extruder
A: the helix angle of the screw
A D d (^) c
pitch Flow Direction
Channel w (^) c Flight w (^) f
screw
Barrel
D
A π
tan =^ pitch
A
Pitch
π D
In relation to the extrusion screw ( )
c
c f
d d
v r DN A
w w D A w A D A
=
= =
= = − ≈ cos
tan cos sin ϖ π
π π Assuming wc>>wf
Transport Mechanism: Drag Flow between barrel and channel
ME477 Kwon 6
Analysis of Extrusion
Into the eq. from a plate model
Q (^) d = 0. 5 π^2 D^2 Ndc sin A cos A Back pressure flow
L
pDd A dl
Dd A dp Q (^) b c c η
π η
π 12
sin 12
(^3) sin 2 3 2 ⎟^ ≈ ⎠
⎞ ⎜ ⎝
= ⎛
The resulting flow rate, assuming no leak flow
L
pDd A Q (^) x Qd Qb DNdc A A c η
π π 12
sin
- 5 sin cos
3 2 = − =^2 2 − Design Parameters: D, dc and A Operating Parameters: N, p and η
p
position
ME477 Kwon 7
Analysis of Extrusion
Zero flow condition due to high back pressure Qx = Qd − Qb = 0 To find the back pressure
max 2
6 cot d c
DNL A p π η =
Extruder Characteristics
Die characteristics
Extruder characteristics
Operating Point
Die Characteristics
d
d x s s L
D Q Kp K η
π 128
where
4 = =
Q (^) max
p (^) max
when Q (^) b =
ME477 Kwon 8
Die Configuration & Defects
- Extruded shape
- Solid Profiles
- Hollow Profiles such as tubes
- Wire and Cable coating (see text)
- Defects
- Melt fracture
- Sharkskin – residual stress on surface
- Bambooing
Extrusion Die
Extrudite Profile
ME477 Kwon 9
3. Production of Sheet & Film
- 0.5mm < Sheet thickness < 12.5mm
- Film thickness < 0.5mm
- Continuous & High Production
- Slit-die Extrusion
- Water Quenching bath
- Chill roll extrusion
- Blown-film Extrusion (Fig. 13.16)
- Calendering(2.5m/s)
Manifold
ME477 Kwon 10
4. Fiber & Filament Production
- Melt Spinning
- Dry Spinning – polymer in
solution and the solvent
evaporates
Spinneret
ME477 Kwon 11
5. Coating Processes
- Wire and Cable coating
- Planar coating
- Contour Coating
ME477 Kwon 12
6. Injection Molding
- Video in class
- Three Mold Types
- The Mold, Injection and Clamping Units
- Shrinkage:
- Defects
- Short Shot
- Flashing
- Sink mark and void
- Weld line
- Other Types (e.g.: Reaction Injection Molding)
Shrinkage(Table 13.1)
MoldPartDimension
DimensionCavity
2
=
=
=
= + +
S
D
D
D D DS DS
p
c
c p p p
ME477 Kwon 19
11. Polymer Foam Processing
- Polymer Foam – a composite of polymer
and gas (air, nitrogen and carbon dioxide)
- Introduction of gas
- mechanical agitation
- physical blowing agents
- chemical blowing agents
- Depending on the amount of gas and processing, open or closed cells
ME477 Kwon 20
12. Design Consideration
- General consideration
- Strength and Stiffness
- Impact Resistance
- Service temperature
- Thermal expansion
- Degradation
- Extruded Plastics
- Wall thickness
- Hollow sections
- Corners
- Molded Part
- Economic production quantities
- Part Complexity
- Wall thickness: reinforcing ribs
- Corner radii ad Fillet
- Holes but careful
- Draft
- Tolerance
See Table 13.
ME477 Kwon 21
RUBBER PROCESSING
TECHNOLOGY
- Rubber Processing and Shaping
- Manufacture of Tire and other Rubber Products
- Design Consideration
ME477 Kwon 22
Introduction
- Similar to many production methods for plastics
- But different from the plastics industry
- Dominated by one product: tires
- Technological breakthrough
- Vulcanization (cross-linking) to transform weak natural rubber into a stronger material.
- The introduction of synthetic rubbers such as Styrene-butadiene rubber (SBR), Butadiene Rubber (BR) and Ethylene-Propylene-diene rubber (EPDM) (around WWII)
ME477 Kwon 23
Rubber Processing and Shaping
- Two basic steps
- Production - Agricultural crop or Petroleum
- Shaping of rubber into finished goods
- Compounding – Addition of Sulfur for Vulcanization
- Mixing - Additives such as carbon black or calcium carbonate, china clay, silica and other polymers
- Shaping – extrusion, calendering, coating, molding and casting
- Vulcanization – A curing (cross-linking) process developed by Goodyear Synthetic strength time time
Natural
ME477 Kwon 24
Production of Natural Rubber
- Natural Rubber
- Rubber trees ( Hevea brasiliensis ) grown on plantations in Southeast Asia and other part of the world -> Latex (a colloidal dispersion (30%) of solid particles called polymer polyisoprene in water)
- The latex is collected in large tanks - Diluted to 50% with additional water and coagulated by adding formic or acetic acids.
- Coagulum , now soft solid slabs, is then squeezed through a series of rollers to loose water.
ME477 Kwon 25
Production of Natural Rubber
- Ribbed smoked sheet in dark brown color - The sheets draped over wooden frames is dried in smokehouses for several days, which are folded into large bales.
- Air-dried sheet - A better grade of rubber can be attained by drying in hot air rather than smokehouses.
- Pale crepe rubber in light tan - A even better grade involves two coagulation steps and warm air drying. ME477 Kwon 26
Production of Synthetic Rubber
- Most synthetic rubbers are produced from
petroleum by the same polymerization
techniques.
- Unlike shaping polymers in the form of
pellets or liquid resins, synthetic rubbers
start in the form of large bales.
ME477 Kwon 27
Shaping of rubber:
Compounding
- The specific rubber is designed by vulcanization, (adding sulfur) or fillers.
- Fillers to enhance the rubber's mechanical properties (reinforcing fillers) or to extend the rubber to reduce cost (non-reinforcing fillers)
- Carbon black , a colloidal form of carbon, obtained by thermally decomposing hydrocarbons (soot) - to increase tensile strength and resistance to abrasion and tearing - To protect from ultraviolet radiation - Appear black in color (^) ME477 Kwon 28
Shaping of rubber:
Compounding
- China clays - hydrous aluminum silicates (Al 2 Si 2 O 5 (OH) 4 ) for other colors but less reinforcing than carbon black.
- Calcium carbonate (non-reinforcing) and Silica
- Other polymers (styrene, PVC, and phenolics)
- Recycled rubber (usually 10% or less)
- Antioxidants (anti-aging by oxidation); fatigue- and ozone-protective chemicals; coloring pigments; plasticizers and softening oils; blowing agents in the production of foamed rubber; and mold release compounds
ME477 Kwon 29
Shaping of rubber: Mixing
- The additives must be thoroughly mixed to achieve uniform dispersion of ingredients
- Mechanical working of the rubber can increase its temperature up to 150°C (300°F)
- An early introduction of vulcanizing agents would result in the “rubber processor's nightmare”
- To avoid this, a two-stage mixing process Stage 1 - carbon black and other non-vulcanizing additives ( masterbatch) Stage 2 - After some time for cooling, vulcanizing agents are added. (^) ME477 Kwon 30
Shaping of rubber: Mixing
- Many products require filament reinforcement to reduce extensibility but retain the other desirable properties of rubber. - Examples: tires, conveyor belts - Filaments include cellulose, nylon, and polyester. - Fiber-glass and steel (e.g., steel-belted radial tires) - Continuous fiber materials must be added during shaping; not mixed like the other additives.
ME477 Kwon 37
Vulcanization
- Cross-linking of elastomer molecules to make stiffer and stronger while retaining extensibility.
- On a submicroscopic scale, the long-chain molecules of rubber become joined at certain tie points (1 or 2 cross-links per 1000 mers).
soft rubber
hard rubber ME477 Kwon 38
Vulcanization Chemicals and
Times
- First invented by Goodyear in 1839,
vulcanization used sulfur at 140°C (280°F)
for about 5 hours.
- Now various other chemicals are
combined with smaller doses of sulfur to
accelerate and strengthen the treatment
resulting in the cure time of 15-20 minutes.
- A variety of non-sulfur vulcanizing
treatments have also been developed.
ME477 Kwon 39
Tires
- Functions of vehicle tires:
- Support the weight of the vehicle, passengers, and cargo
- Transmit the motor torque
- Absorb road vibrations and shock
- Automobiles, trucks, buses, farm tractors, earth moving equipment, military vehicles, bicycles, motorcycles, and aircraft
- A tire is an assembly of many parts about 50 to as many as 175 components - The internal structure, known as the carcass , consists of multiple layers of rubber coated cords, called plies - The cords are strands of nylon, polyester, fiber glass, or steel, which provide inextensibility to reinforce the rubber in the carcass ME477 Kwon 40
Manufacture of Tire and Others
- Footwear, Seals, Shock-absorbing parts,
Conveyor belts, Hose, Foamed rubber
products, Sports equipment
- ¾ of rubber product: Tire
- Three basic constructions (see Fig. 16.6)
- Diagonal ply
- Belted Bias
- Radial ply
ME477 Kwon 41
Diagonal ply Belted bias
Radial ply ME477 Kwon 42
Tire Production Sequence
- Three steps: 1.Preforming of components 2.Building the carcass and adding rubber strips to form the sidewalls and treads 3.Molding and curing the components into one integral piece
- Variations in processing depending on
construction, tire size, and type of vehicle
ME477 Kwon 43
Preforming of Components
- The carcass consists of a number of
components, most of which are rubber or
reinforced rubber
- These, as well as the sidewall and tread
rubber, are produced by continuous
processes and then pre-cut to size and
shape for subsequent assembly
- The components include: bead coil, plies,
inner lining, belts, tread, and sidewall
ME477 Kwon 44
Building the Carcass
The carcass is traditionally assembled using a machine known as abuilding drum, whose main element is a cylindrical arbor that rotates. Tire just before removal from building drum, but prior to molding and curing
ME477 Kwon 45
Molding and Curing
Tire molding: (1) uncured tire is placed over expandable diaphragm; (2) mold is closed and diaphragm is expanded to force uncured rubber against mold cavity, impressing tread pattern into rubber; mold & diaphragm are heated to cure rubber
ME477 Kwon 46
Other Rubber Products -
Rubber Belts
- Widely used in conveyors and mechanical power transmission systems
- Rubber is an ideal material for these products but the belt must have little or no extensibility - Reinforced with polyester or nylon fibers
- Fabrics of these polymers are usually coated by calendering, assembled together to obtain required number of plies and thickness, and subsequently vulcanized by continuous or batch heating processes
ME477 Kwon 47
Other Rubber Products – Hose
- Two basic types of Hose:
- Plain hose is extruded tubing
- Reinforced tube consists of:
- Inner tube - extruded of a rubber compounded for particular liquid that will flow through it
- Reinforcement layer - applied to the inner tube as a fabric, or by spiraling, knitting, braiding
- Outer layer – compounded for environmental conditions and applied by extrusion
ME477 Kwon 48
Other Rubber Products –
Footwear
- Rubber components in footwear include soles, heels, rubber overshoes, and certain upper parts
- Molded parts are produced by injection molding, compression molding, and certain special molding techniques developed by the shoe industry
- The rubbers include both solid and foamed
- For low volume production, manual methods are sometimes used to cut rubber from flat stock
ME477 Kwon 55
Open Mold Process
- Mold – Negative or positive mold
- Lay-up – wet lay-up or Prepregs
- Hand lay-up – high labor cost but strong
- Spray lay-up - randomly oriented short fibers, not as strong
- Boat hulls, bathtubs, automobile body parts, furniture, large structural panels, containers, Movie and stage props
- Automated Tape-laying - dispensing a prepreg tape onto a mold following a programmed path
- Curing for thermosetting resins (Crosslinking)
- Room temp, Oven, Microwave, Autoclave
- Autoclave - an enclosed chamber equipped to apply heat and/or pressure at controlled levels
ME477 Kwon 56
Hand Lay-up
(1) mold is treated with mold release agent; (2) thin gel coat (resin, colored) is applied, to be the outside surface of molding; (3) layers of resin and fiber, the fiber in the form of mat or cloth; each layer is rolled to impregnate the fiber with resin and remove air; (4) part is cured; (5) fully hardened part is removed from mold
ME477 Kwon 57
Spray-up
ME477 Kwon 58
Automated tape-laying machine
(courtesy Cincinnati Milacron)
ME477 Kwon 59
Closed Mold Processes
- Match Die (negative and positive) Molding
- Compression molding
- Transfer molding
- Injection molding
- More Tooling cost due to the more complex equipment
- Advantages:
- good finish on all part surfaces
- higher production rates
- closer control over tolerances, and
- more complex three-dimensional shapes ME477 Kwon 60
Filament Winding
ME477 Kwon 61
Pultrusion
ME477 Kwon 62
Pultrusion
- Common resins: unsaturated polyesters, epoxies, and silicones, all thermosetting polymers
- Reinforcing phase: E-glass is most widely, in proportions from 30% to 70%
- Products: solid rods, tubing, long flat sheets, structural sections (such as channels, angled and flanged beams), tool handles for high voltage work, and third rail covers for subways.
ME477 Kwon 63
Other PMC Shaping
- Centrifugal casting
- Tube rolling
- Continuous laminating
- Gathering either impregnated or woven fabric with resin
- Compacting with roller and curing
- Many of the traditional thermoplastic shaping processes are applicable to FRPs (with short fibers) - Blow molding - Thermoforming - Extrusion
- Cutting of FRPs
ME477 Kwon 64
Cutting methods
- Uncured (prepregs, preforms, SMCs, and etc.):
- Cut to size for lay-up, molding, etc.
- Typical cutting tools: knives, scissors, power shears, and steel-rule blanking dies
- Nontraditional methods (laser beam cutting and water jet cutting)
- Cured FRPs are hard, tough, abrasive, and difficult-to-cut
- To trim excess material, cut holes and outlines, etc.
- For glass FRPs, cemented carbide cutting tools and high speed steel saw blades
- For other advanced composites, diamond cutting tools
- Water jet cutting reduces dust and noise problems
ME477 Kwon 65
GLASSWORKING
1. Raw Materials
2. Shaping
3. Heat Treatment & Finishing
4. Production Design
Consideration
ME477 Kwon 66
Introduction
- Glass is one of three types of ceramic materials. The other two are traditional and new ceramics.
- A type of ceramics which is Non-crystalline [SiO 2 (sand) +other oxides]
- Shaping: melting, casting, pressing and blowing or rolling.
- Glass remain in the glass state even after cooling.
- Typical Processing steps
Sand (^) Molten glass
Glassware
Raw materials Melting^ Shaping Heat treatment
