shaping processes for plastics

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What are some of the reasons why plastic shaping processes are important?
The processes are a net shape processes, less energy is employed, handling of tools is simplified
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What are the main categories of plastics shaping processes, as classified by the resulting product geometry?.
Continuous sheets and films, castings, foamed products
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Upon what parameters does viscosity depend?
The temperature, shear rate, and the molecular weight
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How does the viscosity of a polymer melt different from most newtonian fluids
A polymer melt exhibits pseudo plasticity, which mans its value decreases as shear rate increases
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What does Viscoelastcity mean when applied to a polymer melt
Viscoelasticity is a combination of viscous and elastic properties which cause them to melt with exhibit memory. They tend to return to their original shape
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Describe the plastic extrusion process
A polymer melt is where a material is forced through a die orifice at one continuous length.
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What are the three sections of a barrel and screw extruder
The feed section, the compression section and the metering section
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What are the functions of the screen pack and beaker plate at the die end of the extruder barrell
The functions are, filter dirt and lumps, build pressure, straighten the flow and remove the memory of the polymer melt
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What are the various forms of extruded shape and corresponding dies
Solid profiles, hollow profiles, wire and cable coating, sheet and film, filaments
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Describe the ejection moulding process
Is a process where a polymer is heated to an elastic state and then forced to flow under a high pressure mold cavity where it solidifies
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What are the two principal components I'm injection moulding
The injection unit and the clamping unit
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What are the function of the gates in the injection molds
Its function is to constrict the flow of Polten plastic into the cavity which increases its viscosity
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What are the advantages of a three plate mold over a two plate mold
A three plate mold automatically separates the moulded part from the runner
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What are some of the significant differences in the equipment and operating procedures between injection and moulding of thermoplastics and injection moulding of thermosets
The differences are shorter barrel length, lower temperatures to prevent curing and the use of a heated mould to cause cross linking
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What is reaction injection moulding
This involves mixing two reactive liquid ingredients and injecting them into a mould cavity where it solidifies due to chemical reaction.
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What are some of the general considerations that product designers must keep in mid when designing components out of plastic
Plastics are not s strong as metals, god impact resistance, thermal expansions are greater than metals, some plastics degrade in oxygen and and are soluble in many common solvents
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What kind of products are produced by blow moulding
Produces hollow, seamless containers
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What is the form of the starting material in thermoforming
It starts with a thermoplastic sheet or film
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What is the difference between a positive mould and negative mould in thermoforming
A positive mould has a complex shape, a thermoplastic has a concave cavity
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Why are the moulds generally are costly in mechanical than in pressure or vacuum thermoforming?
In mechanical thermoforming, matching mold halves are required; while in other thermoforming processes, only one mold form is required.
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What is the distinction between plastic sheet and film
Sheet stock has a thickness greater than 0.5 mm where fin stock is less than 0.5 mm thick
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What is the blown-film process for producing stock
This is a widely used process for making thin polythene, it combines extrusion and blowing to produce a tube of thin film
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Describe the calendaring process
It produces sheet and film stock out of rubber.The initial feedstock is passed through a series of rolls and the material is reduced to its desired gage
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Polymer fibers and filaments are used in several applications; what is the most important commercial application?
Textiles
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What is the technical difference between a fiber and a filament?
. A fiber is a long, thin strand of material of finite length; a filament of continuous length
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Other cards in this set

Card 2

Front

What are the main categories of plastics shaping processes, as classified by the resulting product geometry?.

Back

Continuous sheets and films, castings, foamed products

Card 3

Front

Upon what parameters does viscosity depend?

Back

Preview of the front of card 3

Card 4

Front

How does the viscosity of a polymer melt different from most newtonian fluids

Back

Preview of the front of card 4

Card 5

Front

What does Viscoelastcity mean when applied to a polymer melt

Back

Preview of the front of card 5
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