Lecture 7: Plastic Flashcards
What is the goal of most processes for plastics?
Most processes aim to achieve net-shape or near-net-shape production, completing the part in one process to minimize costs.
Define polymer.
A polymer is an extremely large molecule composed of a repetitive pattern of an unspecified number of monomers.
Why are additives added to polymers?
Additives enhance various properties of plastics, such as flexibility, color, resistance to UV radiation, and flame retardancy.
What are composites?
Composites are materials made by combining chemically distinct and insoluble phases with a recognizable interface.
Name three types of fibers commonly used in composites.
Glass fiber, Aramids (e.g., Twaron, Kevlar), and Carbon fiber are commonly used fibers in composite materials.
describe Extrusion
shaping viscous plastics by pushing
them through mold/die
a. Can only be done with thermoplastics and elastomers
i. Not with thermosetting plastics
because we need viscous material, so
we need to heat it up, which is
impossible with thermosetting plastics
What is injection molding?
Injection molding is a process of filling a mold with high pressure (70-200 MPa) to allow viscous material to fill every part of the mold.
What are 4 advantages of injection molding?
It is used in mass production, offers high accuracy, excellent surface finish, and allows for the creation of complex products in one go.
What is the primary disadvantage of injection molding?
The complexity and cost of the dies required, as defects in the die can be replicated on the product surface, necessitating high-quality, expensive dies.
What types of materials are commonly used in injection molding?
Thermoplastics and elastomers are heated until viscous and then injected into the mold. Thermosetting plastics undergo a chemical reaction inside the mold, making them irreversible.
What is rotational molding?
Rotational molding involves pouring material into a mold and rotating it to coat the walls, allowing for the creation of large product geometries and hollow products.
What are some 3 drawbacks of rotational molding?
It results in considerable variance in wall thickness, lower quality surface finish, and is a slower process suited for small batches.
what are some advantages of rotational molding and material used
1.Large product geometries possible
2.Dies are fairly cheap
3.We can make hollow products ➔ they are fairly light
We have to heat up the material so it becomes viscous
and sticks to the wall ➔ we use thermoplastics, not
thermosetting plastics
Describe the process of extrusion blow-molding.
In extrusion blow-molding, a tube of plastic is extruded, and a blow pin blows air into the tube to expand it and assume the shape of the mold.
What are the characteristics of extrusion blow-molding materials?
The material is heated to become viscous, allowing it to deform and expand to fill the mold. This process is suitable for thermoplastics due to their ability to be reheated.
the bigger the diameter of the mold, the thinner the walls will be
* example – water bottles have thin walls except for their necks and bottoms which are pretty sturdy
c. fairly cheap process ➔ mass production
What is injection blow-molding?
Injection blow-molding involves creating a small shape using an injection molding machine, then placing it into a larger mold and expanding it until it touches the die.
What advantage does injection blow-molding offer in terms of wall thickness?
It allows for the creation of different wall thicknesses, resulting in less variation between the wall thickness and bottoms and necks of bottles.
How does the precision of injection blow-molding compare to other methods?
The process is more precise but also more expensive compared to other molding methods.
What is calendaring?
Calendaring is the process of pressing material together with rolls to create foil, film, or sheet.
What is thermoforming?
Thermoforming involves heating a plastic sheet, pushing the die up to create a vacuum, and then trimming the sheet to create a usable product.
What types of materials are used as the base material in thermoforming?
Thermoplastics in the form of foil or sheet are commonly used as the base material for thermoforming.
How is heating achieved in thermoforming?
Heating can be done using an oven or infrared heat sources to soften the plastic sheet for forming.
What are some characteristics of molds used in thermoforming?
Molds used in thermoforming are relatively cheap, require low forces, and allow for varying wall thicknesses in the final product.
