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Presentation on:
Processing of plastic materials
Contents:
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Submitted by:
1.ASH2004026M
2 MUH2004O27M
3.BFH2004O28F
Plastic
Classification of plastics
Processing of thermoplastic materials
Processing of thermosetting materials
Environmental aspects of plastic material
Course Code: ACCE-3109
Course Title: Material Science and Engineering
Plastic
Plastic is a synthetic material made from polymers, which are long chains of molecules. It is a
versatile material that can be molded into various shapes and forms. Plastics are widely used in
many industries and in our daily lives due to their durability, lightweight nature, and low cost of
production.
Some examples of plastics are Polyvinyl Chloride (PVC or Vinyl), Polystyrene, polycarbonate,
polypropylene etc.
Classification of plastic: Plastics are divided into two types. they are:
 Thermoplastics
 Thermosetting.
Thermoplastics: Thermoplastics are polymers that can be melted and remolded multiple
times without undergoing significant chemical change. They are characterized by their ability to
soften when heated and solidify when cooled, making them highly versatile and suitable for
various applications.
Key characteristics:
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Melting and Remolding
Recyclability
Having low mechanical strength
Exhibit good dimensional stability
Flexibility
Chemical resistance
Hardness and toughness
Transparency
Electrical insulation
Some examples of thermosetting plastics are polyethylene, polystyrene, PVC etc.
Thermosetting: Thermosetting are polymers that undergo a chemical change during heating
and permanently solidified.
Example of thermosetting plastics include Boke lite, Epoxy resin, melamine etc.
Key characteristics:
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It cannot be remolded after curing.
Exhibit high mechanical strength and heat resistance.
Excellent electrical insulation properties
Dimensional stability
Flame retardancy
Stability and durability
Chemical heat resistance
Processes Used for Thermoplastic Materials
Injection molding process: The injection molding process for thermoplastic materials
is a widely used manufacturing method. Here are the steps involved in the injection molding
process for thermoplastic materials:
Material Preparation: Thermoplastic materials are typically in the form of small pellets or
granules. The desired thermoplastic resin is selected based on the specific properties required for
the part being
Material Melting: The thermoplastic material is fed into a heated barrel of an injection molding
machine. Inside the barrel, a reciprocating screw or a plunger mechanism melts and homogenizes
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the material by applying heat and mechanical mixing. The temperature is carefully controlled to
achieve proper melting without degradation of the material.
Injection: Once the molten plastic reaches the desired temperature and consistency, it is injected
into a mold cavity. The mold consists of two halves: the stationary side (cavity) and the moving
side (core). The molten plastic is injected under high pressure into the mold cavity through a
nozzle, filling the space and taking the shape of the desired part.
Cooling and Solidification: After the mold is filled, the molten plastic begins to cool and
solidify inside the mold cavity. Cooling is often facilitated by the circulation of coolant or water
through channels within the mold. The cooling time depends on the thickness and complexity of
the part, as well as the cooling medium used.
Mold Opening and Ejection: Once the plastic has solidified and cooled sufficiently, the mold is
opened, separating the two halves. The ejector system, typically comprising pins or plates,
pushes the part out of the mold cavity. The part may have small protrusions, called sprues and
runners, which are trimmed off in subsequent steps.
Post-Molding Operations: After ejection, the part may require additional operations, such as
trimming excess material, deburring, surface finishing, or assembly with other components.
These steps ensure the final part meets the desired specifications and appearance.
Repeat Cycle: The injection molding process is cyclical. Once the part is ejected, the mold is
closed again, and the process begins anew with material preparation, melting, injection, cooling,
and ejection. The cycle time varies depending on the part size, complexity, and the properties of
the thermoplastic material being used.
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Advantages:
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High efficiency and production rate
Material versatility
Good surface finish
Low cost
Automated process
Consistency and reproducibility
Disadvantages:
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Installment cost is high
Design limitation
Material selection limitation
Longer lead time
Extrusion molding process: Extrusion molding is the process where molten plastic is
forced through a specially designed die to create continuous shapes with a constituent crosssectional profile. The steps are:
Material Preparation: Thermoplastic material, typically in the form of pellets or granules, is
prepared. The material is selected based on its properties and suitability for the desired
application.
Heating and Melting: The thermoplastic material is fed into an extruder, which consists of a
heated barrel with a rotating screw inside. The material is heated and melted as it is conveyed
along the barrel by the rotating screw. The heating zone of the barrel gradually raises the
temperature to the melting point of the material.
Extrusion and Shaping: Once the material is melted, it is forced through a shaped opening
called a die. The die determines the final shape and dimensions of the extruded product. The
molten material is subjected to high pressure, pushing it through the die and forming a
continuous profile.
Cooling and Solidification: As the molten material exits the die, it enters a cooling process to
solidify. Cooling can be achieved by various methods, such as passing the extruded product
through a water bath or using cooling fans or air cooling systems. The cooling process solidifies
the material and sets its shape.
Sizing and Cutting: After solidification, the extruded product may undergo sizing or cutting
operations. Sizing ensures the final dimensions and tolerances of the product are achieved.
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Cutting can be performed using saws, knives, or other cutting tools to obtain the desired length
or shape of individual parts.
Additional Post-Processing: Depending on the specific requirements, the extruded product may
undergo additional post-processing steps. These can include surface treatments, machining,
drilling, or other operations to achieve the desired final properties and appearance.
Advantages:
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Low cost per part
Good mixing and efficient melting
Continuous process and better grain structure
Design flexibility
Energy efficiency
Disadvantages:
1. Variations in size
2.High compressive force is required
3.Not efficient for small production scale
Blow molding process: Blow molding is a manufacturing process in which a hollow
plastic part is created and air is blown into cavity. The steps are:
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Material Preparation: Thermoplastic material, usually in the form of small pellets or granules,
is prepared. The material is selected based on its properties and suitability for blow molding,
such as HDPE (high-density polyethylene), PET (polyethylene terephthalate), or PP
(polypropylene).
Parison Formation: The thermoplastic material is fed into an extruder, where it is heated and
melted. The molten plastic is then extruded through a die head to form a hollow tube called a
parison. The die head controls the dimensions and thickness of the parison, which is determined
by the design of the final part.
Mold Clamping: The parison is captured between two halves of a mold, which are brought
together and clamped with significant force to ensure a tight seal. The mold consists of two parts:
the cavity, which defines the shape of the final product, and the core, which forms the internal
features of the part.
Blow Molding: With the mold closed, a blow pin is inserted into the parison, and compressed air
is injected through the blow pin into the parison. The pressurized air inflates the parison, causing
it to conform to the shape of the mold cavity. The plastic material solidifies and takes on the
shape of the mold.
Cooling and Solidification: After the part has assumed the desired shape, cooling is applied to
solidify the plastic. Cooling can be achieved through a combination of natural cooling,
circulating cool air, or water-based cooling systems. The cooling time varies depending on the
material and part thickness.
Mold Opening and Ejection: Once the part has sufficiently cooled and solidified, the mold is
opened, and the formed part is ejected. Ejection pins or mechanical systems push the part out of
the mold cavity. Some molds have automated systems to assist in part ejection.
- The formed part may undergo trimming or additional post-processing steps to remove excess
material, smooth rough edges, or add any necessary features or details. This step ensures the final
part meets the desired specifications and aesthetic requirements.
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Advantages:
1. Required very small finishing
2. Fast production rate
Disadvantages:
1. Thickness of wall control is tough.
2. Low strength
Processes Used for Thermosetting Materials
Compression molding process: Compression molding is a process involving
processing a deformable material charge and give desired product.
The steps are:
Material Preparation: Thermosetting material, usually in the form of pre-measured granules,
powders, or preforms, is prepared. The material is selected based on its properties and the desired
characteristics of the final product.
Mold Preparation: A two-part mold, typically made of metal, is prepared. The mold consists of
an upper and lower half, which fit together to form a cavity. The mold cavity is designed to have
the desired shape and features of the final product.
Material Loading: The pre-measured thermosetting material is placed into the lower half of the
mold cavity. The amount of material should be carefully controlled to ensure proper filling and
minimize excess material or voids.
Mold Closure: The upper half of the mold is closed and brought into contact with the lower half,
enclosing the thermosetting material. The mold is securely clamped to maintain the desired
pressure during the molding process.
Heat and Pressure Application: Heat and pressure are applied to the mold to initiate the curing
process of the thermosetting material. The mold is heated to a temperature above the curing
temperature of the material, allowing it to undergo a chemical reaction and transform from a
liquid or soft state to a solid state. The pressure applied ensures uniform distribution of the
material within the mold cavity and aids in achieving the desired shape and density of the final
product.
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Curing and Cooling: The thermosetting material remains under heat and pressure for a specific
duration, known as the curing time. This allows the material to fully cure and solidify. After the
curing process, the mold is cooled, either by natural convection or using cooling systems, to
facilitate the solidification and dimensional stability of the part.
Mold Opening and Part Removal: Once the curing and cooling process is complete, the mold
is opened, and the solidified part is removed. The part may require additional trimming or
finishing to remove any excess material, improve surface quality, or achieve the desired final
dimensions.
Advantages:
1.Short cycle time
2. Processes are automated
Disadvantages:
1.Secondary operation may be required
2.Scrap cannot be reprocessed
Transfer molding: Transfer molding is a process of forming components in a closed
mold from a thermosetting material that is conveyed under pressure.
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The steps are:
Mold Preparation: A metal mold, typically made of steel, is prepared. The mold consists of two
halves, an upper and a lower half, with a cavity in the shape of the desired part. The mold is
cleaned and coated with a release agent to facilitate easy part removal.
Material Preparation: The thermosetting material, usually in the form of granules, pellets, or
preforms, is prepared. The material is pre-measured and heated to a temperature above its
melting point but below its curing temperature. This preheating softens the material and allows
for easier flow during the molding process.
Loading: The preheated thermosetting material is placed into a transfer pot or chamber. The
transfer pot is equipped with a plunger or piston that can apply pressure to the material. The
material is loaded into the transfer pot in a measured amount to ensure consistent and accurate
parts.
Mold Closure: The mold halves are closed, and the transfer pot is positioned above the mold
cavity. The upper half of the mold is typically equipped with a sprue or gating system to allow
the transfer of the material into the mold cavity.
Transfer: Pressure is applied to the transfer pot, forcing the softened thermosetting material to
flow through the sprue and into the mold cavity. The pressure and flow rate are controlled to
ensure complete filling of the cavity and to minimize air entrapment.
Curing: Once the mold cavity is filled, the entire mold assembly is transferred to a curing
station. The mold is heated to a temperature above the curing temperature of the thermosetting
material. The material undergoes a chemical reaction, known as curing or polymerization, which
transforms it from a soft or molten state to a solid state. The curing process takes place over a
specific time period to ensure proper curing and dimensional stability.
Cooling and Demolding: After the curing process is complete, the mold is cooled, either by
natural convection or using external cooling systems. The cooled mold is then opened, and the
solidified part is removed. The part may undergo additional trimming or finishing processes as
required.
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Injection molding:
Injection molding is the modern process for making thermosetting
plastics by reciprocating- screw injection molding machines. Special heating and cooling jacket
is added and good venting is required. In future, injection molding will probably become more
important for producing thermosetting parts because of the efficiency of this process.
Environmental aspects of plastic processing
Plastic materials and their processing can have both positive and negative environmental aspects.
Here are some environmental considerations related to plastic materials during processing:
Resource Consumption: The production of plastic materials requires the extraction and
processing of raw materials, such as petroleum or natural gas. These processes can have
significant environmental impacts, including habitat disruption, water pollution, and carbon
emissions. Additionally, plastic production consumes energy, contributing to greenhouse gas
emissions and climate change.
Waste Generation: Plastic processing can generate waste in the form of scrap, trimmings, or
rejected parts. This waste needs to be managed properly to minimize environmental impacts.
Recycling and proper disposal methods are crucial to reduce the accumulation of plastic waste in
landfills and marine environments, which can harm ecosystems and wildlife.
Energy Consumption: The processing of plastic materials requires energy for heating, melting,
molding, and other manufacturing processes. Energy consumption contributes to carbon
emissions and dependence on fossil fuels. Implementing energy-efficient practices, such as
optimizing processes and using renewable energy sources, can help reduce environmental
impacts.
Chemical Use and Emissions: Plastic processing may involve the use of chemicals, including
additives, colorants, and solvents. The release of these chemicals during processing can pose
environmental risks if not properly managed. Proper handling, containment, and treatment of
chemical substances are necessary to prevent pollution and protect the environment.
Air and Water Pollution: Plastic processing can lead to air and water pollution if not managed
appropriately. Emissions from the production process, including volatile organic compounds
(VOCs) and particulate matter, can contribute to air pollution. Effluents generated during plastic
processing, such as cooling water or cleaning solvents, need to be treated properly to avoid water
pollution and contamination of aquatic ecosystems.
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Recycling and Circular Economy: Implementing recycling initiatives and promoting a circular
economy for plastic materials can help mitigate environmental impacts. By recycling and reusing
plastic materials, we can reduce the need for virgin plastic production, conserve resources, and
reduce waste. Developing technologies for more efficient and effective plastic recycling is
crucial for minimizing environmental impacts.