Plaster and Investment Casting Processes

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Questions and Answers

What distinguishes plaster mould casting from sand mould casting?

It uses thicker materials for improved durability.

It allows for the casting of ferrous materials.

It produces castings with greater dimensional accuracy and smoother surfaces. (correct)

It is a cheaper alternative that requires less preparation.

Which of the following is NOT a plaster mould casting process?

Match Plate Pattern Plaster Mould Casting

Foamed Plaster Process

Conventional Plaster Mould Casting

Investment Casting (correct)

What type of products is most commonly produced by plaster mould casting?

High-temperature furnace parts

Large structural beams

Heavy machinery components

Near-net shape castings such as compressor wheels (correct)

What is a characteristic of castings produced by plaster mould casting regarding their weight?

About 90% weigh less than 9 kg (20 lbs). Signup and view all the answers

What is the fate of the pattern in investment casting after its use?

It is destroyed during the recovery process. Signup and view all the answers

What is one limitation of permanent mould casting?

Some shapes may be difficult to produce due to undercuts. Signup and view all the answers

Which of the following metals can be cast using permanent mould casting?

Aluminum Signup and view all the answers

Which casting method is characterized by the use of hydraulic energy for rapid filling of a die?

Die casting Signup and view all the answers

What are the types of centrifugal casting processes?

Centrifugal, Semi-centrifugal, and Centrifuged casting Signup and view all the answers

What process is NOT suitable for extrusion moulding?

Thermosetting plastics Signup and view all the answers

In which moulding process is the material heated to temperatures between 180 degrees to 280 degrees Celsius?

Injection die moulding Signup and view all the answers

What is the first step in the sand casting process flow?

Preparation of a pattern Signup and view all the answers

What is the main advantage of permanent mould casting compared to sand casting?

It offers superior surface finish and dimensional tolerances. Signup and view all the answers

What is a unique feature of the centrifugal casting process?

It uses centrifugal force to ensure high density of castings. Signup and view all the answers

Which process allows the production of components from plastics in granular or powder form?

Injection die moulding Signup and view all the answers

Which type of casting produces parts that are free from impurities due to the use of centrifugal force?

Centrifugal casting Signup and view all the answers

What is the role of coatings in permanent mould casting?

To protect the mould from damage by molten metal. Signup and view all the answers

What type of mould is typically used in the compression moulding process?

Metal moulds with multiple parts Signup and view all the answers

What is the advantage of using plastic materials in extrusion moulding?

Continuous and cost-effective production Signup and view all the answers

What is the primary role of the pattern in the sand-casting process?

To produce the moulds for casting Signup and view all the answers

Which component is used to shape the internal passageways within a casting?

Cores Signup and view all the answers

What is the primary function of risers in the casting process?

To provide a liquid-metal reservoir Signup and view all the answers

What differentiates an electric furnace from an oil-fired or coal-fired furnace?

It produces impurity-free metals Signup and view all the answers

Which characteristic of the cupola furnace contributes to its efficient melting of cast iron?

Utilization of coke as a fuel source Signup and view all the answers

What is a significant benefit of induction furnaces over traditional melting methods?

Excellent metallurgical control Signup and view all the answers

What is the purpose of a wind box in a cupola furnace?

To supply air for combustion Signup and view all the answers

Which of the following is true about channel induction furnaces?

They require a supply of molten metal to start Signup and view all the answers

What aspect of channel induction furnaces limits their efficiency in metal melting?

Small amount of metal receiving energy Signup and view all the answers

In coreless induction furnaces, what is crucial for ensuring good electrical coupling?

Water-cooling channel design Signup and view all the answers

Which of the following is a disadvantage of channel induction furnaces?

Technological innovations are slower to develop Signup and view all the answers

What is the composition of the core used to shape internal casting features?

Sand and rubber Signup and view all the answers

What role do gates play in the casting process?

They control the flow of molten metal into the mould cavity Signup and view all the answers

What must be done to operate induction furnaces efficiently?

They must be continuously maintained in a molten state Signup and view all the answers

Study Notes

Plaster Mould Casting

A specialized casting process producing nonferrous castings with high dimensional accuracy, smooth surfaces, and fine detail.
Similar to sand casting but uses plaster of Paris.
Four recognized plaster mould processes: conventional, match plate pattern, Antioch, and foamed plaster.
Applications include near-net shape castings like compressor wheels, impellers, electronics gear components, tire molds, and aerospace fuel pump systems.
Machining costs are significantly higher for these parts cast in other moulds.
Plaster mould castings usually weigh less than 9 kg (20 lbs) but substantial quantities of castings up to 34 kg (75 lbs) are made.
An aluminum alloy casting of 1815 kg (4000 lb) has been successfully produced.

Investment Casting

A ceramic slurry is applied around a disposable pattern (usually wax) to create a casting mold.
The pattern and mold are disposable.
Two distinct processes: solid investment (solid mold) process and ceramic shell process.
The ceramic shell process is more common in engineering applications.

Permanent Mould Casting

Also known as gravity die casting.
A metal mold (two or more parts) is repeatedly used to produce many castings.
Simple cores are metal; complex cores are sand or plaster (semi-permanent).
Used for high-volume production of castings with uniform wall thickness and limited intricate coring.
Can produce complex castings, but production volume must justify mold costs.
More uniform castings, closer tolerances, and improved surface finish are features compared to sand casting.
Limitations: Not all alloys are suitable, low production quantities are expensive due to tooling, some shapes are not possible.
Suitable metals include aluminum, magnesium, zinc, copper alloys, and hypereutectic gray iron.

Die Casting

Characterized by rapidly injecting molten metal into a metal die using hydraulic energy.
The die absorbs stresses, dissipates heat, and facilitates part removal for the next cycle.

Centrifugal Casting

Molten metal is poured into a revolving mold, solidified by centrifugal force.
Used for mass production of circular castings which are free from impurities, and produce high-density, strong castings.
Castings experience directional solidification (colder metal outside, molten inside).
Suitable for cylindrical parts and pipes.

Centrifugal Casting Types

True centrifugal casting
Semi-centrifugal casting
Centrifuged casting

Plastics Moulding Processes

Methods for creating components from granular, powder, or other forms of plastic materials.
Processes: compression molding, transfer molding, injection molding, cup molding, extrusion molding, calendaring, thermoforming, casting.

Injection Die Moulding

Thermoplastic materials soften when heated and re-harden when cooled (no chemical change).
Granular material is fed into a heating cylinder which fills the mold.
The injection ram pushes the material into a cylinder, forcing it through a nozzle and into mold cavities.
The mold then closes and cools the part.
Material heating temperatures are typically 180-280°C.
Automated systems maintain mold temperature.
Primarily for thermoplastics but adaptable to thermosets and rubbers.

Extrusion Moulding

Thermoplastic materials are suitable for extrusion into rods, tubes, sheets, film, pipes, and ropes.
Thermosets aren't suitable.
Continuous process with a low initial cost.

Sand Casting Process Flow

Pattern creation, mold preparation, metal melting, pouring, mold breaking, cleaning, inspection (fettling).
Sand moulds are created using patterns and cores.
Cores are shaped pieces made of sand or rubber to form internal features.
- Mold halves (drag and cope) hold the core.
Molten metal is poured into the mold cavity, then solidified.
Castings are removed, and unwanted parts (risers, gates) are removed.

Furnace

Used to heat metal above its melting point.
Types: electric (impurity-free, expensive), oil-fired (metal picks up impurities), coal-fired (metal picks up impurities).

Cupola

Used for melting cast iron.
Economical and convenient.
Uses coke as fuel.

Induction Furnaces

Commonly used to melt iron and non-ferrous alloys due to excellent metallurgical control and relatively pollution-free operation.
Coreless and channel induction furnaces exist in varying sizes to suit the metal needed for the production to fit.
Large high-powered induction furnaces are operated at 60Hz.
Modern units use medium frequencies due to efficiency and quick start-up/shutdown capability.

Coreless Induction Furnace

Refractory-lined crucible surrounded by water-cooled copper coil.
All metal in crucible is the secondary.
Commonly used for melting and superheating.

Channel Induction Furnace

Coil surrounds only an inductor, which the molten metal forms a loop.
Surrounding copper coil is the primary.
Primarily for superheating, duplexing, and holding. Often used for copper alloys.
Has limitations compared to the coreless induction furnace.

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Description

Explore the specialized techniques of plaster mould and investment casting. Understand their unique processes, applications, and the dimensional accuracy they provide in nonferrous castings. This quiz will challenge your knowledge on these essential manufacturing methods.