Permanent Mould Casting Flashcards
Describe the process of die casting
Molten metal is injected into a closed metal die under high pressure
Pressure is maintained during solidification
Die is separated and casting ejected
Centrifugal Casting - What does True Centrifugal Casting produce
Hollow cylindrical parts (pipes, gun barrels, streetlamp posts etc)
What are single crystal solids desirable for?
Single crystal solids are desirable for the production of high strength materials with low thermal creep, such as those required for turbine blades
Die Casting - Describe the hot chamber process
An injection system forces molten metal out of the gooseneck into the die cavity where the metal rapidly solidifies
Whole chamber is kept hot
What are the applications of slush casting?
Hollow castings with thin walls, decorative/ornamental objects, common in theatre/film industry for making latex/silicone props and costumes
What is the main benefit of single crystal casting?
Casting keeps its shape and dimensions at high temperatures
Centrifugal Casting - What are the advantages of True Centrifugal Casting?
Good quality (impurities are moved to centre by CF forces so can be removed, creating a high purity casting) Good dimensional accuracy
What are the applications of single crystal casting?
Gas turbines, aircraft engines
Die Casting - What are the applications of the hot chamber process?
Primarily used with zinc-, tin- and lead-based alloys
Die Casting - What are the advantages of the cold chamber process?
Good strength product
Excellent dimensional precision
Excellent surface finish
Die Casting - What are the disadvantages of the cold chamber process?
Expensive dies
Requires high production rate to justify the usage
The need to transport molten metals
Die Casting - What are the advantages of the hot chamber process?
No transfer process of molten metal, as it is melted in the chamber from which it is injected into the die cavity
Fast cycling times
Good strength product
Excellent dimensional precision and surface finish
What are the applications of centrifugal casting?
Bushes, bearing houses etc
What are the applications of pressure casting?
High quality casting of components
What are the advantages of single crystals?
Processing of superalloy turbine blades has lead to a huge leap forward in terms of high-temperature operating capability
Substantial further improvements, with corresponding benefits in engine performance and fuel efficiency, are now possible
Die Casting - What are the disadvantages of the hot chamber process?
Expensive as the dies are made from hardened hot-worked tool steels (resists temperatures used)
Requires high production rate to justify the usage
Cannot be used for high MP metals
What are the disadvantages of centrifugal casting?
Shape is limited
Expensive spinning equipment required
What are the advantages of centrifugal casting?
Able to produce a wide range of cylindrical parts
Good dimensional accuracy
Describe the process of centrifugal casting
Pour molten metal into rotating mould
Utilises inertial force caused by rotation to distribute molten metal into mould cavities
Metal is held against the mould wall by centrifugal force until it is solidified
What are the 2 types of die casting?
Hot Chamber
Cold Chamber
What are the 3 main types of centrifugal casting?
True Centrifugal Casting
Semi-Centrifugal Casting
Centrifuging
Centrifugal Casting - What is semi-centrifugal casting used for?
To create parts with rotational symmetry
Die Casting - What are the applications of the cold chamber process?
Employed for die casting of materials that are not suitable for hot chamber design, e.g. Al, Mg, Cu
What is pressure casting also known as?
Pressure pouring
Low pressure casting
Describe the process of slush casting
Molten metal poured into the metal mould, when desired thickness of solidified skin is obtained mould is inverted and remaining liquid metal is poured out. Mould halves are then opened and casting is removed
What are the advantages of pressure casting?
Avoids rapid oxidation of the metal
Mould cooling is designed to promote directional solidification (top down)
Describe the process of pressure casting
Molten metal forced upwards by gas pressure into a graphite or metal mould, or a vacuum, which removes gas and gives the casting a lower porosity.
Pressure maintained until metal has completely solidified in the mould
Centrifugal Casting - Describe the process of Centrifuging
Mould cavities of any shape are placed at a certain distance from the axis of rotation
Molten metal is poured from the centre and is forced into the mould by centrifugal forces
Name and describe the methods of producing single crystals
Czochralski Process - A seed of single-crystal silicon contacts the top of the molten silicon. As the seed is slowly raised, atoms of the molten silicon solidify in the pattern of the seed and extend the single-crystal structure
Single Crystal Solidification - (superalloy turbine blades to reduce grain boundaries) Helical channel above a water-cooled solidification “starter block” permits only a single growing grain to pass through
Die Casting - Describe the cold chamber process
Metal is melted in a separate furnace and is transported to the die casting machine
Molten metal is fed into an unheated chamber
A mechanical plunger forces the molten metal into the die cavity where the metal solidifies
Centrifugal Casting - Describe the True Centrifugal Casting process
Mould normally made of steel, iron, or graphite and may be coated with a refractory lining to increase the mould life
Mould surfaces can be shaped so that pipes with various outer shapes, including square or polygonal, can be cast.
Inner surface of casting remains cylindrical as the molten metal is uniformly distributed by CF forces.
Die Casting - How is the lifespan of the die improved in the hot chamber process and aided in the rapid cooling?
Dies are usually cooled by circulating water/oil through passageways in the die block
What are the disadvantages of pressure casting?
Long cycle time
