Chapter 6 Flashcards
Adv and disadv of expendable
More complex shapes.
Production rates limited since longer to make mold than the casting itself
Adv and Disadv of permanent
Higher production rate
Geometries limited by need to open mold
Pattern materials (3)
Wood, metal, and plastic
Pattern types (4)
Solid pattern
Split pattern
Match-plate pattern
Cope and drag pattern
Definition of chaplets
Hold cores in place during pouring
Silica SiO2 properties for small, large, and irregular
Good refractory properties
Small grain size for better surface finish
Large grain is more permeable allowing gases to escape during pouring
Irregular grain strengthen molds due to interlocking but reduces permeability
Typical mix
90% sand, 3% water, and 7% clay
Types of Sand Mold (3)
Green-sand - Mixture that has moisture
Dry-sand - Organic binders instead of clay
Skin-dried - Drying green-sand to a depth of 10 -25 mm using torches or heating lamps
Shell molding and Adv3/Disadv1
Heated pattern covered in thermosetting resin. Then heated. Then used to be a mold. Better surface finish Good dimensional accuracy Mass production Expensive
Expanded Polystyrene Process and Adv2/Dadv2
Lost pattern so foam pattern coated with refractory compound. Poured into it.
No need to remove pattern
Speeds mold-making because no need for two halves.
New pattern needed every time.
Cost of producing patterns makes it expensive or not
Investment Casting and Adv(4)/Disa(2)
Lost wax process
Make wax pattern. Cover in refractory coat. Melt wax away leaving shell. Pour.
Very complex parts made
Very accurate
Wax reused
Net shape process
Requires many steps
Expensive
Explain Sand casting
Pattern made. Pack sand around it. Then separate sand into two parts. Pour then break sand off.
Plaster mold casting
Adv(2) Disa(3)
Similar to sand casting but made of plaster. Mixture of plaster and water flows around pattern improving details and surface finish.
Good accuracy and surf finish
Capable of thin cross sections
Must bake to remove moisture
Mold strength lost if over bake
Limited to low melt. point alloys
Ceramic Mold Casting
Similar to plaster and sand but refractory ceramic higher temp.
Too similar . Just does high temp alloys.
Permanent Mold material for low melting point alloys and for steel
Lower melting point - Steel and cast iron
Steel - refractory material
