The pattern must be slightly larger than the finished part you want to produce, as metal shrinks when it cools (about 10mm/meter, depending on the lengh)
STRONGLY SUGGEST that presenter be prepared with props:
Note that the top form and bottom form lock together; they always fit together the same way!
In “dry sand casting,” the molds filled with sand are baked to increase the strength of the sand. In green sand casting, the water with which the clay is mixed is not evaporated.
Sometimes the molds filled with sand are baked to increase the strength of the sand
For very large parts, sand set on the shop floor forms the bottom half of the mold. This is “floor molding”
Key hazards: burns, silicosis (from inhalation of dust), toxic fumes when organic binders are volatilized by molten metal.
Mr.B.Ramesh, M.E., (Ph.D.),
Research Scholar, CEG, Anna University, Chennai.
Department of Mechanical Engineering,,
St. Joseph’s College of Engineering,
Jeppiaar Trust, Chennai-119
What is a Foundry?
• Casting is one of the oldest industrial processes
• There are different casting processes.
The focus here is: “GREEN SAND” CASTING
A foundry is:
a factory that pours molten metal into molds,
producing cast metal objects.
in jet engines
mixed with clay binder &
water (so it will hold its
shape) plus coal dust to
improve surface finish
(a copy of the shape
you want to produce,
made of wood, plastic
Basic materials & equipment for green sand-casting
Container of molten metal
(filled from furnace) Top and bottom mold forms
(made of metal, open at top and bottom)
Rammer (tool to compact the sand;
often a pressing machine is used)
into bottom mold
Pattern placed into mold
A very basic summary of the sand casting
process. . .
First of all,
mix the sand.
the top mold
4 MOLDING: Fill top form
with compacted sand.
A tube or pipe provides
a path to pour the
Pattern is still inside!
Take the top
mold off and
& pipe or post
6 MOLDING: Replace the
top mold and fasten
In the middle of the
sand is a cavity
shaped like the
Pour the metal (container is
filled from furnace immediately
before you are ready to pour)
8 Wait for the metal to cool
(minutes to days,
depending on the size of
8 SHAKE OUT: Break apart the two
halves of the mold & take out the
part—usually requires vibrating or
striking the mold to break apart the
CLEANING. Sand is
cleaned off the part, the
“tab” where metal flowed
in must be removed.
A copy of the pattern
has now been made
10 Mold forms are reused
Sand is broken up,
screened to remove
debris and clumps, and
sent for remixing
Sand-casting is simple
in concept, but
execution. It is a
process essential to
making basic and
advanced products. . .
it is also hazardous
Sand Casting: Parts of a Sand Mold (expendable mold)
Flask, Cope, Drag, Sprue, Runner, Gate, Riser, Mold Cavity, Core, Parting
Line, Draft (not shown).
What is pattern?
• Approximate duplicate of product
• Patterns are made in the shape of the casting
• Pattern Materials: Wood, Plastic or metal.
• One piece or multiple piece pattern
Types of Patterns
Types of patterns used in sand casting:
(a) solid pattern
(b) split pattern
(c) match plate pattern‑
(d) cope and drag pattern
One piece or Solid Pattern
Cope & Drag PatternMatch Plate Pattern
Patterns are made larger than the casting to compensate
contraction of the liquid while freezing.
For internal cavities the allowances should be negative.
Allowance required to remove the rough cast surface. 2 to 25 mm
(0.1 to 1’)
To facilitate ease of removal, usually ½ to 2 deg.
Normal shrinkage: Cast iron 0.83 to 1.3%
Aluminum - 1.3%
• Cores are used to create internal cavities.
• Should have similar properties as the mold.
• Shaken out after casting is produced.