Foundry 1

Foundry – A place or a factory where metal products (castings) are produced.

Its consists of: pattern → mold (gating and riser system) → furnace (molten metal) → pouring molten metal in mold → casting → cleaning.

• Casting:Process in which molten metal flows by gravity or other force into a mold cavity where it solidifies in the shape of the mold cavity.

Steps:1. Melt the material in suitable furnace 2. Pour it into a mold3. Solidification/Cooling

Different Components…Different Aspects

Capabilities and Advantages• Versatile: complex geometry, internal cavities, hollow sections

• Versatile: small (~10 gms) to very large parts (~1000 Kg)– Engine blocks and heads, machine frames, railway wheels, pipes, church, bells etc.

– Dental crowns, jewelry, small statues, frying pans

• ECONOMICAL: little wastage (extra metal is re-used)

• ISOTROPIC: cast parts have same properties along all directions

• Some casting methods are suited to mass production

• All varieties of metals can be cast, ferrous and nonferrous

• High complexity with few steps (usually)

Castings offer cost and performance advantages because of their shape.

The molten metal is poured or injected and allowed to cool. The

composition, structure, and properties can be tailored for a specific end

product.

Disadvantages of Casting

• Limitations on mechanical properties (Castings have lower strength than

formed parts).

• Poor dimensional accuracy and surface finish for some processes;

e.g., sand casting

• Safety hazards to workers due to hot molten metals

• Environmental problems

• Expensive and time-consuming patterns/molds/dies

• Solidification issues: shrinkage, porosity, ~low strength, brittleness

• Some methods require many steps

Green Sand molding/casting

Classification of casting processes

Pattern » Mold » Pour » Cool » Remove » Inspect

• When the mold is used for single casting, it made of sand and known as

expendable mold

• When the mold is used repeatedly for number of castings and is made of metal

or graphite are called permanent mould

• For making holes or hollow cavities inside a casting, cores made of either sand

or metal are used.

Requirements• Mold : single or multiple use

• Melting Process

• Pouring Technique

• Solidification Process

• Mold removal

• Clean, Finish, Inspection

Variety of patters are used in casting and the choice depends on the

configuration of casting and number of casting required

Single-piece pattern

Split pattern

Follow board pattern

Cope and drag pattern

Match plate pattern

Loose-piece pattern

Sweep pattern

Skeleton pattern

Patterns

(a)Split pattern

(b) Follow-board

(c) Match Plate

(d) Loose-piece

(e) Sweep

(f) Skeleton pattern

Pattern materials:

– Wood - common material because it is easy to work, but it

warps

– Metal - more expensive to make, but lasts much longer

– Plastic - compromise between wood and metal

Pattern Material Characteristics

Types of patterns used in sand castings:

(a) solid pattern, (b) split pattern, (c) match-plate pattern (d) cope and drag pattern

Pattern allowances

• Shrinkage allowance

• Draft allowance (taper, angle)

• Machining allowance

• Distortion allowance

• Patternmakers account for solidification shrinkage and thermal contraction

by making mold cavity oversized

• Amount by which mold is made larger relative to final casting size is called

pattern shrinkage allowance

• Casting dimensions are expressed linearly, so allowances are applied

accordingly

Shrinkage allowance for sand molds

(10mm/m to 20mm/m)

Solidification

Solidification:• Transformation of molten metal back into solid state

• Influence shape, size, uniformity and chemical composition

• Types

– Pure Metal

– Alloys

– Eutectic Alloy

(1) Cooling of melt by heat flow outward through the mold walls(2) Nucleation of crystals, accompanied with additional heat lossin the form of latent heat.(3) Growth of crystals, either opposite or parallel to heat flowdirection, which results in overall morphological changes

The material is a single crystal inside a dendrite, just like a grain.