Metal Casting

Introduction

Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired  shape, and then allowed to solidify.

The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process.

Advantages of casting process:
  • Molten metal flows into ant small section in molten cavity, hence any complex shape can be easily produced.
  • Practically any type of material can be casted.
  • Due to small cooling rate from all directions, the properties of casting are same in all directions.
  • Any size of casting can be produced like up to 200 tonnes.
  • Heavy equipment like machine leads, ship’s propeller etc. can be cast easily in the required size rather than fabricating them by joining  several small pieces.
Applications
  • Transport : Automobile, aerospace, railways and shipping
  • Heavy Equipment : Construction, farming and mining
  • Machine Tools : Machining, casting, plastics molding, forging, extrusion and forming
  • Plant Machinery : Chemical, petroleum, paper, sugar, textile, steel and thermal plants
  • Defense : Vehicles, artillery, munitions, storage and supporting equipment
  • Electrical Equipment Machines : Motors, generators, pumps and compressors
  • Household : Appliances, kitchen and gardening equipment, furniture and fittings
Pattern
  • Pattern is defined as a model or replica of an object to be cast
  • The type of pattern to be used for a particular casting depends upon many factors like design of casting, complexity of shape, number of casting required [bulk of casting], mould process, surface finish and  accuracy.
Functions of the Pattern
  • A pattern prepares a mold cavity for the purpose of making a casting.
  • A pattern may contain projections known as core prints if the casting  requires a core and need to be made hollow.
  • Runner, gates, and risers used for feeding molten metal in the mold  cavity may form a part of the pattern.
  • Patterns properly made and having finished and smooth surfaces  reduce casting defects.
  • A properly constructed pattern minimizes the overall cost of the  castings.
Pattern material
  • Wood
  • Metal
  • Plastic
  • Plaster
  • Wax
Features of the Pattern material
  • Easily worked, shaped and joined
  • Light in weight
  • Strong, hard and durable
  • Resistant to wear and abrasion
  • Resistant to corrosion, and to chemical reactions
  • Dimensionally stable and unaffected by variations in temperature and humidity
  • Available at low cost
Wood
  • Advantages
    Cheap, easily available, light, easiness in  surfacing, preserving (by shellac coating),  workable, ease in joining, fabrication
  • Disadvantages
  1. Moisture effects, wear by sand abrasion, warp  during forming, not for rough use.
  2. Must be properly dried/ seasoned,  free from knots, straight grained

Egs.  Burma teak, pine wood, mahogany, Sal,  Deodar, Shisham, Walnut, Apple tree

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