13-06-2012, 04:40 PM
INTRODUCTION OF CASTING PROCESS
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INTRODUCTION TO CASTING
Since the evolution of mankind, man has used his intelligence and creative instinct to develop things that will reduce his labour. He shaped bowls, tools and weapons out of stones and wood which was naturally found in nature.With the passage of time he discovered other element in nature like gold, silver and copper which were readily available in nature in the form of nuggets. He melted and shaped these metal according to his desires. He probably discovered gold pebbles with stone and copper from the copper bearing ores that line the fire pits. He found it easy to melt the iron, copper and gold using the firewoods and charcoal, and hence in differerent ages iron and copper became the most profusely used natural materials.
Metal Castings
A metal casting can be defined as a metal object formed when molten metal is poured into a mould which contains a cavity of the desired shape and is allowed to solidify.
The casting process is used most often to create complex shapes that would otherwise be difficult or impossible to make using conventional manufacturing practices.
CASTING GEOMETRY
To rectify the defects like gas and shrink porosity within the casting; casting geometry is used as a tool. A foundry engineer studies the geometry of the part and plans to control the heat removal process within the casting structure and to improve the eminence of the casting. However, to identify the best possible geometry to adhere to solidification shrinkage requirements of the casting is required.
IDENTIFYING GEOMETRIC PATTERN
Identifying the best possible geometry can be an easy task in some alloys and can be a real difficult task in others where high technical design is required. In such case, where obtaining geometry requires skilled jobs, the foundry engineers work on “thermal trickery” to draft flow of energy in the form of fluids, and capture heat transfer patterns.
Characteristics affecting casting geometry:
There are various physical and mechanical characteristics, which affects the geometry of the castings. The physical characters effecting geometry of the designs are life of the fluid being used, shrinkage of the component while undergoing shrinkage process, slag formation affinity and pouring temperatures.
CASTING PATTERN MAKING
It's the science of making an original pattern or form which will be used to make a mold. The mold will allow for mass production of the original pattern by poring some sort of casting material such as metal, resin, plaster, or other material. A pattern can be both simple and complex for e.g an object that has detail on only one side like a plaque, or with detail on all sides, like a machine part. Factors that go into making a pattern includes durability, shrinkage, machine allowances, draft and undercuts.
In sand casting, the pattern is usually of wood, whereas it may be of metal or other materials in pressure or centrifugal casting. The patternmaker also decides where the sprues and risers (inlet and outlet for molten material) will be placed with respect to the pattern. Objects which have holes or depressions in some of its parts are taken care of by inserting cores. Sometimes patterns may also contain chills, solid pieces of the final material, to enable rapid cooling, resulting in quench hardening in the neighborhood of the chill.