CASTING PROCESS

• Casting is a manufacturing process by which a liquid material is usually poured into a mould, 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 mould to complete the process.

FLOW CHART OF CASTING PROCESS

Basic processPattern makingCore makingMould makingMelting and pouringSolidification and mould breakingCleaning,finisshing and inspection.

ComponentsPatternsToolsMoulding box and materialsChillsCores

Design requirements

The part to be made and its pattern must be designed to accommodate each stage of the process, as it must be possible to remove the pattern without disturbing the moulding sand and to have proper locations to receive and position the cores. A slight taper, known as draft, must be used on surfaces perpendicular to the parting line, in order to be able to remove the pattern from the mould. This requirement also applies to cores, as they must be removed from the core box in which they are formed. The sprue and risers must be arranged to allow a proper flow of metal and gasses within the mould in order to avoid an incomplete casting. Should a piece of core or mould become dislodged it may be embedded in the final casting, forming asand pit, which may render the casting unusable. Gas pockets can cause internal voids. These may be immediately visible or may only be revealed after extensive machining has been performed. For critical applications, or where the cost of wasted effort is a factor, non-destructive testing methods may be applied before further work is performed.

PROPERTIES OF SAND USEDRefractoriness

Chemical inertness Permeability

Good Surface finish Cohesiveness (or bond)

FlowabilityCollapsibility

Availability/cost 

Types of base sandsSilica sand : Silica (SiO2)

Olivine sandChromite sand

Zircon sandChamotte sand

Binders

Clay and waterOil

ResinSodium silicate

casting Defects

The terms "defect" and "discontinuity" refer to two specific and separate things in castings. Defects are defined as conditions in a casting that must be corrected or removed, or the casting must be rejected. Discontinuities, also known as "imperfections", are defined as "interruptions in the physical continuity of the casting". Therefore, if the casting is less than perfect, but still useful and in tolerance, the imperfections should be deemed "discontinuities".

CASTING DEFECTS

ADVANTEGES

any complex shape can be easily producedPractically any type of material can be casted.Ideal method is by producing small quantities.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.

DISADVANTAGESBad surface finish.Many defects arise in the casting.Not suitable for mass production.Dangerous operation, may cause harmful injuries.Only good for basic shapes. Can usually only be used once.Accuracy of casting sizes aren't great.Defects are unavoidable.Sand casting is labor intensive.

SAND CASTING APPLICATIONSTransport: automobile, aerospace, railways and shippingHeavy equipment: construction, farming and miningMachine tools: machining, casting, plastics molding, forging, extrusion and

formingPlant machinery: chemical, petroleum, paper, sugar, textile, steel and

thermal plantsDefense: vehicles, artillery, munitions, storage and supporting equipmentElectrical machines: motors, generators, pumps and compressorsMunicipal castings: pipes, joints, valves and fittingsHousehold: appliances, kitchen and gardening equipment, furniture and

fittingsArt objects: sculptures, idols, furniture, lamp stands and decorative items.