SELECTION OF METAL (3)

APPLICATIONS & LIMITATIONS

Every metal has its own applications and limitations ex :- We cannot use carbon steel in the manufacturing of crusher jaw plates instead of manganese steel. In this example application is manganese steel, and limitation is carbon steel . We cannot choose manganese steel in the manufacturing of bowl mill castings. Here application is carbon steel, and limitation is manganese steel.

I considered Chemical composition, Mechanical properties, Applications, Limitations as Selection criteria of metal in Selection of metal.

In the coming chapters we will discuss in brief selection criteria of Iron castings ( Grey Iron , White Cast Iron, Malleable Cast Iron, S.G.iron/Nodular Cast iron) , Cast steels ( Carbon Steel, Low alloy steels, High alloy steels) , Non-ferrous metals (Copper alloy, Aluminium alloy).

SELECTION OF METAL (2)

MECHANICAL PROPERTIES

Tensile strength, yield strength, elongation , reduction area , hardness, impact strength and bend abilities are called mechanical properties.

SELECTION OF METAL (1)

Selection of metal is most important and first step in Casting design. Every metal has its own chemical composition, mechanical properties, applications and limitations. Without understanding these , we can not design good castings.

Chemical composition:

The combination of materials at atomic level.

The combination of iron, carbon, silicon, manganese, phosphorous, sulpher and its alloying elements ( An element that is intentionally added to a metal in order to change its properties) can be briefly described as chemical composition for steel castings. According to the nature of the material percentage of alloying element may vary. ex :- In stainless steel castings chromium added for hardness and wear resistance . so here chromium is the alloying element.

So many development studies are available for us in taking the decision of whats the best combination that fits to our application of the job.

IMPORTANT INDUSTRIAL SECTORS USING CASTINGS

I. Mining and Mineral Processing

Very large and growing requirement of steel and alloy steel castings is existed in mining and processing minerals like coal,  iron ore, chromium, diamonds, copper, zinc, Limestone, alumina, uranium etc... Typical castings are crusher plates, earth moving machinery parts like tooth points, side cutters, adopters, conveyor parts, grinding equipment parts.

II. Core - Sector

Core sector items like steel, cement, thermal, hydro and nuclear power need many iron, steel, alloy steel castings and heat resistant castings. Typical castings are turbine and bowl mill items, klintyres, ingot molds, furnace parts, crushing and grinding equipment parts etc...

III. Chemicals

Requirement of many  corrosion resistant alloy steel castings valves, pump parts, heat resistant castings is in the industries like petro refineries, fertiliser plants, sugar and chemicals.

IV. Machine tools, transport, textiles

Industries like machine tools, transport, textiles require different types of cast irons in the manufacturing of machine tools, textile machinery, railway rolling stock etc...

V. Automobiles

There is a huge requirement of cast iron and non-ferrous castings in automobile industries. Some important castings are cylinder heads, crankcase castings, carburators, crank shafts etc...

ADVANTAGES OF THE CASTING PROCESS

Many organisations now getting some materials in the casting process before what they used to got in some other processes to save the cost and time factors ex :- Instead of forging they are getting material in casting process. By this both the cost and time factors can be saved. In the forging processes separate dies to be prepared and then go for production. But in the casting process we can prepare wooden patterns in 3-4 days time. If quantity is less (1 or 2 Nos of castings) there is an option of thermocol patterns which can be prepared more quickly within1-2 days. So the sample can be taken out within a week.

These days organisations asking suppliers to supply some of the critical castings in the casting process what they previously done through fabrication. In the fabrication so many parts to be combined each time, when this changed in to the casting process lot of time can be saved by eliminating welding, cutting, bending,
gas cutting.

Some of the important advantages of the casting process is -

(1)There is no restriction on the type of metal or alloy for casting operation. we can produce high alloy steels of  high melting temperature to low melting aluminium alloys.

(2) There is no restriction on the size of the component for casting. We can produce a few grams
(Watch cases) to many tons (Hydro electric plant parts weighting up to 200 tonnes)weight castings.
(3) The most critical internal and external shapes can be formed by casting process by suitable molding and core-making techniques. As a result many other operations such as machining, forging and welding can be minimised or eliminated ex - Impellers in Pumps, Cylinder heads , Crankcases in Automobiles. 

(4) We can combine (Cast) so many shapes together. As a result we can avoid assembly of several pieces which will be required by the other processes.

(5) By adopting suitable choice of alloy and heat treatment we can produce special properties like
heat resistance , corrosion resistance, hardenability,high strength , lightness in certain light metal alloys,damping capacity etc...

(6) The Casting process is economically suitable for both small quantity jobbing production as well as mass production.

(7) The Casting process is still the most economised technique for forming many components from
raw material to final usable stage. So it remains the fundamental manufacturing process inspite of many developments in other fields.

FLOW CHART FOR MAJOR FOUNDRY ACTIVITIES

 

FLOW CHART FOR MAJOR FOUNDRY ACTIVITIES

DEFINATION OF CASTING

Casting is a manufacturing process of pouring molten metal in to the shaped cavity of a mold to produce an object of desired shape.

An object of desired shape obtained by solidification of a substance in a mold.

Casting materials are usually metals or various cold setting material ex :- Concrete, Epoxy, Plaster etc...

Casting is most often used for making complex shapes that would be otherwise difficult or uneconomical to make by other methods ex :- Forging , Fabrication etc...

The Process of Casting involves the basic operations of selection of metal, pattern making, sand preparation , molding, solidification, gating, risering system design, melting of metal, pouring in molds, cooling, knockout, fettling , heat treatment, finishing, Inspection and despatch.