17MEX18 METAL CASTING TECHNOLOGY UNIT 1 FOUNDRY TECHNOLOGY AND SAND MOLDING PROCESSES Metal casting classification of foundries challenges in foundry industrial sectors sand molding processes function of molding sand classification ingredients core sands testing and control pattern equipment types of molding practical aspects mold coatings casting defects due to sand molding and pattern METAL CASTING What is Metal Casting Metal casting is defined as the process in which molten metal is poured into a mould that contains a hollow cavity of a desired geometrical shape and allowed to cool down to form a solidified part The term casting is also used to describe the part made by the casting process which dates back 6000 years Historically it is used to make complex and or large parts which would have been difficult or expensive to manufacture using other manufacturing processes Metal casting is one of the most ancient techniques used for manufacturing metal parts The process of casting involves the basic operations of Pattern making Sand preparation Molding Melting of metal Pouring in molds Cooling Shake out fettling Heat treatment Finishing and Inspection The flow chart is given below Advantages of metal casting 1 There is no restriction on the type of metal or alloy for casting operation In other processes like forging only a few ductile materials can be formed whereas a brittle metal like cast iron cannot be manufactured Eg 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 Items from a few grams to many tons weight are produced by casting process There are severe problems in manufacturing larger parts by processes like powder metallurgy forging etc Eg Watch cases of few grams to rolling mill housings kiln tyres of 50 tons each The most intricate external and internal shapes can be formed by casting process by suitable molding and core making techniques No such possibility exists in the other forming methods as rolling Eg Automobile cylinder blocks carburettors valve bodies 3 A wide range of properties can be obtained in cast parts by suitable choice o alloy and heat treatment Special properties like corrosion resistance resistance damping capacity high strength etc are possible 4 The casting process is economically suitable for both small quantity job production as well as mass production by automatic machines In the order process like rolling or forging it is difficult to have flexibility in production without increasing cost 5 The casting process is still the cheapest available technique for forming many components from raw materials to the final usable stage So fundamental manufacturing process inspite of many developments in the order fields it remains the Disadvantages of metal casting 1 Metal casting involves melting of metal which is a high energy consuming process Due to the growing cost of energy many restrictions are being imposed on the energy intensive metal casting units in several countries For example about 2000 KWH of power is required to produce a ton of finished steel castings 2 Metal casting is still highly labour intensive compared to other processes 3 The quantum of raw materials required for producing a ton of castings is quite high needing exhaustive buildings handling systems large space and inventory costs For example for producing each ton of steel castings about 2 2 tons of metallics 0 3 ton refractories 1 2 ton of facing sand 4 tons of backing and are needed apart from many other minor materials 4 The time required for the process of making castings starting from receipt of drawing is quite long compared to other processes like machining On an average a medium size ferrous casting takes 2 to 4 months for the first casting Thus the entire cycle of order execution for castings can take between 3 months to one and a half years depending on size intricacy composition quantity to be cast etc 5 The working condition in foundries due to heat dust fumes heaps of scrap castings and slag etc at different stages are quite bad compared to other process industries The environmental pollution is high in metal casting industries Classification of foundries Metal casting units are classified generally according to the type of metal alloy cast in the unit 1 Ferrous Foundries casting carbon steels alloy steels gray cast iron S G iron malleable iron etc 2 Nonferrous Foundries include aluminum copper alloys etc 3 Jobbing foundries execute casting orders for even small quantities like one to two pieces per item specializing in hand molding and heavy items 4 Mechanised foundries have machines to make large batches of items specially in sand mixing molding etc where batches form 50 to a flew hundreds can be cast per item 5 Mass production foundries have automation to a high degree with production runs of a few thousand pieces per item They have automatic molding pouring and even finishing lines with very little manual handling This type of foundries produce castings for automobiles valves etc needed in very large quantities for cach pattern 6 Captive foundries Captive foundries are those which cater for the needs of the main industry to which the foundry belongs For example all integrated Steel Plants have captive foundries Foundries using metal molds for making castings with gravity or pressure injection of metal are known as Die casting units Special foundries having techniques for high precision small castings fall under investment or precision casting foundries Challenges for Indian foundry industry 1 Lack of quality raw material like metallurgical coke pig iron refractories etc Due to the high ash content of over 25 cast iron foundries in India have the perennial problem of non availability of good metallurgical coke Poor metal temperature bridging of cupola low melting rate etc are Common Many units had to switch over to electric induction melting even though costlier only due to this Shortage of proper grade pig iron is another great problem faced by Indian cast iron foundries specially those in Western and Southern India Similarly steel foundries suffer due causing to poor quality refractories for arc furnaces frequent lining repairs damages to sides and root and consequent production losses 2 The shortage of electric power The shortage of electric power in many regions in India specially during in summer Season causes power cuts foundries which are the main high tension