Introduction to Foundry Technology PDF

# Introduction to Foundry Technology Foundry engineering deals with the process of making castings in molds formed in either sand or some other material. The art of the foundry is ancient; dating back to the dawn of civilization. Even in prehistoric times, as far back as 5000 BC, metallic objects i...

# Introduction to Foundry Technology Foundry engineering deals with the process of making castings in molds formed in either sand or some other material. The art of the foundry is ancient; dating back to the dawn of civilization. Even in prehistoric times, as far back as 5000 BC, metallic objects in the form of knives, coins, arrows, and household articles were in use, as observed from the excavations of Mohenjodaro and Harappa. One of man's first operations with metal was melting the ore and pouring it into suitable molds. The casting process is said to have been practiced in early historic times by the craftsmen of Greek and Roman civilizations. Since then, the role of metals has acquired unique significance. Copper and bronze were common in ancient times, but evidence indicates that iron also had been discovered and developed in the period around 2000 BC, though its use was greatly restricted. The earliest use of the metal was mostly for the purpose of knives, arrow points, coins, and tools. The molds were made in stone or sand. Around 500 BC started the era of religious upheavals, and metals began to be used for statues of gods and goddesses. Bronze was still the most popular metal. It was at this time that lost wax process made its impact. Subsequently, a still greater application of metals figured in armory, guns, and war material. Even in those days, the superior quality of metals and the absence of any impurities in them emphasize the ability and precise quality control of the refining process. The greatest breakthrough in the application of metals for gunnery and other arms possibly took place at the time when Alexander was contemplating victory over the entire Eurasian continent. Since then, the whole art of metal founding has emerged as an exact science. Today, we have a variety of molding processes and melting equipment and a host of metals and their alloys. And though the techniques and methods of production have changed considerably, the basic principles still remain almost the same. Castings have several characteristics that clearly define their role in modern equipment used for transportation, communication, power, agriculture, construction, and in industry. Cast metals are required in various shapes and sizes and in large quantities for making machines and tools, which in turn work to provide all the necessities and comforts of life. ## Principles of Foundry Technology Other metal-shaping processes, such as hot working, forging, machining, welding, and stamping, are of course, necessary to fulfill a tremendous range of needs. However, certain advantages inherent in castings - design and metallurgical advantages, and in the casting process itself, endow them with superiority over other methods. ### Design Advantages of Castings The need of designers for objects having certain structural and functional shapes that can withstand stress and strain, fulfill other service conditions, possess a desirable appearance, and have an acceptable cost is remarkably satisfied by castings. The metal can be shaped to almost any configuration and may be produced with only slight limitations in size, accuracy, and complexity. The main design advantages are: - **Size:** Castings may weigh as much as 200 tons or be as small as a wire of 0.5 mm diameter. In fact, casting is the only method available for producing massive objects in one single piece. - **Complexity:** The most simple or complex curved surfaces, inside or outside, and complicated shapes, which would otherwise be very difficult or impossible to machine, forge, or fabricate, can usually be cast. - **Weight Saving:** As the metal be placed exactly where it is required, large saving in weight is achieved. Such weight saving leads to increased efficiency in transportation and economy in transport charges. - **Production of Prototypes:** The casting process is ideally suited to the production of models or prototypes required for creating new designs. - **Wide Range of Properties and Versatility:** Castings offer the most complete range of mechanical and physical properties available in metals and as such fulfill a large majority of service requirements. In fact, some alloys can only be cast to shape and cannot be worked mechanically. Almost any requirement such as mechanical strength, wear resistance, hardness, strength-to-weight ratio, heat and corrosion resistance, electrical and thermal conductivity, and electrical resistance, can be satisfied by cast alloys. In many cases, the appearance of the component plays a part in enhancing its value. The blending together of various sections through the use of angles, curves, and streamlining can produce a pleasing appearance in castings. ### Advantages of Casting Process - **Low Cost:** Casting is usually found to be the cheapest method of metal shaping. - **Dimensional Accuracy:** Castings can be made to fairly close dimensional tolerances by choosing the proper type of moulding and casting process. Tolerances as close as ±0.1 mm can be achieved depending on the cast metal, the casting process, and the shape and size of the casting. The surface finish can also be controlled and may vary from 5 microns to 50 microns. - **Versatility in Production:** Metal casting is adaptable to all types of production. It is as suitable for jobbing work as for mass production. For example, a large number of parts required for the automotive industry, agricultural implements, home appliances, construction, and transportation are all produced by the casting process. ### Metallurgical Advantages - **Fibrous Structure:** Wrought metals have a fibrous structure, mainly due to a stringer-like arrangement of the inclusions of non-metallic impurities. In cast metals, the inclusions are more or less randomly distributed during the solidification process. When wrought metals are worked, the inclusions are strung out in the direction of working, and so the fibrous nature results in marked directional properties. Cast alloys do not usually exhibit any fibering or directionality of properties, except under unfavourable conditions of solidification. - **Grain Size:** Although mechanical working of wrought metals causes breaking up of coarse grains, and promotes fine grain size, many castings have grain sizes not very different from those of the former. Most non-ferrous alloys retain the grain size attained during freezing of the casting. Subsequent heat treatment of castings can also help in improving the grain size. - **Density:** The density of cast alloys is usually identical to that of wrought alloys of the same chemical composition and heat treatment, when both are fully sound. Today, it is becoming increasingly difficult to cope with the growing demand for various types of castings as required for automobiles, scooters, tractors, earth-moving machinery, and railways. Sophisticated castings needed for aeronautics, atomic energy, defence, and space research pose yet another challenge in terms of stringent requirements of quality. The problem is more or less similar in all developing countries. To achieve self-reliance, the foundry industry has to accept the challenge and quickly learn the new technology, methods, and know-how already available and in use elsewhere. It is also possible, through a sharper awareness and greater appreciation of the need for improved materials and more efficient methods, to increase production with the existing level of inputs in terms of equipment and manpower. Adequate means of quality control at all levels of production, steps to keep the wastage of materials and unproductive efforts at the minimum through proper organisation and coordination, and the use of enlightened human relations can go a long way in enhancing production and productivity in foundries. The casting process is basically one of introducing molten metal into a cavity in the mould, previously shaped as desired, and allowing it to solidify. The mould is usually prepared in sand; an object similar in shape and size to the casting required, which is called a "pattern", embedded in the sand. The pattern is thus an exact facsimile of the articles to be cast. The whole process of producing castings may be classified into five stages: - **Patternmaking:** In the patternmaking section the patterns are designed and prepared as per the drawing of the casting received from the planning section and according to the moulding process to be employed. The material of the pattern may be selected from a wide range of alternatives available, the selection depending on factors such as the number of castings required, the possibility of repeat orders, and the surface finish desired in the casting. Core boxes needed for making cores and all other auxiliary tooling items are also manufactured in the patternmaking section. - **Moulding and Coremaking:** After the patterns are prepared, they are sent to the moulding section. The molds are prepared in either sand or a similar material with the help of the patterns so that a cavity of the desired shape is produced. For obtaining hollow portions, cores are prepared separately in core boxes. The molds and cores are then baked to import strength and finally assembled for pouring. The moulding work may be carried out either by hand or with the help of machines, depending on the output required. Proper mould design and arrangement for flow of molten metal is very important for the production of sound castings. The last 25 years have witnessed far-reaching developments in the moulding materials and processes. - **Melting and Casting:** The metal of correct composition is melted in a suitable furnace. When molten, it is taken into ladles and poured into the moulds. The moulds are then allowed to cool down so that the metal solidifies. The castings are finally extracted by breaking the moulds and are sent to the cleaning section. - **Fettling:** The castings as obtained from the moulds are not fit for immediate use or for work in the machine shop as they carry unwanted metal attached in the form of gates, risers, etc. Sand particles also tend to adhere to the surface of the castings. The castings are therefore sent to the fettling section where the unnecessary projections are cut off, the adhering sand removed, and the entire surface made clean and uniform. The castings may also need heat treatment depending on the required specific properties. - **Testing and Inspection:** Finally, before the casting is despatched from the foundry, it is tested and inspected to ensure that it is flawless and conforms to the desired specifications. In case any defects or shortcomings are observed during inspection which may render the casting unfit, analysis is necessary to determine the causes of these defects, so as to prevent their recurrence. The production process then has to be corrected accordingly. All the five stages of casting are comprehensively covered in this book. Certain chapters deal with gating and risering of castings and the modernisation and mechanisation of foundries. Foundry mechanisation and modernisation are of considerable importance today when the foundry has evolved from an ancient art into a modern science. The various steps involved in producing a casting, as already mentioned, the economical considerations involved in such production, and measures that ensure quality and quantity are also discussed in this text. Computers have entered into all industrial applications, and more so in foundry technology. A separate chapter has therefore been added on computer-applications in foundry. ### Review Questions 1. What are the main design advantages of castings? Explain with examples. 2. Explain the metallurgical advantages of castings, in comparison to other products. 3. Describe the various stages of casting production in brief.