Chapter 4 PDF

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Chapter 4 Metal Casting 1 - i) Define a metal casting . ii) What are the essential steps for any casting process? i) It may be defined as a metal object produced by pouring molten metal into a mold containing a cavity which has the desired shape of the casting, and allowing the molten metal to solidify in the cavity. ii) Steps A - Melting a metal charge in a furnace. B - Pouring the melt into a previously prepared mold. C - Extraction of heat from the melt and solidifications. D - Removal and cleaning (fettling) and possibly, treatment of solidified part.

2-What are the main advantages of casting process? 1-Possibility of manufacturing parts of complex shape or intricate design 2-Some alloys and metals cannot be formed except be casting like cast iron. 3-Possibility of producing large parts which may weight several tons. 4-Possibility of mechanizing and automating casting operations in foundries.

3-classify the casting methods and what are the factors for choice the suitable casting method? 1-sand casting 2-Die casting 3-investment casting 4-continouous casting 5-centrifugal casting Factors: 1

1-The metal to be cast 2-The shape to be produced 3-The allowable costs 4-The quantity to be produced 4-Compare between the ordinary and special casting processes

Examples

Ordinary Processes Sand Casting

Special Processes (die-investment-continuous-centrifugal) Casting

Accuracy

Poor, inaccurate

Good accurate

Finish

Poor produce (semi product) Good produce (final products)

Economics Suitable for small quantities

Suitable for large quantities

5- Illustrate the sand casting process. Sand casting is the most widely used casting process. In this method, the metal is cured into a mold or cavity that is formed in special sand. The metal to be east is melted in a suitable furnace and brought to the mold in a ladle, from which it is poured into the mold. When the metal has solidified and cooled to a suitable temperature, the mold is broken up, and the casting removed. 6- What is the pattern and its allowances should be taken into consideration in sand casting process? List four materials used to make patterns. The pattern is a model (replica) of the required casting, but it will be overall larger than the casting to allow for the taper, shrinkage and machining allowances. The pattern will be used to form the cavity in the sand mold. Most patterns are made of wood, which is inexpensive and can be worked easilyPatterns are also made of aluminum, brass or plastic if more than 500 parts are to be cast from one pattern.

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7) What are the molding sand and its essential properties?

The molding sand is a mixture of sand. Clay, water and certain additives. The basic for molding sand is clean silica sand. The main additives added to the mixture are cereal flours, coal, dusts and oil. The water Content of the molding sand is important; it is usually 3 to 4% by weight. Properties\ (permeability, plasticity, flowability, cohesion, refractoriness) 8 - List the advantage of die casting process as a compared with sand casting? A. The dies can be immediately used again to produce another casting when the solidified casting has been removed B. The rate of casting production is greatly increased resulting in a lower –cost product C. This process produces good accuracy and finish 9- What is the difference between the gravity die casting and pressure die casting processes? Gravity die casting, in which the metal is poured into a metallic mold from up to down by gravity . Pressure die casting, in which a machine is used to inject the metal into the metallic mold.

10- For what materials die casting is suited? Mention some items that made by this technique. Both method of die casting are suitable for low and medium melting point metals and alloys say, aluminum alloys, zinc alloys, and brass.

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