6. processing of ceramics
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6. processing of ceramics

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Basic concept on Processing of ceramics

Basic concept on Processing of ceramics

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6. processing of ceramics 6. processing of ceramics Presentation Transcript

  • ME 312 Manufacturing Technology Vikrant Sharma, Mechanical Engineering Department. FET. MITS
  • Introduction: The metallic and nonmetallic materials are not suitable for certain engineering applications- for example  an electrical insulator to be used at high temperature  floor tiles to resist spills, scuffing and abrasion  a transparent baking dish For such applications we need materials that have properties such as high temperature strength; hardness; inertness to chemicals, food; resistance to wear and corrosion. Few of such materials are ceramics, glass, graphite, diamond etc. Vikrant Sharma , FET. MITS ME 312 Manufacturing Technology
  • For purposes of organization, we classify ceramic materials into three basic types: (1) traditional ceramics—silicates used for clay products such as pottery and bricks, common abrasives, and cement (2) new ceramics—more recently developed ceramics based on nonsilicates such as oxides and carbides, and generally possessing mechanical or physical properties that are superior or unique compared to traditional ceramics; and (3) glasses—based primarily on silica and distinguished from the other ceramics by their noncrystalline structure. Vikrant Sharma , FET. MITS ME 312 Manufacturing Technology
  • Ceramics : Ceramics are compound of metallic and non metallic elements. The word ceramic traces from the Greek keramos meaning potter’s clay and keramikos meaning clay products. Among the oldest of the raw materials used for making ceramics is clay. The most commonly given example is kaolin (from Kao-ling, a hill in China)  Other major raw materials for ceramics that are found in nature are flint (a rock composed of very fine-grained silica, SiO2 and feldspar ( a group of crystalline minerals consisting of aluminum silicates plus potassium, calcium or sodium) Vikrant Sharma , FET. MITS ME 312 Manufacturing Technology
  • Shaping Ceramics: (Adapted from Fundamentals of Modern Manufacturing M. P. Groover) Vikrant Sharma , FET. MITS ME 312 Manufacturing Technology
  • Preparation of Powders: (Adapted from Fundamentals of Modern Manufacturing M. P. Groover) Vikrant Sharma , FET. MITS ME 312 Manufacturing Technology
  • (Adapted from Fundamentals of Modern Manufacturing M. P. Groover) Vikrant Sharma , FET. MITS ME 312 Manufacturing Technology
  • Shaping Processes: The shaping processes can be divided according to the consistency of the mixture: (1) slip casting, in which the mixture is a slurry with 25% to 40% water; (2) plastic-forming methods that shape the clay in a plastic condition at 15% to 25% water; (3) semi-dry pressing, in which the clay is moist (10% to 15% water) but has low plasticity; and (4) dry pressing, in which the clay is basically dry, containing less than 5% water. Dry clay has no plasticity. Vikrant Sharma , FET. MITS ME 312 Manufacturing Technology
  • Slip Casting: A suspension of ceramic powders in water, called a slip, is poured into a porous plaster of paris mold so that water from the mix is absorbed into the plaster to form a firm layer of clay at the mold surface. The slip composition is 25% to 40% water. Two principal variations: – Drain casting - the mold is inverted to drain excess slip after a semi- solid layer has been formed, thus producing a hollow product. – Solid casting - to produce solid products, adequate time is allowed for entire body to become firm.  Used for large parts, complex shapes; low equipment cost.  Low production rate, limited dimensional accuracy. Vikrant Sharma , FET. MITS ME 312 Manufacturing Technology
  • (Adapted from Fundamentals of Modern Manufacturing M. P. Groover) Vikrant Sharma , FET. MITS ME 312 Manufacturing Technology
  • Vikrant Sharma , FET. MITS ME 312 Manufacturing Technology
  • Plastic Forming:  Plastic forming, also called soft, wet forming, can be carried out by various methods, such as extrusion, injection molding, or molding and jiggering. (Adapted from Manufacturing Engineering and Technology, S. Kalpakjian) Vikrant Sharma , FET. MITS ME 312 Manufacturing Technology
  • Semi dry pressing: (Adapted from Fundamentals of Modern Manufacturing M. P. Groover) Vikrant Sharma , FET. MITS ME 312 Manufacturing Technology
  • Dry Pressing: Process sequence is similar to semi-dry pressing - the main distinction is that the water content of the starting mix is typically below 5%. Dies must be made of hardened tool steel or cemented carbide to reduce wear since dry clay is very abrasive. No drying shrinkage occurs, so drying time is eliminated and good dimensional accuracy is achieved in the final product. Typical products: bathroom tile, electrical insulators, refractory brick, and other simple geometries. Vikrant Sharma , FET. MITS ME 312 Manufacturing Technology
  • Drying and Firing:  The next step in ceramics processing is to dry and fire the part to give it the proper strength and hardness.  Water plays an important role in most of the traditional ceramics shaping processes. Thereafter, it serves no purpose and must be removed from the body of the clay piece before firing.  Shrinkage is a problem during this step in the processing sequence because water contributes volume to the piece, and when it is removed, the volume is reduced. As water is removed from the wet clay, the volume of the piece shrinks. Vikrant Sharma , FET. MITS ME 312 Manufacturing Technology
  • The drying process occurs in two stages: • Stage 1 - drying rate is rapid and constant as water evaporates from the surface into the surrounding air and water from the interior migrates by capillary action to the surface to replace it. • Stage 2 - the moisture content has been reduced to where the ceramic grains are in contact. Vikrant Sharma , FET. MITS ME 312 Manufacturing Technology
  •  Firing also called sintering, involves heating the part to an elevated temperature in a controlled environment.  A process similar to the sintering employed in powder metallurgy.  Firing gives the ceramics part its strength and hardness.  This improvement in properties results from, a) development of strong bond between the complex oxide particles in the ceramics, and b) reduced porosity. Vikrant Sharma , FET. MITS ME 312 Manufacturing Technology