Miscellaneous of processing of metal:

Miscellaneous of processing of metal:

Powder metallurgy:

It is the fabrication of technique that involves the compaction of powder metal that is collection of small grains of metals. This technique is followed by heat treatment to produce more dense material. There is diffusion process during the heat treatment this makes the piece of materials non-porous. This technique is used for low ductile materials. Metals having high melting temperature are difficult to melt and cost and fabrication is done by powder metallurgy.

Wielding

It is the fabrication technique in which two or more metal parts are joined to form a single piece. Both similar and dissimilar metals may be welded. The bond during welding is metallic bond. Verity of welding method exists:-

1. Ach welding
2. Gas welding
3. Brazing and soldering

During arc and gas welding, the work piece to be joined and the filter material (welding rods) are heated sufficiently high temperature to cause the both to made upon solidification the filter material forms a fusion join between these two piece.

In soldering, a substance that has low melting point is used to join two metal pieces. The substances which melts and join the materials. Generally the melting temperature of filling material is about \(450^\circ\)c. if the temperature of filling material is above \(425^\circ\) then it is called brazing.

Pressing process of ceramics

Powder pressing

Powder pressing in ceramics is used to fabricate both clay and non-clay composition including electronic and magnetic ceramic product. It is analogous to powder metallurgy.

A powder mass containing small amount of water is compressed in desired shaped by the application of pressure. The degree of compaction is maximum to minimize void apce by using fine particles in appropriate proportion. The three types of powder pressing procedure are ;

1. Uniaxial pressing
2. Isostatic pressing
3. Hot pressing

In uniaxial pressing the powder ceramic is compressed in metal die by pressure applied in single direction. The formed piece tales on the configuration of die and becomes the flat through the application of pressure.

In isostatic pressing powder ceramic material is enclose in rubber envelope and pressure is applied of same magnitude from all direction. Different complicated shapes are possible in this type of pressing.

In both uniaxial pressing and isostatic pressing operation, firing is required to decrease in the porosity and increase mechanical integrity. In case of heat pressing, the ceramic material in the powder form is prssed due to the application of heat treatment. The powder aggregate is compacted at high temperature. This procedure is used for material that do not formed a liquid phase expect at very high temperature. It is utilize when high densities without appreciable grain growth are required. In case of heat pressing the size of pore decreases with increase in temperature that is shown in figure

Tape casting

It is a type of ceramic fabrication in which thin sheets of flexible tape are produced by means of a casting process. These sheets are prepared from slip in many respects similar to the slip casting in clay. This type of slip casting in clay. These types of slip consist of suspension of ceramic material in organic liquid. In slip casting any tapped air or solvent vapor bubble can act as crack initiation side in the finished piece. To remove this crack drying process is required. In this process there is evaporation of volatile slip component. Normally the thickness of tape is 0.1 mm to 2 mm.

Cementation

It is also consider to be a ceramic fabrication process. The cemented material when mixed is water formed a paste. In this paste can be used in a desired shape which harder is result of chemical reaction .

Fabrication of the fiber and films:

1. The process by which bulk polymer material is transferred into fibers is known as spinning. Most often fibers are spun from molten state in a process called melt spinning.
2. The material is heated to form viscous liquid.
3. It is pumped through a plate called spinneret which consist of numerous holes usually in round shape.
4. As the molten material is passes through a each hole a single fiber is formed.
5. The fiber is solidified by cooling air blower or water bath.
6. The strength of fiber is increased by a process called drawing. Drwing is simply the permanent mechanical of fiber. In this process the molecular chain oriented in direction of drawing.
7. The two other techniques to produce fiber from solution of dissolve polymer are 1.dry spinning 2. Wet spinning

In dry spinning, polymer is dissolve in volatile solvent. Polymer solvent solution is poured through spinneret into a heated zone. The fiber solidified and solvent evaporate.

In wet spinning, polymer solvent solution that pass through spinneret directly into second solvent that causes the polymer fiber to precipitated from the solution. In this way fiber are fabricates.

Films:

1. Films are simply made from thin die sheet slit.
2. The material pass through slit is made thin by rolling or drawing operation.
3. In other method, film may be blown continuous tubing extruded through ‘annular die’. The material expands like air bubble(like balloon).
4. As the material is blown in a cylinder or spherical surfaces its thickness goes on decreasing and finally a thin film is formed from polymer.

References:

Callister, W.D and D.G Rethwisch. Material Science and Engineering. 2nd. New Delhi: Wiley India, 2014.

Lindsay, S.M. Introduction of Nanoscience . New York : Oxford University Press, 2010.

Patton, W.J. Materials in industry . New Delhi : Prentice hall of India, 1975.

Poole, C.P. and F.J. Owens. Introduction To Nanotechnology. New Delhi: Wiley India , 2006.

Raghavan, V. Material Science and Engineering. 4th . New Delhi: Pretence-Hall of India, 2003.

Tiley, R.J.D. Understanding solids: The science of Materials. Engalnd : John wiley & Sons , 2004.