ADVANTAGES OF POWDER METALLURGY PROCESS

The following are the advantages of powder metallurgy ,

1. Although the first cost of metal powder is high , there is no loss of material. The components can be produced clean and bright, ready for use.

2. Perhaps the greatest advantage possessed by the process is the case in which the composition of the product can be controlled. Besides, the material does not run the risk of contamination with any unwanted substance.

3. Close dimensional tolerances can be maintained especially if a sizing operation is used.

4. Non metallic substances can be introduced as required and in any proportion to get the desired properties.

5. A wide range of properties such as density, porosity and particles size can be obtained for particular applications.

6. It is possible to unite materials that cannot be alloyed in the usual sense or would not yield the desired characteristics if they were joined mechanically.

7. The process is also the advantage in the production of magnetic cores having special desirable properties.

8. A considerable decrease in production time and consequently high production rate may be achieved by adaptation of the process, since this is automated.

9. Highly skilled labor is not required.

10. The process facilitates saving in material as there is no waste during fabrication.

11. Composition , structure and properties can be controlled more easily and closely than any other fabricating processes. The components can be produced clean and bright, ready for use.

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THROTTLE GOVERNING OF STEAM TURBINES

Steam Pressure at inlet to a steam turbine is reduced by throttling process to maintain the speed of the turbine constant at part load and hence this method of governing is called "Throttle Governing". Construction : Throttle governing system consists of a centrifugal governor, a lever , an oil pump , a pilot piston , control valve , a relay piston and a throttle valve. The throttle valve is moved by a relay piston. The relay piston is actuated by pilot piston control valve. There are two piston valves covering ports in the pilot piston control valve without any overlap. These piston valves are operated by lubricating oil supplied by a gear pump at 2 to 4 bar. The oil returns to the drain from this chamber. Working : When the turbine works on full rated load, the throttle valve will remain open. When the load is decreased, the energy output of the turbine becomes in excess and the turbine shaft speed increases. Hence, governor sleeve will lift. The upward movement of the

ELECTRICAL COMPARATORS AND ITS WORKING

Electrical Comparators are used as a means of detecting and amplifying small movements of a work contacting elements. An electrical comparator consists essentially of a pick-up head or transducer for converting a displacement into a corresponding change in current and a meter or recorder connected in the circuit to indicate the electrical change, calibrated to show in terms of displacement. Generally, an amplifier is needed to provide the requisite sensitivity and to match the characteristics of different parts of the circuit. Electrical comparators can be classified according to the electrical principle used in the pick-up head. Most of the comparators use either a differential transformer, an inductance bridge, a strain gauge or a capacitor as a means of detecting movement of the gauging element. There are different types of electrical comparators. One kind called an electrolimit gauge is used to check or measure the outside diameter of a roll. The object to be checked is place

Advantages And Disadvantages Of Air Refrigeration System :

Advantages Of Air Refrigeration : 1. The refrigerant used namely air is cheap and easily available. 2. There is no danger of fire or toxic effects due to leakages. 3. The weight to ton of refrigeration ratio is less as compared to other systems. Disadvantages Of Air Refrigeration : 1. The quantity of Refrigerant used per ton of refrigeration is high as compared to other systems. 2. The COP of the system is very low. Therefore running cost is high. 3. The danger of frosting at the expander valves is more as the air contains moisture content.

Mechinopedia For Mechanical Engineers

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