Carbon Arc Welding And Its Process

In this method, a rod of carbon is used as negative electrode and the work being welded as a positive. The arc produced between these two electrodes heats the metal to the melting temperature. This is about 3200*C on the negative electrode, and 3900*C on the positive electrode. The reason to use carbon rod as negative electrode is that less heat will be generated at the electrode tip than that the workpiece , and carbon from the electrode will not fuse and mix up with the job. If this so happens the resultant weld will be rich in carbon, and consequently very much brittle and unsound. In carbon - Arc welding, DC is always used. The use of ac is not recommended because no fixed polarity can be maintained.

The process is best applied to the joints which need only to be melted without the addition of filler metal (e.g., flange or edge joints) but fuller metal, if needed, may be added in the form of the welding rod as in oxy-acetylene welding. Some protection for the molten weld metal may be provided by using a long arc which produces a carbon-monoxide gas envelope. In addition, a flux may be used, and welding rods usually incorporate a deoxidizer such as a silicon or phosphorous. This process is used is used for welding sheet steel, copper alloys, brass, bronze, and aluminum.

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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.

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

Mechinopedia For Mechanical Engineers

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