DIFFUSION WELDING AND ITS PROCESS

Diffusion welding is a process that does not necessarily need heat to produce a fusion weld. Rather it needs two kinds of surfaces that can come into intimate contact under pressure. This pressure is applied for a period of hours. In this process, although heating is not essential , if the temperature is raised, the diffusion rate will be cut sufficiently. It might take many hours to perform a certain bonding, but with heat the time element can be cut to a matter of hours of minutes.

The goldsmith has for centuries made filled gold by placing a weight on top of a sandwich composed of silver or copper core with gold face sheets. When this is held in a furnace for a prolonged time, a permanent bond is obtained. That is what is done in diffusion bonding in principle.

This process makes it possible to join metal to metal , metal to ceramic, and metal to metal with intermediate bonding materials, Temperatures that approach is approximately 900*C. This extreme temperature limits diffusion bonding of steel. Diffusion bonding incorporates three basic techniques practically having same principle as explained. These are : gas - pressure bonding, vacuum fusion bonding, and eutectic fusion bonding.

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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.

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 objec...

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 movemen...

Mechinopedia For Mechanical Engineers

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