LOAM MOULD AND ITS MAKING

Loam is clay and sand mixed with water to form a thin plastic mixture from which molds are made. Loam sand also contains fire clay or ganisters. The loam must be sufficiently adhesive so that it can cling to the vertical surfaces. Loam molds always require special provision to secure adequate ventilation. The object is to open out pores in the otherwise compact, closely knit mass, by artificial means. Thus various kinds of organic matter such as chopper straw, and particularly horse manure, is mixed up with the sand . A typical loam sand mixture is ,

1. Silica - 22 %

2. Clay - 5 %

3. Coke - 10 %

4. Moisture - 18-20 %

This is applied as plaster to the rough structure of the mold usually made of brickwork and the exact shape is given by a rotating sweep around a central spindle.

Cast iron plates and bars are used to reinforce the brickwork which retains the molding material. Loam molds may also be prepared by use of a skeleton pattern made of wood. The surfaces of loams are blackened and are dried before the assembled.

Loam molds are employed chiefly in the making of large castings for which it would be too expensive to use full patterns and ordinary flask equipment. Objects such as large cylinders , round-bottomed kettles, chemical pans, large gears, and other machine parts are produced in loam molds.

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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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