VARIOUS TYPES OF THERMOPLASTICS USED IN DAY TO DAY LIFE

Thermoplastics are linear polymers, the molecules of which are synthesized in the shape of long threads. They undergo no chemical change in the molding operation and is often with the application of heat and harden upon cooling. They can be reshaped while in the softened state and they will reharden ; thus the scrap can be used again. They may become too soft to use at temperatures from 66 to 315*c. Since they become increasingly softer with increase temperature, certain numbers of the thermoplastic family are liable to permanent distortion under mechanical strain at relatively low temperature. The may flow to an appreciable extent under load at room temperature. They may flow to an appreciable extent under load at room temperature. Most of the plastics in use today are Thermoplastics.

1. Cellulosic

2. Nylons.

3. Polyethylene resins.

4. Polystyrene & Polypropylene.

5. Polycarbonate.

6. Acrylic resin.

7. Acetal ( Poly acetal ).

8. Vinyl plastics.

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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...

SIMPLE CARBURETOR - CONSTRUCTION AND WORKING

CONSTRUCTION OF SIMPLE CARBURETOR : The main Components of Simple Carburetor are : Float Chamber, float, nozzle, venturi, throttle valve, inlet valve, and metering jet . In the float chamber, a constant level of petrol is maintained by the float and a needle valve. The float chamber is ventilated to atmosphere. This is used to maintain atmospheric pressure inside the chamber. The float which is normally a metallic hollow cylinder rises and closes the inlet valve as the fuel level in the float chamber increases to certain level. The mixing chamber contains venturi, nozzle and throttle valve. The venturi tube is fitted with the inlet manifold. This tube has a narrow opening called venturi. A nozzle is provided just below the centre of this venturi. The nozzle keeps the same level of petrol as that of the level in the float chamber. The mixing chamber has two butterfly valves. One is to allow air into the mixing chamber known as choke valve. The other is to al...

Mechinopedia For Mechanical Engineers

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