Process of Plastic casting

Casting, that is, pouring a liquid into a mold without pressure, can be done with several plastics. When there is not sufficient justification for making expensive dies, the casting process is generally used.

Open molds into which the liquid resin , mixed with a catalyst or hardener , is poured can be used for most plastics.

Centrifugal casting, using the same methods can be used with several plastics to such as polyesters.

Shell molding is some what similar to casting in that no pressure is used. In this process, powdered resin is placed in a heated mold until a layer fuses to the desired thickness. The unfused resin inside is taken out of the mold and the hollow molding removed. Sometimes the mold is rotated in what is called rotational molding.

Slush molding is similar to shell molding. It employs a thermoplastic-resin slurry or "slush" which is poured into a preheated mold. The heat causes slurry to set in a viscous layer of the desired wall thickness.

Both shell and slush molding produce thin-walled products such as toys and gloves.

Hand Lay-up is a simple method to form plastic materials into a required shape. Special shapes like boats , tanks and big-sized parts of plastics are produces by this method. First a mold of desirable shape is prepared. The mold is covered by fiber mats of desired thickness and plastic resin (such as epoxy) is draped over the mold and allowed to harden.

Comments

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...

TOP POLLUTION RECORDED IN WORLD

CHERNOBYL NUCLEAR DISASTER (NUCLEAR POLLUTION) : In April 26,1986, the melt down of the Chernobyl nuclear reactor , in Russia, has leaked out the radioactive rays and radioactive materials. Effects : 1. In this Pollution nearly 2000 persons have been killed by the accident. 2. People suffered due to the illness such as, degeneration of the cells, severe bleeding, anemia, skin cancer. 3. Animals, Plants are also affected by nuclear radiation. MINAMATA EPIDEMIC (1953) : MARINE POLLUTION ( CASE STUDY ) Minamata is a small coastal village in Japan. The Chisso Chemical Company , which produces vinyl polymer plastics used organomercurial compound. The industry released its effluent into Minamata sea. The effluent containing mercury ions is converted into methyl mercury, which is highly toxic. The marine organisms like phytoplankton and zoo-planktons easily absorb the toxic methyl mercury compound. These organisms are consumed by small fishes and these are in ...

Mechinopedia For Mechanical Engineers

Search This Blog