Skip to main content

PLASTER MOLDING PROCESS AND ITS ADAVANTAGES

 In this method, the mold is prepared in gypsum or plaster of Paris. In practice, The plaster of Paris is mixed with talc, asbestos, fibers, silica flour, and a controlled amount of water to form a slurry. This plaster slurry is poured over the metallic pattern confined in a flask. The mold is vibrated and the slurry allowed to set. The pattern is removed after about  30 minutes when the setting is complete and the mold is dried. and backed by slowly heating it to about 200*C in a conveyor oven. Inserts and cores are placed, cope and drag matched by guide pins. Molten metal is then poured into the mold. Finally, the casting is cooled in the mold, shaken out and the mold is destroyed. Castings are then trimmed of gates, sprues and flash.


Plaster molding process


Advantages of Plaster Molding are :

1. Warping and Distortion of thin sections can be avoided since plaster has no chilling              tendency due to  low rate of heat conductivity.

2. A high degree of dimensional accuracy and surface finish is obtained, and machining           cost, is therefore , eliminated. 

3. Highly suitable for reproduction of fine form and detail as are necessary for ornamental        castings , statues, jewelry, etc.  besides being used for engineering components.

Limitations of  Process are :

1. Low Permeability of Plaster of Paris.

2. Suitable only for non-ferrous castings owing to the fact  that plaster of Paris destroys at 1200*C

Labels:

Comments

Post a Comment

Popular posts from this blog

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. 
Post a Comment
Read more

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...
Post a Comment
Read more

MELTING FURNACES FOR FERROUS METALS : CUPOLA AND ITS WORKING

Various types of melting furnaces are used in different foundry shops, depending upon the quantity of metal to be melted at a time, and the nature of work that is carried out in the shop.  The primary objective in cupola is to produce iron of desired composition, temperature and properties at the required rate in the most economical manner. Besides, this furnace has many distinct advantages over the other types, e.g., simplicity of operation, continuity of production, and increased output coupled with a high degree of efficiency.  Description Of a Cupola : The Cupola Furnace consists of a vertical, cylindrical steel sheet, 6 to 12 mm thick, and lined inside with acid refractory bricks or acid tamping clay. The refractory bricks or the tamping clay used consist of  silicon oxide acid (SiO2) and alumina (Al2O3). The lining is generally thicker in the lower where the temperatures encountered are higher than in the upper region. The shell is mounted either on a brick work fo...
Post a Comment
Read more