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Plastic moulding is the process of pouring liquid plastic into a specific container or mold so that it hardens into that customized shape.
i) Transparency
ii) Flexibility
iii) Elasticity
iv) Permeability
v) Water Resistance
vi) Electrical Resistance
vii) Solubility
viii) Chemical Resistance
ix) Thennal Stability
x) Flammability
i) Compression moulding
ii) Transfer Moulding
iii) Injection moulding
iv) Blow moulding
v) Extrusion moulding
vi) Calendaring
vii) Thermoforming
The blow moulding is used to create hollow particals like bottles, drums, barrels and container. The process, heated the plastic tube (Parison) sticks mould around the tube. The shape of parison stick is hollow. Air under pressure is through parison stick to expand the parison required shape of the mould. After cooling, the mould is open and the article is removed.
Hollow object like bottles, drums,, vessels.
It is commonly used for thermoplastics. The powder is first heated to drive moisture and after feed in to the hopper. When the rain is drawn back, some of the powder drops in to the chamber. Close mold and ram is moved forward applied pressure behind the powder. Compresses and pushes forward through the thin space left around the heated torpedo.
The material will come in contact with heated sources and solution. The material during heating in the chamber rises the temperature between 1750c to 2750c.
This heated material is poured into the mold and then the mold is cooled and opened. The article is hit out by knockout pins.
1) It is a faster process and best suitable for mass production .
2) Intricate shape can be produced.
3) Good dimensional accuracy can be obtained.
1) Machine cost is high.
2) Molded design is complicated and costlier.
Plastic jugs, knobs, electrical equipment components etc.
The blow moulding process begins with melting down the plastic and forming it into parison or in the case of injection and injection blow moulding perform.
o The parison is tube like piece of plastic with hole in one end through which compressed air can pass.
o The parison is then also clamped into a mould and air is blown into it. The air pressure also then pushes the plastic out to match the mould. As the plastic cools and hardens, the mold opens and the part is ejected.
Intricate shape is easily formed by the operation of pressure or vacuum on the plastic sheet draped over the mould. The operation consist of stretched the sheet over the mould cavity form a seal, heating it by suitable means and after drawing the air out the space between the sheet and the mould. Some typical vacuum forming examples are shown in Fig.
(a) only vacuum is used for drawing the heated sheet in the mould .
(b) the formed mould presses down the heated sheet, forming it partially, followed by pulling the vacuum through the mould to complete the forming .
(c) a cored plug is used to push the heated sheet into the mould, followed by applying air pressure through the plug to complete the process.
[1] The extrusion machine can make solid rods, pipe or tubing, U, J, Y or other sections.
[2] Extruders are generally designed so that the die may be changed to suit the shape required.
[3] Granular material is fed by hopper into a heating cylinder through screw into a heated die.
[4] As continuous pressure is required, the driving force is provided jy a screw.
[5] Continuous lengths of extruded sections are produced at a rate of 150 to 300 meters per hour, the hot material after extruded through the die cools and hardens on the take-off belts.
[6] Generally, the thermoplastic material is simply extruded.
[1] Material thickness can be controlled. [2] Production rate is high.
[1] It is difficult to create internal profiles like cavities, slots.
[2] Cannot be manufactured easily for large components.
Calendering is a process in which heat and pressure are applied to fabric by passing it through heated rollers, providing a flat, shiny, smooth surface.During the calendering process, the material is passed through several pairs of heated rollers to give a shiny surface. Lustre(i.e.finishing) increases when the degree of heat and pressure is increased.
Calendaring is applied to fabrics in which a smooth, flat surface is desirable, such as most cotton.many linens and silks and various n]man made fabrics.Calendering is used for polymer materials. Extruded PVC sheets are produced by this process.
