Injection Moulding Process | Types of Injection Moulding Process

INJECTION MOULDING

WORKING PRINCIPLE

Injection moulding process is generally used to achieve high speed moulding of thermo plastic. It works on the principle that the molten thermo plastic is injected into a mould and a high pressure is applied the desired shape is obtained. Plunger system is used for achieving high pressure.

OPERATION

The material that is to be used for moulding is loaded into hopper from where it is transferred to the heating section. It is transferred using a feeding device where the temperature is about 150°C – 370°C.The material is melted and it is forced by an injection ram or by a plunger through a nozzle in a closed mould. There are two types of injection moulding. They are,

RAM OR PLUNGER TYPE INJECTION MOULDING

01 - PLUNGER TYPE INJECTION MOULDING - TYPE OF INJECTION MOULDING

This type of injection moulding system has two units. They are the injection unit and clamping unit. In some cases these units may be split inorder to eject the finished component. First the selected thermosetting plastic is filled in a hopper. Then it goes to the heating section where the thermo setting plastic is melted and the pressure is increased. With the help of ram the heated material is injected under pressure. This makes the material to get filled in the mould cavity through the nozzle to get the required shape of the plastic. In this type of moulding system water is generally is used for cooling purpose.

SCREW TYPE INJECTION MOULDING

This type of moulding also has two units to split and eject the finished components. The two units are injection unit and clamping unit.

01 - SCREW TYPE INJECTION MOULDING - TYPE OF INJECTION MOULDING

The injection unit consists of hopper, screw and the heating section. Mould cavity is present in the clamping unit. In this type of moulding machine the pellets are first fed into the hopper. The resins are pushed along with the reciprocating screw which is in the heated condition. The screw is moved forward to push the plastic material into the mould. The screw itself moves backward and allows the accumulation of enough material to fill the mould. The rotation of the screw provides the plasticizing action by frictional and shearing effects. The axial motion of the screw provides the filling action. The jet moulding process is used for finding the problems occurring in the injection moulding process. The reaction moulding is the recent development in injection moulding. In reaction moulding, the low viscosity monomers are used in the mould. There is a chemical reaction taking place between the resins at low temperatures and a polymer is created.

In the jet moulding process the thermo setting plastic is preheated about 93°C in the cylinder surrounding nozzle. The reaction moulding is suitable for the production of polyurethane moulding.

It used in the manufacturing of parts of complex threads. Production of intricate shapes like thin walled parts is made easier using this process. Mainly used for the Production of electrical and communication components like telephone cables.

Thermo Plastics | Types of Thermo Plastics | Types of Cellulose Derivatives | Types of Synthetic Resins

Thermo plastics

These kinds of plastics have long separate and large molecules arranged side by side. The various types of thermoplastics are discussed below.

Cellulose derivatives

Cellulose nitrate is generally obtained by treating the cellulose with a mixture of nitric acid and sulphuric acid. It has high toughness, good resistance to moisture and it is highly inflammable. It is mostly used for making spectacle frames, toilet wares, pen bodies, etc.

  • Cellulose acetate

01 - thermoplastic - Cellulose acetate

It is obtained by treating the cellulose with acetic acid. It is inserted and compressed in the mould for better stability and for obtaining high mechanical strength. It has the tendency to absorb moisture and is less in weight. It is used for manufacturing photographic films, buttons, radio panels, sheets, tubes, toys, etc.

  • Ethyl cellulose

01 - thermoplastic - Ethyl cellulose

It is the most lightest of all cellulose derivatives. It has very good electrical properties, chemical resistance, surface hardness and strength. Generally used for making jigs, fixtures, nozzles and moulded articles.

  • Cellulose acetate – butyrate

01 - thermoplastic - Cellulose acetate - butyrate

It is obtained by treating cellulose with acetic acid and butoric acid. It has a good stability against light and heat and moisture absorption tendency. Cellulose acetate can also be used for injection moulding. It is used for making radio cabinets, pipes, steering wheels, handles and coating.

  • Cellophane

01 - thermoplastic - Cellophane

It is generally available in extruded form. It has an attractive appearance and good resistance to moisture, solvents and fire. Generally used for making curtains and packaging materials.

  • Cellulose propionate

01 - thermoplastic - cellulose propionate

It has low tendency for moisture absorption. Cellulose propionate can withstand temperatures upto 93°C and can be easily moulded. Used for making fountain pens, telephones and flashlight cases.

Synthetic resins

The following are the synthetic resin.

  • Polyethylenes

01 - thermoplastic - Polyethylenes

It has very high resistance to acids, alkalizes and the solvents can also be made flexible, tough and good insulators. It has low water absorption. It is used for making fabrics, trays, pipes and for corrosion resistant coatings and packaging works.

  • Polystyrenes

01 - thermoplastic - Polystyrenes

it is available in any form and any color.it has good dimensional stabilities and strain resistance. Polystyrenes are easily joined by cementing. It is used for making boxes, cases, radio parts, table ware and insulation parts.

  • Acrylic resins

01 - thermoplastic - Acrylic resins

It has a high transparency tendency. It is made in any color with high dielectric properties, good strength, and resistance to moisture and very good light transmitting power. This material can be casted, injection moulded, extruded and can be stretched into sheets. It is used for manufacturing tubes, plates, lamination, display cases, helmets and valves.

  • Vinyles

01 - thermoplastic - Vinyles pipes

It is generally called as PVC. They are flexible and rigid. It has good electrical and weather resistance. These are resistant to water and available in variety of colors.

  • Polytetra fluoroethylene

01 - thermoplastic - Polytetra fluoroethylene

It is named after Teflon. It has good chemical resistance and can withstand temperatures upto 288°C. it cannot be dissolved in any solvent. It has high electrical resistance, low friction and very low adhesion to other substances. It mostly available in the form of sheets, rods and tubes. It is used for making gaskets, electrical insulators, etc.

  • Nylon

01 - thermoplastic - Nylon wires

It is also known as polyamide. It has high strength, toughness and elasticity. It can be moulded and extruded into rods. The powder metallurgy methods can also be used for this type of plastics. It is a good insulator and has good wear resistance. Used for making Yarn for making clothes, insulation wires and combs.

  • Methyl methacrylate

01 - thermoplastic - Methyl methacrylate

Its trade name is Lucite and plexiglass. It is easily formed at temperatures around 120°C. it is known for its clear color and high light transmission ability. Used or manufacturing aircraft parts, bowls, contact lenses and various surgical instruments.