Introduction to Injection Moulding

Awanti Polymoulds, a Blow Mould Manufacturer in India, started its journey in the industry of precision machining and Mould Manufacturing more than three decades ago. In the initial years, along with PET Blow Moulds, Awanti manufactured Injection Moulds for various products in the beverage industry and automotive industry.

Injection moulding, as the title suggests is implemented using an injection technique. It is a manufacturing process to produce different parts or moulded products by injecting molten material into the moulds and then cooling and solidifying them. Injecting moulding involves six steps like clamping, injection, dwelling, cooling, mould opening, and removal of the product.

The clamping unit is used for the opening and closing of the die. It helps in the product’s ejection at the end of the process. The clamping unit is of 2 types: toggle type and straight-hydraulic type. The injection unit is used to melt the plastic by heat. This molten plastic is then injected into a mould. The machine controls the injection speed and dwell pressure after cavities are filled with molten plastic. Screw-type plunger is used to force molten plastic into the mould cavity. Dwelling pressure is the pressure applied to ensure that all the Mould cavities are filled, leaving no empty bubbles or spaces. The core side requires more cooling as large material is in contact with the core. This process removes heat from the mould making it safe to remove the moulded part. This helps keep the mould dimensionally stable. Molding condition means cylinder temperature, injection speed, mold temperature etc. set in a molding machine to obtain required moldings, and the number of combinations of conditions is innumerable. Depending on the conditions selected, the appearances, dimensions, and mechanical properties of the molded products change considerably. An injection mould is generally multi-cavity, meaning multiple moulded parts are produced in a single shot.

Injection Moulding and PET

Polyethylene terephthalate plastic resin (PET) has an enhanced melting point near 270 degrees Celsius. The effect of the pressure on the gluiness is larger than that of the temperature. Temperature supervision of the mould and temperature managing of the plastic are obligatory items with PET. PET is highly sensitive to water and hence preliminary drying of moulding pellets is compulsory. A crystalline reinforcing agent is used to improve the crystallinity of the material. PET is used to make transparent products that have glossiness and heat distortion temperature.

In the beverage industry, the largest application of injection moulding is manufacturing of preforms. A preform is an intermediate product that is subsequently blown into a polyethylene terephthalate (PET) container or bottle. Preforms vary in neck finish, weight, colour, and shape, and are specifically designed to meet the needs of customers in different market segments. Preform weight depends on the end container’s desired volume. Preforms can be single-layer or multilayer. Barrier preforms provide additional benefits and increased beverage shelf life, thanks to a special layer embedded in several layers of polyethylene terephthalate. The colour and neck finish depends on the product application. These preforms are then fitted on blow moulds to manufacture PET bottles.