Hydraulic Plastic Injection Moulding Machine

Plastic injection molding machines help to manufacture plastic products in the required shape and dimension. Most of the plastic products in automotive body parts, phone cases, toys, etc… are manufactured in bulk quantities using the injection molding process. The common thermoplastics and thermosetting polymers used as raw materials in injection molding are ABS, Polypropylene, PVC, Nylon, Polyetherimide (PEI), Polyoxymethylene (POM), and more. The commonly used ABS material offers excellent impact resistance, processability, and toughness. The dimensionally stable Polyoxymethylene(POM) thermoplastic used in mechanical automotive, gears, business machines, household appliances, bushings, etc., offers high stiffness and low friction. Polycarbonate is suitable for applications that require excellent thermal stability and strength. Thermoplastic Polyetherimide(PEI) are found in applications like aircraft interiors, cooking utensils, electronic parts, etc., that deals with high temperature. Likely, PVC and Nylon are polymers with features like insulation property, abrasion resistance, and mechanical properties.

           The injection moulding machines can be classified into hydraulic, electric, and hybrid based on the type of drive system. Till the 1980s, injection molding machines utilized hydraulics for their operation and it offers exceptional clamping force and resistance to wear and tear. The next invention was the electric plastic injection moulding machine in 1984 and it was powered by digitally controlled high-speed servo motors. The hybrid injection molding machines use a combination of both these technologies together.

          The injection molding machine consists of an injection unit and a clamping unit. The injection unit includes components like a screw motor drive, heaters, thermocouple, ring plunger, reciprocating screw, and barrel; and it melts the polymer resins and injects it into the mold. The clamping unit components are mould, clamping motor drive, and tie bars. The clamping unit places two parts of the mould together tightly for the melted polymer resigns to be injected.

          If considering the process of injection molding, the thermoplastic or thermoset molding polymer in powder or mold granular form is selected according to the product specification and is fed into the heated barrel by a hopper. The frictional action of a reciprocating screw in heater bands will melt these raw materials and with a nozzle, the melted plastic is injected into the mold cavity that is made with steel, aluminum, or other metals. The melted raw materials inside the mold cavity will cool and solidify to obtain the shape of the mold cavity.

Hydraulic Plastic Injection Moulding Machine Operation

Similar to every hydraulic system used, it is the pressure of the hydraulic fluid that makes injection molding machine operation smooth and safe. The hydraulic pump is powered, and the fluid inside the reservoir gets pressurized and is pumped toward other hydraulic components in the circuit. The relief valve will regulate the fluid pressure according to the system requirements.

          In hydraulic plastic injection machines, hydraulics plays a key role in both the clamping unit and injection unit. The linear/rotary movement of the screw in the injection unit will melt the polymer resins stored in a hopper and injects melted particle through a nozzle into the mold cavity. This back-and-forth operation of this screw inside the heaters is controlled by a hydraulic cylinder. In the clamping unit, a hydraulics cylinder is used for the opening/closing and clamping of mold tools. Also, the hydraulically-operated ejector will push the finished plastic product out of the mold.