Q. What is Injection moulding?
An important industrial method of producing articles of thermoplastics is injection moulding. The moulding material is loaded into a hopper from which it is transferred to a heating section by a feeding device, where the temperature is raised to
150 c to 370 c. and pressure is built up. The material melts and is forced by an injection ram at high pressure through a nozzle and sprue into a closed mould which forms the parts. The mould is in at least two sections, so that it may be spilt in order to eject the finished component. For the process to be competitive the mould must be fairly cool and consequently the mold must be cooled by circulating water. Injection moulding machines have a high production capacity: some can produce from 12 to 16 thousand parts per shift. This method is suitable for making parts within complex threads and intricate shapes, thin-walled parts etc.
The limitation of the process is:- Equipment of cylinder and die should be non- corrosive. Also, reliable temperature controls are essential. Injection moulding machines range in size from an injection capacity of 12,000 mm3 to 2,200,000 mm3. The locking forces are applied to be the mould usually by hydraulic means, and may vary from 0.1 MN to 8.0 MN or even more. The injection pressure may range from 100 MPa to 150 MPa.