Plastic Manufacturing Processes: Techniques and Applications

Compression Molding

Compression is applied with thermoset plastics. Plastic is placed in a steel mold and heated until it becomes pasty. A hydraulic press applies pressure to the plastic to take the shape of the mold. Once cooled, the part is extracted from the mold. This method is used to manufacture parts that must withstand high temperatures, such as pan handles, electrical insulators, doorknobs, and wristbands.

Extrusion

Extrusion consists of passing a fluid plastic mass through an orifice or nozzle, which determines the appearance of the final product. It uses a machine called an extruder, comprising:

• Hopper: Where the raw material enters.
• Worm: Presses the plastic against the mouthpiece.
• Heater: Melts the plastic.

This process is used to manufacture pipes and hoses.

Injection Molding

Raw material is introduced into a hopper, where a compact extruder melts the plastic. It is subsequently pressed into a metal mold, cooled to harden, and the finished product is removed. This allows for complex shapes with very precise measurements. Examples include plates, glasses, mobile phone housings, and other electronic devices.

Blow Molding

An extruder shapes the molten plastic into a tube. It is then fed into a mold, and air is blown inside until it conforms to the shape of the walls. This is used to manufacture all types of containers and hollow objects, such as water bottles and shampoo bottles.

Vacuum Forming

A mold is placed inside the machine, and a plastic sheet is secured over it with clamps. Electrical resistance softens the plastic sheet. The sheet contacts the mold, and air is extracted between them so the plastic fits the mold walls. This is used to manufacture thin-walled objects such as cups and plates.

Calendering

This process uses a machine called a calendar. Molten plastic is introduced into a hopper at the top and passed between rollers that shape it into a sheet or plate. It is used to make PVC plates and sheets for greenhouses.

Rotational Molding

Rotational molding involves slowly spinning a mold that contains molten plastic. Centrifugal force causes the plastic to coat the walls of the mold, taking the shape of the object. It is used to make large objects where injection molds would be too expensive, such as recycling containers, canoes, water tanks, or oil tanks.

Dip Molding

In dip molding, a porcelain or glass mold is dipped into a bath of molten plastic. The plastic sticks to the walls of the mold in a thin layer. The mold is removed from the bath and dried with heaters. Once the plastic has solidified, the mold is removed. This is used for making gloves, balloons, and swimming caps.