Extrusion Molding of Plastic Resins

While the term “extrusion molding” might be unfamiliar to most people, those same people likely know and use many extruded products. Extrusion molding of plastic resins is a manufacturing process that yields various goods, including hoses, pipes, plastic tubing, sheeting, and much more.

To demystify extrusion molding, think of the process as forcing molten plastic material through a die that shapes the plastic.

To extrude means to “thrust or force out.” (Dictionary.com) Melted plastic material gets forced through a die and comes out the other side in a continuous, linear shape. A hose, for instance, might be extruded to any length. The manufacturer can cut the hose to desired lengths.

The Process of Extrusion Molding

The extrusion molding process begins by feeding plastic resin pellets into a hopper that feeds the material into a heated barrel. As the resin melts, it gets mixed inside the barrel to form a homogeneous molten plastic material. Next, the molten plastic is forced through a shaped opening (the die), which determines the final shape of the extruded product. Finally, after the plastic material exits the dice, it is cooled by water or air and cut to the desired length.

Several plastic resin options exist for extrusion molding. Most commonly, manufacturers choose polyethylene, polypropylene, polystyrene, or PVC. The choice of plastic depends on the application’s specific requirements, such as strength, flexibility, and chemical resistance.

Extrusion Molding vs. Injection Molding

Injection and extrusion molding are two standard methods for manufacturing plastic products. While both processes involve melting plastic resins and shaping them into a specific form, they have significant differences regarding how they operate and the types of products they can produce.

First, injection molding provides a process whereby molten plastic fills a mold cavity under high pressure. The molten plastic, forced into the mold cavity through a nozzle, cools and solidifies to take the desired shape of the product. Injection molding is a highly efficient process capable of producing high volumes of plastic products with consistent quality and precision. Injection molding serves many needs, often used for manufacturing small to medium-sized objects, such as toys, automotive parts, and medical devices.

The versatility of the Extrusion Molding of Plastic Resins

Extrusion molding serves many needs as well. But extrusion molding creates long, continuous forms. The molten plastic gets pushed through the die by a screw or ram, and the material cools and solidifies as it exits the die. Extrusion molding furnishes a highly versatile process that produces products in different shapes and sizes, including plastic pipes, tubes, sheets, and films.

In summary, the main differences between injection molding and extrusion molding are:

• Injection molding produces discrete, three-dimensional objects, while extrusion molding produces continuous, two-dimensional shapes.
• Injection molding produces high-precision, small to medium-sized objects, while extrusion molding makes larger, continuous shapes.
• Injection molding is a higher-pressure process that involves injecting molten plastic into a mold cavity. In comparison, extrusion molding is a lower-pressure process that forces molten plastic through a die.