A Comprehensive Guide: What Is Extrusion Molding & How Does It Work?
This form of production is simple but can be highly tailored to various products and needs. When you start your new plastic extrusion process, come to us for all your mold cleaning and maintenance needs! We even offer free samples to help you try out new products and see the difference Stoner Solutions can make!
What Is Extrusion Molding?
This molding process is simple: plastic material granules are melted into a soft or liquid state, then forced through a die - a shaped hole. This process is similar to injection molding but with a hole to shape the plastic rather than a cavity to fill. You might think this type is a limited format of molding, but many innovations allow manufacturers across dozens of industries to use the extrusion process to output unexpected and unique products.
Preparing
A base material, usually plastic granules, is mixed with any colors, stabilizers, or other additives. These can impart flame resistance, lubrication for easier molding, or other qualities. This one can be the lengthiest step, especially when extruding multiple materials or creating products with particular needs.
Melting
These materials are mixed and slowly melted in the extrusion equipment. The stress and pressures that push polymer through the machine also heat and melt it. The mixing process melts the product while keeping the resulting mixture homogenous, preventing weak spots and errors.
Shaping
The molten material is driven through screens, which filter out contaminants and ensure even melt temperature and pressure throughout the system. This further heats the plastic through friction, providing a smoother shape as the material is forced through the die into its final shape.
Cooling
Finally, the shaped and molded plastics are cooled to hold the shape. Some products or plastics are more prone to deforming post-extrusion molding, requiring more care with post-processing. This step is essential for quality control and preventing defects.
The extrusion molding process is relatively simple, and many kinds of plastic can be used to produce a wide variety of pieces. Extrusion molding plastic is one of the most common molding processes used by industrial and technical manufacturers.
What Are the Types of Extrusion Molding?
Molten plastic extrusion is a general form of plastic molding with various sub-categories. While extrusion molding can simply pull out ‘strings’ of plastic, there are many other ways to work with extrusion. These can provide high-volume manufacturing processes for in-demand plastic materials and material products.
Sheet Film Extrusion
Films and sheets are commonly used in packaging and shipping, but you might be surprised at the number of products that are simply flat extrusion molded plastic. Sheet extrusion pushes the material through a T- or coat-hanger-shaped die, then pulls it along several cooling rolls to solidify and cure the sheet.
BlowN Film Extrusion
Blow molding produces a similarly thin sheet of material but uses a cross-head, 'spider,' or spiral-shaped die to produce a circular shape. This creates a tube, which is then expanded by blowing air into the middle of it. This process is most commonly used to create plastic shopping bags.
Tubing Extrusion
PVC pipes are the most common tubing extrusion product, created using dies similar to blow film. Because tube and pipe materials are often denser than those used in blow molding, more pressure is used to keep the plastic in the desired shape out of the die.
Over Jacketing Extrusion
Jacketing tooling products include wires and cables, in which a plastic jacket or sleeve is extruded over an internal material. There are two ways of performing this jacketing—running the wire through the melted materials or introducing the materials right before extrusion. The first produces a more tightly adhered coating.
Coextrusion and Extrusion Coating
While not extrusion methods themselves, these two techniques deserve mention as they are usable with the other processes described above. Coextrusion describes the commonplace practice of using multiple materials in an extrusion machine. This standard method is used because a single material can't meet all needs.
Extrusion coating is a process that uses blown or film extrusion to coat a material—commonly paper, foil, or film. This method is helpful in providing water resistance or for adhering two materials together.
What Materials are Most Common in Extrusion Molding?
Extrusion molding plastics can be highly diverse, especially with different raw material preparation and processing. Thermoplastics are best suited for the process because of the need for molten plastic in the extrusion process.
Polyethylene
This material is the most common plastic on the market, with favorable strength, chemical resistance, and performance at lower temperatures. However, this material does deform more often and has poor heat stability. Because of these qualities, polyethylene is most common in packaging, such as films and containers.
Polypropylene
Polypropylene is also standard in the plastic extrusion process. This plastic is inexpensive and has higher flex strength. It also has good water and chemical resistance, though these also make it harder to form. This balanced material is familiar to tubing and interior trim and is a viable replacement for metal parts.
Nylon
Nylon, or polyamide, has a high strength-to-weight ratio alongside high temperature and chemical resistance. These properties make extruded nylon fairly attractive in tubing and containers for vehicles, engines, and other high-stress environments.
Acrylic
Extruded acrylic can be easily formed with heat and pressure, making it an attractive material for extrusion molding. This material resists UV light, is electrically resistant, and is naturally see-through. Extruded materials with these properties are beneficial for aquarium panes, chemical processing, medical tubing, and healthcare equipment, for which this clarity is required.
These are just a few of the many materials used in the plastics extrusion and molding industry to significant effect. Dozens of thermoset plastics can be used in plastic extrusion, and our experts are knowledgeable in the unique natures of these industry-staple materials.
Enjoy a Continuous Production Process with Stoner Molding!
When you are working with extrusion molding, from plastic sheets to drinking straws, we want to help you get the most out of your production. No matter what your extrusion molding type, the plastic used, or the extruding equipment used, we can provide the products that will keep your machines clean and functioning.
If you struggle with poor dimensional stability, wall thickness, or maintaining a high-volume manufacturing process, call the experts who can provide solutions! We have a team of experts in every type of plastic molding, from thermoset plastics to composites, rubber to polyurethane. Contact us, and we’ll take the time to learn about your production and help you get the most out of it!