What is structural foam molding?
Sometimes, you need to manufacture parts that are larger in size than those made with traditional materials. How to create these parts without sacrificing strength, rigidity and overall quality? Fortunately, there is a simple and affordable solution: structural foam.
Structural foam is a manufacturing material that pairs the foam core with a strong external "skin" instead of always being strong. Compared with traditional polymers (such as polyurethane, polyester or epoxy resin), it is lightweight and flexible, while maintaining good strength and rigidity. Structural foam can produce parts of unprecedented dimensions, leading to a revolution in the production of roofs, interior and exterior body panels, medical device shells and even snowboards.
What is structural foam?
Structural foam is a composite material, usually a thermosetting (but can be thermoplastic) polymer mixed with an inert physical gas (such as nitrogen) or a chemical blowing agent during the molding process. The result is not a solid material, but a low-density micropore "core" and a high-density external "skin". The core reduces the total weight of the material, while the strong skin keeps it strong and impact resistant.
The structure of the material is similar to a sandwich structure, with a low-density core completely surrounded by a high-density skin. The texture of the core is often described as similar to "sponge" or "honeycomb". Due to its unique core texture, structural foam is generally 20% to 40% lighter than solid polymers, aluminum, steel, sheet molding compounds, or other commonly used materials.
Due to its less robust nature, the base material used to produce structural foam is usually a thermoplastic polymer rather than a thermosetting material. Commonly used thermoplastics include, but are not limited to: polyurethane, polycarbonate, polyphenylene ether (Noryl), polybutylene terephthalate (Valox), and acrylonitrile butadiene styrene.
Structural foam molding process
The process of forming parts with structural foam is very similar to traditional reactive injection molding methods. Store the two ingredients, such as polyol and isocyanate (they are combined to produce polyurethane), in a separate container in liquid form. They are mixed together to form a resin, which is then injected into a pre-prepared mold and cured by chemical reaction.
However, there is an important difference in producing structural foam rather than solid polymers. In addition to polyols and isocyanates, inert gases or chemical blowing agents are added to the mixture during the injection process. This changes the nature of the chemical reaction that ultimately occurs.
Compared with standard solid polyurethane reactive injection molding, less polyol and isocyanate are used, so the resin will not completely fill the mold. Instead, the gas or blowing agent is activated by the reaction between the two components. It expands, filling the empty space of the mold with foam. This creates a "honeycomb" texture, and the inner core of structural foam is well known. When the surface elements are in contact with the mold wall, they collapse, forming a strong skin around the outside of the material.