Structural Foam Molding can be broken down into several processes and techniques. Imperial Plastics is one of the pioneers in the industry using both Low Pressure Multi Nozzle Structural Foam / Web and High Pressure Injection Foam. Structural Foam molding can be processed using commodity resins as well as engineered grade resins. The process requires an inert gas (nitrogen) or a pelletized chemical blowing agent. The process is to mix the inert gas / blowing agent with the specific resin of choice inside the barrel or extruder.
The resin is then injected into the mold. Injection pressures are much lower than straight injection molding, as the mold front fills the cavity of the mold the gas expands and packs out the cavity. As the mold front fills the cavity it creates a hard surface against the walls of the mold. The center section of the nominal wall is where the cell structure / foam occurs. Typical wall sections for Structural Foam range from .180” to .250”. Thicker wall sections are common but will control cycle times. Typical weight reductions will range from 8 to 15 percent.
There are tooling advantages to the Low Pressure Structural Foam process. With the injection pressures being significantly lower than the standard injection process, tooling can be constructed out of aluminum instead of steel. Choosing the right tool material is dependent on the types of resin selected and the accumulated volumes expected for the tool life. A steel tool may be required if the resin of choice is a glass filled material or an aggressive abrasive material.