Plastic parts made using the Structural Foam process have a cellular or a structural core, surrounded with a thick outer layer (skin) that combine to give the products a greater strength to weight ratio and up to as much as twice the rigidity of the solid plastic products that are of the same material and weight.
The structural foam molding process uses nitrogen gas as a foaming agent, which is introduced in the barrel of the extruder. This yields parts that are much larger and sturdier than injection molded parts. Parts produced through the structural foam molding process are structurally sound, nearly stress-free and have minimal warpage.
Low pressure injection molding (LPIM) machinery is recommended for injection molding large structural plastic products such as material handling bulk bins, pallets, tool boxes, building products, pool panels and ladders, fencing, retail display racks, tote bins, storage sheds, shelving, cargo systems, in ground enclosures, recreational slides and toys, outdoor furniture, water storage tanks and drainage systems, burial vaults, garden lattice, dog houses, dock systems, janitorial and restaurant products, and industrial carts to name a few.
Key benefits of the structural foam process:
- Part weight reduced
- Increased strength and stiffness due to sandwich structure
- Capable of molding large, complex parts without sink marks
- Capable of molding parts as thick as ½” (12.7mm).
Lower Material Costs – In the structural foam process, the part weight can be reduced by up to 30% in some cases. Although, density reductions of 15-20% are more typical, thus, lowering the material costs without compromising the structural integrity of the part. High recycled content parts can easily be made in Structural Foam Injection Molding with recycled contents up to 100%.
Large Part Capability – Shot sizes up to 400 lbs. and large platen sizes up to 100” x 210” allow for very large parts or families of parts to be molded together in one cycle.
Multi-Nozzle Machine – Low pressure Structural Foam machines have multi-nozzle capability using a configurable and modular hot runner system that is part of the machine. That means multiple molds can be processed at the same time and on the same machine, as compared to Injection Molding where typically only one mold is used. This allows for higher efficiencies and flexibility in production.
Lower Tooling Costs – As compared to conventional injection molding, tooling for Structural Foam is about one third to one half of the cost of injection mold tooling for the same part geometry. The lower cost is due to the fact that no dedicated hot runner system is needed on the mold because of the use of a configurable & modular hot runner on the machine. Secondly, most Structural Foam tooling is aluminum, and because of the lower cavity pressures seen in structural foam molding, the molds can be thinner and do not require as much support as a typical injection mold. Lighter molds also have the benefit of smaller infrastructure to hang the molds in the machine (smaller crane requirements) and move them around the plant.
One of the largest advantages of Low Pressure Structural Foam Injection Molding is that part weight is reduced anywhere from 10% to 30% giving a lower cost part without any resulting effect on the structural integrity of the part. The higher strength to weight ratio than a solid injection molded part, low molded in stresses, elimination of sink marks, and reduction of warpage are the key benefits to the technology. The high material throughput capabilities of the machine result in a better utilization ratio than injection molding with multiple machines or changing molds, thus producing large parts or families of large parts very cost-effectively.