Typical wall section design diagram.
Close up cross section of structural foam molding process.
Structural Foam molding is a way to injection mold large parts. Thermoplastic materials such as HDPE, Polypropylene, ABS and Styrene are used along with a blowing agent which produces a molded article with a cellular core and solid skins. The following is how the process works:
Illustration 1. Prior to resin injection the mold is clamped with 1/4 ton per square inch minimum clamping pressure. The pre-blended material is held in the machine in an accumulator prior to injection. The machine injects a precisely measured short shot of material.
Illustration 2. Structural Foam’s thicker wall section along with the blowing agent boost allows rapid and low pressure filling.
Illustration 3. After resin injection the cavity pressure is isolated and the blowing agent pressure continues to fill the mold cavity.
Illustration 4. The blowing agent pressure continues to pack the mold even after the mold cavity is completely filled. This blowing agent pressure compensates for volumetric shrinkage as the plastic cools. The blowing agent becomes an internal “cushion”.
Information above provided by Steve Ham Plastics, 537 Hickory Street Highlands, NC 28741 USA
The low pressure molding of thermoplastics allows for:
- Larger part size – Shot sizes up to 200 lbs.
- Durability, strength, and manufacturing efficiency
- Dimensional accuracy over the entire production run
- Weight reduction up to 15% (by volume) compared to standard injection molding
- Superior impact resistance
- Parts that are impervious to the elements
- Color consistency and complete range of colors
- Two different materials can be molded simultaneously
- Ability to mold two colors simultaneously
- Consistent surface finish
- Parts are recyclable and returnable for supply chain cost effectiveness
- Aluminum molds are less costly than steel