Processes

Structural Foam Molding

Methods of Producing Structural Foam

The Low Pressure Process
To achieve consistent quality mouldings, it is recommended to use dedicated special purpose injection moulding machines. The machines introduce a gas into the melted plastic which when injected into the closed mould tool subsequently foams the plastic material of the component being produced.

Conventional Moulding Machines
Another widely used method is the use of standard injection moulding machines with added "blowing agents" incorporated into the material. Using dry chemical blowing agents mixed in with the granules of plastic, the plastic is melted in the barrel of the machine. A measured charge is injected into the mould tool. The heat of the melted plastic causes the blowing agent to react, which forms a gas, which in turn foams the plastic.

Typical Mouldings Produced
The use of the more controlled Low Pressure Process enables larger mouldings to be produced. Almost all thermoplastic materials can be foamed and wall sections at 5 -- 15 mm, are thicker than compact (normal) injection mouldings. Limited only by the size of moulding machines, mouldings of up to 40 kgs and in excess of one meter have been produced.

The nature of the process leaves a rough streaky surface finish on the surface of mouldings. If this is not acceptable, then a subsequent filling and painting operation is applied. Often this painted surface is of a textured type thus minimizing any irregularities in the moulded surface.

Mould Tools
With the low cavity fill pressures the mould tools can be made in lighter grade materials, Cast Aluminium and Cast Steel. As such the costs are cheaper than with normal injection moulding.

When Structural Foam mouldings are made using Conventional Moulding Machines, invariably the mouldings are for engineering applications. In both processes, the foaming action within the material demands that the material is fed into the mould tools quickly and as such large feed gates are utilized and high injection speeds are necessary.

Whilst the process has lower cavity fill pressures than conventional injection moulding, if the mouldings are being made in conventional machines, then the tools are often constructed in a more robust manner to take into account the possibility of the higher machine clamp pressures being used.

Materials
Many people are under the impression that all structural foam applications are manufactured with HDPE, and this is not the case. While HDPE is often the choice for many applications, including containers and dunnage, it is not the only one. HDPE is a popular commodity resin that offers good performance and chemical resistance in many applications, as well as the most competitive price point available ( an important consideration, when looking at parts that may weigh twenty or thirty pounds or more). However, other materials, including ABS and PPO, can be utilized in structural foam applications where higher levels of performance, including stiffness and dimensional repeatability, are required.

Manufacturing Capabilities

• Capacity: 100 to 1,000 ton
• Shot size: 1 - 250 lbs.

Advantages

• Very strong products, heavy products
• Uses less material than injection molding; parts are 20% lighter
• Large molded parts
• Wide choice of materials
• Low tooling costs
• Fast mold turn-around
• Higher stiffness-to-weight ratios
• Greater chemical resistance

Applications

• Material Handling products - Totes, Trays, Pallets, Bulk Containers
• Shipping Dunnage
•  Toys
• Burial Vaults
• Robotic Handling Trays
• Consumer Products
• Drain Cover
• Water Heater Stand