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ArrowArrow education > the molding process

Actually making parts is a multi-step process...

The word 'plastic' comes from a Greek word plastikos. This translates as 'capable of being molded' and describes a very important characteristic of all plastics. At some stage in their life, all plastics can be molded or shaped very easily.

1. Begining Production
Unlike other thermoplastic processes, the production of molded foam products requires that the raw materials be pre-expanded prior to the final molding process. The raw material ("expandable plastic" or "bead") has a spherical shape and is similar to sugar in appearance.

2. Pre-expansion
The tiny spherical beads are expanded to about 40 times their original size using a small quantity of pentane (typically 4% ~ 6%  by weight) as a blowing agent. This process involves the heating of beads, using a flow of steam, which causes the blowing agent to boil and thus a honeycomb of closed cells is formed.

3. Expanded Material Aging
As the material cools the pentane liquefies and a partial vacuum is formed inside the bead. The beads are returned to a holding bag for approximately twelve hours to allow the pressure differential to equalize, thus achieving a stabilized bead (material).



4. Molding
In this final stage the pre-expanded stabilized beads are reheated with steam in a mold. The final expansion takes place and the beads coalesce to produce a “shaped molding”. In this final form the molded foam  is made up of 98% air.


5. The Machines and Tools
The molded foam is produced in aluminum tools. These are generally of male and female form, with the shape between the two halves of the mold creating a void where the “shape molded” part is being produced. The mold tool is fitted into a press, which has the facility to introduce steam from behind each half of the tool. The steam is introduced through small slotted vents, which have been machined into the mold tool when it was manufactured. Once material has been fused by the steam, water and/or vacuum are used to “cool” the tooling and thus once again stabilize the material (molded foam part).


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