Expanded Polystyrene foam, also known as EPS is a highly durable material that is used in a wide variety of consumer products. It can be found nearly everywhere, in you local food store (plates, cups, food containers etc) and the local electronics stores (insulation for refrigerators, coolers etc), plastic utensils are made of Styrene, CD cases and cloth hangers are all made of Styrene. It is also an excellent insulation material.
EPS foam starts at very small beads, also known as granules, similar to sand in texture.
In order to make an EPS foam block out of these raw small beads, they need to be “blown” into larger beads, about 50 times its original size. This is called the pre-expansion process. Depending on the density required, the beads are blown using steam in a machine called expander or steamer. The expander can be a simple manual machine that a worker places the raw material in, then turns on the steam. Or, it can be an automatic machine where the material is blown stems automatically. At this stage, the beads – up to 50 times their original size – are called pellets and are ready to be molded.
Continuous pre-expanders are operated without pressure and are equipped with an open- top agitator tank in which raw material is continuously fed from the bottom by an adjustable screw conveyor. Steam is also fed continuously into the pre-expanding room through openings that are positioned shortly above the tank.
No matter which pre-expander is used, they all trickle the expanded beads into a so-called fluid bed dryer, where they are dried and stabilized before they are transported into the storage silos.
The next step is to mold the expanded beads. There are 2 options for molding. One is using a shape molding machine, which molds the foam into precise shape and size required. The other is using a block molding machine which will result in creating foam blocks or sheets, 3′ x 2′ x 8′ up to 5′ x 5′ x 24′. The EPS expanded beads are poured into the molding machine for a second heating with steams. This will result in the foam beads being swelled and pressed against each other, until they become one solid piece of foam
The two most common blowing agents used are pentane and carbon dioxide. This process called polymerization fills the polystyrene with millions of air pockets, which helps it to expand and also gives it a low thermal conductivity. During expansion, the product can be molded into a variety of shapes and sizes. The final product is 90% air, but amazingly, EPS can have a compressed strength up to 40 psi.
In the last step, the EPS foam is removed from the molding machine and cooled down. If you used the shape molder and created a smaller EPS shape, then the cooling time will be shorter than when creating a whole foam block. The larger the foam – the longer it takes for it to cool. The molded EPS should be kept at room temperature (about 70F)