Expanded polystyrene foam, also known as EPS, is a highly durable material used in a wide variety of consumer products. It can be found just about everywhere, at your local grocery store (plates, cups, food containers, etc.) and local electronics stores (insulation for refrigerators, coolers, etc.), plastic utensils are made of styrene, CD cases and fabric hangers are made. of styrene. It is also an excellent insulating material.
EPS foam starts with very small pearls, also known as granules, similar in texture to sand.
To make a block of EPS foam from these small raw beads, you need to “blow” them into larger beads, approximately 50 times their original size. This is called the pre-expansion process. Depending on the required density, the pearls are blown using steam in a machine called an expander or a steamer. The expander can be a simple manual machine in which a worker places the raw material and then turns on the steam. Or, it can be an automatic machine where the material is automatically blown. At this stage, the beads, up to 50 times their original size, are called pellets and are ready to be molded.
Continuous pre-expanders work without pressure and are equipped with an open agitated tank into which raw material is continuously fed from the bottom by an adjustable screw conveyor. Steam is also continuously fed into the pre-expansion room through openings positioned just slightly above the tank.
No matter which pre-expander is used, they all drop the expanded beads into a so-called fluid bed dryer, where they are dried and stabilized before being transported to storage silos.
The next step is to mold the expanded beads. There are 2 options for shaping. One is using a shape molding machine, which molds the foam into the precise shape and size required. The other is to use a block molding machine which will result in the creation of foam blocks or sheets, from 3′ x 2′ x 8′ up to 5′ x 5′ x 24′. The expanded EPS beads are poured into the molding machine for a second heating with vapors. This will result in the foam beads swelling up and pressing 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 Styrofoam with millions of air pockets, which helps it expand and also gives it low thermal conductivity. During expansion, the product can be molded into a variety of shapes and sizes. The end product is 90% air, but amazingly, EPS can have a compressed force of up to 40 psi.
In the last step, the EPS foam is removed from the molding machine and cooled down. If you used the shaper and created a smaller EPS shape, then the cool down time will be shorter than creating a full foam block. The larger the foam, the longer it takes to cool down. Molded EPS should be kept at room temperature (around 70F)