Expanded Polystyrene foam is manufactured from the by-products, or left overs, from the oil refining process. These blocks are then cut into smaller usable sizes that vary with the application. The description below explains how the manufactures the EPS foam pieces and sheets you are familiar.
We buys raw material in the form of resin or beads of styrene. Each bead has a microscopic dot of Pentane formed into its center. This material is furnished in air tight bags. These bags keep the beads “fresh” by assuring that the Pentane within each bead can not escape into the atmosphere and render the material.
These beads of Styrene are about the size of a grain of salt and have a similar consistency. It is crucial that the beads are stored in a tightly controlled environment where the amount of Pentane within their plastic shell remains consistent. Each step of EPS production requires strict adherence very tightly controlled quality standards.
These beads of resin are loaded into a machine called a “pre-expander”. It does exactly what the name implies. Steam is injected into the beads at 212 degrees F. The heat accomplishes two things. The wall of each bead is softened and becomes flexible and the increased temperature also causes the Pentane to expand within the softened beads. The beads puff up like popcorn to 30 times their original size.
The next step is the molding process. It is at this point that the individual expanded beads are molded into a single, homogeneous block. This is the most crucial stage in the production process and it is essential that very strict quality control standards are adhered.
Once again, steam is used to deliver heat to the process. A precisely measured quantity of beads is blown into a steel mold. Steam is then injected into the pre-expanded beads to heat the mix to 212 degrees F. This heat causes the wall of each bead to soften and the remaining pentane within each bead expands. This expansion causes the beads to increase in size within the steel mold. This expansion increases the pressure and the beads are forced together to form a single block. The soft bead walls actually allow the beads to melt together into a single solid block. At this point the mold opens like a clam shell and the block of EPS foam is removed.
After the block has been removed from the mold it is carefully weighed and marked so it can be traced throughout the production process. Adherence to the proper weight assures that the correct “density” or “weight per cubic foot” is maintained. A needle is injected into the center of the block and pressurized air is applied. The degree to which the block restricts the flow of compressed air is an indication of the proper amount of fusion between the individual beads within the block.
Immediately after coming out of the mold, the surface of each block is perforated with thousands of tiny holes. The purpose of this step is to help moisture to escape the freshly molded block. The molding process leaves a smooth skin on the outside of each block and the perforator allows the moisture, a result of the steam, to more easily escape from the block.
Once the blocks have been molded, perforated, weighed, and tested for proper fusion, they are moved to the “drying room”. Within this room the temperature is maintained at approximately 140 degrees F. There are large blowers that circulate the air within this room. These steps are designed to remove as much of the moisture from the block as possible. The increased temperature also helps to reduce any internal stresses that may exist within the block as a result of the molding process.
If flat sheets are desired, a series of wires are connected to a “slicer” with the proper horizontal spacing to give the exact dimensions needed. The wires are heated with electric current and melt through the foam leaving a smooth, consistent, surface. If irregular shaped parts are required, a computerized contour cutter is used to duplicate whatever shape has been programmed into the machine’s software. A variety of cutting techniques is used to achieve the varied demands of our customers.