The Cube Process
Virgin Plastic
Prime Grade, High Molecular Weight, High Density Polyethylene (HMWHDPE) is single sourced. Utilizing a proprietary gas phase technology; natural gas, chemicals and heat are used to produce a high pure, food grade, virgin, natural, HMWHDPE pellet. These pellets are shipped to PolyCube in both rail cars and bulk trucks which are blown or vacuumed into our indoor, dedicated silo storage system
Melt
The blended material is gravity fed into the extruder. The extruder is a long metal tube called a barrel with a large metal screw inside. The screw turns, driving the HMWHDPE forward between the narrow gap of the screw flights and the barrel wall. This causes frictional heat and the plastic melts.
Blow Mold
The Parison is then automatically cut from the head and mechanically transferred into the aluminum mold. The mold automatically closes while blow pins rise from the bottom. While air is blowing through the pins the mold is held tightly closed using hydraulic pressure. Next the Parison is blown into the walls of the mold. Chilled water is being pumped through small capillary tunnels inside the walls of the mold. This process transfers the heat from the plastic through the aluminum molds. The neck and back vents are also formed during this step. The Cube is now formed. We have different molds for different sizes and configurations.
Post Mold Cooling
The warm Cube is positively cooled in an additional three post mold cooling stations. In these stations the Cubes are further cooled with aluminum plates with chilled water running through their walls similar to in mold cooling. This process step insures the necks are round and the side walls and bottoms are flat.
Weighing and Traceability Marking
All Cubes are automatically weighed. The recipe for the production run has a target weight and a tolerance of plus or minus 50 grams. If the Cube is out of tolerance it will be automatically rejected from the line and sent to the grinder for reprocessing. Weight tolerances are important because they are a leading indicator to shifts in Parison lengths which can lead to field stacking issues. All Cubes are then automatically laser engraved with the date, time and shift for individual Cube identification and for complete traceability.
Visual Inspection / Capping Package / Bundle / Inventory
After all of these automated systems there is a final Blow Mold Operator light inspection of the cube for any visual defects such as carbon spots or thread deformations. If the operator determines the Cube meets the entire quality standard for the Customer then all, if any, back vents are torqued sealed.. If any neck closures are required they will also be installed hand tight and then the Cube is placed into a shipping tray. The Cubes are packed in custom sized bundles per our customer specifications. They are than automatically shrink wrapped with packing slips on all four sides identifying the Cube configuration, the date, shift produced and resin lot number.
Blend
Prior to being vacuumed to the extruder, the HMWHDPE is air conveyed into a Blender / Mixer where precise amounts of colorant and production flash regrind are volumetrically mixed according to an exact computer controlled recipe.
Extrude
The melted plastic is driven into the Head of the Blow Molder from the extruder. Inside the head are proprietary mechanics and technology that, utilizing a computer generated recipe pre-set by our process engineers, squeezes and shapes the plastic into a tube called the Parison. This insures the exact and correct amounts of plastic are in the right parts of the Parison so when in the mold the Cube will have precise wall distribution.
In Mold
De-flashing
Once the molding process is complete, the molds release their air and hydraulic pressures. The formed Cube is mechanically removed from the mold. The flash and excess plastic are precisely removed through an automated positive control trimming process. The flash is conveyed into a grinder for reprocessing.
Leak Testing
All Cubes are than automatically air leak tested at the prescribed Department of Transportation (DOT) required test pressure of 3 psi. We utilizing an authorized test method called “Differential Air Testing”. If any Cube fails the leak test they are automatically ejected from the line and are sent to the grinder for reporessing.
Enhanced Label Adhesion Treatment
In this process, the exterior surface of the polyethylene side walls are automatically heat treated to create a condition that better adapts to labels and environments that pose difficult adhesion conditions.
Post Manufacturing Quality Control
A minimum of 6 cubes per shift are quality checked by a quality trained PolyCube Supervisor Inspector. They complete a 70 point written check-list measuring for ovality and wall thickness/distribution to insure the Cubes are within preset tolerances. The test sheets are reviewed and maintained by the Operations Manager. Other in house testing performed is hydrostatic and freezer drop. Lastly, official United Nations Department of Transportation testing is done annually to certify each design type by an independent third party DOT approved testing laboratory.
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