For products commonly made from high-density polyethylene (HDPE), polypropylene (PP), polyethylene terephthalate (PET), and polyvinyl chloride (PVC), experts rely on extrusion blow molding machinery the most. With this, you can create a broad range of plastic bottles, fuel tanks, children’s toys, holding tanks, and more.
Using extrusion blow molding machines, molten resin extrudes into a parison, which has a cylindrical shape. While hanging in a downward position, two halves of a mold close firmly around it. At both the top and bottom portion of the mold, the cylindrical shape pinches tight while leaving a hollow tube in the center.
The machine then forces pressurized air through a needle inserted in this tube, causing the walls to expand and stretch to the point of conforming to the mold. Once the resin cools and becomes solid, the mold opens, making it possible to remove the finished product. If necessary, the manufacturer can add colorants mixed in with the resin, as well as adhesive or barrier layers.
As a respected and trusted extrusion blow molding manufacturer, you have confidence in providing your customers with precision products. Although there are slight differences in design, depending on the type of extrusion blow molding machines used, they typically include the following:
- Material hopper
- Hydraulic cylinder (for wall thickness)
- Accumulator head (also called the parison head)
- Blow pin (for stretching)
- Closing clamp
- Blow Mold
- Mold platen and clamping unit
For seamless operation, it is imperative you keep all the different parts clean. In particular, you want to focus on the head of an extrusion blow molding machinery.
Before starting the cleaning process on the heads of extrusion blow molding machines, always disconnect or shut off the auxiliary feeding equipment. For precision and high-performance products, it is essential you keep the accumulator/parison head clean.
The problem is some polymers degrade during the molding process, especially when running the machine at high temperatures. If not cleaned on a regular basis, the degraded material accumulates in the head. When that happens, it creates what appears as stripes on the surface, which then compromises the product’s appearance.
Before removing the head from the machine, use an electric heater to bring its temperature above the point required to melt the plastic. From there, remove and open the head, followed by using a scraper made of copper-beryllium or copper to collect the majority of the melted resin. Next, use high-pressure air in combination with brass cotton to eliminate any remaining material. As for melted plastic on the thread portion of the head, you can use a quality anti-sticking agent.
With the cleanup complete, you can start up the extrusion blow molding machinery by following the manufacturer’s protocol. Keep in mind that during this process, you want to eliminate as much of the contamination as possible. If you struggle, you can always install a new screen pack and make necessary adjustments to the clearance of the head.