APS "all-purpose screw"
Many injection molding firms are catagorized as a "custom molder," meaning there are numerous resin and mold changes on a given press. Due to these frequent changes in materials and parts produced, many injection molding firms do not invest in high performance screws, but rather depend on the poor performance of general purpose or "GP" screw designs. It is commonly believed that a GP screw can process a wide range of materials successfully. These GP screws were developed in the 1950s and are simply cheap to produce. Major advancements in technology, materials, and parts produced have been made since these antiquated designs were developed.
It is not always feasible to inventory a host of high performance screws for an injection molding firm due to cost and space allowance. To better accommodate these injection molding firms, we have developed the All-Purpose Screw.
Click here to learn about the downfalls of traditional General Purpose Screws.
How It Works
Improving the quality of the final product starts by getting the injection or extrusion process right. Several screw designers have developed offerings for better material mixing applicable to a range of processes.
Higher melt temperatures experienced by the resin results in reduced physical properties. It takes energy to heat the polymers and also to cool them; therefore, a lower melt temperature reduces energy consumption, cycle time and line speeds. Lower melt temperature in virtually every way is a plus. Molders processing a range of materials with a general-purpose screw have had to rely on back pressure to improve mixing and dispersion. However, raising back pressure also increases melt temperature, lengthening cycle times.
The All-Purpose Screw is a innovative mixing screw that improves processing performance and offers a much wider processing window across a wide range of materials as compared to traditional GP screws. Rather than relying on excessive backpressure and heat to compensate for poor performance, the APS overcomes solid bed break up and provides a high quality isothermal melt. The APS mixing design causes the resin to converge and diverge repeatedly down the length of the mixing section. Unlike popular "wave" designs, the APS is self cleaning with no areas of low flow allowing for material to hang up and degrade.
In larger diameter screws the All-Purpose Screw (APS) design can be equipped with specially designed dams to modify the flow of material around the screw. This allows the processor to tailor the mixing effect of the screw to the material while keeping melt temperatures as low as possible. Users can alter the level of dispersive and distributive mixing in the mixing section of the screw by switching out one or several of the dams. Changing the clearance between the dam and the barrel wall allows for the improvement in the mixing. Users have a screw design that can be modified at the site by removing the screw far enough to expose the removable dams and then replacing the dams as required. In this way, any change in polymer, regrind percentage, or changes done to improve operating conditions can be accommodated on site.