The benefits of PVD coatings for plastic molding applications
Are you looking to increase your productivity and machine uptime in plastic molding? Protecting your molds and dies against wear with Ionbond’s PVD coatings is a good place to start! Read our article to learn more.
Plastic molding is a critical growth industry, enabling the success of many sectors such as fields such as packaging, automotive, sport and leisure, consumer electronics and cosmetics. To keep costs low in this competitive sector, high productivity and machine uptime are critical. Another key aspect to cost efficiency is increasing your tool lifetime: the dies and molds used in high-volume processes such as plastic injection molding and plastic film extrusion are typically highly complex in shape, time-consuming to make and thus expensive.
Surface treatments and coatings that increase the reliability, longevity and productivity of plastic forming dies and molds, such as PVD coatings, can add significant technological and economic value. These treatments often also help reduce maintenance, because they create surfaces that are easy to clean, and improve product quality with tight tolerances and a very high surface quality.
Many wear and damage mechanisms during plastic processing
Plastic processing is a complex tribological system, which means many different wear and damage mechanisms are in play. Let’s take an extruder screw for plastic injection molding of polypropylene (PP) as an example. There are typically three zones on the screw (feeding – compression – metering) each with different damage mechanisms present in different proportions (see Figure 1).
- Abrasive wear is caused by hard, embedded particles in the plastic to be processed, such as glass fibers (600 HV), TiO2 (1,200 HV) or Cr2O3 (2,300 HV). These embedded particles act as tiny tools themselves, shaping the mold or die in a process known as micro-machining.
- Erosion iscaused by abrasive particles in the flowing plastic melt scraping over the surface.
- Adhesive wear (build-up) is based on cold welding, chemical bonds, eletrostatic forces, wetting and micro-cratering.This leads to abrasive wear and tribo-oxidation.
- Cavitation iscaused by local negative pressure in the flowing plastic melt. The bubbles formed during processing implode when the pressure near the wall increases, thereby damaging the tool surface.
- Corrosion is caused by corrosive substances formed during plastic processing, e.g. HCl from processing polyvinylchloride (PVC).
PVD coatings have a wide range benefits in protecting dies and molds
PVD coatings have a chemically saturated functional surface, which reduces adhesive wear and the build-up of deposits. This improves the flow behavior of the plastic melt and helps prevent stick/slip effects and burners or streaks on the product.
The coating’s high hardness increases the wear resistance of the coated die or mold, protecting it from abrasive wear from hard, embedded particles in the plastic. This helps maintain the surface integrity during daily production, cleaning (e.g. between two plastic colors) and handling.
Lastly, PVD multilayer coatings help prevent catalytic decomposition of the plastic by preventing contact with iron (Fe). They also protect the dies and molds from corrosion caused by chemical compounds that are formed during processing.
Incredible cost saving potential
These protective characteristics add up to a tremendous cost saving potential over time. Let’s assume a valuation period of 6 years for the previously discussed extruder screw. We will compare the Ionbond™ 30 (CrN) PVD coating to hardfacing, a popular surface treatment. As seen in Figure 2, that leads to savings of 60 %.
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