RePEEK: PEEK coatings using a hybrid process
In the RePEEK project, the surface engineering team is investigating how PEEK-based coatings can be applied to metal components used in heavily loaded, moving systems. They are focusing on applications in mechanical engineering, including large plain bearings, seals, piston, and solenoid valves. Large plain bearings used in wind turbines provide a particularly clear example of the challenge. A shaft rotates within a coated bearing shell, which is currently protected in most cases by PTFE-based coating systems. As its name suggests, RePEEK replaces PTFE with PEEK.
"Today, PEEK is often applied to large components either as a film or as a powder that is subsequently bonded by heat," says Samuel Fink. "That approach can work well for small components. With metal parts weighing several tons, however, it becomes far more complicated. The entire component has to be heated in a furnace to a high temperature and then cooled down slowly." The process consumes large amounts of energy, takes considerable time and heats far more material than is actually required for the coating itself.
The researchers first use a laser-based deposition process to create a metallic surface layer. This deliberately rough surface provides mechanical anchoring for the polymer. They then apply PEEK powder within the same process environment and melt it locally with the laser. The polymer becomes anchored in the rough metallic surface, creating a composite coating consisting of a metallic functional layer and a PEEK-based topcoat.
The team has developed a specially designed nozzle for the PEEK powder and has already filed a patent application for the process. The cyclone nozzle greatly reduces the gas flow, allowing the powder to reach the surface at a much lower velocity instead of bouncing off it. As a result, the process uses more of the applied powder efficiently and is easier to control.
EPOS: Multilayer PEEK coatings for large plain bearing
Building on the RePEEK project, Delil Idris Demir at Fraunhofer ILT is investigating how PEEK-based coatings can be deposited reliably onto large plain-bearing components in multiple layers. Applying the coating step by step makes it possible to build up greater coating thicknesses without having to heat components weighing several tons entirely in a furnace. ACS Coating Systems contributes its extensive experience in PEEK coatings, particularly for plain-bearing applications. The company has been developing these coating systems since the mid-1990s and now produces coatings ranging in thickness from just a few micrometers to one millimeter. Managing Director Dr. Christoph Stecher is supporting the project by providing his expertise in coating design, industrial-scale application and the transition to full-scale manufacturing.
Polymer Service Merseburg (PSM), led by Dr. Katrin Reincke, tests and evaluates the resulting coating systems. Their work focuses on the crystallinity, microstructure and thermal condition of the PEEK layer, as well as its mechanical and thermomechanical properties. These data will help optimize both the laser process and the multilayer coating strategy so that the coating bonds uniformly to the substrate and withstands the long-term mechanical stresses encountered in plain bearings. EPOS therefore brings together Fraunhofer ILT's expertise in laser-based process development, ACS's industrial experience in coating technology and PSM's materials science expertise.
LEMBAS: Non-stick coatings for sensitive elastomer rollers
The LEMBAS project focuses on elastomer rollers used in film manufacturing, the packaging industry, paper production, and medical technology. In these applications, even small particles released from the roller surface can quickly become a problem.
"Silicone coatings are still widely used for these applications," explains Adam El-Sarout, also a member of the Thin Film Processing Group at Fraunhofer ILT. "While they provide the required non-stick properties, they do not always offer the durability demanded by today's high-speed manufacturing processes." Together with the coating specialist Rhenotherm, the LEMBAS team is developing laser-based manufacturing processes that use high-performance polymers such as PEEK, polyamide and polypropylene. Compared with silicone, these materials offer greater resistance to wear, improved chemical stability and a longer service life, all without the use of PFAS.
"The real challenge is the processing window," says El-Sarout. "High-performance polymers require high melting temperatures, but elastomers such as EPDM can tolerate only limited heat. Heating an entire rubber roller in a furnace would damage the substrate." The laser solves precisely this problem by generating high temperatures only where they are needed and only for a very short time within the coating material. The functional layer melts, while the elastomer component beneath it remains largely protected from thermal damage.
To ensure long-term adhesion, the researchers are developing not only the non-stick coating itself but also an intermediate layer that protects the elastomer and strengthens the bond to the functional topcoat. They are also tailoring the optical and rheological properties of the materials to the laser process while investigating suitable coating and laser pre-treatment methods.
"A replacement material must do more than provide the required functionality," says Vedder. "It also has to be compatible with the component, the substrate's temperature limits and the manufacturing process." If that step succeeds, the process offers several advantages: reduced wear, fewer product contaminants, less cleaning and lower solvent consumption and significantly lower energy requirements than conventional furnace-based processes.
pureWaterSeal: PFAS-free seals for water-based lubricants
In the pureWaterSeal project, researchers at the Fraunhofer Institutes for Laser Technology ILT and for Mechanics of Materials IWM are developing sustainable seals that eliminate the need for PFAS and operate with water-based lubricants. The project addresses two environmental challenges at the same time: PFAS persist in the environment indefinitely, while oil-based lubricants contaminate soil and water.
Around one million tons of oil-based lubricants are consumed in Germany every year," says Matthias Laermann, Head of the Surface Structuring Team at Fraunhofer ILT. "Just one liter of oil can contaminate up to one million liters of groundwater. The consequences include polluted soils, contaminated food supplies and damaged ecosystems. We are developing solutions that address both challenges simultaneously."
Researchers at Fraunhofer IWM have developed diamond-like carbon (DLC) coatings specifically for PFAS-free polymer components. The Fraunhofer ILT team then used a laser to structure the coating, locally relieving internal stresses and mechanical loads without compromising the stability of the coating as a whole. At the same time, the combination of the coating and laser structuring reduces friction, improves wear resistance and extends the service life of the seals.
The first prototypes are already operating in pumps used at geothermal power plants. Together with industrial partners, the researchers are now adapting the seals for additional applications, including passenger vehicles, ship propellers, wind turbines and agricultural machinery. At the same time, the team is preparing to scale up the technology for larger systems and industrial production.
The laser makes the material transition practical
The various projects at Fraunhofer ILT demonstrate that replacing PFAS involves more than simply substituting one material for another. It also requires manufacturing and surface engineering processes capable of applying those new materials reliably. Here, the laser plays a key role. It deposits materials locally, melts them precisely where needed or structures functional coatings without placing unnecessary thermal stress on the underlying component.
This gives industry greater flexibility. They do not have to wait for a single replacement that can address every PFAS application. Together with industry partners, Fraunhofer ILT is developing customized coating systems for various components and requirements: low-friction surfaces for plain bearings, wear-resistant release coatings for rollers and PFAS-free sealing systems for water-based lubricants.
(Source: Fraunhofer ILT)
