HYDRAULICS When discussing the behaviour of hydraulic piston rods, Mattias Awad begins by stressing the importance of surface protection. A thin layer of chrome or nickel chrome has long been relied upon to deliver low friction, wear resistance and corrosion protection. However, he notes that this protective layer only performs as expected if the underlying steel maintains very consistent quality. Because Ovako Cromax controls production from the steel mill through to final plating, the company can maintain the tight tolerances needed to achieve consistent coating results. In many applications a hard chrome layer on its own is sufficient. In more demanding environments such as mining, offshore equipment or chemical processing plants, manufacturers often add a nickel underlayer. Awad explains that this layer significantly improves corrosion resistance by preventing pitting and slowing the penetration of corrosion into the steel, even when lubrication is disturbed or surface damage occurs. Traditionally the top layer in these duplex systems has been hexavalent chrome. Although this material has performed well for decades, it is subject to strict controls under the REACH regulation. Combined with growing customer interest in sustainability, this led Ovako Cromax to pursue an alternative. NiKrom III is the result. It retains the established nickel underlayer but replaces the hexavalent chrome with a hard trivalent chrome surface. Developing the NiKrom III process Awad explains that shifting to CrIII required a significant research effort. The chemical behaviour of trivalent chrome is more sensitive than that of hexavalent chrome, and maintaining stability in the plating bath requires strict control. Ovako Cromax worked with a major chemical supplier and relied heavily on its own experience in duplex coatings to establish a process that could deliver the same level of corrosion resistance as the existing NiKrom products. The first demonstrator rods were produced in 2017 at the company’s facility in Redon, France. These initial samples were produced on a manually operated pilot line. Since then the process has been refined, and a pre-series production line is now in operation. It can coat bars up to 3 metres in length and with diameters from 20 to 140 millimetres. A key requirement during development was that NiKrom III should work with existing hydraulic cylinder designs. According to Awad, the coating needed to match the hardness, surface structure and friction characteristics of conventional chromium coatings so that sealing systems and mechanical interfaces would not need to be redesigned. This compatibility has been achieved. NiKrom III can also be applied to any Ovako Cromax steel grade without additional heat treatment, so established mechanical 18 HYDRAULICS & PNEUMATICS November/December 2025 www.hpmag.co.uk A new sustainable coating for hydraulic piston rods As hydraulic systems move into more corrosive, demanding and environmentally regulated conditions, surface technology is becoming a central design consideration. H&P spoke to Mattias Awad, Head of Marketing and Technology at Ovako Cromax, to discuss the company’s development of NiKrom III, a new CrVI-free duplex coating. He explained how the technology was created, why it addresses the industry’s sustainability challenges and what early field trials with Sandvik Mining and Rock Solutions reveal about its performance. properties and fatigue behaviour are preserved. These attributes make NiKrom III suitable for heavy duty environments, but also for exposed applications that remain in service for long periods. Examples include snow ploughs, tailgate lifts and ski lift systems. Figure 1 shows a typical application on a Sandvik loader. Field performance One of the earliest adopters of the new coating has been Sandvik Mining and Rock Solutions. The company operates in some of the harshest industrial environments and has placed increasing emphasis on machine reliability as automation and remote monitoring become more widely used. Sandvik also has Science Based Targets initiative validated sustainability goals which include a 50 per cent reduction in scope 1 and 2 greenhouse gas emissions and a 30 per cent reduction in scope 3 emissions by 2030. After an introduction by Ovako NiKrom III lift cylinder rods on a Sandvik loader operating in harsh mining conditions.
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