Hydraulic Cylinders: Chrome plating vs. laser cladding
Moving towards chrome plating replacement
An insight by Antonis Kalampokas
About the chrome plating method
Chrome plating offers high hardness and corrosion resistance at a reasonable cost. For years, it has been the preferred method (the other being metal spray) for coating hydraulic cylinder piston rods and various other critical components. For the above reason, the chrome plating method is found in parts used for a variety of different applications. These are hydraulic cylinders for cranes, cargo hold hatch covers on ships, rods used in various demanding offshore environments such as drill ships and oil platforms, as well as on mining and earth moving machinery.
Chrome plating limitations and disadvantages
On the other hand, chrome plating also has severe limitations and disadvantages, which in the last years have become more and more obvious as equipment downtime becomes less and less tolerable by owners, plant operators, and inspecting bodies. Additionally, in chrome-plated rods, the adhesion of the chrome coating with the parent material is often poor, resulting in peeling off. Chrome-plated rods are also vulnerable to impact, creating surface defects that destroy the coating and the seals.
Another limitation is that with chrome plating, we can apply only very thin coatings with a thickness that usually does not exceed a few tenths of a millimeter which, combined with the natural micro-cracking of the chrome-plated surface. This leads to penetration of air and water, oxidization of base metal, and eventual destruction of the chrome-plated coating. Oxidization is an issue very common in marine environments where salt water and humidity demand very high corrosion resistance. Marine superintendents and offshore engineers often witness corrosion that starts from the upper part of the rod, which stays out of the liner and the protection the oil offers, and eventually progresses all over the rod surface.
Chrome plating disadvantages at a glance:
- Equipment downtime
- Thin coatings
- Oxidization
- Long delivery times
- Materials and Workshop unavailability
Adding up to that, the requirement for various sizes of plating baths and long delivery times, in case of re-chroming, are also disadvantages of chrome plating, which I am sure superintendents reading this article have experienced during drydocks. How many times superintendents of bulk carrier vessels have been told that ten or more days are required for chrome plating of 20 pcs of their damaged hatch cover rods. Similarly, container vessel superintendents with big crane hydraulic cylinder rods may have an unpleasant surprise when they learn that no local chrome plating facility can accommodate their 5-meter long rod and need to spend time and big money to get their cylinders back to operation. If a rod is so damaged that can not be chrome plated, then a new one has to be manufactured, and sourcing the right material locally is always an issue, particularly nowadays.
Of course, the most important disadvantage of chrome plating is its heavy environmental impact. Hexavalent chrome is a toxic, carcinogenic material requiring special treatment. Environmental sustainability and health and safety have become, and rightfully so, extremely important. The usage of chrome is heavily regulated all over the world, with the EU and USA especially imposing very strict regulations, which will eventually lead to the banning of chrome plating. Regulations, restrictions, and social pressure incur additional costs to chrome plating, rendering the procedure sooner rather than later obsolete.
Alternative repair solution: laser cladding
Laser cladding, a technology that started its industrial use the previous decade, is now emerging as the best alternative to chrome plating for hydraulic cylinder rods as well as other components. That is because laser cladding solves many of the problems mentioned above.
Laser cladding advantages at a glance:
- Environmentally friendly / Sustainability
- Fast delivery times
- Accuracy
- Overall performance
- Reduce overall costs
First of all, it is a much more environmentally friendly process. Moreover, since it is essentially welding, it creates a full metallurgical bond between coating and base material. This prevents peeling off and offers high resistance to impact. With the laser cladding technology, we have the ability to apply thin or thick coatings depending on the requirements, which, combined with the absence of microcracking, offer high resistance to corrosion and prevent oxidization. Nowadays, there is a large variety of different coating powders to suit each specific application’s requirements, and of course, laser cladding being a highly automated process ensures much faster delivery times with high quality and with fewer limitations in the size of parts to be coated. Big thickness, fast delivery, and automation make laser cladding an ideal repair solution for hydraulic cylinder piston rods.
Initially, laser cladding being a new technology, although overall better in all respects, had the disadvantage of a relatively higher cost compared to chrome plating. As laser technology reaches maturity, new technologies are being implemented, reducing costs to the same or sometimes lower compared to chrome plating. Industrial lasers can now have capacities of more than 10KW at reasonable costs making them faster, while EHLA (high-speed laser cladding) is making its way into commercial applications with an impressive performance on time and material usage, further reducing overall costs.
At INJEGOV, we have long seen the trend shifting towards laser cladding instead of chrome plating and have invested in a versatile laser cladding machine allowing us to process parts of various sizes. Seeing the benefits firsthand and taking positive feedback from our clients, we now move on to expanding our capabilities by stepping into an even higher capacity of lasers and introducing high-speed laser cladding. Over the years, we have accumulated a great wealth of experience in hydraulic rod repairs both by chrome plating and laser cladding and can measure and appreciate the differences; this is why we are eager to test our new toys and see what they can do. Expectations are high, so I will keep you posted!