The hydraulic cylinder rod is exposed to the most extreme environments of any part in a machine. One end of the rod is in clean oil, while the other end is in salt spray, mud, humidity, and wash-down water. Seals are worn out when the surface of the rod fails. For cylinders used in coastal areas or export markets, the choice of coating on the hydraulic cylinder rod affects the service life of the cylinder.
The Leadership of Hard Chrome
Hard chrome plating has been the standard for many years and for many good reasons. It is a hard, smooth surface that protects seals. A good hard chrome plating will have a thickness of 20 to 50 microns over a ground and polished steel rod. The main drawback of hard chrome is micro-cracking. Moisture can move through the cracks. Lead to pit corrosion. Some rules say that a coating needs to survive a salt spray test that lasts, between 100 and 200 hours. This test follows the ASTM B117 standard.
Other Coatings
Nickel-chrome duplex plating has a harder chrome layer with a lower chrome plating cracking and a salt spray lifespan that is many times that of standard hard chrome. An extremely hard coatings made from HVOF tungsten carbide and chromium carbide have high erosion and corrosion resistance and are suited for offshore and dredging applications. Hydraulic cylinder rod coating options such as laser cladding, where a corrosion-resistant alloy is bonded to the rod, are better suited for impact and have a better service life than a thin plating, and are suited for food and marine applications, and chemical processing.
Comparing Real-World Performance
There is a consistent failure pattern in construction and industrial duty. Chrome rods in humid ports start to rust with seal damage or wiper wear. Duplex and laser-clad rods last, for service intervals when used with a sealed and wiped bushing.. Duplex and laser-clad rods are expensive and need finishing and grinding. HVOF coatings perform well. Hvof coatings repairs are difficult and the lead time is long.
Practical Selection Checklist
Understand the application. Coastal, offshore and chemical applications require clad, HVOF rods. Dry indoor applications may require hard chrome rods. Obtain salt spray test results and coating thickness and surface roughness results from suppliers. Check if the material of the rod is compatible with the seal and wiper. Request samples from the same lot you will receive. And lastly consider the total cost of the cylinder over its life as opposed to just the initial cost.
Environmental and Compliance Notes
Hexavalent chromium plating baths are regulated under REACH in Europe and through exposure limits in the workplace. Every market has its own regulations and regulations can change at any time. Export buyers need to verify that their supplier follows the regulations. Trivalent chromium plating and thermal spray are two options. Each should be validated for your specific duty cycle.
Final Thoughts
No coating is ideal for all hydraulic cylinder applications. Choose a coating for your cylinder that takes into account the real operating conditions of your equipment. Ask to see test data. Establish a maintenance plan. Teutonic Engineering works with our customers to understand the climate in which the equipment will operate to recommend the most appropriate cylinder for that duty. Contact our Engineering team.