Hydraulic cylinders are not restricted to a particular type of application. You can find hydraulic cylinders in almost every application in the hydraulics industry and there is no need to mention their importance. But, not all are the same in design and operation. I.e; single-acting, double-acting, welded, telescoping, and tie-rod are common cylinder categories with varying appearance, applications, and operating features. These cylinders used exposed to environmental, chemical, thermal, mechanical, and physical conditions can get damaged easily. Any such damage to the hydraulic cylinder can affect the productivity and accuracy of operation along with costly repairs. With proper hydraulic cylinder coatings, the risk of abrasion, adhesion, corrosion, wear, high temperature, and pitting can be reduced to a certain extent thereby improving the service life of cylinders. In this blog, more details on hydraulic cylinder coatings are explained.
Hydraulic cylinder coating can be done internally and externally. The primary aim of coating is to protect the cylinder from chemical and physical attacks. I.e; interior coating in cylinders will protect the cylinder from chemical attacks caused by the reaction of cylinder material with fluid or contaminants, extreme temperature, etc... External coatings are also for providing protection to the cylinder surface for reducing corrosion and wear. The different approaches for cylinder coatings are plasma spray, laser cladding, thermal spray coatings, and weld overlay. Among these, Plasma spray coating is a traditional approach that is ideal for high-temperature environments that experience wear and corrosion. This high heat thermal spray system combines both flame and arc spray with both flame and arc spray. Chrome oxide and aluminum oxide ceramic, T800, aluminum polyester abradable, etc… are common coating materials of plasma coating. But, this approach is not much used currently and the following section explains the latest coating techniques.
Laser Cladding (Hard Facing or Surfacing): The laser cladding approach utilizes a high-power laser beam as a heat source for melting the coating material and subsequently applies it on the base metal or substrate for improving its properties. In this laser cladding process, nozzles having different shapes can be used. A layer of powder coating is produced on the substrate surface due to the contact of the laser beam from the nozzle with different powder mixtures. The different lasers used for the cladding process are diode lasers, CO2 lasers, fiber lasers, etc… Also, other applications where laser coating can be used are pump & turbine components, cylinders & rolls, exhaust valves in engines, sealing joints, and more.
Thermal Spray: Thermal spraying is the approach mostly used on printing presses, food machinery, mining & quarrying machinery, earthmovers, valves, aerospace turbine repairs, etc… High-velocity oxyfuel technique, arc spraying, flame spraying, and plasma spraying are some of the sub-categories of the thermal spraying approach. This method utilizes metals, ceramic, or plastic as a coating material and it is applied to the base metal surface by melting the clad material using a heat source and then projected as a spray.
Weld Overlay: Weld overlay is a cost-effective method for improving the corrosion resistance or mechanical properties of base metal. This approach uses a welding procedure for melting the coating material and applying it on top of base metal.
Hard Chrome Plating: Hard chrome plating for cylinders utilize a chromic acid-based electrolyte for the electrolytic process. Low friction, wear and corrosion resistance, abrasion resistance, low deposition temperature, attractive finishing, excellent substrate adhesion, stable plating, etc… are important benefits of hard chrome plating. This procedure is applicable on different substrates such as cast iron, stainless steels, brasses and bronzes, aluminum alloys, nickel-based alloys, titanium alloys, and more. The thickness of this plating ranges from 2 to 250µm.
Ceramic Plating: Ceramic plating is mostly used in the automobile, aerospace, and military industry on cylinder heads, pistons, intake manifolds, and piston skirts. The primary goal of ceramic plating is to protect the component from wear, reduce friction, and increase heat shielding. To apply a ceramic coating on a surface, the surface needs to be treated with a smoothing agent or sandblasting and then the surface is heated in an oven to reduce its molecular porosity. In the next stage, ceramic coating(titanium/tungsten) is applied to the surface using a gravity-fed spray gun.
Black color coating for subsea applications: Subsea hydraulic systems in vessels, rigs, ships, etc… are exposed to saline water and it can cause pitting corrosion and bacterial corrosion. With this black color coating, it is possible to offer corrosion resistance, electrical insulation, chemical shielding, wetting properties, wear resistance, etc… Among black color coating, liquid nitrating is a popular surface treatment that offers high surface hardness and corrosion resistance. The liquid nitrating procedure will include stages like cleaning and super-polishing the material and then vertically submerged into an electrically controlled liquid tank. With this process, a thin uniform and extremely hard iron nitride layer is generated.