Machine builders and end users have many factors to consider when choosing linear motion components and systems – travel length, speed, acceleration, positioning accuracy and repeatability, just to name a few. But sometimes the most challenging requirement isn’t a traditional application spec. It’s the environment that the system will be working in.
Many industries have processes that take place in extreme environments – food processing and packaging; medical devices and life sciences; and semiconductor and electronics manufacturing. From concerns over human safety to the aggressiveness of acidic or corrosive chemicals, these industries present some of the most demanding material requirements in the linear motion world.
Taking into account that linear bearings are primarily made of carbon steel for high load capacities and machinability, the solutions for these environments can seem to be quite limited, with the best alternative being costly design compromises to minimize risk and maximize safety. But with the right coating or plating material, it is possible to use standard linear motion components and systems even in the most severe conditions. To help you navigate the range of solutions, we take a look at five common plating and coating options.
Thin Dense Chrome
Thin dense chrome (TDC) is a type of hard chrome plating which is deposited via a highly controlled electroplating process. It provides a very hard, very dense coating, and because the surface finish is nodular, it provides excellent wear properties and very low friction. TDC plating resists most organic and inorganic compounds, with the exception of sulfuric and hydrochloric acids. Offered by several companies under proprietary trade names, TDC has been approved for use on equipment by the USDA and the FDA.
Electroless plating is an autocatalytic process, which means it is achieved through chemical reactions, in contrast to the traditional electroplating process, which uses an electrical current to facilitate plating. The electroless process provides a more uniform plating thickness, with no additional buildup on edges or corners and more reliable plating of holes and depressions. Electroless nickel consists of a nickel-phosphorus alloy, with the amount of phosphorus determining the hardness and corrosion resistance. Electroless nickel can be provided with a PTFE (Teflon®) topcoat for added lubricity, although alkaline or chlorine solutions can affect the longevity of the topcoat.
Electroless Nickel with PTFE
Another variation of electroless nickel plating includes sub-micron particles of PTFE dispersed throughout the nickel-phosphorus matrix. This gives a higher durability than typical PTFE coatings, combined with the benefits of electroless nickel. Electroless nickel plating with PTFE can withstand extended exposure to acidic or caustic chemicals with a PH range of 3-9.
Nickel cobalt plating is also achieved via the electroless process, making it suitable for complex parts and parts with tight tolerances. A highly corrosion-resistant option, nickel cobalt plating is often regarded as the best solution for washdown environments, especially those which include additives (alkaline or chlorine).
Hard Coat Black Anodize
Hard coat black anodize with PTFE is the best solution for aluminum components that require both corrosion resistance and high durability, such as sliding bearings and linear actuator housings. This coating produces a surface whose hardness (60-65 Rc) is comparable to case-hardened steel, giving it high durability and high corrosion resistance. It also has a low coefficient of friction and dry lubricating properties, which are important for sliding or rolling bearing surfaces
While many factors must be considered to determine the suitability of a plating or coating, understanding the environmental, chemical, and regulatory requirements of your application, coupled with the material and performance requirements of your linear system, will help you choose the best solution to increase the safety and extend the life of your equipment.
Teflon® is a registered trademark of E. I. du Pont de Nemours and Company Armoloy® is a registered trademark of Armoloy Company TDC-1®, TDNC®, and Ni-Comp-100® are registered trademarks of Hi-Tec Plating, Inc. NiCoTef® and Nituff® are registered trademarks of Pioneer Metal Finishing NiColoy® is a registered trademark of NiCoForm, Inc.