The two elements critical to how well hydraulic and pneumatic systems function and their longevity are a tight and lasting seal between parts and the correct level of friction as the system moves. This involves ensuring the surface of the parts have the correct level of smoothness.
Errors in the parts’ level of smoothness impact longevity as follows:
- If they are not smooth enough, there will be too much friction that will wear down the part, prematurely.
- If they are too smooth, there will be too little friction, resulting in a weak seal and poor fluid retention.
Either condition will cause the system to fail prematurely.
What is Electropolishing?
Electropolishing, also known as “reverse plating,” is a metal finishing process that can be used on virtually any metal alloy. It removes a controlled amount of metal from a surface, making it smooth and corrosion-resistant. The result is a brighter, smoother, cleaner, deburred surface that resists metal fatigue and will not attract contaminants.
How Does Electropolishing Work?
Metal parts are racked and submerged in an electrolytic chemical bath in which electrical current is introduced. The chemical bath acts as a conductor for the removal of the metal ions.
A rubber-lined tank is used to hold the chemical bath, inside which:
- On the negative (-) side of the power source, a series of copper or stainless-steel cathode plates are installed.
- On the positive (+) side of the power source, a part or group of parts is fixed to a rack made of titanium, copper, or bronze.
Direct current is then applied, which removes the ions from the metallic part and holds them in the solution. Following the electrolytic process, clinging electrolytes are removed with a series of additional rinsing and drying steps. The part is left with an ultraclean, bright surface.
It is important to note that optimal results depend on:
- Careful control over the density of the current;
- The precise chemical composition of the chemical bath;
- The temperature and agitation of the bath; and
- The length of time to which the metal is exposed to the current.
Benefits of Electropolishing Over Other Finishing Methods
There are a variety of other surface finishing methods, such as bright dip and acid pickling. However, electropolishing offers several benefits over these other methods. Perhaps the most important is the ability to ensure a precise and consistent finish across all parts. This is accomplished by precisely controlling the removal of material and the smoothness of the surface. The chemical bath used in electropolishing is much more stable for a longer period of time than a traditional acid bath, which becomes weaker and less reactive.
Intergranular attack is not uncommon with acid-only processes because they are much more volatile and can etch the surface of the parts. With electropolishing, the material removal is controlled and uniform, and is normally in the range of .0005 in. and .001 in. (.00025 in. and .0005 in. per surface). It is an effective method for removing heat tint and scale resulting from heat treating. Because the process doesn’t remove a lot of material, the hardness is not affected.
What Can Electropolishing Do for Hydraulic/Pneumatic Systems?
Piston rod performance demands a highly precise degree of smoothness for peak function, and electropolishing is a cost-effective method of achieving this level of smoothness. It is also suitable for both large- and small-volume applications. Some of the key benefits of electropolishing include:
- Removal of contaminants embedded in a surface. Electropolishing removes a thin layer of the metal’s outer surface. This eliminates foreign particulate and residue that remain after machining or subsequent secondary operations.
- Virtually unmatched tolerance levels. Optimal performance from hydraulic and pneumatic systems relies on a high degree of precision. Electropolishing can hold tolerances of +/- .0001 in.
- Ability to accommodate custom shapes and contours. To achieve the overall smoothness that your parts require, electropolishing can treat complex geometries and even sharp edges.
- High efficiency at a relatively low cost. Rather than treating parts individually, a rack of metal parts can be immersed in the chemical bath at one time.
Electropolishing Optimizes Part Performance within Hydraulic, Pneumatic Systems
Precise control over the smoothness or roughness of the surface of metal parts is critical to ensuring their oil retention and the performance of both liquid and air seals. These two key factors in extending the lifespan of hydraulic and pneumatic systems can best be achieved with electropolishing. It will not affect a metal’s hardness, heat tolerance, or other properties, and will help you realize the best possible value from your investment.
Scott Potter is the vice president of sales at Able Electropolishing Co. Inc., an electropolishing specialist. Potter manages sales and marketing efforts, which largely include educating metalworking companies about the effectiveness and added value of electropolishing, and other types of metal finishing they provide.