The piston rod — simple, yet critical

The piston rod — simple, yet critical

Not much can go wrong with a hydraulic cylinder. As long as they are designed properly for the application, they should provide years of rugged, trouble-free performance. When premature failure does occur, it’s usually from unforeseen conditions or misapplication.

The piston rod is a fundamental and critical component of every hydraulic or pneumatic cylinder. The piston rod typically is a precision machined length of hard chrome plated cold finished steel bar which transmits the force created by the piston to the machine component doing the work. Although a vital part of the hydraulic cylinder, the rod is often taken for granted — until a problem arises.

The biggest enemy of any cylinder is seal or piston rod failure. A major cause of this failure is rust or other corrosion, which can dramatically drive up costs through:
• higher frequency and cost of warranty claims,
• lower reliability of the machine in the field, which can degrade customer satisfaction, and
• degraded loyalty to your brand, stemming from both of the above.

Proper selection can make the piston rod made from chrome plated bar a big difference to your bottom line. Recognizing the critical nature of this component, manufacturers of chrome plated bars have taken on the corrosion resistance challenge.

Rod producers have continually addressed this issue through the years. Technological and process improvements, coupled with individual innovations, have advanced the corrosion battle to a point today that was not imaginable 25 years ago.

Hours of salt spray testing without failure, which is the accepted benchmark for corrosion resistance, has increased almost exponentially. Twenty-four hours was the norm in the 1980s. But today, results to 1000 hr and beyond can be routinely achieved.

Twenty-five years ago, a seven-year replacement cycle for piston rods was an acceptable practice. Today, the expectation of some piston rod manufacturers is for their products to outlive the machine they power. The piston rod performance bar has indeed been raised!

If you make your own cylinders, the price of the piston rod should not be the main purchasing consideration. In the event of failure, the previously mentioned warranty costs, brand loyalty, and down time considerations can quickly turn the tables on any cost advantage of low-cost chrome plated piston rods. It is recommended that you explore the total value equation in procurement rather than just the initial savings.

Total process consistency
The ultimate goal in the corrosion battle is to extend salt spray time corrosion resistance qualities of the product you are buying. In this case, more is better. Higher salt spray results begin with the raw material. The supplier’s dedication to reducing variability throughout the process makes a big difference. Points to consider include:
• steel bar preparation — who turns and grinds the material, and to what quality level?
• chrome plating and hardening process controls, and
• machining of finished piston rods.

Each of these steps — the base product, the chrome plating solution, the polishing, and handling — bears periodic review and updating of your piston rod specifications. Benchmark the industry’s salt spray testing, verify the results, and specify the latest technology available.

Global application
Today, every company that builds a hydraulic cylinder participates in a global market. The company that uses the old accepted product in today’s environment is at a disadvantage and risks excessive warranty claims and deterioration of brand identity and loyalty. The current tight economic conditions present the opportunity to help to differentiate the design of the piston rod.

This information was provided by Steve Schaus, vice president, engineered products at Industrial Hard Chrome, Geneva, Ill., which produces ChromeXL chrome plated steel bar. Call him at (630) 208-7000 or e-mail [email protected]