We have developed a unique online tool, called the Piston Rod Predictor, to compare the resistance of different steel grades to buckling in piston rod applications. The emphasis is on buckling because it is the key design consideration for hydraulic cylinders, especially in single-action, push-only applications.
Buckling is a sudden, large and unstable lateral deflection associated with just a small increase in axial compressive load above a critical level - the buckling load. The stress corresponding to the buckling load can be far less than the yield strength of the material used to manufacture the rod.
Should buckling occur, it will result in instability and collapse of the piston rod. Buckling is therefore regarded as a highly dangerous failure mode that might result in serious accidents.
Using steel with higher strength provides better resistance to buckling. That offers the possibility to downsize piston rods, with a consequent reduction in both weight and cost. Ovako manufactures a range of hard-chrome-plated or nickel-chrome-plated ready-to-use bars and tubes, known as Cromax® developed specifically for hydraulic cylinders. The Piston Rod Predictor enables you to compare our Cromax steel grades with the most commonly used standard grades. If the grade you wish to compare is not listed, you can still enter its relevant mechanical properties manually.
You can use the Piston Rod Predictor in two ways. You could choose to use input an existing rod diameter to calculate what diameter would be required to achieve the same safety factor with an alternative steel grade. Or you could keep the diameter the same, but evaluate how using a stronger steel intended specifically for piston rods might enable the design load to be uprated.
Alternatively, you can use your maximum load and desired safety factor to calculate the minimum rod diameter for different steel grades.