Judging Rod Straightness
While dealing with the bent hydraulic cylinder rods, the first and foremost thing is to check the rod straightness. The best time to check rod straightness is the time when the the hydraulic cylinder being repaired or re-sealed. The rods should be placed on rollers the run-out has to be measured with a dial gauge (as shown in the figure below). The rods are needed to be positioned in such a way, that, there is maximum possible amount of gap between the rollers (L). The mid-point run-out time is then measured between the rollers (L/2).
Calculating Run-Out
Though the cylinder rod should ideally be as straight as possible, but still a run-out of 0.5 millimeters can be managed and thus, is considered as normal. Maximum permissible run-out time (measured at L/2) can be calculated using the following formula:
Run-out max. (mm) = 0.5xL/1000
[here, L is equal to the distance between rollers in millimeters]
This can be understood with the help of an example, where the distance between the rollers is 1.2 meters then the allowable or acceptable run-out would be measured as:
0.5 x 1200 / 1000 = 0.6mm
which means, that a 0.6mm run-out is acceptable with the rollers having a difference of 1.2 meters.
Potential Solutions
Most often the bent rods are straightened in a press. At times, the hydraulic cylinder rods can be straightened without any damage to the hard-chrome plating, but in case the chrome is damaged, the ultimate solution is to either replace or re-chrome the rod.
While tackling a bent rod, it is always wise to compare the actual rod loading with the permissible rod loading as per the tensile strength of the rod material and cylinder's mounting arrangement. The obvious solutions in case of rod load crossing permissible load is, either a new rod of higher tensile material or increased diameter of the rod to prevent it from bending.
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