Science of Straightening Bent Steel

There are multitudinous ways in which a bent shaft can occur. Some of the most common ways that steel shafts are bent are damage during shipping, through rigging or operational activity. There are several shaft straightening method that when conducted properly, will allow a company to salvage a shaft that might otherwise have to be discarded. This can be more challenging than it sounds. One of the primary reasons that it can be so challenging is the fact that there are so many different variances that must be considered that shaft straightening has become the culmination of art and science.

Defining a Bent Shaft

Okay, here is the scientific side of the equation. When a shaft is perfectly straight, the center of the shaft cross-sections from end-to-end on a perfectly straight line. A shaft is considered bent when its axis is different than the axis of rotation.

Some of the negative consequences of operating equipment with a bent shaft are:

• The vibration of the equipment due to an imbalance caused by the bent shaft
• Material fatigue
• Contact and possible seizure of movement with close-clearance surfaces
• Significant bearing damage
• Seal and coupling damage
• Misalignment of the shaft

The Best Method of Bent Shaft Straightening

Here is where the art joins the science. With all of the technology and machinery available today, there is no simple solution to straightening a bent shaft. There are so many variables that must be considered that a cookie-cutter approach does not work. This means that a method that is successful is straightening a bent shaft in one instance may not work in another.

Generally speaking, the most successful method will be one that requires straightening press and the fewest steps or corrections to achieve the level of straightness that is desired. The less that the shaft is manipulated the fewer stresses to the shaft. The more that a shaft is stressed during the straightening process the more the chance of creating additional issues that will totally negate the benefit of straightening the shaft.

When an ideal shaft straightening is done, the process will actually work to relax the stresses that resulted in the shaft being bent in the first place. So, this means that the straightening is not only done to reestablish the straight line of the shaft’s axis, but to also reestablish the integrity of the shaft. When the integrity is not addressed at the time that the shaft is straightened, it can result in the repeated failure of the shaft.

What determines if a Successful Straightening is Feasible?

There are a number of variables that determine whether or not it will be possible to achieve a successful shaft straightening. Some of the most prevalent considerations are:

• Cause of the bend — which is one of the most important variables to consider. For instance, a shaft that was bent due to mechanical overload is much easier to diagnose and ultimately straighten when compared to other types of bends.
• Type of bend — is an equal consideration. The manner in which the shaft is bent must also be considered. A shaft with a single deflection will be much easier to repair than one with multiple bends.
• Shaft material and design — are also important. The type of material that the shaft is made from may not stand up to the stresses of straightening. The design may also inhibit effective and accurate straightening.

Straightening a bent shaft requires a hydraulic straightening press and skill, expertise and eye that only experience can create. The good news is that a significant number of bent shafts can be straightened. The cause for concern is that not just anyone can do it right.