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Watching out for dynamic runout

Shaft misalignment can compromise your seals

Distorted or misaligned radial shafts can cause problems for the seals that protect your machinery. Misalignment or shaft damage can result in dynamic run out, a condition that will shorten the life of your seals and could contribute to mechanical failures. Here’s what to look out for.

Radial shaft seals play a mission-critical role in all manner of industrial, civil, and military applications, including automobiles and airplanes. They keep lubricants like grease and oil on the inside of your mechanical housing and dust particles and dirt on the outsideMisalignment of radial shafts can negatively affect seal performance and shorten seal lifespanLeaky seals can result in breakdowns and other serious mechanical complications 

To ensure your seals stay in peak working order, it’s important to watch out for problems that can result from misaligned shafts. Typically, these are a form of dynamic runout. 

What is dynamic runout? 

Dynamic runout (DRO)—sometimes called simply “runout”—occurs when the center axis of a radial shaft is not aligned properly with the axis of its housing. Industrywide, DRO is sometimes used as an umbrella term for misalignment. But at SKF, we use it to refer to radial runout, condition in which a shaft’s axis is positioned at an angle to that of its housingThis angular misalignment results in a wobble, as shown in our animation. That wobbling effect loads seal unevenly, compressing it too much and then too little, as the shaft spins.  

The DRwobbling effect is often the result of a bent radial shaft, but a certain amount of DRO might occur whenever shafts spin at very high speeds. This can exacerbate even a miniscule deviation in a shaft’s center of gravity.  

Measuring dynamic runout.  

SKF seals accept a certain amount of DRO. But to make sure DRO doesn’t become a problem, it’s important to take occasional measurements of shaft alignment. Once you’ve measured the total indicated run-out with a dial indicator, simply refer to our catalogue. There, you can find the maximum permissible figures as a function of rotational speed. If your DRO falls outside what’s considered permissible, you should check your shafts for damage, realign them or replace them as needed, and make sure your seals are not compromised.