By now, if you’ve kept up with the VibrAlign balancing “how-to” blogs, you should see that balancing is mostly just a math problem – counteracting forces. But we haven’t discussed when the balance job is through.
When I started balancing fans many years ago, I stopped balancing when:
None of these are very scientific, so let’s look at some specifications.
ISO 1940/1 covers balance grade qualities for many different types of machines – from slow-speed reciprocating engines, all the way down to gyroscopes. In the cases of most industrial machines, the specification is G 6.3. The 6.3 denotes the amount of residual vibration at running speed, in mm/sec.
Some high speeds applications, or electric motors operating “stand alone” might specify a G 2.5, or 2.5 mm/sec.
These are quite achievable, in most cases, IF unbalance is the only vibration at 1 times the rpm, and the machine is not operating in resonance. But there are other sources of vibration that manifest themselves at 1 x rpm, such as misalignment, a bent shaft, looseness, and so on.
So, how do you know “when to stop”?
Balancing is both a mathematical, and a logical process. If you add a correction weight to the right spot, you should expect the vibration to drop, and the phase angle to stay relatively steady. Even a trim run should be predictable. But if the vibration amplitude or phase does not perform as expected, look for:
Lastly, most manufacturers of machinery specify balance quality for their machine. You should balance to the manufacturer’s recommendations.