We know that small interruptions to productive work time are a hassle that nobody wants. That is why we often find that customers will ignore the alarm notifications when vibration testing is performed on their machinery.
Frankly, we do understand the impulse. Why pull a machine out of service when everything seems, at face value, to be operating properly? The answer is that if an alarm was triggered, things are not, in fact, operating properly. In reality, bearing frequencies are far outside our hearing range. When bearings start degrading, you won’t hear it or feel it anything out of the norm. Further, once you can hear or feel the vibration, it’s too late. The damage is done.
The small pause now to correct the issue is going to save you huge costs down the road. The longer you ignore them, the greater the repair costs will be.
Understanding the Thresholds and When to Take Action
We’ve discussed unbalance before, and we will do it again in the future. This is because it is one of the biggest causes of issues in spindles, and one of the major reasons why our customers end up pulling spindles from the production line. Remember, it’s imbalance that induces impact, and slowly destroys the bearing over time. We still often see that many manufacturers will still ignore the early signs and run their spindles to failure, which is certainly not the most economical approach long term.
When unbalance is detected and addressed earlier on — by properly setting and paying attention to threshold alarms on your preventative maintenance system’s vibration sensors, for example — it could have been quickly, easily, and, most importantly, cost-effectively corrected. Keep in mind that you don’t have to pull a spindle in order to correct the balance, it could be done right on the machine.
Let’s look at the specifics. If you remove your spindle when vibration and acceleration levels hit the lower end of threshold values roughly 0.1 inches/second and 2.5 Gs respectively, you will most likely prevent extensive, costly damage. Repairs usually consist of bearing replacement and minimal grind-chrome plate-regrinding, if required at all.
If removing the spindle when vibration levels are in the upper end of their thresholds, you still reduce the potential for extensive damage and repair. This usually consists of, but is not limited to, bearing replacement and limited grind-chrome plate-regrind.
If you allow vibration and acceleration to build beyond their thresholds — 0.2 in/sec and 4 Gs — you’re looking at excessive and unnecessary damage. Repairs include, but are not limited to, bearing replacement, grind-chrome plate-regrind of shaft bearing journals and housing bores, and/or stator rewinds. All of which is completely avoidable.
Three Approaches to Maintenance and Their Average Costs
As you can see, catching issues early saves you time and money, both in terms of the ever-dreaded unplanned downtime, but also in overall maintenance costs.
Of the three primary maintenance ideologies — predictive, preventative, and reactive — predictive has been found, time and again, to be the least expensive in terms of per horsepower maintenance costs.
In fact, a study by ASME found that predictive maintenance bears an overall cost of $8/hp for industrial equipment, where reactive maintenance costs an average of $17/hp, more than 100% more. (Preventative maintenance came in roughly between the two, at $12/hp.)
Bottom line is to make sure that you have a maintenance plan in place that avoids costly damage before it happens. We have the technology and the tools today to achieve this, but it does take time and commitment from operations and maintenance management and personnel. Think of it as an investment you make today that pays dividends in the long run. And remember, don’t hit that snooze button!
At GTI Spindle, we do everything we can to get you working spindles at the lowest possible cost. That’s why every spindle that we receive is non-invasively tested for unbalance and other non-bearing related issues before any disassembly. If we confirm that unbalance (which is very often the case) or an alternate issue exists, we can save you from an unnecessarily hefty repair bill.