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Ultrasonic Inspections on Ball Screws, Gearboxes, and Transfers

At DMAX-LTD we not only assemble the Duramax Diesel Engine for General Motors Heavy Duty Trucks, we also machine the Cylinder Block, Cylinder Head, Crank, and the Connecting Rod. Dmax tracks any downtime greater than 10 minutes on the Assembly Line and 15 minutes on the Machining Lines. With this in mind we have come up with some creative ways to monitor our equipment without invasive PM's. Ultrasound and IR are the tools we use to accomplish this task. We use IR, Ultrasonic, Vibration, and MCA at our plant. All 4 tools are used through-out DMAX. However, we have come to the conclusion that before we purchased the UE 10,000, we had no idea how much we would use it or how much money it would save us. You can use Ultrasound to check anything from a conveyor bearings to ball screws, to spindles and gearboxes, and even hard to see or reach transfer bearings.

We purchased ultrasound primarily for finding compressed air leaks. Once we started using it we discovered many other uses. We have over 1500 pumps, spindles, gearboxes and motors on vibration routes at our plant (see figure 1). We have two predictive techs, so it is not hard to figure out there is no way to check all the equipment as often as we need to with vibration. Ultrasound on the other hand is quick and when used with vibration can be effective in monitoring this same equipment. So we started creating Ultrasonic routes at semi-annual intervals and vibration routes annually (see figures 2 & 3). We trend all of our Ultrasonic Solutions 2.0 On the readings, so if we notice an increase of noise over time we do a special vibration check to pinpoint the problem. We have saved millions of dollars at DMAX-LTD using this method.

Figure 1 Gearbox CB-120

Figure 2 Gearbox Trend

Figure 3 Vibration Data

Here at Dmax we have in excess of 500 ball screws (see figure 4). For those of you who are not familiar with ball screws, they are worm gears driven with a servo motor (see figure 5). We hold tolerances in microns at our plant. Which means any ball screw failure not only effects machine production but could very easily effect quality. Ball screw motors are generally accessible on the outside of the machine so an ultrasonic check can be done with the machine running. With 500 like components trending is a snap. We have not lost a ball screw during production due to bearing failure in over two years. Even on operations where the ball screw is not assessable it only takes a few minutes to run a check and the machine is back up and operational. This is a totally non-intrusive PM.

Figure 4 Ball ScrewFigure 5Ball Screw Gearbox

If we could do it with ball screws, why not try it on hard reach or even see transfer bearings. This is where our plant has seen the most cost savings. If you loose a transfer bearing during production, you are probably looking at least 8 to 24 hours repair time and even more downtime depending on the machine. We have many multi station transfer machines, replacing the bearings, bushings, support arms, brackets, and even the transfer bar itself costs ten's of thousands of dollars. Twice a year we empty the machine and perform an ultrasonic PDM. It takes about an hour on each machine and we trend all the transfer components (see figures 6 & 7). This is a totally non-intrusive PM and the hour of downtime can be planned so the machine has a bank to run during the check. We generated follow-up work based on our trends, so we may only need to replace one bearing and it was caught before we lost the bushing or the support arm.

Figure 6 Transfer GearboxFigure 7 Transfer Bearing Trends

We have had some great success with Ultrasound here at DMAX-LTD. We have also learned some valuable lessons a long the way. We aren't always going to be right. You can trend and analyze all the data, but you are still going to miss diagnosis every now and again. We are human and we miss things! 500 ball screws is a lot of ball screws and a lot of trending. Excel spreadsheets can be your friend and your enemy. Keep an open mind, try all your PDM tools on all components. See what fits best. The technologies work best when they are used together to identify problems and their solutions.

In conclusion let's look at some hard facts. Non-intrusive PM's are the key to keeping production running without excessive downtime and still maintain the machinery's integrity. Trending is the key ingredient to using ultrasound effectively. Trending specific components enables maintenance to replace only those components nearing failure. By finding failures before they are critical, companies not only save money by not having collateral damage, the job is planned so downtime is minimal. Parts are ordered well in advance, so no special shipping charges apply. Parts are ordered when they are needed. Inventory is kept to a minimum. At Dmax using Ultrasonic in 2008 we saved $13,421,714, in January 09 we saved $481,248, in February 09 we saved $344,935, in March 09 we saved $2,436,205, and in April we saved $481,248 (see figures 8 & 9). We had a return on our Ultrasonic investment within 1 month of it's purchase. The bottom line is that Predictive works. It saves time and money, not to mention improves quality and safety. What is the worst that can happen? It may no not work, oh well you tried. What is the best that can happen? You could save your company hundreds of thousands of dollars with just one find! Predictive Technologies really can make a difference and impact your plant in a positive way if you are willing to think out of the box and give it a chance.

Figure 8 2008 Cost Savings  Figure 9 2009 Cost Savings 

Article provided by: Deborah Hays

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