Murphy and the art of motor maintenance
Dayton Electric Motors have been manufactured since 1937. To celebrate their 75th anniversary Grainger, Inc., Dayton’s owner and exclusive distributor, set out to find the oldest operating Dayton motor in industrial use. The winning entry belonged to Daniel Williams, proprietor of the Letterpress Service Agency in Houston, Texas.
Daniel’s Dayton motor originally powered a free-standing fan that was used in his grandfather’s shop, beginning after its manufacture in the late 1940s. After a long career driving the fan, the motor spent some time in storage until it was acquired by Daniel and placed back into service running the fan. More recently the motor was removed from the old fan and retrofit to power an even older Ludlow Typograph machine. The Typograph casts large-sized lead type for book binding and other special applications.
The Dayton, a 1/10 horsepower unit, replaced a worn out ¼ horsepower motor on the Ludlow and is still working today. Daniel characterizes the retrofit as “kind of outrageous.” Daniel is correct.
|J. Stanton McGroarty, CMfgE, CMRP, is senior technical editor of Plant Services. He was formerly consulting manager for Strategic Asset Management International (SAMI), where he focused on project management and training for manufacturing, maintenance and reliability engineering. He has more than 30 years of manufacturing and maintenance experience in the automotive, defense, consumer products and process manufacturing industries. He holds a bachelor of science degree in mechanical engineering from the Detroit Institute of Technology and a master’s degree in management from Central Michigan University. He can be reached at firstname.lastname@example.org or check out his Google+ profile.|
Daniel’s Dayton drives the Ludlow through a flat belt from a home-made motor mount, so alignment is most likely imprecise. Lubrication has been whatever was provided to a fan in a Houston print shop since 1949, followed by whatever is provided to a replacement motor sitting just above the floor in the same environment.
We can safely characterize the reliability strategy for the motor as “run to failure.” Vibration analysis, thermography, tribology, ultrasound testing and any other PdM have not been part of the maintenance program supporting Daniel’s Dayton. The term “precision maintenance” did not occur in the article about the oldest motor.
In the preparation of this report, I reviewed the case of the oldest motor with a couple of independent engineers. Our total experience exceeds 100 years and an immense quantity of lager. The conclusion of this august body is that some equipment runs forever just to annoy us. This finding may even support a new corollary to Murphy’s Law, stating that some equipment will refuse to wear out just to discredit the rules of reliability.
The panel also achieved consensus around the notion that, if you’re looking for equipment that is just too ornery to die, Houston is probably a good place to start. Better yet, make it summer in Houston. That’ll weed out the weak ones.
The reliability of this motor actually does not surprise me at all, not even considering that is took the place of a motor 2.5 times its rating. Blame it on period technology. Efficiency and precision have improved over the decades since this motor was manufactured, but nothing beats the design fudge factors used in the slide rule days to improve longevity. It was not uncomon for a motor to be capable of twice its rated load without overheating. Bearings were much beefier too. It was also considered good practice to specify a larger motor than needed to power a particular piece of equipment. I have often requested that motors of 60s vintage and older be rebuild instead of replaced simply because they will withstand a lot more abuse and inattention than their modern counterparts. This is not to say that I don't believe in progress. Todays motors are more efficient, smother running, lighter weight, and less expensive to manufacture. However when the cost of a new motor is higher than the combined cost of a rewind and the net present value of the energy savings, why throw it out?