July 2006 - The Risks of Non-OEM Spares

Big Risk for Small Savings

We recently received an emergency request for a new crank assembly from one of our valued customers.  They were in a bind due to a run of third party reworked cranks that had failed on their Ragsdale Bodymakers.

The customer supplied me pictures of their latest failure, which in their own words, “was lucky not to have caused personal injury” to any of their plant staff when it failed.  The offending reworked crank sheared off after the bearings, allowing the whole flywheel to fall at operational speed into the guard!  It was most fortunate that the guards and the clam shell brake managed to retain the assembly, which weighs approximately 2.5 tons.

You can clearly see the point of failure in the first photo.  It is at the end of the keyway at the top left and is indicated by the ‘circular pattern’ on the metal.  But equally important is the fact that there’s obvious evidence that prior metal fatigue had already taken place in the discolored area.

Cranks have a certain life expectancy, and as such, reworking them after ear breakages or other problems should be avoided.  Dye penetrant checks are unable to detect metal fatigue, and only show obvious surface cracks.  This is made worse if there are any fitting errors, which can set up abnormal stress in the shaft and keyway areas as shown in the photographs.

On this occasion, the customer was very fortunate that no one was injured and that we had spare crank assembly that we could ship within 24 hours so that he could recover and have a spare.  Not a risk worth taking!
 
The problem with reworking crank assemblies is that in the absence of new manufacture process and its associated inspection techniques, it’s not possible to guarantee part integrity. The repercussions of catastrophic failure on plant personnel and equipment can be significant.

If you have any questions please call me anytime, or e-mail me at the address below.

Graham Price
VP Technology & Spare Parts
Stolle Machinery LLC
Phone:  303.708-5153
Cell:  720.934-9007
Graham.Price@stollemachinery.com