Excessive Gearbox Wear

Published:  22 May, 2007

The answer to this month's trouble shooting teaser is supplied by Bob Orme of Henkel.

 

Q: 

We have a gearbox that has excessive wear between the bearing and output shaft. We are able to get hold of a new bearing, but a replacement shaft is only available with a long lead-time.  Our production schedules are such that we simply cannot afford the time to wait. Is there a way of re-using the worn shaft so the unit can be back in production with the minimum of delay?

 

A: 

There are three options, depending on how much wear has occurred. Where small gaps - say, up to 0.08mm - are involved, a regular anaerobic retaining adhesive can be applied to both surfaces of the assembly and the parts reassembled.  For gaps up to 0.50mm, what you need is a non-running anaerobic adhesive gel that can be smoothed on to mating surfaces to fill imperfections in the shafts.  Being anaerobic, these materials only harden when the metal parts are brought together and all oxygen is excluded from the joint.   Although these adhesives contain no metal, once assembled they harden to create a joint that can have up to twice the strength of a press fit. The repair with either of these methods can be carried out without fully dismantling the assembly and will less than 12 hours. For larger gaps, the answer is to use a meal-filled epoxy. The adhesive is applied to the shaft to a level just above the desired measurement. After the adhesive is cured, the repair can be machined to the required dimensions. Once this has been achieved, the joint between the shaft and gear should be retained using the anaerobic gel already mentioned. In all, this is a 24 hour job.