justloveplanes From United States of America, joined Jul 2004, 1146 posts, RR: 1 Posted (2 years 11 months 1 week 5 days 21 hours ago) and read 3713 times:
This is being discussed elsewhere, but I wanted to dig deeper into the following question:
Did GE change their coating process for the shafts on the GEnx? If so, why, what was the target benefit? Obviously they have alloys and process from the past that are reliable. Is GE regressing to previous practice to solve the current issue?
MarkC From United States of America, joined Apr 2006, 259 posts, RR: 0
Reply 1, posted (2 years 11 months 1 week 5 days 20 hours ago) and read 3688 times:
I am not familiar with the GENX, but I have overhauled this part on the PW4000 and GP7000. I have been out of the business for 4 months and did not hear about this. Wow, thats bad.
In reading the related articles it appears that GE is making a change to the antigalling compound that goes on the splines and the threads of this part. It mentioned that they are going to change to one that has more lead. Apparently, this caused galvanic corrosion. This happens when dissimilar metals are in contact with each other. This part is made from titanium, and mates with the nut and LPT shaft, which are steel. Also mates with bearings. This part is not coated on the shaft. Just antigall on the splines and threads. LPT shafts are coated, but not on the splines. The splines also have antigall.
PW uses several types of antigall coatings on their engines, depending upon application. Looks like GE chose the wrong type initially. Maybe they changed the alloy of one of the parts from a previous engine which they were familiar with, and assumed it would work the same.