I have a 20" Sun Rims CR-18 rear rim. This rim has a cylindrical metal sleeve that goes through the valve hole. Not sure where that came from, as I inherited the rim with the bike when I bought it used.
When I was changing the tires after riding this bike through the New England winter, I noticed that the valve on my tube was stuck to this sleeve in the rim. I used locking pliers to attempt to wiggle the valve free, but instead, it sheared off the end of the valve and left the rest of the valve fused inside the rim.
I had to drill the remainder of the valve out. When it eventually dislodged, it released some gray powder.
What caused these two parts to fuse together like this, and how can I prevent it in the future?