Pedestal Work, Aug 16, 2007


Operations were suspended at the end of June to allow for replacement of the main azimuth bearing. The pedestal is a big heavy item (24,000 lbs) which requires a certain amount of heavy lifting to replace the azimuth bearing. Fortunately, we were able to use NCAR's Marshall lab high bay garage so much of the work could be conducted inside. The CHILL pedestal uses a king-post design with a cross-roller main bearing at the top of the king-post, and a radial roller bearing about two feet below to resist the overturning moment.

When the main bearing was removed it was found to have indeed failed and was shedding hardened metal flakes. Since the recirculating oil lubrication in use at CHILL would likely take these metal flakes through the lower bearing also, the entire rotating part of the pedestal was lifted off to expose the lower bearing. The lower bearing did show the imprint of the metal flakes on the bearing surface, so a replacement was sought. This two piece bearing proved impossible to find in stock, but Jack Fox and Karl Schwenz of NCAR's Design and Fabrication Service were able to adapt a standard ball bearing to the kingpost. This one-peice ball bearing proved more difficult to install than the original, but it is now in place and appears to be working well.

The sliprings have to be removed to replace either of the azimuth bearings. Upon inspection, it was found that the lower slipring bearing had completely failed and taken out several of the lower brushes as well. Since these sliprings had been in service for 35+ years, they were sent back to the original manufacturer (Fabricast) for refurbishing. The bearings were replaced, the rings were polished, and the brushes were replaced restoring the unit to like-new condition. The only downside of the refurbishment is that it took about 8 weeks to complete.