Does your facility suffer from SCL and maybe you don’t know about it? It’s an insidious failure mode that might be causing you grief and you may not know about it or maybe you have just come to accept it as part of doing business.
We were working with a brewery and we asked the students in the reliability class what their most common failure mode was. The answer from the crew of mechanics … “SCL”. We had never heard the acronym before, but were intrigued, and of course since they had given this failure mode an acronym, we knew that it had to be real. So, what is SCL? Answer: Stuff Comes Loose… just the students used a different “s” word, one that is a little more descriptive and emphatic, but you get the idea.
When it comes to threaded fasteners, we should not accept that stuff coming loose is normal. Nor should we go and get the Loctite, split washers and a different grade of bolts. SCL is an indication that there is both a gap in knowledge and in procedures on how to correctly and consistently tighten threaded fasteners. There is a lot of science involved in correctly designing a bolted joint, and it would be pretty straight forward if not for the friction we have to overcome between the threads and between the head of the bolt and the washer. Eighty five percent of the force used to tighten a bolt is lost due to overcoming the friction forces and only fifteen percent of the force goes to actually stretching the bolt which provides the clamping force.
Check out this video on some bolt tightening ideas and don’t forget to check out the app stores for the free Reliability Solutions App that has access to over fifty practical and applicable reliability how to video