A skip in West Virginia utilizes two vertical lifts to remove coal from 800 feet below ground. Each lift has a bucket that weighs 44 tons when fully loaded with coal and is guided by rails on each side to travel at a rate of 1000ft/minute. To hold the guide rails in place, standard nuts and nylon-inserted locknuts had been used to secure the rail clip to the supporting beam. The underground mine needed to perform inspections every 2 to 4 weeks in order to maintain those nut and bolt assemblies. Inspection often revealed loose nuts and bolts, which had to be frequently retightened during 16-hour shifts. The underground mine needed a solution to reduce the frequency of maintenance as well as decrease the risk of shutdown. If the nuts loosened and fell off, the bucket could jam in the shaft. If the lift was not operational, the mining operation would grind to a halt, resulting in expenses of $50,000 to $90,000 per hour.
The mining operation replaced the standard nuts with Security Locknuts. Over 600 of the 3/4 x 10 Heavy Hex Security Locknuts were installed to secure the rail clip to the supporting beam. The Security Lock nuts stay tight on all the bolted
joints. As an added benefit, the Security Locknuts can be removed and reused as needed for maintenance of other mine skip components without reduction in locking performance.