Superbolt® Application:
Marion 8750 Dragline - Swing Rack Segments
Problem: To
turn the massive weight of this dragline requires a large gear and 16 drive
pinions. There are 4 of this model of dragline in the world and early in the
life of the machine it was found that there was not enough clamping force
holding the
segments down. The gear is made up of 24 segments, all bolted to the
base in a circle with 22 long, highly torqued studs. There was no solid retainer
and some of the segments would slide back out of position which caused gear
tooth misalignment and subsequent segment damage. The manufacturer, at great
cost, had already replaced 28 segments under warranty on this machine alone and
had to find a permanent solution soon.
Solution: Superbolt® Inc. was approached to provide a
bolting system that would both increase the clamping force and elasticity of the
joint without having to modify the existing segments. The studs currently being
used were 1-3/4” and 2-1/4” in
diameter x 31” long. Along with the use of high
powered Superbolt® tensioners on the top and flexnuts on the bottom, Superbolt®
designed and manufactured studs that had a yield strength of 155,000 psi. The
studs were easily fit into the existing segments and tightened to 105,000 psi
stud load using ˝” air impact wrenches and hand held torque wrenches to confirm
the torque. While substantially increasing the clamping force per stud, the
flexing action of the Superbolt® tensioner and flexnut reduced stress
concentrations in the threads, doubled the elasticity of the joint and
distributed the load out to a larger area away from the bolt hole.
| 260,000 lbs preload @ 113ft-lb input on the 1-3/4” tensioners |
| 439,000 lbs preload @ 240ft-lb input on the 2-1/4” tensioners |
Marion has used the Superbolt® solution on 3 other machines, solving an expensive bolting problem.