Sheaves The condition and contour of sheave grooves have a major influence on rope life. The grooves must be smooth and slightly larger than the rope to prevent it from being pinched or jammed in the groove. The more closely the contour of the groove approaches that of the wire rope the greater becomes the area of contact between the two. This minimizes rope distortion, bending fatigue and eases sheave rotation. If the groove diameter is too large, the rope will not be properly supported and will tend to flatten and become distorted. This accelerates bending fatigue in individual wires and can cause premature failures. If the sheave groove is too narrow for the rope the operating tension will draw the rope deeply into the groove, causing it to be pinched and subjecting both the rope and sheave to severe abrasion. This condition can arise if new ropes are installed over old sheaves. One of the fastest ways to ruin a rope is to operate it over small sheaves. The excessive and repeated bending and straightening of the wires leads to premature failure from fatigue. Use the maximum possible diameter of sheave that the equipment will carry. Inadequate lubrication or a sheave that is too heavy for the load will cause the rope to slip in the sheave whenever the rope velocity changes. The momentum of the heavy sheave will cause it to continue turning after the rope has stopped. This grinding wheel action causes severe rope abrasion and will wear flat spots in the sheave that further damages the rope. If the sheaves are carrying ropes that can be momentarily unloaded, as in the case of a hoist line, then the sheave must be equipped with cable-keepers that prevent the unloaded rope from leaving the groove. Badly worn sheaves have an adverse effect on rope life and must be examined at regular intervals. Inspect the sheaves carefully for any sign of cracks in the flanges. If the flange breaks off it will allow the rope to jump free with disastrous results. The groove surfaces on sheaves should be perfectly smooth. Those which have taken the imprint of the outer wires will exert a grinding action on the ropes. Each sheave is to be examined for the following: - Groove depth, width and contour. - Groove smoothness. - Broken or chipped flanges. - Cracks in hubs, spokes, etc. - Signs of rope contact with guards. - Sheave bearings and shaft. - Out-of-round condition. - Alignment with other sheaves. A Few Tips: - Do not hesitate to remove the sheave and inspect. - Remove the pin and its securing mechanism. - Remove the bushings / bearing race if you can do so without damage. Look for scoring of the bushing and free rotation of the bearing race. Replace if you think necessary. - Clean all components completely before inspection. - Inspect the entire sheave, and its supporting pin. - A sheave badly corrugated by the rope's "print", a condition which could seriously damage the wire rope. - Ensure the greaseways and grease nipples are clear and free. Replace the grease nipple if necessary. - Hang the sheave from a piece of twine and tap it with a hammer. It should ring - if not it may be cracked. - This is also an ideal opportunity to take photos of, or sketch, anything unusual. This may be of use in the future. - Make notes of what you found, where you found it and what, if anything, you did about it. - Measure the groove with a groove gauge. - A proper fitting sheave groove should support the rope over 135-150 degrees of rope circumference. Observe the groove so that it may be clearly seen whether the contour of the gauge matches the contour of the bottom of the groove. - Measure the cross-section of the pin in at least three places to record wear. - Grease it well and re-install. - Ensure the cotter pin or other securing mechanism is in good condition. - Wire Rope Industries web page Inspecting Sheaves. Refer to the Construction Safety Association of Ontario "Rigging Manual", Chapter 4, Rigging Hardware - Sheaves.