A process we are often asked to perform is reconditioning sheave grooves or, as it’s often called, re-grooving a sheave. To determine if a sheave can or can’t be re-grooved there are measurable geometries on the sample sheave that can definitively decide if it’s a good candidate. Contrary to popular belief, it is not a gut feeling or a subjective determination. There are a handful of other considerations to account for when deciding if a sheave is a candidate for a regroove or not.
First and foremost is measuring the material thickness under the groove seat (root thickness). On inspection, the sheave’s root thickness must have enough material to allow for the machining process to reduce all groove pitch diameters to precisely match each other. This would often be determined by establishing the rope pitch diameter of the most worn groove, assuming 1/16” additional depth, and then machining all grooves equally to the newly established rope pitch diameter.
While this step is straightforward, because of the diversity in casting shapes and geometries for sheaves, a variety of measuring techniques may need to be employed (e.g. simple calipers, micrometers, complex portable and stationary CMM equipment, or a standard ground finished shank of an end mill and a precision straight edge).
After determining whether the casting has the requisite material thicknesses to further machine it and re-groove it as necessary, there are additional considerations that may affect the outcome or the sheaves’ performance thereafter.
Firstly, there are code requirements for a sheave’s overall diameter as it relates to cable diameter. This ratio is 40:1. So, for example, if your worn sheave is 20 inches in diameter utilizing half-inch cables, the sheave is considered non-regroovable by virtue of the fact that reducing its rope pitch diameter below twenty inches would result in a sheave diameter: cable diameter of less than 40:1.
Also, sheave castings, from which sheaves are machined, are inherently softer as you machine deeper into the material. It’s important to consider this when a sheave may have already undergone a re-groove and has the proper material thickness to accommodate an additional re-groove. You may find that the material’s brinell hardness has degraded well below original specifications and would then wear unacceptably quickly when compared to the original. Also, there are sheave specifications in use today that require high-strength cables. That cable may also contribute to accelerated wear of the rope grooves if they are softer than originally specified.
Lastly, while not common, there is an elevated risk that deepening a rope groove will expose porosity or voids in the underlying sheave material that went previously undetected. While cosmetic flaws in the sidewalls of sheaves or supporting structure may be patched and/or graded a “pass” because they do not degrade the sheave’s commercial operation, a void or pore in the groove could be exposed once machining has begun and ultimately scrap the sheave.
There are objective measurements to determine the suitability of a sheave for regrooving.
Casting material is softer the deeper your machine
Voids or porosity can be exposed when deepening a rope groove
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