Sheave Basics:
Sheaves are widely used throughout the industry for a variety of pulling and lifting functions. Sheaves are available in a variety of materials including steel, plastic, or stainless steel. There are many configurations available including HiLoad sheaves, LoLoad sheaves, fibrous rope sheaves, and wire rope sheaves. You can source sheaves with bearings or bushings and some sheaves come very specialized.
Specifying a Sheave:
To specify a sheave you must consider design, quality of components used, type of groove, working load limits, annual usage, and the application.
HiLoad vs LoLoad Sheaves:
HiLOAD indicates a premium, larger diameter sheave suitable for 180° degree rope turns (see Figure 1) with a high D/d ratio, which is the ratio of the diameter around which the rope is bent, divided by the body diameter of the rope (see Figure 3). LoLOAD indicates a smaller diameter sheave designed for economical small deflection turns less than 90 degrees with a lower D/d ratio (see Figure 2).
Wire Rope vs Fibrous Rope Sheaves:
Wire rope sheaves have a narrower tapered groove and fibrous rope sheaves have a wider rounded groove to capture the rope (see Figure 4).
Stainless Steel Sheave Working Load Limits:
Work load is important for both wire rope and fibrous rope sheaves, but work load limit (WLL) is critical with wire rope sheaves due to the comparative increased capacity of wire rope.
Quality sheaves should meet ASME B30.26-2610 and exceed the minimum 4:1 design factor. In most instances, the WLL for Suncor sheaves is significantly higher than comparable products and proof loads (or max WLL) are twice the WLL. Generally, twice the WLL of the wire represents the wire maximum load with a 180° wire wrap around the sheave.
Stainless Steel Sheave Wear and Design:
A critical, and often overlooked area, is the wear exerted on the sheave during use. Throat angle, groove diameter, and sheave size are three significant factors of wear for sheaves. Sheaves are often designed with thin straight sided grooves which can cause scrubbing on the side walls and unnecessary wear on the rope and the sheave (see Figure 6). Suncor’s sheaves were designed with wide sheave grooves that provide a proper throat angle to permit slight rope lead misalignment without damaging the rope or wearing the sheave groove (see Figure 5).
The groove diameter is critical for proper wire rope support under load and has a significant effect on the overall safety and lifespan of the sheave and rope. If the sheave groove diameter has too much clearance, it will not support the rope properly leading to distortion, increased fatigue, failure, and costly repair. Conversely, if the sheave groove diameter has too little clearance the rope will not fit properly causing excessive wear and accelerated abrasion, which results in lost performance (see Figure 7).
In conclusion, when specifying stainless steel sheaves, you should:
- Identify your use and material, wire rope or fibrous rope, and size.
- Confirm sheave manufacturer qualifications and the specifications the sheaves meet.
- Identify your application as HiLoad or LoLoad.
- Identify the sheave mounting diameter and if you want bearings or bushings. If unsure, ask the manufacturer.
