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How to Select the Right Type of Wire Rope Pulley

How to Select the Right Type of Wire Rope Pulley

Tuesday, October 12, 2020
Posted in: Pulleys & Sleeves

Pulleys make up some of the most crucial and reliable devices used with mechanical cable to actuate and redirect motion. Pulleys may guide a cable's motion or reduce the amount of work needed to lift or move a given load. Pulleys are used across a massive amount of motion control devices, instruments, machinery, aircraft, vessels and vehicles. More simply put, pulleys are among the most essential components found around the world to help achieve and facilitate mechanical motion. 

It is not an overstatement to say that pulleys have kept you and everyone you care about safe and even alive in the time you have been on earth.

Making Pulleys

Pulleys are manufactured from various materials, including many industrial plastics and a variety of metals. When advising mechanical engineers on the right pulley choice, the pulley manufacturers must advise on the diameter of the pulley, to ensure that the right size is paired with the right mechanical cable. Doing so, ensures prolonged cable life and reduces the potential for a mechanical failure to occur within sensitive, mission-critical or even life-saving motion control systems. However, not all manufacturers can produce the quality of cable pulleys that Carl Stahl Sava Industries has for 50 years now. 

If you are in the market for a cable pulley, the following guide will help you make the best decision.

Diameter of the Pulley

No matter the pulley's application, size plays a vital role in determining the quality and performance of the motion control system. For any application, pulley specifications are determined by several factors, including the cable's diameter, its construction and the load it’s meant to support. 

The pulley’s groove diameter and its radius play into the overall size considerations when pairing a pulley with mechanical cable. Too wide a groove and the cable may fail prematurely. Too narrow, and the cable may be pinched and fail prematurely.

There are recommended groove diameters-to-cable diameter ratios for each cable construction.  Most flexible cables, such as a 7x49 construction suggest a 15x ratio to maximize life. As stranding constructions simplify, the ratios increase. For instance, 7x19 wire rope has a 25x ratio, while 7x7 cables have a 40x ratio. Use these ratios as a basis for maximizing the cable life. But this is only one variable that needs to be carefully balanced along with the load requirements and materials used.

Getting the mating of the pulley and cable correctly configured requires mechanical design engineering experience that Sava’s been perfecting for five decades. Ask us to help you get this critical detail just right.

Trade-Offs

 Although a pulley with a large diameter is more efficient, it has increased costs, weight and bulk, compared to one with a smaller diameter. The main tradeoff that happens with pulleys is usually that small pulleys wear out cables much faster. 

On the other hand, large pulleys are not suited for most applications. Using a pulley that is bigger than the required size is mainly disadvantageous when it comes to the costs involved and the space required. 

Engineers can design a pulley that will fit a particular application’s requirements. Many times, designers and manufacturers do not allow for a large enough pulley, for example, which will limit the cable's life span. It is therefore important to maximize the pulley’s groove diameter wherever possible for maximum service life as suggested by the pulley ratios.

Lubrication & Abrasion

If you find that your cable is failing too quickly in your application because the pulley is too small, the cable’s life may be extended by lubricating it. Sava lubricates all of its miniature stainless steel cables that are extruded with nylon. If you find that you've been using a small pulley for the wrong application, you can extend the cable's lifespan by lubricating it. By lubricating your mechanical cables, you will ensure you get as much as twice or three times the life of an otherwise single lifespan cable if the pulley is small. 

If possible, cables and pulleys should be selected to avoid metal-to-metal contact. Too often, such combinations result in premature cable malfunction due to abrasion. Coated cables are suitable where metal pulleys are involved while bare cables are suited for plastic pulleys. 

Get In Touch With Us

 If you're looking for high-quality wire pulleys, trust the industry experts at Sava and view our catalog of cables, fittings and tools. Our sales and engineering expertise gives us an edge and allows us to meet your cable needs. Contact us today and let us guide you.

October 12, 2020