Raw-Edge vs. Wrapped V-Belts

Wrapped belts could be considered the standard v-belt. The term wrapped comes from fabric that covers the internals of the belt, giving it a very uniform look and feel, as well as reasonably quiet operating characteristics.

 

The V-belt has become an essential component in power transmission, though this was not always the case. The first recorded mention of a V-belt appeared in The Horseless Age (1916), an automotive trade magazine. At that time, the belt was made of leather, and the publication criticized its inconsistent tolerances, noting contact angles ranging from 38° to 60°. They already recognized the importance of maintaining proper tension to take up any slack in the belt.

 

Just a year later, in 1917, the first rubber V-belt was developed. Since then, V-belts have been standardized by trade and manufacturing organizations, and their types and designs have diversified to meet a wider array of applications. From conventional or wedge profiles to wrapped or cogged designs, and a variety of materials used, the range of V-belts available today is extensive.

 

This article specifically focuses on comparing cogged (raw-edge) V-belts with smooth (wrapped) V-belts. Before examining their advantages and disadvantages, it is helpful to understand how these belts function.

 

 

V-Belt Similarities

 

V-belts transmit power through the mechanical advantage of a wedge. When properly mounted and tensioned, they can drive heavy loads and achieve high speeds efficiently. A subset known as wedge V-belts (such as 3V, 5V, 8V) provides an enhanced wedging effect within the sheave groove compared to conventional V-belts, resulting in higher tension and greater power transmission.

 

While all V-belts function on the same basic principle, their tension ratings and power capacity vary depending on the specific application and belt type. Conventional belts (A, B, C) share the same contact angle, as do the wedge types mentioned above.

 

The construction of V-belts is generally consistent: they consist of rubber layers on the top and bottom, with tension cords embedded in between and surrounded by cushioning rubber. The materials used for the rubber compounds and cords differ by manufacturer and belt model. For example, polychloroprene rubber and polyester cords are common, while more demanding or high-power applications may use aramid fibers (such as Kevlar) for added strength.

 

The key difference between wrapped and raw-edge belts lies in their exterior design.

 

Wrapped (or smooth) V-belts

 

Wrapped belts could be considered the standard v-belt. The term wrapped comes from fabric that covers the internals of the belt, giving it a very uniform look and feel, as well as reasonably quiet operating characteristics.

 

The wrap on a V-belt serves two main purposes. First, the fabric provides abrasion resistance, enhancing the belt's durability. Since the belt maintains constant contact with the sheave—often at very high speeds—this added protection helps prevent wear and contamination of both the belt and the sheave. As a result, the belt operates longer before it becomes too worn to effectively transmit power.

 

A second important benefit is related to belt slip. Although it might seem counterintuitive, controlled slipping can protect the system from damage. During torque spikes or sudden changes in drive speed, a wrapped belt slips more easily than a raw-edge belt. This slipping helps prevent harmful forces from being transmitted back to the gearbox or motor. In many cases, the belt will break before causing damage, so its ability to slip acts as a valuable safety feature.

 

Additionally, the fabric wrap offers high resistance to oil. Raw-edge belts are more prone to clogging with contaminants and absorbing moisture, which can cause the rubber to swell and eventually lead to belt failure.

 

Raw-Edge (Cogged) V-Belts

 

Raw-edge belts feature cogs along the bottom section and lack the fabric wrapping on the belt's exterior, leaving the interior materials exposed at the sides. This design increases the belt's coefficient of friction, enabling it to grip the sheaves more effectively. As a result, raw-edge belts can transmit up to 30% more horsepower at higher speeds compared to wrapped belts.

 

This boost in power transmission can have significant effects on the overall drive system. For instance, in multi-belt drives, the higher power capacity may allow the removal of one belt, which in turn:

 

- Reduces sheave size from 4 grooves to 3, lowering costs

- Decreases the drive's overall weight

- Lowers the overhung load, extending bearing life

 

Reducing overhung load means less stress on the nearest bearing, improving its longevity. While these benefits may encourage quick adoption of raw-edge belts, it's important to note that they generally come at a higher cost than wrapped belts. However, in some cases, switching to raw-edge belts can actually reduce overall application expenses.

 

Beyond increased power, raw-edge belts offer other advantages. Thanks to their cogs, they can better wrap around smaller sheaves, run cooler at high speeds, and have improved temperature resistance.

 

Finally, raw-edge belts can lead to energy savings due to their higher efficiency—typically 3 to 4% better than wrapped belts. Although this efficiency gain seems modest, it can add up significantly over time. The U.S. Department of Energy recommends raw-edge belts for energy savings, estimating that in a 100 HP motor application, annual savings can exceed 16,000 kWh, translating to over \$1,000 in cost reductions depending on electricity rates. These savings assume a properly tensioned and well-maintained belt drive.

 

Which Is Better? Smooth or Cogged V-Belts?

 

It's difficult to make a one-size-fits-all judgment because exceptions always exist. After learning about raw-edge belts, some might assume they're the obvious choice. However, raw-edge belts typically cost more than wrapped belts. For single-belt drives, there are no cost savings from reducing the number of grooves on sheaves, nor are there weight reductions that would lessen the overhung load on bearings. Thus, the extra benefits of raw-edge belts are limited in these cases.

 

While raw-edge belts do offer advantages such as higher power capacity, smaller wrap diameter, and quieter operation—even on single-groove sheaves—the additional benefits are fewer. Importantly, the ability of wrapped belts to slip more easily within the sheave is a critical feature that shouldn't be overlooked, as it protects the drive system under sudden load changes.

 

Every component in power transmission has its place, from basic to high-performance applications. Assessing the specific demands of your drive—such as torque spikes and overloads—will help guide your choice. For single-belt drives, selecting the best belt may come down to judgment and priorities. In multi-belt setups, potential energy savings could be a decisive factor.

 

There's no definitive right or wrong answer—only information to help you determine what works best for your unique situation.