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Selecting V-belts and V-belt pulleys

Basic knowledgeTransmission

V-belts and V-belt pulleys are basic components of belt drives and are used in many mechanical systems in the industrial sector. Belt drives transfer rotary motion, torque, and power from a drive element to a driven element. In contrast to toothed belt drives that transfer power with an interlocking mechanism, belt drives work in a friction-locking manner. It is characteristic of belt drives that they ensure efficient friction-based power transfer and a longer service life while simultaneously providing a simple bearing arrangement.

General description of V-belts

The function of a V-belt is based on the friction-locking connection between the belt and the rotating V-belt pulleys. The rotational movement of the driven belt pulley is transferred to the V-belt.

Compared to a flat belt drive, the wedge-shaped design of the V-belt enlarges the surface area between the belt and the pulleys . This increases the friction connection and thus the force transfer efficiency through increased friction. The tapered wedge shape also supports centering the belt on the belt pulleys.

A V-belt is a flexible band made of rubber or similar material with a wedge-shaped cross-section. In a belt drive, a V-belt pulley is attached to each of two rotating shafts. Both shafts are connected to each other by a V-belt running in the V-belt pulleys. An additional V-belt tensioning roller exerts the tension on the belt required to transfer force.

V-belt function

The main function of V-belts is to transfer the rotational movement and torque from a belt pulley or a drive pulley to one or more belt pulleys or wheels. Other functions include:

  • Transfer of force: V-belts transfer the mechanical force from one belt pulley to another.
  • Speed ratio: The gear ratio between drive and output can be controlled by selecting belt pulleys with different diameters, allowing for adjustment of speed and torque.

V-belt types

There are different types of V-belts that can be selected depending on the application. The classic V-belt with V-profile is widely used in vehicles and industrial systems. V-belts with variable speed are designed so that they can vary in speed by moving them to different pulley diameters. The belt pulleys are, for example, adjustable or conical in shape to change the effective size of the belt pulleys. V-ribbed belts are a mix of flat belts and V-belts, wherein several V-profiles are arranged next to each other on the belt surface for effective frictional connection. They are especially suitable for modern vehicles and air conditioners. High-performance V-belts are reinforced and designed for demanding applications and extreme ambient conditions. MISUMI covers a variety of options with its range of belt pulleys, idler pulleys and V-belts.

Difference between toothed belts and V-ribbed belts

Toothed belts (also: synchronous belts) are drive belts with a straight profile or a toothed profile (serrated or toothed) on the inside. These teeth engage in corresponding grooves on the belt pulleys. As a result, they enable an interlocking, slip-free transfer of the rotary movement and a precise positioning of driven components. This means that toothed belts are used in applications that require precise time control or synchronization, such as motors, printing machines or CNC machines.

  1. V-belt, toothed
  2. V-ribbed belt
  3. Narrow V-belts
  4. Composite V-Belts

Although V-ribbed belts also have flanks, they belong to the category of belt drives and transfer power with a friction lock. V-ribbed belts have a flat transverse profile on the outside with several parallel grooves on the inside. They are flatter and wider than V-belts due to their design. In general, an Idler Pulley is also installed on V-ribbed belts. V-ribbed belts are often used when dynamic force transfer is required at high speeds coupled with high transverse stiffness.

Measuring the length of the V-belt

The dimensions for the belt length and the cross-section can be taken to determine what V-belt is required. The belt length is divided into three lengths: Outer length, inside length and the effective length or overall width:

To measure the length of the belt, place the tape measure around the outer ring for the outer length and around the inner ring for the inside length. If the belt is torn, the effective length can be determined by measuring the total length.

In addition to the length of the belt, the cross-section (width and height) can be measured. Since the numbers are specified differently depending on the profile, there are V-belt tables for conversion.

V-belt wheels and belt pulleys

The v-belt wheels, also called belt pulleys, are responsible for the efficient transfer of force and for transferring the rotary movement from a drive source to a driven element.

V-belt function

The main function of V-belt pulleys is to transfer the movement and power from the drive shaft to the V-belt and from the V-belt to the driven element. They are designed to guide the V-belt securely and to maximize friction between the belt and belt pulleys. The profile of the belt pulleys must correspond to that of the V-belt, e.g. wedge-shaped tapering, in order to ensure a reliable friction connection.

Selecting the correct V-belt wheels

Several factors must be taken into account when selecting V-belt wheels. The diameter ratio of the two belt pulleys affects the gear ratio and the speed of the driven element. For example, a larger belt pulley on the drive side leads to higher circumferential speeds of the belt. It is also important to select the correct belt pulley profile to ensure optimal power transmission. High-quality materials and surface finish contribute to durability, while the number of belt drives connected in series influences the resulting gear ratio.

Calculating the appropriate V-belt length for V-belt wheels

The calculation depends on the size of the belt pulleys, the distance between the belt pulleys and the desired tension of the V-belt. The formula is as follows:

L=2\times C + \frac{\pi\times(D_1+D_2)}{2}+\frac{(D_1+D_2)^2}{4\times C}
  • C = Distance between belt pulleys
  • D1 = Diameter of larger belt pulley
  • D2 = Diameter of smaller belt pulley

Calculating belt drives

Calculating belt drives requires an understanding of the various parameters and variables that affect the performance and efficiency of the drive system:

Transferable power through belt drives

The transferable power is the power that the belt drive can safely transfer without overloading. It is measured in kilowatts (kW) or horsepower.

Belt speed (V)

The belt path speed is the speed at which the belt runs over the belt pulleys. It is usually measured in meters per second (m/s). It can be calculated using the following formula:

V=\pi \times D \times \frac{n}{60 s/min}
  • V = belt speed in m/s
  • D = belt pulley diameter in meters
  • n = speed of rotation of belt pulley in revolutions per minute (1/min)

Belt tension

Belt tension is the tensile force that acts on the belt and is responsible for transferring the power. It is measured in Newton (N) or Pound (lbf). Belt tension depends on the transferred power, belt speed and belt pulley diameter. The exact formula varies depending on the belt type and can be found in the manufacturer's information.

Selecting pulley diameters

Choosing the correct belt pulley diameter is critical to achieving the desired gear ratio and speed. It depends on the speed of rotation and torque of the driven shaft drive. The pulley diameters can be selected to provide the correct gear ratio to achieve the desired speed and torque

Safety with V-belts

When selecting and calculating belt drives, it is important to consider a safety factor to include unexpected loads or operating conditions in the calculation. The safety factor indicates how much higher the load limit of a material is compared to the calculated loads. The higher the safety factor, the more reliable the component or material is. It should normally be above 1.

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