Flat Belts Information

Flat belts are designed for light-duty power transmission and high-performance conveying. They are best-suited for applications with smaller pulleys and large central distances. Flat belts can connect inside and outside pulleys and can come in both endless and jointed construction. They have a high power transmission efficiency, are cost effective, and are easy to use and install.


The small bending cross-section of the flat belt causes little bending loss. The frictional engagement on the pulley outer surface requires only a small cross-section and makes flat belts very flexible, resulting in negligible energy loss. A flat belt does not require grooves, minimizing the energy loss and wear from the belt wedging in and pulling out from the grooves.

Additional benefits of flat belts include energy savings, a long service life of belts and pulleys, less down time and high productivity, and low noise generation from a smooth belt operation. Flat belts can be installed simply and securely. Belts are tensioned to the calculated initial tension by means of simple measuring marks to be applied to the belt. There is a constant tension on the belt so the belt will not need to be re-tensioned.

A disadvantage of flat belts is their reliance on belt tension to produce frictional grip over pulleys. This high belt tension required to transmit power often shortens bearing life. Another disadvantage is their failure to track properly since they tend to climb towards the higher side of the pulley, which is why V-belts have grown in popularity. A V-belt is a basic belt for power transmission. They are generally endless in construction and their cross-section shape is trapezoidal, giving it the name V-belt. The V shape of the belt tracks in a mating groove in the pulley so that the belt cannot slip off.

The video below demonstrates a flat belt in use.

Flat mining conveyor belt.

Video Credit: asciencecom


Three common designs of flat belts include:

Fabric ply belts consist of several plies or layers that are made of cotton or synthetic fiber, with or without rubber impregnation. The number of plies determines the belt thickness that will help determine the minimum pulley diameter for the drive.

Fabric cord belts are constructed with multiple cords made from cotton or synthetic fibers such as rayon, nylon, plastic, or Kevlar. They are incased in rubber and covered with a fabric/runner covering. This type is generally classed as a heavy-duty flat belt, used for high speeds, small pulley diameters, and shock loads. Steel cables can also be used as they have higher capacity and lower stretch than fabric cord flat belts.

Synthetic flat belts are made from nylon. Nylon offers flexibility, extremely high tensile strength, and operates effectively at high rim speeds. The belts are thin and they may consist of several plies of thin nylon bonded together to form a tough but flexible flat belt.

Flat belts generally have a traction layer made of oriented polyamide with two covers of elastomer leather or textile material and one intermediate layer of fabric on each side. The traction layer absorbs the forces exerted on the belt when power is transmitted. The friction cover ensures that the peripheral force acting on the belt pulleys is transmitted to the belt and vice-versa.


Specifications that are important to consider include: belt type, belt width, and initial elongation. If any of these factors change, the belt must be recalculated.

Power transmission belt material types include polyester, aramide, and polyamide.

Polyester is the most common material due to it price-to-value ratio. It supplies a versatile belt that can be used in a wide range of operating temperatures with low energy consumption, high flexibility, and reliable performance.

Aramide is a strong choice for long belts due to the short take-up and high accuracy for number of revolutions (RPM) and belt speed. It is highly flexible, simple to join, has a high E-modulus, and low energy consumption.

Polyamide is reliable and has a long service life. It can work in a variety of conditions and functions well in extreme environments with intermittent overload and high temperatures. Polyamide is shock resistant and grooves enable high grip. 

Belt width is simply the width of the belt. The tensile force for 1% elongation per unit of width after running-in (N/mm), k1% a.r.i., is the decisive value for calculating the required belt width and the resulting shaft load after belt relaxation

Correct and sufficient initial elongation is a pre-requisite for trouble-free operation of power transmission flat belts. The calculated initial elongation (ε0) must be observed. In systems with a tensioning pulley, the pulley is placed on the slack side and pushes the belt to provide the required initial elongation. In systems without a tensioning device the required initial elongation is determined by reducing the length of the shortened belt length, which is the fabrication length. Always use the calculated initial elongation provided by the manufacture when installing a belt.

When selecting a belt drive it is important to consider the speeds of and power transmitted between drive and driven unit, suitable distance between shafts, and appropriate operating conditions.

The equation for power is:

Power (kw) = (torque in newton-meters) x (rpm) x (2∏ radians)/(60 sec x 1000W)


The power transmission flat belt can be used in many forms of power transmission. It is known as a two pulley drive, consisting of a driving pulley, a driven pulley, and the belt. Below are examples of pulley design variations.

Flat belts may be customized for a wide range of applications. Such configurations include an incline to carry product to another level. Flat belts may also have a tracking sleeve under the system to ensure that the belt does not slip, or that the coefficient of friction can be adjusted to prevent slippage.

Typical applications include conveyors, compressors, machine tools, and other heavy industrial equipment.


Flat belts must adhere to certain standards and specifications to ensure proper design and functionality. JIS B 1852 is important for pulleys for flat transmission belts and ISO 22 is used to identify dimensions and tolerances for flat transmission belts and corresponding pulleys.


Belt Drives (Industrial Wiki)

Power Transmission Belts - Engineering Guide (.pdf; from habasit)

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