How to choose the right belt drive?
How does a belt drive work and what different types of belt drives exist?
In a belt drive, power is transmitted between two (usually) parallel shafts on which pulleys are mounted that are connected by means of a toothed belt, v-belt, flat belt, round belt, stud belt, variator belt, etc. With this connection, a rotational movement can be transferred from one shaft to the other. Belt drives are often used because of their damping nature. Except for the variator belt drive, this form of drive has a fixed speed ratio. There is a wide range of different types of belt drives on the market.
Which belt drive is right for your drive?
Do you have high power with bumping loads? Can or should the drive be allowed to slip? Does precision play a role? Here you can find more information about the different belt drives.
Slip or synchronous drive?
Belt drives are available as synchronous drives. Here, a tooth profile engages the pulleys to be driven. This creates a slip-free transmission. This may be desirable when different drive parts must always be driven/moved under a predetermined position relative to each other. There are also belt drives that transmit torque by friction. Here, the flanks of, for example, a v-shaped belt push into the groove of a v-belt disc. Due to the force and the surface of the material, friction is created. When a machine is jammed, this type of drive can function as a safety device, preventing overloading. On the other hand, such a string drive cannot be used where synchronization of parts is desired.
Determine belt profile
There are many different types of drive belts on the market. Each belt has its specific characteristics. The noiseless flat drive belt that can accommodate large misalignments or even drive at an angle. Within the timing belts, there are types that can transmit high power and others are just very accurate or suitable for high turnover applications. The v-belt drive is a common belt drive. Widely used, economically priced, are readily available and have a high degree of interchangeability.
Installation space of a belt drive
There are many types of belts, each with its own area of application. How much space is available? What are the maximum diameters and widths of the pulleys? What is the center-to-center dimension (HOH) of the pulleys? Flat belts are made to any length dimension. However, with many types of belt drives, there is a set program of belt lengths. It may be wise to consider these lengths when constructing a machine. Many times a drive needs to be disassembled or adjusted during installation/replacement.
Material of a drive belt
Drive belts are available in many different materials. There is a belt for every application. Often, standard belts are made of a rubber (Polychloroprene) or Polyurethane. In addition, there are conditions (think extreme temperatures, chemicals or weather conditions) that these materials cannot withstand. A list of the chemical resistance of plastics and rubbers can be found here. Belts can also be provided with a top layer (e.g. for a higher coefficient of friction) or attachments can be manufactured on them. Furthermore, it is important to know whether drive belts must be statically conductive. For example, when they are used in an environment with a risk of explosion (ATEX ISO9563). There are tensile cords in most drive belts that largely determine the strength and damping character of the belt. These tensile cords can be made of fiberglass, steel, carbon (carbon) or aramid.
Calculating tensile force in a drive belt
The power, RPM, and any acceleration or deceleration of the drive are also determining factors in choosing which type of drive belt to use. These data determine the forces occurring in the belt or string.
How to calculate the tensile force in a drive belt? When the torque or output torque of the drive is known, the tensile load in the drive belt can be calculated. To determine this load, the following formula applies:
Fg = Md2 : r
Herein is:
Fg = Acting tensile force in the drive belt (N)
Md2 = Torque (Nm)
r = Radius of belt pulley (m)
Service factor determination
The service factor (also known as operating factor) (fs) is partly decisive in choosing the right drive. It represents the load changes and overloads a drive can be subjected to in daily operation. Select the appropriate number of operating hours per day from the table below. Using one of the three load curves and the number of starts per hour, the service factor can be read off. The designations K1 - K3 indicate the values of the operating classes; steady load, light bumping load, and heavy bumping load. For fuel engine drives, an additional factor of 1.5 may be added. This is due to the bumping nature of the drive.
What are the operating conditions?
It is important to know the operating conditions of a belt drive. This is because it can have a major impact on performance and service life. Consider:
Will the belt come into contact with chemicals? Then consider the Chemical resistance
Is there a lot of contamination? Dust fiber or abrasive agents like sand etc. can build up between the belt and pulley.
Explosion hazard (ATEX). Here the belts must be statically conductive according to ISO9563.
Extreme temperatures (or fluctuations)
Inrush time number of starts/stops per hour. Vibration and/or impact loads affect Service factor
Belt tensioning on the back. Not every belt is the belt suitable for counterbending, for example, when using back tension rollers.
