Basic Technology

Belt Drives, Types, Advantages and Disadvantages of Belt Drives

Olawunmi Omosanya - Fri, 09th August, 2019 @ 14:42: PM

What are Belt Drives?

Belt drives are one of the drive meachnisms or transmissions employed in machines to bring about its mechanical movement via power transmission. It is important to understand that the most ideal and simplest form of transmitting mechanical power is via the rotational motion; and the belt drive proves to be very useful here. For instance, a pepper grinder uses a drive (in the form of a belt) to propel forward its shaft. Similarly, a sewing machine utilizes a belt (as its drive) that can be mechanically moved via the foot actions of the tailor.

Image Credit: Nptel

From the diagram above, we can see that the belt drive requires a belt as its mechanism for mechanical power transmission. Apart from belt drives, Other methods of mechanical power transmission includes:

  • Chain Drives
  • Gear Drives

In the drive system, the machines are driven by rotational motion through its shaft to the other parts around it.

The driving pulley of the machine is termed the Driver System while that which is driven is termed the Driven System.

Note:  A pulley is a wheel or sets of wheel over which a belt or chain is attached in order to create a movement or motion.

In this article, we will explore on the Belt Drives.

 

Belt and Pulley Drives

The belt drives are frictional drives that transmit mechanical energy on a dry surface from one shaft to another in a pulley-like system. For the belt drive to work properly, both sides of the shaft must be dry and separated (by some distance). Either shafts or pulleys do not necessarily need to rotate at the same speed; neither must they be of the same size. The tension between both sides of the belt will depend heavily on the angle of contact such that the tight side is always below while the slack end stays above. Please see tha above disgram.

The area of belt having a lesser tension (less tightly stretched) is generally referred to as the slack side while that having a higher tension (more tightly stretched) is the tight side.

Think of tension as the level of tightness at which something is stretched

Note: The mechanical power is usually transmitted from the driving pulley to the driven pulley via a rotational motion.

Based on the fact that belt drives are used in conjunction with pulleys; some of the mechanisms that utilize belt drives include:

  • Pepper Grinder
  • Sewing Machines
  • Industrial Generators
  • Motor Cars and so on

 

The belts used in the above machines can be any of the followings:

Image Credit: SlideShare

  1. Flat Belts: These belts are somewhat rectangular in shape; and they bring about rotational movement over long distances and with a very low noise. The flat belts have a very high efficiency of about 98%.
  2. Vee Belts: They are used with grooved pulleys and can allow for high speed and rotation. They are relatively common because of their low cost and numerous size ranges.
  3. Circular Belts: These belts are circular in shape. They can also be used with the grooved pulleys.
  4. Cylindrical Belts: This is a looped flat belt and are often used in milling machines.

Note: Materials used in making the various kinds of belt drives include rubber, plastic, fabric, leather and other synthetic materials.

 

Types of Belt Drives in pulley systems

  • Open Belt Drive

Image Credit: SlidePlayer

The open belt drive is used when the two parallel shaft are needed to rotate in the same direction. When the open belt drive is in used on a widely separated shaft, the upper side of the belt must be the slack side while the lower side becomes the tight side.

Please read on lines here.

Note: If we made the upper side the slack side (in a separated shaft), sagging will occur and the contact arc will be increased.

 

  • Cross Belt Drive

Image Credit: Quora

The cross belt drive is used when two parallel shaft are needed to rotate in the opposite direction. Due to the crossing nature of this belt, the belts rub against itself at a specific junction, resulting to its wearing off and eventual damage.

Note: In order to reduce the excessive wear caused from the meeting point of the crossed belts, the shafts should be placed at an optimum distance from each other; while been operated at low speeds.

 

  • Fast and Loose Pulley Drive

Image Credit: Mecholic

A fast and loose pulley drive is often used when the driven pulley is required to be started or stopped without creating an interference with the driving pulley.

Note: A pulley keyed to the machine shaft is referred to as the fast pulley. The fast pulley runs at the same speed with that of the machine shaft. The loose pulley on the other hand runs freely over the machine shaft without transmitting any power.

 

Advantages of Belt Drives

  1. They are economical.
  2. They are great shock absorbers.
  3. They don’t usually generate noise.
  4. They have a high efficiency rate (up to 98% efficiency rate).
  5. They are excellent in transmitting power between widely spaced shafts.
  6. The shafts do not need to be parallel to one another.
  7. They show you visual signs when they begin to fail.
  8. They don’t requiring oiling or lubrication.

 

Disadvantages of Belt Drives

  1. They deteriorate when exposed to chemicals.
  2. The effectively operate only at a temperature of about -35oC – 38oC.
  3. Once damaged, they can’t be repaired.
  4. It builds up heat.
  5. Belt drives can occupy larger space in the machine.
  6. The slipping of belt occurs thereby disrupting speed.

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