Sprocket pitch diameter: why it’s important and how to measure it

Sprocket pitch diameter: why it’s important and how to measure it

When replacing an existing (from another supplier) plastic modular belt with a new Habasit belt, it’s important to know the sprocket pitch diameter used on the current conveyor.This is because matching the new sprocket pitch diameter to the originally installed sprockets is essential for ensuring smooth and easy transition to the new belt, and avoiding the need to adjust the dimensions of the conveyor or change the speed of the belt (assuming of course that the existing conveyor is performing well).

Let’s look in more detail at sprocket pitch diameter: how it is determined, how it interacts with other conveyor dimensions, and how to measure sprocket pitch diameter on an existing conveyor. We also have tips on what to do if you need to change sprocket pitch diameter when replacing a belt because the existing dimensions are delivering unsatisfactory results.

Determining sprocket pitch diameter

The initial specifications for sprocket pitch diameter are determined mainly by the product transfer requirements of the application. Product tables and Engineering Guide provide the necessary information.

Conveyor dimensions

Once the sprocket pitch diameter has been decided, several conveyor dimensions can be set to optimize sprocket life and product transfer.

  • Key: A1 is the distance from the center of the sprocket to the top of the belt carryway/slider support
  • C is the distance from the top of the sprocket to the end of the carryway/slider support

When these dimensions are incorrect there will be problems with belt- and sprocket life, and as a result, with productivity. To avoid this, always refer to the product tables setting out the correct distances for A1 and C. A troubleshooting guide is also available with instructions on what to do if there is excessive sprocket wear caused by improper A1 or C dimensions.

How to measure the sprocket pitch diameter

To measure the existing sprocket pitch diameter, wrap the sprocket with the belt and measure  the distance at an angle of 180 degrees from rod head to rod head.

  • Key: dp is the sprocket pitch diameter

Another way to determine sprocket pitch diameter is to identify the belt manufacturer, count the number of teeth, and use the manufacturer’s tables to correlate this to the pitch diameter.

What to look out for when changing sprocket pitch diameter

If it is clear that the existing sprocket pitch diameter needs to be changed because of sprocket issues such as abnormal wear or high noise, it will probably be necessary to adjust the shaft height and/or the conveyor bed dimensions in order to achieve proper belt and sprocket engagement.

Belt speed is always affected by changes to the sprocket pitch diameter. If speed matching is required, adjust the shaft speed via the motor speed control or by adjusting the gear box.

Increases in the sprocket pitch diameter can also affect the torque applied to the shaft because the length of the moment arm is increased.  A shaft load calculation using Selecalc or other tools can be used to determine the effect of the changed pitch diameter on the shaft.

Feel free to contact us if you have any questions about sprockets. There is also more information about sprockets here: http://blog.habasit.com/2017/06/what-is-chordal-action-or-the-polygon-effect/

2020 May 7  |  Posted by

Bart Natoli

Bart Natoli is a Chief Application Engineer at Habasit America and has been with the company since 1986. He has a Bachelor of Science, a degree in Mechanical Engineering, Associates in Engineering Degree and Architectural Engineering Technology. Bart Natoli is an expert in fabric conveyor belts and power transmission belts.

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