Measuring a Conveyor Belt

Posted by: Willie Costa on June 2, 2010

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The correct measurement of a conveyor belt is one of the most important factors that contribute to the correct operation of any conveyor. The width measurement is fairly straightforward, and involves merely measuring the with of the belt with a measuring tape perpendicular to its edge.  As with most things, there are tolerances for conveyor belt dimensions. These tolerances should be kept in mind when ordering a replacement belt, and are given by the National Industrial Belting Association (NIBA) as:

 

Belt Width (inches)	Molded Width Tolerance	Maximum Width Variation In Any one Belt	Cut Width Tolerance
24 or less	± 1/4"	± 1/4"	± 1/8"
25 to 36	± 3/8"	± 3/8"	± 3/16"
37 to 48	± 1/2"	± 1/2"	± 1/4"
49 to 53	± 7/32"	± 7/32"	± 7/64"
54 to 59	± 19/32"	± 19/32"	± 19/64"
60 to 71	± 23/32"	± 23/32"	± 23/64"
72 to 78	± 25/32"	± 25/32"	± 25/64"
79 to 84	± 27/32"	± 27/32"	± 27/64"
85 to 90	± 29/32"	± 29/32"	± 29/64"
91 and over	± 1%	± 1%	± 1/2%

 

 

Similarly, NIBA also has length tolerances for conveyor belts, which are given as:

 

Endless-Net Endless Length (NEL)	Loop Belt	± 1%
	Vulcanized	± 1/2%
Specified Length - Cut Ends		± 1/2%
Specified Length - Laced with Mechanical Fasteners (measured Pin to Pin)		± 1/2%
Roll - Bulk Quantities		± 10%

 

The simplest way to measure the length of a conveyor belt is the "mark and jog" method: mark the belt every 3 - 5 feet or so, using a measuring tape to locate the marks equidistant from each other, and jog the conveyor until the original mark cycles through the entire system. The distance between the last mark and the first mark is added to the last mark, and that is the total belt length.

 

However, this method only yields the belt length at the moment that it is measured, and fails to account for belt elongation over time. A more accurate method is given as follows:

 

1. Retract all pulleys over which the belt runs (drive pulley, tail pulley, tensioning pulley, etc.) to their minimum takeup position.

 

2. For a simple line conveyor, measure the center-to-center distance of the drive and tail pulleys. Mark this measurement "L₀." For serpentine pulleys, add the center-to-center distances of all slave and tensioning pulleys, nosebars, etc.

 

3. Measure the diameters of the drive and tail pulley, and calculate the circumference of each. Label these values C_d and C_t, respectively. Recall that the circumference of the pulley is equal to its diameter times pi, or approximately 3.14159. For a serpentine conveyor, you will have to do this for each pulley over which the belt is tensed.

 

4. Multiply L₀ by two, and add one-half of all the pulley circumferences to it.

 

5. Add these values together to obtain the minimum length required for the belt.

 

This is stated as a simple formula, which is:

 

L_minimum = 2L₀ + 0.5C_d + 0.5C_t

 

As an example, consider two pulleys which are 45" apart. Both the drive pulley and the tail pulley have a diameter of 4". For this example,

 

L₀ = 2*45in = 90in.

 

The drive and tail pulleys are both 4" in diameter, so

 

C_d = 3.14159 * 4in. = 12.5662in.

C_t = 3.14159 * 4in. = 12.5662in.

 

Thus,

 

L_minimum = 2L₀ + 0.5C_d + 0.5C_t

L_minimum = 90in. + (0.5 * 12.5664in) + (0.5 * 12.5664in)

L_minimum = 102.5664in.

 

Note that 0.5664 inches is a bit difficult to measure on a standard tape measure; for most instances, rounding a calculation like this to 102.5", or 8' 6.5", will probably be sufficient.  Keep in mind that it may be wise to add in a couple of inches to this calculated length in order to account for the need to bring the takeups out a bit in order to create tension in the system. Also remember that as soon as the belt is tensed, the fibers that make up its composition will also be tensed, and will be resisting a tendency to elongate; this is another reason why measuring the belt with the "mark and jog" method mentioned earlier is unwise.

 

 

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http://www.conveyorbelt.com

http://www.conveyorbeltguide.com

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