Gates Mectrol
N. America +1 (603) 890-1515
Europe +49 (0) 6157-9727-0
Mexico +52 (552) 000-2700
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Cord Tensioning

Critical to Belt Performance

Effect On Belt Performance

Cord tension affects several aspects of a timing belt; belt pitch, belt straightness, trackability, tensile strength, settling time and slittability.

Belt Pitch. The pitch of the belt is controlled by either increasing or decreasing the cord tension in the manufacturing process. Increasing the tension shortens the length, and decreasing makes the belt longer. Good control of pitch length requires control of tension.

Belt Straightness. Uniform tension across the band of cords yields straight belt. If the cords on one side of the belt are tensioned more than the other side of the belt in manufacturing, the belt will curve in the direction of the tight cords. These cords want to be shorter than the looser cords.

Belt Tracking. Non uniform cord tension has the same effect as having one section of the belt shorter or longer than another. This is the same as having uneven center distances between pulleys in the system. This is also the same as having non parallel pulleys. All of these contribute to making a belt difficult to track.

Tensile Strength. If any cords in a belt are pretensioned more than another cord in the production process, in application, these cords will be the first to carry the load. They will also be the first cords to reach their fatigue point and rupture under extreme load. If some cords rupture early in the load, then the remaining cords now carry increased unit loading. If all of the cords carry the load equally and rupture at the same time, ultimate failure point will be at a greater force.

Settling Time. When a belt begins to run in an application, there is a certain period of time where the belt elongates and settles into a relatively stable length and tension state. If all of the cords in a belt are pretensioned uniformly, this settling time is very quick. If there is a great deal of non-uniformity, the time can be very long.

Slittability: Slitting belts with non-uniform tension will result in belts with curvature.

Gates Mectrol’s Tensioning Vs. The Competition

The Differences
  • When we produce belt, we extrude the belt at the widest reasonable width, and then slit the belt down to the required width. In order to insure that all of our belt is straight after slitting, it is mandatory that the cords all be equally tensioned. Further, there are important performance characteristics that are improved with proper cord tensioning.

  • We pay a great deal of attention during the process, and continuously inspect for equal cord tension. With many accounts, this has been one of the most significant selling points that we have.

  • Our competitors have a very different approach to cord tensioning. They extrude the majority of their belt to the finished width. As a result, they are not concerned about slitting. When they extrude, they only manipulate the tension in the two outside edge cords in the belt. By loosening or tightening one or the other pair, they can control the pitch length and the straightness of the belt. They ignore the other cords in the belt.

A diagram showing the difference between cord tensions is below.

Even Belt Cord Tension
Gates Mectrol Belt with even tensioning

Uneven Belt Cord Tension
Competitors' uneven tensioning

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