Doug White from Rydell Industrial (Belting) Co , reviews some of the common belt identification points relating to miniature pitch belts.
With dozens of tooth profiles, pitch sizes and various rubbers and urethanes as well as a diverse selection of tensile reinforcement cords, finding the right belt can be difficult.
Toothed belts come in an enormous variety of shapes and sizes. The part numbering systems or nomenclature designates three dimensions of the belt: the pitch, the pitch length and the width.
The pitch is best defined as the measurement from any point on one tooth to the corresponding point on the adjacent tooth.
The pitch length of the belt is best defined as the number of teeth on the belt multiplied by the pitch dimension. On miniature pitch belts it may be necessary to take measurements using some form of magnification such as an optical comparator.
For instance, a timing belt part number might be T2.5-120-04 where T2.5 designates the pitch 2.5mm, 120 designates 120mm pitch length (48 teeth) and 04 designates the last component of the belts dimension – the width.
Although the nomenclature differs for imperial and metric belts, and dimensions can be given in fractions of an inch or multiple decimal places, virtually all aftermarket part numbers follow a system of this kind.
For example, an imperial part number may show the length first instead of the pitch.
In the part number 560MXL025, the length is 5.6” and MXL is the industry standard designation for Mini Extra Light pitch, which is 0.08 inch and evenly divisible into 5.6 inches. Thus the belt has 70 teeth.
What is particularly important to note, is that many of these pitch dimensions are exceptionally hard to tell apart visually and there are several different belt tooth profiles, which are designed to run in their own specific pulleys. These very slight differences require careful identification.
Similarly, stock standard timing belts may be available in a variety of cord reinforcement materials such as steel wire, fibre glass, polyester and aramid. Each material type has unique performance characteristics for flex fatigue, elongation, UTS and thermal reaction.
Applications such as servo and encoder drives, plotters, robotics, high speed machine tools, vending and ticket dispensing machines as well as ATMs and medical diagnostic equipment rely on precision timing belts. Selecting the correct replacement belt therefore, can be critical.
In addition to the various tooth profiles, pitches and cord types, many belts are manufactured using polymers or elastomers designed to meet specific performance parameters such as temperature resistance, cleanliness, static conductivity, smooth operation at high speeds and positioning accuracy.