Part Numbers for Poly Chain® GT® and PowerGrip® GT®2 Belts

The part numbers for Poly Chain® GT® and PowerGrip® GT®2 belts are very similar, which can sometimes lead to mix-ups. Here is an example to explain the subtle difference:

The Poly Chain part number 8MGT-640-12 identifies:
1-pitch (8 mm)
2-belt length (640 mm)
3-belt width (12 mm)

The PowerGrip part number 640-8MGT-12 identifies:
1-belt length (640 mm)
2-pitch (8 mm)
3-belt width (12 mm)

The two part numbers indicate the same belt dimensions. However, the Poly Chain part number will start with the pitch first and the PowerGrip part number will start with the length.

What Design Flex® Pro™ Drive Noise Estimates Really Mean

Gates Design Flex^® Pro^™ software is the premier belt drive design software available, and can be downloaded for free at http://www.gates.com/designflex/.  Of the wealth of information available on Design Flex Pro printouts, drive noise estimates for PowerGrip^® GT^®2 and Poly Chain^® GT^® Carbon belt drives are an option that can be included.  It is important, though, to have a correct understanding of what these noise estimates actually represent.

While it is often assumed that the noise estimate represents the total environmental noise level with the belt drive operating, this is not the case.  Noise emissions from all sources within an environment all combine for a total environmental noise level.  Belt drives are only one of many sources of noise in specific  environments.

It may also be assumed that the noise estimates represent the noise level that synchronous belt drives are expected to contribute to the total environmental noise level, and this is also not the case.  The noise level generated by synchronous belt drive systems is dependent upon many factors including individual belt drive components, actual drive loading, the belt drive design including belt width, belt tension levels, drive alignment, possible reflection or echoing effects, the distance from the noise source and more.  It is unfortunately not possible to consider the effects of so many factors in a simple noise estimate.

The calculation for belt drive noise estimates is really quite simple, as is their intended use.  Individual drive noise estimates are intended to be compared with one another so the lowest noise options can be selected.  Drive design options within Design Flex Pro can be sorted by decibels (dB) or frequency (hz) or a combination.  This allows users to select drives with either the lowest sound pressure level (dB) or the lowest frequency or the lowest overall noise level. 

While Gates belt drive noise estimates are not intended to represent environmental noise levels or actual noise levels generated by belt drive candidates, they do allow users to compare and select belt drives with the lowest noise levels expected.  Selecting quiet drive candidates will reduce total environmental noise levels, and this is the ultimate objective in the end.

What is Draftguard®?

Draftguard® is an anti-rotation device typically used to stop ACHE fans from rotating backwards.    Reverse rotation can strain the motor system during start up and pose a safety hazard to maintenance workers; eliminating reverse rotation can improve safety and reduce maintenance.  

While Draftguard has typically been applied to ACHE fans,  it can be used in other applications to limit rotation to a single direction.  Draftguard can be mounted to the following bushings:

• 3020, 3525, 3535, and 4030 (TL style)
• E, F, and J (QD style)

A locking ring is also available to mount Draftguard in cases where it can not be mounted directly to the bushing.

 Learn more about Gates' Draftguard anti-rotation solution at www.gates.com/draftguard/. 

Gates MSDS (OSHA Form 20) for Belts

We are often asked to provide MSDS on our belt products; however, they have little value and don't apply.

It is Gates interpretation of the Hazard Communication Standards and Right to Know Laws that chemical manufacturers must assess the hazards of the chemicals they produce and inform persons who use their chemicals in manufacturing processes of the hazards associated with their use. The standards and laws furthermore do not apply to manufactured articles which do not cause exposure to hazardous chemicals under normal use.

The ingredients of the belts Gates sells are chemically bonded formulations of compounds and polymers which are not free to be given off to the environment as discernible substances or in hazardous quantities. Consequently they do not fall under MSDS intent and OSHA Form 20 is not required.

Choosing the Proper Belt for ACHE Applications

Synchronous belts are the most efficient option, but there can be confusion when selecting the proper Gates product line. The two best options are Poly Chain GT Carbon and PowerGrip GT2.

Poly Chain GT Carbon is the superior belt to PowerGrip GT2, but they both have advantages over the other. Poly Chain belts are stronger and have a higher modulus which can contribute directly to energy efficiency and longer belt life. Also, narrower Poly Chain belts and smaller diameter sprockets can be used in place of larger PowerGrip drives.

PowerGrip belts are available in longer lengths and have different sprocket sizes that can achieve some speed ratios Poly Chain can’t. Also, if necessary, we have ACHE PowerGrip GT2 belts which have Z twist tensile cords that are made to track in only one direction. This feature is used for fan applications with large speed ratios and vertical shafts. The belts are designed to oppose gravity and stay in track on the large flangeless sprocket.

In some cases, Gates synchronous belts could be too heavy duty for ACHE applications. Drives that use motors smaller than 15 HP may not be rigid enough to handle our synchronous products. People often try to convert V-belts to synchronous belts on small motors to achieve energy savings, but there's not much efficiency that can be gained from low power motors. The advantage of switching to a synchronous belt in such a circumstance is the lack of maintenance and replacement. Most times, Gates has an equivalent notched or aramid/Kevlar^TM* V-belt that will produce similar results without the initial cost of replacing the belt and pulleys.

The bottom line is you should use Poly Chain unless you’re constrained to only use PowerGrip or if the motor is less than 15 HP.

*Kevlar is a registered trademark of E. I. du Pont de Nemours and Company

What is Datum Diameter?

The term “Datum” was first adopted by the International Standards Organization (ISO 1081-1980) and recently by the Rubber Manufacturers’ Association Engineering Standard f or Classical V-belt and Sheaves (IP-20-1988, Gates Form # 14495-B). Classical sheaves were specified by pitch diameters until 1988, when the Datum System was adopted by the USA. This change was necessary because the nominal pitch diameter of a sheave no longer corresponded with the actual pitch line of the modern V-belt as it passes through the sheave groove.

Over several decades, construction improvements enhanced the performance of V-belts in many ways. New, advanced cord materials allowed the move from multiple unit tensile belts to high performance single unit tensile constructions which dramatically improved the horsepower capacity of V-belts. For example, a B-Section belt in 7.0 inch sheaves was rated at 4.2 HP (1750 RPM) by 1945 RMA standards. Today, a Gates Hi-Power II belt is rated at over 11 HP under the same conditions. This increased capacity is due in part to the move of the center of the tensile cord line to a location higher in the V-belt.

In general, the center of the tensile cord is associated with the pitch line. In the new higher position, the load carrying tensile has a greater torque carrying moment arm and more undercord support through which to transmit normal force to the sheave walls. In addition, manufacturers have determined that the optimum position for the tensile cord is very close to the outside diameter o f a standard depth sheave. So the diameter through which the pitch line passes is nearly equal to the outside diameter for most belts.

By definition, the diameter through which the pitch line passes should be the pitch diameter. This is precisely what the Datum System accomplishes. Figure No. 1 illustrates the construction change and its effect on the location of the pitch line.

Originally, machining standards for classical sheaves were established with the pitch diameter as a basis. The system is built around the notion of constant "pitch width" as the basis for machining standards. The pitch width sheave specification is tabulated f or each V-belt cross-section. Because V-belt cross-sections distort more as they bend around smaller sheaves, sheave groove angle is varied with sheave diameter.

In classical sheaves, the groove angle is pivoted about the old pitch width at the old pitch diameter. Figure 2 illustrates the old pitch system and the new Datum System as related to sheave angle. Note that Datum diameter/width directly replaces pitch diameter width as the “base” dimensions about which the machining dimensions are derived.

Because of the shortcomings of the old system, Datum diameters have been adopted by the industry as the means of designating sheave size. Datum diameters are now used to place an order for Classical sheaves. An old pitch diameter (PD) designated sheave is directly replaced by the new Datum diameter (DD) designation (i.e., old 8 .0 inch Pitch Sheave = 8.0 inch Datum Sheave.)

To simplify, modern pitch diameters are equivalent to outside diameters (OD) for standard depth sheaves for most belts. An exception is A-section belts or AX-section belts in A/B Combination Sheaves. Conversion values for PD to OD for these exceptions and DD to OD values are tabulated in manufacturers’ design manuals.

Essentially, the Datum System removes complexity and inaccuracy from the V -belt drive design process. The challenge for power transmission professionals is using a new name for an old term.

Figure 1                                                                                                Figure 2

Made To Order Metals

There are often opportunities for belt drives where non-stock hardware (sheaves, sprockets, bushings) is required. What types of things could require using non-stock hardware? Special attachments to a hub, special materials, plating, corrosion resistance, non-standard sizes (both width and diameter), and special configurations are just a few of the examples of non-stock hardware requirements. Gates has a special department that is responsible for providing non-stock hardware quotes. Whether you are an end user or an Original Equipment Manufacturer, the MTO Metals team can help with special hardware requirements. If you have a system need for non-stock hardware, contact the MTO Metals group by calling 1-800-709-6001, or email them at makemymetal@gates.com .