Tuesday, July 31, 2012

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/KevlarTM* 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 .

Friday, July 20, 2012

V-Belt Drives With A Twist

Once in a long while people have a need for a drive to twist. While this is not a great way to design a drive, sometimes it’s unavoidable. With V-belts, we can offer a solution. Here are some guidelines that may help produce the best belt life possible:

*Use as few belts as possible

*Make the center distance long

*Keep the sheave diameters small

*Keep the ratio as small as possible

*Use deep groove sheaves with classical section belts

Twisting the belt is going to reduce life, and make installation difficult, but using the above guidelines will help to produce the best results.

Tuesday, July 10, 2012

Flaking / Dusting From Poly Chain® GT® Carbon Belts

Poly Chain® GT® Carbon belts are sometimes observed to generate flakes or dust soon after they are initially installed. This is not abnormal, and a basic understanding of the belt construction will help to explain why.

The heavy nylon jacket covering the teeth of Poly Chain GT Carbon belts is coated with a very thin layer of polyethylene material that gives the belt teeth their distinctive blue color. This polyethylene layer not only provides belt identity, but also serves a very useful purpose in the manufacturing process. During molding operations, the liquid polyurethane material encapsulates the nylon jacket material, but must be constrained from contacting the mold. The thin polyethylene layer serves this purpose by acting as a barrier.

After Poly Chain GT Carbon belts are installed and placed into service, the blue polyethylene layer has already served it's useful purpose. As belts operate, this thin polyethylene layer may slowly wear away in the form of dust and even small flakes. The rate of wear will vary from application to application depending on a variety of factors. The potential for debris will be greatest initially and then decline rapidly as belts wear in over the first 24 to 48 hours or so.

While the appearance of debris from new Poly Chain GT Carbon belts may be concerning, it is a very normal part of their initial run in period and nearly always declines considerably after a short period of operation. If belt flaking or dusting continues, feel free to contact Gates Product Application Engineering at 303-744-5800 or ptpasupport@gates.com to discuss your belt application in greater detail.

Tuesday, July 3, 2012

New Gates Tension Tools

Gates Product Application Engineering recently added two new online tools to calculate tension for Poly Chain® GT® Carbon™ and PowerGrip® GT®2 belt drives.
The new tool is simple to use.  Just input the belt pitch, belt length, belt width, sprocket sizes (number or grooves), motor hp, and driveR rpm and then hit calculate. Check out the new calculators at http://www.gates.com/drivedesign/. 

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