Minimum Diameters

Different belts have different dimensions. They also use different materials; for instance, the cord inside an A section V-belt is smaller than the cord inside a B section V-belt. While this larger cord gives a B section belt more power capacity, it also means that your sheaves have to be above a larger minimum size than an A section belt’s sheaves. This applies to all of our belt lines. The smaller section belts can use smaller diameter sheaves and sprockets. The same concept applies to backside idlers as well. Going below these minimums on either the inside, or the backside of the belts can have a significant affect on belt life. To find out what minimum diameter sheave, sprocket, or idler your belt needs, check out our Belt Preventive Maintenance Manual available for free at www.gates.com/catalogs Click on the hyperlink for Power Transmission Catalog Collection to get to the page where you can download it.

Belt Drives and Dissipating Static Charge Buildup

All types of belts can generate electrical charges while operating in belt drive systems. Factors such as humidity and operating speed influence the charge potential. With static charges present there is potential for arcing or sparking in flammable environments. Other possible issues may be found with material handling processes or sensitive electronics.

In order to minimize possible issues with static charge build up, V-belts are generally manufactured in conductive constructions (Predator and PowerRated belts are not static conductive), and rubber synchronous belts can be produced in conductive constructions on a made-to-order basis. Note that Poly Chain GT Carbon belts cannot be produced in a conductive construction. The Association for Rubber Products Manufacturers (ARPM; formerly Rubber Manufacturers Association) defines standards for static conductive belts in their bulletin IP-3-3.

Static conductive belts meeting the ARPM Standard IP-3-3 should have sufficient conductivity to prevent measurable static charge buildup, thus preventing static discharges. Belt drive systems operating in potentially hazardous environments, though, must be properly grounded. A continuous conductive path from belt to ground is necessary to bleed off static charges. This path includes a static conductive belt, a conductive sprocket, a conductive bushing, a conductive shaft, and conductive bearings, all along the path to ground.

In hazardous environments, additional protection should be employed to assure that there are no accidental static spark discharges. Unusual or excessive debris or contaminant on belt contact surfaces or sprocket grooves, for example, can reduce the ability of belts to conduct static charges into hardware. In addition, belt conductivity properties are known to decline over time from normal use. Static conductive brushes or similar devices should be employed to bleed off any residual static buildup that might remain around belts.

Power and Fan Speed for Belt Drive Conversions

The power required to drive a fan relates to the fan shaft speed as follows:

Initial_Horsepower/New_Horsepower = (Initial_Fan_RPM/New_Fan_RPM)^3

A small speed change can result in a substantial increase in power consumption. Therefore, this relationship should be considered when replacing a V-belt drive with a synchronous belt drive for energy savings.

To ensure that the fan speed does not increase, the design speed ratio should be based on a measured fan shaft RPM of the existing V-belt drive. This measurement can be made with a contact or a strobe tachometer.

Technical Drawings and CAD Files

People often call to ask where they can get drawings of CAD files for our belts and sheaves. There are two places to look. The easiest is our online catalog:
www.gates.com/partview

By searching your part number in the top left, you can go directly to the product page. Each page has a general product overview with basic dimensions and information. A 2D spec sheet is usually available in the bottom of the "Attachments" section, and a 3D CAD model may be available to download near the top of the page.

If information is not available on PartView, you can find detailed sprocket specification tables in our drive design manuals. The manuals are broken down into belt lines such as Poly Chain GT Carbon, PowerGrip GT2 and Heavy Duty V-Belt. Small pitch (2, 3, 5mm) synchronous belts including PowerGrip GT2, HTD and Timing will be located in our Light Power and Precision Manual. All of these manuals are available to download along with our catalog here:
http://gates.com/catalogs/index.cfm?requesting=ptcatalog&location_id=2999

These manuals also contain horsepower ratings and many other great design and engineering resources.

Safety First

Gates publishes a detailed Preventive Maintenance manual, with strong content regarding safety practices.  Most of these are common sense - lock out the drive before touching the mechanical system, for example.

When working with any electrical power source, take extra care to make sure to avoid any hazardous situations.   Many years ago, during a power survey, I had a near miss when hooking up a data logger in the power supply box.   While I had many, many, experiences setting up the test equipment, this particular time I was shocked (literally) when clamping on an amperage probe.   I was very lucky - just a few hours of a numb arm and no lasting effects.

What is the point?   Never assume that the system is safe.  Ask, ask again, and double check to make sure every appropriate safety precaution has been properly taken before working on a belt drive system.  Accidents happen because people get in a hurry, or overlook the obvious, or make an improper assumption.  Remember - you're talking about your health - act accordingly and be mindful of the proper safety measures when doing any installation or maintenance work.

Finding NEMA

If you are using an electric motor to run your belt drives and are having problems with the life of the bearings and/or shafts, your motor pulley may be smaller than recommended. As the pulley size on the motor decreases, the magnitude of the belt pull increases, thus exerting a higher load on the bearings and shafts of the motor. NEMA (National Electrical Manufacturers Association) issues a list of minimum recommended sizes for various NEMA frame electric motors. Staying above these values should extend the life of the bearings and shafts on the motor and should prevent any premature failures from occurring. Below is the NEMA table taken out of the Gates Polychain Carbon Drive Design Manual:

These standards can be found on the NEMA website at http://www.nema.org/, or in any of the Gates Drive Design Manuals found at www.gates.com/partview

What Belt Length Do I Need?

One of the most common questions we get is: “What belt length do I need?” Well, there are a couple of ways to figure this out. First, lets do it the hard way. You can use the equation:

Lp = 2C + 1.57(D + d) + ((D – d)^2 / 4C)

Where:
Lp = belt pitch length, inches
D = diameter of large sprocket, inches
D = diameter of small sprocket, inches
C = center distance, inches

Now if doing the math isn’t for you, there are a couple of easier ways to get this figured out. I would recommend our free software. We offer both Design Flex (Web and Pro versions), and Design IQ. You can download either of these at www.gates.com/drivedesign Design Flex is a two point drive design program that is tailored to help you easily design drives, and find proper tension. Design IQ is a little more complex; it is designed to help with drives no matter how many sprockets or sheaves.

With Design Flex, you will need to enter in a load in order to get it to calculate a belt length. While this load doesn’t need to be accurate for calculating belt length, you do need proper loading for trying to design or find the correct tension for a given drive.

With Design IQ, you don’t need to enter a load to get a belt length, but you need to understand where you are placing the sprockets/sheaves. Starting with the driver at the coordinates (0,0), place the driven at the measured center distance in the X coordinate and 0 in the Y coordinate, you can easily find the two belt lengths that are closest (one shorter, and one longer) by selecting the belt length button. When you select one of the belt lengths, the program will then show you what your actual center distance will be in the driven sprockets/sheave’s X coordinate box.

As always, if you have any questions, or would like us to walk you through an example of how to do this, you can call us at 303-744-5800.