Belt Drives and Environmental Temperature

Both high and low environmental temperatures can present problems with belt drive systems.

In general, the maximum recommended temperature for belt drive systems for standard belts is 185 deg. F (85 deg. C). For rubber belts, temperatures exceeding this can result in gradual compound hardening and eventual cracking as belts stiffen. For urethane belts such as Poly Chain GT Carbon, the urethane will may begin to soften and will eventually melt at temperatures exceeding 200 deg. F (93 deg. C). There are a few options for belt drives operating in high temperature applications, but belts made from materials with higher temperature resistance are still limited to a maximum temperature of about 230 deg. F (110 deg. C).

Belts can "overheat" from slippage even when environmental temperatures are not excessively hot. If belts are hard and appear glazed from heat, always check to make sure the tension is at the recommended level, and that sheave grooves are not worn excessively. In most normal environments, belt surface temperatures do not typically exceed 120 deg. F (49 deg. C) or so.

Belts are generally limited to a minimum temperature of about -30 deg. F (-34 deg. C). Rubber belts operating in temperatures lower than this can harden and crack. Cold soaked belt drive starts are especially vulnerable to belt cracking. Poly Chain GT Carbon belts are capable of operating at temperatures down to -65 deg. F (-54 deg. C).

Gates Launches New Metals Technical Guide

Earlier this month, Gates published a new Metals Technical Guide. The guide provides general background information on hardware topics such as:

• Material considerations
• Manufacturing and process capability
• Bushing capability
• Sheave specifications
• Sprocket specifications
• Gates Made-to-Order Metals team

The guide is available for download at www.gates.com/catalogs/ under the Power Transmission Catalog Collection link.

Designing Replacements for Existing Drives

When customers come to us looking for a replacement for a current belt or chain drive, sometimes they do not know the horsepower/torque and rpm of the motor. This is very important for us to know because we try not to design belt drives based on only the old drives ratings.

While we can calculate the power ratings for the old drive, if we design the new drive based on the old drives ratings we are trusting that it was designed properly in the first place. However, it is entirely possible that the old drive was improperly sized because the customer is replacing it for a reason! By knowing the horsepower and rpm of the motor, as well as the components of the old drive we can follow our proven design procedure to give the best results to the customer.

To design a belt drive we need to know:
-Horsepower and rpm of the motor
-Ratio of any gearbox in between the motor and belt drive if applicable
-Desired speed ratio for the belt drive (The old pulley sizes can tell us this)
-Center distance (The pulleys and belt length can tell us this)
-Shaft diameters
-A description of the operating conditions (24/7/365 or high shock loads?)

Synchronous Belt Meshing Frequency

Meshing frequency is defined as the number of belt teeth that enter and exit the sprocket grooves per unit of time. Meshing frequency is assumed to be the primary frequency of noise generated by synchronous drives since the noise is generated from meshing interference and land impact during operation. The most common unit of meshing frequency is # teeth/sec. This is equivalent to cycles/sec. Each sprocket may have its own meshing frequency, but the major noise generator tends to be the driveR with the belt entering at its highest tension.

Meshing frequency can be calculated as follows:

(# Sprocket Grooves x rpm) / 60 = cycles/sec

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.