Calculating Rim Speeds

You may know that our stock metal is all statically balanced to 6500 ft/min, but some of you may not know how to find out what rpm and diameter combination that equates to.  I’ll show you how.  This can be useful for not only maximum rim speeds, but also when you need to find out what rpm at which to run a head roll of a conveyor.

You need the sheave/sprocket outer diameter and RPM.  For this example, let’s use a 10” diameter and 200rpm.

Step 1, Find Perimeter.

Perimeter = 2*pi*r          or            Perimeter = pi*d

Where r = radius and d = diameter

Example: pi*10” = 31.415”

Step 2, Calculate Rim Speed

Rim Speed = Perimeter*RPM

Example: 31.415” * 200rpm = 6283 in/min

Step 3, Convert to proper units

12” = 1ft

Example 6283 in/min * (1ft/12in) = 523.59 ft/min

As always, feel free to call us if you have any questions.

If It Leaves the Ground, a Gates Belt Can't be Found

The purpose of this blog post is to expand on a previous blog regarding Aircraft Applications.

The Gates Corporation has had a long standing policy of not recommending the use of our power transmission products on aircraft, including kit, home-built or ultra light aircraft.  Whether the aircraft is FAA certified does not change this policy. This policy applies to any application where the equipment leaves the ground. A recent request serves as a great example. A customer called to receive assistance for designing a belt drive on a pump. The pump itself didn't leave the ground, but it supplied water at a high pressure to a water powered jet pack. Clearly, we could not support this customer because the application goes against our safety policy.

Only automotive and industrial belts and belt drives are sold through Gates distributors or the open market. Those belts and drives are NOT designed or made for aircraft.  DO NOT purchase Gates belts or belt drives for use on aircraft. This is a safety issue. Airplanes and cars are quite different as far as belts and belt drives are concerned. 

To emphasize this important point, do not use any Gates belt, pulley, or sprocket on a propeller-driven or rotor drive aircraft, and not with any in-flight accessory drive application or other drive in an aircraft.  For all types of applications, belt drives must be properly designed, installed, tested, and maintained.  It is impossible to inspect a belt and predict the remaining belt life. A broken belt means immediate loss of power and ability to fly! 

Feel free to contact us at ptpasupport@gates.com or 303-744-5800 if you have any questions or comments.

HP and Torque

People use the words hp and torque quite a bit, however, they don’t always understand the relationship between the two units.  I’m going to attempt to clear that up a little bit, and maybe make designing a little easier in the process.

Torque (Q) is basically a force at a distance.  If you think of a ratchet that is one foot long, and you apply 2lbs of force at the end of the ratchet, you are applying 2ft*lbs of torque (1ft x 2lbs).

Horsepower (hp) is a unit of measure of the rate at which work is done.  Let’s take the example above.  We are going to assume that applying the 2lbs of force will allow the ratchet to turn the bolt.  We count every time we make a complete circle (revolution) over a specific amount of time.  If we use minutes, we have RPM (revolutions per minute).  To calculate hp from torque and rpm you can use the following equations:

hp = (Q * RPM)/5252      This equation is when Q is given as ft*lbs

hp = (Q * RPM)/63025   This equation is when Q is given as in*lbs

You can see that hp is always a function of torque and rpm.  In the case above, if we can turn the ratchet 300 time per minute, with 2lbs of force, we are creating a huge 0.114hp.  These equations really start to become useful when you need to calculate the amount of torque that can be produced at a driven sprocket after a gearbox.  This will allow you to determine if your motor is big enough, and your reduction ratios are correct.

Diameter Differences

When asking questions about a drive, a lot of the time people take a diameter measurement to give to us.  On a synchronous sprocket, this can be a little deceptive.  There are three main diameters that are important, and this may not be obvious to the person taking the measurement.

First, if at all possible, always get a tooth count (or the part number).  Tooth count is exact, and is the best way to get you the correct answer.  If a diameter measurement is the only option, there are a few things that you need to know to get the best result.

Pitch Diameter (PD):  This is a theoretical diameter, and cannot easily be measured by hand.  However, this can be calculated.  The formula is:

(#teeth*pitch)/pi.  Pitch diameter is slightly larger than outer diameter (OD).  The diameter listed in the catalog is the PD, so if you are measuring the sprocket trying to identify the tooth count, the PD number should be slightly bigger than your OD.

OD:  Outer diameter is measured on the tooth surface.  This is the measurement we need if you can’t provide a tooth count.  Be careful when measuring this, as there is not always the tip of a tooth 180 degrees apart from one another, and you could get a measurement that is a little smaller than your actual sprocket.

Flange Diameter:  This is the one that gets people into trouble.  The flange is the largest diameter of the sprocket; it’s the part that keeps the belt from running off of the edge of the sprocket.  Not all sprockets have flanges, and sometimes the same flange is used for a couple of different sprocket sizes.  This means that if you provide us a flange diameter, we have to guess as to what sprocket you may actually be using.  Avoid measuring the flange if at all possible, but if you must, make sure that you tell us that it is a flange that you are measuring, and not the OD.

Sheave Gauges

Sheave gauges are a great tool that surprisingly people don’t always know about. They have been around for quite a few years, and are just as useful as ever. They are small plastic cutouts that you place inside a sheave groove to see if there is enough wear that the sheave should be replaced. If more than 1/32” of wear can be seen between the gauge and the sidewall of the groove, the sheave should be replaced. Worn sheaves are a big contributor to premature belt failure.

With the set, you get a gauge for multiple sections, and each gauge has 3 different angles for measuring a wide range of diameters within that belt section. These can also be used to help identify what type of belt a particular sheave is designed for if it is not significantly worn down. There is also a belt gauge in the set that can be used to help identify the particular belt section as well.

Stainless Steel Poly Chain® Flange Color

Customers sometimes ask about the pinkish color of Gates stainless steel Poly Chain sprocket flanges. The discoloration is a result of the high temperature shrink process used to mount the flanges.

Flange discoloration is seen in both the stainless steel and the standard Poly Chain sprocket lines. During the shrink fit process, the standard sprocket flanges (low carbon steel) usually turn black or brown.  Conversely, the stainless steel flanges typically take on more of a pink hue.

Flange discoloration is normal and will not impact the performance of the product.



Standard Sprocket

Stainless Steel Sprocket

FIRST Come, FIRST Served

It's getting close to the end of the year, and you know what that means. The kickoff of the 2013 FIRST Robotics Competition (FRC) is around the corner! Starting the week after the kickoff, Gates will allow teams to order belts and sprockets online at www.Gates.com/FIRST. All of the available components will be 5mm pitch, 15mm wide, PowerGrip HTD belts and sprockets. There will be several predetermined sizes available to teams and they are provided in a first come, first served basis. There will also be a limit on the parts so we recommend designing the belt drive first then ordering the parts you'll need.
As always, go to www.Gates.com/FIRST for belt drive assistance.

Internal Combustion Horsepower Ratings

When designing a belt drive with an internal combustion (I.C.) engine it’s important to understand that an IC engine is not like an electric motor. The horsepower rating for a NEMA motor is not the same as a horsepower rating for an IC engine. There is no conversion factor. HP is a HP is a HP. Engines just have different characteristics. Electric motors may have a hard start whereas IC engine may not. IC engines can’t run at their peak torque for a long time. An IC Engine with a HP rating higher than the power needed should be selected. Altitude and other factors can affect an IC engine’s performance.

Internal combustion engines are typically rated based on brake horsepower (BHP), or maximum BHP.

This BHP rating of an engine usually means the horsepower produced by a test engine in a laboratory.  During the test an engine is ran without a fan, generator and other accessories.  The ambient temperature is corrected to some standard, such as 60°F., and the atmospheric pressure is corrected to some given altitude, such as sea level.  The BHP rating should not be used for design, since the standard production engine, with accessories, cannot reach this output in actual usage.  Gross BHP is the term used for test data without any accessories and net BHP is with all of the standard accessories.  This is the horsepower measured at the crankshaft flywheel.  An I.C. engine spec will not contain any other mention of horsepower.

Several decades ago it was more common to refer to a maximum intermittent HP.  For short durations this was generally 85% of BHP.  Continuous duty or rated BHP was 75%-80% of maximum BHP for long duration service.  These terms are not referred to today in engine specifications.

It is still important to verify the horsepower versus engine rpm curves for those applications where the engine and drive are not intended to run at one speed continuously.  A percent time duty cycle is also helpful in selecting a belt drive.

Actual HP

Do you know that people are constantly using bigger motors than necessary? It can be a big problem, and doing so can lead to using bigger belt drives than necessary too. There is a common belief that bigger is always better. This is not always the case when it comes to power transmission components. Designing around actual loads not only saves on initial purchase price, but can also save money on replacement parts caused by excessive tensions, such as those placed on bearings when too big of a drive is used.

If you think your motor is too big for the load you are using, here is an easy way to calculate actual HP draw.

Actual HP = (Nameplate HP)x(Measured Amps) / (Nameplate Amps)

This means that if you measure the amperage draw of your motor, you can use the nameplate to find out what your actual HP draw is. Now sometimes it’s worth it to design around the rated load instead of the actual load. In situations such as hard starts, or unknown shock loads, having additional service factor is good, but when max loads are known, or size/cost is a priority, we can use the above info to get just the right size drive.

Tension Gauges: Pencil vs. Krikit

We all know that tension is important, and measuring tension with a gauge is a great way to prevent belt drive problems. However, there are a few options out there, and sometimes people are confused as to what they need.

Two of the lower cost options that Gates offers for tension testers are the Pencil Type Gauge, and the Krikit Gauge. Both of these are easy to use tools that allow the user to measure tension in the belt, and compare it to recommended tensions, but they function a little differently.

The Krikit gauge is generally seen as an automotive gauge used on front end accessory drives for cars and trucks. The way this gauge works is by depressing the finger pad on the gauge with the bottom of the gauge against the belt. The belt will deflect downward and push the arm of the Krikit up across a scale on the top of the gauge. At a certain amount of force applied to the finger pad, the Krikit will ‘click’. When the user hears the click, pressure should be released, and you can read the amount of tension in the belt by looking at where the front of the arm crosses the scale.

The Pencil gauge is generally seen as an industrial gauge, and uses two o-rings and a spring. You place the big end of the gauge on the belt, and set the bottom o-ring to the recommended deflection distance. You will need a straight edge, piece of string, or a mark on the wall next to the belt to determine starting height of the back of the belt. Set the plunger o-ring to zero, and push down on the plunger until the bottom o-ring meets the reference point you set for the starting height of the back of the belt. At this point, release the pressure on the plunger, and read the force recorded by the movement of the plunger o-ring. This is the value that you will want to compare to the recommended tension values for your drive.

As described above, there are obvious differences in how the gauges function, but the one thing that may not be obvious is the tensions that they are reading. The Krikit measures tension ‘in’ the belt, while the pencil gauge measures deflection force at a certain distance. This is important to note because different sources will recommend tension differently, either direct tension that the belt is seeing (the tension in the belt), or as a matter of deflection force and deflection distance.

Both of these tools are offered in several capacities for measuring tension, and both work very well, but they work in two different ways. It’s important to know which way your tension measurement is being given so that you can select the proper tool.

V80 and Belt Matching

A lot of people call us asking about a matched set of V-belts. This is an important design aspect, as drives that use multiple V-belts have to have belt lengths that are close to work properly. Back in 1980 Gates made a change to their manufacturing process that allowed us to meet RMA V-belt matching standards with our standard line product in the Super HC, Hi-Power II, and Tri-Power belt lines. Using any of these belts made to our V80 standard means that you can use off the shelf belts of the same size and not worry about matching them. This can save considerable time trying to find a set of belts.

We do have product lines that are not V80 approved, and do require belts to be matched. Our Predator line of V-belts are a good example. Because of the Kevlar tensile cords used in Predator, matching the belts to the same punch number is required.

Benefits of the Gates EZ Align Precision Laser Tool

Accurate pulley alignment is very important in maximizing the performance and longevity of belt drive systems. Measuring and correcting misalignment is not always easy, though, so laser type tools can be very helpful. While a number of different types can be found, the Gates EZ Align Precision Laser Tool is definitely a best in class device and should be seriously considered.

EZ Align cases are made of tough machined aluminum with a durable finish allowing survival in industrial environments and in tool bags. Strong rare earth magnets mount emitter and target units securely. The lasers are bright with high quality optics, and units can be calibrated for accuracy or repaired as needed. The new EZ Align Green model uses an even brighter green laser for outdoor use in bright sunlight. The EZ Align Green laser is 10 times brighter than the standard EZ Align laser and can reach up to 15 feet.



The EZ Align Tool is capable of indicating misalignment in three different planes.  The reflective method used in the measuring process is what really sets the EZ Align apart from other laser alignment tools.  Reflecting the beam from the target unit back to the emitter unit multiplies angular misalignment making it highly visible for accurate correction.  Angular misalignment is multiplied 20 times greater than other non-reflective laser tools.  Types of misalignment indicated by the EZ Align Tool are illustrated below:

Laser alignment tools are invaluable in accurately indicating pulley alignment and should be a part of every preventative maintenance program.   Gates EZ Align and EZ Align Green tools are the best available and are well worth their cost.

Self-Generated Tension

All synchronous belt drives exhibit a self-generating or self-tightening characteristic when transmitting a load. Laboratory testing has shown this characteristic to be similar with all tooth profiles. The designer/user should be aware that self-tensioning can result in increased bearing and shaft loads and reduced drive performance; i.e., short belt life. This can be avoided by following proper tensioning procedures.

While belt overtensioning can impose higher bearing and shaft loads and lead to reduced belt life, undertensioning can result in self-tensioning. Properly designed and tensioned drives will not be significantly affected by self-generated tension.

When a belt is too loose for the design load, the self-tensioning characteristic results in the belt teeth climbing out of the sprocket grooves, leading to increased stresses on the belt teeth, accelerated tooth wear and reduced belt life. When a belt is severely undertensioned, this self-tensioning characteristic can result in the belt ratcheting (jumping teeth). When this occurs, significant shaft separation forces are instantaneously developed in the drive, resulting in damage to bearings, shafts, and other drive components including the belt.

NOTE: This is true for all synchronous belts.

Maximum drive performance and belt life are achieved when the belt is properly tensioned for the design load and maintained.

Belt Dressing

Gates does not recommend applying dressing to belt drives. While belt dressing may temporarily quiet a slipping V-belt drive, it only masks the real problem (i.e. low belt tension). If a belt is slipping, it should be re-tensioned.

Additional information on drive inspection and troubleshooting is available in the Belt Drive Preventive Maintenance & Safety Manual at http://www.gates.com/brochure.cfm?brochure=1224&location_id=3288/.

FIRST Things First

January 5 is the kickoff for the 2013 FIRST Robotics Competition and once again Gates will be providing belts and sprockets in the kit of parts. We encourage teams to gain experience with belt drives before the build season which is why Gates is currently accepting preseason orders. After the FRC kickoff Gates will be offering several belts and sprockets as part of our in-season ordering. Then, after the season is over scholarships will be available to Seniors whose robots contained at least one Gates belt.

Please email ptpasupport@gates.com for more information about preseason orders. If you need help selecting parts or want to find more information about Gates and FIRST go to www.Gates.com/FIRST. You can also go here http://thinktank.wpi.edu/article/199 to watch the Gates presentation shown at FRC Kickoff Workshops last year.

V-Belt Sheaves in High Humidity or Corrosive Environments

Many industrial applications face problems associated with rusting parts. Numerous applications in the food and beverage industry are located in areas that require periodic washdown. Unless a drive is completely shielded and protected from wash down, rust and corrosion will be rapidly apparent in these types of environments. This is equally true of sheaves when used in very wet or humid environments, such as seen with air moving drives on cooling towers or wood kilns. The constant effects of the wet air surrounding the belt drive can cause excessive rust, and allow the belts to slip. Corrosion attacks sheave grooves, building up rust deposits. The corrosion will increase over time, building up in the sheave grooves and non-driving surfaces (bushing face). Sheaves with corrosion in the grooves can rapidly wear the belt and wear through the abrasion resistant tooth fabric, resulting in premature belt failure.

Troubleshooting Tips for the 507C Sonic Tension Meter

The Gates Sonic Tension Meter is an excellent tool for measuring belt tension. It is the most reliable and easiest to use electronic belt tension tool in the industry. Despite this, some explanations to a few reoccurring questions might be helpful to Sonic Tension Meter users.

 

1)  Don’t Know Whether The Readings Are Correct For the Belt Drive. The Sonic Tension Meter measures belt tension levels, but does not indicate if the readings are correct. Determine the correct belt tension levels using Design Flex Web / Design Flex Pro / or Design IQ drive design software. Drive design printouts provide recommended belt tension levels as well as all meter constants. All Gates drive design tools are available at www.gates.com/drivedesign.

2)  Can’t Obtain A Belt Tension Reading. The green light illuminates during the tension reading process indicating the meter is receiving a signal from the sensor. If the green light does not illuminate, move the sensor closer to the vibrating belt span or pluck the belt span harder. The belt may also not be tight enough to generate a signal, so tightening the belt may help.

The meter may also be set in an inappropriate frequency range. The frequency range setting can be seen in the upper left corner of the screen. “L” = Low (10 - 50 hz); “S” = Standard (10 – 600 hz); “H” = High (500 – 5000 hz). The “S” or standard range is sufficient for the vast majority of readings. To change, hold the “0” or “Range” button down for 2 sec and press the “Up” and “Down” buttons. Save the selection by pressing “Measure” or by powering the meter off (press the “Power” button for 2 sec). 

Lastly, standard microphone sensors cannot detect frequencies less than about 30 hz. Use the optional Inductive Sensor to read frequencies down to 10 hz. The Inductive Sensor is also very helpful in windy or noisy environments when microphone sensors do not deliver belt tension signals.

3)  Meter Displays Tension In The Wrong Units. The Sonic Tension Meter can display belt tension in units of Newtons, Pounds and Kilograms. With the meter powered off, press “0” and “9” and “Power” buttons at the same time and the three unit options will appear. Then select a unit using the “Select” button and save by powering the meter off (press the “Power” button for 2 sec.).

4)  Meter Displays “Error” When Taking Tension Readings. The “Error” message indicates that an error has been encountered in computing belt tension. The red light typically illuminates on the first reading, then the “Error” message is displayed on the third reading and the meter freezes. When this occurs, power the meter off and on and then confirm that the correct “Mass”, “Width” and “Span” constants are correct.

Note that non-zero register values are required to prevent errors in the internal meter computations from division by zero. Also note that non-zero register values are required even if using the meter in the frequency only mode. While the register values don’t have to be correct for belt span frequency readings, they can produce an “Error” message if the calculations overflow the meter display. If so, using correct constants will eliminate the “Error” message.

5)  Battery Life Is Short. Fresh alkaline batteries should provide 20 to 24 hours of continuous meter operation. Rechargeable batteries are not recommended as the voltage output is less than the required 1.5 volts, so will not power the meter sufficiently. Because of this, the meter may indicate that non alkaline batteries are discharged prematurely.

 

If you have additional questions,feel free to email the Gates Product Application Engineering Group at ptpasupport@gates.com or call us at (303) 744-5800.

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 .

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.

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.

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/. 

Minimum Belt Wrap and Tooth Engagement

Synchronous belt horsepower ratings listed in our catalogs are based on a minimum of six teeth in mesh between the belt and the sprocket. The ratings must be corrected for excessive tooth loading if there are less than six teeth in mesh. The number of teeth in mesh can either be calculated using Design IQ or the simple formula below

Where:                   D = pitch diameter, large sprocket, inches

d = pitch diameter, small sprocket, inches

C = center distance between shafts, inches

Ng = number of grooves in small sprocket

In cases where fewer than six teeth are in full contact, 20% of the horsepower rating must be subtracted for each tooth less than six not in full contact.
In addition to the number of teeth in mesh, some drives with more than two shafts may have a greater potential for the belts to ratchet where loaded sprockets have six teeth in mesh, but a small arc of contact. In order to minimize this condition, each loaded sprocket in the drive system should have an arc of contact, or belt wrap angle, of at least 60 degrees. Non-loaded idler sprockets do not have tooth meshing or wrap angle requirements.

8M / 14M PowerGrip GT2 Belts Are Now Static Conductive

PowerGrip GT2 belts in 8mm and 14mm pitches are now being manufactured in a static conductive construction that meets the ISO 9563 international standard for belt conductivity.  Belt labels now include "Antistatic To ISO 9563".  This will allow 8M and 14M PowerGrip GT2 belts to dissipate static electric charges into sprockets, and hopefully safely to ground.  This is important for belt drive applications operating in hazardous applications where sparks can ignite flammable substances as well as for belts used in equipment that must meet European ATEX requirements.

Using conductive belts is important when belt drives are operating in hazardous environments.  It is equally important, though, for there to be a conductive path from the sprockets to ground in order for static charges to be safely dissipated.  Motor and equipment mountings, shaft mountings, bearings, etc. can all influence the overall conductivity of the path to ground.  For this reason, secondary measures such as grounding straps or cables and grounding brushes are recommended to ensure safe dissipation of static electric charges.

What is Belt Pull?

Belt pull estimates the force a belt exerts on a shaft. It is the force applied to a shaft by the two belt spans entering and exiting a pulley.  Belt pull does not account for pulley weight or pulley location on a shaft.  While related, bell pull should not be considered to be interchangeable with bearing load or over hung load values. 

Belt pull values can be calculated using Gates Design Flex® and Design IQ® software programs, or by using formulas found in the Gates drive design manuals.

Gates PT Toolkit App for your smartphone!

Gates has recently come out with the mobile PT Toolkit App for your iPhone and Droid! With the mobile app you will be able to:

• Calculate energy savings                                                   
• Calculate belt drive center distance
• Calculate recommended belt tension
• Convert unit measurements

   

The PT Toolkit App is available for FREE at the market place for Droid's and at App Store for iPhone's. The app is not supported on Blackberries at this time.

Watch a tutorial on the PT Toolkit on YouTube: 

• Android: http://www.youtube.com/watch?v=Qj4lKD6D48A
•  iPhone: http://www.youtube.com/watch?v=wWND7qnnTr8

New Gates Carbon Drive Belt and Sprocket Calculator

If you have been following Gates Carbon Drive at all, you may be aware of the CDX Center Track system for bicycles. This system has changed bicycle belts completely. But beyond the simple performance and size benefits of the system, we are also offering an larger sprocket product line than we have in the past. Because Carbon Drive is 11mm specific, none of our other design programs will help you design for the proper ratio and center distance, including our online calculators at www.gatescarbondrive.com That is until now. We have a new online spreadsheet loaded up that has all of the new Gates Carbon Drive sprockets loaded into it. Check it out at: http://www.gatescarbondrive.com/installation.php?lang=us To get to the calculator, click on the link for Belt and Sprocket Size Calculator listed on the lower right hand side of the screen. Happy riding!

Preventing Potential Pitfalls in TaperLock Bushing Installations

TaperLock bushings have been in use in the Power Transmission Industry for over 30 years. With proper application and installation, they are highly reliable components. Based on questions that we receive, though, users should be aware of a couple of preventable pitfalls with their installation.

TaperLock bushings are sometimes accused of loosening after installation. TaperLock bushings need a little help beyond bolt tightening in order to grip hubs and shafts tightly. After the recommended bolt torque has been reached, the bushing faces should be tapped several times with a drift or punch in a circular pattern (don’t hammer bushing faces directly). This seats bushings more deeply into the tapered pulley or sheave hubs, increasing the gripping force. The bolts now need to be re-torqued to the recommended torque level as they will have loosened some. This process ensures that bushings are completely and tightly seated so will not loosen with usage over time.

Shaft keys are sometimes not held securely between shaft and bushing key seats and work out over time. They sometimes literally fall out in vertical shaft applications. This is due to manufacturing tolerance accumulations with shafts, bushings and keys so is only occasional. There are a couple of viable solutions. One is to apply a Loctite type adhesive to keys and key seats during assembly. Another is to punch keys several times on each side with a sharp center punch to raise the key surface slightly around the depressions. This will increase the total key thickness slightly enabling compression between shafts and bushings.

To learn more, watch our video on Taper-Lock Bushing Installation.

Check Out Gates Engineers on YouTube

In addition to blogging, our engineering group also creates short technical videos. The videos provide Gates customers a quick and simple means to learn about common topics. Some of the current videos topics available include:

• Belt Handling
• Belt Identification
• Bushing Installation
• Checking Wear with V-Belt Sheave Gauges
• Measuring Tension with the Sonic Tension Meter or Force Deflection Gauges
• Strobe Tachometer Use
• The Affinity Laws for Pump and Fan Applications
• Using the Design Flex Pro Belt Drive Design Software
• Using the Online Catalog (PartView)

Check out the videos at: http://www.youtube.com/user/GatesPT

Do Belt Drives Generate Dust?

Belt drive systems are reliable, require low maintenance and are clean running. It is normal, however, for belts to generate small quantities of dust and particulates during operation. Rubber V-belts, Micro-V, Polyflex JB, rubber synchronous, TruMotion, Poly Chain, etc. belts all have individual and unique dusting characteristics, so “normal” behaviors will vary.

The quantity of dust generated from all belt drives is influenced by many factors including belt type, sheave and sprocket surface finish, drive alignment, belt installation tension or slippage, whether belts are new or used, and others. And not surprisingly, smaller drives tend to generate less dust than larger drives.

New belt drives generate the most dust during the first 24 to 48 hours of operation, and then dusting should taper off significantly. If dusting seems unusually heavy or continues after the initial run in period, this is abnormal and users should look more closely for possible causes.

For small synchronous belt applications that are sensitive to dusting, the Gates TruMotion construction is available on a made-to-order basis. TruMotion belts utilize materials and treatments that minimize dusting, so are well suited for clean operations.

Design Flex Pro: US and UK Version Correction

If you use Design Flex Pro for US customers, you must check your installation – see below.

Many of the new computer images have the default language/culture set to English-UK. This makes the computer look OK to English-US users, but does not make Design Flex Pro (DF-Pro) work correctly for US users.

• Notes required by US legal do not show up correctly for people using English UK.
• Some fields used for NA but not used in Europe do not show when English UK is selected.

Once DF-Pro is installed, changing the computer culture will not change the selected language.

Design IQ is not affected as it does not have a separate language for English-UK.

To correct this for DF-Pro:

• Open DF-Pro – make sure it is the only copy open
• Go to Tools Languages and make sure the language selected is correct for your area. If in the US, this should be English, not English-UK.
• Close DF-Pro to make the selection stick.

Gates 2012 FIRST Robotics Scholarships

Gates is excited to offer six $2000 scholarships to seniors using a Gates belt drive on their 2012 FIRST Robotics competition robot. In addition to using a belt, students will also answer a challenge question involving creative problem solving with belt drives. Application instructions, detailed requirements, and the challenge question are now available at www.gates.com/FIRST. All entries must be submitted online by May 15,2012 to qualify.

Good luck FIRST Seniors!!

Belt Failures - Tensile Cord Crimp

A very common failure mode for a synchronous belt is when the tensile cord is "crimped", occurring when the tensile member is bent to a radius smaller than recommended by the belt manufacturer. Crimping the belt will damage the tensile members and reduce the structural integrity of the belt.

Belt Crimp

Tensile cord crimp can happen by mishandling the belt, hanging the belt on a nail (or similar object), or by running the belt on a smaller than recommended pulley diameter. Another common cause of a belt crimp is when the belt ratchets over a sprocket groove. The instantaneous motion of a belt tooth exiting one groove and entering the adjacent groove can crimp the tensile cord in the area where the tooth jumped the groove.

After the tensile cord is crimped it loses tensile strength which the belt relies on to transmit the load. If the crimp is bad, the belt will fail exactly in spot where the tensile cord was damaged by shearing straight across the width of the belt in a clean break.

Crimp Failure

Ways to avoid a crimp failure with a synchronous belt are as follows:

1. Be careful when handling the belt, especially when installing the belt in a tight area.
2. If storing the belt, do not hang it on a nail or similar object. Use a saddle or rack at least as large as the minimum diameter sheave or sprocket recommended for the belt cross section.
3. Follow the manufacturer's recommended tension for the belt drive to ensure proper tension. If you notice that the belt is about to ratchet teeth or already has done so, increase the tension in the drive until the tooth has a tight fit with the sprocket groove.
4. Follow the manufacturer's minimum recommended diameter specification for the belt cross section being used. Gates' recommendations for minimum pulley diameters can be found in the preventive maintenance manual at www.gates.com/catalogs.

Belt Drives and Ozone Exposure

Ozone is a naturally occuring gas that is found in the air that we breathe. It consists uniquely of three oxygen molucules bonded together rather than the two of normal oxygen. Ozone is produced during lightening storms and is responsible for the fresh smell of the air afterwards. Electrical arcs from arc-welding or from around the brushes of electrical motors or ultraviolet light all produce ozone gas. It can often be detected by it's very unique chlorine bleach like smell in more concentrated form. Ozone is a powerful oxidant, so is sometimes used in air and water purification systems. To much, though, can have detrimental effects on plants, lung tissues, and organic materials like latex, plastics, and rubber.

The potential for excessive ozone concentrations is low for most environments in which belt drive systems are found. There are industrial environments, though, with higher concentrations of ozone gas making belt performance and durability a concern.

While all belts are designed for resistance to ozone, excessive concentrations can still affect rubber belts in much the same way as high environmental temperatures. Ozone slowly errodes the chemical composition resulting in rubber hardening and cracking. The amount of degradation is a function of the ozone concentration and the time of exposure. To prevent excessive detrimental effects on rubber power transmission belts, the following concentration levels should not be exceeded: (pphm = parts per hundred million)

Non-Conductive Belt Constructions: 100 pphm
Conductive Belt Constructions: 75 pphm
Non Marking Constructions: 20 pphm
Low Temperature Constructions: 20 pphm

The polyurethane material used in Poly Chain GT Carbon belts is considerably more resistant to ozone degradation than conventional rubber materials. Poly Chain GT Carbon drives are an excellent choice for drive applications located in environments with ozone concentrations.

Overhung Load

To prevent premature failures, manufacturers typically publish overhung load values for the speed reducers they offer. When designing a belt drive for use on a reducer, it is important to review the maximum published overhung load value to prevent overload of the bearings and shaft.

Along with their overhung load ratings, each speed reducer manufacturer publishes unique overhung load equations and constants. Therefore, it is crucial to obtain the correct overhung load calculation procedure from the reducer manufacture and to use their corresponding ratings.

If the overhung load is too high, the designer may consider increasing the pulley diameters, reducing the belt width, and/or mounting the pulley closer to the bearing. Following design adjustments, the overhung load calculations should be re-run to ensure that the drive is acceptable.

Right from the Start - Belt Storage

To get the most from a belt drive, its important to properly store a belt -all the proper installation procedures and design practices can be for nothing if a belt is improperly stored or damaged in storage.

A few of the major belt storage guidelines:

1) Belts can be stored up to 6 years if properly stored at temperatures less than 85 degrees F, and less than 70% relative humidty.

2) Make sure the belts are not bent to diameters smaller than the minimum recommended diameter for that cross section.

3) V-belts can be stored by hanging on a wall rack if they are hung on a saddle or diameter at least as large as the minimum diameter recommended for the cross section. Don't hang from a pin or nail!

4) Don't store in direct sunlight.

5) Don't store near heating devices.

6) Don't store near ozone generating devices such as transformers or electric motors.

7) Don't store belts where they are or could be exposed to solvents or chemicals.

8) Don't store on the floor unless in a proctive container.

9) Don't crimp belts, either in storage or handling.

Complete guidelines can be found in the Gates Belt Drive Preventive Maintenance & Safety Manual.