9.1 LOW-SPEED OPERATION
Synchronous drives are especially well-suitable for low-speed, high torque applications. Their positive driving nature stops potential slippage connected with V-belt drives, and even allows significantly higher torque carrying capacity. Small pitch synchronous drives working at speeds of 50 ft/min (0.25 m/s) or less are considered to be low-speed. Care should be used the get selection procedure as stall and peak torques can sometimes be very high. While intermittent peak torques can often be carried by synchronous drives without special factors, high cyclic peak torque loading ought to be carefully reviewed.
Proper belt installation tension and rigid get bracketry and framework is vital in stopping belt tooth jumping less than peak torque loads. Additionally it is beneficial to design with more than the normal minimum of 6 belt tooth in mesh to make sure sufficient belt tooth shear power.
Newer generation curvilinear systems like PowerGrip GT2 and PowerGrip HTD ought to be used in low-speed, high torque applications, as trapezoidal timing belts are even more susceptible to tooth jumping, and have significantly much less load carrying capability.
9.2 HIGH-SPEED OPERATION
Synchronous belt drives are often found in high-speed applications despite the fact that V-belt drives are usually better suitable. They are often used due to their positive driving characteristic (no creep or slip), and because they might need minimal maintenance (don’t stretch significantly). A substantial drawback of high-velocity synchronous drives can be drive noise. High-swiftness synchronous drives will almost always produce even more noise than V-belt drives. Small pitch synchronous drives working at speeds in excess of 1300 ft/min (6.6 m/s) are believed to be high-speed.
Special consideration should be given to high-speed drive designs, as a number of factors can considerably influence belt performance. Cord fatigue and belt tooth wear are the two most significant factors that must definitely be controlled to have success. Moderate pulley diameters should be used to reduce the price of cord flex fatigue. Designing with a smaller sized pitch belt will often offer better cord flex exhaustion characteristics when compared to a bigger pitch belt. PowerGrip GT2 is particularly perfect for high-swiftness drives due to its excellent belt tooth entry/exit characteristics. Even interaction between your belt tooth and pulley groove minimizes wear and sound. Belt installation stress is especially important with high-velocity drives. Low belt stress allows the belt to ride out from the driven pulley, resulting in rapid belt tooth and pulley groove wear.
9.3 SMOOTH RUNNING
Some ultrasensitive applications require the belt drive to use with as little vibration aspossible, as vibration sometimes has an effect on the system procedure or finished manufactured product. In these cases, the features and properties of most appropriate belt drive products ought to be reviewed. The ultimate drive system selection should be based on the most critical style requirements, and may need some compromise.
Vibration isn’t generally considered to be a issue with synchronous belt drives. Low degrees of vibration typically derive from the process of tooth meshing and/or as a result of their high tensile modulus properties. Vibration caused by tooth meshing is usually a normal characteristic of synchronous belt drives, and can’t be completely eliminated. It could be minimized by avoiding small pulley diameters, and instead choosing moderate sizes. The dimensional precision of the pulleys also influences tooth meshing quality. Additionally, the installation tension has an effect on meshing quality. PowerGrip GT2 drives mesh very cleanly, leading to the smoothest possible operation. Vibration resulting from high tensile modulus could be a function of pulley quality. Radial go out causes belt stress variation with each pulley revolution. V-belt pulleys are also manufactured with some radial run out, but V-belts have a lower tensile modulus resulting in less belt tension variation. The high tensile modulus within synchronous belts is necessary to maintain appropriate pitch under load.
9.4 DRIVE NOISE
Drive noise evaluation in any belt drive system ought to be approached with care. There are numerous potential sources of noise in something, including vibration from related components, bearings, and resonance and amplification through framework and panels.
Synchronous belt drives typically produce even more noise than V-belt drives. Noise results from the process of belt tooth meshing and physical contact with the pulleys. The sound pressure level generally raises as operating velocity and belt width increase, and as pulley diameter reduces. Drives designed on moderate pulley sizes without excessive capacity (overdesigned) are generally the quietest. PowerGrip GT2 drives have already been found to be considerably quieter than various other systems due to their improved meshing characteristic, see Figure 9. Polyurethane belts generally generate more noise than neoprene belts. Proper belt installation tension can be very important in minimizing travel noise. The belt should be tensioned at a level that allows it to run with as little meshing interference as feasible.
Drive alignment also offers a significant influence on drive sound. Special attention should be given to minimizing angular misalignment (shaft parallelism). This assures that belt teeth are loaded uniformly and minimizes aspect monitoring forces against the flanges. Parallel misalignment (pulley offset) isn’t as critical of a concern so long as the belt isn’t trapped or pinched between reverse flanges (start to see the special section coping with get alignment). Pulley materials and dimensional precision also influence travel sound. Some users possess found that 
steel pulleys are the quietest, followed closely by lightweight aluminum. Polycarbonates have been found to become noisier than metallic components. Machined pulleys are usually quieter than molded pulleys. The reasons because of this revolve around material density and resonance characteristics along with dimensional accuracy.
9.5 Taper Pulleys static CONDUCTIVITY
Small synchronous rubber or urethane belts can generate an electrical charge while operating in a drive. Factors such as humidity and working speed impact the potential of the charge. If decided to become a problem, rubber belts can be stated in a conductive construction to dissipate the charge into the pulleys, and also to ground. This prevents the accumulation of electric charges that might be detrimental to materials handling processes or sensitive consumer electronics. It also significantly reduces the prospect of arcing or sparking in flammable environments. Urethane belts can’t be produced in a conductive structure.
RMA has outlined criteria for conductive belts in their bulletin IP-3-3. Unless normally specified, a static conductive structure for rubber belts is on a made-to-order basis. Unless normally specified, conductive belts will be built to yield a level of resistance of 300,000 ohms or much less, when new.
non-conductive belt constructions are also available for rubber belts. These belts are generally built specifically to the customers conductivity requirements. They are usually found in applications where one shaft should be electrically isolated from the various other. It is necessary to note that a static conductive belt cannot dissipate a power charge through plastic material pulleys. At least one metallic pulley in a drive is required for the charge to become dissipated to floor. A grounding brush or equivalent device could also be used to dissipate electric charges.
Urethane timing belts aren’t static conductive and cannot be built in a particular conductive construction. Unique conductive rubber belts should be utilized when the existence of an electrical charge is certainly a concern.
9.6 OPERATING ENVIRONMENTS
Synchronous drives are ideal for use in a wide variety of environments. Particular considerations could be necessary, nevertheless, depending on the application.
Dust: Dusty environments usually do not generally present serious problems to synchronous drives so long as the contaminants are fine and dry out. Particulate matter will, however, act as an abrasive producing a higher rate of belt and pulley use. Damp or sticky particulate matter deposited and loaded into pulley grooves could cause belt tension to increase considerably. This increased tension can influence shafting, bearings, and framework. Electrical charges within a drive system can sometimes entice particulate matter.
Debris: Debris ought to be prevented from falling into any 
synchronous belt drive. Debris caught in the drive is generally either pressured through the belt or outcomes in stalling of the system. In either case, serious damage takes place to the belt and related drive hardware.
Water: Light and occasional connection with water (occasional clean downs) shouldn’t seriously have an effect on synchronous belts. Prolonged get in touch with (continuous spray or submersion) results in considerably reduced tensile power in fiberglass belts, and potential duration variation in aramid belts. Prolonged contact with drinking water also causes rubber substances to swell, although less than with oil get in touch with. Internal belt adhesion systems are also steadily divided with the presence of drinking water. Additives to water, such as lubricants, chlorine, anticorrosives, etc. can have a far more detrimental effect on the belts than pure water. Urethane timing belts also have problems with water contamination. Polyester tensile cord shrinks significantly and experiences lack of tensile power in the existence of drinking water. Aramid tensile cord maintains its strength pretty well, but experiences size variation. Urethane swells more than neoprene in the existence of drinking water. This swelling can increase belt tension significantly, leading to belt and related equipment problems.
Oil: Light connection with oils on an occasional basis won’t generally damage synchronous belts. Prolonged contact with essential oil or lubricants, either directly or airborne, outcomes in significantly reduced belt service life. Lubricants cause the rubber compound to swell, breakdown inner adhesion systems, and reduce belt tensile power. While alternate rubber compounds might provide some marginal improvement in durability, it is best to prevent oil from contacting synchronous belts.
Ozone: The existence of ozone could be detrimental to the substances used in rubber synchronous belts. Ozone degrades belt materials in much the same way as excessive environmental temperatures. Although the rubber materials used in synchronous belts are compounded to withstand the effects of ozone, ultimately chemical breakdown occurs plus they become hard and brittle and begin cracking. The amount of degradation depends upon the ozone concentration and duration of publicity. For good performance of rubber belts, the next concentration levels should not be exceeded: (parts per hundred million)
Standard Construction: 100 pphm
Nonmarking Construction: 20 pphm
Conductive Construction: 75 pphm
Low Temperatures Building: 20 pphm
Radiation: Exposure to gamma radiation could be detrimental to the compounds used in rubber and urethane synchronous belts. Radiation degrades belt materials much the same way extreme environmental temperatures do. The amount of degradation depends upon the strength of radiation and the exposure time. Once and for all belt performance, the next exposure levels should not be exceeded:
Standard Construction: 108 rads
Nonm arking Structure: 104 rads
Conductive Construction: 106 rads
Low Temperatures Construction: 104 rads
Dust Era: Rubber synchronous belts are known to generate little quantities of fine dust, as a natural result of their operation. The amount of dust is normally higher for new belts, because they operate in. The time period for run in to occur depends upon the belt and pulley size, loading and rate. Elements such as for example pulley surface surface finish, operating speeds, installation tension, and alignment impact the number of dust generated.
Clean Room: Rubber synchronous belts might not be suitable for use in clean area environments, where all potential contamination should be minimized or eliminated. Urethane timing belts typically generate significantly less particles than rubber timing belts. Nevertheless, they are suggested limited to light operating loads. Also, they cannot be produced in a static conductive structure to allow electrical charges to dissipate.
Static Sensitive: Applications are sometimes delicate to the accumulation of static electric charges. Electrical costs can affect materials handling processes (like paper and plastic film transportation), and sensitive electronic products. Applications like these need a static conductive belt, so that the static costs produced by the belt could be dissipated into the pulleys, and also to ground. Standard rubber synchronous belts do not fulfill this requirement, but can be produced in a static conductive construction on a made-to-order basis. Regular belt wear resulting from long term operation or environmental contamination can impact belt conductivity properties.
In sensitive applications, rubber synchronous belts are favored over urethane belts since urethane belting cannot be stated in a conductive construction.
9.7 BELT TRACKING
Lateral tracking qualities of synchronous belts is a common area of inquiry. Although it is normal for a belt to favor one aspect of the pulleys while working, it is abnormal for a belt to exert significant pressure against a flange leading to belt edge wear and potential flange failing. Belt tracking is influenced by several factors. In order of significance, debate about these elements is really as follows:
Tensile Cord Twist: Tensile cords are formed into a single twist configuration during their manufacture. Synchronous belts made out of only one twist tensile cords monitor laterally with a substantial drive. To neutralize this tracking push, tensile cords are stated in right- and left-hand twist (or “S” and “Z” twist) configurations. Belts made with “S” twist tensile cords monitor in the contrary path to those constructed with “Z” twist cord. Belts made with alternating “S” and “Z” twist tensile cords monitor with minimal lateral force because the tracking features of both cords offset each other. This content of “S” and “Z” twist tensile cords varies somewhat with every belt that is produced. Because of this, every belt comes with an unprecedented inclination to track in either one path or the other. When an application takes a belt to track in a single specific direction only, an individual twist construction is used. See Figures 16 & Figure 17.
Angular Misalignment: Angular misalignment, or shaft nonparallelism, cause synchronous belts to track laterally. The position of misalignment influences the magnitude and path of the monitoring force. Synchronous belts have a tendency to track “downhill” to circumstances of lower tension or shorter center distance.
Belt Width: The potential magnitude of belt tracking force is directly related to belt width. Wide belts have a tendency to track with more force than narrow belts.
Pulley Diameter: Belts operating on small pulley diameters can have a tendency to generate higher monitoring forces than on large diameters. This is particularly true as the belt width techniques the pulley diameter. Drives with pulley diameters less than the belt width aren’t generally recommended because belt tracking forces may become excessive.
Belt Length: Due to just how tensile cords are applied to the belt molds, brief belts can have a tendency to exhibit higher monitoring forces than longer belts. The helix angle of the tensile cord decreases with increasing belt length.
Gravity: In get applications with vertical shafts, gravity pulls the belt downward. The magnitude of the force is minimal with little pitch synchronous belts. Sag in lengthy belt spans ought to be avoided by applying sufficient belt installation tension.
Torque Loads: Sometimes, while in operation, a synchronous belt will move laterally from side to side on the pulleys instead of operating in a consistent position. While not generally regarded as a significant concern, one explanation for this is normally varying torque loads within the get. Synchronous belts occasionally track in different ways with changing loads. There are numerous potential reasons for this; the root cause is related to tensile cord distortion while under great pressure against the pulleys. Variation in belt tensile loads can also cause adjustments in framework deflection, and angular shaft alignment, leading to belt movement.
Belt Installation Tension: Belt tracking may also be influenced by the amount of belt installation stress. The reasons for this are similar to the result that varying torque loads have on belt tracking. When problems with belt monitoring are experienced, each of these potential contributing elements should be investigated in the order that they are outlined. Generally, the primary problem is going to be recognized before moving totally through the list.
9.8 PULLEY FLANGES
Pulley guideline flanges are necessary to hold synchronous belts operating on the pulleys. As talked about previously in Section 9.7 on belt tracking, it is normal for synchronous belts to favor one side of the pulleys when running. Proper flange design is important in stopping belt edge wear, minimizing sound and preventing the belt from climbing from the pulley. Dimensional recommendations for custom-made or molded flanges are included in tables dealing with these problems. Proper flange placement is important to ensure that the belt is definitely adequately restrained within its operating system. Because design and design of small synchronous drives is so varied, the wide selection of flanging situations potentially encountered cannot very easily be covered in a straightforward set of guidelines without selecting exceptions. Despite this, the next broad flanging guidelines should help the developer in most cases:
Two Pulley Drives: On basic two pulley drives, either one pulley should be flanged on both sides, or each pulley should be flanged on reverse sides.
Multiple Pulley Drives: On multiple pulley (or serpentine) drives, either almost every other pulley should be flanged in both sides, or every single pulley ought to be flanged on alternating sides around the system. Vertical Shaft Drives: On vertical shaft drives, at least one pulley should be flanged on both sides, and the rest of the pulleys ought to be flanged on at least underneath side.
Long Span Lengths: Flanging recommendations for little synchronous drives with lengthy belt span lengths cannot very easily be defined because of the many factors that can affect belt tracking qualities. Belts on drives with lengthy spans (generally 12 times the diameter of small pulley or even more) frequently require even more lateral restraint than with short spans. Because of this, it is generally smart to flange the pulleys on both sides.
Large Pulleys: Flanging large pulleys can be costly. Designers frequently desire to leave large pulleys unflanged to lessen cost and space. Belts generally tend to need less lateral restraint on large pulleys than little and can often perform reliably without flanges. When determining whether to flange, the prior guidelines should be considered. The groove encounter width of unflanged pulleys should also be greater than with flanged pulleys. See Table 27 for recommendations.
Idlers: Flanging of idlers is normally not necessary. Idlers designed to bring lateral side loads from belt tracking forces could be flanged if needed to provide lateral belt restraint. Idlers utilized for this purpose can be utilized on the inside or backside of the belts. The prior guidelines also needs to be considered.
9.9 REGISTRATION
The three primary factors contributing to belt drive registration (or positioning) errors are belt elongation, backlash, and tooth deflection. When analyzing the potential registration features of a synchronous belt drive, the machine must first be decided to end up being either static or dynamic when it comes to its registration function and requirements.
Static Registration: A static registration system moves from its initial static position to a second static position. Through the procedure, the designer is concerned only with how accurately and consistently the drive arrives at its secondary placement. He/she isn’t worried about any potential sign up errors that take place during transport. Therefore, the principal factor adding to registration error in a static registration system is definitely backlash. The consequences of belt elongation and tooth deflection don’t have any impact on the sign up accuracy of this kind of system.
Dynamic Registration: A dynamic registration system must perform a registering function while in motion with torque loads various as the system operates. In cases like this, the designer can be involved with the rotational position of the get pulleys regarding one another at every point in time. Therefore, belt elongation, backlash and tooth deflection will all contribute to registrational inaccuracies.
Further discussion on the subject of each of the factors contributing to registration error is really as follows:
Belt Elongation: Belt elongation, or stretch, occurs naturally whenever a belt is placed under pressure. The total tension exerted within a belt results from set up, in addition to functioning loads. The amount of belt elongation is certainly a function of the belt tensile modulus, which is usually influenced by the kind of tensile cord and the belt construction. The standard tensile cord used in rubber synchronous belts is fiberglass. Fiberglass has a high tensile modulus, is dimensionally steady, and has excellent flex-fatigue characteristics. If a higher tensile modulus is needed, aramid tensile cords can be viewed as, although they are usually used to provide resistance to harsh shock and impulse loads. Aramid tensile cords found in small synchronous belts generally possess just a marginally higher tensile modulus in comparison to fiberglass. When required, belt tensile modulus data is normally obtainable from our Program Engineering Department.
Backlash: Backlash in a synchronous belt drive outcomes from clearance between your belt tooth and the pulley grooves. This clearance is required to allow the belt tooth to enter and exit the grooves effortlessly with a minimum of interference. The quantity of clearance required is dependent upon the belt tooth profile. Trapezoidal Timing Belt Drives are recognized for having relatively little backlash. PowerGrip HTD Drives have improved torque having capability and resist ratcheting, but have a significant quantity of backlash. PowerGrip GT2 Drives have even further improved torque having capability, and also have only a small amount or much less backlash than trapezoidal timing belt drives. In special cases, alterations can be made to travel systems to further lower backlash. These alterations typically result in increased belt wear, increased travel sound and shorter drive life. Get in touch with our Program Engineering Section for additional information.
Tooth Deflection: Tooth deformation in a synchronous belt drive occurs as a torque load is put on the system, and individual belt teeth are loaded. The amount of belt tooth deformation is dependent upon the amount of torque loading, pulley size, installation stress and belt type. Of the three primary contributors to registration error, tooth deflection is the most challenging to quantify. Experimentation with a prototype drive system may be the best means of obtaining practical estimations of belt tooth deflection.
Additional guidelines that may be useful in designing registration important drive systems are the following:
Select PowerGrip GT2 or trapezoidal timing belts.
Style with large pulleys with more teeth in mesh.
Keep belts tight, and control tension closely.
Design frame/shafting to be rigid under load.
Use top quality machined pulleys to minimize radial runout and lateral wobble.