9.1 LOW-SPEED OPERATION
Synchronous drives are specially well-appropriate for low-speed, high torque applications. Their positive generating nature prevents potential slippage connected with V-belt drives, and also allows significantly greater torque carrying capacity. Little pitch synchronous drives working at Gas-cooling Vacuum Pump speeds of 50 ft/min (0.25 m/s) or less are believed to be low-speed. Care should be taken in the drive selection procedure as stall and peak torques can sometimes be very high. While intermittent peak torques can frequently be carried by synchronous drives without special considerations, high cyclic peak torque loading should be carefully reviewed.
Proper belt installation tension and rigid get bracketry and framework is vital in stopping belt tooth jumping under peak torque loads. It is also beneficial to design with more compared to the normal minimum of 6 belt tooth in mesh to ensure adequate belt tooth shear strength.
Newer era 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 prone to tooth jumping, and have significantly much less load carrying capability.
9.2 HIGH-SPEED OPERATION
Synchronous belt drives tend to be used in high-speed applications even though V-belt drives are typically better suitable. They are generally used because of their positive generating characteristic (no creep or slip), and because they might need minimal maintenance (don’t stretch significantly). A significant drawback of high-swiftness synchronous drives is normally get noise. High-rate synchronous drives will nearly always produce more noise than V-belt drives. Small pitch synchronous drives operating at speeds in excess of 1300 ft/min (6.6 m/s) are believed to be high-speed.
Special consideration ought to be given to high-speed drive designs, as several factors can significantly influence belt performance. Cord fatigue and belt tooth wear are the two most significant elements that must be controlled to have success. Moderate pulley diameters should be used to reduce the rate of cord flex exhaustion. Designing with a smaller pitch belt will often offer better cord flex fatigue characteristics than a larger pitch belt. PowerGrip GT2 is particularly well suited for high-swiftness drives due to its excellent belt tooth entry/exit characteristics. Steady interaction between the belt tooth and pulley groove minimizes use and noise. Belt installation pressure is especially crucial with high-velocity drives. Low belt tension allows the belt to trip out from the driven pulley, leading to rapid belt tooth and pulley groove wear.
9.3 SMOOTH RUNNING
Some ultrasensitive applications require the belt drive to operate with only a small amount vibration aspossible, as vibration sometimes impacts the system procedure or finished manufactured product. In these cases, the characteristics and properties of most appropriate belt drive products ought to be reviewed. The final drive system selection should be based on the most significant design requirements, and could require some compromise.
Vibration isn’t generally regarded as a problem with synchronous belt drives. Low degrees of vibration typically derive from the procedure of tooth meshing and/or consequently of their high tensile modulus properties. Vibration resulting from tooth meshing is usually a normal characteristic of synchronous belt drives, and can’t be completely eliminated. It can be minimized by avoiding little pulley diameters, and rather choosing moderate sizes. The dimensional precision of the pulleys also influences tooth meshing quality. Additionally, the installation tension has an impact on meshing quality. PowerGrip GT2 drives mesh extremely 
cleanly, resulting in the smoothest possible operation. Vibration caused by high tensile modulus can be a function of pulley quality. Radial run out causes belt stress variation with each pulley revolution. V-belt pulleys are also produced with some radial run out, but V-belts possess a lower tensile modulus resulting in less belt pressure variation. The high tensile modulus found in 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 resources of noise in something, including vibration from related parts, bearings, and resonance and amplification through framework and panels.
Synchronous belt drives typically produce even more noise than V-belt drives. Noise outcomes from the process of belt tooth meshing and physical connection with the pulleys. The sound pressure level generally increases as operating quickness and belt width boost, and as pulley diameter decreases. Drives designed on moderate pulley sizes without extreme capacity (overdesigned) are usually the quietest. PowerGrip GT2 drives have been discovered to be significantly quieter than various other systems due to their improved meshing characteristic, see Figure 9. Polyurethane belts generally create more noise than neoprene belts. Proper belt installation tension is also very important in minimizing drive noise. The belt ought to be tensioned at a rate which allows it to perform with only a small amount meshing interference as possible.
Travel alignment also offers a significant effect on drive sound. Special attention should be given to reducing angular misalignment (shaft parallelism). This assures that belt tooth are loaded uniformly and minimizes aspect monitoring forces 
against the flanges. Parallel misalignment (pulley offset) is not as essential of a concern as long as the belt isn’t trapped or pinched between contrary flanges (see the particular section coping with drive alignment). Pulley materials and dimensional precision also influence get noise. Some users have discovered that steel pulleys are the quietest, followed closely by lightweight aluminum. Polycarbonates have been discovered to become noisier than metallic components. Machined pulleys are generally quieter than molded pulleys. The reason why because of this revolve around materials density and resonance characteristics in addition to dimensional accuracy.
9.5 STATIC CONDUCTIVITY
Small synchronous rubber or urethane belts can generate a power charge while operating on a drive. Factors such as humidity and operating speed impact the potential of the charge. If determined to be a problem, rubber belts can be stated in a conductive structure to dissipate the charge into the pulleys, and to surface. This prevents the accumulation of electrical charges that may be harmful to material handling processes or sensitive consumer electronics. In addition, it significantly reduces the potential for arcing or sparking in flammable conditions. Urethane belts can’t be stated in a conductive construction.
RMA has outlined criteria for conductive belts within their bulletin IP-3-3. Unless otherwise specified, a static conductive structure for rubber belts is normally on a made-to-order basis. Unless usually specified, conductive belts will be built to yield a resistance of 300,000 ohms or less, when new.
non-conductive belt constructions are also available for rubber belts. These belts are generally built particularly to the customers conductivity requirements. They are generally used 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 an electrical charge through plastic material pulleys. At least one metallic pulley in a drive is required for the charge to become dissipated to ground. A grounding brush or identical device may also be used to dissipate electrical charges.
Urethane timing belts are not static conductive and can’t be built in a particular conductive construction. Special conductive rubber belts should be utilized when the presence of an electrical charge can be a concern.
9.6 OPERATING ENVIRONMENTS
Synchronous drives are ideal for use in a wide selection of environments. Special considerations may be necessary, however, based on the application.
Dust: Dusty conditions do not generally present serious complications to synchronous drives so long as the contaminants are fine and dry. Particulate matter will, however, become an abrasive producing a higher level of belt and pulley put on. Damp or sticky particulate matter deposited and packed into pulley grooves can cause belt tension to increase significantly. This increased tension can influence shafting, bearings, and framework. Electrical charges within a travel system can sometimes get particulate matter.
Debris: Debris should be prevented from falling into any synchronous belt drive. Debris caught in the drive is normally either forced through the belt or outcomes in stalling of the system. In either case, serious damage occurs to the belt and related travel hardware.
Water: Light and occasional contact with water (occasional clean downs) should not seriously impact synchronous belts. Prolonged contact (continuous spray or submersion) results in significantly reduced tensile power in fiberglass belts, and potential duration variation in aramid belts. Prolonged contact with drinking water also causes rubber compounds to swell, although significantly less than with oil contact. Internal belt adhesion systems are also steadily broken down with the presence of water. Additives to drinking water, such as lubricants, chlorine, anticorrosives, etc. can possess a more detrimental influence on the belts than clear water. Urethane timing belts also have problems with water contamination. Polyester tensile cord shrinks significantly and experiences loss of tensile power in the existence of water. Aramid tensile cord maintains its strength pretty well, but encounters size variation. Urethane swells a lot more than neoprene in the presence of drinking water. This swelling can boost belt tension significantly, causing belt and related equipment problems.
Oil: Light connection with natural oils on an intermittent basis will not generally damage synchronous belts. Prolonged contact with essential oil or lubricants, either directly or airborne, results in significantly reduced belt service existence. Lubricants trigger the rubber compound to swell, breakdown inner adhesion systems, and reduce belt tensile strength. While alternate rubber substances may provide some marginal improvement in durability, it is best to prevent essential oil from contacting synchronous belts.
Ozone: The presence of ozone can be detrimental to the substances found in rubber synchronous belts. Ozone degrades belt materials in much the same way as extreme environmental temps. Although the rubber materials found in synchronous belts are compounded to resist the effects of ozone, ultimately chemical breakdown occurs plus they become hard and brittle and begin cracking. The amount of degradation is dependent upon the ozone concentration and duration of publicity. For good overall performance of rubber belts, the next concentration levels shouldn’t be exceeded: (parts per hundred million)
Standard Construction: 100 pphm
Nonmarking Construction: 20 pphm
Conductive Construction: 75 pphm
Low Temperatures Construction: 20 pphm
Radiation: Contact with gamma radiation can be detrimental to the substances found in rubber and urethane synchronous belts. Radiation degrades belt materials much the same way excessive environmental temperature ranges do. The amount of degradation is dependent upon the intensity of radiation and the publicity time. For good belt performance, the next exposure levels should not be exceeded:
Standard Construction: 108 rads
Nonm arking Building: 104 rads
Conductive Construction: 106 rads
Low Temperatures Construction: 104 rads
Dust Generation: Rubber synchronous belts are known to generate small quantities of great dust, as an all natural consequence of their procedure. The number of dust is typically higher for fresh belts, because they run in. The time period for run in to occur is dependent upon the belt and pulley size, loading and quickness. Elements such as for example pulley surface finish, operating speeds, set up pressure, and alignment influence the number of dust generated.
Clean Area: Rubber synchronous belts may not be ideal for use in clean area environments, where all potential contamination must be minimized or eliminated. Urethane timing belts typically generate significantly less particles than rubber timing belts. Nevertheless, they are recommended only for light working loads. Also, they cannot be produced in a static conductive structure to allow electrical fees to dissipate.
Static Sensitive: Applications are sometimes delicate to the accumulation of static electrical charges. Electrical fees can affect materials handling functions (like paper and plastic film transportation), and sensitive electronic apparatus. Applications like these require a static conductive belt, so that the static charges generated by the belt could be dissipated into the pulleys, and to ground. Standard rubber synchronous belts do not satisfy this necessity, but can be manufactured in a static conductive structure on a made-to-order basis. Normal belt wear resulting from long term procedure or environmental contamination can influence belt conductivity properties.
In sensitive applications, rubber synchronous belts are favored over urethane belts since urethane belting can’t be stated in a conductive construction.
9.7 BELT TRACKING
Lateral tracking characteristics of synchronous belts is certainly a common area of inquiry. Although it is regular for a belt to favor one side of the pulleys while working, it is unusual for a belt to exert significant force against a flange leading to belt edge use and potential flange failing. Belt tracking is usually influenced by many factors. In order of significance, conversation about these factors is really as follows:
Tensile Cord Twist: Tensile cords are formed into a single twist configuration throughout their manufacture. Synchronous belts made with only single twist tensile cords monitor laterally with a substantial power. To neutralize this tracking push, tensile cords are stated in right- and left-hands twist (or “S” and “Z” twist) configurations. Belts made with “S” twist tensile cords monitor in the opposite direction to those built with “Z” twist cord. Belts made out of alternating “S” and “Z” twist tensile cords monitor with minimal lateral force because the tracking features of the two cords offset each other. This content of “S” and “Z” twist tensile cords varies somewhat with every belt that’s produced. As a result, every belt has an unprecedented tendency to monitor in each one direction or the various other. When an application takes a belt to track in one specific direction just, an individual twist construction can be used. See Figures 16 & Figure 17.
Angular Misalignment: Angular misalignment, or shaft nonparallelism, cause synchronous belts to track laterally. The angle of misalignment influences the magnitude and direction of the tracking pressure. Synchronous belts tend to track “downhill” to circumstances of lower tension or shorter middle distance.
Belt Width: The potential magnitude of belt tracking force is directly linked to belt width. Wide belts tend to track with more pressure than narrow belts.
Pulley Diameter: Belts operating on little pulley diameters can tend to generate higher monitoring forces than on large diameters. This is particularly true as the belt width approaches the pulley size. Drives with pulley diameters less than the belt width are not generally recommended because belt tracking forces may become excessive.
Belt Length: Because of the way tensile cords are applied on to the belt molds, brief belts can tend 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 this force is normally minimal with small pitch synchronous belts. Sag in lengthy belt spans should be avoided by applying adequate belt installation tension.
Torque Loads: Sometimes, while functioning, a synchronous belt will move laterally laterally on the pulleys rather than operating in a constant position. Without generally regarded as a significant concern, one explanation for this is definitely varying torque loads within the get. Synchronous belts occasionally track differently with changing loads. There are numerous potential reasons for this; the root cause relates to tensile cord distortion while under pressure against the pulleys. Variation in belt tensile loads may also cause changes in framework deflection, and angular shaft alignment, leading to belt movement.
Belt Installation Stress: Belt tracking is sometimes influenced by the amount of belt installation pressure. The reason why for this act like the effect that varying torque loads have on belt tracking. When problems with belt monitoring are experienced, each of these potential contributing factors should be investigated in the purchase they are outlined. Generally, the primary problem will probably be discovered before moving completely through the list.
9.8 PULLEY FLANGES
Pulley guidebook flanges are essential to preserve synchronous belts operating on their pulleys. As talked about previously in Section 9.7 on belt tracking, it really is normal for synchronous belts to favor one part of the pulleys when operating. Proper flange design is essential in preventing belt edge wear, minimizing sound and preventing the belt from climbing out from the pulley. Dimensional recommendations for custom-made or molded flanges are contained in tables dealing with these problems. Proper flange placement is important to ensure that the belt is certainly adequately restrained within its operating system. Because style and layout of little synchronous drives is indeed diverse, the wide variety of flanging situations possibly encountered cannot easily be protected in a simple group of rules without selecting exceptions. Despite this, the next broad flanging guidelines should help the designer in most cases:
Two Pulley Drives: On simple two pulley drives, each one pulley ought to be flanged in both sides, or each pulley ought to be flanged on contrary sides.
Multiple Pulley Drives: On multiple pulley (or serpentine) drives, either every other pulley ought to be flanged in both sides, or every pulley ought to be flanged about alternating sides around the machine. Vertical Shaft Drives: On vertical shaft drives, at least one pulley ought to be flanged on both sides, and the rest of the pulleys ought to be flanged on at least the bottom side.
Long Period Lengths: Flanging recommendations for small synchronous drives with lengthy belt span lengths cannot conveniently be defined due to the many factors that may affect belt tracking qualities. Belts on drives with long spans (generally 12 times the diameter of small pulley or even more) often require more lateral restraint than with brief spans. Because of this, it is generally smart to flange the pulleys on both sides.
Large Pulleys: Flanging huge pulleys can be costly. Designers frequently wish to leave huge pulleys unflanged to lessen price and space. Belts generally tend to need less lateral restraint on huge pulleys than small and can often perform reliably without flanges. When deciding whether or not to flange, the prior guidelines should be considered. The groove face width of unflanged pulleys should also be greater than with flanged pulleys. See Table 27 for recommendations.
Idlers: Flanging of idlers is normally not essential. Idlers designed to carry lateral aspect loads from belt tracking forces can be flanged if needed to offer lateral belt restraint. Idlers used for this purpose can be utilized inside or backside of the belts. The prior guidelines should also be considered.
9.9 REGISTRATION
The three primary factors adding to belt drive registration (or positioning) errors are belt elongation, backlash, and tooth deflection. When analyzing the potential sign up capabilities of a synchronous belt drive, the machine must initial be determined to end up being either static or powerful when it comes to its registration function and requirements.
Static Sign up: A static registration system moves from its initial static position to a secondary static position. During the procedure, the designer is concerned only with how accurately and regularly the drive arrives at its secondary position. He/she is not worried about any potential sign up errors that take place during transport. Therefore, the primary factor adding to registration error in a static sign up system is usually backlash. The consequences of belt elongation and tooth deflection do not have any influence on the registration precision of this kind of system.
Dynamic Registration: A dynamic registration system must perform a registering function while in motion with torque loads varying as the system operates. In this instance, the designer can be involved with the rotational placement of the drive pulleys with respect to each other at every time. Therefore, belt elongation, backlash and tooth deflection will all donate to registrational inaccuracies.
Further discussion about each one of the factors contributing to registration error is really as follows:
Belt Elongation: Belt elongation, or stretch, occurs naturally when a belt is positioned under stress. The total stress exerted within a belt results from installation, as well as working loads. The amount of belt elongation is usually a function of the belt tensile modulus, which is influenced by the kind of tensile cord and the belt construction. The standard tensile cord found in rubber synchronous belts is fiberglass. Fiberglass includes a high tensile modulus, is dimensionally stable, and has excellent flex-fatigue characteristics. If a higher tensile modulus is necessary, aramid tensile cords can be considered, although they are usually used to provide resistance to harsh shock and impulse loads. Aramid tensile cords used in little synchronous belts generally possess only a marginally higher tensile modulus in comparison to fiberglass. When required, belt tensile modulus data is usually available from our Application Engineering Department.
Backlash: Backlash in a synchronous belt drive outcomes from clearance between the belt tooth and the pulley grooves. This clearance is required to allow the belt tooth to enter and exit the grooves efficiently with at the least interference. The amount of clearance required depends upon the belt tooth profile. Trapezoidal Timing Belt Drives are known for having fairly little backlash. PowerGrip HTD Drives possess improved torque transporting capability and withstand ratcheting, but possess a significant quantity of backlash. PowerGrip GT2 Drives have even further improved torque transporting capability, and also have only a small amount or less backlash than trapezoidal timing belt drives. In special cases, alterations can be made to get systems to help expand decrease backlash. These alterations typically lead to increased belt wear, increased drive sound and shorter get life. Contact our Software Engineering Division for more information.
Tooth Deflection: Tooth deformation in a synchronous belt travel occurs as a torque load is applied to 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 tension and belt type. Of the three main contributors to sign up mistake, tooth deflection is the most challenging to quantify. Experimentation with a prototype drive system is the best method of obtaining practical estimations of belt tooth deflection.
Additional guidelines that may be useful in developing registration essential drive systems are as follows:
Select PowerGrip GT2 or trapezoidal timing belts.
Style with large pulleys with an increase of teeth in mesh.
Keep belts limited, and control pressure closely.
Design frame/shafting to end up being rigid under load.
Use high quality machined pulleys to minimize radial runout and lateral wobble.