9.1 LOW-SPEED OPERATION
Synchronous drives are specially well-appropriate for low-speed, high torque applications. Their positive generating nature stops potential slippage associated with V-belt drives, and actually allows significantly higher torque carrying capacity. Little pitch synchronous drives operating at speeds of 50 ft/min (0.25 m/s) or much less are considered to be low-speed. Care ought to be taken in 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 particular factors, high cyclic peak torque loading ought to be carefully reviewed.
Proper belt installation tension and rigid travel bracketry and framework is vital in avoiding belt tooth jumping under peak torque loads. It is also helpful to design with an increase of than the normal the least 6 belt tooth in mesh to make sure sufficient belt tooth shear strength.
Newer era curvilinear systems like PowerGrip GT2 and PowerGrip HTD should be found in low-swiftness, high torque applications, as trapezoidal timing belts are even more susceptible to tooth jumping, and also 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 typically better suited. They are generally used because of their positive traveling characteristic (no creep or slide), and because they require minimal maintenance (don’t stretch considerably). A significant drawback of high-rate synchronous drives is normally get noise. High-swiftness synchronous drives will almost always produce even more noise than V-belt drives. Little pitch synchronous drives operating at speeds more than 1300 ft/min (6.6 m/s) are considered to be high-speed.
Special consideration should be given to high-speed drive designs, as several factors can considerably influence belt performance. Cord fatigue and belt tooth wear are the two most significant elements that must definitely be controlled to ensure success. Moderate pulley diameters should be used to lessen the rate of cord flex exhaustion. Designing with a smaller pitch belt will most likely offer better cord flex exhaustion characteristics when compared to a larger pitch belt. PowerGrip GT2 is particularly perfect for high-swiftness drives because of its excellent belt tooth access/exit characteristics. Simple interaction between your belt tooth and pulley groove minimizes use and noise. Belt installation stress is especially crucial with high-acceleration drives. Low belt pressure allows the belt to ride 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 operation or finished manufactured product. In such cases, the characteristics and properties of most appropriate belt drive products ought to be reviewed. The final drive system selection should be based upon the most significant style requirements, and could need some compromise.
Vibration is not generally regarded as a problem with synchronous belt drives. Low degrees of vibration typically result from the process of tooth meshing and/or consequently of their high tensile modulus properties. Vibration resulting from tooth meshing can be a normal characteristic of synchronous belt drives, and cannot be totally eliminated. It could be minimized by avoiding little pulley diameters, and instead choosing moderate sizes. The dimensional precision of the pulleys also influences tooth meshing quality. Additionally, the installation stress has an impact on meshing quality. PowerGrip GT2 drives mesh very cleanly, resulting in the smoothest possible operation. Vibration caused by high tensile modulus could be a function of pulley quality. Radial go out causes belt tension variation with each pulley revolution. V-belt pulleys are also manufactured with some radial run out, but V-belts have a lower tensile modulus leading to less belt stress variation. The high tensile modulus found in synchronous belts is essential to maintain correct pitch under load.
9.4 DRIVE NOISE
Drive noise evaluation in virtually any belt drive system should be approached with care. There are numerous potential sources of sound in something, including vibration from related elements, 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 connection with the pulleys. The sound pressure level generally increases as operating velocity and belt width increase, and as pulley diameter decreases. Drives designed on moderate pulley sizes without excessive capability (overdesigned) are usually the quietest. PowerGrip GT2 drives have been discovered to be considerably quieter than other systems because of their improved meshing characteristic, see Figure 9. Polyurethane belts generally produce more sound than neoprene belts. Proper belt installation tension is also very essential in minimizing drive noise. The belt should be tensioned at a level which allows it to run with only a small amount meshing interference as possible.
Travel alignment also offers a significant influence on drive sound. Special attention should be given to minimizing angular misalignment (shaft parallelism). This assures that belt tooth are loaded uniformly and minimizes part monitoring forces against the flanges. Parallel misalignment (pulley offset) is not as critical of a problem provided that the belt is not trapped or pinched between opposing flanges (start to see the special section coping with travel alignment). Pulley materials and dimensional accuracy also influence drive noise. Some users have found that steel pulleys are the quietest, accompanied by aluminum. Polycarbonates have been discovered to be noisier than metallic materials. Machined pulleys are generally quieter than molded pulleys. The reason why for this revolve around materials density and resonance features and also dimensional accuracy.
9.5 STATIC CONDUCTIVITY
Small synchronous rubber or urethane belts can generate a power charge while operating about a drive. Factors such as for example humidity and working speed influence the potential of the charge. If identified to be a problem, rubber belts could be stated in a conductive construction to dissipate the charge in to the pulleys, and to floor. This prevents the accumulation of electrical charges that may be harmful to material handling processes or sensitive electronics. In addition, it significantly reduces the prospect of arcing or sparking in flammable conditions. Urethane belts can’t be stated in a conductive structure.
RMA has outlined standards for conductive belts in their bulletin IP-3-3. Unless normally specified, a static conductive structure for rubber belts is normally available on a made-to-purchase basis. Unless otherwise specified, conductive belts will be created to yield a 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 clients conductivity requirements. They are usually found in applications where one shaft should be electrically isolated from the various other. It is important to note that a static conductive belt cannot dissipate an electrical charge through plastic pulleys. At least one metallic pulley in a drive is necessary for the charge to be dissipated to floor. A grounding brush or identical device could also be used to dissipate electric charges.
Urethane timing belts are not static conductive and can’t be built in a special conductive construction. Particular conductive rubber belts ought to be utilized when the existence of a power charge can be a concern.
9.6 OPERATING ENVIRONMENTS
Synchronous drives are ideal for use in a wide variety of environments. Particular considerations could be necessary, however, depending on the application.
Dust: Dusty conditions do not generally present serious problems to synchronous drives provided that the particles are good and dry. Particulate matter will, however, act as an abrasive producing a higher level of belt and pulley use. Damp or sticky particulate matter deposited and loaded into pulley grooves could cause belt tension to improve significantly. This increased stress can impact shafting, bearings, and framework. Electrical charges within a drive system can sometimes catch the attention of particulate matter.
Debris: Debris ought to be prevented from falling into any synchronous belt drive. Debris caught in the travel is normally either pressured through the belt or results in stalling of the system. In any case, serious damage occurs to the belt and related travel hardware.
Water: Light and occasional contact with drinking water (occasional clean downs) shouldn’t seriously have an effect on synchronous belts. Prolonged contact (continuous spray or submersion) results in considerably reduced tensile power in fiberglass belts, and potential size variation in aramid belts. Prolonged connection with drinking water also causes rubber substances to swell, although significantly less than with oil contact. Internal belt adhesion systems are also steadily broken down with the existence of water. Additives to water, such as for example lubricants, chlorine, anticorrosives, etc. can possess a more detrimental influence on the belts than clear water. Urethane timing belts also suffer from water contamination. Polyester tensile cord shrinks considerably and experiences loss of tensile power in the existence of water. Aramid tensile cord maintains its strength fairly well, but encounters duration variation. Urethane swells a lot more than neoprene in the existence of water. This swelling can boost belt tension significantly, causing belt and related equipment problems.
Oil: Light contact with oils on an intermittent basis will not generally harm synchronous belts. Prolonged contact with oil or lubricants, either straight or airborne, outcomes in significantly reduced belt service existence. Lubricants cause the rubber compound to swell, breakdown inner adhesion systems, and decrease belt tensile strength. While alternate rubber compounds may provide some marginal improvement in durability, it is best to prevent essential oil from contacting synchronous belts.
Ozone: The existence of ozone could be detrimental to the compounds used in rubber synchronous belts. Ozone degrades belt materials in much the same way as excessive environmental temps. Although the rubber components found in synchronous belts are compounded to resist the consequences of ozone, ultimately chemical substance breakdown occurs and they become hard and brittle and begin cracking. The amount of degradation depends upon the ozone focus and duration of publicity. For good functionality 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 Construction: 20 pphm
Radiation: Contact with gamma radiation can be detrimental to the compounds used in rubber and urethane synchronous belts. Radiation degrades belt materials much the same way excessive environmental temps do. The quantity of degradation is dependent upon the intensity of radiation and the publicity time. Once and for all belt performance, the following exposure levels shouldn’t be exceeded:
Standard Construction: 108 rads
Nonm arking Construction: 104 rads
Conductive Construction: 106 rads
Low Temperatures Structure: 104 rads
Dust Generation: Rubber synchronous belts are recognized to generate small quantities of fine dust, as a natural consequence of their operation. The number of dust is typically higher for fresh belts, because they operate in. The time period for run in to occur depends upon the belt and pulley size, loading and acceleration. Elements such as for example pulley surface finish, operating speeds, installation stress, and alignment impact the amount of dust generated.
Clean Space: Rubber synchronous belts might not be suitable for use in clean area environments, where all potential contamination must be minimized or eliminated. Urethane timing belts typically generate significantly less debris than rubber timing belts. However, they are recommended only for light operating loads. Also, they cannot be stated in a static conductive construction to allow electrical costs to dissipate.
Static Sensitive: Applications are sometimes sensitive to the accumulation of static electrical charges. Electrical fees can affect material handling functions (like paper and plastic material film transport), and sensitive electronic tools. Applications like these require a static conductive belt, so that the static costs produced by the belt can be dissipated into the pulleys, and to ground. Standard rubber synchronous belts usually do not satisfy this requirement, but could be manufactured in a static conductive building 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 preferred over urethane belts since urethane belting can’t be stated in a conductive construction.
9.7 BELT TRACKING
Lateral tracking qualities of synchronous belts is certainly a common area of inquiry. Although it is regular for a belt to favor one aspect of the pulleys while running, it is irregular for a belt to exert significant push against a flange leading to belt edge use and potential flange failure. Belt tracking can be influenced by several factors. To be able of significance, discussion about these elements is really as follows:
Tensile Cord Twist: Tensile cords are formed into a solitary twist configuration during their produce. Synchronous belts made out of only one twist tensile cords monitor laterally with a substantial push. To neutralize this tracking push, tensile cords are produced in correct- and left-hand twist (or “S” and “Z” twist) configurations. Belts made out of “S” twist tensile cords monitor in the contrary path to those built with “Z” twist cord. Belts made out of alternating “S” and “Z” twist tensile cords track with reduced lateral force since the tracking features of both cords offset one another. 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 tendency to track in each one direction or the additional. When a credit card applicatoin requires a belt to monitor in one specific direction only, an individual twist construction can be used. See Figures 16 & Figure 17.
Angular Misalignment: Angular misalignment, or shaft Screw Air Compressors nonparallelism, cause synchronous belts to track laterally. The position of misalignment influences the magnitude and path of the monitoring drive. Synchronous belts tend to monitor “downhill” to a state of lower tension or shorter center distance.
Belt Width: The potential magnitude of belt tracking force is directly linked to belt width. Wide belts have a tendency to track with more pressure than narrow belts.
Pulley Diameter: Belts operating on little pulley diameters can have a tendency to generate higher tracking forces than on large diameters. This is particularly accurate as the belt width approaches the pulley size. Drives with pulley diameters less than the belt width are not generally suggested because belt tracking forces may become excessive.
Belt Length: Due to just how tensile cords are applied on to the belt molds, brief belts can have a tendency to exhibit higher monitoring forces than very long belts. The helix angle of the tensile cord reduces with increasing belt length.
Gravity: In travel applications with vertical shafts, gravity pulls the belt downward. The magnitude of the force is normally minimal with small pitch synchronous belts. Sag in lengthy belt spans should be prevented by applying adequate belt installation tension.
Torque Loads: Sometimes, while in operation, a synchronous belt can move laterally laterally on the pulleys rather than operating in a constant position. Without generally considered to be a significant concern, one description for this is varying torque loads within the get. Synchronous belts occasionally track differently with changing loads. There are several potential reasons for this; the primary cause relates to tensile cord distortion while under great pressure against the pulleys. Variation in belt tensile loads may also cause adjustments in framework deflection, and angular shaft alignment, resulting in belt movement.
Belt Installation Stress: Belt tracking is sometimes influenced by the amount of belt installation tension. The reasons for this act like the effect that varying torque loads possess on belt tracking. When problems with belt tracking are experienced, each one of these potential contributing elements should be investigated in the purchase that they are outlined. Generally, the principal problem will probably be recognized before moving completely through the list.
9.8 PULLEY FLANGES
Pulley guidebook flanges are essential to hold synchronous belts operating on the pulleys. As discussed previously in Section 9.7 on belt tracking, it is normal for synchronous belts to favor one side of the pulleys when operating. Proper flange style is essential in preventing belt edge use, minimizing sound and stopping the belt from climbing out of the pulley. Dimensional recommendations for custom-made or molded flanges are included in tables coping with these problems. Proper flange positioning is important to ensure that the belt is adequately restrained within its operating system. Because style and layout of small synchronous drives is so varied, the wide variety of flanging situations potentially encountered cannot conveniently be protected in a simple group of guidelines without obtaining exceptions. Not surprisingly, the following broad flanging suggestions should help the designer generally:
Two Pulley Drives: On simple two pulley drives, either one pulley should be flanged about both sides, or each pulley should 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 single pulley ought to be flanged on alternating sides around the system. 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 Span Lengths: Flanging suggestions for little synchronous drives with long belt span lengths cannot quickly be defined because of the many factors that can affect belt tracking qualities. Belts on drives with long spans (generally 12 times the diameter of the smaller pulley or more) often require more lateral restraint than with short spans. Due to this, it really is generally a good idea to flange the pulleys on both sides.
Large Pulleys: Flanging huge pulleys can be costly. Designers often wish to leave huge pulleys unflanged to reduce price and space. Belts tend to require less lateral restraint on huge pulleys than small and can often perform reliably without flanges. When determining whether to flange, the previous guidelines should be considered. The groove face width of unflanged pulleys should also be higher than with flanged pulleys. See Table 27 for recommendations.
Idlers: Flanging of idlers is normally not necessary. Idlers made to carry lateral part loads from belt tracking forces can be flanged if needed to offer lateral belt restraint. Idlers used for this purpose can be used inside or backside of the belts. The prior guidelines also needs to be considered.
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 features of a synchronous belt drive, the system must 1st be identified to end up being either static or powerful with regards to its sign up function and requirements.
Static Registration: A static registration system moves from its preliminary static position to a secondary static position. Through the procedure, the designer is concerned only with how accurately and consistently the drive finds its secondary placement. He/she isn’t worried about any potential sign up errors that happen during transport. Therefore, the primary factor contributing to registration mistake in a static registration system can be backlash. The consequences of belt elongation and tooth deflection don’t have any impact on the registration precision of this type of system.
Dynamic Sign up: A powerful registration system must perform a registering function while in motion with torque loads various as the machine operates. In this instance, the designer can be involved with the rotational position of the get pulleys regarding each other at every point in time. Therefore, belt elongation, backlash and tooth deflection will all donate to registrational inaccuracies.
Further discussion about each of the factors adding to registration error is as follows:
Belt Elongation: Belt elongation, or stretch out, occurs naturally when a belt is placed under stress. The total stress exerted within a belt results from set up, along with functioning loads. The quantity of belt elongation is usually a function of the belt tensile modulus, which is certainly influenced by the type of tensile cord and the belt construction. The standard tensile cord used in rubber synchronous belts is definitely fiberglass. Fiberglass includes a high tensile modulus, is dimensionally steady, and has excellent flex-fatigue characteristics. If a higher tensile modulus is necessary, aramid tensile cords can be viewed as, although they are generally used to provide resistance to severe shock and impulse loads. Aramid tensile cords used in little synchronous belts generally possess only a marginally higher tensile modulus compared to fiberglass. When required, belt tensile modulus data is normally obtainable from our Application Engineering Department.
Backlash: Backlash in a synchronous belt drive outcomes from clearance between your belt tooth and the pulley grooves. This clearance is needed to permit the belt tooth to enter and exit the grooves effortlessly with at the least interference. The amount of clearance required depends upon the belt tooth account. Trapezoidal Timing Belt Drives are known for having relatively small backlash. PowerGrip HTD Drives possess improved torque transporting capability and withstand ratcheting, but possess a significant amount of backlash. PowerGrip GT2 Drives have even more improved torque carrying capability, and also have only a small amount or less backlash than trapezoidal timing belt drives. In unique cases, alterations can be made to drive systems to help expand lower backlash. These alterations typically lead to increased belt wear, increased get noise and shorter get life. Contact our Program Engineering Department for additional information.
Tooth Deflection: Tooth deformation in a synchronous belt travel occurs as a torque load is applied to the machine, and individual belt teeth are loaded. The amount of belt tooth deformation depends upon the quantity of torque loading, pulley size, installation stress and belt type. Of the three primary contributors to sign up error, tooth deflection is the most challenging to quantify. Experimentation with a prototype get system is the best means of obtaining realistic estimations of belt tooth deflection.
Additional guidelines that may be useful in developing registration important drive systems are the following:
Select PowerGrip GT2 or trapezoidal timing belts.
Design with large pulleys with more teeth in mesh.
Keep belts tight, and control pressure closely.
Design body/shafting to end up being rigid under load.
Use high quality machined pulleys to reduce radial runout and lateral wobble.