9.1 LOW-SPEED OPERATION
Synchronous drives are specially well-suited for low-speed, high torque applications. Their positive generating nature prevents potential slippage associated with V-belt drives, and also allows significantly higher torque carrying capacity. Small pitch synchronous drives working at speeds of 50 ft/min (0.25 m/s) or less are believed to be low-speed. Care ought to be used the get selection procedure as stall and peak torques can sometimes be high. While intermittent peak torques can often be carried by synchronous drives without unique considerations, high cyclic peak torque loading ought to be carefully reviewed.
Proper belt installation tension and rigid travel bracketry and framework is vital in preventing belt tooth jumping under peak torque loads. It is also beneficial to design with an increase of than the normal minimum of 6 belt tooth in mesh to ensure sufficient belt tooth shear strength.
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 more prone 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 usually better suited. They are often used due to their positive traveling characteristic (no creep or slide), and because they might need minimal maintenance (don’t stretch significantly). A substantial drawback of high-quickness synchronous drives is usually get noise. High-quickness synchronous drives will nearly always produce more noise than V-belt drives. Little pitch synchronous drives operating at speeds more than 1300 ft/min (6.6 m/s) are believed to be high-speed.
Special consideration ought to be directed at high-speed drive designs, as a number of factors can considerably influence belt performance. Cord fatigue and belt tooth wear will be the two most crucial factors that must definitely be controlled to ensure success. Moderate pulley diameters ought to be used to reduce the rate of cord flex exhaustion. Designing with a smaller sized pitch belt will often provide better cord flex exhaustion characteristics when compared to a larger pitch belt. PowerGrip GT2 is particularly well suited for high-acceleration drives due to its excellent belt tooth access/exit characteristics. Simple interaction Die Casting between the belt tooth and pulley groove minimizes wear and sound. Belt installation pressure is especially important with high-acceleration drives. Low belt tension 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 operate with only a small amount vibration aspossible, as vibration sometimes impacts the system operation or finished produced product. In such cases, the features and properties of all appropriate belt drive products should be reviewed. The final drive system selection ought to be based on the most significant style requirements, and may require some compromise.
Vibration isn’t generally considered to be 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 caused by tooth meshing is normally a normal characteristic of synchronous belt drives, and can’t be totally eliminated. It can be minimized by staying away from small 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 very cleanly, leading to the smoothest possible operation. Vibration caused by high tensile modulus can be a function of pulley quality. Radial go out causes belt stress variation with each pulley revolution. V-belt pulleys are also produced with some radial go out, but V-belts have a lower tensile modulus leading to less belt stress variation. The high tensile modulus within synchronous belts is necessary to maintain proper pitch under load.
9.4 DRIVE NOISE
Drive noise evaluation in virtually any belt drive system ought to be approached with care. There are several 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 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 increases as operating velocity and belt width increase, and as pulley size decreases. Drives designed on moderate pulley sizes without excessive capability (overdesigned) are generally the quietest. PowerGrip GT2 drives have been found to be considerably quieter than other systems because of their improved meshing characteristic, see Figure 9. Polyurethane belts generally generate more sound than neoprene belts. Proper belt installation tension is also very essential in minimizing travel noise. The belt should be tensioned at a rate which allows it to run with as little meshing interference as possible.
Drive alignment also offers a significant influence on drive noise. Special attention ought to be given to minimizing angular misalignment (shaft parallelism). This assures that belt tooth are loaded uniformly and minimizes side tracking forces against the flanges. Parallel misalignment (pulley offset) isn’t as essential of a concern as long as the belt isn’t trapped or pinched between opposing flanges (see the particular section coping with drive alignment). Pulley components and dimensional accuracy also influence travel sound. Some users possess discovered that steel pulleys are the quietest, accompanied by aluminium. Polycarbonates have already been found to end up being noisier than metallic components. Machined pulleys are generally quieter than molded pulleys. The reasons for this revolve around materials density and resonance features along with dimensional accuracy.
9.5 STATIC CONDUCTIVITY
Little synchronous rubber or urethane belts can generate a power charge while operating about a drive. Factors such as for example humidity and operating speed impact the potential of the charge. If decided to become a issue, rubber belts could be stated in a conductive construction to dissipate the charge in to the pulleys, and to surface. This prevents the accumulation of electric charges that may be detrimental to materials handling procedures or sensitive consumer electronics. It also significantly reduces the prospect of arcing or sparking in flammable conditions. Urethane belts cannot be stated in a conductive construction.
RMA has outlined requirements for conductive belts within their bulletin IP-3-3. Unless normally specified, a static conductive structure for rubber belts is definitely on a made-to-order basis. Unless usually specified, conductive belts will be created 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 usually built specifically to the customers conductivity requirements. They are generally 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 material pulleys. At least one metallic pulley in a drive is necessary for the charge to be dissipated to floor. A grounding brush or equivalent device may also be used to dissipate electric charges.
Urethane timing belts are not static conductive and cannot be built in a particular conductive construction. Special conductive rubber belts should be used when the presence of a power charge is certainly a concern.
9.6 OPERATING ENVIRONMENTS
Synchronous drives are ideal for use in a wide variety of environments. Unique considerations could be necessary, nevertheless, depending on the application.
Dust: Dusty environments usually do not generally present serious problems to synchronous drives provided that the contaminants are fine and dry out. Particulate matter will, however, become an abrasive resulting in a higher level of belt and pulley use. Damp or sticky particulate matter deposited and packed into pulley grooves can cause belt tension to improve significantly. This increased stress can effect shafting, bearings, and framework. Electrical charges within a travel system will often attract particulate matter.
Debris: Debris ought to be prevented from falling into any synchronous belt drive. Debris captured in the get is generally either pressured through the belt or results in stalling of the machine. In either case, serious damage occurs to the belt and related get hardware.
Water: Light and occasional connection with water (occasional wash downs) shouldn’t seriously have an effect on 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 connection with water also causes rubber compounds to swell, although less than with oil get in touch with. Internal belt adhesion systems are also steadily divided with the existence of water. Additives to water, such as lubricants, chlorine, anticorrosives, etc. can have a more detrimental influence on the belts than clear water. Urethane timing belts also suffer from drinking water contamination. Polyester tensile cord shrinks considerably and experiences lack of tensile strength in the presence of water. Aramid tensile cord maintains its power pretty well, but encounters size variation. Urethane swells more than neoprene in the presence of drinking water. This swelling can increase belt tension significantly, causing belt and related equipment problems.
Oil: Light contact with oils on an occasional basis won’t generally harm synchronous belts. Prolonged contact with essential oil or lubricants, either straight or airborne, results in considerably reduced belt service existence. Lubricants trigger the rubber compound to swell, breakdown inner adhesion systems, and reduce belt tensile strength. While alternate rubber compounds might provide some marginal improvement in durability, it is best to prevent essential oil from contacting synchronous belts.
Ozone: The presence of ozone could be detrimental to the substances found in rubber synchronous belts. Ozone degrades belt materials in quite similar way as excessive environmental temps. Although the rubber components found in synchronous belts are compounded to withstand the effects of ozone, eventually chemical substance breakdown occurs plus they become hard and brittle and begin cracking. The quantity of degradation is dependent upon the ozone concentration and duration of publicity. For good overall performance of rubber belts, the following 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 can be detrimental to the compounds used in rubber and urethane synchronous belts. Radiation degrades belt materials quite similar way excessive environmental temperatures do. The quantity of degradation depends upon the intensity of radiation and the exposure time. Once and for all belt performance, the following exposure levels shouldn’t be exceeded:
Standard Construction: 108 rads
Nonm arking Structure: 104 rads
Conductive Construction: 106 rads
Low Temperatures Building: 104 rads
Dust Generation: Rubber synchronous belts are recognized to generate little quantities of fine dust, as an all natural consequence of their operation. The amount of dust is typically higher for new belts, because they operate in. The period of time for run directly into occur depends upon the belt and pulley size, loading and acceleration. Factors such as pulley surface surface finish, operating speeds, installation pressure, and alignment influence the amount of dust generated.
Clean Space: 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 considerably less debris than rubber timing belts. Nevertheless, they are suggested limited to light working loads. Also, they cannot be stated in a static conductive construction to permit electrical charges to dissipate.
Static Sensitive: Applications are occasionally delicate to the accumulation of static electrical charges. Electrical costs can affect material handling functions (like paper and plastic material film transportation), and sensitive digital devices. Applications like these require a static conductive belt, so that the static costs generated by the belt could be dissipated into the pulleys, and also to ground. Regular rubber synchronous belts usually do not fulfill this requirement, but could be manufactured in a static conductive structure on a made-to-order basis. Regular belt wear caused by long term operation or environmental contamination can impact belt conductivity properties.
In delicate 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 definitely a common area of inquiry. While it is regular for a belt to favor one side of the pulleys while operating, it is unusual for a belt to exert significant pressure against a flange leading to belt edge put on and potential flange failing. Belt tracking is influenced by many factors. To be able of significance, dialogue about these elements is really as follows:
Tensile Cord Twist: Tensile cords are formed into a one twist configuration during their manufacture. Synchronous belts made with only solitary twist tensile cords monitor laterally with a substantial pressure. To neutralize this tracking push, tensile cords are stated in correct- and left-hand twist (or “S” and “Z” twist) configurations. Belts made with “S” twist tensile cords monitor in the opposite path to those built with “Z” twist cord. Belts made with alternating “S” and “Z” twist tensile cords monitor with minimal lateral force because the tracking characteristics of the two cords offset one another. This content of “S” and “Z” twist tensile cords varies somewhat with every belt that is produced. Consequently, every belt comes with an unprecedented inclination to track in either one path or the additional. When a credit card applicatoin takes a belt to track in a single specific direction just, a single twist construction can be 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 direction of the tracking drive. Synchronous belts tend to monitor “downhill” to circumstances of lower tension or shorter middle distance.
Belt Width: The potential magnitude of belt monitoring force is directly related to belt width. Wide belts have a tendency to track with more power than narrow belts.
Pulley Size: Belts operating on small pulley diameters can have a tendency to generate higher tracking forces than on large diameters. That is particularly true as the belt width approaches the pulley size. Drives with pulley diameters less than the belt width aren’t generally recommended because belt tracking forces can become excessive.
Belt Length: Due to just how 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 reduces with increasing belt length.
Gravity: In travel applications with vertical shafts, gravity pulls the belt downward. The magnitude of this force is minimal with little pitch synchronous belts. Sag in lengthy belt spans ought to be prevented by applying adequate belt installation tension.
Torque Loads: Sometimes, while in operation, a synchronous belt will move laterally from side to side on the pulleys rather than operating in a constant position. Without generally considered to be a substantial concern, one description for this is normally varying torque loads within the drive. Synchronous belts sometimes track in a different way with changing loads. There are numerous potential known reasons for this; the root cause relates to tensile cord distortion while under great pressure against the pulleys. Variation in belt tensile loads can also cause changes in framework deflection, and angular shaft alignment, leading to belt movement.
Belt Installation Tension: Belt tracking is sometimes influenced by the amount of belt installation pressure. The reasons for this are similar to the result that varying torque loads have got on belt tracking. When problems with belt monitoring are experienced, each one of these potential contributing factors ought to be investigated in the order they are listed. Generally, the primary problem will probably be recognized before moving totally through the list.
9.8 PULLEY FLANGES
Pulley guideline flanges are essential to preserve synchronous belts operating on the pulleys. As talked about previously in Section 9.7 on belt tracking, it really is regular for synchronous belts to favor one side of the pulleys when operating. Proper flange style is essential in stopping belt edge wear, minimizing noise and stopping the belt from climbing from the pulley. Dimensional recommendations for custom-produced or molded flanges are contained in tables dealing with these problems. Proper flange placement is important so that the belt is definitely adequately restrained within its operating system. Because design and layout of small synchronous drives is so different, the wide variety of flanging situations potentially encountered cannot quickly be covered in a simple set of guidelines without obtaining exceptions. Not surprisingly, the next broad flanging recommendations should help the designer generally:
Two Pulley Drives: On basic two pulley drives, either one pulley ought to be flanged in both sides, or each pulley should be flanged on reverse sides.
Multiple Pulley Drives: On multiple pulley (or serpentine) drives, either every other pulley should be flanged in both sides, or every single pulley should be flanged in 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 remaining pulleys should be flanged on at least underneath side.
Long Span Lengths: Flanging recommendations for small synchronous drives with lengthy belt span lengths cannot quickly be defined due to the many factors that may affect belt tracking qualities. Belts on drives with long spans (generally 12 times the size of the smaller pulley or even more) frequently require even more lateral restraint than with brief spans. Because of this, it really is generally a good idea to flange the pulleys on both sides.
Huge Pulleys: Flanging large pulleys could be costly. Designers frequently wish to leave large pulleys unflanged to reduce price and space. Belts tend to need much less lateral restraint on huge pulleys than small and can often perform reliably without flanges. When determining whether or not to flange, the prior guidelines should be considered. The groove encounter width of unflanged pulleys also needs to be higher than with flanged pulleys. See Table 27 for recommendations.
Idlers: Flanging of idlers is normally not necessary. Idlers made to carry lateral aspect loads from belt tracking forces could be flanged if had a need to provide lateral belt restraint. Idlers utilized for this function can be utilized on the 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 evaluating the potential sign up capabilities of a synchronous belt drive, the system must initial be decided to end up being either static or dynamic in conditions of its registration function and requirements.
Static Sign up: A static registration system moves from its preliminary static position to a second static position. Through the procedure, the designer is concerned just with how accurately and consistently the drive arrives at its secondary position. He/she isn’t worried about any potential sign up errors that occur during transport. Therefore, the primary factor adding to registration mistake in a static registration system is definitely backlash. The consequences of belt elongation and tooth deflection do not have any impact on the registration accuracy of this kind of system.
Dynamic Registration: A dynamic registration system is required to perform a registering function while in motion with torque loads varying as the machine operates. In cases like this, the designer can be involved with the rotational position of the travel 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 adding to registration error is really as follows:
Belt Elongation: Belt elongation, or stretch, occurs naturally whenever a belt is positioned under tension. The total stress exerted within a belt results from set up, as well as operating loads. The quantity of belt elongation is a function of the belt tensile modulus, which is normally influenced by the kind of tensile cord and the belt construction. The standard tensile cord found in rubber synchronous belts can be fiberglass. Fiberglass has a high tensile modulus, is dimensionally steady, and has excellent flex-fatigue features. If an increased tensile modulus is needed, aramid tensile cords can be viewed as, although they are generally used to supply resistance to harsh shock and impulse loads. Aramid tensile cords used in little synchronous belts generally have just a marginally higher tensile modulus in comparison to fiberglass. When needed, belt tensile modulus data can be obtainable 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 permit the belt teeth to enter and exit the grooves efficiently with a minimum of interference. The quantity of clearance required is dependent upon the belt tooth account. Trapezoidal Timing Belt Drives are known for having relatively little backlash. PowerGrip HTD Drives have improved torque transporting capability and withstand ratcheting, but possess a significant amount of backlash. PowerGrip GT2 Drives possess even more improved torque having capability, and have as little or less backlash than trapezoidal timing belt drives. In special cases, alterations could be made to get systems to help expand lower backlash. These alterations typically result in increased belt wear, increased drive sound and shorter drive life. Contact our Software Engineering Division for additional information.
Tooth Deflection: Tooth deformation in a synchronous belt travel occurs as a torque load is put on the machine, and individual belt teeth are loaded. The amount of belt tooth deformation is dependent upon the quantity of torque loading, pulley size, installation pressure and belt type. Of the three major contributors to registration mistake, tooth deflection is the most challenging to quantify. Experimentation with a prototype drive system is the best means of obtaining practical estimations of belt tooth deflection.
Additional guidelines that may be useful in developing registration essential drive systems are the following:
Select PowerGrip GT2 or trapezoidal timing belts.
Style with large pulleys with an increase of tooth in mesh.
Keep belts tight, and control pressure closely.
Design framework/shafting to end up being rigid under load.
Use top quality machined pulleys to minimize radial runout and lateral wobble.