9.1 LOW-SPEED OPERATION
Synchronous drives are especially well-suitable for low-speed, high torque applications. Their positive generating nature prevents potential slippage connected with V-belt drives, and actually allows significantly better torque carrying capacity. Little pitch synchronous drives working at speeds of 50 ft/min (0.25 m/s) or much less are believed to be low-speed. Care ought to be taken in the get selection process 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 should be carefully reviewed.
Proper belt installation tension and rigid drive bracketry and framework is essential in stopping belt tooth jumping less than peak torque loads. It is also helpful to design with an increase of than the normal minimum of 6 belt tooth in mesh to ensure adequate belt tooth shear power.
Newer era curvilinear systems like PowerGrip GT2 and PowerGrip HTD ought to be used in low-swiftness, 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 tend to be found in high-speed applications despite the fact that V-belt drives are usually better suited. They are generally used because of their positive driving characteristic (no creep or slip), and because they might need minimal maintenance (don’t stretch significantly). A significant drawback of high-quickness synchronous drives is travel noise. High-speed synchronous drives will almost always produce even 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 end up being high-speed.
Special consideration ought to be directed at high-speed drive designs, as several factors can considerably influence belt performance. Cord fatigue and belt tooth wear are the two most crucial elements that must be controlled to ensure success. Moderate pulley diameters ought to be used to reduce the rate of cord flex exhaustion. Developing with a smaller sized pitch belt will most likely provide better cord flex fatigue characteristics when compared to a bigger pitch belt. PowerGrip GT2 is particularly perfect for high-rate drives due to its excellent belt tooth entry/exit characteristics. Simple interaction between your belt tooth and pulley groove minimizes use and noise. Belt installation tension is especially crucial with high-velocity drives. Low belt tension allows the belt to ride out of 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 all appropriate belt drive products ought to be reviewed. The ultimate drive program selection should be based upon the most critical style requirements, and may require some compromise.
Vibration is not generally regarded as a problem with synchronous belt drives. Low levels of vibration typically result from the procedure of tooth meshing and/or as a result of their high tensile modulus properties. Vibration caused by tooth meshing is certainly a normal characteristic of synchronous belt drives, and can’t be completely eliminated. It could be minimized by avoiding little pulley diameters, and instead choosing moderate sizes. The dimensional accuracy of the pulleys also influences tooth meshing quality. Additionally, the installation pressure has an impact on meshing quality. PowerGrip GT2 drives mesh extremely cleanly, resulting in the smoothest feasible 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 go out, but V-belts possess a lesser tensile modulus resulting in less belt tension variation. The high tensile modulus within synchronous belts is essential to maintain appropriate pitch under load.
9.4 DRIVE NOISE
Drive noise evaluation in virtually any belt drive system ought to be approached carefully. There are various potential sources of sound 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 results from the process of belt tooth meshing and physical contact with the pulleys. The sound pressure level generally boosts as operating velocity and belt width increase, and as pulley diameter reduces. Drives designed on moderate pulley sizes without extreme capacity (overdesigned) are usually the quietest. PowerGrip GT2 drives have been found to be considerably quieter than additional 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 essential in minimizing get noise. The belt should be tensioned at a rate that allows it to run with only a small amount 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 tooth are loaded uniformly and minimizes part monitoring forces against the flanges. Parallel misalignment (pulley offset) is not as vital of a problem provided that the belt isn’t trapped or pinched between contrary flanges (start to see the particular section dealing with travel alignment). Pulley components and dimensional precision also influence get noise. Some users possess found that steel pulleys will be the quietest, followed closely by light weight aluminum. Polycarbonates have already been found to be noisier than metallic materials. Machined pulleys are usually quieter than molded pulleys. The reason why because of this revolve around materials density and resonance features and also dimensional accuracy.
9.5 STATIC CONDUCTIVITY
Little synchronous rubber or urethane belts can generate a power charge while operating in a drive. Elements such as humidity and working speed impact the potential of the charge. If established to become a issue, rubber belts could be produced in a conductive construction to dissipate the charge in to the pulleys, and also to surface. This prevents the accumulation of electric charges that may be harmful to material handling procedures or sensitive consumer electronics. It also greatly reduces the prospect of arcing or sparking in flammable environments. Urethane belts cannot be stated in a conductive construction.
RMA has outlined criteria for conductive belts in their bulletin IP-3-3. Unless in any other case specified, a static conductive structure for rubber belts is certainly on a made-to-purchase basis. Unless usually specified, conductive belts will be created to yield a resistance of 300,000 ohms or much less, when new.
Nonconductive belt constructions are also available for rubber belts. These belts are generally built specifically to the clients conductivity requirements. They are usually used in applications where one shaft must be electrically isolated from the additional. It is necessary 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 may also be used to dissipate electrical charges.
Urethane timing belts aren’t static conductive and can’t be built in a particular conductive construction. Special conductive rubber belts ought to 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 selection of environments. Particular considerations could be necessary, nevertheless, depending on the application.
Dust: Dusty conditions do not generally present serious problems to synchronous drives as long as the contaminants are fine and dry. Particulate matter will, however, become an abrasive resulting in a higher rate of belt and pulley wear. Damp or sticky particulate matter deposited and loaded into pulley grooves could cause belt tension to increase significantly. This increased pressure can influence shafting, bearings, and framework. Electrical fees within a travel system will often draw in particulate matter.
Debris: Debris ought to be prevented from falling into any synchronous belt drive. Debris caught in the get is normally either forced through the belt or results in stalling of the machine. In either case, serious damage happens to the belt and related travel hardware.
Drinking water: Light and occasional connection with drinking water (occasional wash downs) should not seriously influence synchronous belts. Prolonged get in touch with (continuous spray or submersion) results in considerably reduced tensile strength in fiberglass belts, and potential size variation in aramid belts. Prolonged contact with water also causes rubber substances to swell, although significantly less than with oil contact. Internal belt adhesion systems are also gradually broken down with the presence of water. Additives to 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 strength in the existence of drinking water. Aramid tensile cord keeps its strength fairly well, but experiences size variation. Urethane swells more than neoprene in the presence of water. This swelling can boost belt tension significantly, causing belt and related hardware problems.
Oil: Light contact with natural oils on an occasional basis won’t generally harm synchronous belts. Prolonged contact with essential oil or lubricants, either directly or airborne, Rotary Air Compressor outcomes in significantly reduced belt service existence. Lubricants cause the rubber compound to swell, breakdown internal adhesion systems, and decrease belt tensile strength. While alternate rubber substances may provide some marginal improvement in durability, it is advisable 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 quite similar way as extreme environmental temperature ranges. Although the rubber materials used in synchronous belts are compounded to withstand the consequences of ozone, eventually chemical substance breakdown occurs plus they become hard and brittle and start cracking. The quantity of degradation depends upon the ozone focus and duration of publicity. For good efficiency 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: 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 temps do. The amount of degradation is dependent upon the intensity of radiation and the exposure time. Once and for all belt performance, the following exposure levels should not be exceeded:
Standard Construction: 108 rads
Nonm arking Structure: 104 rads
Conductive Construction: 106 rads
Low Temperatures Building: 104 rads
Dust Era: Rubber synchronous belts are recognized to generate little quantities of good dust, as an all 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 quickness. Factors such as for example pulley surface end, operating speeds, set up pressure, and alignment impact the amount of dust generated.
Clean Area: Rubber synchronous belts might not be ideal for use in clean room environments, where all potential contamination must be minimized or eliminated. Urethane timing belts typically generate considerably less particles than rubber timing belts. Nevertheless, they are recommended limited to light operating loads. Also, they can not be produced in a static conductive building to permit electrical charges to dissipate.
Static Sensitive: Applications are sometimes sensitive to the accumulation of static electric charges. Electrical costs can affect materials handling functions (like paper and plastic material film transport), and sensitive digital devices. Applications like these need a static conductive belt, to ensure that the static costs produced by the belt could be dissipated in to the pulleys, and also to ground. Regular rubber synchronous belts usually do not meet this requirement, but could be produced in a static conductive structure on a made-to-order basis. Regular belt wear caused by long term procedure or environmental contamination can influence belt conductivity properties.
In delicate applications, rubber synchronous belts are favored over urethane belts since urethane belting cannot be produced in a conductive construction.
9.7 BELT TRACKING
Lateral tracking qualities of synchronous belts is a common area of inquiry. While it is regular for a belt to favor one side of the pulleys while working, it is irregular for a belt to exert significant power against a flange leading to belt edge use and potential flange failing. Belt tracking can be influenced by many factors. To be able of significance, conversation about these elements is as follows:
Tensile Cord Twist: Tensile cords are formed into a single twist configuration during their produce. Synchronous belts made out of only single twist tensile cords track laterally with a significant drive. To neutralize this tracking force, tensile cords are produced in correct- and left-hand twist (or “S” and “Z” twist) configurations. Belts made with “S” twist tensile cords monitor in the opposite direction to those constructed with “Z” twist cord. Belts made out of alternating “S” and “Z” twist tensile cords monitor with minimal lateral force since the tracking features of both cords offset each other. This content of “S” and “Z” twist tensile cords varies somewhat with every belt that’s produced. Because of this, every belt comes with an unprecedented inclination to track in each one direction or the other. When an application takes a belt to track in one specific direction just, a single twist construction is 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 path of the monitoring push. Synchronous belts tend to track “downhill” to circumstances of lower stress or shorter middle distance.
Belt Width: The potential magnitude of belt monitoring force is directly linked to belt width. Wide belts have a tendency to track with more force than narrow belts.
Pulley Size: Belts operating on little pulley diameters can tend to generate higher tracking forces than on large diameters. That is particularly true as the belt width methods the pulley size. Drives with pulley diameters significantly less than the belt width aren’t generally suggested because belt tracking forces can become excessive.
Belt Length: Because of just how tensile cords are applied to the belt molds, brief belts can have a tendency to exhibit higher tracking forces than very long belts. The helix angle of the tensile cord decreases with increasing belt length.
Gravity: In travel applications with vertical shafts, gravity pulls the belt downward. The magnitude of the force is certainly minimal with small pitch synchronous belts. Sag in long belt spans should be avoided by applying adequate belt installation tension.
Torque Loads: Sometimes, while in operation, 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 usually varying torque loads within the drive. Synchronous belts occasionally track in different ways with changing loads. There are various potential reasons for this; the primary cause is related 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, resulting in belt movement.
Belt Installation Pressure: Belt tracking is sometimes influenced by the level of belt installation tension. The reason why for this are similar to the result that varying torque loads have got on belt tracking. When problems with belt monitoring are experienced, each of these potential contributing elements should be investigated in the purchase that they are outlined. In most cases, the principal problem will probably be discovered before moving completely through the list.
9.8 PULLEY FLANGES
Pulley information flanges are essential to preserve synchronous belts operating on the pulleys. As discussed previously in Section 9.7 on belt tracking, it is regular for synchronous belts to favor one part of the pulleys when working. Proper flange design is important in stopping belt edge use, minimizing noise and stopping the belt from climbing from the pulley. Dimensional suggestions for custom-produced 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 design and design of small synchronous drives is so varied, the wide selection of flanging situations possibly encountered cannot very easily be protected in a simple set of guidelines without getting exceptions. Despite this, the next broad flanging recommendations should help the developer generally:
Two Pulley Drives: On basic two pulley drives, either one pulley ought to 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 about 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 remaining pulleys ought to be flanged on at least the bottom side.
Long Period Lengths: Flanging suggestions for little synchronous drives with lengthy belt span lengths cannot conveniently be defined because of the many factors that may affect belt tracking characteristics. Belts on drives with long spans (generally 12 times the size of small pulley or even more) often require even more lateral restraint than with short spans. For this reason, it is generally smart to flange the pulleys on both sides.
Huge Pulleys: Flanging large pulleys can be costly. Designers often desire to leave huge pulleys unflanged to lessen price and space. Belts tend to require much less lateral restraint on huge pulleys than little and can frequently perform reliably without flanges. When determining whether to flange, the prior guidelines is highly recommended. 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 generally not necessary. Idlers made to bring lateral aspect loads from belt tracking forces could be flanged if had a need to offer lateral belt restraint. Idlers used for this function can be utilized on the inside or backside of the belts. The previous guidelines also needs to be considered.
The three primary factors contributing 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 machine must 1st be established to end up being either static or powerful when it comes to its sign up function and requirements.
Static Sign up: A static registration system moves from its preliminary static position to a secondary static position. Through the process, the designer is concerned only with how accurately and consistently the drive finds its secondary placement. He/she is not concerned with any potential registration errors that take place during transport. Therefore, the primary factor contributing to registration mistake in a static registration system is definitely backlash. The consequences of belt elongation and tooth deflection do not have any influence on the sign up precision of this kind of system.
Dynamic Registration: A powerful 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 placement of the get pulleys regarding one another 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 contributing to registration error is really as follows:
Belt Elongation: Belt elongation, or stretch, occurs naturally when a belt is positioned under tension. The total pressure exerted within a belt results from installation, in addition to functioning loads. The amount of belt elongation is a function of the belt tensile modulus, which is definitely influenced by the kind of tensile cord and the belt construction. The typical tensile cord found in rubber synchronous belts is normally fiberglass. Fiberglass includes a high tensile modulus, is dimensionally steady, and has excellent flex-fatigue characteristics. If an increased tensile modulus is necessary, aramid tensile cords can be considered, although they are generally used to supply resistance to harsh shock and impulse loads. Aramid tensile cords used in little synchronous belts generally possess just a marginally higher tensile modulus compared to fiberglass. When needed, belt tensile modulus data is definitely obtainable from our Program Engineering Department.
Backlash: Backlash in a synchronous belt drive outcomes from clearance between your belt teeth and the pulley grooves. This clearance is required to allow the belt teeth to enter and exit the grooves effortlessly with at the least interference. The amount of clearance necessary depends upon the belt tooth profile. Trapezoidal Timing Belt Drives are known for having relatively little backlash. PowerGrip HTD Drives possess improved torque carrying capability and withstand ratcheting, but possess a significant quantity of backlash. PowerGrip GT2 Drives have even further improved torque transporting capability, and have only a small amount or much less backlash than trapezoidal timing belt drives. In particular cases, alterations can be made to drive systems to further lower backlash. These alterations typically result in increased belt wear, increased drive noise and shorter travel life. Contact our Application Engineering Department for more information.
Tooth Deflection: Tooth deformation in a synchronous belt drive 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 amount of torque loading, pulley size, installation stress and belt type. Of the three primary contributors to sign up error, tooth deflection is the most difficult to quantify. Experimentation with a prototype travel system is the best method of obtaining realistic estimations of belt tooth deflection.
Additional guidelines which may be useful in developing registration essential drive systems are the following:
Select PowerGrip GT2 or trapezoidal timing belts.
Design with large pulleys with more tooth in mesh.
Keep belts limited, and control stress closely.
Design frame/shafting to be rigid under load.
Use top quality machined pulleys to reduce radial runout and lateral wobble.