9.1 LOW-SPEED OPERATION
Synchronous drives are specially well-suitable for low-speed, high torque applications. Their positive generating nature helps prevent potential slippage connected with V-belt drives, and also allows significantly greater torque carrying ability. Little pitch synchronous drives operating at speeds of 50 ft/min (0.25 m/s) or less are believed to be low-speed. Care should be taken in the get selection process as stall and peak torques can often be very high. While intermittent peak torques can often be carried by synchronous drives without particular considerations, high cyclic peak torque loading ought to be carefully reviewed.
Proper belt installation tension and rigid travel bracketry and framework is vital in stopping belt tooth jumping under peak torque loads. Additionally it is helpful to design with more compared to the normal minimum of 6 belt tooth in mesh to make sure adequate belt tooth shear power.
Newer generation curvilinear systems like PowerGrip GT2 and PowerGrip HTD ought to be found in low-speed, high torque applications, as trapezoidal timing belts are more susceptible to tooth jumping, and have significantly less load carrying capacity.
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 appropriate. They are often used because of their positive traveling characteristic (no creep or slide), and because they require minimal maintenance (don’t stretch considerably). A substantial drawback of high-quickness synchronous drives is normally drive noise. High-quickness synchronous drives will nearly always produce even more noise than V-belt drives. Small 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 significantly influence belt performance. Cord exhaustion and belt tooth wear are the two most crucial elements that must be controlled to ensure success. Moderate pulley diameters should be used to lessen the rate of cord flex exhaustion. Designing with a smaller sized pitch belt will often offer better cord flex exhaustion characteristics when compared to a larger pitch belt. PowerGrip GT2 is particularly well suited for high-speed drives because of its excellent belt tooth entry/exit characteristics. Clean interaction between your belt tooth and pulley groove minimizes use and noise. Belt installation tension is especially crucial with high-rate drives. Low belt stress allows the belt to trip 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 as little vibration aspossible, as vibration sometimes impacts the system procedure or finished produced product. In these cases, the characteristics and properties of all appropriate belt drive products ought to be reviewed. The final drive program selection ought to be based upon the most critical style requirements, and could require some compromise.
Vibration is not generally considered to be a issue with synchronous belt drives. Low levels of vibration typically derive from the procedure of tooth meshing and/or consequently of their high Electric Motors tensile modulus properties. Vibration resulting from tooth meshing is normally a normal characteristic of synchronous belt drives, and cannot be totally eliminated. It can be minimized by avoiding small pulley diameters, and instead selecting moderate sizes. The dimensional precision of the pulleys also influences tooth meshing quality. Additionally, the installation pressure has an effect on meshing quality. PowerGrip GT2 drives mesh extremely cleanly, resulting in the smoothest feasible operation. Vibration resulting from high tensile modulus could be a function of pulley quality. Radial run out causes belt tension variation with each pulley revolution. V-belt pulleys are also manufactured with some radial run out, but V-belts have got a lower tensile modulus resulting in less belt pressure 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 ought to be approached with care. There are many potential resources of sound in something, including vibration from related components, bearings, and resonance and amplification through framework and panels.
Synchronous belt drives typically produce even more noise than V-belt drives. Noise results from the procedure of belt tooth meshing and physical contact with the pulleys. The sound pressure level generally raises as operating quickness and belt width increase, and as pulley size decreases. Drives designed on moderate pulley sizes without excessive capacity (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 produce more sound than neoprene belts. Proper belt installation tension is also very important in minimizing travel noise. The belt should be tensioned at a rate that allows it to perform with only a small amount meshing interference as possible.
Drive alignment also offers a significant effect on drive noise. Special attention ought to be given to reducing angular misalignment (shaft parallelism). This assures that belt teeth are loaded uniformly and minimizes part tracking forces against the flanges. Parallel misalignment (pulley offset) isn’t as essential of a problem as long as the belt is not trapped or pinched between opposite flanges (see the special section dealing with travel alignment). Pulley materials and dimensional accuracy also influence drive sound. Some users possess discovered that steel pulleys are the quietest, accompanied by lightweight aluminum. Polycarbonates have already been found to be noisier than metallic materials. Machined pulleys are usually quieter than molded pulleys. The reason why for this revolve around material density and resonance characteristics in addition to dimensional accuracy.
9.5 STATIC CONDUCTIVITY
Small synchronous rubber or urethane belts can generate an electrical charge while operating in a drive. Factors such as humidity and working speed influence the potential of the charge. If established to become a issue, rubber belts could be produced in a conductive construction to dissipate the charge into the pulleys, and to ground. This prevents the accumulation of electrical charges that may be harmful to materials handling procedures or sensitive electronics. It also greatly reduces the prospect of arcing or sparking in flammable conditions. Urethane belts can’t be stated in a conductive building.
RMA has outlined specifications for conductive belts within their bulletin IP-3-3. Unless otherwise specified, a static conductive building for rubber belts is certainly available on a made-to-order basis. Unless in any other case specified, conductive belts will be built to yield a resistance of 300,000 ohms or much less, when new.
Nonconductive belt constructions are also designed for rubber belts. These belts are generally built specifically to the clients conductivity requirements. They are generally found in applications where one shaft should be electrically isolated from the various other. It is necessary to note that a static conductive belt cannot dissipate a power charge through plastic pulleys. At least one metallic pulley in a drive is required for the charge to end up being dissipated to ground. A grounding brush or identical device could also be used to dissipate electrical charges.
Urethane timing belts aren’t static conductive and cannot be built in a particular conductive construction. Unique conductive rubber belts should be used when the existence of an electrical charge is usually a concern.
9.6 OPERATING ENVIRONMENTS
Synchronous drives are suitable for use in a wide variety of environments. Particular considerations could be necessary, nevertheless, based on the application.
Dust: Dusty environments do not generally present serious complications to synchronous drives provided that the particles are good and dry out. Particulate matter will, however, become an abrasive producing a higher rate of belt and pulley use. Damp or sticky particulate matter deposited and packed into pulley grooves could cause belt tension to increase significantly. This increased stress can influence shafting, bearings, and framework. Electrical charges within a get system will often appeal to particulate matter.
Debris: Debris should be prevented from falling into any synchronous belt drive. Particles caught in the travel is normally either forced through the belt or results in stalling of the system. In any case, serious damage happens to the belt and related get hardware.
Water: Light and occasional connection with water (occasional clean downs) shouldn’t seriously have an effect on synchronous belts. Prolonged contact (continuous spray or submersion) results in significantly reduced tensile strength in fiberglass belts, and potential length 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 drinking water. Additives to drinking water, such as lubricants, chlorine, anticorrosives, etc. can have a more detrimental effect on the belts than clear water. Urethane timing belts also have problems with drinking water contamination. Polyester tensile cord shrinks significantly and experiences loss of tensile strength in the existence of water. Aramid tensile cord keeps its power fairly well, but experiences duration variation. Urethane swells a lot more than neoprene in the presence of water. This swelling can increase belt tension significantly, leading to belt and related hardware problems.
Oil: Light connection with natural oils on an occasional basis will not generally harm synchronous belts. Prolonged contact with oil or lubricants, either straight or airborne, results in significantly reduced belt service life. Lubricants cause the rubber substance to swell, breakdown inner adhesion systems, and reduce belt tensile power. While alternate rubber substances may provide some marginal improvement in durability, it is advisable to prevent oil from contacting synchronous belts.
Ozone: The existence of ozone can be detrimental to the compounds used in rubber synchronous belts. Ozone degrades belt materials in much the same way as extreme environmental temperatures. Although the rubber materials found in synchronous belts are compounded to resist the consequences of ozone, ultimately chemical substance breakdown occurs plus they become hard and brittle and begin cracking. The amount of degradation is dependent upon the ozone focus and duration of publicity. For good performance of rubber belts, the next concentration levels should not be exceeded: (parts per hundred million)
Standard Construction: 100 pphm
Nonmarking Construction: 20 pphm
Conductive Construction: 75 pphm
Low Temperatures Structure: 20 pphm
Radiation: Exposure to gamma radiation can be detrimental to the substances used in rubber and urethane synchronous belts. Radiation degrades belt materials quite similar way excessive environmental temps do. The amount 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 Construction: 104 rads
Conductive Construction: 106 rads
Low Temperatures Structure: 104 rads
Dust Generation: Rubber synchronous belts are known to generate small quantities of fine dust, as an all natural result of their procedure. The amount of dust is typically higher for new belts, because they run in. The period of time for run directly into occur is dependent upon the belt and pulley size, loading and rate. Factors such as pulley surface surface finish, operating speeds, installation stress, and alignment influence the amount of dust generated.
Clean Room: Rubber synchronous belts may not be suitable for use in clean room environments, where all potential contamination should be minimized or eliminated. Urethane timing belts typically generate significantly less debris than rubber timing belts. However, they are suggested limited to light working loads. Also, they cannot be stated in a static conductive structure to permit electrical charges to dissipate.
Static Sensitive: Applications are sometimes sensitive to the accumulation of static electric charges. Electrical fees can affect material handling processes (like paper and plastic film transportation), and sensitive electronic products. Applications like these need a static conductive belt, so that the static charges produced by the belt can be dissipated in to the pulleys, and also to ground. Regular rubber synchronous belts usually do not fulfill this requirement, but can be manufactured in a static conductive construction on a made-to-order basis. Normal belt wear caused by long term procedure or environmental contamination can impact belt conductivity properties.
In delicate applications, rubber synchronous belts are preferred over urethane belts since urethane belting cannot be produced in a conductive construction.
9.7 BELT TRACKING
Lateral tracking qualities of synchronous belts is definitely a common area of inquiry. Although it is regular for a belt to favor one part of the pulleys while operating, it is unusual for a belt to exert significant force against a flange resulting in belt edge use and potential flange failure. Belt tracking is usually influenced by many factors. In order of significance, discussion about these elements is as follows:
Tensile Cord Twist: Tensile cords are shaped into a solitary twist configuration during their produce. Synchronous belts made with only one twist tensile cords monitor laterally with a substantial drive. To neutralize this tracking power, tensile cords are produced in right- and left-hands twist (or “S” and “Z” twist) configurations. Belts made with “S” twist tensile cords monitor in the contrary direction to those constructed with “Z” twist cord. Belts made with alternating “S” and “Z” twist tensile cords monitor with reduced lateral force because the tracking characteristics of both cords offset each other. The content of “S” and “Z” twist tensile cords varies slightly with every belt that is produced. Because of this, every belt comes with an unprecedented inclination to monitor in either one direction or the additional. When a credit card applicatoin requires a belt to monitor in a single specific direction just, an individual twist construction is used. See Figures 16 & Figure 17.
Angular Misalignment: Angular misalignment, or shaft nonparallelism, cause synchronous belts to track laterally. The position of misalignment influences the magnitude and direction of the monitoring push. 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 tend to track with an increase of force than narrow belts.
Pulley Size: Belts operating on little pulley diameters can tend to generate higher tracking forces than on large diameters. This is particularly accurate as the belt width methods the pulley size. Drives with pulley diameters less than the belt width aren’t generally recommended because belt tracking forces may become excessive.
Belt Length: Due to just how tensile cords are applied on to the belt molds, brief belts can tend to exhibit higher tracking forces than long belts. The helix angle of the tensile cord decreases with increasing belt length.
Gravity: In drive 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 sufficient belt installation tension.
Torque Loads: Sometimes, while functioning, a synchronous belt will move laterally from side to side on the pulleys rather than operating in a consistent position. Without generally regarded as a substantial concern, one explanation for this is varying torque loads within the drive. Synchronous belts occasionally track differently with changing loads. There are plenty of potential known reasons for this; the primary cause is related to tensile cord distortion while under great pressure against the pulleys. Variation in belt tensile loads may also cause changes in framework deflection, and angular shaft alignment, resulting in belt movement.
Belt Installation Tension: Belt tracking may also be influenced by the level of belt installation stress. The reason why for this are similar to the effect that varying torque loads have got on belt tracking. When problems with belt tracking are experienced, each one of these potential contributing factors should be investigated in the order that they are shown. Generally, the primary problem is going to be discovered before moving completely through the list.
9.8 PULLEY FLANGES
Pulley information flanges are necessary to hold synchronous belts operating on their pulleys. As discussed previously in Section 9.7 on belt tracking, it is normal for synchronous belts to favor one aspect of the pulleys when running. Proper flange design is essential in avoiding belt edge put on, minimizing sound and avoiding the belt from climbing from the pulley. Dimensional recommendations for custom-made or molded flanges are contained in tables coping with these problems. Proper flange placement is important to ensure that the belt is definitely adequately restrained within its operating-system. Because design and layout of little synchronous drives is so different, the wide variety of flanging situations potentially encountered cannot very easily be covered in a simple set of guidelines without finding exceptions. Not surprisingly, the following broad flanging suggestions should help the designer in most cases:
Two Pulley Drives: On simple two pulley drives, either one pulley ought to be flanged on both sides, or each pulley ought to be flanged on reverse sides.
Multiple Pulley Drives: On multiple pulley (or serpentine) drives, either every other pulley should be flanged about both sides, or every pulley should be flanged about alternating sides around the machine. Vertical Shaft Drives: On vertical shaft drives, at least one pulley should be flanged on both sides, and the remaining pulleys should be flanged on at least underneath side.
Long Span Lengths: Flanging suggestions for small synchronous drives with long belt span lengths cannot easily be defined due to the many factors that can affect belt tracking characteristics. Belts on drives with lengthy spans (generally 12 times the diameter of the smaller pulley or more) frequently require even more lateral restraint than with brief spans. Due to this, it really 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 reduce cost and space. Belts generally tend to need less lateral restraint on large pulleys than little and can often perform reliably without flanges. When deciding whether to flange, the previous 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 designed to carry lateral side loads from belt tracking forces can be flanged if had a need to offer lateral belt restraint. Idlers utilized for this function can be used on the inside or backside of the belts. The previous 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 capabilities of a synchronous belt drive, the machine must initial be determined to become either static or powerful with regards to its registration function and requirements.
Static Sign up: A static registration system moves from its initial static position to a secondary static position. Through the process, the designer can be involved only with how accurately and consistently the drive finds its secondary position. He/she isn’t worried about any potential sign up errors that take place during transport. Therefore, the principal factor contributing to registration error in a static sign up system is usually backlash. The consequences of belt elongation and tooth deflection don’t have any influence on the sign up accuracy of this kind of system.
Dynamic Sign up: A dynamic registration system is required to perform a registering function while in motion with torque loads various as the system operates. In this case, the designer is concerned with the rotational position of the get pulleys regarding one another at every time. Therefore, belt elongation, backlash and tooth deflection will all contribute to registrational inaccuracies.
Further discussion about each one of the factors adding to registration error is as follows:
Belt Elongation: Belt elongation, or stretch out, occurs naturally whenever a belt is positioned under stress. The total tension exerted within a belt results from set up, and also operating loads. The amount of belt elongation is usually a function of the belt tensile modulus, which is certainly influenced by the kind of tensile cord and the belt construction. The standard tensile cord found in rubber synchronous belts is normally fiberglass. Fiberglass has a high tensile modulus, is dimensionally stable, and has exceptional flex-fatigue characteristics. If an increased tensile modulus is necessary, aramid tensile cords can be considered, although they are generally used to provide resistance to severe shock and impulse loads. Aramid tensile cords used in little synchronous belts generally possess just a marginally higher tensile modulus in comparison to fiberglass. When required, belt tensile modulus data is normally obtainable from our Application Engineering Department.
Backlash: Backlash in a synchronous belt drive outcomes from clearance between the belt teeth and the pulley grooves. This clearance is needed to allow the belt teeth to enter and exit the grooves easily with at the least interference. The amount of clearance necessary depends upon the belt tooth profile. Trapezoidal Timing Belt Drives are recognized for having fairly little backlash. PowerGrip HTD Drives have improved torque carrying capability and resist ratcheting, but possess a significant quantity of backlash. PowerGrip GT2 Drives possess even further improved torque carrying capability, and have only a small amount or less backlash than trapezoidal timing belt drives. In particular cases, alterations could be made to drive systems to further lower backlash. These alterations typically lead to increased belt wear, increased drive noise and shorter drive life. Get in touch with our Software Engineering Section for more 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 tension and belt type. Of the three main contributors to registration error, tooth deflection may be the most challenging to quantify. Experimentation with a prototype travel system may be the best method of obtaining realistic estimations of belt tooth deflection.
Additional guidelines which may be useful in designing registration important drive systems are as follows:
Select PowerGrip GT2 or trapezoidal timing belts.
Design with large pulleys with more teeth in mesh.
Keep belts restricted, and control tension closely.
Design frame/shafting to end up being rigid under load.
Use high quality machined pulleys to reduce radial runout and lateral wobble.