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 associated with V-belt drives, and even allows significantly better torque carrying ability. 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 should be used the travel selection process as stall and peak torques can sometimes be high. While intermittent peak torques can often be carried by synchronous drives without unique factors, high cyclic peak torque loading should be carefully reviewed.
Proper belt installation tension and rigid get bracketry and framework is essential in stopping belt tooth jumping in peak torque loads. Additionally it is beneficial to design with an increase of compared to the normal the least 6 belt teeth in mesh to make sure adequate belt tooth shear strength.
Newer generation curvilinear systems like PowerGrip GT2 and PowerGrip HTD should be found in low-swiftness, high torque applications, as trapezoidal timing belts are more prone to tooth jumping, and have significantly much less load carrying capacity.
9.2 HIGH-SPEED OPERATION
Synchronous belt drives are often used in high-speed applications despite the fact that V-belt drives are typically better suitable. They are generally used because of their positive driving characteristic (no creep or slide), and because they might need minimal maintenance (don’t stretch considerably). A substantial drawback of high-swiftness synchronous drives can be get noise. High-velocity synchronous drives will almost always produce even more noise than V-belt drives. Little pitch synchronous drives working at speeds more than 1300 ft/min (6.6 m/s) are believed to be high-speed.
Special consideration ought to be given to high-speed drive designs, as a number of factors can significantly influence belt performance. Cord exhaustion and belt tooth wear are the two most significant elements that must be controlled to ensure success. Moderate pulley diameters ought to be used to lessen the price of cord flex fatigue. Developing with a smaller pitch belt will most likely offer better cord flex exhaustion characteristics when compared to a bigger pitch belt. PowerGrip GT2 is particularly well suited for high-quickness drives due to its excellent belt tooth access/exit characteristics. Smooth interaction between the belt tooth and pulley groove minimizes put on and sound. Belt installation pressure is especially essential with high-rate drives. Low belt stress allows the belt to trip out of the driven pulley, resulting in rapid belt tooth and pulley groove wear.
9.3 SMOOTH RUNNING
Some ultrasensitive applications require the belt drive to use with only a small China Pulley amount vibration aspossible, as vibration sometimes impacts the system procedure or finished manufactured product. In such cases, the characteristics and properties of all appropriate belt drive products ought to be reviewed. The ultimate drive system selection should be based upon the most critical design requirements, and may require some compromise.
Vibration isn’t generally considered to be a issue with synchronous belt drives. Low degrees of vibration typically derive from the process of tooth meshing and/or as a result of their high tensile modulus properties. Vibration resulting from tooth meshing is a standard characteristic of synchronous belt drives, and can’t be totally eliminated. It can be minimized by avoiding small pulley diameters, and rather choosing moderate sizes. The dimensional accuracy of the pulleys also influences tooth meshing quality. Additionally, the installation pressure has an effect on meshing quality. PowerGrip GT2 drives mesh very cleanly, resulting in 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 manufactured with some radial go out, but V-belts have a lesser tensile modulus resulting in less belt pressure variation. The high tensile modulus found in synchronous belts is necessary to maintain proper pitch under load.
9.4 DRIVE NOISE
Drive noise evaluation in virtually any belt drive system should be approached carefully. There are numerous potential resources of sound in something, including vibration from related elements, bearings, and resonance and amplification through framework and panels.
Synchronous belt drives typically produce more noise than V-belt drives. Noise results from the procedure of belt tooth meshing and physical connection with the pulleys. The sound pressure level generally boosts as operating velocity and belt width increase, and as pulley size reduces. Drives designed on moderate pulley sizes without excessive capability (overdesigned) are usually the quietest. PowerGrip GT2 drives have already been discovered to be significantly quieter than additional systems because of their improved meshing characteristic, see Figure 9. Polyurethane belts generally create more sound than neoprene belts. Proper belt installation tension is also very important in minimizing travel noise. The belt ought to be tensioned at a level that allows it to run with only a small amount meshing interference as feasible.
Travel alignment also offers a significant effect on drive noise. Special attention ought to be given to minimizing angular misalignment (shaft parallelism). This assures that belt teeth are loaded uniformly and minimizes aspect tracking forces against the flanges. Parallel misalignment (pulley offset) is not as important of a problem so long as the belt isn’t trapped or pinched between opposite flanges (see the unique section coping with drive alignment). Pulley components and dimensional precision also influence travel noise. Some users have 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 usually quieter than molded pulleys. The reason why because of this revolve around material density and resonance characteristics along with dimensional accuracy.
9.5 STATIC CONDUCTIVITY
Little synchronous rubber or urethane belts can generate a power charge while operating on a drive. Elements such as humidity and working speed influence the potential of the charge. If established to become a problem, rubber belts can be produced in a conductive structure to dissipate the charge in to the pulleys, and also to floor. This prevents the accumulation of electric charges that may be harmful to materials handling procedures or sensitive electronics. It also significantly reduces the prospect of arcing or sparking in flammable conditions. Urethane belts cannot be stated in a conductive building.
RMA has outlined standards for conductive belts in their bulletin IP-3-3. Unless in any other case specified, a static conductive building for rubber belts is normally on a made-to-purchase basis. Unless usually specified, conductive belts will be built to yield a level of resistance of 300,000 ohms or much less, when new.
Nonconductive belt constructions are also available for rubber belts. These belts are usually built specifically to the customers conductivity requirements. They are usually used in applications where one shaft should be electrically isolated from the additional. It is necessary to note a static conductive belt cannot dissipate a power charge through plastic material pulleys. At least one metallic pulley in a drive is necessary for the charge to end up being dissipated to surface. A grounding brush or comparable device could also be used to dissipate electrical charges.
Urethane timing belts are not static conductive and cannot be built in a special conductive construction. Particular conductive rubber belts ought to be used when the presence of an electrical charge is certainly a concern.
9.6 OPERATING ENVIRONMENTS
Synchronous drives are suitable for use in a wide variety of environments. Special considerations could be necessary, however, depending on the application.
Dust: Dusty conditions do not generally present serious problems to synchronous drives provided that the contaminants are great and dry out. Particulate matter will, however, become an abrasive producing a higher level of belt and pulley wear. Damp or sticky particulate matter deposited and loaded into pulley grooves could cause belt tension to improve considerably. This increased stress can influence shafting, bearings, and framework. Electrical charges within a get system can sometimes attract particulate matter.
Debris: Debris should be prevented from falling into any synchronous belt drive. Particles caught in the drive is normally either forced through the belt or results in stalling of the machine. In any case, serious damage takes place to the belt and related travel hardware.
Drinking water: Light and occasional contact with drinking water (occasional clean downs) shouldn’t seriously have an effect on synchronous belts. Prolonged get in touch with (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 significantly less than with oil get in touch with. Internal belt adhesion systems are also gradually divided with the presence of drinking water. Additives to drinking water, such as lubricants, chlorine, anticorrosives, etc. can have a far more detrimental influence on the belts than clear water. Urethane timing belts also have problems with water contamination. Polyester tensile cord shrinks considerably and experiences loss of tensile strength in the existence of drinking water. Aramid tensile cord maintains its strength fairly well, but experiences length variation. Urethane swells more than neoprene in the presence of drinking water. This swelling can increase belt tension significantly, leading to belt and related equipment problems.
Oil: Light connection with oils on an occasional basis will not generally damage synchronous belts. Prolonged connection with essential oil or lubricants, either straight or airborne, results in significantly reduced belt service life. Lubricants trigger the rubber compound to swell, breakdown internal adhesion systems, and reduce belt tensile power. While alternate rubber compounds may 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 used in rubber synchronous belts. Ozone degrades belt materials in quite similar way as excessive environmental temperature ranges. Although the rubber materials found in synchronous belts are compounded to resist the effects of ozone, eventually chemical substance breakdown occurs and they become hard and brittle and start cracking. The amount of degradation is dependent upon the ozone focus and duration of publicity. For good functionality 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 Structure: 20 pphm
Radiation: Contact with gamma radiation could be detrimental to the compounds used in rubber and urethane synchronous belts. Radiation degrades belt materials quite similar way extreme environmental temperatures do. The quantity of degradation is dependent upon the strength of radiation and the publicity time. For good belt performance, the next exposure levels shouldn’t be exceeded:
Standard Construction: 108 rads
Nonm arking Building: 104 rads
Conductive Construction: 106 rads
Low Temperatures Building: 104 rads
Dust Generation: Rubber synchronous belts are known to generate small quantities of great dust, as a natural result of their operation. The amount of dust is normally higher for fresh belts, because they run in. The period of time for run directly into occur depends upon the belt and pulley size, loading and rate. Elements such as pulley surface end, operating speeds, set up stress, and alignment influence the amount of dust generated.
Clean Room: 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 particles than rubber timing belts. Nevertheless, they are recommended only for light working loads. Also, they cannot be stated in a static conductive building to permit electrical costs to dissipate.
Static Sensitive: Applications are occasionally delicate to the accumulation of static electric charges. Electrical fees can affect materials handling processes (like paper and plastic film transportation), and sensitive digital apparatus. Applications like these require a static conductive belt, to ensure that the static costs produced by the belt can be dissipated in to the pulleys, and also to ground. Standard rubber synchronous belts do not meet this necessity, but could be produced in a static conductive building on a made-to-order basis. Regular belt wear resulting from 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 stated in a conductive construction.
9.7 BELT TRACKING
Lateral tracking qualities of synchronous belts is certainly a common area of inquiry. While it is regular for a belt to favor one part of the pulleys while running, it is abnormal 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. In order of significance, dialogue about these elements is as follows:
Tensile Cord Twist: Tensile cords are formed into a one twist configuration during their manufacture. Synchronous belts made out of only single twist tensile cords monitor laterally with a significant power. To neutralize this monitoring power, tensile cords are stated in correct- and left-hands twist (or “S” and “Z” twist) configurations. Belts made out of “S” twist tensile cords track in the contrary direction to those built with “Z” twist cord. Belts made with alternating “S” and “Z” twist tensile cords track with reduced lateral force since the tracking characteristics of the two cords offset each other. This content of “S” and “Z” twist tensile cords varies slightly with every belt that is produced. As a result, every belt comes with an unprecedented tendency to track in each one direction or the other. When a credit card applicatoin takes a belt to monitor in a single specific direction just, an individual twist construction can be used. See Figures 16 & Figure 17.
Angular Misalignment: Angular misalignment, or shaft nonparallelism, cause synchronous belts to track laterally. The angle of misalignment influences the magnitude and path of the monitoring drive. Synchronous belts have a tendency to monitor “downhill” to circumstances of lower tension or shorter middle distance.
Belt Width: The potential magnitude of belt tracking force is directly related to belt width. Wide belts tend to track with an increase of pressure than narrow belts.
Pulley Diameter: Belts operating on little pulley diameters can tend to generate higher tracking forces than on large diameters. That is particularly accurate as the belt width techniques the pulley diameter. Drives with pulley diameters significantly 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 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 drive applications with vertical shafts, gravity pulls the belt downward. The magnitude of this force can be minimal with little pitch synchronous belts. Sag in long belt spans ought to 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 instead of operating in a constant position. Without generally regarded as a significant concern, one description for this is varying torque loads within the travel. Synchronous belts occasionally track in a different way with changing loads. There are several potential reasons for this; the primary cause is related to tensile cord distortion while under 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 may also be influenced by the amount of belt installation stress. The reasons for this are similar to the effect that varying torque loads have on belt tracking. When issues with belt monitoring are experienced, each one of these potential contributing factors should be investigated in the order they are listed. In most cases, the primary problem is going to be identified before moving completely through the list.
9.8 PULLEY FLANGES
Pulley guide flanges are essential to keep synchronous belts operating on the pulleys. As talked about previously in Section 9.7 on belt tracking, it is regular for synchronous belts to favor one side of the pulleys when working. Proper flange design is essential in preventing belt edge wear, minimizing noise and avoiding the belt from climbing out from the pulley. Dimensional suggestions for custom-made or molded flanges are contained in tables coping with these problems. Proper flange positioning is important so that the belt is definitely adequately restrained within its operating-system. Because style and design of small synchronous drives is so varied, the wide selection of flanging situations potentially encountered cannot quickly be protected in a straightforward group of rules without locating exceptions. Not surprisingly, the next broad flanging recommendations should help the designer in most cases:
Two Pulley Drives: On simple two pulley drives, each one pulley should 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 in both sides, or every pulley should be flanged in alternating sides around the system. Vertical Shaft Drives: On vertical shaft drives, at least one pulley should be flanged on both sides, and the rest of the pulleys should be flanged on at least the bottom side.
Long Period Lengths: Flanging suggestions for small synchronous drives with lengthy belt span lengths cannot easily 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 small pulley or even more) often require more lateral restraint than with brief spans. Due to 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 desire to leave huge pulleys unflanged to lessen cost and space. Belts generally tend to need much less lateral restraint on huge pulleys than small and can frequently perform reliably without flanges. When determining whether to flange, the previous guidelines is highly recommended. The groove encounter width of unflanged pulleys should also be greater than with flanged pulleys. See Table 27 for recommendations.
Idlers: Flanging of idlers is generally not essential. Idlers made to bring lateral part loads from belt tracking forces could be flanged if needed to offer lateral belt restraint. Idlers utilized for this function can be used 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 features of a synchronous belt drive, the system must first be established to become either static or powerful in conditions of its sign up function and requirements.
Static Sign up: A static registration system moves from its initial static position to a second static position. Through the process, the designer is concerned just with how accurately and consistently the drive arrives at its secondary placement. He/she is not worried about any potential registration errors that take place during transportation. Therefore, the principal factor adding to registration mistake in a static sign up system is certainly backlash. The effects of belt elongation and tooth deflection don’t have any influence on the registration accuracy of this type of system.
Dynamic Sign up: A powerful registration system is required to perform a registering function while in motion with torque loads varying as the system operates. In cases like this, the designer is concerned with the rotational position of the drive 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 really as follows:
Belt Elongation: Belt elongation, or stretch out, occurs naturally whenever a belt is positioned under pressure. The total stress exerted within a belt results from installation, in addition to operating loads. The quantity of belt elongation is normally 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 is definitely fiberglass. Fiberglass has a high tensile modulus, is dimensionally stable, and has exceptional flex-fatigue characteristics. If a higher tensile modulus is necessary, aramid tensile cords can be considered, although they are generally used to supply resistance to severe shock and impulse loads. Aramid tensile cords found in small synchronous belts generally have got only a marginally higher tensile modulus compared to fiberglass. When required, belt tensile modulus data can be obtainable from our Software 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 smoothly with at the least interference. The quantity of clearance necessary is dependent upon the belt tooth profile. Trapezoidal Timing Belt Drives are recognized for having fairly little backlash. PowerGrip HTD Drives have improved torque holding capability and withstand ratcheting, but possess a significant quantity of backlash. PowerGrip GT2 Drives have even more improved torque carrying capability, and have only a small amount or much less backlash than trapezoidal timing belt drives. In unique cases, alterations can be made to drive systems to further decrease backlash. These alterations typically result in increased belt wear, increased drive sound and shorter drive life. Get in touch with our Program Engineering Section for additional information.
Tooth Deflection: Tooth deformation in a synchronous belt drive occurs as a torque load is applied to the system, and individual belt teeth are loaded. The quantity of belt tooth deformation is dependent upon the quantity of torque loading, pulley size, installation pressure and belt type. Of the three primary contributors to registration mistake, tooth deflection is the most difficult to quantify. Experimentation with a prototype travel system may be the best means of obtaining realistic estimations of belt tooth deflection.
Additional guidelines that may be useful in developing registration crucial drive systems are the following:
Select PowerGrip GT2 or trapezoidal timing belts.
Style with large pulleys with more tooth in mesh.
Keep belts tight, and control stress closely.
Design frame/shafting to end up being rigid under load.
Use high quality machined pulleys to minimize radial runout and lateral wobble.