9.1 LOW-SPEED OPERATION
Synchronous drives are specially well-appropriate for low-speed, high torque applications. Their positive generating nature prevents potential slippage connected with V-belt drives, and also allows significantly higher torque carrying ability. Small pitch synchronous drives operating at speeds of 50 ft/min (0.25 m/s) or much less are considered to be low-speed. Care should be taken in the travel selection procedure as stall and peak torques can sometimes be high. While intermittent peak torques can frequently 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 essential in preventing belt tooth jumping less than peak torque loads. It is also beneficial to design with an increase of compared to the normal minimum of 6 belt teeth in mesh to make sure sufficient belt tooth shear power.
Newer generation curvilinear systems like PowerGrip GT2 and PowerGrip HTD should be used in low-velocity, high torque applications, as trapezoidal timing belts are even more susceptible to tooth jumping, and also have significantly less load carrying capacity.
9.2 HIGH-SPEED OPERATION
Synchronous belt drives are often used in high-speed applications even though V-belt drives are usually better appropriate. They are generally used because of their positive generating characteristic (no creep or slide), and because they require minimal maintenance (don’t stretch significantly). A significant drawback of high-quickness synchronous drives is definitely drive noise. High-acceleration synchronous drives will nearly always produce more noise than V-belt drives. Little pitch synchronous drives operating at speeds in excess of 1300 ft/min (6.6 m/s) are considered to be high-speed.
Special consideration should be given to high-speed drive designs, as a number of factors can considerably influence belt performance. Cord exhaustion and belt tooth wear are the two most crucial elements that must be controlled to have success. Moderate pulley diameters should be used to lessen the price of cord flex fatigue. Designing with a smaller pitch belt will most likely provide better cord flex fatigue characteristics when compared to a larger pitch belt. PowerGrip GT2 is particularly perfect for high-acceleration drives due to its excellent belt tooth access/exit characteristics. Clean interaction between your belt tooth and pulley groove minimizes use and sound. Belt installation tension is especially vital with high-acceleration drives. Low belt stress allows the belt to ride out from the driven pulley, leading to rapid belt tooth and pulley groove wear.
9.3 SMOOTH RUNNING
Some ultrasensitive applications require the belt drive to use with only a small amount vibration aspossible, as vibration sometimes has an effect on the system operation or finished manufactured product. In these cases, the characteristics and properties of all appropriate belt drive products should be reviewed. The final drive program 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 result from the process of tooth meshing and/or because of this of their high tensile modulus properties. Vibration resulting from tooth meshing is definitely a standard characteristic of synchronous belt drives, and can’t be completely eliminated. It can be minimized by avoiding little pulley diameters, and instead selecting moderate sizes. The dimensional precision of the pulleys also influences tooth meshing quality. Additionally, the installation pressure has an impact 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 run out causes belt tension 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 essential to maintain proper pitch under load.
9.4 DRIVE NOISE
Drive noise evaluation in virtually any belt drive system ought to be approached carefully. There are plenty of potential sources of noise 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 outcomes from the procedure of belt tooth meshing and physical contact with the pulleys. The sound pressure level generally boosts as operating acceleration and belt width boost, and as pulley size reduces. Drives designed on moderate pulley sizes without extreme capacity (overdesigned) are generally the quietest. PowerGrip GT2 drives have already been found to be significantly 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 can be very important in minimizing travel noise. The belt should be tensioned at a rate which allows it to perform with as little meshing interference as feasible.
Travel alignment also offers a significant influence on drive sound. Special attention ought to be given to minimizing angular misalignment (shaft parallelism). This assures that belt teeth are loaded uniformly and minimizes aspect monitoring forces against the flanges. Parallel misalignment (pulley offset) is not as important of a concern provided that the belt is not trapped or pinched between opposing flanges (see the unique section coping with travel alignment). Pulley components and dimensional precision also influence drive sound. Some users possess found that steel pulleys are 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 Motorbase molded pulleys. The reason why for this revolve around material density and resonance features in addition to dimensional accuracy.
9.5 STATIC CONDUCTIVITY
Small synchronous rubber or urethane belts can generate an electrical charge while operating on a drive. Elements such as for example humidity and working speed impact the potential of the charge. If motivated to become a issue, rubber belts could be produced in a conductive building to dissipate the charge in to the pulleys, and also to surface. This prevents the accumulation of electric charges that may be detrimental to materials handling processes or sensitive electronics. In addition, it significantly reduces the potential for arcing or sparking in flammable conditions. Urethane belts can’t be stated in a conductive construction.
RMA has outlined criteria for conductive belts within their bulletin IP-3-3. Unless in any other case specified, a static conductive building for rubber belts is available on a made-to-purchase basis. Unless otherwise specified, conductive belts will be built to yield a resistance of 300,000 ohms or much less, when new.
non-conductive belt constructions are also available for rubber belts. These belts are usually built particularly to the clients conductivity requirements. They are generally found in applications where one shaft must be electrically isolated from the 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 end up being dissipated to ground. A grounding brush or related device could also be used to dissipate electric charges.
Urethane timing belts aren’t static conductive and cannot be built in a special conductive construction. Special conductive rubber belts should be utilized when the existence of a power charge is usually a concern.
9.6 OPERATING ENVIRONMENTS
Synchronous drives are suitable for use in a wide variety of environments. Special considerations may be necessary, nevertheless, based on the application.
Dust: Dusty conditions do not generally present serious complications to synchronous drives provided that the particles are fine and dry. Particulate matter will, however, become an abrasive resulting in a higher rate of belt and pulley put on. Damp or sticky particulate matter deposited and packed into pulley grooves can cause belt tension to improve significantly. This increased tension can impact shafting, bearings, and framework. Electrical charges within a travel system can sometimes attract particulate matter.
Debris: Debris ought to be prevented from falling into any synchronous belt drive. Particles caught in the travel is normally either forced through the belt or outcomes in stalling of the system. In any case, serious damage takes place to the belt and related travel hardware.
Water: Light and occasional contact with drinking water (occasional wash downs) should not seriously influence synchronous belts. Prolonged contact (continuous spray or submersion) results in considerably reduced tensile power in fiberglass belts, and potential duration variation in aramid belts. Prolonged connection with water also causes rubber substances to swell, although significantly less than with oil get in touch with. Internal belt adhesion systems are also gradually divided with the existence of drinking water. Additives to water, such as for example lubricants, chlorine, anticorrosives, etc. can possess a far more detrimental influence on the belts than pure water. Urethane timing belts also suffer from water contamination. Polyester tensile cord shrinks significantly and experiences loss of tensile strength in the presence of water. Aramid tensile cord keeps its strength fairly well, but experiences size 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 contact with oils on an intermittent basis will not generally damage synchronous belts. Prolonged connection with essential oil or lubricants, either directly or airborne, results in significantly reduced belt service lifestyle. Lubricants cause the rubber substance to swell, breakdown inner adhesion systems, and reduce belt tensile strength. While alternate rubber compounds may provide some marginal improvement in durability, it is best to prevent essential oil from contacting synchronous belts.
Ozone: The presence of ozone can be detrimental to the compounds 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 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 concentration and duration of publicity. For good functionality of rubber belts, the following concentration levels shouldn’t 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 could be detrimental to the substances found in rubber and urethane synchronous belts. Radiation degrades belt materials quite similar way extreme environmental temperature ranges do. The amount of degradation depends upon the strength of radiation and the exposure time. For good 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 Structure: 104 rads
Dust Era: Rubber synchronous belts are known to generate small quantities of fine dust, as an all natural consequence of their procedure. The quantity of dust is normally higher for fresh belts, because they operate in. The time period for run directly into occur depends upon the belt and pulley size, loading and velocity. Elements such as for example pulley surface finish, operating speeds, set up tension, and alignment impact the quantity of dust generated.
Clean Space: Rubber synchronous belts may not be ideal for use in clean area environments, where all potential contamination should be minimized or eliminated. Urethane timing belts typically generate considerably less particles than rubber timing belts. However, they are suggested limited to light operating loads. Also, they cannot 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 material handling processes (like paper and plastic material film transportation), and sensitive electronic products. Applications like these require a static conductive belt, to ensure that the static fees produced by the belt could be dissipated in to the pulleys, and also to ground. Regular rubber synchronous belts usually do not meet this necessity, but could be produced 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 sensitive applications, rubber synchronous belts are preferred over urethane belts since urethane belting can’t be stated in a conductive construction.
9.7 BELT TRACKING
Lateral tracking characteristics of synchronous belts is normally a common area of inquiry. Although it is regular for a belt to favor one side of the pulleys while working, it is unusual for a belt to exert significant push against a flange leading to belt edge wear and potential flange failure. Belt tracking can be influenced by several factors. In order of significance, discussion about these elements is really as follows:
Tensile Cord Twist: Tensile cords are formed into a one twist configuration throughout their produce. Synchronous belts made with only one twist tensile cords track laterally with a significant pressure. To neutralize this tracking pressure, tensile cords are stated in correct- and left-hands twist (or “S” and “Z” twist) configurations. Belts made with “S” twist tensile cords track in the contrary path to those constructed with “Z” twist cord. Belts made with alternating “S” and “Z” twist tensile cords track with minimal lateral force because the tracking features of both cords offset one another. The content of “S” and “Z” twist tensile cords varies slightly with every belt that is produced. As a result, every belt has an unprecedented inclination to monitor in each one direction or the various other. When a credit card applicatoin requires 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 position of misalignment influences the magnitude and direction of the tracking drive. Synchronous belts tend to track “downhill” to a state of lower tension or shorter center distance.
Belt Width: The potential magnitude of belt tracking force is directly related to belt width. Wide belts have a tendency to track with an increase of force than narrow belts.
Pulley Size: Belts operating on little pulley diameters can tend to generate higher monitoring forces than on large diameters. This is particularly accurate as the belt width techniques the pulley diameter. Drives with pulley diameters less than the belt width are not generally suggested because belt tracking forces can become excessive.
Belt Length: Because of just how tensile cords are applied on to the belt molds, brief belts can have a tendency 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 the force is certainly minimal with little pitch synchronous belts. Sag in long belt spans ought to be prevented by applying sufficient belt installation tension.
Torque Loads: Sometimes, while in operation, a synchronous belt can move laterally laterally on the pulleys instead of operating in a constant position. While not generally considered to be a significant concern, one explanation for this is definitely varying torque loads within the drive. Synchronous belts sometimes track differently with changing loads. There are various 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 tension. The reasons for this act like the effect that varying torque loads possess on belt tracking. When issues with belt monitoring are experienced, each of these potential contributing factors should be investigated in the purchase that they are shown. Generally, the primary problem will probably be recognized before moving completely through the list.
9.8 PULLEY FLANGES
Pulley guideline flanges are essential to keep synchronous belts operating on their pulleys. As discussed 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 use, minimizing noise and avoiding the belt from climbing from the pulley. Dimensional suggestions for custom-produced or molded flanges are included in tables dealing with these problems. Proper flange positioning is important so that the belt is normally adequately restrained within its operating-system. Because design and design of little synchronous drives is indeed different, the wide selection of flanging situations possibly encountered cannot easily be covered in a straightforward set of rules without obtaining exceptions. Not surprisingly, the next broad flanging suggestions should help the developer in most cases:
Two Pulley Drives: On simple two pulley drives, either one pulley ought to be flanged about both sides, or each pulley ought to be flanged on opposite sides.
Multiple Pulley Drives: On multiple pulley (or serpentine) drives, either almost every other pulley ought to be flanged in both sides, or every single pulley ought to 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 ought to be flanged on at least the bottom side.
Long Period Lengths: Flanging recommendations for little synchronous drives with long belt span lengths cannot quickly be defined due to the many factors that may affect belt tracking qualities. Belts on drives with lengthy spans (generally 12 times the size of small pulley or more) frequently require even more lateral restraint than with short spans. Because of this, 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 reduce cost and space. Belts tend to need less lateral restraint on large pulleys than small and can frequently perform reliably without flanges. When choosing 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 essential. Idlers made to bring lateral aspect loads from belt tracking forces could be flanged if had a need to provide lateral belt restraint. Idlers utilized for this purpose can be used inside or backside of the belts. The prior guidelines should also 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 identified to become either static or dynamic in terms of its sign up function and requirements.
Static Registration: A static registration system moves from its initial static position to a secondary static position. Through the procedure, the designer is concerned just with how accurately and regularly the drive finds its secondary position. He/she isn’t concerned with any potential registration errors that occur during transport. Therefore, the primary factor adding to registration mistake in a static sign up system is usually backlash. The effects of belt elongation and tooth deflection don’t have any impact on the sign up accuracy of this type of system.
Dynamic Registration: A dynamic registration system must perform a registering function while in motion with torque loads various as the machine operates. In this case, the designer is concerned with the rotational position of the drive pulleys with respect to one another at every time. Therefore, belt elongation, backlash and tooth deflection will all donate to registrational inaccuracies.
Further discussion about each one of the factors adding to registration error is as follows:
Belt Elongation: Belt elongation, or stretch, occurs naturally when a belt is positioned under pressure. The total tension exerted within a belt results from set up, and also working loads. The quantity of belt elongation is definitely a function of the belt tensile modulus, which is usually influenced by the type of tensile cord and the belt construction. The standard tensile cord used in rubber synchronous belts is fiberglass. Fiberglass has a high tensile modulus, is dimensionally steady, and has superb flex-fatigue characteristics. If an increased tensile modulus is necessary, aramid tensile cords can be considered, although they are usually used to provide resistance to severe shock and impulse loads. Aramid tensile cords found in small synchronous belts generally have only a marginally higher tensile modulus compared to fiberglass. When needed, belt tensile modulus data is usually obtainable from our Application Engineering Department.
Backlash: Backlash in a synchronous belt drive outcomes from clearance between your belt tooth and the pulley grooves. This clearance is required to permit the belt teeth to enter and exit the grooves easily with at the least interference. The quantity of clearance necessary is dependent upon the belt tooth account. Trapezoidal Timing Belt Drives are recognized for having relatively small backlash. PowerGrip HTD Drives possess improved torque having capability and withstand ratcheting, but have a significant amount of backlash. PowerGrip GT2 Drives have even further improved torque transporting capability, and have as little or less backlash than trapezoidal timing belt drives. In particular 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 Software Engineering Department for additional information.
Tooth Deflection: Tooth deformation in a synchronous belt get 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 amount of torque loading, pulley size, installation pressure and belt type. Of the three primary contributors to sign up error, tooth deflection may be the most challenging to quantify. Experimentation with a prototype travel system is the best means of obtaining realistic estimations of belt tooth deflection.
Additional guidelines that may be useful in developing registration crucial drive systems are as follows:
Select PowerGrip GT2 or trapezoidal timing belts.
Design with large pulleys with an increase of tooth in mesh.
Keep belts tight, and control pressure closely.
Design body/shafting to end up being rigid under load.
Use top quality machined pulleys to reduce radial runout and lateral wobble.