9.1 LOW-SPEED OPERATION
Synchronous drives are specially well-appropriate for low-speed, high torque applications. Their positive generating nature helps prevent potential slippage associated with V-belt drives, and even allows significantly higher torque carrying capability. Small pitch synchronous drives working at speeds of 50 ft/min (0.25 m/s) or less are considered to be low-speed. Care should be used the get selection process as stall and peak torques can often be 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 drive bracketry and framework is vital in preventing belt tooth jumping less than peak torque loads. It is also beneficial to design with more compared to the normal minimum of 6 belt tooth in mesh to make sure sufficient belt tooth shear power.
Newer generation curvilinear systems like PowerGrip GT2 and PowerGrip HTD should be found in low-acceleration, high torque applications, as trapezoidal timing belts are even more prone to tooth jumping, and have significantly much less load carrying capability.
9.2 HIGH-SPEED OPERATION
Synchronous belt drives are often found in high-speed applications despite the fact that V-belt drives are typically better appropriate. They are often used because of their positive traveling characteristic (no creep or slip), and because they require minimal maintenance (don’t stretch significantly). A significant drawback of high-rate synchronous drives is certainly drive noise. High-velocity synchronous drives will almost always produce more noise than V-belt drives. Small pitch synchronous drives operating at speeds more than 1300 ft/min (6.6 m/s) are considered to end up being high-speed.
Special consideration ought to be directed at high-speed drive designs, as a number of factors can considerably influence belt performance. Cord fatigue and belt tooth wear are the two most crucial elements that must be controlled to ensure success. Moderate V Belt Pulley pulley diameters should be used to reduce the price of cord flex exhaustion. Designing with a smaller sized pitch belt will often offer better cord flex fatigue characteristics than a bigger pitch belt. PowerGrip GT2 is especially well suited for high-velocity drives due to its excellent belt tooth access/exit characteristics. Smooth interaction between your belt tooth and pulley groove minimizes use and noise. Belt installation stress is especially critical with high-acceleration drives. Low belt pressure allows the belt to trip 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 use with as little vibration aspossible, as vibration sometimes impacts the system operation or finished produced product. In such cases, the characteristics and properties of all appropriate belt drive products should be reviewed. The ultimate drive program selection ought to be based on the most significant design requirements, and may require some compromise.
Vibration is not generally regarded as a problem with synchronous belt drives. Low degrees of vibration typically derive from the procedure of tooth meshing and/or consequently of their high tensile modulus properties. Vibration resulting from tooth meshing can be a normal characteristic of synchronous belt drives, and can’t be totally eliminated. It could be minimized by staying away from little pulley diameters, and rather selecting moderate sizes. The dimensional accuracy of the pulleys also influences tooth meshing quality. Additionally, the installation stress has an effect on meshing quality. PowerGrip GT2 drives mesh extremely cleanly, resulting in the smoothest feasible operation. Vibration resulting from high tensile modulus can be a function of pulley quality. Radial go out causes belt pressure variation with each pulley revolution. V-belt pulleys are also produced with some radial run out, but V-belts possess a lower tensile modulus leading to less belt stress variation. The high tensile modulus within synchronous belts is essential to maintain correct pitch under load.
9.4 DRIVE NOISE
Drive noise evaluation in any belt drive system ought to be approached with care. There are numerous 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 results from the process of belt tooth meshing and physical connection with the pulleys. The sound pressure level generally raises as operating speed and belt width increase, and as pulley size decreases. 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 various other systems due to 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 ought to be tensioned at a rate which allows it to run with only a small amount meshing interference as possible.
Travel alignment also offers a significant effect on drive sound. Special attention ought to be given to minimizing angular misalignment (shaft parallelism). This assures that belt tooth are loaded uniformly and minimizes aspect tracking forces against the flanges. Parallel misalignment (pulley offset) is not as vital of a concern provided that the belt isn’t trapped or pinched between opposite flanges (start to see the unique section dealing with get alignment). Pulley materials and dimensional precision also influence get noise. Some users possess found that steel pulleys will be the quietest, followed closely by aluminum. Polycarbonates have already been found to become noisier than metallic materials. Machined pulleys are generally quieter than molded pulleys. The reason why because of this revolve around material 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. Factors such as humidity and operating speed influence the potential of the charge. If identified to become a issue, rubber belts can be produced in a conductive building to dissipate the charge into the pulleys, and to surface. This prevents the accumulation of electric charges that might be harmful to materials handling procedures or sensitive electronics. It also greatly reduces the potential for arcing or sparking in flammable conditions. Urethane belts can’t 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 construction for rubber belts is usually on a made-to-order basis. Unless otherwise 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 designed for rubber belts. These belts are usually built specifically to the clients conductivity requirements. They are generally found in applications where one shaft must be electrically isolated from the additional. 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 required for the charge to end up being dissipated to floor. A grounding brush or identical 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. Unique conductive rubber belts ought to be utilized when the presence of an electrical charge is certainly a concern.
9.6 OPERATING ENVIRONMENTS
Synchronous drives are ideal for use in a wide variety of environments. Unique considerations could be necessary, however, based on the application.
Dust: Dusty environments do not generally present serious problems to synchronous drives so long as the particles are fine and dry. Particulate matter will, however, act as an abrasive producing a higher rate of belt and pulley wear. Damp or sticky particulate matter deposited and loaded into pulley grooves can cause belt tension to increase significantly. This increased stress can impact shafting, bearings, and framework. Electrical fees within a get system will often appeal to particulate matter.
Debris: Debris ought to be prevented from falling into any synchronous belt drive. Debris caught in the travel is normally either forced through the belt or results in stalling of the system. In either case, serious damage takes place to the belt and related get hardware.
Water: Light and occasional connection with water (occasional clean downs) should not seriously impact synchronous belts. Prolonged get in touch with (constant spray or submersion) results in significantly reduced tensile strength in fiberglass belts, and potential size variation in aramid belts. Prolonged connection with water also causes rubber substances to swell, although significantly less than with oil contact. Internal belt adhesion systems are also steadily broken down with the existence of drinking water. Additives to drinking water, such as for example lubricants, chlorine, anticorrosives, etc. can have a far more detrimental effect on the belts than clear water. Urethane timing belts also suffer from drinking water contamination. Polyester tensile cord shrinks considerably and experiences loss of tensile strength in the presence of drinking water. Aramid tensile cord keeps its power pretty well, but encounters size variation. Urethane swells more than neoprene in the presence of water. This swelling can boost belt tension significantly, causing belt and related equipment problems.
Oil: Light connection with natural oils on an intermittent basis will not generally harm synchronous belts. Prolonged contact with essential oil or lubricants, either straight or airborne, outcomes in considerably reduced belt service lifestyle. Lubricants trigger the rubber substance to swell, breakdown internal adhesion systems, and decrease 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 presence of ozone could be detrimental to the compounds found in rubber synchronous belts. Ozone degrades belt materials in much the same way as extreme environmental temperatures. Although the rubber components found in synchronous belts are compounded to withstand the consequences of ozone, ultimately chemical breakdown occurs plus they become hard and brittle and begin cracking. The amount of degradation depends upon the ozone concentration 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 Building: 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 excessive environmental temps do. The amount of degradation depends upon the strength of radiation and the exposure time. For good belt performance, the next 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 known to generate little quantities of good dust, as an all natural consequence of their operation. The number of dust is typically higher for fresh belts, because they run in. The time period for run directly into occur depends upon the belt and pulley size, loading and quickness. Elements such as pulley surface end, operating speeds, set up tension, and alignment impact the amount of dust generated.
Clean Room: Rubber synchronous belts might 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 particles than rubber timing belts. Nevertheless, they are recommended limited to light operating loads. Also, they can not be produced in a static conductive construction to permit electrical charges to dissipate.
Static Sensitive: Applications are occasionally sensitive to the accumulation of static electrical charges. Electrical costs can affect materials handling processes (like paper and plastic material film transport), and sensitive digital apparatus. Applications like these need a static conductive belt, so that the static costs generated by the belt can be dissipated in to the pulleys, and also to ground. Regular rubber synchronous belts do not meet this requirement, but can be manufactured in a static conductive structure 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 produced in a conductive construction.
9.7 BELT TRACKING
Lateral tracking characteristics of synchronous belts is certainly a common area of inquiry. Although 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 resulting in belt edge wear and potential flange failing. Belt tracking is definitely influenced by several factors. In order of significance, debate about these elements is as follows:
Tensile Cord Twist: Tensile cords are shaped into a one twist configuration during their produce. Synchronous belts made with only one twist tensile cords track laterally with a substantial force. To neutralize this tracking pressure, tensile cords are stated in right- and left-hands twist (or “S” and “Z” twist) configurations. Belts made with “S” twist tensile cords monitor in the contrary path to those constructed with “Z” twist cord. Belts made with alternating “S” and “Z” twist tensile cords track with reduced lateral force since the tracking features of the two cords offset each other. This content of “S” and “Z” twist tensile cords varies somewhat with every belt that is produced. Consequently, every belt comes with an unprecedented tendency to monitor in either one direction or the additional. When an application requires a belt to track in one specific direction only, 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 angle of misalignment influences the magnitude and path of the tracking push. Synchronous belts tend to monitor “downhill” to a state of lower stress or shorter middle distance.
Belt Width: The potential magnitude of belt monitoring force is directly related to belt width. Wide belts have a tendency to track with more pressure 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 true as the belt width techniques 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: Because of the way tensile cords are applied to the belt molds, short belts can tend to exhibit higher tracking forces than very long 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 normally minimal with small pitch synchronous belts. Sag in lengthy belt spans should be prevented by applying sufficient belt installation tension.
Torque Loads: Sometimes, while functioning, a synchronous belt can move laterally from side to side on the pulleys instead of operating in a consistent position. Without generally considered to be a substantial concern, one description for this is usually varying torque loads within the travel. Synchronous belts sometimes track in different ways with changing loads. There are various potential known reasons for this; the root cause relates 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, resulting in belt movement.
Belt Installation Pressure: Belt tracking is sometimes influenced by the amount of belt installation stress. The reason why for this act like the effect that varying torque loads possess on belt tracking. When problems with belt monitoring are experienced, each one of these potential contributing elements ought to be investigated in the purchase they are shown. In most cases, the principal problem is going to be determined before moving completely through the list.
9.8 PULLEY FLANGES
Pulley information flanges are necessary to preserve synchronous belts operating on the pulleys. As discussed previously in Section 9.7 on belt tracking, it really is normal for synchronous belts to favor one part of the pulleys when running. Proper flange style is essential in avoiding belt edge use, minimizing sound and avoiding the belt from climbing from the pulley. Dimensional recommendations for custom-made or molded flanges are included in tables dealing with these problems. Proper flange positioning is important so that the belt is usually adequately restrained within its operating system. Because style and design of small synchronous drives is so different, the wide variety of flanging situations possibly encountered cannot very easily be covered in a straightforward set of rules without selecting exceptions. Despite this, the next broad flanging recommendations should help the developer in most cases:
Two Pulley Drives: On basic two pulley drives, each one pulley ought to be flanged in both sides, or each pulley should be flanged on contrary sides.
Multiple Pulley Drives: On multiple pulley (or serpentine) drives, either every other pulley ought to be flanged about both sides, or every pulley ought to be flanged in alternating sides around the system. Vertical Shaft Drives: On vertical shaft drives, at least one pulley ought to be flanged on both sides, and the rest of the pulleys should be flanged on at least the bottom side.
Long Period Lengths: Flanging recommendations for little synchronous drives with lengthy belt span lengths cannot easily be defined because of the many factors that can affect belt tracking characteristics. Belts on drives with lengthy spans (generally 12 times the diameter of small pulley or even more) often require even more lateral restraint than with short spans. For this reason, it is generally a good idea to flange the pulleys on both sides.
Huge Pulleys: Flanging large pulleys could be costly. Designers often wish to leave huge pulleys unflanged to lessen cost and space. Belts tend to require much less lateral restraint on huge pulleys than little and can often perform reliably without flanges. When determining whether or not to flange, the previous guidelines is highly recommended. The groove encounter width of unflanged pulleys also needs to be greater than with flanged pulleys. See Table 27 for recommendations.
Idlers: Flanging of idlers is generally not necessary. Idlers designed to carry lateral aspect 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 previous 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 features of a synchronous belt drive, the system must first be established to be either static or dynamic with regards to its registration function and requirements.
Static Registration: A static registration system moves from its initial static position to a second static position. Through the process, the designer can be involved just with how accurately and consistently the drive finds its secondary position. He/she isn’t concerned with any potential sign up errors that occur during transport. Therefore, the primary factor adding to registration error in a static sign up system is definitely backlash. The consequences of belt elongation and tooth deflection don’t have any impact on the sign up accuracy of this type of system.
Dynamic Sign up: A powerful registration system must perform a registering function while in motion with torque loads varying as the system operates. In cases like this, the designer can be involved with the rotational position of the travel pulleys regarding each other at every time. Therefore, belt elongation, backlash and tooth deflection will all contribute to registrational inaccuracies.
Further discussion about each of the factors contributing to registration error is as follows:
Belt Elongation: Belt elongation, or stretch, occurs naturally when a belt is placed under stress. The total tension exerted within a belt results from installation, along with operating loads. The amount of belt elongation is usually a function of the belt tensile modulus, which is certainly influenced by the type of tensile cord and the belt construction. The typical tensile cord found in rubber synchronous belts can be 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 generally used to provide resistance to harsh shock and impulse loads. Aramid tensile cords found in little synchronous belts generally have just a marginally higher tensile modulus in comparison to fiberglass. When required, belt tensile modulus data is available from our Program Engineering Department.
Backlash: Backlash in a synchronous belt drive results from clearance between the belt teeth 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 amount of clearance required depends upon the belt tooth account. Trapezoidal Timing Belt Drives are recognized for having fairly small backlash. PowerGrip HTD Drives have improved torque holding capability and resist ratcheting, but possess a significant amount of backlash. PowerGrip GT2 Drives possess even more improved torque carrying capability, and have as little or much less backlash than trapezoidal timing belt drives. In particular cases, alterations could be made to get systems to help expand decrease backlash. These alterations typically result in increased belt wear, increased travel noise and shorter travel life. Contact 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 is dependent upon the quantity of torque loading, pulley size, installation pressure and belt type. Of the three principal contributors to sign up mistake, tooth deflection may be the most difficult to quantify. Experimentation with a prototype get system may be the best method of obtaining realistic estimations of belt tooth deflection.
Additional guidelines which may be useful in designing registration essential drive systems are the following:
Select PowerGrip GT2 or trapezoidal timing belts.
Design with large pulleys with an increase of teeth in mesh.
Keep belts limited, and control tension closely.
Design body/shafting to end up being rigid under load.
Use top quality machined pulleys to reduce radial runout and lateral wobble.