Timing Belts and Pulleys – Operations

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 actually allows significantly better torque carrying capability. 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 taken in the travel selection process as stall and peak torques can sometimes be very high. While intermittent peak torques can often be carried by synchronous drives without special factors, high cyclic peak torque loading should be carefully reviewed.

Proper belt installation tension and rigid drive bracketry and framework is essential in avoiding belt tooth jumping less than peak torque loads. It is also beneficial to design with more compared to the normal the least 6 belt teeth in mesh to ensure sufficient belt tooth shear strength.

Newer generation curvilinear systems like PowerGrip GT2 and PowerGrip HTD ought to be found in low-velocity, high torque applications, as trapezoidal timing belts are more prone to tooth jumping, and also have significantly less load carrying capability.

9.2 HIGH-SPEED OPERATION
Synchronous belt drives tend to be used in high-speed applications even though V-belt drives are typically better suited. They are often used due to their positive driving characteristic (no creep or slip), and because they require minimal maintenance (don’t stretch considerably). A substantial drawback of high-speed synchronous drives is definitely get noise. High-swiftness synchronous drives will almost always produce even more noise than V-belt drives. Small pitch synchronous drives working at speeds more than 1300 ft/min (6.6 m/s) are believed to end up being high-speed.

Special consideration should be given to high-speed drive designs, as several factors can considerably influence belt performance. Cord exhaustion and belt tooth wear will be the two most crucial factors that must definitely be controlled to have success. Moderate pulley diameters ought to be used to lessen the price of cord flex exhaustion. Designing with a smaller pitch belt will most likely provide better cord flex fatigue characteristics than a bigger pitch belt. PowerGrip GT2 is particularly perfect for high-acceleration drives because of its excellent belt tooth entry/exit characteristics. Clean interaction between your belt tooth and pulley groove minimizes put on and sound. Belt installation tension is especially essential with high-swiftness drives. Low belt stress allows the belt to trip 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 operate with as little vibration aspossible, as vibration sometimes impacts the system procedure or finished manufactured product. In such cases, the characteristics and properties of most appropriate belt drive products should be reviewed. The ultimate drive system selection ought to be based on the most significant design requirements, and could require some compromise.

Vibration isn’t generally considered to be a problem with synchronous belt drives. Low levels of vibration typically result from the procedure of tooth meshing and/or because of this of their high tensile modulus properties. Vibration resulting from tooth meshing is a normal characteristic of synchronous belt drives, and can’t be totally eliminated. It can be minimized by avoiding little pulley diameters, and rather choosing moderate sizes. The dimensional accuracy of the pulleys also influences tooth meshing quality. Additionally, the installation tension has an effect on meshing quality. PowerGrip GT2 drives mesh extremely cleanly, leading to the smoothest feasible operation. Vibration caused by high tensile modulus could 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 possess a lesser tensile modulus leading to less belt stress variation. The high tensile modulus within synchronous belts is necessary to maintain correct pitch under load.

9.4 DRIVE NOISE
Drive noise evaluation in any belt drive system should be approached carefully. There are various potential sources 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 outcomes from the procedure 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 excessive capacity (overdesigned) are usually the quietest. PowerGrip GT2 drives have already been found to be considerably quieter than various 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 drive noise. The belt should be tensioned at a level which allows it to perform with only a small amount meshing interference as possible.

Travel alignment also offers a significant effect on drive sound. Special attention should be given to reducing angular misalignment (shaft parallelism). This assures that belt teeth are loaded uniformly and minimizes side monitoring forces against the flanges. Parallel misalignment (pulley offset) isn’t as essential of a concern as long as the belt is not trapped or pinched between opposite flanges (see the particular section coping with get alignment). Pulley materials and dimensional precision also influence get noise. Some users have found that steel pulleys will be the quietest, followed closely by aluminum. Polycarbonates have already been found to be noisier than metallic materials. Machined pulleys are generally quieter than molded pulleys. The reasons for this revolve around material density and resonance features as well as dimensional accuracy.

9.5 STATIC CONDUCTIVITY
Small synchronous Water-lubricated Air Compressors rubber or urethane belts can generate a power charge while operating about a drive. Factors such as for example humidity and working speed influence the potential of the charge. If established to be a issue, rubber belts could be produced in a conductive construction to dissipate the charge into the pulleys, and to floor. This prevents the accumulation of electrical charges that could be detrimental to materials handling procedures or sensitive consumer 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 usually specified, a static conductive construction for rubber belts can be on a made-to-purchase basis. Unless in any other case specified, conductive belts will be built to yield a resistance of 300,000 ohms or less, when new.

Nonconductive belt constructions are also available for rubber belts. These belts are generally built specifically to the customers conductivity requirements. They are usually used 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 comparable device may also be used to dissipate electric charges.

Urethane timing belts are not static conductive and cannot be built in a particular conductive construction. Particular conductive rubber belts should be used when the presence of a power charge is definitely a concern.

9.6 OPERATING ENVIRONMENTS
Synchronous drives are ideal for use in a wide selection of environments. Unique considerations may be necessary, however, depending on the application.

Dust: Dusty environments usually do not generally present serious problems to synchronous drives so long as the particles are great and dry out. Particulate matter will, however, act as an abrasive resulting in a higher level of belt and pulley use. Damp or sticky particulate matter deposited and loaded into pulley grooves could cause belt tension to increase considerably. This increased stress can influence shafting, bearings, and framework. Electrical fees within a travel system can sometimes get particulate matter.

Debris: Debris ought to be prevented from falling into any synchronous belt drive. Particles captured in the get is generally either pressured through the belt or outcomes in stalling of the machine. In any case, serious damage takes place to the belt and related get hardware.

Water: Light and occasional contact with drinking water (occasional wash downs) should not seriously impact synchronous belts. Prolonged get in touch with (continuous spray or submersion) results in considerably reduced tensile power 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 get in touch with. Internal belt adhesion systems are also gradually divided with the existence of drinking water. Additives to drinking water, such as for example lubricants, chlorine, anticorrosives, etc. can possess a more detrimental effect 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 power in the presence of drinking water. Aramid tensile cord maintains its power pretty well, but encounters length variation. Urethane swells a lot more than neoprene in the presence of drinking water. This swelling can increase belt tension significantly, causing belt and related hardware problems.

Oil: Light contact with natural oils on an intermittent basis will not generally damage synchronous belts. Prolonged contact with essential oil or lubricants, either straight or airborne, results in significantly reduced belt service lifestyle. Lubricants trigger the rubber compound to swell, breakdown internal adhesion systems, and reduce belt tensile power. While alternate rubber substances might provide some marginal improvement in durability, it is advisable to prevent essential oil from contacting synchronous belts.

Ozone: The existence of ozone could be detrimental to the substances used in rubber synchronous belts. Ozone degrades belt materials in quite similar way as extreme environmental temperature ranges. Although the rubber components found in synchronous belts are compounded to withstand the effects of ozone, ultimately chemical breakdown occurs and they become hard and brittle and start cracking. The quantity of degradation depends upon the ozone focus 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: 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 is dependent upon the strength of radiation and the exposure time. Once and for all belt performance, the next 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 good dust, as a natural consequence of their procedure. The number of dust is typically higher for fresh belts, because they run in. The time period for run in to occur is dependent upon the belt and pulley size, loading and speed. Factors such as for example pulley surface surface finish, operating speeds, set up tension, and alignment influence the quantity of dust generated.

Clean Room: 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 significantly less particles than rubber timing belts. Nevertheless, they are recommended only for light operating loads. Also, they can not be produced in a static conductive construction to permit electrical charges to dissipate.

Static Sensitive: Applications are sometimes sensitive to the accumulation of static electrical charges. Electrical charges can affect material handling processes (like paper and plastic material film transport), and sensitive electronic apparatus. Applications like these need a static conductive belt, so that the static costs produced by the belt can be dissipated in to the pulleys, and to ground. Regular rubber synchronous belts usually do not fulfill this requirement, but can be manufactured in a static conductive building on a made-to-order basis. Normal belt wear caused by long term operation or environmental contamination can impact belt conductivity properties.

In delicate applications, rubber synchronous belts are favored 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 certainly a common area of inquiry. Although it is regular for a belt to favor one side of the pulleys while working, it is irregular for a belt to exert significant drive against a flange resulting in belt edge put on and potential flange failing. Belt tracking is normally influenced by many factors. In order of significance, conversation about these factors is as follows:

Tensile Cord Twist: Tensile cords are formed into a single twist configuration during their manufacture. Synchronous belts made out of only single twist tensile cords track laterally with a significant push. To neutralize this tracking pressure, tensile cords are stated in right- and left-hands twist (or “S” and “Z” twist) configurations. Belts made out of “S” twist tensile cords track in the opposite path to those built with “Z” twist cord. Belts made with alternating “S” and “Z” twist tensile cords monitor with reduced lateral force because the tracking characteristics of the two cords offset one another. The content of “S” and “Z” twist tensile cords varies somewhat with every belt that’s produced. Consequently, every belt has an unprecedented tendency to track in either one path or the other. When an application requires a belt to monitor in a single specific direction only, a single twist construction can be 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 path of the monitoring pressure. Synchronous belts have a tendency to monitor “downhill” to circumstances of lower stress or shorter center distance.

Belt Width: The potential magnitude of belt tracking force is directly linked to belt width. Wide belts have a tendency to track with an increase of drive than narrow belts.

Pulley Size: Belts operating on small pulley diameters can have a tendency to generate higher monitoring forces than on large diameters. That is particularly accurate as the belt width techniques the pulley size. Drives with pulley diameters less than the belt width are not generally suggested because belt tracking forces can become excessive.

Belt Length: Because of the way tensile cords are applied to the belt molds, brief belts can have a tendency to exhibit higher monitoring 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 can be 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 functioning, a synchronous belt can move laterally laterally on the pulleys rather than operating in a consistent position. Without generally regarded as a significant concern, one description for this is varying torque loads within the get. Synchronous belts sometimes track in a different way with changing loads. There are many potential known reasons for this; the root cause relates to tensile cord distortion while under pressure against the pulleys. Variation in belt tensile loads may also cause changes in framework deflection, and angular shaft alignment, leading to belt movement.

Belt Installation Tension: Belt tracking is sometimes influenced by the level of belt installation tension. The reason why for this act like the effect that varying torque loads have on belt tracking. When problems with belt monitoring are experienced, each one of these potential contributing factors should be investigated in the purchase they are outlined. In most cases, the primary problem is going to be discovered before moving totally through the list.

9.8 PULLEY FLANGES
Pulley information flanges are essential to preserve 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 part of the pulleys when working. Proper flange style is essential in stopping belt edge wear, minimizing sound and preventing the belt from climbing out of the pulley. Dimensional suggestions for custom-produced or molded flanges are included in tables coping with these problems. Proper flange positioning is important so that the belt is normally adequately restrained within its operating-system. Because style and design of small synchronous drives is so varied, the wide variety of flanging situations potentially encountered cannot easily be protected in a straightforward set of guidelines without acquiring 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 should be flanged about both sides, or each pulley ought to be flanged on contrary sides.

Multiple Pulley Drives: On multiple pulley (or serpentine) drives, either every other pulley should be flanged about both sides, or every pulley ought to be flanged on 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 ought to be flanged on at least underneath side.

Long Period Lengths: Flanging recommendations for small synchronous drives with long belt span lengths cannot easily be defined due to the many factors that may affect belt tracking qualities. Belts on drives with lengthy spans (generally 12 times the diameter of small pulley or even more) often require 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 can be costly. Designers often wish to leave large pulleys unflanged to reduce cost and space. Belts tend to require less lateral restraint on huge pulleys than little and can often perform reliably without flanges. When determining whether to flange, the previous guidelines is highly recommended. The groove face 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 part loads from belt tracking forces can be flanged if had a need to provide lateral belt restraint. Idlers utilized for this function can be utilized inside or backside of the belts. The prior guidelines should also be considered.

9.9 REGISTRATION
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 1st be motivated to be either static or powerful with regards to its sign up function and requirements.

Static Sign up: A static registration system moves from its initial static position to a secondary static position. During the process, the designer is concerned only with how accurately and consistently the drive arrives at its secondary placement. He/she is not concerned with any potential registration errors that happen during transport. Therefore, the primary factor adding to registration error in a static sign up system can be backlash. The effects of belt elongation and tooth deflection do not have any impact on the registration 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 varying as the machine operates. In this instance, the designer can be involved with the rotational placement of the travel pulleys with respect to each other at every point in time. Therefore, belt elongation, backlash and tooth deflection will all contribute to registrational inaccuracies.

Further discussion on the subject of each of the factors contributing to registration error is as follows:

Belt Elongation: Belt elongation, or stretch out, occurs naturally whenever a belt is placed under pressure. The total stress exerted within a belt results from set up, along with functioning loads. The amount of belt elongation can be a function of the belt tensile modulus, which is normally influenced by the kind of tensile cord and the belt construction. The typical tensile cord used in rubber synchronous belts is usually fiberglass. Fiberglass includes a high tensile modulus, is dimensionally steady, and has superb flex-fatigue features. If an increased tensile modulus is needed, aramid tensile cords can be viewed as, although they are usually used to supply resistance to severe shock and impulse loads. Aramid tensile cords found in little synchronous belts generally have only a marginally higher tensile modulus compared to fiberglass. When needed, belt tensile modulus data is definitely available from our Software Engineering Department.

Backlash: Backlash in a synchronous belt drive outcomes from clearance between your belt tooth and the pulley grooves. This clearance is needed to allow the belt teeth to enter and exit the grooves effortlessly 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 fairly small backlash. PowerGrip HTD Drives possess improved torque transporting capability and resist ratcheting, but possess a significant quantity of backlash. PowerGrip GT2 Drives have even more improved torque carrying capability, and also have as little or much less backlash than trapezoidal timing belt drives. In special cases, alterations could be made to get systems to help expand decrease backlash. These alterations typically lead to increased belt wear, increased drive sound and shorter drive life. Contact our Application Engineering Department for more 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 amount of belt tooth deformation is dependent upon the quantity of torque loading, pulley size, installation tension and belt type. Of the three primary contributors to sign up mistake, tooth deflection is the most difficult to quantify. Experimentation with a prototype drive system may be the best method of obtaining reasonable estimations of belt tooth deflection.

Additional guidelines which may be useful in developing registration essential drive systems are the following:
Select PowerGrip GT2 or trapezoidal timing belts.
Style with large pulleys with more tooth in mesh.
Keep belts limited, and control stress closely.
Design body/shafting to end up being rigid under load.
Use top quality machined pulleys to minimize radial runout and lateral wobble.

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