Timing Belts and Pulleys – Operations

9.1 LOW-SPEED OPERATION
Synchronous drives are especially well-suitable for low-speed, high torque applications. Their positive traveling nature stops potential slippage connected with V-belt drives, and even allows significantly higher 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 ought to 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 special factors, high cyclic peak torque loading should be carefully reviewed.

Proper belt installation tension and rigid travel bracketry and framework is vital in avoiding belt tooth jumping in peak torque loads. It is also helpful to design with an increase of compared to the normal the least 6 belt tooth in mesh to make sure sufficient belt tooth shear strength.

Newer era curvilinear systems like PowerGrip GT2 and PowerGrip HTD should be used in low-velocity, high torque applications, as trapezoidal timing belts are more susceptible to tooth jumping, and also have significantly less load carrying capacity.

9.2 HIGH-SPEED OPERATION
Synchronous belt drives are often found in high-speed applications despite the fact that V-belt drives are typically better suitable. They are generally used because of their positive traveling characteristic (no creep or slip), and because they require minimal maintenance (don’t stretch considerably). A substantial drawback of high-quickness synchronous drives is normally drive 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 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 have success. Moderate pulley diameters ought to be used to reduce the rate of cord flex exhaustion. Designing with a smaller sized pitch belt will most likely provide better cord flex fatigue characteristics than a larger pitch belt. PowerGrip GT2 is particularly perfect for high-swiftness drives due to its excellent belt tooth entry/exit characteristics. Even interaction between the belt tooth and pulley groove minimizes use and noise. Belt installation tension is especially important with high-speed drives. Low belt pressure allows the belt to ride out of 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 as little vibration aspossible, as vibration sometimes impacts the system operation or finished manufactured product. In such cases, the features and properties of all appropriate belt drive products should be reviewed. The final drive system selection ought to be based on the most significant design requirements, and may require some compromise.

Vibration is not generally considered to be a issue with synchronous belt drives. Low degrees of vibration typically result from the procedure of tooth meshing and/or because of this of their high tensile modulus properties. Vibration caused by tooth meshing is usually a normal characteristic of synchronous belt drives, and cannot be completely eliminated. It could be minimized by staying away from little pulley diameters, and rather choosing moderate sizes. The dimensional accuracy of the pulleys also influences tooth meshing quality. Additionally, the installation pressure has an impact on meshing quality. PowerGrip GT2 drives mesh very cleanly, leading to the smoothest possible operation. Vibration resulting from high tensile modulus can be a function of pulley quality. Radial go out causes belt Low Backlash Gear box stress variation with each pulley revolution. V-belt pulleys are also manufactured with some radial go out, but V-belts have got a lower tensile modulus leading to less belt tension variation. The high tensile modulus within synchronous belts is necessary to maintain appropriate pitch under load.

9.4 DRIVE NOISE
Drive noise evaluation in any belt drive system should be approached with care. There are several potential sources of sound in a system, including vibration from related parts, bearings, and resonance and amplification through framework and panels.

Synchronous belt drives typically produce even 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 raises as operating acceleration and belt width boost, and as pulley size decreases. Drives designed on moderate pulley sizes without excessive capability (overdesigned) are usually the quietest. PowerGrip GT2 drives have been discovered to be considerably quieter than other systems because of their improved meshing characteristic, see Figure 9. Polyurethane belts generally create more noise than neoprene belts. Proper belt installation tension is also very important in minimizing travel noise. The belt should be tensioned at a level that allows it to perform with as little meshing interference as possible.

Travel alignment also has a significant effect on drive noise. 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 important of a concern as long as the belt isn’t trapped or pinched between contrary flanges (see the unique section dealing with drive alignment). Pulley components and dimensional precision also influence drive sound. Some users have discovered that steel pulleys are the quietest, followed closely by light weight aluminum. Polycarbonates have been found to be noisier than metallic components. Machined pulleys are usually quieter than molded pulleys. The reason why because of this revolve around materials density and resonance characteristics in addition to dimensional accuracy.

9.5 STATIC CONDUCTIVITY
Small synchronous rubber or urethane belts can generate an electrical charge while operating about a drive. Elements such as for example humidity and operating speed impact the potential of the charge. If decided to become a problem, rubber belts could be stated in a conductive construction to dissipate the charge into the pulleys, and to surface. This prevents the accumulation of electric charges that could be harmful to materials handling processes or sensitive electronics. It also greatly reduces the prospect of arcing or sparking in flammable environments. Urethane belts can’t be stated in a conductive structure.

RMA has outlined specifications for conductive belts in their bulletin IP-3-3. Unless in any other case specified, a static conductive construction for rubber belts is normally on a made-to-purchase basis. Unless usually specified, conductive belts will be created 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 customers conductivity requirements. They are usually used in applications where one shaft must be electrically isolated from the various other. It is important to note a static conductive belt cannot dissipate an electrical charge through plastic 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 identical device could also be used to dissipate electric charges.

Urethane timing belts are not static conductive and can’t be built in a special conductive construction. Special conductive rubber belts should be used 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. Unique considerations could be necessary, however, depending on the application.

Dust: Dusty conditions do not generally present serious complications to synchronous drives so long as the particles are great and dry out. Particulate matter will, however, become an abrasive producing a higher rate of belt and pulley use. Damp or sticky particulate matter deposited and loaded into pulley grooves could cause belt tension to increase considerably. This increased pressure can influence shafting, bearings, and framework. Electrical fees within a drive system will often entice particulate matter.

Debris: Debris ought to be prevented from falling into any synchronous belt drive. Debris caught in the get is normally either forced through the belt or outcomes in stalling of the machine. In either case, serious damage happens to the belt and related get hardware.

Water: Light and occasional connection with drinking water (occasional wash downs) should not seriously impact 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 contact with drinking water also causes rubber compounds to swell, although significantly less than with oil contact. Internal belt adhesion systems are also gradually divided with the presence of drinking water. Additives to water, such as lubricants, chlorine, anticorrosives, etc. can possess a far more detrimental effect on the belts than clear water. Urethane timing belts also suffer from water contamination. Polyester tensile cord shrinks considerably and experiences lack of tensile strength in the presence of water. Aramid tensile cord maintains its power pretty well, but encounters length variation. Urethane swells more than neoprene in the presence of water. This swelling can increase belt tension significantly, leading to belt and related equipment problems.

Oil: Light contact with natural oils on an intermittent basis won’t generally damage synchronous belts. Prolonged contact with oil or lubricants, either directly or airborne, outcomes in considerably reduced belt service lifestyle. Lubricants trigger the rubber compound to swell, breakdown internal adhesion systems, and decrease belt tensile strength. While alternate rubber compounds might provide some marginal improvement in durability, it is best to prevent 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 extreme environmental temperatures. Although the rubber components used in synchronous belts are compounded to withstand the effects of ozone, ultimately chemical breakdown occurs and they become hard and brittle and begin cracking. The quantity of degradation depends upon the ozone focus and duration of exposure. For good efficiency of rubber belts, the next 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 can be detrimental to the substances found in rubber and urethane synchronous belts. Radiation degrades belt materials quite similar way excessive environmental temperatures do. The quantity of degradation is dependent upon the intensity of radiation and the publicity time. Once and for all belt performance, the following 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 fine dust, as a natural result of their procedure. The quantity of dust is typically higher for fresh belts, as they run in. The period of time for run directly into occur depends upon the belt and pulley size, loading and quickness. Elements such as pulley surface finish, operating speeds, set up pressure, and alignment influence the amount of dust generated.

Clean Area: Rubber synchronous belts may not be suitable for use in clean room environments, where all potential contamination must be minimized or eliminated. Urethane timing belts typically generate considerably less particles than rubber timing belts. However, they are suggested only for light working loads. Also, they cannot be produced in a static conductive building to allow electrical costs to dissipate.

Static Sensitive: Applications are sometimes delicate to the accumulation of static electric charges. Electrical fees can affect materials handling functions (like paper and plastic film transportation), and sensitive electronic products. Applications like these require a static conductive belt, to ensure that the static fees generated by the belt could be dissipated into the pulleys, and also to ground. Standard rubber synchronous belts usually do not satisfy this requirement, but can be manufactured in a static conductive structure on a made-to-order basis. Regular belt wear caused by long term procedure or environmental contamination can impact belt conductivity properties.

In sensitive applications, rubber synchronous belts are preferred over urethane belts since urethane belting cannot be produced in a conductive construction.

9.7 BELT TRACKING
Lateral tracking qualities of synchronous belts is usually a common area of inquiry. Although it is regular for a belt to favor one aspect of the pulleys while operating, it is abnormal for a belt to exert significant push against a flange resulting in belt edge use and potential flange failing. Belt tracking can be influenced by many factors. To be able of significance, dialogue about these elements is as follows:

Tensile Cord Twist: Tensile cords are shaped into a one twist configuration during their manufacture. Synchronous belts made out of only single twist tensile cords track laterally with a substantial pressure. To neutralize this monitoring pressure, tensile cords are produced in correct- and left-hands twist (or “S” and “Z” twist) configurations. Belts made out of “S” twist tensile cords monitor in the contrary path to those built with “Z” twist cord. Belts made out of alternating “S” and “Z” twist tensile cords track with minimal lateral force because the tracking characteristics of both cords offset one another. The content of “S” and “Z” twist tensile cords varies slightly with every belt that is produced. Consequently, every belt comes with an unprecedented tendency to track in each one direction or the additional. When an application requires a belt to monitor in a single specific direction just, an individual twist construction is used. See Figures 16 & Figure 17.

Angular Misalignment: Angular misalignment, or shaft nonparallelism, cause synchronous belts to track laterally. The position of misalignment influences the magnitude and 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 monitoring force is directly related to belt width. Wide belts have a tendency to track with more force than narrow belts.

Pulley Size: Belts operating on little pulley diameters can tend to generate higher monitoring forces than on large diameters. That is particularly true as the belt width methods the pulley size. Drives with pulley diameters less than the belt width aren’t generally suggested because belt tracking forces can become excessive.

Belt Length: Because of the way 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 decreases with increasing belt length.

Gravity: In get applications with vertical shafts, gravity pulls the belt downward. The magnitude of this force is normally minimal with small pitch synchronous belts. Sag in long belt spans ought to be avoided by applying sufficient belt installation tension.

Torque Loads: Sometimes, while in operation, a synchronous belt will move laterally laterally on the pulleys instead of operating in a consistent position. Without generally considered to be a significant concern, one description for this is normally varying torque loads within the travel. Synchronous belts sometimes track differently with changing loads. There are several 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 may also be influenced by the amount of belt installation tension. The reason why for this act like the result that varying torque loads have on belt tracking. When problems with belt tracking are experienced, each of these potential contributing elements ought to be investigated in the purchase they are listed. In most cases, the principal problem will probably be identified before moving totally through the list.

9.8 PULLEY FLANGES
Pulley guidebook flanges are necessary 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 aspect of the pulleys when running. Proper flange style is important in stopping belt edge wear, minimizing sound and preventing the belt from climbing out of the pulley. Dimensional recommendations for custom-produced or molded flanges are included in tables coping with these issues. Proper flange positioning is important to ensure that the belt can be adequately restrained within its operating-system. Because design and layout of little synchronous drives is indeed different, the wide variety of flanging situations potentially encountered cannot quickly be protected in a simple group of guidelines without finding exceptions. Not surprisingly, the following broad flanging recommendations 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 opposite sides.

Multiple Pulley Drives: On multiple pulley (or serpentine) drives, either every other pulley ought to be flanged about 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 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 small synchronous drives with lengthy belt span lengths cannot conveniently be defined due to the many factors that can affect belt tracking characteristics. Belts on drives with long spans (generally 12 times the size of small pulley or more) frequently require more lateral restraint than with brief spans. Because of this, it is generally smart to flange the pulleys on both sides.

Large Pulleys: Flanging large pulleys can be costly. Designers frequently desire to leave huge pulleys unflanged to lessen price and space. Belts generally tend to need less lateral restraint on large pulleys than small and can frequently perform reliably without flanges. When choosing whether or not to flange, the prior guidelines should be considered. The groove encounter width of unflanged pulleys should also be higher than with flanged pulleys. See Table 27 for recommendations.

Idlers: Flanging of idlers is normally not necessary. Idlers designed to carry lateral aspect loads from belt tracking forces could be flanged if had a need to offer lateral belt restraint. Idlers utilized for this purpose can be used on the inside or backside of the belts. The previous guidelines also needs to be considered.

9.9 REGISTRATION
The three primary factors contributing 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 machine must first be identified to be either static or powerful when it comes to its sign up function and requirements.

Static Sign up: A static registration system moves from its preliminary static position to a second static position. Through the process, the designer can be involved just with how accurately and consistently the drive arrives at its secondary placement. He/she is not concerned with any potential sign up errors that happen during transportation. Therefore, the primary factor contributing to registration mistake in a static sign up system is certainly backlash. The consequences of belt elongation and tooth deflection don’t have any impact on the registration precision of this type of system.

Dynamic Registration: A dynamic registration system is required to perform a registering function while in motion with torque loads different as the machine operates. In this case, the designer is concerned with the rotational position of the travel 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 one of the factors contributing to registration error is as follows:

Belt Elongation: Belt elongation, or stretch out, occurs naturally whenever a belt is positioned under stress. The total tension exerted within a belt results from set up, along with functioning loads. The amount of belt elongation can be a function of the belt tensile modulus, which can be influenced by the kind of tensile cord and the belt construction. The typical tensile cord used in rubber synchronous belts is normally 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 supply resistance to harsh shock and impulse loads. Aramid tensile cords used in little synchronous belts generally have just a marginally higher tensile modulus compared to fiberglass. When needed, belt tensile modulus data is definitely available 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 allow the belt tooth to enter and exit the grooves smoothly with at the least interference. The amount of clearance necessary is dependent upon the belt tooth profile. Trapezoidal Timing Belt Drives are recognized for having relatively little backlash. PowerGrip HTD Drives possess improved torque having capability and resist ratcheting, but possess a significant amount of backlash. PowerGrip GT2 Drives have even more improved torque having capability, and have as little or less backlash than trapezoidal timing belt drives. In unique cases, alterations could be made to get systems to help expand decrease backlash. These alterations typically result in increased belt wear, increased drive noise and shorter travel life. Get in touch with our Program Engineering Department for more information.

Tooth Deflection: Tooth deformation in a synchronous belt get occurs as a torque load is put on the system, and individual belt teeth are loaded. The amount of belt tooth deformation depends upon the amount of torque loading, pulley size, installation pressure and belt type. Of the three principal contributors to sign up mistake, tooth deflection is the most difficult to quantify. Experimentation with a prototype travel system is the best means of obtaining practical estimations of belt tooth deflection.

Additional guidelines that may be useful in designing 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 restricted, and control tension closely.
Design body/shafting to be rigid under load.
Use top quality machined pulleys to minimize radial runout and lateral wobble.