Timing Belts and Pulleys – Operations

9.1 LOW-SPEED OPERATION
Synchronous drives are specially well-appropriate for low-speed, high torque applications. Their positive traveling nature prevents potential slippage connected with V-belt drives, and also allows significantly higher torque carrying capacity. Small pitch synchronous drives operating 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 procedure as stall and peak torques can sometimes be very high. While intermittent peak torques can frequently be carried by synchronous drives without special considerations, high cyclic peak torque loading should be carefully reviewed.

Proper belt installation tension and rigid travel bracketry and framework is vital in stopping belt tooth jumping less than peak torque loads. It is also helpful to design with more compared to the normal the least 6 belt tooth in mesh to ensure sufficient belt tooth shear power.

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

9.2 HIGH-SPEED OPERATION
Synchronous belt drives tend to be used in high-speed applications despite the fact that V-belt drives are typically better suitable. They are often used due to their positive generating characteristic (no creep or slide), and because they require minimal maintenance (don’t stretch considerably). A significant drawback of high-swiftness synchronous drives is drive noise. High-speed synchronous drives will nearly always produce even 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 end up being high-speed.

Special consideration ought to 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 significant factors that must definitely be controlled to have success. Moderate pulley diameters ought to be used to lessen the price of cord flex exhaustion. Developing with a smaller sized pitch belt will often offer better cord flex exhaustion characteristics when compared to a bigger pitch belt. PowerGrip GT2 is particularly perfect for high-speed drives due to its excellent belt tooth entry/exit characteristics. Clean interaction between your belt tooth and pulley groove minimizes use and noise. Belt installation stress is especially important with high-quickness drives. Low belt tension allows the belt to trip 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 as little vibration aspossible, as vibration sometimes has an effect on the system procedure or finished manufactured product. In these cases, the characteristics and properties of most appropriate belt drive products ought to be reviewed. The final drive program selection ought to be based on the most critical design requirements, and may require some compromise.

Vibration is not generally considered to be 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 completely eliminated. It could be minimized by avoiding small pulley diameters, and rather selecting moderate sizes. The dimensional precision of the pulleys also influences tooth meshing quality. Additionally, the installation tension has an impact on meshing quality. PowerGrip GT2 drives mesh very cleanly, resulting in the smoothest possible operation. Vibration caused by high tensile modulus could 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 go out, but V-belts have a lower tensile modulus resulting in less belt stress variation. The high tensile modulus found in 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 noise in a system, including vibration from related parts, bearings, and resonance and amplification through framework and panels.

Synchronous belt drives typically produce more noise than V-belt drives. Noise results from the procedure of belt tooth meshing and physical connection with the pulleys. The sound pressure level generally increases as operating acceleration and belt width boost, and as pulley diameter reduces. Drives designed on moderate pulley sizes without excessive capability (overdesigned) are usually the quietest. PowerGrip GT2 drives have been found to be significantly quieter than other systems due to their improved meshing characteristic, see Figure 9. PolyOil less Air Compressors urethane belts generally produce more sound than neoprene belts. Proper belt installation tension is also very essential in minimizing get noise. The belt ought to be tensioned at a rate which allows it to run with only a small amount meshing interference as feasible.

Get alignment also has a significant influence 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 monitoring forces against the flanges. Parallel misalignment (pulley offset) isn’t as crucial of a concern so long as the belt is not trapped or pinched between opposing flanges (see the special section dealing with get alignment). Pulley materials and dimensional accuracy also influence travel noise. Some users have found that steel pulleys will be the quietest, followed closely by lightweight aluminum. Polycarbonates have already been found to be noisier than metallic components. Machined pulleys are generally quieter than molded pulleys. The reasons because of this revolve around materials density and resonance characteristics and also dimensional accuracy.

9.5 STATIC CONDUCTIVITY
Small synchronous rubber or urethane belts can generate a power charge while operating about a drive. Elements such as for example humidity and operating speed influence the potential of the charge. If identified to be a problem, rubber belts could be produced in a conductive building to dissipate the charge into the pulleys, and also to floor. This prevents the accumulation of electrical charges that may be harmful to materials handling procedures or sensitive consumer electronics. It also significantly reduces the prospect of arcing or sparking in flammable conditions. Urethane belts can’t be produced 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 structure for rubber belts is available on a made-to-purchase basis. Unless in any other case specified, conductive belts will be created to yield a level of resistance of 300,000 ohms or much less, when new.

non-conductive belt constructions are also available for rubber belts. These belts are generally built particularly to the customers conductivity requirements. They are generally used in applications where one shaft should be electrically isolated from the various other. It is necessary to note a static conductive belt cannot dissipate an electrical charge through plastic 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 may also be used to dissipate electric charges.

Urethane timing belts aren’t static conductive and can’t be built in a particular conductive construction. Unique conductive rubber belts ought to be used when the presence of a power charge is normally a concern.

9.6 OPERATING ENVIRONMENTS
Synchronous drives are suitable for use in a wide selection of environments. Special considerations could be necessary, however, based on the application.

Dust: Dusty environments usually do not generally present serious complications to synchronous drives so long as the particles are great and dry. Particulate matter will, however, become an abrasive resulting in a higher rate of belt and pulley wear. Damp or sticky particulate matter deposited and packed into pulley grooves could cause belt tension to improve significantly. This increased tension can impact shafting, bearings, and framework. Electrical fees within a travel system can sometimes appeal to particulate matter.

Debris: Debris ought to be prevented from falling into any synchronous belt drive. Particles caught in the travel 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 travel hardware.

Drinking water: Light and occasional connection with water (occasional clean downs) shouldn’t seriously have an effect on synchronous belts. Prolonged get in touch with (continuous spray or submersion) results in considerably reduced tensile strength in fiberglass belts, and potential duration variation in aramid belts. Prolonged contact with water also causes rubber substances to swell, although significantly less than with oil contact. Internal belt adhesion systems are also steadily divided with the existence of water. Additives to drinking water, such as for example lubricants, chlorine, anticorrosives, etc. can possess a far more detrimental effect on the belts than pure water. Urethane timing belts also have problems with water contamination. Polyester tensile cord shrinks significantly and experiences loss of tensile power in the existence of water. Aramid tensile cord keeps its power pretty well, but experiences length variation. Urethane swells more than neoprene in the presence of water. This swelling can increase belt tension significantly, causing belt and related equipment problems.

Oil: Light connection with natural oils on an occasional basis will not generally harm synchronous belts. Prolonged contact with essential oil or lubricants, either directly or airborne, outcomes in significantly reduced belt service life. Lubricants trigger 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 existence of ozone could be detrimental to the compounds found in rubber synchronous belts. Ozone degrades belt materials in quite similar way as excessive environmental temperatures. Although the rubber materials found in synchronous belts are compounded to resist the effects of ozone, ultimately chemical breakdown occurs and they become hard and brittle and begin cracking. The amount of degradation depends upon the ozone concentration and duration of exposure. For good efficiency of rubber belts, the following concentration levels should not be exceeded: (parts per hundred million)
Standard Construction: 100 pphm
Nonmarking Construction: 20 pphm
Conductive Construction: 75 pphm
Low Temperatures Structure: 20 pphm

Radiation: Contact with gamma radiation can be detrimental to the substances found in rubber and urethane synchronous belts. Radiation degrades belt materials much the same way extreme environmental temperatures do. The quantity of degradation is dependent upon the intensity of radiation and the exposure time. For good belt performance, the following exposure levels should not 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 recognized to generate little quantities of great dust, as an all natural consequence of their operation. The number of dust is normally higher for brand-new belts, as they operate in. The time period for run directly into occur depends upon the belt and pulley size, loading and acceleration. Elements such as for example pulley surface end, operating speeds, installation pressure, and alignment influence the amount of dust generated.

Clean Space: Rubber synchronous belts may 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 debris than rubber timing belts. However, they are recommended only for light operating loads. Also, they can not be produced in a static conductive structure to permit electrical charges to dissipate.

Static Sensitive: Applications are sometimes delicate to the accumulation of static electrical charges. Electrical costs can affect materials handling functions (like paper and plastic film transport), and sensitive electronic apparatus. Applications like these need a static conductive belt, to ensure that the static fees generated by the belt can be dissipated into the pulleys, and to ground. Standard rubber synchronous belts usually do not meet this requirement, but can be produced in a static conductive building on a made-to-order basis. Normal belt wear resulting from long term procedure or environmental contamination can impact belt conductivity properties.

In delicate applications, rubber synchronous belts are favored over urethane belts since urethane belting cannot be stated in a conductive construction.

9.7 BELT TRACKING
Lateral tracking qualities of synchronous belts is certainly a common area of inquiry. Although it is normal 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 is normally influenced by many factors. To be able of significance, debate about these elements is really as follows:

Tensile Cord Twist: Tensile cords are formed into a solitary twist configuration throughout their manufacture. Synchronous belts made with only solitary twist tensile cords monitor laterally with a substantial power. To neutralize this monitoring force, tensile cords are produced in right- and left-hands twist (or “S” and “Z” twist) configurations. Belts made out of “S” twist tensile cords monitor in the opposite path to those constructed with “Z” twist cord. Belts made out of alternating “S” and “Z” twist tensile cords monitor with reduced lateral force since the tracking characteristics of the two cords offset one another. This content of “S” and “Z” twist tensile cords varies slightly with every belt that’s produced. As a result, every belt comes with an unprecedented tendency to monitor in either one path or the various other. When a credit card applicatoin requires a belt to monitor 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 angle of misalignment influences the magnitude and direction of the monitoring drive. Synchronous belts tend to track “downhill” to a state of lower stress or shorter middle 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 pressure than narrow belts.

Pulley Diameter: 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 significantly less than the belt width aren’t generally recommended because belt tracking forces may become excessive.

Belt Length: Due to just how tensile cords are applied to the belt molds, brief belts can have a tendency to exhibit higher tracking forces than longer 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 is certainly minimal with small pitch synchronous belts. Sag in lengthy belt spans ought to be prevented by applying adequate belt installation tension.

Torque Loads: Sometimes, while functioning, a synchronous belt can move laterally laterally on the pulleys instead of operating in a consistent position. While not generally regarded as a significant concern, one explanation for this is varying torque loads within the travel. Synchronous belts occasionally track differently with changing loads. There are plenty of potential known reasons for this; the root 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, resulting in belt movement.

Belt Installation Pressure: Belt tracking is sometimes influenced by the amount of belt installation stress. The reason why for this are similar to the effect that varying torque loads possess on belt tracking. When problems with belt monitoring are experienced, each of these potential contributing elements should be investigated in the order they are shown. Generally, the primary problem will probably be identified before moving completely through the list.

9.8 PULLEY FLANGES
Pulley guide flanges are essential to hold synchronous belts operating on the 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 running. Proper flange design is essential in avoiding belt edge wear, minimizing sound and preventing the belt from climbing out of the pulley. Dimensional recommendations for custom-made or molded flanges are included in tables dealing with these issues. Proper flange positioning is important so that the belt is usually adequately restrained within its operating-system. Because style and layout of little synchronous drives is indeed diverse, the wide selection of flanging situations potentially encountered cannot conveniently be protected in a simple set of rules without finding exceptions. Despite this, the following broad flanging suggestions should help the designer generally:

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 almost every other pulley ought to be flanged on 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 ought to be flanged on both sides, and the rest of the pulleys ought to be flanged on at least underneath side.

Long Span Lengths: Flanging recommendations for small synchronous drives with long belt span lengths cannot quickly be defined due to the many factors that can affect belt tracking characteristics. Belts on drives with lengthy spans (generally 12 times the diameter of the smaller pulley or more) often require more lateral restraint than with short spans. For this reason, it is generally smart to flange the pulleys on both sides.

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

Idlers: Flanging of idlers is generally not necessary. Idlers designed to bring lateral part loads from belt tracking forces can be flanged if needed to offer lateral belt restraint. Idlers utilized for this function can be utilized on the inside or backside of the belts. The prior guidelines also needs to 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 registration capabilities of a synchronous belt drive, the machine must initial be identified to end up being either static or dynamic 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 procedure, the designer is concerned only with how accurately and regularly the drive arrives at its secondary position. He/she is not worried about any potential sign up errors that take place during transportation. Therefore, the primary factor contributing to registration error in a static sign up system can be backlash. The consequences of belt elongation and tooth deflection do not have any impact on the sign up precision of this kind of system.

Dynamic Sign up: A powerful registration system is required to perform a registering function while in motion with torque loads varying as the machine operates. In cases like this, the designer is concerned with the rotational placement of the drive pulleys regarding each other at every time. Therefore, belt elongation, backlash and tooth deflection will all contribute to registrational inaccuracies.

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

Belt Elongation: Belt elongation, or stretch out, occurs naturally when a belt is positioned under tension. The total tension exerted within a belt results from installation, and also operating loads. The quantity of belt elongation is a function of the belt tensile modulus, which is influenced by the type of tensile cord and the belt construction. The typical tensile cord found in rubber synchronous belts is usually fiberglass. Fiberglass has a high tensile modulus, is dimensionally steady, and has exceptional flex-fatigue characteristics. If a higher 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 got just a marginally higher tensile modulus in comparison to fiberglass. When required, belt tensile modulus data is certainly obtainable from our Program Engineering Department.

Backlash: Backlash in a synchronous belt drive outcomes from clearance between your belt teeth and the pulley grooves. This clearance is required to allow the belt teeth to enter and exit the grooves effortlessly with at the least interference. The amount of clearance required is dependent upon the belt tooth account. Trapezoidal Timing Belt Drives are known for having fairly small backlash. PowerGrip HTD Drives possess improved torque holding capability and resist ratcheting, but have a significant quantity of backlash. PowerGrip GT2 Drives have even further improved torque carrying capability, and also have only a small amount or less backlash than trapezoidal timing belt drives. In particular cases, alterations could be made to get systems to further decrease backlash. These alterations typically result in increased belt wear, increased drive 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 amount of torque loading, pulley size, installation pressure and belt type. Of the three primary contributors to registration mistake, tooth deflection may be the most challenging to quantify. Experimentation with a prototype drive system is the best means of obtaining realistic estimations of belt tooth deflection.

Additional guidelines that may be useful in developing registration important drive systems are the following:
Select PowerGrip GT2 or trapezoidal timing belts.
Design with large pulleys with an increase of tooth in mesh.
Keep belts tight, and control tension closely.
Design frame/shafting to end up being rigid under load.
Use high quality machined pulleys to minimize radial runout and lateral wobble.