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Timing Belts and Pulleys – Operations

Synchronous drives are especially well-suitable for low-speed, high torque applications. Their positive generating nature stops potential slippage associated with V-belt drives, and even allows significantly better torque carrying capacity. Small pitch synchronous drives working at speeds of 50 ft/min (0.25 m/s) or much less are considered to be low-speed. Care ought to 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 considerations, high cyclic peak torque loading ought to 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 helpful to design with an increase of than the normal the least 6 belt tooth in mesh to make sure adequate belt tooth shear power.

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

Synchronous belt drives tend to be used in high-speed applications despite the fact that V-belt drives are typically better appropriate. They are often used because of their positive generating characteristic (no creep or slip), teeth bore timing belt pulleyand because they require minimal maintenance (don’t stretch significantly). A substantial drawback of high-acceleration synchronous drives is get noise. High-quickness synchronous drives will nearly 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 will be the two most crucial factors that must be controlled to ensure 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 fatigue characteristics when compared to 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 sound. Belt installation pressure is especially critical with high-swiftness drives. Low belt pressure allows the belt to trip out of the driven pulley, leading to rapid belt tooth and pulley groove wear.

Some ultrasensitive applications require the belt drive to use with only a small amount vibration aspossible, as vibration sometimes has an effect on the system procedure or finished manufactured product. In these cases, the features and properties of all appropriate belt drive products ought to be reviewed. The final drive program selection should be based on the most significant style requirements, and could need some compromise.

Vibration is not generally regarded as a Gear problem with synchronous belt drives. Low levels of vibration typically result from the procedure of tooth meshing and/or consequently of their high tensile modulus properties. Vibration caused by tooth meshing is usually a normal characteristic of synchronous belt drives, and cannot be totally eliminated. It could be minimized by avoiding small pulley diameters, and rather choosing moderate sizes. The dimensional precision of the pulleys also influences tooth meshing quality. Additionally, the installation pressure has an impact on meshing quality. PowerGrip GT2 drives mesh extremely cleanly, resulting in the smoothest possible operation. Vibration resulting from high tensile modulus can be a function of pulley quality. Radial go out causes belt stress variation with each pulley revolution. V-belt pulleys are also produced with some radial run out, but V-belts possess a lesser tensile modulus leading to less belt tension variation. The high tensile modulus found in synchronous belts is essential to maintain appropriate pitch under load.

Drive noise evaluation in virtually any belt drive system ought to be approached with care. There are plenty of potential resources 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 procedure of belt tooth meshing and physical contact with the pulleys. The sound pressure level generally boosts as operating acceleration and belt width increase, and as pulley size reduces. Drives designed on moderate pulley sizes without excessive capability (overdesigned) are generally the quietest. PowerGrip GT2 drives have already been discovered to be significantly quieter than various other systems due to their improved meshing characteristic, see Figure 9. Polyurethane belts generally generate more noise than neoprene belts. Proper belt installation tension is also very essential in minimizing drive noise. The belt ought to be tensioned at a level that allows it to perform with only a small amount meshing interference as possible.

Travel 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 teeth are loaded uniformly and minimizes side monitoring forces against the flanges. Parallel misalignment (pulley offset) isn’t as important of a problem as long as the belt is not trapped or pinched between reverse flanges (see the unique section coping with get alignment). Pulley materials and dimensional precision also influence get sound. Some users have found that steel pulleys are the quietest, followed closely by light weight aluminum. Polycarbonates have been discovered to become noisier than metallic materials. Machined pulleys are generally quieter than molded pulleys. The reason why for this revolve around material density and resonance features and also dimensional accuracy.

Small synchronous rubber or urethane belts can generate an electrical charge while operating in a drive. Elements such as humidity and working speed impact the potential of the charge. If decided to become a problem, rubber belts could be produced in a conductive building to dissipate the charge into the pulleys, and to ground. This prevents the accumulation of electric charges that might be harmful to material handling procedures or sensitive consumer electronics. In addition, it significantly reduces the potential for arcing or sparking in flammable environments. Urethane belts can’t be stated in a conductive structure.

RMA has outlined requirements for conductive belts in their bulletin IP-3-3. Unless usually specified, a static conductive structure for rubber belts is definitely on a made-to-purchase basis. Unless otherwise specified, conductive belts will be created 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 generally found in applications where one shaft must be electrically isolated from the other. It is necessary to note that 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 be dissipated to surface. A grounding brush or very similar device could also be used to dissipate electrical charges.

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

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

Dust: Dusty environments do not generally present serious complications to synchronous drives so long as the particles are fine and dry out. Particulate matter will, however, become an abrasive resulting in a higher level of belt and pulley use. Damp or sticky particulate matter deposited and packed 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 appeal to particulate matter.

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

Drinking water: Light and occasional connection with water (occasional clean downs) should not seriously influence synchronous belts. Prolonged contact (continuous spray or submersion) results in considerably reduced tensile power in fiberglass belts, and potential size variation in aramid belts. Prolonged contact with drinking water also causes rubber compounds to swell, although significantly less than with oil get in touch with. Internal belt adhesion systems are also steadily broken down with the existence of drinking water. Additives to drinking water, such as lubricants, chlorine, anticorrosives, etc. can possess a far more detrimental influence on the belts than pure water. Urethane timing belts also have problems with water contamination. Polyester tensile cord shrinks significantly and experiences lack of tensile strength in the existence of water. Aramid tensile cord keeps its strength pretty well, but encounters size variation. Urethane swells a lot more than neoprene in the existence of water. This swelling can boost belt tension significantly, causing belt and related hardware problems.

Oil: Light contact with natural oils on an intermittent basis won’t generally damage synchronous belts. Prolonged contact with oil or lubricants, either straight or airborne, outcomes in significantly reduced belt service existence. Lubricants trigger the rubber compound to swell, breakdown inner adhesion systems, and reduce belt tensile strength. While alternate rubber substances may 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 found in rubber synchronous belts. Ozone degrades belt materials in much the same way as extreme envtiming belt pulleysironmental temps. Although the rubber components used in synchronous belts are compounded to resist the consequences of ozone, eventually chemical substance breakdown occurs plus they become hard and brittle and begin cracking. The quantity of degradation is dependent 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 Structure: 20 pphm

Radiation: Exposure to gamma radiation could be detrimental to the substances used in rubber and urethane synchronous belts. Radiation degrades belt materials quite similar way extreme environmental temperatures do. The quantity of degradation depends upon the strength of radiation and the publicity 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 Construction: 104 rads

Dust Generation: Rubber synchronous belts are recognized to generate small quantities of good dust, as a natural result of their procedure. The number of dust is typically higher for fresh belts, as they operate in. The time period for run directly into occur depends upon the belt and pulley size, loading and rate. Factors such as for example pulley surface end, operating speeds, set up pressure, and alignment influence the amount of dust generated.

Clean Space: Rubber synchronous belts may not be suitable 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 suggested only for light operating loads. Also, they cannot be produced in a static conductive structure to allow electrical fees to dissipate.

Static Sensitive: Applications are occasionally sensitive to the accumulation of static electrical charges. Electrical costs can affect material handling processes (like paper and plastic material film transport), and sensitive electronic products. Applications like these need a static conductive belt, to ensure that the static costs produced by the belt could be dissipated into the pulleys, and also to ground. Standard rubber synchronous belts usually do not meet this necessity, but can be manufactured in a static conductive construction on a made-to-order basis. Regular belt wear resulting from long term procedure or environmental contamination can influence 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.

Lateral tracking characteristics of synchronous belts is definitely a common area of inquiry. Although it is regular for a belt to favor one aspect of the pulleys while running, it is abnormal for a belt to exert significant power against a flange leading to belt edge put on and potential flange failing. Belt tracking is normally influenced by several factors. To be able of significance, conversation about these factors is as follows:

Tensile Cord Twist: Tensile cords are formed into a solitary twist configuration during their manufacture. Synchronous belts made with only one twist tensile cords track laterally with a significant push. To neutralize this tracking push, tensile cords are produced in correct- and left-hand twist (or “S” and “Z” twist) configurations. Belts made out of “S” twist tensile cords monitor in the contrary direction to those constructed with “Z” twist cord. Belts made out of alternating “S” and “Z” twist tensile cords track with reduced lateral force since the tracking characteristics of the two cords offset each other. The content of “S” and “Z” twist tensile cords varies somewhat with every belt that’s produced. As a result, every belt comes with an unprecedented tendency to monitor in either one direction or the various other. When an application requires a belt to track in a single specific direction just, 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 direction 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 power than narrow belts.

Pulley Size: Belts operating on small pulley diameters can tend to generate higher tracking 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: Because of just how tensile cords are applied on to the belt molds, brief belts can have a tendency to exhibit higher monitoring forces than very long belts. The helix angle of the tensile cord decreases with increasing belt length.

Gravity: In travel applications with vertical shafts, gravity pulls the belt downward. The magnitude of this force is normally minimal with little 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 will move laterally laterally on the pulleys instead of operating in a constant position. While not generally regarded as a significant concern, one explanation for this is certainly varying torque loads within the travel. Synchronous belts occasionally track in a different way with changing loads. There are several potential reasons for this; the root cause relates to tensile cord distortion while under great pressure against the pulleys. Variation in belt tensile loads may also cause adjustments in framework deflection, and angular shaft alignment, resulting in belt movement.

Belt Installation Stress: Belt tracking is sometimes influenced by the level 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 one of these potential contributing elements should be investigated in the order they are listed. Generally, the primary problem will probably be discovered before moving completely through the list.

Pulley guide flanges are necessary to keep synchronous belts operating on the pulleys. As talked about previously in Section 9.7 on belt tracking, it really is normal for synchronous belts to favor one part of the pulleys when operating. Proper flange style is important in preventing belt edge use, minimizing noise and stopping the belt from climbing out from the pulley. Dimensional recommendations for custom-produced or molded flanges are contained in tables dealing with these problems. Proper flange positioning is important so that the belt is definitely adequately restrained within its operating-system. Because design and design of little synchronous drives is so varied, the wide selection of flanging situations potentially encountered cannot quickly be covered in a straightforward group of rules without selecting exceptions. Despite this, the next broad flanging guidelines should help the designer generally:

Two Pulley Drives: On simple two pulley drives, each 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 ought to be flanged about both sides, or every single pulley ought to be flanged in alternating sides around the system. Vertical Shaft Drives: On vertical shaft drives, at least one pulley should be flanged on both sides, and the remaining pulleys ought to be flanged on at least underneath side.

Long Period Lengths: Flanging suggestions for small synchronous drives with long belt span lengths cannot very easily be defined due to the many factors that can affect belt tracking qualities. Belts on drives with lengthy spans (generally 12 times the diameter of small pulley or even more) frequently require more lateral restraint than with short spans. Due to this, it is generally smart to flange the pulleys on both sides.

Large Pulleys: Flanging huge pulleys could be costly. Designers often wish to leave huge pulleys unflanged to reduce cost and space. Belts tend to require less lateral restraint on large pulleys than little and can frequently perform reliably without flanges. When determining whether 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 generally not essential. Idlers designed to carry lateral side loads from belt tracking forces could be flanged if needed to offer lateral belt restraint. Idlers used for this function can be utilized inside or backside of the belts. The prior guidelines should also be considered.

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 system must first be established to end up being either static or dynamic when it comes to its sign up function and requirements.

Static Registration: A static registration system moves from its preliminary 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 position. He/she isn’t concerned with any potential registration errors that happen during transport. Therefore, the primary factor contributing to registration mistake in a static registration system is normally backlash. The consequences of belt elongation and tooth deflection don’t have any influence on the sign up precision of this type of system.

Dynamic Sign up: A powerful registration system is required to perform a registering function while in motion with torque loads different as the system operates. In this case, the designer can be involved 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 about each one of the factors contributing to registration error is as follows:

Belt Elongation: Belt elongation, or stretch, occurs naturally whenever a belt is positioned under tension. The total stress exerted within a belt results from set up, as well as 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 can be fiberglass. Fiberglass has a high tensile modulus, is dimensionally steady, and has excellent flex-fatigue features. If an increased tensile modulus is needed, aramid tensile cords can be considered, although they are generally 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 obtainable from our Application Engineering Department.

Backlash: Backlash in a synchronous belt drive outcomes from clearance between your belt tooth and the pulley grooves. This clearance is required to allow the belt tooth to enter and exit the grooves smoothly with at the least interference. The quantity of clearance required depends upon the belt tooth account. Trapezoidal Timing Belt Drives are recognized for having fairly little backlash. PowerGrip HTD Drives possess improved torque having capability and withstand ratcheting, but have a significant quantity of backlash. PowerGrip GT2 Drives have even further improved torque holding capability, and have only a small amount or less backlash than trapezoidal timing belt drives. In unique cases, alterations can be made to get systems to help expand lower backlash. These alterations typically lead to increased belt wear, increased get noise and shorter get life. Contact our Software Engineering Department for more information.

Tooth Deflection: Tooth deformation in a synchronous belt travel 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 quantity of torque loading, pulley size, installation pressure and belt type. Of the three primary contributors to registration mistake, tooth deflection is the most challenging to quantify. Experimentation with a prototype travel system is the best method of obtaining realistic estimations of belt tooth deflection.

Additional guidelines that may be useful in designing registration critical drive systems are the following:
Select PowerGrip GT2 or trapezoidal timing belts.
Style with large pulleys with an increase of teeth in mesh.
Keep belts limited, and control pressure closely.
Design body/shafting to be rigid under load.
Use high quality machined pulleys to reduce radial runout and lateral wobble.



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Sara Jones
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