Timing Belts and Pulleys – Operations

Universal joint synchronous drives are specially well-suited for low-speed, high torque applications. Their positive traveling nature helps prevent potential slippage associated with V-belt drives, and also allows significantly better torque carrying capability. Little pitch synchronous drives working at speeds of 50 ft/min (0.25 m/s) or less are considered to be low-speed. Care ought to be used the get selection process as stall and peak torques can sometimes be very high. While intermittent peak torques can often be carried by synchronous drives without particular factors, high cyclic peak torque loading ought to be carefully reviewed.

Proper belt installation tension and rigid travel bracketry and framework is vital in preventing belt tooth jumping in peak torque loads. Additionally it is beneficial to design with more than the normal the least 6 belt tooth in mesh to ensure adequate belt tooth shear strength.

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

Synchronous belt drives are often used in high-speed applications even though V-belt drives are usually better suitable. They are often used because of their positive driving characteristic (no creep or slip), and because they require minimal maintenance (don’t stretch significantly). A substantial drawback of high-quickness synchronous drives is travel noise. High-quickness synchronous drives will almost always produce more noise than V-belt drives. Small pitch synchronous drives operating at speeds in excess of 1300 ft/min (6.6 m/s) are believed to end up being high-speed.

Special consideration ought to be given to high-speed drive designs, as a number of factors can significantly influence belt performance. Cord exhaustion and belt tooth wear are the two most significant factors that must be controlled to ensure success. Moderate pulley diameters should be used to lessen the price of cord flex fatigue. Designing 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 well suited for high-velocity drives because of its excellent belt tooth access/exit characteristics. Smooth interaction between your belt tooth and pulley groove minimizes wear and sound. Belt installation pressure is especially essential with high-swiftness drives. Low belt tension allows the belt to ride out from the driven pulley, leading to rapid belt tooth and pulley groove wear.

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 produced product. In these cases, the characteristics and properties of most appropriate belt drive products ought to be reviewed. The ultimate drive system selection should be based upon the most critical design requirements, and may require some compromise.

Vibration is not generally regarded as a problem with synchronous belt drives. Low levels of vibration typically result from the process of tooth meshing and/or consequently of their high tensile modulus properties. Vibration resulting from tooth meshing can be a normal characteristic of synchronous belt drives, and can’t be totally eliminated. It can be minimized by avoiding little pulley diameters, and instead choosing moderate sizes. The dimensional accuracy of the pulleys also influences tooth meshing quality. Additionally, the installation stress 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 run 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 leading to less belt pressure variation. The high tensile modulus found in synchronous belts is necessary to maintain appropriate pitch under load.

Drive noise evaluation in virtually any belt drive system ought to be approached carefully. There are plenty of potential resources of sound 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 outcomes from the procedure of belt tooth meshing and physical contact with the pulleys. The sound pressure level generally raises as operating speed and belt width boost, and as pulley diameter reduces. Drives designed on moderate pulley sizes without extreme capacity (overdesigned) are generally the quietest. PowerGrip GT2 drives have been discovered to be considerably quieter than additional systems because of their improved meshing characteristic, see Figure 9. Polyurethane belts generally generate more noise than neoprene belts. Proper belt installation tension is also very important in minimizing get noise. The belt should be tensioned at a level which allows it to perform with only a small amount meshing interference as possible.

Get alignment also offers a significant effect on drive sound. Special attention ought to be given to reducing 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 critical of a problem provided that the belt is not trapped or pinched between opposite flanges (start to see the special section dealing with travel alignment). Pulley materials and dimensional precision also influence travel noise. Some users possess discovered that steel pulleys will be the quietest, accompanied by lightweight aluminum. Polycarbonates have already been found to end up being 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.

Small synchronous rubber or urethane belts can generate an electrical charge while operating about a drive. Factors such as humidity and operating speed impact the potential of the charge. If determined to be a problem, rubber belts can be stated in a conductive structure to dissipate the charge in to the pulleys, and also to surface. This prevents the accumulation of electric charges that may be harmful to material handling procedures or sensitive consumer electronics. In addition, it significantly reduces the prospect of arcing or sparking in flammable conditions. Urethane belts cannot be stated in a conductive building.

RMA has outlined standards for conductive belts within their bulletin IP-3-3. Unless usually specified, a static conductive construction for rubber belts is certainly on a made-to-order basis. Unless normally 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 available for rubber belts. These belts are generally built specifically to the clients conductivity requirements. They are usually found in applications where one shaft should be electrically isolated from the various other. It is important to note a static conductive belt cannot dissipate a power charge through plastic material pulleys. At least one metallic pulley in a drive is required for the charge to be dissipated to floor. A grounding brush or very similar device may also be used to dissipate electrical charges.

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

Synchronous drives are suitable for use in a wide variety of environments. Special considerations may be necessary, nevertheless, based on the application.

Dust: Dusty environments do not generally present serious problems to synchronous drives as 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 loaded into pulley grooves can cause belt tension to increase significantly. This increased tension can effect shafting, bearings, and framework. Electrical fees within a get system can sometimes attract particulate matter.

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

Water: Light and occasional connection with water (occasional clean downs) should not seriously influence synchronous belts. Prolonged contact (continuous spray or submersion) results in significantly reduced tensile strength in fiberglass belts, and potential length variation in aramid belts. Prolonged connection with water also causes rubber substances to swell, although less than with oil get in touch with. Internal belt adhesion systems are also steadily divided with the existence of water. Additives to 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 drinking water contamination. Polyester tensile cord shrinks significantly and experiences loss of tensile power in the existence of drinking water. Aramid tensile cord maintains its strength fairly well, but experiences size variation. Urethane swells more than neoprene in the presence of water. This swelling can boost belt tension significantly, causing belt and related hardware problems.

Oil: Light contact with oils on an occasional basis will not generally harm synchronous belts. Prolonged contact with essential oil or lubricants, either straight or airborne, results in significantly reduced belt service existence. Lubricants cause the rubber compound to swell, breakdown internal adhesion systems, and decrease 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 can be detrimental to the substances found in rubber synchronous belts. Ozone degrades belt materials in quite similar way as excessive environmental temps. Although the rubber components used in synchronous belts are compounded to resist the effects of ozone, ultimately chemical substance breakdown occurs plus they become hard and brittle and start cracking. The quantity of degradation is dependent upon the ozone focus and duration of exposure. For good overall performance 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: Exposure to gamma radiation could be detrimental to the compounds found in rubber and urethane synchronous belts. Radiation degrades belt materials much the same way extreme environmental temperature ranges do. The amount of degradation depends upon the intensity of radiation and the publicity time. Once and for all belt performance, the next exposure levels shouldn’t be exceeded:
Standard Construction: 108 rads
Nonm arking Structure: 104 rads
Conductive Construction: 106 rads
Low Temperatures Building: 104 rads

Dust Generation: Rubber synchronous belts are known to generate little quantities of good dust, as a natural consequence of their procedure. The amount of dust is typically higher for brand-new belts, because they run in. The time period for run directly into occur is dependent upon the belt and pulley size, loading and quickness. Elements such as for example pulley surface surface finish, operating speeds, installation stress, and alignment impact the amount of dust generated.

Clean Room: Rubber synchronous belts might not be suitable for use in clean space environments, where all potential contamination should be minimized or eliminated. Urethane timing belts typically generate significantly less particles than rubber timing belts. However, they are recommended limited to light working loads. Also, they can not be stated in a static conductive structure to permit electrical charges to dissipate.

Static Sensitive: Applications are occasionally 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 products. Applications like these need a static conductive belt, so that the static charges generated by the belt could be dissipated into the pulleys, and to ground. Standard rubber synchronous belts do not satisfy this necessity, but could be produced in a static conductive structure on a made-to-order basis. Regular belt wear caused by 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 qualities of synchronous belts is normally a common area of inquiry. While it is regular for a belt to favor one part of the pulleys while running, it is unusual for a belt to exert significant drive against a flange resulting in belt edge use and potential flange failing. Belt tracking is influenced by several factors. To be able of significance, debate about these elements is as follows:

Tensile Cord Twist: Tensile cords are formed into a solitary twist configuration during their produce. Synchronous belts made out of only one twist tensile cords monitor laterally with a substantial pressure. To neutralize this monitoring drive, tensile cords are stated in right- and left-hand twist (or “S” and “Z” twist) configurations. Belts made out of “S” twist tensile cords monitor in the opposite direction to those built with “Z” twist cord. Belts made with alternating “S” and “Z” twist tensile cords monitor with minimal lateral force because 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 is produced. As a result, every belt has an unprecedented inclination to monitor in either one direction or the 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 path of the tracking pressure. Synchronous belts tend to track “downhill” to circumstances of lower stress or shorter middle distance.

Belt Width: The potential magnitude of belt tracking force is directly related to belt width. Wide belts tend to track with an increase of force than narrow belts.

Pulley Diameter: Belts operating on small pulley diameters can tend to generate higher tracking forces than on large diameters. This is particularly accurate as the belt width techniques the pulley diameter. Drives with pulley diameters 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 tend to exhibit higher tracking forces than long belts. The helix angle of the tensile cord reduces with increasing belt length.

Gravity: In drive applications with vertical shafts, gravity pulls the belt downward. The magnitude of the force is usually minimal with little pitch synchronous belts. Sag in lengthy belt spans ought to be prevented by applying adequate belt installation tension.

Torque Loads: Sometimes, while in operation, a synchronous belt can move laterally laterally on the pulleys instead of operating in a consistent position. While not generally regarded as a substantial concern, one explanation for this is definitely varying torque loads within the get. Synchronous belts occasionally track in different ways with changing loads. There are numerous potential reasons for this; the primary 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 level of belt installation pressure. The reasons for this are similar to the effect that varying torque loads possess on belt tracking. When problems with belt monitoring are experienced, each one of these potential contributing factors should be investigated in the purchase that they are listed. In most cases, the principal problem will probably be recognized before moving completely through the list.

Pulley guide flanges are essential to hold synchronous belts operating on their pulleys. As talked about previously in Section 9.7 on belt tracking, it really is regular for synchronous belts to favor one side of the pulleys when operating. Proper flange style is important in preventing belt edge wear, minimizing sound and avoiding the belt from climbing from the pulley. Dimensional suggestions for custom-produced or molded flanges are contained in tables coping with these issues. Proper flange placement is important so that the belt is normally adequately restrained within its operating-system. Because design and design of small synchronous drives is indeed diverse, the wide selection of flanging situations possibly encountered cannot easily be covered in a simple group of guidelines without locating exceptions. Not surprisingly, the next broad flanging recommendations should help the designer in most cases:

Two Pulley Drives: On basic two pulley drives, either one pulley should be flanged about both sides, or each pulley ought to be flanged on reverse sides.

Multiple Pulley Drives: On multiple pulley (or serpentine) drives, either every other pulley ought to be flanged about both sides, or every pulley ought to be flanged in alternating sides around the machine. 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 suggestions for little synchronous drives with long belt span lengths cannot easily be defined because of the many factors that can affect belt tracking characteristics. Belts on drives with lengthy spans (generally 12 times the diameter of small pulley or more) often require even more lateral restraint than with brief spans. Due to this, it really is generally smart to flange the pulleys on both sides.

Huge Pulleys: Flanging large pulleys could be costly. Designers often wish to leave large pulleys unflanged to reduce cost and space. Belts tend to require less lateral restraint on large pulleys than little and can often perform reliably without flanges. When deciding whether or not to flange, the prior guidelines should be considered. The groove face width of unflanged pulleys should also be greater than with flanged pulleys. See Table 27 for recommendations.

Idlers: Flanging of idlers is normally not essential. Idlers made to bring lateral aspect loads from belt tracking forces could be flanged if had a need to offer lateral belt restraint. Idlers used for this function can be utilized inside or backside of the belts. The prior guidelines also needs to be considered.

The three primary factors adding to belt drive registration (or positioning) errors are belt elongation, backlash, and tooth deflection. When evaluating the potential sign up capabilities of a synchronous belt drive, the system must initial be motivated to be either static or powerful when it comes to its registration function and requirements.

Static Registration: A static registration system moves from its preliminary static position to a second static position. Through the process, the designer is concerned only with how accurately and consistently the drive finds its secondary placement. He/she isn’t worried about any potential sign up errors that occur during transportation. Therefore, the principal factor adding to registration error in a static registration system can be backlash. The consequences of belt elongation and tooth deflection do not have any influence on the registration accuracy of this kind 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 cases like this, the designer is concerned with the rotational position of the drive pulleys with respect to one another at every time. Therefore, belt elongation, backlash and tooth deflection will all contribute to registrational inaccuracies.

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

Belt Elongation: Belt elongation, or stretch, occurs naturally whenever a belt is positioned under tension. The total pressure exerted within a belt results from set up, in addition to working loads. The amount of belt elongation is usually a function of the belt tensile modulus, which is influenced by the kind of tensile cord and the belt construction. The typical tensile cord found in rubber synchronous belts is definitely fiberglass. Fiberglass has a high tensile modulus, is dimensionally stable, and has superb flex-fatigue characteristics. If a higher tensile modulus is needed, aramid tensile cords can be considered, although they are generally used to provide resistance to severe shock and impulse loads. Aramid tensile cords found in small synchronous belts generally possess just a marginally higher tensile modulus in comparison to fiberglass. When required, belt tensile modulus data is usually obtainable from our Application Engineering Department.

Backlash: Backlash in a synchronous belt drive outcomes from clearance between the belt teeth and the pulley grooves. This clearance is needed to permit the belt teeth to enter and exit the grooves easily with a minimum of interference. The quantity of clearance required is dependent upon the belt tooth account. Trapezoidal Timing Belt Drives are known for having relatively small backlash. PowerGrip HTD Drives possess improved torque holding capability and resist ratcheting, but have a significant quantity of backlash. PowerGrip GT2 Drives possess even further improved torque transporting capability, and also have only a small amount or much less backlash than trapezoidal timing belt drives. In unique cases, alterations can be made to drive systems to further decrease backlash. These alterations typically result in increased belt wear, increased drive noise and shorter travel life. Contact our Application Engineering Division for additional information.

Tooth Deflection: Tooth deformation in a synchronous belt travel occurs as a torque load is applied to the machine, and individual belt teeth are loaded. The amount of belt tooth deformation is dependent upon the quantity of torque loading, pulley size, installation pressure and belt type. Of the three primary contributors to sign up error, tooth deflection is the most difficult to quantify. Experimentation with a prototype get 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 as follows:
Select PowerGrip GT2 or trapezoidal timing belts.
Style with large pulleys with an increase of tooth in mesh.
Keep belts tight, and control pressure closely.
Design framework/shafting to be rigid under load.
Use high quality machined pulleys to minimize radial runout and lateral wobble.


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