Timing Belts and Pulleys – Operations

Synchronous drives are specially well-appropriate for low-speed, high torque applications. Their positive driving nature stops potential slippage connected with V-belt drives, and also allows significantly better torque carrying capacity. Little pitch synchronous drives operating at speeds of 50 ft/min (0.25 m/s) or less are believed to be low-speed. Care should be taken in the drive selection procedure as stall and peak torques can often be 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 get bracketry and framework is vital in avoiding belt tooth jumping under peak torque loads. Additionally it is beneficial to design with an increase of compared to the normal the least 6 belt tooth in mesh to ensure adequate belt tooth shear power.

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

Synchronous belt drives tend to be found in high-speed applications despite the fact that V-belt drives are usually better suited. They are generally used due to their positive driving characteristic (no creep or slip), and because they require minimal maintenance (don’t stretch considerably). A substantial drawback of high-speed synchronous drives is drive noise. High-swiftness synchronous drives will almost always produce more noise than V-belt drives. Small pitch synchronous drives working at speeds more than 1300 ft/min (6.6 m/s) are considered to be high-speed.

Special consideration should be directed at high-speed drive designs, as several factors can considerably influence belt performance. Cord exhaustion and belt tooth wear will be the two most crucial elements that must definitely 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 than a bigger pitch belt. PowerGrip GT2 is particularly well suited for high-quickness drives due to its excellent belt tooth access/exit characteristics. Smooth interaction between your belt tooth and pulley groove minimizes use and sound. Belt installation pressure is especially critical with high-velocity drives. Low belt pressure allows the belt to ride out from the driven pulley, resulting in 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 produced product. In such cases, the characteristics and properties of most appropriate belt drive products should be reviewed. The final drive system selection should be based upon the most significant style requirements, and could require some compromise.

Vibration is not generally regarded as a issue with synchronous belt drives. Low degrees of vibration typically result from the process of tooth meshing and/or as a result of their high tensile modulus properties. Vibration resulting from tooth meshing can be a standard characteristic of synchronous belt drives, and can’t be completely eliminated. It can be minimized by avoiding small pulley diameters, and instead selecting moderate sizes. The dimensional precision of the pulleys also influences tooth meshing quality. Additionally, the installation stress has an impact on meshing quality. PowerGrip GT2 drives mesh extremely 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 pressure variation with each pulley revolution. V-belt pulleys are also manufactured 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 proper pitch under load.

Drive noise evaluation in any belt drive system should 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 outcomes from the process of belt tooth meshing and physical connection with the pulleys. The sound pressure level generally boosts as operating rate and belt width increase, and as pulley diameter decreases. Drives designed on moderate pulley sizes without excessive capacity (overdesigned) are usually 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 can be very essential in minimizing get noise. The belt should be tensioned at a rate which allows it to perform with as little meshing interference as feasible.

Get alignment also offers a significant influence on drive noise. Special attention should be given to minimizing angular misalignment (shaft parallelism). This assures that belt teeth are loaded uniformly and minimizes part tracking forces against the flanges. Parallel misalignment (pulley offset) is not as critical of a problem as long as the belt is not trapped or pinched between reverse flanges (see the unique section dealing with get alignment). Pulley materials and dimensional precision also influence travel noise. Some users have discovered that steel pulleys are the quietest, followed closely by light weight aluminum. Polycarbonates have already been found to become noisier than metallic materials. Machined pulleys are usually quieter than molded pulleys. The reasons because of this revolve around materials density and resonance characteristics as well as dimensional accuracy.

Small synchronous rubber or urethane belts can generate an electrical charge while operating on a drive. Elements such as humidity and operating speed influence the potential of the charge. If established to become a problem, rubber belts can be stated in a conductive structure to dissipate the charge in to the pulleys, and also to ground. This prevents the accumulation of electric charges that could be harmful to materials handling processes or sensitive electronics. In addition, it significantly reduces the potential for arcing or sparking in flammable conditions. Urethane belts can’t be produced in a conductive structure.

RMA has outlined specifications for conductive belts within their bulletin IP-3-3. Unless in any other case specified, a static conductive structure for rubber belts is certainly available on a made-to-order basis. Unless in any other case specified, conductive belts will be built to yield a resistance of 300,000 ohms or less, when new.

non-conductive belt constructions are also designed for rubber belts. These belts are usually built particularly to the customers conductivity requirements. They are generally used in applications where one shaft should be electrically isolated from the additional. It is necessary to note that a static conductive belt cannot dissipate a power charge through plastic material pulleys. At least one metallic pulley in a drive is necessary for the charge to end up being dissipated to floor. A grounding brush or equivalent device may also be used to dissipate electrical charges.

Urethane timing belts aren’t static conductive and can’t be built in a special conductive construction. Particular conductive rubber belts should be utilized when the presence of a power charge is a concern.

Synchronous drives are ideal for use in a wide selection of environments. Unique considerations could be necessary, nevertheless, depending on the application.

Dust: Dusty conditions usually do not generally present serious problems to synchronous drives as long as the particles are good and dry out. Particulate matter will, however, act as an abrasive resulting in a higher rate of belt and pulley use. Damp or sticky particulate matter deposited and loaded into pulley grooves can cause belt tension to increase considerably. This increased stress can impact shafting, bearings, and framework. Electrical costs within a drive system will often draw in particulate matter.

Debris: Debris ought to be prevented from falling into any synchronous belt drive. Particles captured in the travel is normally either pressured 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 affect synchronous belts. Prolonged get in touch with (continuous spray or submersion) results in significantly reduced tensile power in fiberglass belts, and potential duration variation in aramid belts. Prolonged connection with water also causes rubber substances to swell, although significantly less than with oil get in touch with. Internal belt adhesion systems are also steadily broken down with the presence of drinking water. Additives to water, such as lubricants, chlorine, anticorrosives, etc. can have a far more detrimental influence on the belts than pure water. Urethane timing belts also have problems with drinking water contamination. Polyester tensile cord shrinks considerably and experiences loss of tensile power in the presence of water. Aramid tensile cord maintains its strength fairly well, but encounters duration variation. Urethane swells a lot more than neoprene in the presence of water. This swelling can boost belt tension significantly, leading to belt and related equipment problems.

Oil: Light contact with oils on an occasional basis will not generally harm synchronous belts. Prolonged connection with essential oil or lubricants, either directly or airborne, results in significantly reduced belt service life. Lubricants cause the rubber substance to swell, breakdown inner adhesion systems, and decrease belt tensile strength. While alternate rubber substances 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 compounds used in rubber synchronous belts. Ozone degrades belt materials in quite similar way as excessive environmental temperatures. Although the rubber components used in synchronous belts are compounded to resist the effects of ozone, eventually chemical breakdown occurs and 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 shouldn’t be exceeded: (parts per hundred million)
Standard Construction: 100 pphm
Nonmarking Construction: 20 pphm
Conductive Construction: 75 pphm
Low Temperatures Construction: 20 pphm

Radiation: Contact with gamma radiation could be detrimental to the compounds used in rubber and urethane synchronous belts. Radiation degrades belt materials much the same way excessive environmental temps do. The amount of degradation is dependent 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 Construction: 104 rads

Dust Era: Rubber synchronous belts are recognized to generate little quantities of fine dust, as an all natural consequence of their procedure. The quantity of dust is normally higher for brand-new belts, because they operate in. The period of time for run in to occur depends upon the belt and pulley size, loading and rate. Factors such as pulley surface finish, operating speeds, installation stress, and alignment influence the quantity of dust generated.

Clean Room: 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 particles than rubber timing belts. Nevertheless, they are recommended only for light working loads. Also, they cannot be produced in a static conductive building to permit electrical charges to dissipate.

Static Sensitive: Applications are sometimes sensitive to the accumulation of static electric charges. Electrical costs can affect materials handling functions (like paper and plastic film transport), and sensitive electronic equipment. Applications like these require a static conductive belt, to ensure that the static charges generated by the belt can be dissipated in to the pulleys, and also to ground. Standard rubber synchronous belts do not satisfy this necessity, but could be produced in a static conductive construction 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 can’t be stated in a conductive construction.

Lateral tracking characteristics of synchronous belts is normally a common area of inquiry. Although it is normal for a belt to favor one aspect of the pulleys while operating, it is unusual for a belt to exert significant power against a flange leading to belt edge use and potential flange failure. Belt tracking is definitely influenced by many factors. In order of significance, conversation about these factors is really as follows:

Tensile Cord Twist: Tensile cords are shaped into a one twist configuration throughout their manufacture. Synchronous belts made with only single twist tensile cords monitor laterally with a substantial power. To neutralize this tracking push, tensile cords are stated in correct- and left-hands twist (or “S” and “Z” twist) configurations. Belts made out of “S” twist tensile cords monitor in the opposite direction to those constructed with “Z” twist cord. Belts made out of alternating “S” and “Z” twist tensile cords track with reduced lateral force because the tracking features of the two cords offset one another. The content of “S” and “Z” twist tensile cords varies somewhat with every belt that’s produced. Consequently, every belt comes with an unprecedented inclination to track in each one path or the other. When an application requires a belt to monitor in a single specific direction only, 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 position of misalignment influences the magnitude and path of the tracking force. Synchronous belts have a tendency to monitor “downhill” to a state of lower pressure or shorter center distance.

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

Pulley Size: Belts operating on little pulley diameters can have a tendency 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 the way tensile cords are applied to the belt molds, brief belts can tend to exhibit higher monitoring forces than longer 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 normally minimal with little pitch synchronous belts. Sag in lengthy belt spans should be avoided by applying sufficient belt installation tension.

Torque Loads: Sometimes, while in operation, a synchronous belt will move laterally from side to side on the pulleys instead of operating in a constant position. While not generally regarded as a substantial concern, one description for this is varying torque loads within the get. Synchronous belts sometimes track Motorbase differently with changing loads. There are numerous potential reasons for this; the primary cause relates to tensile cord distortion while under great pressure against the pulleys. Variation in belt tensile loads may 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 reasons for this are similar to the effect that varying torque loads possess on belt tracking. When issues with belt monitoring are experienced, each of these potential contributing factors should be investigated in the order that they are shown. Generally, the principal problem will probably be discovered before moving totally through the list.

Pulley guide flanges are necessary to keep synchronous belts operating on the pulleys. As discussed previously in Section 9.7 on belt tracking, it is regular for synchronous belts to favor one side of the pulleys when running. Proper flange style is important in preventing belt edge wear, minimizing noise and avoiding the belt from climbing out of 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 certainly adequately restrained within its operating system. Because style and design of small synchronous drives is so diverse, the wide variety of flanging situations potentially encountered cannot very easily be protected in a simple group of guidelines without locating exceptions. Not surprisingly, the next broad flanging guidelines should help the developer generally:

Two Pulley Drives: On basic two pulley drives, either one pulley ought to 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 almost every other pulley ought to be flanged in both sides, or every single pulley should be flanged about 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 should be flanged on at least the bottom side.

Long Span 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 characteristics. Belts on drives with lengthy spans (generally 12 times the diameter of small pulley or even more) often require more lateral restraint than with brief spans. Because of this, it is generally smart to flange the pulleys on both sides.

Huge Pulleys: Flanging large pulleys can be costly. Designers often desire to leave large pulleys unflanged to lessen price and space. Belts generally tend to require less lateral restraint on large pulleys than small and can frequently perform reliably without flanges. When deciding whether or not to flange, the previous guidelines is highly recommended. The groove encounter 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 side 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 inside or backside of the belts. The prior guidelines should also be considered.

The three primary factors adding to belt drive registration (or positioning) errors are belt elongation, backlash, and tooth deflection. When analyzing the potential registration features of a synchronous belt drive, the machine must initial be established to end up being either static or powerful in terms of its registration function and requirements.

Static Sign up: A static registration system moves from its initial static position to a secondary static position. During the procedure, the designer can be involved just with how accurately and regularly the drive arrives at its secondary position. He/she is not worried about any potential sign up errors that happen during transport. Therefore, the principal factor adding to registration mistake in a static sign up system can be backlash. The consequences of belt elongation and tooth deflection do not have any influence on the sign up precision of this type of system.

Dynamic Sign up: A dynamic registration system must perform a registering function while in motion with torque loads varying as the machine operates. In this case, the designer can be involved with the rotational placement of the travel pulleys regarding one another at every point in time. Therefore, belt elongation, backlash and tooth deflection will all donate to registrational inaccuracies.

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

Belt Elongation: Belt elongation, or stretch out, occurs naturally whenever a belt is placed under tension. The total tension exerted within a belt results from set up, along with working loads. The amount of belt elongation is certainly a function of the belt tensile modulus, which is normally influenced by the type of tensile cord and the belt construction. The standard tensile cord used in rubber synchronous belts is normally fiberglass. Fiberglass includes a high tensile modulus, is dimensionally steady, and has exceptional flex-fatigue features. If an increased tensile modulus is necessary, aramid tensile cords can be viewed as, 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 usually available from our Program Engineering Department.

Backlash: Backlash in a synchronous belt drive outcomes from clearance between the belt tooth and the pulley grooves. This clearance is required to permit the belt teeth to enter and exit the grooves effortlessly with at the least interference. The quantity of clearance required depends upon the belt tooth profile. Trapezoidal Timing Belt Drives are recognized for having relatively little backlash. PowerGrip HTD Drives have improved torque holding capability and withstand ratcheting, but have a significant quantity of backlash. PowerGrip GT2 Drives possess even more improved torque carrying capability, and also have as little or less backlash than trapezoidal timing belt drives. In special cases, alterations can be made to travel systems to help expand lower backlash. These alterations typically lead to increased belt wear, increased drive noise and shorter travel life. Get in touch with our Software Engineering Department for additional information.

Tooth Deflection: Tooth deformation in a synchronous belt drive occurs as a torque load is applied to the machine, and individual belt teeth are loaded. The quantity of belt tooth deformation is dependent upon the amount of torque loading, pulley size, installation tension and belt type. Of the three primary contributors to registration error, tooth deflection may be the most challenging to quantify. Experimentation with a prototype get system is the best method of obtaining reasonable 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.
Design with large pulleys with more tooth in mesh.
Keep belts tight, and control tension closely.
Design body/shafting to be rigid under load.
Use high quality machined pulleys to minimize radial runout and lateral wobble.