Timing Belts and Pulleys – Operations

Synchronous drives are especially well-appropriate for low-speed, high torque applications. Their positive generating nature prevents potential slippage connected with V-belt drives, and actually allows significantly greater 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 drive selection process as stall and peak torques can sometimes be high. While intermittent peak torques can often be carried by synchronous drives without particular factors, high cyclic peak torque loading should be carefully reviewed.

Proper belt installation tension and rigid get bracketry and framework is essential in preventing belt tooth jumping in peak torque loads. It is also beneficial to design with more than 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 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 found in high-speed applications even though V-belt drives are typically better suitable. They are often used due to their positive traveling characteristic (no creep or slide), and because they require minimal maintenance (don’t stretch considerably). A substantial drawback of high-velocity synchronous drives is definitely get noise. High-velocity synchronous drives will nearly always produce even more noise than V-belt drives. Little pitch synchronous drives operating at speeds more than 1300 ft/min (6.6 m/s) are considered to be high-speed.

Special consideration ought to be directed at high-speed drive designs, as several factors can significantly influence belt performance. Cord exhaustion and belt tooth wear are the two most crucial factors that must definitely be controlled to ensure success. Moderate pulley diameters ought to be used to reduce the price of cord flex fatigue. Developing with a smaller sized pitch belt will most likely offer better cord flex exhaustion characteristics than a larger pitch belt. PowerGrip GT2 is particularly perfect for high-swiftness drives due to its excellent belt tooth entry/exit characteristics. Clean interaction between your belt tooth and pulley groove minimizes use and sound. Belt installation stress is especially critical with high-velocity drives. Low belt tension allows the belt to trip out from 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 operation or finished produced product. In such cases, the characteristics and properties of all appropriate belt drive products ought to be reviewed. The ultimate drive program selection should be based on the most critical design requirements, and could need some compromise.

Vibration is not generally regarded as a issue with synchronous belt drives. Low levels of vibration typically derive from the procedure of tooth meshing and/or consequently of their high tensile modulus properties. Vibration caused by tooth meshing is definitely a normal characteristic of synchronous belt drives, and can’t be completely eliminated. It can be minimized by staying away from small pulley diameters, and rather choosing moderate sizes. The dimensional precision of the pulleys also influences tooth meshing quality. Additionally, the installation stress has an effect on meshing quality. PowerGrip GT2 drives mesh extremely cleanly, resulting in the smoothest feasible operation. Vibration caused by high tensile modulus can be a function of pulley quality. Radial go out causes belt tension variation with each pulley revolution. V-belt pulleys are also manufactured with some radial run out, but V-belts have a lesser tensile modulus leading to less belt tension variation. The high tensile modulus found in synchronous belts is necessary to maintain correct pitch under load.

Drive noise evaluation in any belt drive system ought to be approached with care. There are plenty of potential resources of noise in something, including vibration from related components, bearings, and resonance and amplification through framework and panels.

Synchronous belt drives typically produce even more noise than V-belt drives. Noise outcomes from the procedure of belt tooth meshing and physical connection with the pulleys. The sound pressure level generally boosts as operating acceleration and belt width increase, and as pulley size decreases. Drives designed on moderate pulley sizes without extreme capacity (overdesigned) are Gear rack usually the quietest. PowerGrip GT2 drives have already been discovered to be considerably quieter than other systems because of their improved meshing characteristic, see Figure 9. Polyurethane belts generally create more noise than neoprene belts. Proper belt installation tension can be very essential in minimizing drive noise. The belt ought to be tensioned at a rate that allows it to run with only a small amount meshing interference as feasible.

Travel alignment also has a significant influence on drive noise. 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 isn’t trapped or pinched between opposite flanges (see the unique section coping with travel alignment). Pulley materials and dimensional accuracy also influence travel sound. Some users possess found that steel pulleys are the quietest, accompanied by lightweight aluminum. Polycarbonates have already been found to become noisier than metallic components. Machined pulleys are generally quieter than molded pulleys. The reason why because of 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 on a drive. Elements such as for example humidity and working speed impact the potential of the charge. If established to become a problem, rubber belts can be produced in a conductive construction to dissipate the charge in to the pulleys, and also to surface. This prevents the accumulation of electrical charges that might be detrimental to material handling processes or sensitive electronics. It also significantly reduces the prospect of arcing or sparking in flammable environments. Urethane belts can’t be stated in a conductive construction.

RMA has outlined specifications for conductive belts within their bulletin IP-3-3. Unless otherwise specified, a static conductive structure for rubber belts is on a made-to-purchase basis. Unless normally 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 usually built specifically to the clients conductivity requirements. They are usually used in applications where one shaft should be electrically isolated from the other. It is important to note a static conductive belt cannot dissipate an electrical 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 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. Special conductive rubber belts should be used when the presence of a power charge is normally a concern.

Synchronous drives are suitable for use in a wide variety of environments. Particular considerations may be necessary, however, depending on the application.

Dust: Dusty environments usually do not generally present serious problems to synchronous drives provided that the particles are great and dry out. Particulate matter will, however, act as an abrasive resulting in a higher level 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 pressure can impact shafting, bearings, and framework. Electrical charges within a travel system will often get particulate matter.

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

Drinking water: Light and occasional connection with drinking water (occasional clean downs) shouldn’t seriously affect synchronous belts. Prolonged contact (continuous spray or submersion) results in considerably reduced tensile power in fiberglass belts, and potential duration variation in aramid belts. Prolonged contact with 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 water. Additives to drinking water, such as for example lubricants, chlorine, anticorrosives, etc. can possess a far more detrimental influence on the belts than pure water. Urethane timing belts also suffer from drinking water contamination. Polyester tensile cord shrinks considerably and experiences loss of tensile strength in the existence of drinking water. Aramid tensile cord keeps its strength pretty well, but experiences length variation. Urethane swells a lot more than neoprene in the existence of water. This swelling can boost belt tension significantly, leading to belt and related hardware problems.

Oil: Light connection with natural oils on an intermittent basis won’t generally damage synchronous belts. Prolonged contact with essential oil or lubricants, either directly or airborne, results in considerably reduced belt service life. Lubricants trigger the rubber compound to swell, breakdown inner adhesion systems, and decrease belt tensile power. While alternate rubber substances may provide some marginal improvement in durability, it is advisable to prevent essential 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 much the same way as excessive environmental temps. Although the rubber components used in synchronous belts are compounded to resist the effects of ozone, ultimately chemical 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 overall performance of rubber belts, the next concentration levels shouldn’t be exceeded: (parts per hundred million)
Standard Construction: 100 pphm
Nonmarking Construction: 20 pphm
Conductive Construction: 75 pphm
Low Temperatures Structure: 20 pphm

Radiation: Contact with gamma radiation could be detrimental to the substances used in rubber and urethane synchronous belts. Radiation degrades belt materials quite similar way excessive environmental temperature ranges do. The amount of degradation is dependent upon the strength of radiation and the publicity time. Once and for all belt performance, the following exposure levels shouldn’t be exceeded:
Standard Construction: 108 rads
Nonm arking Building: 104 rads
Conductive Construction: 106 rads
Low Temperatures Construction: 104 rads

Dust Era: Rubber synchronous belts are recognized to generate small quantities of great dust, as an all natural result of their operation. The number of dust is normally higher for fresh belts, as they operate in. The period of time for run directly into occur is dependent upon the belt and pulley size, loading and acceleration. Elements such as for example pulley surface end, operating speeds, installation stress, and alignment impact the number of dust generated.

Clean Room: Rubber synchronous belts may not be suitable for use in clean area environments, where all potential contamination must be minimized or eliminated. Urethane timing belts typically generate significantly less debris than rubber timing belts. Nevertheless, they are suggested limited to light operating loads. Also, they cannot be stated in a static conductive structure to permit electrical charges to dissipate.

Static Sensitive: Applications are occasionally delicate to the accumulation of static electrical charges. Electrical fees can affect materials handling processes (like paper and plastic material film transport), and sensitive electronic equipment. Applications like these require a static conductive belt, to ensure that the static fees produced by the belt could be dissipated in to the pulleys, and also to ground. Standard rubber synchronous belts do not meet this requirement, but could be produced in a static conductive structure on a made-to-order basis. Normal belt wear resulting from long term operation or environmental contamination can influence belt conductivity properties.

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

Lateral tracking qualities of synchronous belts is usually a common area of inquiry. Although it is regular for a belt to favor one side of the pulleys while operating, it is irregular for a belt to exert significant force against a flange leading to belt edge wear and potential flange failing. Belt tracking is normally influenced by several factors. To be able of significance, discussion about these factors is as follows:

Tensile Cord Twist: Tensile cords are formed into a one twist configuration during their produce. Synchronous belts made out of only solitary twist tensile cords monitor laterally with a significant pressure. To neutralize this monitoring push, 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 path to those constructed with “Z” twist cord. Belts made out of 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. Because of this, every belt has an unprecedented tendency to track in either one path or the additional. When a credit card applicatoin requires a belt to monitor in a single specific direction only, 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 angle of misalignment influences the magnitude and direction of the monitoring power. Synchronous belts tend to monitor “downhill” to a state of lower tension or shorter middle distance.

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

Pulley Size: Belts operating on small pulley diameters can have a tendency to generate higher tracking forces than on large diameters. That is particularly true as the belt width techniques the pulley diameter. Drives with pulley diameters significantly less than the belt width aren’t generally suggested because belt tracking forces may become excessive.

Belt Length: Due to the way tensile cords are applied on to the belt molds, brief belts can have a tendency to exhibit higher monitoring forces than longer belts. The helix angle of the tensile cord decreases with increasing belt length.

Gravity: In 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 adequate belt installation tension.

Torque Loads: Sometimes, while functioning, a synchronous belt can move laterally laterally on the pulleys instead of operating in a constant position. While not generally considered to be a substantial concern, one description for this is definitely 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 is related to tensile cord distortion while under 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 may also be influenced by the level of belt installation stress. The reason why for this act like the result that varying torque loads possess on belt tracking. When problems with belt monitoring are experienced, each of these potential contributing factors ought to be investigated in the order they are outlined. Generally, the principal problem is going to be determined before moving completely through the list.

Pulley information flanges are essential to keep synchronous belts operating on the pulleys. As discussed previously in Section 9.7 on belt tracking, it is normal 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 recommendations for custom-produced or molded flanges are contained in tables dealing with these problems. Proper flange placement is important to ensure that the belt is normally adequately restrained within its operating-system. Because style and design of little synchronous drives is so varied, the wide variety of flanging situations possibly encountered cannot very easily be protected in a straightforward group of guidelines without obtaining exceptions. Not surprisingly, the following broad flanging guidelines should help the developer generally:

Two Pulley Drives: On simple two pulley drives, each one pulley ought to be flanged on 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 about both sides, or every single pulley should be flanged about 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 lengthy belt span lengths cannot easily be defined due to the many factors that can affect belt tracking qualities. Belts on drives with long spans (generally 12 times the diameter of the smaller pulley or even more) frequently require even more lateral restraint than with short 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 frequently wish to leave huge pulleys unflanged to lessen cost and space. Belts tend to require less lateral restraint on large pulleys than small and can frequently perform reliably without flanges. When choosing whether to flange, the prior 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 generally not necessary. Idlers made to bring lateral aspect loads from belt tracking forces can be flanged if needed to provide lateral belt restraint. Idlers used for this purpose can be used on the inside or backside of the belts. The prior guidelines also needs to 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 capabilities of a synchronous belt drive, the machine must 1st be determined to end up being either static or dynamic with regards 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 just with how accurately and consistently the drive finds its secondary placement. He/she is not worried about any potential registration errors that occur during transportation. Therefore, the primary 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 impact on the sign up precision 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 get pulleys with respect to each other at every point in time. Therefore, belt elongation, backlash and tooth deflection will all contribute to registrational inaccuracies.

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

Belt Elongation: Belt elongation, or stretch out, occurs naturally whenever a belt is placed under pressure. The total stress exerted within a belt results from installation, and also functioning loads. The quantity of belt elongation is usually a function of the belt tensile modulus, which can be influenced by the type of tensile cord and the belt construction. The standard tensile cord found in rubber synchronous belts is certainly fiberglass. Fiberglass includes a high tensile modulus, is dimensionally stable, and has exceptional flex-fatigue characteristics. If an increased tensile modulus is needed, aramid tensile cords can be viewed as, although they are generally used to supply resistance to harsh shock and impulse loads. Aramid tensile cords found in small synchronous belts generally have got just a marginally higher tensile modulus compared to fiberglass. When required, belt tensile modulus data is certainly available from our Software 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 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 known for having fairly small backlash. PowerGrip HTD Drives possess improved torque holding capability and withstand ratcheting, but have a significant amount of backlash. PowerGrip GT2 Drives possess even more improved torque transporting capability, and have only a small amount or much less backlash than trapezoidal timing belt drives. In unique cases, alterations can be made to get systems to further decrease backlash. These alterations typically lead to increased belt wear, increased travel noise and shorter get life. Get in touch with our Software Engineering Section 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 is dependent upon the amount of torque loading, pulley size, installation tension and belt type. Of the three principal contributors to registration mistake, tooth deflection is the most challenging to quantify. Experimentation with a prototype get system may be the best method of obtaining practical estimations of belt tooth deflection.

Additional guidelines which may be useful in developing registration critical drive systems are the following:
Select PowerGrip GT2 or trapezoidal timing belts.
Design with large pulleys with more teeth in mesh.
Keep belts tight, and control pressure closely.
Design body/shafting to be rigid under load.
Use high quality machined pulleys to minimize radial runout and lateral wobble.


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