9.1 LOW-SPEED OPERATION
Synchronous drives are specially well-appropriate for low-speed, high torque applications. Their positive driving nature prevents potential slippage associated with V-belt drives, and also allows significantly higher torque carrying ability. Small pitch synchronous drives working at speeds of 50 ft/min (0.25 m/s) or much less are believed to be low-speed. Care should be taken in the travel selection procedure as stall and peak torques can often be very high. While intermittent peak torques can frequently be carried by synchronous drives without particular considerations, high cyclic peak torque loading ought to be carefully reviewed.

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

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

9.2 HIGH-SPEED OPERATION
Synchronous belt drives are often used in high-speed applications even though V-belt drives are typically better suitable. They are generally used due to their positive driving characteristic (no creep or slide), and because they might need minimal maintenance (don’t stretch significantly). A substantial drawback of high-acceleration synchronous drives is usually get noise. High-velocity synchronous drives will almost always produce even more noise than V-belt drives. Small pitch synchronous drives working at speeds in excess of 1300 ft/min (6.6 m/s) are considered to be high-speed.

Special consideration should be directed at high-speed drive designs, as a number of factors can considerably influence belt performance. Cord exhaustion and belt tooth wear are the two most crucial factors that must be controlled to have success. Moderate pulley diameters should be used to lessen the rate of cord flex fatigue. Developing with a smaller sized pitch belt will often offer better cord flex exhaustion characteristics when compared to a bigger pitch belt. PowerGrip GT2 is especially well suited for high-rate drives because of its excellent belt tooth access/exit characteristics. Smooth interaction between the belt tooth and pulley groove minimizes wear and sound. Belt installation tension is especially critical with high-rate drives. Low belt pressure allows the belt to trip out from the driven pulley, leading to rapid belt tooth and pulley groove wear.

9.3 SMOOTH RUNNING
Some ultrasensitive applications require the belt drive to operate with only a small amount vibration aspossible, as vibration sometimes impacts the system operation or finished manufactured product. In such cases, the characteristics and properties of all appropriate belt drive products ought to be reviewed. The ultimate drive system selection ought to be based upon the most critical style requirements, and could need some compromise.

Vibration isn’t generally regarded as a problem with synchronous belt drives. Low degrees of vibration typically result from the procedure of tooth meshing and/or as a result of their high tensile modulus properties. Vibration caused by tooth meshing is definitely a standard characteristic of synchronous belt drives, and cannot be totally eliminated. It could be minimized by staying away from little pulley diameters, and rather choosing moderate sizes. The dimensional accuracy of the pulleys also influences tooth meshing quality. Additionally, the installation pressure has an effect on meshing quality. PowerGrip GT2 drives mesh extremely cleanly, leading to the smoothest possible operation. Vibration resulting from high tensile modulus could be a function of pulley quality. Radial go out causes belt pressure variation with each pulley revolution. V-belt pulleys are also produced with some radial run out, but V-belts have a lower tensile modulus leading to less belt pressure variation. The high tensile modulus within synchronous belts is essential to maintain appropriate pitch under load.

9.4 DRIVE NOISE
Drive noise evaluation in any belt drive system should be approached carefully. There are plenty of potential sources of noise in something, including vibration from related parts, bearings, and resonance and amplification through framework and panels.

Synchronous belt drives typically produce even 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 increases as operating speed and belt width boost, and as pulley diameter reduces. Drives designed on moderate pulley sizes without extreme capacity (overdesigned) are usually the quietest. PowerGrip GT2 drives have already been discovered to be considerably quieter than additional 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 which allows it to perform with only a small amount meshing interference as feasible.

Travel alignment also offers a significant influence on drive noise. Special attention ought to be given to minimizing angular misalignment (shaft parallelism). This assures that belt teeth are loaded uniformly and minimizes side tracking forces against the flanges. Parallel misalignment (pulley offset) isn’t as important of a concern as long as the belt is not trapped or pinched between contrary flanges (see the particular section dealing with get alignment). Pulley materials and dimensional accuracy 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 become noisier than metallic materials. Machined pulleys are usually quieter than molded pulleys. The reasons because of this revolve around materials density and resonance features along with dimensional accuracy.

9.5 STATIC CONDUCTIVITY
Small synchronous rubber or urethane belts can generate a power charge while operating about a drive. Factors such as for example humidity and working speed influence the potential of the charge. If motivated to become a problem, rubber belts can be stated in a conductive structure to dissipate the charge in to the pulleys, and to surface. This prevents the accumulation of electrical charges that may be harmful to materials handling procedures or sensitive consumer electronics. In addition, it greatly reduces the prospect of arcing or sparking in flammable conditions. Urethane belts can’t be produced in a conductive construction.

RMA has outlined requirements for conductive belts within their bulletin IP-3-3. Unless normally specified, a static conductive building for rubber belts is definitely on a made-to-purchase basis. Unless usually specified, conductive belts will be built to yield a resistance of 300,000 ohms or much less, when new.

non-conductive belt constructions are also designed for rubber belts. These belts are generally built particularly to the clients conductivity requirements. They are generally found in applications where one shaft should be electrically isolated from the additional. 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 required for the charge to end up being dissipated to surface. A grounding brush or very similar device could also be used to dissipate electric charges.

Urethane timing belts aren’t static conductive and cannot be built in a special conductive construction. Special conductive rubber belts should be utilized when the existence of a power charge is definitely a concern.

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

Dust: Dusty conditions usually do not generally present serious problems to synchronous drives provided that the contaminants are fine and dry out. Particulate matter will, however, become an abrasive resulting in a higher level of belt and pulley wear. Damp or sticky particulate matter deposited and loaded into pulley grooves could cause belt tension to increase considerably. This increased tension can impact shafting, bearings, and framework. Electrical costs within a travel system will often appeal to particulate matter.

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

Drinking water: Light and occasional connection with water (occasional clean downs) shouldn’t seriously have an effect on synchronous belts. Prolonged get in touch with (constant spray or submersion) results in significantly reduced tensile strength in fiberglass belts, and potential size variation in aramid belts. Prolonged connection with water also causes rubber compounds to swell, although less than with oil get in touch with. Internal belt adhesion systems are also gradually broken down with the presence of water. Additives to drinking water, such as lubricants, chlorine, anticorrosives, etc. can possess a more detrimental influence on the belts than clear water. Urethane timing belts also suffer from water contamination. Polyester tensile cord shrinks considerably and experiences loss of tensile strength in the existence of drinking water. Aramid tensile cord maintains its power fairly well, but experiences size variation. Urethane swells a lot more than neoprene in the existence of drinking water. This swelling can boost belt tension significantly, causing belt and related equipment problems.

Oil: Light contact with natural oils on an occasional basis won’t generally damage synchronous belts. Prolonged connection with oil or lubricants, either straight or airborne, outcomes in considerably reduced belt service lifestyle. Lubricants trigger the rubber compound to swell, breakdown internal adhesion systems, and decrease belt tensile power. While alternate rubber substances might provide some marginal improvement in durability, it is best to prevent oil from contacting synchronous belts.

Ozone: The existence of ozone could be detrimental to the substances found in rubber synchronous belts. Ozone degrades belt materials in much the same way as excessive environmental temperatures. Although the rubber components found in synchronous belts are compounded to withstand the consequences of ozone, ultimately chemical breakdown occurs and they become hard and brittle and start cracking. The quantity of degradation depends upon the ozone concentration and duration of publicity. For good efficiency of rubber belts, the next 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 can be detrimental to the compounds found in rubber and urethane synchronous belts. Radiation degrades belt materials much the same way extreme environmental temps 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 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 great dust, as a natural consequence of their procedure. The amount of dust is normally higher for fresh belts, because they operate in. The period of time for run directly into occur depends upon the belt and pulley size, loading and velocity. Factors such as pulley surface end, operating speeds, set up tension, and alignment influence the quantity of dust generated.

Clean Area: Rubber synchronous belts may not be ideal for use in clean room environments, where all potential contamination should be minimized or eliminated. Urethane timing belts typically generate significantly less debris than rubber timing belts. Nevertheless, they are recommended limited to light working loads. Also, they can not be stated in a static conductive structure to permit electrical costs to dissipate.

Static Sensitive: Applications are occasionally sensitive to the accumulation of static electric charges. Electrical costs can affect materials handling functions (like paper and plastic material film transportation), and sensitive electronic devices. Applications like these require a static conductive belt, so that the static fees produced 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 manufactured in a static conductive structure on a made-to-order basis. Normal belt wear caused by long term procedure or environmental contamination can impact belt conductivity properties.

In delicate applications, rubber synchronous belts are favored over urethane belts since urethane belting can’t be produced in a conductive construction.

9.7 BELT TRACKING
Lateral tracking qualities of synchronous belts is normally a common area of inquiry. Although it is normal for a belt to favor one side of the pulleys while operating, it is unusual for a belt to exert significant pressure against a flange leading to belt edge put on and potential flange failing. Belt tracking is certainly influenced by many factors. In order of significance, conversation about these elements is really as follows:

Tensile Cord Twist: Tensile cords are shaped into a single twist configuration throughout their produce. Synchronous belts made with only one twist tensile cords monitor laterally with a significant drive. To neutralize this tracking force, tensile cords are produced in right- and left-hands twist (or “S” and “Z” twist) configurations. Belts made out of “S” twist tensile cords monitor in the contrary path to those constructed with “Z” twist cord. Belts made with alternating “S” and “Z” twist tensile cords track with minimal lateral force because the tracking features of both cords offset one another. The content of “S” and “Z” twist tensile cords varies slightly with every belt that is produced. Consequently, every belt has an unprecedented tendency to track in each one path or the other. When a credit card applicatoin takes 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 angle of misalignment influences the magnitude and path of the monitoring push. Synchronous belts have a tendency to track “downhill” to a state of lower pressure 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 an increase of push than narrow belts.

Pulley Size: Belts operating on small pulley diameters can tend to generate higher monitoring forces than on large diameters. This is particularly accurate as the belt width approaches the pulley diameter. Drives with pulley diameters significantly less than the belt width aren’t generally recommended because belt tracking forces may become excessive.

Belt Length: Due to just how tensile cords are applied to the belt molds, short belts can tend to exhibit higher tracking forces than very 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 this force is usually minimal with little pitch synchronous belts. Sag in long belt spans should be avoided by applying adequate belt installation tension.

Torque Loads: Sometimes, while functioning, a synchronous belt will move laterally laterally on the pulleys rather than operating in a constant position. Without generally considered to be a significant concern, one description for this is usually varying torque loads within the travel. Synchronous belts occasionally track in a different way with changing loads. There are numerous potential known reasons for this; the primary cause is related 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, leading to belt movement.

Belt Installation Stress: Belt tracking is sometimes influenced by the amount of belt installation tension. The reason why for this are similar to the result that varying torque loads possess on belt tracking. When issues with belt tracking are experienced, each one of these potential contributing elements ought to be investigated in the purchase they are listed. In most cases, the principal problem is going to be discovered before moving totally through the list.

9.8 PULLEY FLANGES
Pulley guidebook flanges are necessary to hold 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 side of the pulleys when running. Proper flange style is essential in avoiding belt edge put on, minimizing sound and preventing the belt from climbing out from the pulley. Dimensional suggestions for custom-produced or molded flanges are included in tables dealing with these problems. Proper flange positioning is important to ensure that the belt is definitely adequately restrained within its operating-system. Because design and layout of small synchronous drives is indeed varied, the wide selection of flanging situations possibly encountered cannot very easily be protected in a straightforward group of guidelines without getting 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 Chain reverse sides.

Multiple Pulley Drives: On multiple pulley (or serpentine) drives, either almost every other pulley should be flanged in both sides, or every single pulley should 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 should be flanged on at least underneath side.

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

Huge Pulleys: Flanging large pulleys could be costly. Designers often desire to leave large pulleys unflanged to lessen price and space. Belts tend to need less lateral restraint on huge pulleys than small and can often perform reliably without flanges. When choosing whether 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 carry lateral aspect loads from belt tracking forces can be flanged if had a need to offer lateral belt restraint. Idlers utilized for this function can be utilized inside or backside of the belts. The previous guidelines also needs to be considered.

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

Static Sign up: A static registration system moves from its initial static position to a secondary static position. Through the procedure, the designer can be involved only with how accurately and regularly the drive finds its secondary position. He/she isn’t worried about any potential registration errors that take place during transport. Therefore, the primary factor contributing to registration error in a static sign up system is certainly backlash. The consequences of belt elongation and tooth deflection don’t have any impact on the sign up accuracy of this type of system.

Dynamic Registration: A dynamic registration system must perform a registering function while in motion with torque loads various as the machine operates. In this instance, the designer is concerned with the rotational position of the travel pulleys with respect to each other 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 adding to registration error is really 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 installation, in addition to functioning loads. The amount of belt elongation is normally a function of the belt tensile modulus, which is usually influenced by the type of tensile cord and the belt construction. The standard tensile cord used in rubber synchronous belts is certainly fiberglass. Fiberglass has a high tensile modulus, is dimensionally steady, and has superb flex-fatigue characteristics. If an increased tensile modulus is needed, aramid tensile cords can be considered, although they are usually used to provide resistance to severe shock and impulse loads. Aramid tensile cords used in small synchronous belts generally possess just a marginally higher tensile modulus in comparison to fiberglass. When required, belt tensile modulus data is certainly obtainable from our Program Engineering Department.

Backlash: Backlash in a synchronous belt drive results 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 smoothly with a minimum of interference. The quantity of clearance necessary depends upon the belt tooth profile. Trapezoidal Timing Belt Drives are known for having fairly little backlash. PowerGrip HTD Drives possess improved torque carrying capability and withstand ratcheting, but possess a significant amount of backlash. PowerGrip GT2 Drives have even more improved torque transporting capability, and have only a small amount or much less backlash than trapezoidal timing belt drives. In special cases, alterations could be made to drive systems to further lower backlash. These alterations typically lead to increased belt wear, increased get sound and shorter get life. Contact our Program Engineering Department for more information.

Tooth Deflection: Tooth deformation in a synchronous belt drive occurs as a torque load is put on the system, and individual belt teeth are loaded. The quantity of belt tooth deformation depends upon the quantity of torque loading, pulley size, installation pressure and belt type. Of the three principal contributors to sign up mistake, tooth deflection is the most difficult to quantify. Experimentation with a prototype travel system may be the best method of obtaining reasonable estimations of belt tooth deflection.

Additional guidelines that may be useful in designing registration vital 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 tight, and control tension closely.
Design framework/shafting to end up being rigid under load.
Use top quality machined pulleys to reduce radial runout and lateral wobble.