9.1 LOW-SPEED OPERATION
Synchronous drives are specially well-appropriate for low-speed, high torque applications. Their positive generating nature helps prevent potential slippage associated with V-belt drives, and even allows significantly higher torque carrying capability. Little pitch synchronous drives working at speeds of 50 ft/min (0.25 m/s) or much less are considered to be low-speed. Care should be taken in the get selection procedure as stall and peak torques can sometimes be very high. While intermittent peak torques can often be carried by synchronous drives without special factors, high cyclic peak torque loading ought to be carefully reviewed.
Proper belt installation tension and rigid travel bracketry and framework is essential in preventing belt tooth jumping under peak torque loads. It is also helpful to design with an increase of compared to the normal the least 6 belt teeth in mesh to make sure sufficient belt tooth shear power.
Newer generation curvilinear systems like PowerGrip GT2 and PowerGrip HTD should be found in low-rate, high torque applications, as trapezoidal timing belts are even more susceptible to tooth jumping, and have significantly less load carrying capability.
9.2 HIGH-SPEED OPERATION
Synchronous belt drives are often used in high-speed applications despite the fact that V-belt drives are typically better suitable. They are often used because of their positive generating characteristic (no creep or slide), and because they require minimal maintenance (don’t stretch considerably). A substantial drawback of high-speed synchronous drives is certainly drive noise. High-swiftness synchronous drives will almost always produce more noise than V-belt drives. Small 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 given to high-speed drive designs, as several factors can considerably influence belt performance. Cord exhaustion and belt tooth wear will be the two most crucial factors that must definitely be controlled to have success. Moderate pulley diameters ought to be used to lessen the price of cord flex fatigue. Developing with a smaller pitch belt will most likely offer better cord flex exhaustion characteristics when compared to a larger pitch belt. PowerGrip GT2 is especially well suited for high-velocity drives because of its excellent belt tooth entry/exit characteristics. Smooth interaction between the belt tooth and pulley groove minimizes use and sound. Belt installation stress is especially crucial with high-rate drives. Low belt pressure allows the belt to ride from the driven pulley, resulting in rapid belt tooth and pulley groove wear.
9.3 SMOOTH RUNNING
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 these cases, the characteristics and properties of most appropriate belt drive products ought to be reviewed. The final drive system selection should be based on the most critical style requirements, and could require some compromise.
Vibration is not generally considered to be a problem with synchronous belt drives. Low levels of vibration typically derive from the process of tooth meshing and/or consequently of their high Gear rack tensile modulus properties. Vibration resulting from tooth meshing can be a standard characteristic of synchronous belt drives, and can’t be completely 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 stress has an effect on meshing quality. PowerGrip GT2 drives mesh extremely 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 stress variation with each pulley revolution. V-belt pulleys are also produced with some radial run out, but V-belts have got a lower tensile modulus leading to less belt stress variation. The high tensile modulus within synchronous belts is essential to maintain proper pitch under load.
9.4 DRIVE NOISE
Drive noise evaluation in any belt drive system should be approached with care. There are numerous potential sources of sound in something, including vibration from related elements, 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 process of belt tooth meshing and physical contact with the pulleys. The sound pressure level generally boosts as operating acceleration and belt width boost, and as pulley size reduces. Drives designed on moderate pulley sizes without extreme capability (overdesigned) are usually the quietest. PowerGrip GT2 drives have been discovered to be significantly quieter than other 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 important in minimizing get noise. The belt should be tensioned at a level which allows it to run with only a small amount meshing interference as feasible.
Get alignment also offers a significant effect on drive sound. Special attention ought to be given to minimizing angular misalignment (shaft parallelism). This assures that belt tooth are loaded uniformly and minimizes side monitoring forces against the flanges. Parallel misalignment (pulley offset) isn’t as vital of a problem as long as the belt isn’t trapped or pinched between opposing flanges (see the special section coping with get alignment). Pulley materials and dimensional accuracy also influence drive sound. Some users possess discovered that steel pulleys will be the quietest, accompanied by light weight aluminum. Polycarbonates have already been discovered to be noisier than metallic components. Machined pulleys are usually quieter than molded pulleys. The reason why because of this revolve around materials density and resonance features as well as dimensional accuracy.
9.5 STATIC CONDUCTIVITY
Little synchronous rubber or urethane belts can generate an electrical charge while operating on a drive. Elements such as for example humidity and operating speed impact the potential of the charge. If established to become a problem, rubber belts could be stated in a conductive building to dissipate the charge in to the pulleys, and to ground. This prevents the accumulation of electrical charges that might be detrimental to materials handling processes or sensitive consumer electronics. It also significantly reduces the prospect of arcing or sparking in flammable conditions. Urethane belts can’t be stated in a conductive building.
RMA has outlined standards for conductive belts in their bulletin IP-3-3. Unless normally specified, a static conductive construction for rubber belts can be on a made-to-purchase basis. Unless normally 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 available for rubber belts. These belts are generally built specifically to the customers conductivity requirements. They are usually found in applications where one shaft should be electrically isolated from the other. It is important to note that a static conductive belt cannot dissipate an electrical charge through plastic pulleys. At least one metallic pulley in a drive is necessary for the charge to end up being dissipated to surface. A grounding brush or related 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. Particular conductive rubber belts should be utilized when the existence of an electrical charge is a concern.
9.6 OPERATING ENVIRONMENTS
Synchronous drives are ideal for use in a wide variety of environments. Special considerations could be necessary, however, depending on the application.
Dust: Dusty environments do not generally present serious complications to synchronous drives so long as the particles are good and dry out. Particulate matter will, however, act as an abrasive producing 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 significantly. This increased stress can impact shafting, bearings, and framework. Electrical charges within a get system can sometimes catch the attention of particulate matter.
Debris: Debris ought to be prevented from falling into any synchronous belt drive. Particles captured in the get is generally either pressured through the belt or outcomes in stalling of the machine. In any case, serious damage takes place to the belt and related travel hardware.
Drinking water: Light and occasional contact with drinking water (occasional clean downs) shouldn’t seriously influence synchronous belts. Prolonged contact (constant spray or submersion) results in significantly reduced tensile strength in fiberglass belts, and potential size variation in aramid belts. Prolonged contact with water also causes rubber compounds to swell, although significantly less than with oil get in touch with. Internal belt adhesion systems are also steadily broken down with the presence of water. Additives to water, such as for example lubricants, chlorine, anticorrosives, etc. can have a far more detrimental influence on the belts than pure water. Urethane timing belts also suffer from drinking water contamination. Polyester tensile cord shrinks significantly and experiences loss of tensile power in the existence of water. Aramid tensile cord maintains its strength pretty well, but experiences duration variation. Urethane swells a lot more than neoprene in the presence of water. This swelling can increase belt tension significantly, causing belt and related hardware problems.
Oil: Light connection with oils on an occasional basis will not generally harm synchronous belts. Prolonged connection with essential oil or lubricants, either directly or airborne, outcomes in considerably reduced belt service existence. Lubricants trigger the rubber compound to swell, breakdown internal adhesion systems, and decrease belt tensile power. While alternate rubber substances 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 much the same way as extreme environmental temps. Although the rubber components found in synchronous belts are compounded to withstand the consequences of ozone, eventually chemical breakdown occurs and they become hard and brittle and begin cracking. The amount of degradation depends upon the ozone focus 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 Construction: 20 pphm
Radiation: Exposure to gamma radiation could be detrimental to the substances found in rubber and urethane synchronous belts. Radiation degrades belt materials quite similar way extreme environmental temps do. The quantity of degradation is dependent upon the intensity of radiation and the publicity time. For good belt performance, the following 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 known to generate little quantities of fine dust, as a natural consequence of their operation. The number of dust is normally higher for brand-new belts, because they run in. The time period for run directly into occur depends upon the belt and pulley size, loading and quickness. Factors such as for example pulley surface surface finish, operating speeds, set up stress, and alignment influence the amount of dust generated.
Clean Space: Rubber synchronous belts may not be suitable for use in clean area environments, where all potential contamination should be minimized or eliminated. Urethane timing belts typically generate significantly less debris than rubber timing belts. However, they are suggested limited to light working loads. Also, they can not be stated in a static conductive building to permit electrical fees to dissipate.
Static Sensitive: Applications are sometimes delicate to the accumulation of static electric charges. Electrical fees can affect materials handling functions (like paper and plastic material film transport), and sensitive digital gear. Applications like these require a static conductive belt, to ensure that the static costs generated by the belt could be dissipated in to the pulleys, and also to ground. Standard rubber synchronous belts usually do not satisfy this necessity, but could be manufactured in a static conductive construction on a made-to-order basis. Normal belt wear resulting from long term operation or environmental contamination can impact belt conductivity properties.
In sensitive applications, rubber synchronous belts are favored over urethane belts since urethane belting cannot be stated in a conductive construction.
9.7 BELT TRACKING
Lateral tracking qualities of synchronous belts is certainly a common area of inquiry. Although it is regular for a belt to favor one part of the pulleys while running, it is abnormal for a belt to exert significant pressure against a flange resulting in belt edge put on and potential flange failing. Belt tracking is normally influenced by several factors. In order of significance, conversation about these elements is really as follows:
Tensile Cord Twist: Tensile cords are formed into a solitary twist configuration during their manufacture. Synchronous belts made out of only one twist tensile cords monitor laterally with a significant force. To neutralize this tracking force, tensile cords are produced in correct- and left-hands twist (or “S” and “Z” twist) configurations. Belts made out of “S” twist tensile cords track in the contrary path to those constructed with “Z” twist cord. Belts made with alternating “S” and “Z” twist tensile cords track with reduced lateral force because the tracking features of both cords offset each other. The content of “S” and “Z” twist tensile cords varies somewhat with every belt that is produced. As a result, every belt comes with an unprecedented tendency to track in either one direction or the various other. When a credit card applicatoin requires a belt to monitor in a single specific direction only, an individual 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 tend to monitor “downhill” to a state of lower tension or shorter middle distance.
Belt Width: The potential magnitude of belt tracking 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 small pulley diameters can have a tendency to generate higher monitoring forces than on large diameters. That is particularly accurate as the belt width techniques the pulley diameter. Drives with pulley diameters significantly less than the belt width are not generally suggested because belt tracking forces may become excessive.
Belt Length: Due to just how tensile cords are applied on to the belt molds, short belts can tend to exhibit higher tracking forces than very long 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 this force is certainly minimal with little pitch synchronous belts. Sag in lengthy belt spans should be avoided by applying adequate belt installation tension.
Torque Loads: Sometimes, while in operation, a synchronous belt can move laterally from side to side on the pulleys instead of operating in a constant position. While not generally considered to be a substantial concern, one explanation for this is usually varying torque loads within the travel. Synchronous belts occasionally track differently with changing loads. There are several potential reasons for this; the root cause is related 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 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 issues with belt monitoring are experienced, each 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 completely through the list.
9.8 PULLEY FLANGES
Pulley guideline 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 normal for synchronous belts to favor one aspect of the pulleys when operating. Proper flange style is essential in avoiding belt edge use, minimizing noise and preventing the belt from climbing out from the pulley. Dimensional recommendations for custom-made or molded flanges are included in tables coping with these problems. Proper flange positioning is important to ensure that the belt is adequately restrained within its operating system. Because design and design of little synchronous drives is indeed different, the wide selection of flanging situations possibly encountered cannot conveniently be protected in a simple group of rules without obtaining exceptions. Not surprisingly, the next broad flanging guidelines should help the developer in most cases:
Two Pulley Drives: On basic two pulley drives, either one pulley should be flanged in 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 pulley ought to be flanged in alternating sides around the system. Vertical Shaft Drives: On vertical shaft drives, at least one pulley ought to be flanged on both sides, and the remaining pulleys ought to be flanged on at least underneath side.
Long Period Lengths: Flanging suggestions for small synchronous drives with lengthy belt span lengths cannot quickly be defined due to the many factors that can affect belt tracking qualities. Belts on drives with lengthy spans (generally 12 times the diameter of the smaller pulley or more) frequently 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 huge pulleys can be costly. Designers frequently desire to leave huge pulleys unflanged to lessen price and space. Belts tend to require much less lateral restraint on large pulleys than small and can frequently perform reliably without flanges. When determining whether or not to flange, the prior guidelines is highly recommended. The groove encounter width of unflanged pulleys should also be higher than with flanged pulleys. See Table 27 for recommendations.
Idlers: Flanging of idlers is normally not essential. Idlers made to carry lateral side loads from belt tracking forces can be flanged if needed to provide lateral belt restraint. Idlers utilized for this purpose can be utilized on the 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 analyzing the potential sign up capabilities of a synchronous belt drive, the system must first be decided to be either static or powerful in conditions of its sign up function and requirements.
Static Registration: A static registration system moves from its initial static position to a secondary static position. Through the procedure, the designer is concerned only with how accurately and consistently the drive arrives at its secondary placement. He/she isn’t worried about any potential registration errors that occur during transport. Therefore, the primary factor contributing to registration mistake in a static sign up system is certainly backlash. The effects of belt elongation and tooth deflection don’t have any impact on the sign up accuracy of this type of system.
Dynamic Sign up: A dynamic registration system must perform a registering function while in motion with torque loads different as the system operates. In this case, the designer can be involved with the rotational position of the drive pulleys regarding each other at every point in time. Therefore, belt elongation, backlash and tooth deflection will all contribute to registrational inaccuracies.
Further discussion about each one 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 stress. The total tension exerted within a belt results from set up, in addition to operating loads. The amount of belt elongation is 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 found in rubber synchronous belts is fiberglass. Fiberglass includes a high tensile modulus, is dimensionally steady, and has superb flex-fatigue features. If an increased tensile modulus is needed, aramid tensile cords can be viewed as, although they are usually used to supply resistance to severe shock and impulse loads. Aramid tensile cords found in small synchronous belts generally have got only a marginally higher tensile modulus compared to fiberglass. When required, belt tensile modulus data is certainly obtainable from our Application 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 allow the belt teeth to enter and exit the grooves smoothly with at the least interference. The quantity of clearance required depends upon the belt tooth profile. Trapezoidal Timing Belt Drives are known for having relatively small backlash. PowerGrip HTD Drives have improved torque having capability and withstand ratcheting, but have a significant amount of backlash. PowerGrip GT2 Drives possess even further improved torque transporting capability, and also have only a small amount or less backlash than trapezoidal timing belt drives. In unique cases, alterations can be made to get systems to further lower backlash. These alterations typically lead to increased belt wear, increased travel 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 quantity of belt tooth deformation is dependent upon the amount of torque loading, pulley size, installation stress and belt type. Of the three major contributors to sign up mistake, tooth deflection is the most difficult to quantify. Experimentation with a prototype get system may be the best method of obtaining realistic estimations of belt tooth deflection.
Additional guidelines that may be useful in developing registration vital drive systems are as follows:
Select PowerGrip GT2 or trapezoidal timing belts.
Style with large pulleys with an increase of teeth in mesh.
Keep belts restricted, and control pressure closely.
Design framework/shafting to end up being rigid under load.
Use top quality machined pulleys to reduce radial runout and lateral wobble.