9.1 LOW-SPEED OPERATION
Synchronous drives are especially well-appropriate for low-speed, high torque applications. Their positive driving nature stops potential slippage associated with V-belt drives, and even allows significantly greater torque carrying ability. Little pitch synchronous drives operating at speeds of 50 ft/min (0.25 m/s) or less are considered to be low-speed. Care should be used the get selection process as stall and peak torques can sometimes be very high. While intermittent peak torques can often be carried by synchronous drives without unique factors, high cyclic peak torque loading should be carefully reviewed.
Proper belt installation tension and rigid drive bracketry and framework is vital in stopping belt tooth jumping in peak torque loads. It is also beneficial to design with an increase of than the normal minimum of 6 belt tooth in mesh to make sure adequate belt tooth shear power.
Newer generation curvilinear systems like PowerGrip GT2 and PowerGrip HTD ought to be used in low-quickness, high torque applications, as trapezoidal timing belts are more prone to tooth jumping, and have significantly much less load carrying capacity.
9.2 HIGH-SPEED OPERATION
Synchronous belt drives are often found in high-speed applications even though V-belt drives are typically better suited. They are often used due to their positive generating characteristic (no creep or slip), and because they require minimal maintenance (don’t stretch considerably). A significant drawback of high-acceleration synchronous drives is usually get noise. High-speed synchronous drives will nearly always produce 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 end up being 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 are the two most significant elements that must definitely be controlled to have success. Moderate pulley diameters should be used to lessen the rate of cord flex exhaustion. Designing with a smaller pitch belt will most likely offer better cord flex exhaustion characteristics than a larger pitch belt. PowerGrip GT2 is especially well suited for high-rate drives because of its excellent belt tooth access/exit characteristics. Smooth interaction between your belt tooth and pulley groove minimizes wear and sound. Belt installation tension is especially crucial with high-rate drives. Low belt tension allows the belt to trip out of the driven pulley, leading to rapid belt tooth and pulley groove wear.
9.3 SMOOTH RUNNING
Some ultrasensitive applications require the belt drive to use with as little vibration aspossible, as vibration sometimes has an effect on the system procedure or finished manufactured product. In these cases, the characteristics and properties of most appropriate belt drive products should be reviewed. The final drive system selection ought to be based upon the most significant design requirements, and may need some compromise.
Vibration is not generally considered to be a problem 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 caused by tooth meshing can be a standard characteristic of synchronous belt drives, and cannot be totally eliminated. It could be minimized by staying away from small pulley diameters, and instead choosing 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 very cleanly, resulting in the smoothest feasible operation. Vibration resulting from 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 go out, but V-belts possess a lesser tensile modulus leading to less belt pressure variation. The high tensile modulus within synchronous belts is necessary to maintain proper pitch under load.
9.4 DRIVE NOISE
Drive noise evaluation in any belt drive system ought to be approached with care. There are numerous potential resources of sound 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 process of belt tooth meshing and physical connection with the pulleys. The sound pressure level generally raises as operating acceleration and belt width boost, and as pulley diameter reduces. Drives designed on moderate pulley sizes without extreme capacity (overdesigned) are generally the quietest. PowerGrip GT2 drives have already been found to be significantly quieter than various other systems due to their improved meshing characteristic, see Figure 9. Polyurethane belts generally produce more sound than neoprene belts. Proper belt installation tension is also very essential in minimizing travel noise. The belt should be tensioned at a rate that allows it to perform with only a small amount meshing interference as feasible.
Get 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 teeth are loaded uniformly and minimizes part monitoring forces against the flanges. Parallel misalignment (pulley offset) is not as vital of a concern so long as the belt is not trapped or pinched between opposite flanges (see the particular section dealing with drive alignment). Pulley materials and dimensional accuracy also influence get sound. Some users possess discovered that steel pulleys are the quietest, followed closely by light weight aluminum. Polycarbonates have already been found to become noisier than metallic components. Machined pulleys are usually quieter than molded pulleys. The reason why because of this revolve around materials density and resonance characteristics along with dimensional accuracy.
9.5 STATIC CONDUCTIVITY
Small synchronous rubber or urethane belts can generate an electrical charge while operating in a drive. Elements such as humidity and working speed impact the potential of the charge. If determined to be a issue, rubber belts could be produced in a conductive building to dissipate the charge into the pulleys, and to floor. This prevents the accumulation of electric charges that might be harmful to material handling procedures or sensitive electronics. In addition, it significantly reduces the prospect of arcing or sparking in flammable environments. Urethane belts can’t be produced in a conductive structure.
RMA has outlined standards for conductive belts in their bulletin IP-3-3. Unless otherwise specified, a static conductive building for rubber belts is certainly available on a made-to-order basis. Unless normally specified, conductive belts will be built to yield a level of resistance of 300,000 ohms or much less, when new.
Nonconductive belt constructions are also available for rubber belts. These belts are generally built specifically to the clients conductivity requirements. They are usually used in applications where one shaft must be electrically isolated from the various other. It is necessary to note a static conductive belt cannot dissipate an electrical charge through plastic material pulleys. At least one metallic pulley in a drive is necessary for the charge to be dissipated to floor. A grounding brush or very similar device could also be used to dissipate electrical charges.
Urethane timing belts aren’t static conductive and cannot be built in a particular conductive construction. Unique conductive rubber belts ought to be used when the presence of an electrical charge is normally a concern.
9.6 OPERATING ENVIRONMENTS
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 complications to synchronous drives as long as the particles are great and dry. Particulate matter will, however, become an abrasive resulting in a higher level of belt and pulley wear. Damp or sticky particulate matter deposited and packed into pulley grooves can cause belt tension to increase considerably. This increased tension can impact shafting, bearings, and framework. Electrical costs within a drive system will often catch the attention of particulate matter.
Debris: Debris ought to be prevented from falling into any synchronous belt drive. Particles caught in the drive is normally either pressured through the belt or outcomes in stalling of the system. In any case, serious damage happens to the belt and related get hardware.
Water: Light and occasional contact with drinking water (occasional clean downs) shouldn’t seriously impact synchronous belts. Prolonged contact (constant spray or submersion) results in significantly reduced tensile strength in fiberglass belts, and potential length variation in aramid belts. Prolonged connection with water also causes rubber substances to swell, although less than with oil get in touch with. Internal belt adhesion systems are also gradually broken down with the presence of water. Additives to drinking water, such as lubricants, chlorine, anticorrosives, etc. can possess a far more detrimental effect on the belts than pure water. Urethane timing belts also have problems with water contamination. Polyester tensile cord shrinks significantly and experiences loss of tensile power in the presence of water. Aramid tensile cord maintains its power fairly well, but encounters length variation. Urethane swells more than neoprene in the existence of water. This swelling can increase belt tension significantly, causing belt and related equipment problems.
Oil: Light contact with oils on an occasional basis won’t generally harm synchronous belts. Prolonged connection with oil or lubricants, either straight or airborne, outcomes in considerably reduced belt service life. Lubricants cause the rubber compound to swell, breakdown inner adhesion systems, and decrease belt tensile strength. While alternate rubber compounds may provide some marginal improvement in durability, it is advisable 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 temps. Although the rubber components found in synchronous belts are compounded to withstand the effects of ozone, eventually chemical breakdown occurs plus they become hard and brittle and begin cracking. The amount of degradation is dependent upon the ozone focus and duration of publicity. For good overall performance 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: Contact with gamma radiation can be detrimental to the substances found in rubber and urethane synchronous belts. Radiation degrades belt materials much the same way extreme environmental temperature ranges do. The amount of degradation depends upon the strength of radiation and the exposure time. For good belt performance, the next exposure levels should not be exceeded:
Standard Construction: 108 rads
Nonm arking Construction: 104 rads
Conductive Construction: 106 rads
Low Temperatures Building: 104 rads
Dust Generation: Rubber synchronous belts are recognized to generate small quantities of good dust, as an all natural result of their procedure. The amount of dust is normally higher for brand-new belts, as they operate in. The period of time for run directly into occur is dependent upon the belt and pulley size, loading and speed. Factors such as for example pulley surface finish, operating speeds, set up tension, and alignment impact the amount of dust generated.
Clean Room: Rubber synchronous belts may not be ideal for use in clean room 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 working loads. Also, they cannot be produced in a static conductive building to permit electrical charges to dissipate.
Static Sensitive: Applications are occasionally delicate to the accumulation of static electric charges. Electrical fees can affect materials handling functions (like paper and plastic film transportation), and sensitive electronic equipment. Applications like these need a static conductive belt, to ensure that the static charges produced by the belt could be dissipated into the pulleys, and to ground. Regular rubber synchronous belts usually do not fulfill this requirement, but can be manufactured in a static conductive building on a made-to-order basis. Regular belt wear resulting from long term procedure or environmental contamination can influence belt conductivity properties.
In delicate applications, rubber synchronous belts are preferred over urethane belts since urethane belting can’t be stated in a conductive construction.
9.7 BELT TRACKING
Lateral tracking qualities of synchronous belts is a common area of inquiry. Although it is normal for a belt to favor one aspect of the pulleys while running, it is abnormal for a belt to exert significant pressure against a flange resulting in belt edge use and potential flange failure. Belt tracking is usually influenced by several factors. In order of significance, debate about these elements is as follows:
Tensile Cord Twist: Tensile cords are formed into a single twist configuration during their produce. Synchronous belts made out of only solitary twist tensile cords track laterally with a substantial drive. To neutralize this monitoring force, tensile cords are stated in correct- and left-hand twist (or “S” and “Z” twist) configurations. Belts made with “S” twist tensile cords monitor in the contrary direction to those constructed with “Z” twist cord. Belts made with alternating “S” and “Z” twist tensile cords monitor with minimal lateral force since the tracking characteristics of the two cords offset each other. 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 various other. When an application requires a belt to monitor in one specific direction just, a single twist Chain 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 tracking force. 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 linked to belt width. Wide belts have a tendency to track with an increase of force than narrow belts.
Pulley Diameter: Belts operating on little pulley diameters can have a tendency to generate higher monitoring forces than on large diameters. This is particularly accurate as the belt width methods the pulley size. Drives with pulley diameters less than the belt width are not generally suggested because belt tracking forces may become excessive.
Belt Length: Due to the way tensile cords are applied on to the belt molds, short belts can tend to exhibit higher tracking forces than long belts. The helix angle of the tensile cord reduces with increasing belt length.
Gravity: In drive applications with vertical shafts, gravity pulls the belt downward. The magnitude of the force is usually minimal with little pitch synchronous belts. Sag in 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 instead of operating in a consistent position. While not generally regarded as a significant concern, one explanation for this is definitely varying torque loads within the get. Synchronous belts sometimes track in a different way with changing loads. There are many potential known reasons for this; the primary cause relates to tensile cord distortion while under pressure against the pulleys. Variation in belt tensile loads can also cause adjustments in framework deflection, and angular shaft alignment, resulting in belt movement.
Belt Installation Tension: Belt tracking is sometimes influenced by the amount of belt installation pressure. The reasons 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 order that they are outlined. Generally, the principal problem will probably be recognized before moving completely through the list.
9.8 PULLEY FLANGES
Pulley information flanges are necessary to preserve 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 part of the pulleys when operating. Proper flange style is essential in stopping belt edge put on, minimizing noise and avoiding the belt from climbing from the pulley. Dimensional recommendations for custom-made or molded flanges are contained in tables coping with these problems. Proper flange placement is important to ensure that the belt is usually adequately restrained within its operating system. Because style and layout of little synchronous drives is indeed varied, the wide selection of flanging situations possibly encountered cannot easily be covered in a straightforward set of rules without acquiring exceptions. Despite this, the following broad flanging recommendations should help the designer generally:
Two Pulley Drives: On simple two pulley drives, either one pulley ought to be flanged about both sides, or each pulley ought to be flanged on reverse sides.
Multiple Pulley Drives: On multiple pulley (or serpentine) drives, either almost every other pulley ought to be flanged on both sides, or every single pulley should be flanged in alternating sides around the machine. Vertical Shaft Drives: On vertical shaft drives, at least one pulley should be flanged on both sides, and the remaining pulleys ought to be flanged on at least the bottom side.
Long Period Lengths: Flanging recommendations for little synchronous drives with long belt span lengths cannot easily be defined due to the many factors that may affect belt tracking characteristics. 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 brief spans. Because of this, it is generally smart to flange the pulleys on both sides.
Huge Pulleys: Flanging large pulleys could be costly. Designers frequently desire to leave huge pulleys unflanged to lessen price and space. Belts generally tend to need less lateral restraint on large pulleys than little and can frequently perform reliably without flanges. When deciding whether to flange, the prior guidelines should be considered. The groove face width of unflanged pulleys also needs to be higher than with flanged pulleys. See Table 27 for recommendations.
Idlers: Flanging of idlers is generally not necessary. Idlers designed to carry lateral part loads from belt tracking forces could be flanged if needed to offer lateral belt restraint. Idlers used for this function can be used 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 registration features of a synchronous belt drive, the system must first be decided to become either static or powerful in terms of its registration function and requirements.
Static Registration: A static registration system moves from its initial static position to a second static position. Through the process, the designer is concerned only with how accurately and consistently the drive finds its secondary placement. He/she is not concerned with any potential sign up errors that take place during transportation. Therefore, the primary factor adding to registration mistake in a static registration system is definitely backlash. The consequences of belt elongation and tooth deflection don’t have any influence on the sign up accuracy of this kind of system.
Dynamic Registration: A powerful registration system is required to perform a registering function while in motion with torque loads different as the system 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 one of the factors contributing to registration error is as follows:
Belt Elongation: Belt elongation, or stretch out, occurs naturally when a belt is positioned under tension. The total stress exerted within a belt results from installation, and also working 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 typical tensile cord used in rubber synchronous belts can be fiberglass. Fiberglass includes a high tensile modulus, is dimensionally steady, and has exceptional flex-fatigue characteristics. If a higher tensile modulus is necessary, aramid tensile cords can be viewed as, although they are usually used to provide resistance to severe shock and impulse loads. Aramid tensile cords used in little synchronous belts generally have only a marginally higher tensile modulus compared to fiberglass. When required, belt tensile modulus data is certainly available 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 permit the belt teeth to enter and exit the grooves easily 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 holding capability and resist ratcheting, but have a significant quantity of backlash. PowerGrip GT2 Drives have even further improved torque transporting capability, and also have as little or less backlash than trapezoidal timing belt drives. In special cases, alterations could be made to travel systems to help expand decrease backlash. These alterations typically result in increased belt wear, increased get noise and shorter drive life. Contact our Software Engineering Division for additional information.
Tooth Deflection: Tooth deformation in a synchronous belt drive occurs as a torque load is put on the machine, and individual belt teeth are loaded. The quantity of belt tooth deformation depends upon the quantity of torque loading, pulley size, installation stress and belt type. Of the three principal contributors to registration error, tooth deflection is the most challenging to quantify. Experimentation with a prototype get system is the best means of obtaining realistic estimations of belt tooth deflection.
Additional guidelines which may be useful in designing registration crucial drive systems are the following:
Select PowerGrip GT2 or trapezoidal timing belts.
Design with large pulleys with more tooth in mesh.
Keep belts limited, and control pressure closely.
Design framework/shafting to end up being rigid under load.
Use top quality machined pulleys to minimize radial runout and lateral wobble.