General Guide Lines
There are several general guidelines which can be applied to all or any timing belts, including miniature and double-sided belts:
Drives should always be made with ample reserve horsepower capacity. Use of overload provider factors is important. Belts ought to be rated of them costing only 1/15th of their respective ultimate strength.
For MXL pitch belts, the tiniest recommended pulley will have 10 teeth. For additional pitches, Table 8, ought to be used.
The pulley diameter should never be smaller compared to the width of the belt.
Belts with Fibrex-glass fiber tension members should not be subjected to sharp bends or rough handling, since this may trigger breakage of the fibers.
To be able to deliver the rated hp, a belt must have six or more tooth in mesh with the grooves of small pulley. The number of tooth in mesh could be attained by formula provided in SECTION 24 TIMING BELT DRIVE SELECTION PROCEDURE. The shear strength of an individual tooth is only a fraction of the belt break power.
Because of a slight side thrust of synchronous belts in movement, at least a single pulley in the drive should be flanged. When the guts distance between the shafts is 8 or more times the size of the smaller pulley, or when the travel is working on vertical shafts, both pulleys should be flanged.
Belt surface velocity should not exceed 5500 feet per minute (28 m/s) for bigger pitch belts and 10000 feet per minute (50 m/s) for minipitch belts. For the HTD belts, a swiftness of 6500 feet each and every minute (33 m/s) is permitted, whereas for GT2 belts, the utmost permitted velocity is 7500 foot per minute (38 m/s). The maximum allowable operating velocity for T series is definitely 4000 feet per minute (20 m/s).
Belts are, generally, rated to yield at the least 3000 hours of useful life if all instructions are properly followed.
Belt drives are inherently efficient. It can be assumed that the effectiveness of a synchronous belt drive is normally higher than 95%.
Belt drives are usually a source of noise. The frequency of the noise level raises proportionally with the belt swiftness. The higher the original belt tension, the greater the noise level. The belt teeth entering the pulleys at high speed become a compressor which creates noise. Some noise is the consequence of a belt rubbing against the flange, which may be the result of the shafts not getting parallel. As demonstrated in Figure 9, the sound level is considerably reduced if the PowerGrip GT2 belt is being used.
If the drive is component of a sensitive acoustical or electronics sensing or recording device, it is recommended that the trunk surfaces of the belt be ground to assure absolutely uniform belt thickness.
For some applications, no backlash between the driving and the driven shaft is permitted. For these situations, special profile pulleys could be produced without any clearance between your belt tooth and pulley. This might shorten the belt life, nonetheless it eliminates backlash. Physique 10 displays the superiority of PowerGrip GT2 profile as far as reduction of backlash is concerned.
Synchronous belts are often motivated by stepping motors. These drives are subjected to continuous and large accelerations and decelerations. If the belt reinforcing fibers, i.e., pressure member, along with the belt materials, possess high tensile power and no elongation, the belt will not be instrumental in absorbing the shock loads. This will lead to sheared belt tooth. Therefore, consider this into account when how big is the smallest pulley and the components for the belt and pressure member are chosen.
The decision of the pulley material (metal vs. plastic material) is definitely a matter of price, desired precision, inertia, color, magnetic properties and, above all, personal preference based on experiences. Plastic pulleys with steel inserts or metal hubs represent an excellent compromise.
The following precautions ought to be taken when installing all timing belt drives:
Timing belt installation should be a snug fit, neither too tight nor too loose. The positive grasp of the belt eliminates the need for high preliminary tension. As a result, a belt, when installed with a snug fit (that’s, not too taut) assures longer life, much less bearing use and quieter operation. Preloading (often the cause of premature failure) isn’t necessary. When torque is normally unusually high, a loose belt may “jump teeth” on starting. In such a case, the tension should be increased gradually, until satisfactory operation is attained. An excellent rule of thumb for installation pressure is as shown in Figure 20, and the corresponding tensioning power is demonstrated in Table 9, both proven in SECTION 10 BELT TENSIONING. For widths other than shown, increase drive proportionally to the belt width. Instrumentation for calculating belt stress is available. Consult the product section of this catalog.
Make sure that shafts are parallel and pulleys are in alignment. On an extended center drive, it is sometimes advisable to offset the powered pulley to compensate for the tendency of the belt to perform against one flange.
On a long center drive, it really is imperative that the belt sag is not large enough allowing tooth on the slack part to engage one’s teeth on the tight part.
It is important that the framework supporting the pulleys be rigid at all times. A nonrigid frame causes variation in center range and resulting belt slackness. This, subsequently, can result in jumping of tooth – especially under starting load with shaft misalignment.
Although belt tension requires little attention after preliminary installation, provision ought to be designed for some middle distance adjustment for ease in installing and removing belts. Usually do not push belt over flange of pulley.
Idlers, either of the within or outside type, are not recommended and really should not be used except for power takeoff or functional make use of. When an idler is necessary, it should be on the slack aspect of the belt. Inside idlers must be grooved, unless their diameters are higher than an equivalent 40-groove pulley. Flat idlers must not be crowned (use advantage flanges). Idler diameters must surpass the tiniest diameter travel pulley. Idler arc of contact ought to be kept to a minimum.
As well as the general guidelines enumerated previously, specific operating features of the drive must be considered.