General Guide Lines
There are several general guidelines which are applicable to all timing belts, including miniature and double-sided belts:
Drives should be designed with ample reserve hp capacity. Usage of overload support factors is essential. Belts should be rated of them costing only 1/15th of their respective ultimate strength.
For MXL pitch belts, the smallest recommended pulley could have 10 teeth. For other 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 stress members should not be put through sharp bends or rough handling, since this may trigger breakage of the fibers.
To be able to deliver the rated horsepower, a belt must have six or more teeth in mesh with the grooves of small pulley. The amount of tooth in mesh may be obtained by formula given in SECTION 24 TIMING BELT DRIVE SELECTION PROCEDURE. The shear strength of a single tooth is a fraction of the belt break power.
Because of a slight aspect thrust of synchronous belts in movement, at least a single pulley in the drive must be flanged. When the center distance between the shafts is 8 or even more times the size of small pulley, or when the travel is operating on vertical shafts, both pulleys should be flanged.
Belt surface acceleration should not exceed 5500 feet each and every minute (28 m/s) for larger pitch belts and 10000 feet per minute (50 m/s) for minipitch belts. For the HTD belts, a rate of 6500 foot each and every minute (33 m/s) is definitely permitted, whereas for GT2 belts, the utmost permitted swiftness is 7500 ft each and every minute (38 m/s). The maximum allowable operating swiftness for T series is 4000 feet each and every minute (20 m/s).
Belts are, in general, rated to yield a minimum of 3000 hours of useful life if all guidelines are properly followed.
Belt drives are inherently efficient. It can be assumed that the performance of a synchronous belt drive is definitely higher than 95%.
Belt drives are often a way to obtain noise. The regularity of the noise level raises proportionally with the belt acceleration. The higher the original belt stress, the greater the noise level. The belt tooth entering the pulleys at high swiftness act as a compressor which creates sound. Some noise is the consequence of a belt rubbing against the flange, which in turn may be the result of the shafts not becoming parallel. As shown in Figure 9, the noise level is substantially decreased if the PowerGrip GT2 belt is being used.
If the drive is part of a sensitive acoustical or consumer electronics sensing or recording device, it is recommended that the back surfaces of the belt be ground to make sure absolutely uniform belt thickness.
For some applications, no backlash between your driving and the driven shaft is permitted. For these situations, special profile pulleys can be produced without any clearance between your belt tooth and pulley. This may shorten the belt life, nonetheless it eliminates backlash. Body 10 shows the superiority of PowerGrip GT2 profile as far as reduction of backlash is concerned.
Synchronous belts tend to be motivated by stepping motors. These drives are subjected to continuous and huge accelerations and decelerations. If the belt reinforcing fiber, i.e., pressure member, as well as the belt material, have got high tensile strength and no elongation, the belt will not be instrumental in absorbing the shock loads. This will lead to sheared belt tooth. Therefore, take this into consideration when how big is the smallest pulley and the components for the belt and tension member are selected.
The decision of the pulley materials (metal vs. plastic material) is a matter of cost, desired precision, inertia, color, magnetic properties and, most importantly, personal preference based on experiences. Plastic material pulleys with steel inserts or metal hubs represent a good compromise.
The following precautions ought to be taken when installing all timing belt drives:
Timing belt set up ought to be a snug in shape, neither too restricted nor too loose. The positive hold of the belt eliminates the need for high initial tension. Consequently, a belt, when set up with a snug fit (that’s, not as well taut) assures much longer life, much less bearing wear and quieter procedure. Preloading (often the reason behind premature failure) isn’t required. When torque is normally unusually high, a loose belt may “leap tooth” on starting. When this happens, the tension should be increased steadily, until satisfactory procedure is attained. An excellent rule of thumb for installation stress is as shown in Figure 20, and the corresponding tensioning push is proven in Table 9, both demonstrated in SECTION 10 BELT TENSIONING. For widths apart from shown, increase push proportionally to the belt width. Instrumentation for measuring belt stress is obtainable. Consult the merchandise portion of this catalog.
Make sure that shafts are parallel and pulleys are in alignment. On an extended center drive, it really is sometimes advisable to offset the driven pulley to compensate for the tendency of the belt to perform against one flange.
On an extended center drive, it is imperative that the belt sag is not large enough allowing tooth on the slack side to engage the teeth on the tight aspect.
It is important that the framework supporting the pulleys be rigid at all times. A nonrigid frame causes variation in middle length and resulting belt slackness. This, in turn, can result in jumping of teeth – specifically under beginning load with shaft misalignment.
Although belt tension requires small attention after initial installation, provision ought to be designed for some middle distance adjustment for ease in installing and removing belts. Usually do not force belt over flange of pulley.
Idlers, either of the within or outside type, aren’t recommended and really should not be used aside from power takeoff or functional make use of. When an idler is necessary, it must be on the slack aspect of the belt. Inside idlers must be grooved, unless their diameters are greater than an comparative 40-groove pulley. Flat idlers must not be crowned (use advantage flanges). Idler diameters must surpass the smallest diameter travel pulley. Idler arc of contact should be held to the very least.
In addition to the general suggestions enumerated previously, particular operating characteristics of the get must be taken into account.