General Guide Lines
There are some general guidelines which can be applied to all timing belts, including miniature and double-sided belts:
Drives should always be made with ample reserve hp capacity. Use of overload services factors is important. Belts should be rated of them costing only 1/15th of their particular ultimate strength.
For MXL pitch belts, the tiniest recommended pulley will have 10 teeth. For other pitches, Table 8, should 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 tough handling, since this may cause breakage of the fibers.
In order to deliver the rated horsepower, a belt must have six or even more tooth in mesh with the grooves of small pulley. The amount of teeth in mesh may be acquired by formula given in SECTION 24 TIMING BELT DRIVE SELECTION PROCEDURE. The shear strength of an individual tooth is only a fraction of the belt break strength.
Because of a slight aspect thrust of synchronous belts in movement, at least 1 pulley in the travel should be flanged. When the center distance between your shafts is 8 or more times the size of the smaller pulley, or when the travel is operating on vertical shafts, both pulleys should be flanged.
Belt surface velocity shouldn’t exceed 5500 feet each and every minute (28 m/s) for larger pitch belts and 10000 feet each and every minute (50 m/s) for minipitch belts. For the HTD belts, a swiftness of 6500 ft each and every minute (33 m/s) is usually permitted, whereas for GT2 belts, the maximum permitted acceleration is 7500 ft each and every minute (38 m/s). The maximum allowable operating velocity for T series is certainly 4000 feet each and every minute (20 m/s).
Belts are, in general, rated to yield at the least 3000 hours of useful lifestyle if all instructions are properly followed.
Belt drives are inherently efficient. It could be assumed that the effectiveness of a synchronous belt drive is definitely greater 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 initial belt tension, the higher the noise level. The belt teeth entering the pulleys at high velocity become a compressor and this creates sound. Some noise may be the result of a belt rubbing against the flange, which in turn could be the result of the shafts not becoming parallel. As proven in Figure 9, the noise level is substantially reduced if the PowerGrip GT2 belt is being used.
If the drive is component of a sensitive acoustical or consumer electronics sensing or recording device, it is recommended that the trunk surfaces of the belt be ground to make sure absolutely uniform belt thickness.
For some applications, no backlash between the driving and the driven shaft is permitted. For these situations, special profile pulleys can be produced without any clearance between the belt tooth and pulley. This might shorten the belt existence, but it eliminates backlash. Body 10 displays the superiority of PowerGrip GT2 profile as far as reduced amount of backlash is concerned.
Synchronous belts are often powered by stepping motors. These drives are put through continuous and huge accelerations and decelerations. If the belt reinforcing fiber, i.e., pressure member, as well as the belt materials, have high tensile power no elongation, the belt will not be instrumental in absorbing the shock loads. This will result in sheared belt teeth. Therefore, consider this into consideration when how big is the tiniest pulley and the components for the belt and pressure member are selected.
The choice of the pulley material (metal vs. plastic material) is usually a matter of cost, desired accuracy, inertia, color, magnetic properties and, most importantly, personal preference predicated on experiences. Plastic pulleys with metallic inserts or metal hubs represent an excellent compromise.
The next 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 grip of the belt eliminates the necessity for high preliminary tension. As a result, a belt, when installed with a snug suit (that is, not too taut) assures much longer life, less bearing use and quieter operation. Preloading (often the reason behind premature failure) isn’t required. When torque can be unusually high, a loose belt may “leap tooth” on starting. In such a case, the tension ought to be increased gradually, until satisfactory operation is attained. A good rule of thumb for installation pressure is as proven in Figure 20, and the corresponding tensioning pressure is shown 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 pressure is obtainable. Consult the product portion of this catalog.
Be sure that shafts are parallel and pulleys are in alignment. On a long center get, it really is sometimes advisable to offset the powered pulley to compensate for the inclination of the belt to perform against one flange.
On an extended center travel, it really is imperative that the belt sag isn’t large enough allowing tooth on the slack side to engage one’s teeth on the tight part.
It is necessary that the framework supporting the pulleys be rigid at all times. A nonrigid body causes variation in middle distance and resulting belt slackness. This, subsequently, can result in jumping of teeth – especially under beginning load with shaft misalignment.
Although belt tension requires little attention after preliminary installation, provision ought to be made for some center distance adjustment for ease in installing and removing belts. Do not force belt over flange of pulley.
Idlers, either of the within or outdoors type, aren’t recommended and really should not be used aside from power takeoff or functional use. When an idler is essential, it should be on the slack side of the belt. Inside idlers should be grooved, unless their diameters are greater than an comparative 40-groove pulley. Flat idlers must not be crowned (use edge flanges). Idler diameters must surpass the tiniest diameter drive pulley. Idler arc of contact ought to be held to a minimum.
As well as the general suggestions enumerated previously, specific operating characteristics of the drive must be taken into account.