General Guide Lines
There are several general guidelines which are applicable to all or any timing belts, including miniature and double-sided belts:
Drives should always be designed with ample reserve hp capacity. Usage of overload assistance factors is important. Belts should be rated at 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, should be used.
The pulley diameter shouldn’t be smaller compared to the width of the belt.
Belts with Fibrex-glass fiber tension members should not be subjected to sharp bends or tough handling, since this could cause breakage of the fibers.
To be able to deliver the rated hp, a belt must have six or even more teeth in mesh with the grooves of the smaller pulley. The number of teeth in mesh may be obtained by formula given in SECTION 24 TIMING BELT DRIVE SELECTION PROCEDURE. The shear power of an individual tooth is only a fraction of the belt break power.
Due to a slight part thrust of synchronous belts in movement, at least 1 pulley in the get must be flanged. When the center distance between the shafts is 8 or more times the diameter of the smaller pulley, or when the drive is working on vertical shafts, both pulleys should be flanged.
Belt surface acceleration shouldn’t exceed 5500 foot 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 acceleration of 6500 foot each and every minute (33 m/s) is usually permitted, whereas for GT2 belts, the utmost permitted acceleration is 7500 foot per minute (38 m/s). The utmost allowable operating quickness for T series is 4000 feet each and every minute (20 m/s).
Belts are, generally, rated to yield a minimum of 3000 hours of useful existence if all instructions are properly followed.
Belt drives are inherently efficient. It can be assumed that the efficiency of a synchronous belt drive is greater than 95%.
Belt drives are often a source of noise. The frequency of the noise level raises proportionally with the belt rate. The higher the initial belt stress, the greater the sound level. The belt tooth entering the pulleys at high acceleration act as a compressor which creates sound. 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 substantially reduced if the PowerGrip GT2 belt is being used.
If the drive is part 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 your driving and the driven shaft is permitted. For these instances, special profile pulleys can be produced without any clearance between your belt tooth and pulley. This may shorten the belt lifestyle, but it eliminates backlash. Physique 10 displays the superiority of PowerGrip GT2 profile so far as reduced amount of backlash is concerned.
Synchronous belts are often driven by stepping motors. These drives are put through continuous and large accelerations and decelerations. If the belt reinforcing dietary fiber, i.e., stress member, as well as the belt material, have got high tensile power no elongation, the belt will never 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 materials for the belt and pressure member are chosen.
The decision of the pulley materials (metal vs. plastic material) is a matter of price, desired precision, inertia, color, magnetic properties and, most importantly, personal preference predicated on experiences. Plastic material pulleys with metal inserts or metallic hubs represent an excellent compromise.
PRECAUTIONS
The next precautions should be taken when installing all timing belt drives:
Timing belt set up ought to be a snug in shape, neither too tight nor too loose. The positive grasp of the belt eliminates the need for high initial tension. Therefore, a belt, when installed with a snug suit (that is, not as well taut) assures longer life, much less bearing use and quieter procedure. Preloading (usually the reason behind premature failure) is not required. When torque is usually unusually high, a loose belt may “jump teeth” on starting. In such a case, the tension ought to be increased steadily, until satisfactory operation is attained. A good rule of thumb for installation stress is as demonstrated in Figure 20, and the corresponding tensioning force is shown in Table 9, both proven in SECTION 10 BELT TENSIONING. For widths other than shown, increase pressure proportionally to the belt width. Instrumentation for measuring belt tension is obtainable. Consult the product section of this catalog.
Be sure that shafts are parallel and pulleys are in alignment. On a long center travel, it really is sometimes recommended to offset the driven pulley to pay for the inclination 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 side to engage one’s teeth on the tight aspect.
It is important that the body supporting the pulleys be rigid all the time. A nonrigid frame causes variation in center length and resul
ting belt slackness. This, in turn, can result in jumping of tooth – especially under starting load with shaft misalignment.
Although belt tension requires small attention after initial installation, provision should be made for some middle distance adjustment for ease in installing and removing belts. Usually do not pressure belt over flange of pulley.
Idlers, either of the within or outside type, aren’t recommended and should not be utilized except for power takeoff or functional use. When an idler is necessary, it should be on the slack part of the belt. Inside idlers should be grooved, unless their diameters are higher than an equivalent 40-groove pulley. Flat idlers must not be crowned (use edge flanges). Idler diameters must surpass the smallest diameter get pulley. Idler arc of contact should be kept to a minimum.
In addition to the general recommendations enumerated previously, particular operating features of the drive must be taken into account.
