General Guide Lines
There are some general guidelines which are applicable to all timing belts, including miniature and double-sided belts:
Drives should be designed with ample reserve hp capacity. Use of overload provider factors is important. Belts should be rated at only 1/15th of their respective ultimate strength.
For MXL pitch belts, the tiniest recommended pulley will have 10 teeth. For various 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 pressure members should not be put through sharp bends or tough handling, since this could cause breakage of the fibers.
In order to deliver the rated hp, a belt must have six or even more teeth in mesh with the grooves of the smaller pulley. The amount of teeth in mesh may be obtained by formula provided in SECTION 24 TIMING BELT DRIVE SELECTION PROCEDURE. The shear strength of a single tooth is only a fraction of the belt break power.
Due to a slight aspect thrust of synchronous belts in motion, at least a single pulley in the get should be flanged. When the center distance between the shafts is 8 or more times the size of small pulley, or when the drive is operating on vertical shafts, both pulleys should be flanged.
Belt surface swiftness should not exceed 5500 ft 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 quickness of 6500 ft each and every minute (33 m/s) can be permitted, whereas for GT2 belts, the utmost permitted swiftness is 7500 ft per minute (38 m/s). The maximum allowable operating speed for T series is usually 4000 feet per minute (20 m/s).
Belts are, generally, rated to yield at the least 3000 hours of useful lifestyle if all guidelines are properly followed.
Belt drives are inherently efficient. It can be assumed that the efficiency of a synchronous belt drive is higher than 95%.
Belt drives are often a way to obtain noise. The regularity of the noise level raises proportionally with the belt quickness. The higher the initial belt pressure, the higher the noise level. The belt teeth entering the pulleys at high swiftness act as a compressor and this creates sound. Some noise is the consequence of a belt rubbing against the flange, which in turn may be the consequence of the shafts not getting parallel. As demonstrated in Figure 9, the sound level is considerably reduced if the PowerGrip GT2 belt has been used.
If the drive is part of a sensitive acoustical or electronics sensing or recording device, it is suggested that the back areas 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 cases, special profile pulleys could be produced with no clearance between the belt tooth and pulley. This may shorten the belt lifestyle, but it eliminates backlash. Physique 10 shows the superiority of PowerGrip GT2 profile as far as reduced amount of backlash can be involved.
Synchronous belts tend to be motivated by stepping motors. These drives are subjected to continuous and large accelerations and decelerations. If the belt reinforcing dietary fiber, i.e., stress member, as well as the belt materials, possess high tensile power no elongation, the belt will not be instrumental in absorbing the shock loads. This will lead to sheared belt teeth. Therefore, consider this into account when the size of the tiniest pulley and the components for the belt and tension member are chosen.
The decision of the pulley material (metal vs. plastic) is certainly a matter of price, desired accuracy, inertia, color, magnetic properties and, most importantly, personal preference based on experiences. Plastic pulleys with metallic inserts or steel hubs represent a good compromise.
The next precautions should be taken when installing all timing belt drives:
Timing belt set up should be a snug in shape, neither too restricted 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 is, not too taut) assures longer life, much less bearing wear and quieter operation. Preloading (often the cause of premature failure) isn’t required. When torque is definitely 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 tension is as proven in Figure 20, and the corresponding tensioning force is proven in Table 9, both proven in SECTION 10 BELT TENSIONING. For widths other than shown, increase pressure proportionally to the belt width. Instrumentation for calculating belt stress is available. Consult the merchandise section of this catalog.
Make sure that shafts are parallel and pulleys are in alignment. On a long center get, it really is sometimes advisable to offset the driven pulley to pay for the tendency of the belt to run against one flange.
On an extended center drive, it is imperative that the belt sag is not large enough to permit tooth on the slack aspect to engage the teeth on the tight part.
It is necessary that the frame supporting the pulleys be rigid all the time. A nonrigid frame causes variation in middle distance and resulting belt slackness. This, in turn, can lead to jumping of teeth – specifically under starting load with shaft misalignment.
Although belt tension requires little attention after preliminary installation, provision should be designed for some middle distance adjustment for ease in installing and removing belts. Usually do not drive belt over flange of pulley.
Idlers, either of the inside or outside type, aren’t recommended and really should not be utilized except for power takeoff or functional make use of. When an idler is necessary, it must be on the slack part of the belt. Inside idlers must be grooved, unless their diameters are higher than an equivalent 40-groove pulley. Flat idlers should not be crowned (use edge flanges). Idler diameters must exceed the smallest diameter drive pulley. Idler arc of contact should be held to the very least.
In addition to the general suggestions enumerated previously, specific operating features of the drive must be taken into account.