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 be made with ample reserve horsepower capacity. Usage of overload program factors is essential. Belts should 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, should be used.
The pulley size shouldn’t 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 may cause breakage of the fibers.
To be able to deliver the rated hp, a belt must have six or even more tooth in mesh with the grooves of the smaller pulley. The amount 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 a fraction of the belt break strength.
Due to a slight aspect thrust of synchronous belts in motion, at least one pulley in the drive should be flanged. When the center distance between your shafts is 8 or even more times the diameter of small pulley, or when the drive is operating on vertical shafts, both pulleys ought to be flanged.
Belt surface speed should not exceed 5500 ft 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 acceleration of 6500 feet each and every minute (33 m/s) can be permitted, whereas for GT2 belts, the maximum permitted swiftness is 7500 feet each and every minute (38 m/s). The utmost allowable operating rate for T series is normally 4000 feet per 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 effectiveness of a synchronous belt drive is definitely greater than 95%.
Belt drives are often a way to obtain noise. The frequency of the sound level raises proportionally with the belt acceleration. The higher the initial belt stress, the higher the sound level. The belt teeth entering the pulleys at high acceleration become a compressor which creates sound. Some noise is the result of a belt rubbing against the flange, which in turn may be the result of the shafts not really being parallel. As shown 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 make sure absolutely uniform belt thickness.
For a few applications, no backlash between the driving and the driven shaft is permitted. For these cases, special profile pulleys could be produced without any clearance between the belt tooth and pulley. This might shorten the belt existence, but it eliminates backlash. Number 10 displays the superiority of PowerGrip GT2 profile so far as reduced amount of backlash can be involved.
Synchronous belts tend to be powered by stepping motors. These drives are put through continuous and large accelerations and decelerations. If the belt reinforcing fibers, i.e., tension member, and also the belt material, possess high tensile strength no elongation, the belt will not be instrumental in absorbing the shock loads. This will lead to sheared belt teeth. Therefore, consider this into consideration when how big is the tiniest pulley and the materials for the belt and pressure member are chosen.
The decision of the pulley materials (metal vs. plastic) is usually a matter of cost, desired accuracy, inertia, color, magnetic properties and, most importantly, personal preference predicated on experiences. Plastic pulleys with metal inserts or steel hubs represent an excellent compromise.
The following precautions should be taken when installing all timing belt drives:
Timing belt installation ought to be a snug fit, neither too limited nor too loose. The positive hold of the belt eliminates the necessity for high initial tension. As a result, a belt, when set up with a snug match (that’s, not too taut) assures much longer life, less bearing use and quieter procedure. Preloading (usually the cause of premature failure) isn’t required. When torque is definitely unusually high, a loose belt may “leap tooth” on starting. When this happens, the tension ought to be increased gradually, until satisfactory operation is attained. An excellent guideline for installation tension is as proven in Figure 20, and the corresponding tensioning force is proven in Table 9, both shown in SECTION 10 BELT TENSIONING. For widths apart from shown, increase power proportionally to the belt width. Instrumentation for calculating belt pressure is available. Consult the merchandise portion of this catalog.
Be sure that shafts are parallel and pulleys are in alignment. On an extended center drive, it is sometimes advisable to offset the driven pulley to pay for the inclination of the belt to run against one flange.
On a long center drive, it really is imperative that the belt sag is not large enough allowing teeth on the slack aspect to engage one’s teeth on the tight side.
It is important that the frame supporting the pulleys be rigid all the time. A nonrigid body causes variation in middle length and resulting belt slackness. This, subsequently, can result in jumping of teeth – specifically under starting 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 utilized except for power takeoff or functional make use of. When an idler is essential, it must be on the slack side of the belt. Inside idlers should be grooved, unless their diameters are higher than an comparative 40-groove pulley. Flat idlers must not be crowned (use advantage flanges). Idler diameters must exceed the tiniest diameter get pulley. Idler arc of contact should be kept to the very least.
As well as the general guidelines enumerated previously, particular operating features of the get must be taken into account.