General Guide Lines
There are several general guidelines which can be applied to all timing belts, including miniature and double-sided belts:
Drives should always be made with ample reserve horsepower capacity. Use of overload assistance 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 could have 10 teeth. For various other pitches, Table 8, ought to be used.
The pulley size 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.
To be able to deliver the rated horsepower, a belt must have six or more tooth in mesh with the grooves of the smaller pulley. The number of tooth in mesh may be obtained by formula provided in SECTION 24 TIMING BELT DRIVE SELECTION PROCEDURE. The shear power of an individual tooth is a fraction of the belt break strength.
Because of a slight part thrust of synchronous belts in motion, at least 1 pulley in the drive should be flanged. When the guts distance between the shafts is 8 or even more times the size of small pulley, or when the drive is operating on vertical shafts, both pulleys ought to be flanged.
Belt surface velocity should not exceed 5500 ft per minute (28 m/s) for bigger pitch belts and 10000 feet per minute (50 m/s) for minipitch belts. For the HTD belts, a speed of 6500 ft each and every minute (33 m/s) is certainly permitted, whereas for GT2 belts, the maximum permitted swiftness is 7500 ft each and every minute (38 m/s). The maximum allowable operating rate for T series is certainly 4000 feet each and every minute (20 m/s).
Belts are, generally, rated to yield a minimum of 3000 hours of useful life if all instructions 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 usually a way to obtain noise. The frequency of the sound level increases proportionally with the belt velocity. The higher the initial belt tension, the higher the noise level. The belt tooth entering the pulleys at high rate act as a compressor and this creates sound. Some noise is the result of a belt rubbing against the flange, which in turn could be the result of the shafts not being parallel. As proven in Figure 9, the noise level is considerably decreased if the PowerGrip GT2 belt is being used.
If the drive is component of a sensitive acoustical or electronics sensing or recording device, it is suggested that the back areas of the belt be ground to assure absolutely uniform belt thickness.
For some applications, no backlash between the driving and the driven shaft is permitted. For these instances, special profile pulleys can be produced with no clearance between the belt tooth and pulley. This might shorten the belt lifestyle, nonetheless it eliminates backlash. Figure 10 shows the superiority of PowerGrip GT2 profile as far as reduced amount of backlash can be involved.
Synchronous belts are often driven by stepping motors. These drives are subjected to continuous and huge accelerations and decelerations. If the belt reinforcing fibers, i.e., tension member, and also the belt material, have got high tensile power and 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 the size of the smallest pulley and the components for the belt and tension member are selected.
The choice of the pulley materials (metal vs. plastic material) is definitely a matter of cost, desired precision, inertia, color, magnetic properties and, above all, personal preference predicated on experiences. Plastic pulleys with metallic inserts or steel hubs represent a good compromise.
The following precautions ought to be taken when installing all timing belt drives:
Timing belt set up should be a snug in shape, neither too limited nor too loose. The positive grip of the belt eliminates the necessity for high initial tension. Consequently, a belt, when set up with a snug fit (that’s, not too taut) assures longer life, much less bearing put on and quieter procedure. Preloading (often the reason behind premature failure) isn’t necessary. When torque can be unusually high, a loose belt may “jump tooth” on starting. When this happens, the tension should be increased gradually, until satisfactory procedure is attained. A good guideline for installation tension is as demonstrated in Figure 20, and the corresponding tensioning push is proven in Table 9, both shown in SECTION 10 BELT TENSIONING. For widths apart from shown, increase force proportionally to the belt width. Instrumentation for measuring belt tension is available. Consult the merchandise portion of this catalog.
Make sure that shafts are parallel and pulleys are in alignment. On an extended center get, it is sometimes recommended to offset the powered pulley to compensate for the tendency of the belt to run against one flange.
On an extended center get, it really is imperative that the belt sag isn’t large enough to permit tooth on the slack part to engage the teeth on the tight aspect.
It is necessary that the frame supporting the pulleys be rigid all the time. A nonrigid body causes variation in center 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 initial installation, provision ought to be made for some middle distance adjustment for ease in installing and removing belts. Do not power belt over flange of pulley.
Idlers, either of the inside 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 must 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 exceed the smallest diameter get pulley. Idler arc of contact ought to be held to a minimum.
As well as the general guidelines enumerated previously, specific operating features of the travel must be taken into account.