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 horsepower capacity. Usage of overload services factors is essential. 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 size shouldn’t be smaller than the width of the belt.
Belts with Fibrex-glass fiber tension members should not be put through sharp bends or tough handling, since this could trigger breakage of the fibers.
In order to deliver the rated horsepower, a belt will need to have six or more tooth in mesh with the grooves of small pulley. The amount of tooth in mesh may be obtained by formula given in SECTION 24 TIMING BELT DRIVE SELECTION PROCEDURE. The shear power of a single tooth is only a fraction of the belt break strength.
Due to a slight part thrust of synchronous belts in motion, at least a single pulley in the drive must be flanged. When the guts distance between the shafts is 8 or more times the size of the smaller pulley, or when the travel is working on vertical shafts, both pulleys ought to be flanged.
Belt surface rate shouldn’t 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 per minute (33 m/s) can be permitted, whereas for GT2 belts, the maximum permitted rate is 7500 foot per minute (38 m/s). The utmost allowable operating rate for T series is normally 4000 feet each and every minute (20 m/s).
Belts are, in general, rated to yield at the least 3000 hours of useful life if all guidelines are properly followed.
Belt drives are inherently efficient. It could be assumed that the efficiency of a synchronous belt drive is definitely higher than 95%.
Belt drives are usually a way to obtain noise. The frequency of the sound level raises proportionally with the belt speed. The higher the initial belt stress, the greater the noise level. The belt teeth entering the pulleys at high speed become a compressor which creates sound. Some noise may be the consequence of a belt rubbing against the flange, which in turn could be the consequence of the shafts not becoming parallel. As demonstrated in Figure 9, the sound level is considerably decreased if the PowerGrip GT2 belt has been used.
If the drive is part of a sensitive acoustical or consumer electronics sensing or recording device, it is recommended 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 situations, special profile pulleys can be produced without any clearance between your belt tooth and pulley. This might shorten the belt existence, but it eliminates backlash. Amount 10 shows the superiority of PowerGrip GT2 profile as far as reduced amount of backlash is concerned.
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., stress member, and also the belt material, have got high tensile strength no elongation, the belt will not be instrumental in absorbing the shock loads. This will result in sheared belt teeth. Therefore, take this into consideration when the size of the smallest pulley and the materials for the belt and pressure member are chosen.
The decision of the pulley material (metal vs. plastic) is normally a matter of price, desired precision, inertia, color, magnetic properties and, most importantly, personal preference based on experiences. Plastic pulleys with steel inserts or steel hubs represent an excellent compromise.
The following precautions ought to be taken when installing all timing belt drives:
Timing belt set up should be a snug fit, neither too restricted nor too loose. The positive grasp of the belt eliminates the need for high preliminary tension. Therefore, a belt, when set up with a snug fit (that’s, not too taut) assures longer life, less bearing use and quieter operation. Preloading (often the reason behind premature failure) is not necessary. When torque is 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 proven in Figure 20, and the corresponding tensioning force is shown in Table 9, both shown in SECTION 10 BELT TENSIONING. For widths apart from shown, increase drive proportionally to the belt width. Instrumentation for measuring belt tension is obtainable. Consult the product section of this catalog.
Make sure that shafts are parallel and pulleys are in alignment. On an extended center get, it is sometimes advisable to offset the powered pulley to pay for the inclination of the belt to run against one flange.
On an extended center travel, it really is imperative that the belt sag is not large enough to permit tooth on the slack aspect to engage one’s teeth on the tight part.
It is important that the frame supporting the pulleys be rigid at all times. A nonrigid framework causes variation in center length and resulting belt slackness. This, in turn, can result in jumping of teeth – specifically under starting load with shaft misalignment.
Although belt tension requires little attention after initial installation, provision should be designed for some center distance adjustment for ease in installing and removing belts. Usually do not push belt over flange of pulley.
Idlers, either of the inside or outside type, aren’t recommended and should not be used except for power takeoff or functional make use of. When an idler is necessary, 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 go beyond the smallest diameter get pulley. Idler arc of contact should be kept to a minimum.
In addition to the general guidelines enumerated previously, particular operating characteristics of the get must be taken into account.