Pubdate：04-20-2022 Views：3691
The belt can be trained with the troughing idlers in two ways. Shifting the idler axis with respect to the path of the belt, commonly known as knocking idlers, is effective where the entire belt runs to one side along some portion of the conveyor. The belt can be centered by knocking ahead (in the direction of belt travel) the end of the idler to which the belt runs (Fig. 1). Shifting idlers in this way should be spread over some length of the conveyor preceding the region of the trouble. It will be recognized that a belt might be made to run straight with half the idlers knocked one way and half the other, but this would be at the expense of increased rolling friction between belt and idlers. For this reason, all idlers initially should be squared with the path of the belt and only the minimum shifting of idlers used as a training means. If the belt is overcorrected by shifting idlers, it should be restored by moving back the same idlers, not by shifting additional idlers in the other direction.
Fig. 1
Such idler shifting is effective for only one direction of belt travel. If the belt is reversed, a shifted idler, corrective in one direction, is misdirective in the other. Hence, reversing belts should have all idlers squared up and left that way. Any correction required can be provided with self-aligning idlers designed for reversing operation. Not all self-aligners are of this type, for some work in one direction only.
Tilting the troughing idler forward (not over two degrees) in the direction of belt travel produces a self-aligning effect. The idlers can be tilted in this manner by shimming the rear leg of the idler stand. Here again, this method is not satisfactory where belts may be reversing. The tilted troughing idler is shown in Fig.2.
Fig. 2
This method has an advantage over knocking idlers in that it will correct for movement of the belt to either side of the idler; hence, it is useful for training erratic bets. This method has the disadvantage of encouraging accelerated pulley cover wear due to increased friction on the troughing rolls. It should, therefore, be used as sparingly as possible, especially on higherangle idlers. Special, self-aligning troughing idlers are available to assist in training the belt (Fig. 3).
Fig. 3
Return idlers, being flat, provide no self-aligning influence as in the tilted troughing idlers. However, by shifting their axis with respect to the path of the belt, the return roll can be used to provide a constant corrective effect in one direction. As in the troughing rolls, the end of the roll toward which the belt is shifting should be moved longitudinally in the direction of return belt travel to provide correction.
Self-aligning return rolls also should be used. These rolls are pivoted about a central pin. Pivoting of the roll about this pin results from an off-center belt and the idler roll axis thus becomes shifted, with respect to the path of the belt, in a corrective direction (Fig. 4).
Fig. 4
Some return idlers are made with two rolls forming a 10-degree to 20-degree V-trough, which is effective in helping to train the return run. The V-return idlers are only recommended for fabric belts wider than 54”. The most important criteria for belt training is idler contact in the center. If the belt has taken a set on the trough side and V-return idlers are being used, the center of the belt is not able to make contact with the center of the V-return idlers. A hold-down roller on the return side will help in training the belt, as it forces the belt to lay flat on the following idlers.
Fig. 5
Rubber-segmented disk return idlers (Fig. 5) are used for cleaning the belt and help in belt training. When one of the discs on the edges falls off, the belt edges tend to get caught, forcing the belt to run one way and become a belt detrainer. Minimum of 8” of belt contact is recommended for disc return idlers.
