Maintaining belts in proper alignment is just as important as aligning shafts. For that reason, laser-guided belt aligning devices are an essential part of an up-to-date maintenance operator’s tool kit.
Belt alignment laser-guided tools consist of two components, a laser emitting unit and a 3-D receiver. The tool uses V-guides along with powerful magnets that quickly attach in the pulley groove to facilitate alignment of pulleys even if they have unequal widths or dissimilar faces.
As with shaft misalignment, there are various types of belt misalignment. In practice, a combination of different misalignments is often encountered simultaneously. For this reason, it is important that an alignment instrument both diagnoses and details the nature of the machine's misalignment. The following illustrations depict the three different types of belt misalignment.
Vertical angle or twisted misalignment occurs when one of the pulleys has an angular error from the vertical angle plane. This is usually caused by incorrect positioning of the machine and can be corrected by lifting either the front or rear feet of the motor to which the pulley is attached, depending on the direction of the vertical angle error. This differs from shaft alignment in that one never moves both feet in a vertical direction to reach the desired result.
Horizontal angle misalignment occurs when the driver and the driven unit are not positioned parallel to each other. Incorrect positioning of applications, such as the motor, typically can cause this type of misalignment. Horizontal angle misalignment generally can be corrected by moving the front or rear feet forward or backward on their guides, depending on the direction of the horizontal angle error, in order to twist the motor around its center.
Parallel misalignment is the least complex form of misalignment. It is often caused by the incorrect positioning of the motor along its shaft axis, positioned either too far forward or backward compared to the other shaft. Or it can be caused by incorrect positioning of the pulleys on their respective shaft, where one of the pulleys needs to be adjusted on the shaft.
Belt alignment can be performed by either traditional visual methods or the laser method. Traditional methods usually employ strings and/or straightedges. Laser methods utilize a laser beam, which provides for a much higher degree of accuracy.
The main advantage of these traditional methods is the limited length of time needed for adjustment, although the use of a straightedge takes more time than visual assessment alone. The major disadvantage is the lack of accuracy. For example, some belt manufacturers recommend a maximum misalignment of 0.5 degrees or even 0.25 degrees, which is difficult to accomplish by using visual assessment. These traditional low-tech methods involve a good deal of trial and error, naked eye approximation, and rough estimates. All told, that means a large margin for error, which is unacceptable for precision pulley alignment.
A laser belt alignment system enables one to adjust alignment with far more speed and accuracy than with traditional methods. Systems available on the market can be categorized according to the way the devices are attached to the pulley and the way they align. Generally, there are two groups, one that aligns the face of the pulleys and one that aligns the grooves of the pulleys.
Most products on the market use the face or side of the pulley as a reference for aligning the pulleys and belts. The advantage of this method is that it can be used for belt types other than V-belts, such as timing belts. V-belts, however, comprise the majority of belts found on the market, especially in industrial applications. The main disadvantage is that the face of the pulley is the only reference point. This means that only the faces of the pulleys are aligned with each other. This method results in varying degrees of accuracy when the pulleys are of different thickness, brands or kinds (e.g. one single-belt pulley and one multiple-belt pulley) or when the faces are not well finished.
Products that align using the grooves of the pulleys in which the belt runs tend to provide substantially higher levels of accuracy regardless of the thickness, brand or type of pulleys.
“Soft foot” is a condition in which one of the feet of a machine does not sit flat on the baseplate. Soft foot is among the most common causes of misalignment. Accordingly, one of the first steps to take in an alignment check is to assess the equipment’s foundation and employ a suitable shaft alignment tool to identify and correct potential soft foot conditions. Some laser-guided alignment tools have a soft foot operation capability that guides the user through corrective procedures. Shim plates generally can be used to bring machines back into both vertical and horizontal alignment.
Bearings out of square with their housings are another common cause of misalignment. Often a condition of wear, the out-of-square bearing and/or its housing will need to be corrected or replaced in order to bring machines back into alignment.
Once misalignment is detected, analyzed and corrected, an ongoing alignment maintenance program is important to keep operations running smoothly. As part of this maintenance, alignment checks should be performed to document alignment conditions before a machine is removed from service. This gives users the ability to install new or rebuilt machines with the same proper alignment values. In addition, a maintenance program should include periodic checks to verify conditions are still within tolerance.
Taking these simple steps to detect, correct and maintain proper shaft and belt alignment can prevent costly, unplanned downtime. Fortunately, there is a range of modern laser-alignment options available to make this process easier than ever before.
Like shaft misalignment, belt misalignment can result in a wide range of detrimental and sometimes dangerous consequences, including: