An effectively implemented, comprehensive preventive and predictive maintenance program for a parallel-drive system will reduce downtime, bring down costs, and create a safer working environment.
Parallel-shaft drive systems include v-belts, synchronous belt drives, conveyor systems, and chain drives. These power transmission systems are used for transmitting power and in some cases conveying product. Optimum performance and maximum service life can be achieved if the systems are correctly installed and properly maintained. All aspects of the inspection, installation, and maintenance process should be measured and documented in an organized and easily accessible manner.
The pie chart shown in Figure 1 depicts common problems in a parallel shaft system; individual slices’ share at a given facility will vary depending on different factors the facility faces. In any event, correct design, proper installation, and proper maintenance will have a significant positive effect on the drive’s life and performance.
Before troubleshooting the drive, all safety procedures should be followed, and a lock-out/tag-out verification start process must be performed. (No exceptions!) This process includes but is not limited to the following:
- Electrically de-energizing the system
- Load leveling or mechanically neutralizing the drive (a shift in load, pressure changes within the system, or the mechanical inertia present may cause things to move)
- Ensuring that all rotating components are properly guarded to prevent access when rotating
- Wearing all required PPE – work smart and safe!
A useful acronym for troubleshooting parallel systems is A.C.T., which stands for Alignment, Condition of the equipment, and Tension. These are the three most important considerations for installing and maintaining parallel shaft drives.
Alignment is needed for the drive to be able to run trouble-free. Misalignment of the sheaves, pulleys, and sprockets can cause vibration, premature wear of components, and additional loading on bearings. The alignment process of the sheaves or sprockets can be accomplished using levels, straight edges, string, and/or laser systems.
There are two types of misalignment: angular and parallel (offset). Parallel misalignment occurs when the driver and driven shafts are parallel, but the driven components, such as a sheaves, lie on two different planes. If the shafts are not parallel, then the drive has angular misalignment. There are two forms of angular misalignment: vertical and horizontal (Figure 2).
The easiest way to correct parallel misalignment is to shift the driver, which is usually an electric motor, or to change the placement of the rotating components on their respective shafts.
Angular vertical misalignment can be corrected by inserting or removing shims from under the front or back mounting pads of one of the machines.
Angular horizontal misalignment can be corrected by shifting, preferably with pusher bolts, the driver’s position so that the shaft centerlines are parallel.
A general guideline for v-belt drives is that they should have less than ½ degree of angularity and offset/parallel of 1/10” per foot of center distance. All synchronous belts and chain drives require alignment tolerances of half of that.