Machine and
bearing condition
Maintenance concepts
Alignment
  Shaft alignment methods
  Soft foot and machine foundation
  Belt or pulley alignment
  Belt alignment methods
   

Belt or Pulley Alignment

As in the case of shaft alignment, belt alignment or pulley alignment is an important maintenance task. When carried out correctly, it can prevent breakdowns and save considerable costs. Belt alignment and pulley alignment are synonymous, as the process of belt alignment hinges on the correct alignment of the pulleys on which the belt runs. For the sake of clarity, however, we will speak of belt alignment.

Belt alignment concerns aligning the belts in a manner that results in the least wear on the belts and lowest energy loss for the machine or driver unit. In practice this means that the grooves of the pulleys are in line with one another.

 

Results of belt misalignment
When a belt is misaligned it can result in various detrimental, and sometimes dangerous, effects. In the first place, the efficiency of the machine is reduced. The wear on the belt itself increases, substantially reducing the life of the belt, and possibly resulting in belt failure. Apart from the annoying and costly downtime needed to replace the belt, should an unguarded belt wear through and snap prematurely it could cause injury to any personnel nearby. Other consequences of belt misalignment are increased vibration and noise level, which in turn shortens the bearing's life.

Unless the alignment is corrected, the new belt will not last much longer than the old one. Continuous operation in a misaligned state will also increase the wear on the pulleys themselves, as well as their axles, shafts and bearings.

Nature of misalignment
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 informs you of the nature of your machine's misalignment. The following illustrations show the three different types of belt, or pulley, misalignment.

Vertical angle misalignment Horizontal angle misalignment Parallel misalignment

Vertical angle or twisted misalignment
This type of 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
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, can cause this type of misalignment. This misalignment can generally 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 centre.

Parallel misalignment
Parallel misalignment is the least complex form of misalignment. It is either caused by the incorrect positioning of the motor along its shaft axis; positioned too far forward or backward compared to the other shaft, as shown in illustration A below, or by incorrect positioning of the pulleys on their respective shaft; one of the pulleys needs to be adjusted on the shaft, as shown in illustration B below.

A B

 
 
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Home Maintenance knowledge Machine and bearing condition Alignment Belt or pulley alignment