It’s estimated that 50 to 70 percent of all vibration problems in machines are caused by misalignment. Rotating equipment, such as pumps and motors, are found in virtually every type of industrial environment and when the centerlines of their rotating shafts don’t match up perfectly, it can lead to wasted power, accelerated component wear, and even the potential for catastrophic equipment failures. By understanding the types, causes and effects of shaft misalignment, a technician will be able to identify it when it occurs, thereby allowing the condition to be corrected.
There are two major types of misalignment, parallel and angular. Parallel misalignment means that both shaft centerlines are parallel, but offset by some distance. The greater the distance, the greater the misalignment. Angular misalignment, on the other hand, refers to a condition where the shaft centerlines are not parallel and intersect at an angle. In most cases, shaft misalignment consists of both parallel and angular misalignment. This type of misalignment is referred to as combination misalignment.
Many causes exist for shaft misalignment. To ensure an alignment is successful, all of the possible causes of misalignment must be addressed. The following are the most prevalent causes:
- Relative Movement – Thermal growth, or expansion, can cause one piece of equipment to move proportionately to another, causing relative movement misalignment. Different materials expand at different rates when heated. Thermal growth must be accounted for when equipment normally operates above ambient temperature.
- Strain – Strain induced by attached piping runs can force equipment out of alignment. Misalignment caused by strain can reoccur after a successful alignment due to the continuous action of forces caused by strained equipment.
- Torsional Movement – The initial high torque caused during startup can force shafts out of alignment, causing torsional movement misalignment.
- Settling – Over time, foundations or base-plates can settle to lower positions, causing settling misalignment. The equipment can be realigned, but without addressing the cause of the misalignment, the problem can reoccur.
- Human Error – A mistake in an alignment procedure or not completing an alignment procedure can cause human error misalignment.
- Misbored Couplings – Manufacturing defects, creating couplings that are misbored or otherwise distorted, can cause misbored coupling misalignment. This form of misalignment is mostly found on new equipment; however, damaging a coupling during an alignment will cause similar problems.
Misalignment in rotating machinery can be detected in many different ways including excessive vibration, excessive bearing temperatures, wear patterns, and noise. Some methods are incorporated into a plant’s preventive maintenance program. Others are inspections that could be used on a regular basis, but usually are performed after the equipment has failed.
The damaging effects of unchecked misaligned shafts include the following:
- Excessive Vibration – Misalignment is one of the leading causes of equipment vibration. In spite of self-aligning bearings and flexible couplings, it is difficult to align two shafts and their bearings so that no forces exist that will cause vibration. The significant characteristic of vibration due to misalignment is that it will be in both the radial and axial directions.
- Noise – Like vibration, noise can be detected simply by noticing a change in the equipment sounds during operation. All running equipment produces a certain normal amount of noise. Only if an operator is familiar with normal equipment noise will they be able to detect abnormal sounds.
- Lost Production – Misalignment can directly affect the lifetime of equipment. With a shortened service life, equipment will require unplanned maintenance, thereby reducing the time available for production.
- Poor Quality of Products – Product quality can suffer directly from equipment misalignment. Misalignment can cause both the manufacturing process to produce defects and directly damage product.
- Higher than Normal Repair Orders – Misalignment-induced failures will increase the amount of unplanned maintenance, causing more repair orders to be generated.
- Increased Inventory of Spare Parts - As the amount of maintenance increases due to misalignment-induced failures, more spare parts will need to be ordered. This results in increased spending and a larger spare parts inventory.
- Reduced Profits – As machines fail early and unexpectedly, more money must be spent for maintenance and spare parts. Coupled with lower production, misalignments can rapidly reduce profitability.
Implementing a well thought out maintenance and training program will help to ensure that your equipment and facility operate at optimum efficiency.
At Technology Transfer Services, we offer a full range of customized maintenance and training programs suited to your exact needs. Please contact TTS at (813)908-1100 to discuss your specific needs.
Created by Dallas Hermanson