Did you know that about 50% of vibration-based damage to rotating equipment is directly related to misalignment? Well-aligned machines help cut operating costs by increasing MTBF and reducing power consumption.
Going green is not something to be taken lightly. Not only is our livelihood at risk, our very lives may depend on how well we meet the challenges of living green. To cover all the benefits of going green would require multiple, book-length documents; therefore, we will limit this discussion to the green benefits of precision machine alignment. Precision alignment produces these types of benefits in four areas: energy savings, improved machine life, better products and less pollution.
Eighty percent of the lifetime cost of owning an electric motor is for the electricity purchased for its operation. Knowing this makes it easy to understand why even a small increase in efficiency leads to substantial savings over the life of the machine. You may have heard that precision shaft alignment makes your machines more efficient, thereby reducing power consumption. But just how does it do it?
A 4"-diameter shaft mounted in antifriction bearings may have an internal bearing clearance of 0.002" or two mils. A human hair, on average, has a diameter of between two and three mils. Using this example, the free space allowed for shaft movement is smaller than the diameter of a human hair. If this shaft is solid-coupled to another shaft and the misalignment between the two shafts exceeds two mils, the internal bearing clearance can no longer provide free space for shaft movement. Any misalignment greater than the mounted internal bearing clearance will produce increased friction in the machine. The bearings are then subjected to additional loading because of the misalignment. Movement is restricted by the bearings, and some of the rotational energy is converted into vibratory energy. This vibration can sometimes be severe. Such vibration is destructive to the machine—and a waste of energy.
We purchase electricity to perform work. The energy converted to vibration is no longer doing useful work. In effect, we are purchasing electricity and converting some of it into a destructive force that destroys machinery. This author remembers being called in to balance a large fan driven by a steam turbine. Vibration tests indicated misalignment—as opposed to imbalance. Movement could be observed in the massive concrete base that supported the machine. There must have been literally thousands of foot-pounds of energy causing the huge structure to shake. The vibratory energy was being converted into heat and pumped back into the earth through the huge base. I can remember thinking that the intention of the plant was surely not to purchase electricity for heating the planet!
Many industry officials believe that flexible couplings eliminate most misalignment problems—therefore, their practices allow for varying degrees of nonaligned (or poorly aligned) machines. Our company is aware of an instance where the coupling manufacturer's tolerance was used as the plant alignment standard. The coupling manufacturer's tolerance, though, is for preventing damage to the coupling, not the coupled machines. Before a coupling can flex, there must be some degree of shaft misalignment. This flexing equates work and requires energy, preventing flexible couplings from being 100% efficient."America's leading industries are not just making beverages and manufacturing chemicals; today, they are also producing real environmental results. They are proving that smart environmental performance is smart business." —EPA Administrator Stephen L. Johnson
Improved machine life
On occasion, maintenance or production managers may ask why particular machines fail so often. Why indeed?
Let us suppose that the cause of failure on a machine operating at 3600 rpm is shaft misalignment. As noted previously, misalignment places additional loading on bearings, which may result in excessive vibration. This vibration is much like hammer blows to the machine—delivered at a rate equal to the vibration frequency. Misalignment most often produces vibration at a frequency equal to two times shaft speed. In our example this would equate to 7200 hammer blows per minute, or over 10 million impacts every 24 hours. Thus, that typical question asked by the managers would seem to be rather poorly phrased. Instead, they should be wondering how their failing machines have managed to run as long as they have, given the abuse they've suffered as a result of shaft misalignment!
In addition to high vibration, shaft misalignment also places shafts in a bind, producing additional loads on both shafts and bearings. If the load on a bearing is doubled, the life of the bearing is reduced by a factor of eight. Severe misalignment can result in broken shafts as well as failed bearings and even failed bearing housing.
Precision shaft alignment will reduce stresses on couplings, bearings, shafts, machine hold-down fasteners, shaft seals and housings. Putting less stress on these components will result in a more reliable machine and longer machine life. This adds up to a greener machine as resources are not wasted on new machine construction when the original is still running and reliable.
Smooth-running machines allow for products that meet the customer's specifications. Rough-running machines are incapable of making smooth products.
It is a win/win/win scenario all the way around, since the elimination of rework reduces costs, as well as stress on machinery—which, in turn, increases machine life.
The leading cause of shaft-seal failure is misalignment. Seal failures can lead to oil, product, water, steam, acid, caustics, dust, air and other types of leaks or spills. The consequences of such events can range from minor to catastrophic.
Many leaks contribute to plant safety hazards and degrade plant morale. At best, a leak is a waste of resources that is likely to contaminate other resources. Leaks of one kind or another can result in the permanent shutdown of a plant. In fact, many of us can probably think of at least one instance where a plant—perhaps even a whole company—has been devastated because of some contaminant emission or seepage.
Leaks and spills cannot be taken lightly—and precision shaft alignment is essential in helping prevent shaft seal failures. Good shaft-alignment practices will certainly help us conform to environmental standards and are a requirement for any plant that operates rotating equipment. Practicing precision shaft alignment may even help reduce the risk of an operation being subjected to an OSHA investigation.
Achieving the benefits
A rough alignment is better than no attempt at alignment—but a rough alignment will not achieve the precision required for maximum machine efficiency. Taper gages, rulers, feeler gages and straight edges are simple tools that can be used in performing a rough alignment; however, the use of such tools will not likely achieve the desired precision.
Let us consider for a moment the difference between rough and precision shaft alignment. Figure 1 depicts a typical alignment chart showing the tolerances required for an alignment to qualify as a precision shaft alignment. In order to obtain the full green benefits of shaft alignment, tools that can meet or exceed the tolerances shown in Fig. 1 need to be used. Keep in mind that state-of-the-art laser-alignment systems provide more accurate and reliable alignment data than conventional methods—and, thus, save significant time and effort on the part of the end-user.
Fig. 1. A typical shaft-alignment-tolerance chart
"Going green" requires having sound operating practices and well-developed procedures in place. Adherence to guidelines where machines are precision-aligned when they are installed—or anytime that they are unbolted for maintenance—should be a priority within every "green" business. Such procedures should also aim to ensure that the machines remain in alignment during operation. This can be accomplished by periodic alignment checks in conjunction with vibration testing.
If operating machines do not remain in alignment, it indicates a fault that demands immediate attention. The cause of such defects should be determined and corrected as quickly as they are diagnosed. By integrating predictive and corrective maintenance technologies, machine reliability can be sustained at a level required by the plant. An added benefit is that healthy machines live longer lives. Keeping machines precision-aligned is a primary factor in making sure that one's business is operating lean and green.
No, precision shaft alignment alone will not make your plant green. But, by the same token, a green plant will be very difficult to achieve without precision shaft alignment. In simple, yet colorful terms, if you want to operate in the black, operate in the green. LMT