The Importance of Shaft Alignment

The Importance of Shaft Alignment in Rotating Machines

Shaft alignment is one of the most important and challenging aspects of rotating machinery operation. The alignment of the shafts in a machine allows for precision movement of the parts it powers, and ensures that wear and tear is minimized.

If the shaft is misaligned by more than 2 mils for a machine running at 3600 rpm, the bearings will be subject to large forces that can cause wear and tear leading to machine downtime or severe damage.

In the most severe cases of shaft misalignment, the stresses from the bending will be too much for the shaft to handle, causing it to snap and break. This article will discuss various types of shaft misalignment, the importance of shaft alignment, how to perform shaft alignment, when to perform a machine alignment inspection, and some tips on detecting shaft misalignment.

So keep reading to learn all you need to know about shaft alignment!

An understanding of shaft alignment

Under normal operating conditions, shaft alignment involves aligning the rotational centers of two or more shafts ( for driving equipment like motor and turbine and driven equipment like pump or compressor) so they are in a straight line.

The total indicator reading (TIR) of the coupling hubs or the shafts is not what dictates proper shaft alignment, but rather it is the proper centers of rotation of the shaft supporting members (the machine bearings) that does.

Types of shaft misalignment

There are two types of misalignment—angular misalignment and offset misalignment or parallel misalignment and they may occur in horizontal plane (axial) and vertical ( Radial) plane.

The distance between the shaft centers of rotation, typically measured at the coupling center, is called offset misalignment, or parallel

misalignment. It is usually expressed in mils (where 1 mil = 0.001 in.).

Angular misalignment is when the slope of one shaft (usually the moveable machine) is different than the slope of the shaft of the other machine (usually the stationary machine). This difference is sometimes referred to as “gap,” “face,” or simply “angularity.”

This measurement is similar to measuring the slope of a roof (i.e., rise/run). Mils are used to measure the rise, while inches are used to

measure the run (distance along the shaft). Mils per inch are used to measure angular misalignment.

Angular and parallel misalignment manifests itself in following interrelated problems Increased vibration

• Increased energy loss and high power consumption.
• Increased load on bearings, seals and other mechanical components
• Reduced production capacity
• Reduced product quality
• Reduced life span
• Coupling failures
• Increased repair time

Even the most conservative surveys carried out over the last ten year in a wide variety of industries indicate that 50% of all machine breakdowns are directly due to poor alignment. Some surveys have shown that as much of 90% of machines are running beyond their recommended tolerances.

Prepare for Shaft Alignment/ Coupling alignment

Here are the steps to follow before you begin precision alignment:

• Ensure that the machine is locked both electrically and mechanically. You don’t want the machine to start running, either from someone accidentally turning on the power, or that a valve is opened somewhere forcing the pump to start spinning.
• Ensure that the bedplate and rotating machine’s mounting faces are clean from paint, rust, weld spatters, burrs or other debris.
• Shims that are rusty, painted, or damaged should not be used anymore and should be thrown away.
• It is important to ensure that the holes for the holding-down bolts are of a sufficient size to allow for adequate movement during the alignment process, as this will help to avoid any unnecessary delays further down the line.
• The distance between the shaft ends (DBSE) should be checked and the machines aligned approximately. A Measuring tape can be used to calculate the distance between the shaft ends. A straight edge can be used to ensure that hub faces are parallel by placing it against the machines.
• One issue that users might not think about during alignment is a soft foot. This is when the machine isn’t sitting evenly on the bedplate, which can twist the machine frame and put an unexpected load on the bearings. This can cause the frame to fracture.

Test for a soft foot by attaching a bracket with a dial indicator to one shaft and placing the plunger on the second shaft, while lightly tightening all holding-down bolts. You should then loosen one bolt at a time, working around the machine.

If the indicator moves too much, it means there is a soft foot, which means the user will need to put shims on the machine before starting the alignment. It is possible to check for soft foot with some laser alignment equipment using a program instead of manually doing so.

Checklist for Precision shaft alignment

In preparation for precision alignment, end users can use the following checklists. Depending on the alignment method and the machine, the lists can be adjusted accordingly.

Checklist for Off-Site Work

• Safety regulations
• Working permits
• Time limits for stopping production
• Alignment allowed tolerances as per RPM or from OEM
• Type of coupling – Gear Coupling, Flexible Couplings, rigid etc.
• Thermal offsets Corrections
• Available space
• Shaft rotation
• Alignment system
• Batteries, if required for laser equipment
• Specifications for the machine setup

Checklist for on-site inspections

• Machine serial numbers
• Safety conditions
• Available space
• Foundation condition
• Bedplate condition
• Bolt condition
• Adjustment capacity
• Shim condition
• Presence of leaks
• An alignment checklist for pre-alignment
• Machine temperature
• Gross soft foot check
• Replacement of old shims for alignment corrections
• Coupling assembly
• Adjustment of any mechanical looseness
• Run-out conditions
• Pipe strain
• Final soft foot check to adjust small errors after removing gross soft foot
• Repeatability
• test to ensure that tightening and loosening the feet bolts gives consistent results; this test also checks the condition of any shims or binding of bolts.

Alignment Table

Choose an Alignment Method, Shaft alignment system, alignment tools ( Brackets, Dials or laser shaft alignment tool)

End users must pick an appropriate precision alignment technique based on available alignment tools for their equipment after they’ve prepared for alignment.

Brackets and arms are required for installation of measuring equipment in several alignment approaches along with face dial indicators. As the arms get longer, they become more prone to sagging, which may cause significant measuring mistakes if end users don’t factor it into account; as a result, the arms become more prone to sagging.

Laser system with sensors are more accurate and less prone to sagging. It can be used to correct both horizontal misalignment and vertical misalignment.

Method 1 — RIM AND FACE DIAL METHOD

The oldest and most commonly utilized dial indicator technique is the Rim and Face technique. This is ideal for hubs with a short distance between shaft ends and large diameter. The method requires use of dial gauges horizontally and vertically to achieve correct shaft alignment.

Alignment measurements of driver and the driven piece of equipment may be offset as per manufacturer.

Advantages for RIM and Face Method:

• Rotating one shaft is all that is required.
• This method is simpler than others when trying to see the placement of the shaft.

Disadvantages of RIM and Face Method:

If there is any axial float, it is difficult to obtain face readings.

• Typically, the coupling must be removed by the user.
• Graphical calculations are more complicated than other methods.
• If the hub periphery is not round or flat and square relative to the shaft, the readings will be affected; if the hub face is out-of-square or out-of-round.

Method 2 — Reverse Dial Method

For most alignments, reverse Dial (indicator) is the most optimal method.

Advantages of Reverse Dial Method:

• In general, it is more accurate than the face and periphery methods.
• The readings are not affected by axial float, out-of-roundness, or out-of-squareness in the hub.
• Graphs can be plotted more easily than other methods.
• Measuring can be done with the coupling installed.

Disadvantages of the Reverse Dial Method:​

• Both shafts must be rotated by the end user.
• The method is not accurate for shafts that are closely coupled.

Method 3 — The Laser Shaft Alignment System​

There are two types of laser shaft alignment systems: those using two laser/detection units and those using one laser and a mirror/prism reflector (sensor). 

There is a laser/detector attached to each shaft, and the laser/detector is connected by cable or wireless Bluetooth to a keyboard/display. Using reverse periphery, the laser system measures the misalignment by measuring the movement of the laser beams.

Advantages of Laser Shaft Alignment System:​

• The system fits a variety of shafts.
• There is no need for end users to remove the coupling.
• There are no sagging issues with long spans for end users.
• There is no effect of axial float on it.
• Soft foot condition can be easily detected by the system.

Disadvantages of Laser Shaft Alignment System:​

• In the case of couplings with backlash, the system is not suitable.
• Its accuracy can be affected by heat or steam.
• It is expensive to use the system.

Alternative Alignment Methods​

A shaft-to-coupling spacer is another method of alignment, as are optical systems and electronic indicators, and feeler gauges.

It is possible to check the alignment of the shaft of one shaft and the spacer of the second shaft for equipment with long distances between shaft ends by fitting the coupling and checking the alignment from one shaft to the spacer.

How Often Do You Need a Machine Alignment Inspection?​

We Recommend to perform alignment as part of routine maintenance on facilities critical equipment. This way a baseline is established and can help you see alignment changes year over year.

What is Thermal Growth?​

If you're working with rotating machinery, it's important to have your shaft alignment in check. This can prevent thermal growth and metal fatigue, which can lead to failure.

To ensure your shaft alignment is optimal, ask a technician for help. If you're having trouble getting your machine aligned, chances are good that it's not aligned properly. Don't take the risk - get in touch with a technician and they'll take a look. Proper alignment is crucial for optimal performance and durability, so make sure to take the time to get it right.

What is Soft Foot?​

Shaft alignment is essential for the smooth operation of a rotating machine. For accurate milling results, make sure your machine has soft foot - a feature that allows it to rotate more easily.

This in turn results in shorter machining times and improved accuracy. By ensuring proper shaft alignment, you're also reducing wear and tear on the parts being milled, improving output by up to 20%. So, wouldn't it be wise to invest in a machine with soft foot? It sure would!

What is a Shim?​

Shaft alignment is vital to the smooth rotation of your rotating machines. A shim is a small, thin piece of metal that helps to align the drive shaft and input shaft of your machine. It's important to replace worn-out or broken shims as soon as you notice them, to keep your machine running smoothly.

When your shim wears down or breaks, it can cause problems with your machine's alignment and rotation. So, make sure to keep an eye out for signs that your shim is in need of replacement, and take corrective action as soon as possible!

How to detect shaft Misalignment?

One way to detect shaft misalignment is by using a dial indicator. This is done by attaching the dial indicator to the shaft and then rotating the shaft. If the shaft is misaligned, the dial indicator will show a difference in readings between the two points where it is attached. Another way to detect shaft misalignment is by using an alignment laser alignment system.

Why is shaft alignment important?

Shaft alignment is important because this prevents excessive wear on the shafts and bearings, and helps to keep the machine running smoothly. Proper alignment also helps to extend the life of the machine and its components.

What are the benefits of shaft alignment?

There are many benefits to shaft alignment, but some of the most notable are increased efficiency, reduced wear and tear on components, and extended equipment life. By aligning the shafts of rotating equipment, bearings and other moving parts are able to operate with less friction, which leads to improved efficiency.

In addition, properly aligned shafts result in less vibration and noise, as well as reduced wear on bearings and other moving parts. This can lead to significant cost savings over the life of the equipment.

Alignment procedure should be a standard practice in plants and alignment training detailing alignment using dial indicator method involving complicated alignment in horizontal and vertical planes should be part of standard induction training.

Turbo Airtech has prepared ready to use PDF forms with predesigned fields using formula for motor shaft alignments in various industries including the compressor and marine industry, ready with tolerated margin sheets which can be readily be used in advanced manufacturing industries with industry 4.0 philosophy and reduced the need of multiple documents and calculation sheets susceptible to errors.

Proper use of alignment practices increases the efficiency and uptime of plant equipment’s

Conclusion

Shaft alignment is an important process in rotating machines that can impact the running of the machine and the quality of the output. If shaft alignment is not carried out correctly, it can cause wear and tear on the machine and lead to decreased production.

In order to ensure that your rotating machines are running correctly, it is essential to have them checked and aligned by a qualified technician.

Contact Turbo Airtech Today for expert services.