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Types of Shaft Misalignment

There are two types of misalignment: parallel and angular misalignment. With parallel misalignment, the center lines of both shafts are parallel, but they are offsets. With angular misalignment, the shafts are at an angle to each other.

The parallel misalignment can be further divided up into horizontal and vertical misalignment. Horizontal misalignment is a misalignment of the shafts in the horizontal plane, and vertical misalignment is a misalignment of the shafts in the vertical plane:

• Parallel horizontal misalignment is where the motor shaft moves horizontally away from the pump shaft, but both shafts are still in the same horizontal plane and parallel.
• Parallel vertical misalignment is where the motor shaft moves vertically away from the pump shaft, but both are still in the same vertical plane and parallel.

Similar, angular misalignment can be divided into horizontal and vertical misalignment:

• Angular horizontal misalignment is where the motor shaft is under an angle with the pump shaft, but both shafts are still in the same horizontal plane.
• Angular vertical misalignment is where the motor shaft is under an angle with the pump shaft, but both shafts are still in the same vertical plane.

Errors of alignment can be caused by parallel misalignment, angular misalignment, or a combination of the two.

Typical problems arising from poor machine alignment are:

• Leaking seals
• Increased vibration levels
• Higher energy consumption
• Bearing failure
• Shaft breakage
• Coupling wear
• Quality problems
• Bad working environment
• Lost production time

What Causes Misalignment?  

These are the primary triggers:

• Settling of a baseplate resulting in soft foot
• Shaft deformation caused by torsion during startup
• Insufficient or poor-quality alignment measurements due to human error
• Pipe strain that leads to parallel and angular misalignment
• A thermal expansion that can make one piece of equipment moves proportionally to another

Misalignment of shaft centerlines can give shaft wobbling and significant vibration, leading to seal damage and bearing and coupling destruction. Identifying misalignment and the underlying causes is imperative if a machine reaches its expected life.

What is Thermal Growth?

When operating at high temperatures, expansion of the driveshaft and other pump components can cause a pump’s position. Thermal growth must consider when selecting and fitting a shaft coupling and correcting shaft alignment.

TYPES OF LASER-BASED SHAFT ALIGNMENT

1. HORIZONTAL SHAFT ALIGNMENT

Horizontal Shaft Alignment (HSA) is the process of aligning shafts with each other so they are within a certain tolerance. It is essential for machinery before being put into service. When a driver like electric motors or turbines is coupled to a pump, generator, or another piece of equipment, the shafts are aligned in two parts.  

Any misalignment between the ball and socket joint will increase stress on the shafts and cause them to break down prematurely. It can be very expensive. If the equipment is down, then production might be down. If bearings or mechanical seals are worn out and not working correctly, they may need to be replaced.

Flexible couplings allow a driver (such as an electric motor, engine, turbine, or hydraulic motor) to be attached to the driven equipment. Flexible couplings allow for a slight degree of misalign­ment. They are typically used in shafts having different diameters. Tools used to achieve proper alignment may be mechanical or opti­cal, like the laser shaft alignment method, or Gyroscopic is a system that can be operated very efficiently. They can also be used when the shafts have a great distance (for example, on marine vessels).

The foundation for the driver and the drive piece must be designed and installed correctly before aligning them. If that is the situation, it is time to start the alignment procedure.

Alignment is basically about accurately measuring the positions of motors and pumps’ shafts at two or several points or locations. We provide laser-based TORSION SHAFT ALIGNMENT SERVICES up to 20 meters in length within acceptable tolerances in CEMENT INDUSTRY, MINING INDUSTRY, STEEL PLANT, etc.

2. VERTICAL SHAFT ALIGNMENT

Vertical pumps are used for many different applications in industry. Many vertical pumps use a C-face flanged mounting arrangement. One end of the motor shaft mounts onto the adaptor plate in this arrangement. It is held in position by bolts but positioned in a groove around the periphery of motors and plate.

This joint typically places the motor shaft centerline coaxially with the pump shaft within a few inches of accuracy.

It means that the alignment quality of the machine-checked, especially if it vibrates excessively or if its seals and bearings need frequent replacement.

Some of the more commonly encountered reasons for the misalignment of vertical pumps include:

• Dirt, paint, and other contaminants on the mounting surfaces of the motor or plate
• Rarely machining errors may occur on the mounting surfaces.

When these motors took out of service for maintenance, great care must avoid damaging the mounting surfaces. The engine should be placed on wooden cribbing. Before remounting the motor again, the mounting surfaces should first be cleaned, sanded, and checked for any damage or other imperfections. Ensure that the groove on the C-Face mounting is clean so that there are no contaminants in the track.

When these motors took out of service for maintenance, great care must avoid damaging the mounting surfaces. The engine should be placed on wooden cribbing. Before remounting the motor again, the mounting surfaces should first be cleaned, sanded, and checked for any damage or other imperfections. Ensure that the groove on the C-Face mounting is clean so that there are no contaminants in the track.

Many laser alignment tools allow you to perform a vertical alignment if precise alignment is needed.

3. SOFT FOOT

A soft foot is a term we use when talking about shaft alignment. To be sure, you must always perform the soft foot check before the alignment work can begin. It is an essential part of ensuring a reliable installation. We’ll go through the different types and why they occur.

I mean that the machine is resting unevenly on all feet by soft foot. Another expression you may have heard is machine frame distortion.

Why do we need to check and correct soft foot? Can it be that big a problem if there is a tiny gap underneath one machine foot or a little pile of dirt under another? Well, yes. Because if the machine is not standing perfectly flat on the machine base, you can (and most likely will) run into problems such as shaft deflection, increased vibrations, bearing failure – and, in the end, machine breakdown. And that will be a lot more expensive than fixing the soft foot problem in the first place! Luckily, all Laser shaft alignment systems come with a program for soft foot check that tells you which feet you need to adjust and how much.

There are four types of soft foot which all have one thing in common: one or more feet are not resting firmly on the machine base. And there are different reasons for that. So, let’s take a look.

A) Parallel Soft Foot

Parallel soft foot (sometimes also referred to as rocking soft foot) means that not all four feet are on the same plane. Think of a wobbly table at a restaurant, where you can swing it back and forth. In this case, the laser system software will show high readings (>0,05 mm) for the soft foot at opposite corners. You can determine which foot or feet you need to shim with a feeler gauge and how much. 

There are three possible reasons for parallel soft foot:

• The leg is too short.
• The base plate or mounting pads are not coplanar.
• Missing shims under one or more feet.

To correct parallel soft foot, you add enough shims to remove the rocking effect (use as few as possible, and no more than four shims).

B) Bent Foot / Outside Angled Soft Foot

This is a common type of soft foot that occurs when the foot’s bottom is at an angle relative to the base. If you’re standing three or four feet from the laser system, it will show a high soft reading. The foot with the widest air gap between the heel and toe will have mild, mild foot pressure.

There can be several reasons for this condition, for example:

• The machinery has been dropped or roughly handled.
• The base plates are bent or poorly machined.
• There’s a severe vertical angular misalignment.
• The feet are welded.
• Foundation settling has occurred.

The best way to fix this problem is to remanufacture the feet, the base, or both. If this isn’t possible, step shimming is an option. You might want to avoid it, though.

C) Squishy Foot

The soft foot is sometimes also called the spring foot. The feeler gauges will not detect gaps under the foot with a soothing foot. There may also be a build-up of other unwanted materials, such as dirt or rust underneath the foot.

Reasons for squishy soft foot may be:

• Dirt, grease, paint, or rust between the foot and the base.
• Too many shims (remember, you should not use more than four shims per foot).
• Bent shims.
• Shims with burrs or thread marks.

To fix this problem, clean the area around and under the foot thoroughly and replace old shim stock with new, crush-proof ones.

D) Induced Soft Foot

The induced soft foot can be caused by external forces that influence the machine frame, which is challenging to detect. The laser system will tell you if there are multiple soft feet, usually on the same leg of the same side of the machine. The feeler gauge is used to find a gap, usually a parallel or near parallel.

Some possible causes of the induced soft foot are:

• Coupling or pipe stress.
• Overhung machines.
• Belts or chain loads on pulleys and gears.
• The flex conduit is excessively rigid.
• Structural bracing is attached to the device.
• The jacking bolts are inadvertently left tight.

To correct induced soft feet, you need to remove any external forces causing them. You may need more than one soft foot check because these forces can occur during the shaft alignment process.

E) Machine Train Alignment 

It’s a multi-coupled alignment where two or more successive machines must be adjusted. For example, a 3-coupling train (4 devices), such as a Gas Turbine driving 3 Compressors.

Note: A 2 coupling (3 machines) train, such as a Pump–Gearing–Motor, where the Gearing in the middle is determined not to be movable, is NOT a Machine Trains; it could be treated like one, but that is not always the best option. It is best to think of these as two separate alignments, using the Gearbox as a stationary machine. Align the pump to the Gearbox in one alignment, then align the motor to the Gearbox in another alignment.

4. CARDAN SHAFT ALIGNMENT

A Cardan drive consists of a driver and a driven shaft. It is installed and operated with a relatively large offset between the driver (which rotates) and the driven shaft (which moves). The spacer shaft has a minimum angle of usually four degrees to six degrees to ensure sufficient lubricant flow to prevent the universal joints from seizing. Excessive misalignment occurs between the rotor and stator, and the driven shaft RPM can rapidly fluctuate during operation.

This can cause severe damage to electronic controlled synchronous and asynchronous AC drives. The machine must be aligned to parallel its driving and driven machine shafts. Precise alignment minimizes the rotational irregularities of a Cardan shaft. The uneven bearing loadings during Cardan shaft rotation and also minimized, extending the component’s service life and reducing the chance of unexpected machine failures.

If excessive angularity exists between these components, the resulting fluctuation of the driveshaft RPM will be rapid. It causes damage to the machine, which leads to premature wear of critical machine components, including bearings, gears, and belts. Precise alignment reduces these rotational irregularities, so uneven bearing loading during Cardan shaft rotation is also reduced. Therefore, the service life of components is extended, and the chances of unexpected machine failures are reduced.

Using laser shaft alignment to detect and correct problems

To accurately align the driver to the driven machinery, the Cardan shaft and the couplings must first be removed. With the laser alignment system and specially constructed Cardan, the angles between the machines can be accurately determined and corrected. After removing the Cardan shaft from the device, the Cardan bracket was mounted to the shaft face.

The bracket will be attached directly to the roll shaft if a motor is connected to a roll. The frame can be mounted to the shaft using the coupling bolts or if available utilizing a threaded hole in the center. The laser is mounted on a bracket, and the receiver (the part that receives the signal from a laser) is mounted onto the drive shaft (the part that rotates the wheels). Measurements are taken, and the condition of alignment is determined.

5. TORSION SHAFT LASER ALIGNMENT

It’s estimated that up to 50 to 70% of all vibration problems in machinery are caused by misalignment. Rotating equipment, including pumps and motors, are often found in virtually every type of industrial environment.

When the centers of their rotating shafts do not align perfectly, it can lead to waste power, accelerate component wear, and even have the potential for catastrophic equipment failures. Understanding the different types, causes, and symptoms of shaft misalignment allows a technician to identify it when it happens, thereby correcting the condition of shaft misalignment.

Types

There exist two major types of misalignments, parallel and angular. Parallel misalignment occurs when both shaft centerlines are aligned, offset by distance. The greater the distance between the two points, the greater the degree of misalignment. On the other hand, angular misalignment is when two shaft centers are not parallel and intersect at an angle. Most often, shaft misalignment involves both parallel and angular misalignments. Combination misalignment is when two or more different types of misalignments co-occur.

Causes

There are many reasons why a person may have a misaligned shoulder. All possible reasons for not aligning must be addressed. The following are the leading causes:

1. Relative movement – thermal growth, or expansion, causes one piece of equipment to expand proportionally to another, causing relative motion misalignment. Different materials expand at varying rates when heated. When equipment operates typically above ambient temperatures, thermal growth must be accounted for.
2. Strains – caused by attached piping run can cause equipment to be out of alignment. Misalignment caused by pressure can recur after a successful alignment because of the continuous action of forces from strained equipment.
3. Torsional Movement- Torque is the initial high torque caused during start-up. It can cause shafts to be forced out of alignment, which causes torsional movement misalignments.
4. Settling – Over time, foundations or bases can settle to lower positions, causing settling misalignment. If the equipment can be realigned without addressing the cause of its misalignment, the issue can recur.
5. Human Error– Mistakes in an alignment procedure or failing to complete an alignment procedure can result in human error misalignment
6. Misfired Couplings– Manufacturing defects such as misaligned couplings can cause misfired coupling alignment. This type of misalignment is most often found on new equipment. However, if you damage a collar during an alignment, you’ll get similar results.

Effects

Various methods, including excessive vibration, can identify alignment issues in rotating machinery, extreme bearings temperatures, wear patterns, or noise. Some ways are incorporated as part of a plant’s preventative maintenance program. Other checks include inspections that could be done regularly but are usually performed after the equipment has broken down.

The damaging effects of an unaddressed misalignment include the following:

1. Excessive vibration– misalignment is one of the leading causes of equipment vibration. Despite self-aligning bearings, flexible couplings, and other features, it is difficult to properly align two shafts and approaches so that no forces will cause vibrations. The significant characteristic of misalignment is that vibrations will occur in both the radial and the axial directions.
2. Noise -Like Vibration – Noise can be detected simply by noting equipment sound changes during operation. All running equipment produces some noise. Only if an operator knows what normal equipment noise sounds like will they be able to hear abnormal noises.
3. Lost production – misalignment can directly affect equipment life. If you shorten the service life of equipment, it will need unplanned maintenance, which will reduce the time available for production, thus increasing the cost of production.
4. Poor quality products – may be caused by equipment misalignment. For example, suppose your camera lens is not perfectly aligned with your sensor. In that case, manufacturing defects and product damage caused by misalignment can be avoided if the alignment is correct.
5. Higher than average repair orders– Misalignment-related failures will cause more unplanned maintenance, which will result in more repair orders.
6. Increased inventory of spare parts– As the number of maintenance increases due to misalignment-induced failures, more spare parts need to be ordered. Output is a list of sentences generated by the paraphrase module. 
7. Reduced profits – Machines fail early and unexpectedly, so more money must be spent on maintenance and spare parts. With lower productivity, misalignment can quickly reduce profitability.

Alignment is based on accurately measuring the motor and pump shaft positions at two points or more. We provide laser-based torsion alignment service up to 20 meters long of torsion shaft within accepted tolerances in the cement industry mining industry and steel plants.