Shaft alignment: laser processes and tolerances for rotating machines

1. Introduction

The precise alignment of shafts in rotating machines is a crucial factor for the operational safety, energy efficiency and service life of industrial systems. Misalignments, even in the micrometer range, lead to increased vibration, bearing and seal damage, increased wear on couplings and a significant increase in energy consumption. Studies show that up to 50% of all machine failures can be attributed to poor shaft alignment. Correct alignment using laser technology is therefore not just a maintenance measure, but a strategic investment in system availability and production stability. UNITEC-D GmbH supplies components that are critical for the precise function of these machines and supports operators in selection and maintenance.

2. Fundamental principles

2.1 Physical principles of shaft alignment

Shaft alignment refers to the correct positioning of the axes of rotation of two or more coupled shafts. Ideal alignment means that the axes of rotation are exactly coaxial and collinear. In practice, two main types of misalignment are distinguished: parallel (radial) misalignment and angular (axial) misalignment. Both forms often occur at the same time.

• Parallel misalignment: The shaft axes are parallel to each other but laterally offset. This leads to cyclic loads in the radial direction on the coupling, bearings and seals.
• Angle misalignment: The shaft axes intersect at an angle. This creates oscillating axial forces and bending moments that drastically reduce the life of bearings and seals.

Misalignments create unwanted forces and moments in the drive train. These forces induce dynamic loads on the rotor bearings, increasing the operating temperature and accelerating the material fatigue process. The thermal expansion of the machine components during operation must also be taken into account. A machine that is perfectly aligned at room temperature may exhibit significant misalignment at operating temperature. Therefore, knowledge of the thermal shift and its compensation during cold alignment (offset) is critical.

2.2 How laser shaft alignment works

Modern laser shaft alignment systems use two laser transmitter/receiver units that are attached to the shaft halves of the machines to be aligned. Each unit projects a laser beam onto the detector of the opposite unit. By rotating the shafts (often in at least three positions, e.g. 9, 12, 3 o'clock) the exact positions of the laser points on the detectors are recorded. Based on these measurements, the system software precisely calculates the current shaft position and the necessary corrections.

The system delivers the required movements (vertical and horizontal) on the bearing feet of the moving machine (e.g. motor) in real time. This enables iterative adjustment until the specified tolerances are reached. The advantages over traditional methods (dial gauge) are higher precision (typically up to 0.001 mm), faster measurement, lower susceptibility to errors due to human factors and the ability to document the measurement results.

3. Technical Specifications & Standards

3.1 Applicable standards and guidelines

Shaft alignment is regulated in various national and international standards that place requirements on measurement tolerances, procedures and documentation:

• DIN ISO 21940-11:2016: Mechanical vibrations - Shaft alignment - Part 11: Methods for shaft alignment. This standard describes in detail the various methods and their application.
• VDI 2060: Assessment of the balancing quality of rotors. Although primarily designed for balancing, it contains important information about the effects of rotational errors.
• ISO 1940-1:2003: Mechanical vibrations - requirements for the balancing quality of rotors in a constant (rigid) state.
• Manufacturer-specific guidelines: Many machine and coupling manufacturers publish their own detailed alignment tolerances and procedures, which are often more stringent than general standards. These must always be given priority.

The CE marking of machines requires, among other things, compliance with relevant safety and health requirements, which indirectly also includes correct assembly and maintenance, including shaft alignment, in order to minimize risks from vibrations. ATEX-certified systems (Directive 2014/34/EU) also have special requirements for preventing flying sparks and overheating, which is supported by correct alignment.

3.2 Alignment tolerances

The permissible alignment tolerances depend largely on the speed of the machine and the coupling type. Higher speeds require tighter tolerances. General guidelines for parallel and angular misalignment are summarized in the following table. These values ​​serve as orientation; However, manufacturer-specific information is binding. The dimensions are given in millimeters and refer to the coupling diameter or the distance between the measuring points.

These tolerances are maximum permissible deviations. For critical systems, such as pumps in chemical processes or compressors, significantly stricter values ​​of <0.01 mm radial and <0.01 mm/100mm axial are often aimed for in order to achieve an MTBF (Mean Time Between Failures) of over 50,000 operating hours. TUV-certified systems require strict compliance with these requirements.

4. Selection & Sizing Guide

4.1 Selection of the laser alignment system

Selecting the appropriate laser alignment system depends on various factors:

• Measuring distance: Systems vary in the maximum distance between waves, typically 0.1 m to 10 m.
• Machine type: Specialized functions for vertical machines, cardan shafts or machines with multiple clutches.
• Ambient conditions: Dust, vibrations, bright light can influence the measurement accuracy. IP protection rating (e.g. IP65) is important for harsh environments.
• Ease of use: Intuitive operation, graphical user interface and wireless connectivity (Bluetooth/WLAN) are advantageous.
• Software features: Real-time correction suggestions, documentation and reporting functions.
• Budget: Systems vary greatly in price, depending on precision and functionality.

4.2 Consideration of thermal expansion

Taking thermal expansion into account is a critical step. Machines change position when switching from cold to running states. This can be done by:

• Thermal calculation: Based on material expansion coefficients and temperature differences (ΔT). Steel expands approx. 12 µm/m K. For a pump with a shaft height of 500 mm and a temperature difference of 60 K (operation to environment), this results in a vertical expansion of 500 mm * 12 µm/m K * 60 K = 0.36 mm.
• Empirical measurements: Monitoring of the machine position during start-up using laser or infrared systems.

The resulting thermal offset must be taken into account in the cold alignment. Most modern laser alignment systems can store these offsets and include them in the calculations.

4.3 Decision matrix for alignment procedures

The following table assists in selecting the appropriate alignment method based on machine criticality and resource availability.

5. Installation & commissioning best practices

5.1 Preparation of the machine and surroundings

Careful preparation is crucial for the success of shaft alignment:

• Machine cleaning: Removing dirt, rust and old shims from machine feet and base plate.
• Check foot condition: Make sure that all machine feet lie flat on the base plate (no “soft foot” conditions). A soft foot of >0.05 mm can seriously distort the alignment.
• Anchor bolts: Tighten all anchor bolts evenly. A torque wrench should be used to avoid deformation.
• Check shaft play: Check axial and radial play of the shafts to rule out coupling problems or bearing damage.
• Clutch inspection: Check clutch for wear, damage or contamination. Couplings according to DIN 818, e.g. torsion coupling type from Flender, must be in good condition.
• Environment: Maintain stable ambient temperatures to minimize thermal drift during measurement.

5.2 Carrying out laser alignment

1. System assembly: The laser units are mounted securely and stably on the shafts. The detectors must be able to receive the laser beam.
2. Rough alignment: Make an initial rough alignment using a ruler or visual inspection so as not to exceed the measuring range of the laser system.
3. Data input: Input of the machine dimensions (distance of feet, distance of coupling) into the laser system.
4. Measurement: Rotate shafts in at least three positions (e.g. 9-12-3 o'clock or 10-2-6 o'clock for optimal results) and record measurements. Modern systems with gyroscopic technology enable measurements at any angle (e.g. 25-55-90 degrees).
5. Analysis and correction suggestions: The laser system's software calculates the current misalignment and displays the necessary corrections (vertically using shims, horizontally by moving the machine) on the machine feet.
6. Vertical correction: The moving machine is corrected vertically by adding or removing precision shims (according to DIN 988 or manufacturer specific). Max. 4 panels per foot, total height not to exceed 15mm.
7. Horizontal correction: The moving machine is moved horizontally to eliminate the radial misalignment.
8. Verification: After each correction, re-measure to check progress and ensure tolerances are met. This iterative process is repeated until all parameters are within acceptable limits.
9. Final inspection and documentation: After successful alignment, tighten all anchor bolts to the correct torque (according to DIN 934 or manufacturer's specifications) and document the final measurement.

6. Failure Modes & Root Cause Analysis

Misalignment is one of the most common causes of machine damage. The typical error modes and their causes are:

6.1 Typical damage patterns

• Bearing damage: Increased radial and axial loads lead to premature wear of rolling bearings (DIN 625, DIN 628). This manifests itself in increased noise levels, increased storage temperatures (often > 80°C) and signs of seizure.
• Coupling wear: Excessive misalignment stresses the coupling elements (elastomers, plates) beyond their design limits. The result is cracks, breakage or increased wear on the coupling halves. Elastic couplings according to DIN 740 can compensate for certain misalignments, but only within their specification limits.
• Seal damage: Shaft movements due to misalignment lead to excessive friction and wear on shaft seals (DIN 3760) or mechanical seals. This manifests itself in leaks and media loss.
• Shaft breakage: In extreme cases or during prolonged operation with high levels of misalignment, material fatigue and excessive bending moments can lead to shaft breakage.
• Foundation cracks: Transmitted vibrations can cause cracks in the foundation, affecting the stability of the entire machine installation.

6.2 Causes of misalignment

• Improper Installation: Lack of care during initial installation or maintenance.
• Thermal expansion: Position changes due to operating temperature not taken into account or incorrectly calculated.
• Foundation settlement: Movement or deformation of the machine foundation over time.
• Piping forces: On pumps or compressors, poorly supported or braced pipelines can exert significant forces on the housing and distort the shaft. Maximum permissible forces and moments must be observed in accordance with EN 13480 or API 610.
• Soft Foot: The machine feet rest unevenly on the base plate.
• Deformation of the machine frame: Due to aging, corrosion or overload.
• Clutch Wear: A worn clutch can increase the effects of misalignment.

7. Predictive Maintenance & Condition Monitoring

The early detection of misalignments is crucial in order to avoid major damage and unplanned downtime. Condition monitoring plays a central role here:

• Vibration Analysis: This is the primary method for detecting misalignment. Typical signs are increased vibration levels at 1x and 2x the rotation frequency in the axial and radial directions. Analysis of the frequency spectra enables the distinction between parallel and angular misalignment. Systems according to ISO 10816 provide the basis for the evaluation.
• Temperature monitoring: Elevated temperatures on bearings, couplings and seals can indicate excessive friction due to misalignment. Infrared cameras or permanently installed temperature sensors (PT100 according to IEC 60751) are suitable for this.
• Oil Analysis: Particles in the lubricating oil, such as iron, chromium or nickel, may indicate increased bearing or gear wear caused by misalignment.
• Acoustic Analysis: A trained ear can detect changes in machine noise that indicate misalignment, although this is less precise than vibration analysis.

By integrating these monitoring techniques into a comprehensive predictive maintenance program, maintenance intervals can be optimized, system availability increased and operating costs reduced. The limit values ​​for monitoring must be determined based on DIN ISO 21940-11 and VDI 3832.

8. Comparison matrix for laser alignment technologies

The market offers various laser alignment systems with different features. The following matrix compares common technologies and their suitability for different applications.

9. Conclusion

Precise shaft alignment using laser technology is an indispensable measure to ensure the operational safety and cost-effectiveness of rotating machines. By complying with established standards such as DIN ISO 21940-11 and taking thermal expansion into account, system operators can significantly extend the service life of their machine components, reduce unplanned downtimes and optimize energy consumption. The investment in high-quality laser alignment systems and trained personnel quickly pays for itself through lower maintenance costs and increased production efficiency.

As your certified partner, UNITEC-D GmbH offers a wide range of high-quality components for drive trains, bearings and seals, which are essential for the reliable operation of your optimally aligned machines. From precise couplings to long-lasting bearings – our products are tailored to the demanding conditions of the DACH manufacturing industry and meet CE, TUV and ATEX standards.

Visit our e-catalogue to find the right components for your systems and to ensure optimal performance: https://www.unitecd.com/e-catalog/

10. References

• DIN ISO 21940-11:2016, Mechanical vibrations - Shaft alignment - Part 11: Methods for shaft alignment. Beuth Verlag, Berlin.
• VDI 2060, assessment of the balancing quality of rotors. Association of German Engineers, Düsseldorf.
• ISO 10816-1:1995, Mechanical vibrations - Measurement and assessment of machine vibrations - Part 1: General requirements. International Organization for Standardization.
• Pruftechnik AG, “Fundamentals of Shaft Alignment”, Technical Manual, 2022.
• API Standard 610, “Centrifugal Pumps for Petroleum, Petrochemical and Natural Gas Industries”, 12th Edition, 2020.