Gene Vogel
Pump & Vibration Specialist
EASA
St. Louis, MO
The paper "Overview of the New Shaft Alignment Standard" by Gene Vogel, presented at the EASA Convention 2018, introduces the ANSI ASA S275 Part 1: General Principles, Methods, Practices, and Tolerances standard for shaft alignment. This standard was developed by the Vibration Institute in collaboration with the Acoustic Society of America (ASA) to provide a comprehensive and consistent approach to shaft alignment across various industries. Prior to this, there was no national or international standard for shaft alignment, leading to inconsistencies in methodologies and tolerances.
The standard focuses on machine configurations commonly found across industries, specifically "4 bearing sets," which consist of two independent shafts each supported by a pair of bearings and coupled by a flexible coupling. Examples include horizontal motor-pump or motor-fan combinations. The intention is to expand this initial document with additional standards addressing other machine configurations, such as vertical machines and 3 bearing sets.
The standard provides guidelines on shaft alignment tolerances, base flatness and level, shaft runout, coupling runout, pipe and conduit strain, soft foot, and offline-to-running (OLTR) machinery movement. It emphasizes the importance of turning both shafts when making alignment measurements to ensure accuracy. Tolerances for pipe and conduit strain are set to prevent changes in shaft alignment greater than 50 micrometers (2 mils) vertically or horizontally at the coupling.
A holistic approach to the shaft alignment process is presented, including a flow chart documenting key steps and decision points. The standard includes informative annexes covering alignment principles, machine move calculation formulas, identifying and correcting pipe strain, OLTR methods, laser detector systems, graphic alignment modeling, repeatability, and an alignment and machinery installation checklist.
Alignment principles are explained through two common methods: offset and angularity between shaft centerlines, and flex plane angles at the coupling mechanical link (CML). The flex plane angles more accurately represent the work done by the coupling and are used to establish alignment tolerances. Alignment Quality Grades are provided based on flex plane angles and machine operating speed, with three grades: AL4.5 (Minimal), AL2.2 (Acceptable), and AL1.2 (Excellent).
The standard also addresses practical concerns related to moving machine cases, such as soft foot, base-bound, and bolt-bound conditions. It provides guidelines for controlled machine positioning and emphasizes the importance of proper axial spacing (coupling gap).
Several annexes offer detailed instructions on related topics. Annex B covers correction move formulas for various dial indicator setups. Annex D explains OLTR movement and how to establish target values for alignment. Annex F discusses alignment modeling, which helps visualize and calculate machine case moves. Annex H provides a machinery installation checklist to ensure important steps are not missed.
Key Points Covered:
- Development and scope of the ANSI ASA S275 Part 1 standard
- Focus on "4 bearing sets" machine configurations
- Guidelines on shaft alignment tolerances and related factors
- Holistic approach to the shaft alignment process
- Alignment principles and methods
- Alignment Quality Grades based on flex plane angles and machine speed
- Practical concerns related to moving machine cases
- Detailed instructions in annexes on correction moves, OLTR movement, alignment modeling, and installation checklist
Key Takeaways:
- The new standard provides a consistent approach to shaft alignment across industries.
- Focus on common machine configurations with plans to expand to other setups.
- Emphasis on accurate alignment measurements and tolerances.
- Holistic approach includes flow charts and detailed annexes.
- Flex plane angles are used to establish alignment tolerances.
- Alignment Quality Grades help determine acceptable alignment based on machine speed.
- Practical guidelines for moving machine cases and addressing alignment issues.
- Comprehensive annexes offer valuable instructions for various aspects of shaft alignment.
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