Overview
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ABSTRACT
Controlled tightening of screws and bolts is of growing importance in various sectors, where assembly defects caused by insufficient, excessive or heterogeneous tightening could be a hazard. To avoid or mitigate failures attributable to improper tightening, the measurement and control of tightening is necessary to ensure perfect sealing and stiffness that enables the assembly to withstand external static and dynamic stresses. This paper presents the technology implemented, the principle of ultrasonic measurement and some industrial applications.
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Farid BELAHCENE: Doctor of Engineering, founder of ULTRA RS (France)
INTRODUCTION
Insufficient, excessive or heterogeneous tightening accounts for around 30% of static failures, and poor tightening conditions for 45% of fatigue failures. They are a recurring problem in all industries: transport, refineries, nuclear power, shipbuilding, etc., with a major financial and human impact.
Screwed and bolted assemblies are at the heart of the safety of many industrial structures.
To achieve a reliable assembly, it is necessary to use quality fasteners that comply with standardized mechanical characteristics, to control their installation by ensuring reproducibility, and to check their resistance over time.
To optimize the reliability of an assembly, two phases are necessary: prototype and production.
In the prototype phase, the aim is to verify and validate the minimum clamping conditions: tests involving dropping the assembly, shocks, repeated vibrations and temperature increases to which an assembly is subjected. A precise control method is needed to verify the clamping tension values after these tests.
In the production phase, the aim is to create an assembly specification including all its characteristics, and in particular the following points: assembly parts, clamping instructions, precision class, clamping means, method of checking clamping tensions...
Validation of this specification must be approved and validated by the design, methods and quality departments.
Hence the need to master the clamping operation with precise, reliable tooling.
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KEYWORDS
acoustic waves | ultrasound | tightening force |
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Bibliography
Standards and norms
- Fastening elements – Torque/voltage tests – Amendment 1 - NF EN ISO 16047/A1 - 01-13
- Éléments de fixation. Assemblages vissés. Conception, calcul et conditions de montage - FD E 25-030 - 08-84
- Articles de boulonnerie d'usage général. Spécifications techniques. Réception. Commande. Livraison - NF E 27-005 - 10-69
- Éléments de fixation. Essais de fatigue sous charge axiale - NF E 27-009 - 10-69 ...
Patents
US8037772B2. Thread forming fasteners for ultrasonic load measurement and control.
EP787980B1. Measuring a load on a part and monitoring the integrity of the part | Belastungsmessung eines Elementes und Überwachung seiner Integrität | Mesure de la charge dans une pièce et surveillance de l'intégrité de cette pièce.
US5301574A. Hydraulic wrench and piston has rack gear meshed with...
Directory
Manufacturers – Suppliers – Distributors (non-exhaustive list)
• The SKF Group's technical guide to clamping
http://www.skf.com/binary/12-126662/Serrage- hydraulique_10061_FR.pdf
• ULTR A-RS website
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