DNV awards Intellifast a tightening factor of 1.1

Speyer. The tightening factor plays a crucial rule in the dimensioning of bolted joint connections by considering the accuracy of the tightening tool in achieving the design bolt load. VDI-2230 creates a design to accommodate the fastener load scatter created by the assembly tool. The renowned certification service DNV (Det Norske Veritas) confirmed Intellifast a tightening factor of 1.1

A simplified example of torque controlled assembly makes it clear how dominant this design factor is in the selection of the bolt diameter: Wide variation in the under head and thread friction coefficients during assembly gives a normal scatter of the clamp load ± 30% around the mean. If the necessary minimum clamp load for safe function of the bolted connection is approx. 50% of the bolt tensile strength, then an average value of 70% gives a maximum value of 90%. This maximum value typically is also specified, and can be found in many standards. As a result the tightening factor calculates to a value of 1.8 (90/50). In the design of bolted joints, many companies internally specify a tightening factor of 2.0 for bolt dimensioning if torque controlled assembly is selected.

A tightening factor of 1.1 (retaining the maximum pre-load value) increases the achieved minimum clamp load to approx. 82%, maximising the strength properties in the bolt material. As a result, smaller or fewer bolts are required in specifying the fasteners for the joint. Another possibility is the selection of a more cost-effective bolt material, with a lower tensile strength. Thus, the tightening factor is a valuable means of weight and cost reduction.

The certified 1.1-tightening factor using Intellifast equipment is developed using ultrasonic controlled assembly tools with corrosion resistant permanent transducers on every bolt. These transducers also allow inspection of the actual clamp load during the life time of the bolted joint connection.

Based on a license agreement with digifast® from Schrauben Betzer Intellifast equips every bolt with a 2D matrix code, storing the identification number, the joint application identifier as well as the reference ultrasonic time of flight on the bolt. These parameters are read using off the shelf barcode readers. The barcode avoids confusion and provides instant verification and documentation of load inspection with no additional data management requirements.

An assembly tightening factor of 1.1, the certified corrosion resistance of the permanent transducers (up to 1440 hours standard salt spray test) and the use of the digifast® technology makes the Intellifast technology a necessary partner in the new mega-trends in the bolted joint design and assembly: weight reduction, complete documentation and 100% traceability.