8 THE DISTRIBUTOR’S LINK Bengt Blendulf Bengt Blendulf was educated in Sweden and moved to the US in 1974 to start a subsidiary for a Swedish fastener manufacturer. After working as a technical consultant on the faculty of the College of Engineering and Science at Clemson University, he established EduPro US in 1997 to teach highly rated courses in Fastening Technology in the US, Canada, Mexico, Europe and Asia. Being one of the founders, Bengt served as the chairman of ASTM F16.96 Bolting Technology from 1996 to 2006. In 2006 he received the Fred F. Weingruber award from ASTM for “his efforts to promote and develop standards for the fastener industry.” In 2013 he also received IFI’s Soaring Eagle Award for “significant contributions to the technological advancement of the fastener industry”. Bengt is the author of an extensive lecture book, well over 110 articles and “Mechanical Fastening and Joining”, a book published in 2013 by the Industrial Fasteners Institute. He can be contacted through www.edupro.us or by email bblendulf@yahoo.com. VDI 2230 AND SR1- A SYSTEMATIC WAY OF DEVELOPING RELIABLE JOINTS When I joined the fastener industry back in 1966 (50 years next year!!), bolted/screwed joints were often subjects to a lot of guesswork. Honestly, that is still case too many times. The German Society of Engineers, VDI, had just initiated a very serious and detailed study of high strength bolted/screwed joints, laying the ground work for what was to become the VDI 2230 design guideline. We worked along the same line at the Swedish company I worked for (Bulten) at the time (1966-1978). We were fortunate to have Dr. Karl-Heinz Kübler on our engineering staff. Dr. Kübler later became one of the leading members of the VDI 2230 development group, which also included Gerhard Junker. Herr Junker, who worked as the Director of Engineering for Unbrako – SPS Technologies in Europe, served as the chairman for VDI 2230 in the beginning. The guideline was first published in 1977 by VDI. It is still an ongoing engineering project and is continuously updated with new research being completed. To use the guideline manually is a very complex and time consuming methodology requiring both patience and a high level of discipline from the design engineer using a calculator or slide rule (maybe not anymore). Jakob Kluser, at that time the engineering manager for Bossard in Switzerland, contacted Texas Instrument in Switzerland, Dr.-Ing. Michael Galwelat at the Technical University in Berlin and myself to discuss the possibility of finding a way to simplify the use of VDI 2230 by employing electronic media. This work eventually resulted in the Bossard Screw Calculator, based on a modified T-58 programmable calculator. I introduced this concept in the United States in 1983 and it was met with a great deal of interest by engineers from the automotive industries, NASA and independent bolting experts. The predicted sales success for the calculator did not materialize since CONTRIBUTOR ARTICLE corporate lawyers warned engineering from using it due to its “foreign” origin and its complexity. The, however unlikely, possibility of mis-use resulting in lawsuits scared the day-light out of the non-engineers who could not understand and/or appreciate the obvious design benefits. Hindsight is always 20/20. If we had waited a couple of more years we could have had the guideline on floppy discs to be used on personal computers, more and more common on the desks of engineers in the 1980’s. There would also have been lots of recommendations available from industrial users in Europe where engineers, not lawyers, typically make technical decisions. That is, of course, now “water under the bridge”. The interesting, and for me gratifying, thing was that within the next 10-20 years many industries in the US and other countries adopted the VDI 2230 concept (not the calculator) for the majority of their critical joint designs. Even those engineers, who were earlier frightened by lawyers and other “joint ignorant” individuals, joined in. What helped in this process was the development of computer software to make the guideline more practical to work with. With all the “ready-made” mathematic formulae and the access to a broad data base for materials, tightening methods and many other variables, designing a highly stressed bolted/screwed joint now became almost like a “walk in the park.” Let me now illustrate how this design tool (SR1) makes it possible to verify a joint and to make necessary adjustments when needed. Figure 1 shows a relatively straight forward bolted joint using a Hex Head Bolt and a Hex Nut to clamp two steel plates together. In my 2-day fastener engineering class my students will learn how to do the initial estimates of size and property classes and to verify by using VDI 2230. CONTINUED ON PAGE 134
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