8100/08.02 Joining together! Böllhoff GmbH Archimedesstraße 1 – 4 · 33649 Bielefeld · Germany Phone +49 (0)5 21 / 44 82 - 03 · Fax +49 (0)5 21 / 44 93 64 www.boellhoff.com The Manual of Fastening Technology The Manual of Fastening Technology TheThe ManualManual ofof FasteningFastening TechnologyTechnology 5th edition 2 Introduction Dealing with the complex field of fastening these factors are significant, and outlines technology every day means there are always important aspects for everyday use. questions to answer that go beyond the information normally provided in the standards. The first edition of “The Manual of Fastening The aim of this manual is to provide an overview Technology” was published in 1987. The content of the technology associated with threaded of the third edition published in 2002, which this fasteners, in order to help users in answering edition supersedes, has been comprehensively these questions. revised and updated. The information provided brings together details Our Application Engineering team is always of the relationships between products and their standing by to offer expert advice should you mechanical properties, gives advice for arrang- require any further support. ing, securing and fitting fasteners, explains why ECOTECH – After defining the specific requirements for a ECO TECH project, our Application Engineering department nomic nical Engineering works together with the customer to develop appropriate solutions, and offers design support Depending on requirements, a wide range of where this is required. additional services are also available: ■ Assembly optimisation, including on-site Benefits of using ECOTECH customer service ■ Shorter development times ■ Standardisation and optimisation ■ Documented basis for decision making ■ Information and consulting ■ Latest fastening technology ■ Customer seminars ■ Reduction of storage costs ■ Manufacturing process optimisation ■ Optimisation of the cost of assemblies 3 We connect tradition to Wilhelm Böllhoff Josef Böllhoff Wilhelm A. Böllhoff/Dr. Wolfgang W. Böllhoff/Michael W. Böllhoff 4 the future. The Böllhoff Group's corporate identity is o built in part on over 130 years of independ- ence as a family business. This independence will also set the pace for the future development of the company. Experience breeds trust. Three generations of Böllhoffs have continuously built on the success of the company's founder. And our children remain the guarantee for the future. 5 “Our product development: 6 We never stand still We “Products and markets change at a breath- taking pace - and with them the require- ments of our customers. Product development must therefore always be one your advantage” step ahead. We are already thinking about tomorrow, today. It doesn't matter whether it's about developing a new product from scratch, or working hand in hand with the customer to solve a specific problem. For me, every challenge is also a chance to deliver impressive performance. That's how genuine innovation is born of ideas, and new markets are born of innovation.” 7 8 Contents Page Selection and analysis 10 – 15 Section 1 Standards 16 – 25 Section 2 Materials 26 – 43 Section 3 Manufacture 44 – 51 Section 4 Threads 52 – 60 Section 5 Assembly 61 – 66 Section 6 Self-tapping fasteners 67 – 74 Section 7 Fastener retention 75 – 83 Section 8 Corrosion protection 84 – 100 Section 9 ECOTECH 101 – 102 Section 10 9 Selection and analysis The threaded fastener is one of the most univer- due to the forces acting on the connection. sal and widely used types of fastener and is Conversely, the preload force selected must not manufactured in a wide variety of shapes and be so high as to cause the permissible stresses sizes. Many types of design are standardised in- in the joined components to be exceeded during ternationally and available throughout the world. service. The classic threaded connection is formed by The proper design of a threaded connection for 1 joining two or more components by means of a given set of components is not only dependent form-fit or friction-fit fasteners. The tightening on positioning and the selection of an torque applied to the threaded fastener gener- appropriate assembly method, but also, most ates a preload force that clamps the compo- importantly, on the quality of the design of the nents together, thereby creating a frictional fastener itself. A large number of different sizes, connection between all the contacting surfaces. standards, materials and property classes are available. It remains the task of the user to make With a properly designed threaded connection, the correct choice to provide the preload force the preload force is high enough to prevent any required in each case. relative movement between the components E C n O A ig T ss es em d E b / d Ge l n oa C ne y o el H r p ti r at r a p f e o l e e o p c u in c r r e c r c e s l e m o l s a r f o a C e t d e D Designing ECOTECH a threaded ECOTECH s r M e connection d n a a e o i t n l f s o e e t R a r a r c c f r e i p n e o t f d d e p e n r n e a d t t l o s a i a h o t e E d i n r W h t C m f e o O t h s o e i d t r T e p o r P E C H 10 Selection and analysis Threaded connections should be designed in such a way that the permissible stresses in the mating components are never exceeded by the Clamping length forces acting on the connection as a whole. The tightening torque should be selected such Threaded that the preload force produced creates a purely Contact surfaces fastener frictional connection between the components Tightening torque 1 and thus prevents them from sliding against each Preload force other or having to be supported by the shaft of the fastener (as compared to a rivet connection). Guideline value: Preload force should be at Nut least equal to 75% of the yield stress in the Washer Washer fastener. Clamped components A detailed procedure for the analysis and design of threaded connections can be found in VDI Guideline 2230. All forces that occur give rise to deformation and the possibility of displacement of the joined com- ponents. As long as the sum of all forces does not cause failure of one of the components or fasteners, the assembly acts as a unit. However, where dynamic loads are present –particularly vibration – it is possible for effects to occur that cause the threaded connection to work loose, although the permissible values are not ex- ceeded, e.g. due to components moving relative to each other along the axis of the fastener. This effect is referred to as self-loosening. Applying a tightening torque indirectly causes a preload force to act on the fastener, which in turn leads to elongation of the fastener and con- traction of the joined components. Forces that occur in use are distributed according to the elasticity of the mated parts. Under tensile stress, the load on the fastener is only reduced slightly, whereas the remaining clamping force decreases significantly. 11 Selection and analysis The elastic elongation of the fastener that occurs require additional retention measures, provided as a result of the preload force means that the that no increased dynamic loads are likely, espe- frictional connection between the components cially perpendicular to the axis of the fastener. remains intact under additional loading, particu- In other cases, the use of additional means of larly impact loading. fastener retention should be considered. With a clamping length ratio of Lk/DNom > 5, Important: Any compressible spring elements 1 a low number of contact surfaces and sufficient used in conjunction with the fastener will affect preload force, metallic components do not the load ratios. Sum of forces acting on the fastener Preload force Force occurring in service Clamping force Contraction of the preloaded components Preload force Preload Elongation of the fastener Change in length Preload diagram 12 Selection and analysis Effects of friction During fitting of the threaded fastener, the friction characteristics is of decisive importance. preload force can only be regulated indirectly It is necessary to distinguish between the friction via the tightening torque that is applied, which in the thread itself and that at the bearing means that a precise knowledge of the surfaces. 1 Normal Friction angle μ force FG Friction force FR The friction angle, μ, describes the ratio of the is therefore possible to either increase the thread normal force, FG, to the friction force, FR, which it friction or to reduce the thread pitch. generates. The effect of friction at the bearing surfaces is Taken in the context of a threaded connection, considerably more difficult to determine. It is normal force and preload force can be consid- nonetheless possible to establish that, for a ered equal as a first approximation. given tightening torque, an increase in friction, e.g. below the head of the fastener, on the one Provided that the pitch angle, ϕ, of the thread is hand reduces the preload force, but on the other greater than the friction angle, μ, the thread will hand counteracts self-loosening of the fastener. be self-locking. In order to enhance this effect, it 13 Selection and analysis Design The selection of the required fastener diameter It is necessary here to distinguish between and property class relies upon a precise knowl- connections formed using a clearance hole edge of all loads that might occur, and is thus (bolts) and internally threaded holes (screws).