Stahlbau Calendar 2011 Ebook

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Fastening screws, like powder-actuated fasteners, are made from hardened carbon steel or stainless steel. The various screw types are differentiated mainly in the ways in which they are used. A self-tapping screw, for example, is driven in a pre-drilled hole. The screw forms its own thread in the base material as it is driven. A self-drilling screw, on the other hand, is equipped with a drill point, so no predrilling is necessary.

The screw drills the hole and forms a thread simultaneously in a single operation. Figure 1 shows typical examples of powder-actuated fastening and screw fastening applications in light-gauge steel construction:. Fastening thin-gauge trapezoidal metal sheets or liner trays to hot-rolled beams or thin C- or Z-profiles,. Joints between cold-formed thin-gauge profiles. The decision to use powder-actuated fasteners or metal construction screws depends, from a technological point of view, on the thickness of the supporting base material.

In order to ensure a reproducible driving process, the material into which powder-actuated fasteners are driven must meet minimum thickness requirements. Depending on the fastening system used, this minimum thickness is between 3 and 8 mm. Accordingly, the powder-actuated fasteners currently available on the market are unsuitable for the purpose of fastening profile metal sheets at overlap joints (sheet to sheet) or for fastening Z-brackets to profile metal sheets. Self-drilling screws are used predominantly in the field of construction where sheets of this thickness are involved. The main cost-efficiency advantage of powder-actuated fasteners lies in the high productivity that can be achieved with systems of this kind.

When compared with fastening screws, this advantage becomes even greater as the thickness and strength of the base material increases, especially where the powder-actuated fastening system is capable of covering the entire strength tolerance range of S355 material. In the 3 to 8 mm thickness range the productivity advantage of powder-actuated fastening is less pronounced as the driving time for fastening screws in this material thickness range is only about one second per millimeter of material thickness. The values given in Table 1 provide a guide concerning the base material thickness range that can be covered (component II) as well as the thicknesses of the metal sheets to be fastened (component I) for currently approved fasteners.

Other possible areas of use for powder-actuated fasteners and fastening screws, e.g. As a means of joining materials, fastening wood or wood materials or fastening base profiles for glass facades, will be discussed in this report in conjunction with the corresponding applications. The first European Technical Approval for fastening profile metal sheets was granted in 2004 to a powder-actuated fastener 6.

Since 2005, the basis for European Technical Approval of metal construction screws and sandwich panel screws has been under development. The first European Technical Approval for fastening screws was granted in the year 2010 and approval for sandwich panel screws is expected to be awarded in 2011. When DIN EN 1993-1-1 7 comes into force there will then be complete formal agreement with the European Technical Approvals. In many cases, these will take over completely from the previous national means of product qualification in the form of general construction supervisory authority approvals Z-14.1-4 8 or, respectively, Z-14.4-407 9. The European approval specifications are thus presented alongside the previous national German regulations in order to allow comparison of the earlier German approval concept with the new European Technical Approval provision both for powder-actuated fasteners as well as fastening screws. Fasteners for metal sheets and liner trays.

Nevertheless, the relevance and influence the individual parameters have on loading capacity can be interpreted from The approval data – especially for powder-actuated fasteners – only to a certain extent. A further motivating reason for writing this article is thus to illustrate, by means of example, the influence of individual parameters on loading capacity and thereby provide a better understanding of the possible applications of powder-actuated fastening as well as its application limits. The applicable technical data is generally determined from tests. The fundamental technical relations are thus explained in this paper on the basis of examples and test results. Figures given apply only to the fastening system tested and to the specific application conditions. A quantified generalization of the information given here to cover powder-actuated fasteners and fastening screws from other manufacturers or, respectively, fasteners of a different type from the same manufacturer, is possible only after consultation with the applicable manufacturer.

2 Powder-actuated fastening technology 2.1 Basic principles 2.1.1 Methods and terminology The powder-actuated fastening technique involves using a fastening tool to drive a high-strength steel fastener (nail or threaded stud) directly into the base material. Penetration of the fastener causes plastic displacement of the base material (Figure 2). A portable, hand-held, powder-actuated fastening tool is used to drive the fasteners.

For applications in steel construction the driving energy is usually provided by firing a cartridge containing a combustible propellant in powder form. Other possible energy sources are compressed air or gas combustion. In the construction industry, so-called piston-type (Class A) tools are used exclusively 10. In tools of this type, the piston functions as an inter-mediate element between the fastener and the propellant cartridge, with the effect of reducing the velocity at which the fastener is driven.

Fasteners for metal sheets and liner trays. The fastener, the fastening tool and the driving energy together make up the fastening system, Figure 3. The quality of the fastening obtained depends not only on the fastener but also on the fastening tool, as the tool has a decisive influence on the quality and reproducibility of the driving operation. With a view to limiting the recoil of the tool, the maximum driving energy used with portable, powder-actuated fastening tools is restricted to approx. With this available energy, the fastening tools in use in the construction industry are capable of driving fasteners of up to approx. 5 mm shank diameter into steel base material.

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Although driving fasteners of greater diameter would be technically possible, the tools required could no longer be held by hand. For comparison: The maximum driving energy provided by compressed-air tools is approx. 250 J while gas combustion tools achieve approx. Propellant cartridges are available in various calibers and lengths. The calibers in common use are 6.3 and 6.8 mm. Cartridge power levels are indicated by a cartridge color code in accordance with 11 and by a number, as follows. The driving velocity is the key physical parameter that determines whether it is possible to drive a fastener into a hard supporting material such as steel.

Even a technically “perfect” fastener could never be pressed statically into solid steel or driven by hand into a hard supporting material with a few hammer blows. The terminology used has not been standardized. In English, the fasteners are known as “powder-actuated fasteners” or “cartridge-fired pins”. In German, the word “Setzbolzen” has become established as the generic term for all types of powder-actuated fasteners. These terms refer to the nails equipped with steel washers for fastening profile metal sheets and the nails for general (non-removable) fastening applications as well as the threaded studs used to create removable fastenings (Figure 6).

Components of direct fastening systems. 2.1.2 From high-velocity tools to low-velocity piston tools The history of direct fastening using powder-actuated tools goes back to the beginning of the 20th century. The Englishman Robert Temple invented an explosively actuated penetrating means in 1915. This high-velocity fastening tool was developed by Temple for use by the navy in special underwater applications 12. The technique could be used, for example, to make temporary repairs to the hulls of ships by “nailing” metal sheets over the leaking or damaged area.

The first high-velocity fastening tools for use in applications in the construction industry appeared on the market in the USA in the 1940s. As the name implies, high-velocity fastening tools are characterized by the velocity of the fastener (up to 600 m/s) as it leaves the muzzle of the tool. This high velocity is the result of the energy released on ignition of the propellant acting directly on the fastener (Figure 4). The fastener then leaves the tool with high kinetic energy, similar to that of a bullet fired from a gun.

This presents a hazard not only to the operator of the tool but also to any bystanders in the vicinity. Penetration of the fastener in the material is uncontrolled. The fastener may, in fact, be driven right through (so-called through-shot) 13 if the supporting material behind the part to be fastened is not as expected, i.e. Too light and flimsy or if no supporting material is present at that point. The motivating factor behind further development of these tools was the improvement of working safety. The goal was to develop fastening tools capable of providing high fastener driving energy but, at the same time, with a low muzzle velocity. Placement of a piston between the fastener and the cartridge was found to be the solution.

This captive piston, accelerated by the energy released as the cartridge is fired, then drives the fastener into the supporting material. Although the entire energy released by combustion of the propellant is available to the driving operation, the free-flight energy transferred to the fastener is greatly reduced – according to the piston/fastener mass ratio. The first piston-principle tools became available in 1958 14.

These tools quickly became established and high-velocity tools for use in the construction industry disappeared from the European and American market by the end of the 1960s. Further development of piston-type tools then concentrated on increased productivity in practical use. Today, in addition to tools for driving single fasteners, there are also semi-automatic and fully-automatic tools on the market. Fully-automatic tools make use of fasteners and cartridges in magazine strips and the tool’s piston is returned automatically to the starting position after each fastener is driven. Semi-automatic tools require a manual cycling action to return the piston to its outset position. High-velocity tool principle versus low-velocity piston principle. Semi-automatic and fully-automatic tools can generally also be converted for use as single-fastener tools simply by replacing the fastener magazine with a single-fastener baseplate.

Each fastener must then be inserted in the tool manually. The propellant cartridges for almost all powder-actuated fastening tools available today come in plastic magazine strips. Gas-actuated tools, which use a combustible gas propellant contained in a replaceable canister (the so-called “gas can”), are fully-automatic fastening tools capable of high productivity. The capacity of the gas can is sufficient for approx. 750 fastenings. 2.1.3 CE marking and C.I.P.

Approval of powder-actuated fastening tools Powder-actuated fastening tools were integrated in the new edition of the Machinery Directive 15 for the first time in 2006. Until then, the legal basis for the approval of tools of this kind in European states was, for historical reasons, provided by weapon laws. The necessary approvals for powder-actuated fastening tools were issued in accordance with the resolutions 16 of the C.I.P. – The Permanent International Commission for the Proof of Small-Arms 1. The Machinery Directive 15, generally speaking, defines the most important requirements to be met by machinery. The detailed safety requirements, the necessary tests and how they are to be evaluated are laid out in a harmonized standard.

These requirements to be met by powder-actuated tools have been worked out by CEN over the last few years on the basis of a European Commission mandate. The current version takes the form of preliminary standard (FprEN 17) and is expected to be issued as the standard EN 15895 in the very near future. This standard will cover only powder-actuated fastening tools equipped with a piston and with a maximum fastener exit speed (muzzle velocity) of 100 m/s.

In accordance with the nomenclature used in 10 und 16, these powder-actuated fastening tools are powder-actuated tools of the class A. The first powder-actuated fastening tools carrying CE marking were brought onto the market on the basis of FprEN 15895 in the year 2010. Assessment of their conformity was carried out in accordance with 15 on the basis of EC type testing 18 which had to be carried out by an accredited, independent testing agency. In Germany this agency is the Physikalische Technische Bundesanstalt Braunschweig und Berlin (PTB). As of mid 2011, all powder-actuated tools on the market must bear CE marking. FprEN 15895 has adopted the previous stringent safety and test requirements of the C.I.P. Or, respectively, extended these with the addition of ergonomic requirements.

The following points, among others, require to be verified:. The robustness of the fastening tool in the event of unforeseen excess pressure within the tool.

The contact pressure required to trigger the tool. This must be at least 1.5 times the weight of the tool and at least 50 N. Safety measures to prevent the tool firing in the event of it falling from a height of between 1.5 and 3.0 m. Is an international organization with European and Non-European member countries.

In order to ensure that the tools can be used outside Europe, powder-actuated fastening tools must, as before, be approved in accordance with the C.I.P. The type identification plates on tools of this kind then bear the C.I.P. Mark as well as CE marking as confirmation of their conformity with the Machinery Directive (Figure 5). The cartridges to be used require their own approval in accordance with the C.I.P. Resolutions 16.

The approvals are split between testing of the propellant (the so-called “ammunition” approval), e.g. 19, as well as a system test of the cartridge in conjunction with a certain fastening tool, e.g. During this test, the influence of unforeseen excessively high pressure on the cartridge and the cartridge magazine strip is tested. This test is to be carried out for all tools in which the cartridge is to be used. The corresponding list of tools with which the cartridge can be used must appear on the cartridge package, stating the system approval number. Conformity marking of powder-actuated tools. Standardizing activities with the objective of introducing CE marking for cartridges are also currently taking place, but in a time frame that differs to that of the tools.

The cartridges are covered by the Pyrotechnics Directive 2007/23/EC 21 that was published in 2007. A harmonized European testing standard for cartridges is currently in preparation. It is expected that cartridges bearing CE marking will be brought onto the market as of mid 2013.

In contrast to powder-actuated tools, compressed air or gas-driven fastening tools were covered by the Machinery Directive right from the beginning. Tests and safety requirements for these tools are listed in EN 792-13 22. Confirmation of conformity is provided by CE marking. 2.1.4 Powder-actuated fasteners: Features and characteristics Figure 6 provides an overview of the range of fasteners available, their main features and their areas of application. 2.1.4.1 Geometry and form Powder-actuated fasteners of the types 1 to 9, as shown In Figure 6, consist of 3 sections: the point, the shank and the head.

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The head of the threaded stud takes the form of a taper at the end of the threaded section. When driven, the point of the fastener penetrates the supporting material, the shank transmits the driving forces and the head forms the interface with the driving piston in the fastening tool. In the completed connection, the shape of the head determines the pullover loading capacity of the component or material fastened.

Shear and tensile forces are transmitted by the shank, whereby shear forces are transferred to the supporting material by way of bearing pressure. Tensile forces are resisted by the anchorage obtained in the contact area between the fastener and the base material. The length of the fastener is determined by the material and thickness of the component to be fastened and by load requirements. In the case of powder-actuated fasteners for profile metal sheets, the maximum thickness to be fastened occurs at combined side lap and end overlap locations (four layers of sheeting, fastening type d, Figure 63) and the minimum thickness to be fastened is a single layer of thin sheet metal (0.6 mm or 0.75 mm). In order to reliably obtain a cost-efficient loading capacity, the fastener must be long enough to achieve a certain type-specific minimum depth of penetration at the maximum fastening thickness. The fastener, however, should not be too long.

Only a fastener with a comparatively short shank is capable of penetrating solid steel and thus providing the suitability desired in practice for a broad range of application conditions. The geometry of powder-actuated fasteners for profile metal sheets is thus optimized for fastening thin, cold-rolled profile sheets: it is short and compact. Fasteners with a correspondingly longer shank are required for fastening thicker components.

Powder-actuated fasteners for applications on steel. Powder-actuated fasteners have a shank diameter of between 3.0 and 5.0mm. Higher forces can be taken up by thick fasteners during driving. This allows the use of higher driving energy, resulting in an increase in the range of application conditions under which the fastener can be used. The fastener’s diameter also has an influence on the minimum thickness of the material into which it can be driven, e.g.

6 mm thickness for fasteners with a diameter of 4.5 mm, which is the typical diameter for profile metal sheet fasteners used in European steel construction applications. Fasteners with a diameter of 3.7 mm or less, sometimes with a conical shank, are used on thinner supporting materials. 2.1.4.2 Knurling The fine pattern of grooves on the surface of the point or shank of a zinc-plated powder-actuated fastener is known as knurling. It forms a micro-keyed hold between the fastener and the supporting material, thus increasing the loading capacity of the anchorage obtained by the fastener and reducing pullout load value scatter. All powder-actuated profile metal sheet fasteners available on the market today are designed to be used on steel base material and thus feature knurling.

Use of smooth-shank, unknurled, galvanized carbon steel fasteners on construction steel is basically possible (see Section 5.6). Knurled fasteners, however, are clearly superior to those with smooth shanks, not only with regard to their loading capacity but also in terms of the range of application conditions under which they can be used. Stainless steel powder-actuated fasteners require no knurling due to their different contribution of anchoring mechanisms.

2.1.4.3 Washers Washers help to guide and center the fasteners in the powder-actuated fastening tool. The steel washers fitted to profile metal sheet fasteners, in conjunction with the head, improve the metal sheet’s ability to resist pullover failure and ensure that the sheet is pressed tightly against the supporting material when fastened. When the component to be fastened has a certain minimum thickness (approx. 2.5 to 3.0 mm), no steel washers are required to improve pullover failure resistance relative to the values achieved with a standard head (typically 8 or 10 mm diameter) as the anchorage obtained then determines the fastening’s tensile loading capacity. Plastic washers generally break and disintegrate when the fastener is driven. 2.1.4.4 Fastener materials and mechanical properties To allow a fastener to be driven into steel, its hardness and strength must be approximately 4 to 5 times that of the base material.

Depending on the material from which they are made, powder-actuated fasteners have a hardness of between 49 and 58 HRc. The corresponding guide values for the strength and fracture forces of fasteners with a shank diameter of 4.5 mm are given in Table 2 23–25.

The wire material used in the manufacturing of galvanized powder-actuated fasteners is generally a heat-treatable type with a carbon content of approx. 0.65% and a tensile strength of about 600 N/mm 2.

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