Aluminium Design and Construction John Dwight

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Figure 2.8 Production of hollow section by extrusion over a mandrel. An alternative technique for producing hollow shapes, which eliminates seam welds, is ‘extrusion over a mandrel’ (Figure 2.8). A suitable press is needed for this (a ‘piercing press’) in which the main ram is bored out to accommodate a separately controlled inner one. A simple die is used to define the outside of the section, while the internal profile is generated by a tipped mandrel carried on the inner ram and passing through a hole in the billet. The method is slow to set up and more costly. Also there is a tendency for the long mandrel to deflect sideways, causing eccentricity of the interior of the section relative to its exterior. The technique is used when the very slight risk from the presence of seam welds is unacceptable. 2.3.6 Extrudability of different alloys The extrusion alloys par excellence are the 6xxx series. They extrude nearly as readily as pure aluminium and are highly suitable for the production of slender profiles, especially the weaker type such as 6063. They are also ideal for the extrusion of hollow sections through a bridge die. They have the further advantage that reliable properties can be achieved by quenching at the press (spray quenching). Extrusion speeds of 25 m/min or more are quite normal with 6063 extrusions. The weaker (i.e. weldable) type of 7xxx-series material also extrudes well, and is again suitable for hollow shapes. But such material extrudes more slowly, and the same degree of section slenderness cannot be achieved as with 6xxx material. Also the solution treatment has to be done as a separate operation, and not by spray quenching at the die. The 2xxx-series alloys, and also the stronger type of 7xxx alloys, are altogether less convenient for extrusion. They extrude slowly and are no good for the production of hollows using bridge dies. Extruded sections in non-heat-treatable aluminium (1xxx, 5xxx series) are of limited use for structural profiles, because they have to be supplied in the relatively soft as-extruded F condition; there is no way of hardening them by cold work, extrusion being a hot process. Therefore they are only called for when high ductility is needed. Pure aluminium extrudes very readily. The 5xxx-series alloys are generally poor for extrusion, Copyright 1999 by Taylor & Francis Group. All Rights Reserved.
especially the stronger alloys in the group (such as 5083). These come out slowly from the die, and cannot be used with bridge dies. 2.3.7 Size and thickness limits Precise data on the limiting geometry for extruded profiles is impossible in a book such as this, and we can only give general guidance. It is obviously essential to confer with the extruder if there is any chance that a proposed section may cause problems. (a) Length For material that is unsuitable for spray quenching, such as 2xxx or 7xxxseries material, the maximum length is governed by the heat-treatment set-up. Typical rough figures might be 6 m for vertical quenching, and 10 m for horizontal. This restriction does not apply with 6xxx-series material quenched at the press, for which the probable limitation is transport. With a very thick section, the available length may be restricted by the amount of metal in the billet. (b) Width There is no difficulty in obtaining extrusions up to 300 mm wide, for which there are many presses with a large enough container. Twice this width is possible from the largest presses, 600 mm or more, but these exist in only a few countries. (c) Thickness A designer will often want to make a section as thin as possible, for economy. The minimum thickness depends partly on what can be extruded, depending on the alloy, and partly on the control of distortion. It is generally a function of the overall size of the section. As a very rough guide, the minimum practicable thickness for a non-hollow in the weaker type of 6xxx-series alloy (such as 6063) is the greater of (a) 1.2 mm; and (b) 1% of the section size. It is emphasized that these are approximate values, and that the minimum possible thickness for a given profile may sometimes turn out to be thicker and sometimes thinner. Value (b), which refers to general thickness rather than small ribs, etc., is more likely to be achieved when the T5 condition is specified (air quenched). For hollows, the minimum thickness will probably be some 25% higher than for nonhollows. For the stronger type of 6xxx material, the minimum available thickness tends to be slightly greater. For the weaker (weldable) type of 7xxx Copyright 1999 by Taylor & Francis Group. All Rights Reserved.
Page 1 and 2: Aluminium Design and Construction C
Page 3 and 4: First published 1999 by E & FN Spon
Page 5 and 6: 2.2.1 Rolling mill practice 2.2.2 P
Page 7 and 8: 5 Limit state design and limiting s
Page 9 and 10: 8.2.6 Use of interpolation for semi
Page 11 and 12: 10.3.2 Inertias for a section with
Page 13 and 14: Preface Aluminium is easily the sec
Page 15 and 16: List of symbols The following symbo
Page 17 and 18: uu, vv principal axes w effective s
Page 19 and 20: 1.1.3 The industrial metal It is on
Page 21 and 22: where A is the section area (mm 2 )
Page 23 and 24: 1.3.1. The good points about alumin
Page 25 and 26: Deflection Because of the lower mod
Page 27 and 28: 1.4.4 Establishment of the alloys I
Page 29 and 30: 1.5.2 New technology Most of alumin
Page 31 and 32: large span, where self-weight is a
Page 33 and 34: These tend to be in all-aluminium c
Page 35 and 36: Close-up of the M-dec system, which
Page 37 and 38: Aluminium glazing system for commer
Page 39 and 40: Nat West Media Centre, Lords Cricke
Page 41 and 42: The main requirements for the produ
Page 43 and 44: in which t and w are in mm. These a
Page 45 and 46: Figure 2.1 Extrusion process (direc
Page 47 and 48: Figure 2.2 Typical extrusion die. t
Page 49: Figure 2.6 ‘Semi-hollow’ profil
Page 53 and 54: Figure 2.9 Conventional profiles. 2
Page 55 and 56: 2.4 TUBES By tubes we mean hollow s
Page 57 and 58: CHAPTER 3 Fabrication 3.1 PREPARATI
Page 59 and 60: Figure 3.1 Alternative designs for
Page 61 and 62: Figure 3.2 Thread insert. a coil-sp
Page 63 and 64: 3.3 ARC WELDING 3.3.1 Use of arc we
Page 65 and 66: adjusted. The technique is claimed
Page 67 and 68: For welds of minimum or fatigue qua
Page 69 and 70: Figure 3.5 Friction-stir welding: s
Page 71 and 72: are, and the designer/fabricator mu
Page 73 and 74: cartridge, and mixing takes place a
Page 75 and 76: 3.7.4 Painting Alloys having durabi
Page 77 and 78: Where a range is given, as for the
Page 79 and 80: will be only slightly above that fo
Page 81 and 82: heating the metal to a temperature
Page 83 and 84: Table 4.4 Characteristics of differ
Page 85 and 86: softening in the heat-affected zone
Page 87 and 88: 60 alloys, are: BSEN.485 plate and
Page 89 and 90: Firure 4.3 Nominal composition and
Page 91 and 92: popular alloys in the series are: 6
Page 93 and 94: Figure 4.6 Variation of tensile str
Page 95 and 96: undercarriages of aircraft. They ar
Page 97 and 98: Figure 4.11 Minimum stress-strain c
Page 99 and 100: AC.51400 This is another non-heat-t
Page 101 and 102:
times that of the actual pits) prod
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The severity of bimetallic corrosio
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Nominal loading. Nominal loads are
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2. Material factor (� m ). In the
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design does not, because stress at
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Table 5.2 Summary of limiting stres
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Figure 5.4 Plastic strain at workin
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example, a reduced value might be t
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The parameter � depends purely on
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CHAPTER 6 Heat-affected zone soften
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area of softening. With 7xxx-type m
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Figure 6.3 Typical hardness plots a
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6.4 SEVERITY OF HAZ SOFTENING 6.4.1
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Figure 6.6 Categories of welded joi
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Figure 6.10 One-inch rule, extent o
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e allowed for in design by replacin
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Figure 6.13 Predicted area (A z ) o
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Figure 6.15 Overlapping HAZs. nomin
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In determining A zp , an appropriat
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failure plane in the HAZ, close to
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With MIG welding, an electrode-posi
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CHAPTER 7 Plate elements in compres
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(a) Compression member elements The
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Table 7.1 Classification of element
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Figure 7.4 Slender internal element
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Figure 7.7 shows curves of � ° p
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(7.9a) (7.9b) The strain gradient c
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(through the centroid) for ß S . F
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Figure 7.13 Outstands under strain-
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Figure 7.15 Reinforced elements. Th
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Figure 7.18 Stiffener location for
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Figure 7.20 Slender reinforced inte
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CHAPTER 8 Beams 8.1 GENERAL APPROAC
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8.2.2 Section classification The di
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that for the gross section. It woul
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the usual manner. Line 1 in the fig
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1. Fully compact sections. The limi
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Figure 8.8 Transverse and longitudi
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8.3.4 Shear resistance of bars and
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Figure 8.12 Tension-field action. i
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Figure 8.14 Moment/shear interactio
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depending on the estimated degree o
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where a is the stiffener spacing an
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plates (if fitted), p v =limiting m
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ending moment diagram. Two cases ar
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Figure 8.23 Sections covered in Tab
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where: I yy , I vv =inertia about m
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post (Section 8.6.4) or by some oth
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Figure 8.26 Components of deflectio
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9.1.2 Classification of the cross-s
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hole. Alternatively, it might fail
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Figure 9.2 Limiting stress p b for
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The determination of l involves a c
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Figure 9.6 Monosymmetric section. I
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Figure 9.9 Limiting stress p b for
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where s=� s /� t s =slenderness
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Figure 9.11 Type-R sections covered
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Figure 9.14 Four standardized profi
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9.7.2 Secondary bending in trusses
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Table 9.5 Necessary checks for memb
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Figure 9.18 Axial load with biaxial
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1. Tension members. The localized f
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Figure 10.1 Symmetric plastic bendi
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We now turn to monosymmetric sectio
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distance of its centroid from the n
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Figure 10.6 Elements of sections. I
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10.3.3 Product of inertia The produ
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Usually the conditions are such as
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Table 10.2 Torsion constant. Factor
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Figure 10.12 Warping. Conventional
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where b, t=element width and thickn
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10.5.3 Evaluation of warping When t
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For sections where the position of
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(10.31) where: e=distance that S li
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10.5.9 Asymmetric sections Before s
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CHAPTER 11 Joints This chapter cons
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the use of limiting stresses taken
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and the summation is made for all t
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Figure 11.3 Interaction diagram for
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k in order to give a fair compariso
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3. The design is satisfactory if fo
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When the method of surface preparat
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11.3.3 Weld force arising In many c
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Table 11.6 Limiting stress p w (N/m
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where p a =limiting stress for unwe
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Figure 11.11 Interaction diagram fo
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Manufacturers of structural adhesiv
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11.4.6 Creep Shear strength figures
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Figure 11.15 Effect of glue-line th
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Table 11.7 and Figure 11.17 provide
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11.4.11 Resistance calculations for
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high value reflects the various unc
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therefore usually presented in term
Page 287 and 288:
For example: The loading spectrum i
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act on the structure. However, BS.8
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Figure 12.4 Crack propagation: (a)
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12.5 CLASSIFICATION OF DETAILS 12.5
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i.e. a joint extending in the same
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when the design life is low or when
Page 299 and 300:
Methods (2) and (3) are difficult t
Page 301:
it reverts to line 1. The slope s o
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Aluminium Design and Construction John Dwight

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