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Steel Designers' Manual - 6th Edition (2003)
structural bolts, normally have a protective coating which gives them a bright
appearance, and are available in a range of tensile strengths.
Friction-grip bolts
Friction-grip bolts are normally supplied with a protective coating and are differentiated
by material grade. Friction-grip bolts are used in connections which resist
shear by clamping action, in contrast to structural bolts which resist shear and
bearing. When considering the use of friction-grip bolts during the fabrication
process, adequate means of access must be provided so that the bolt can be properly
tensioned.
Close-tolerance bolts
This type of bolt differs from a structural bolt in that it is manufactured to closer
tolerances. To gain the full benefit of close-tolerance bolts, they should be used in
close-fitting holes produced by reaming, which adds considerably to the expense of
fabrication. Where a limited slip connection is required, close-tolerance bolts can
be used in holes of the same nominal diameter as the bolt but not reamed; this gives
a connection which is subject to far less slip than would be the case for structural
bolts in clearance holes.
32.4.3 Hole forming
Bolting 957
To gain the best output, computer numerically controlled (CNC) machines are
incorporated in conveyor lines. There is an infeed line which takes the unprocessed
raw steel and an outfeed line which distributes the finished product either to the
despatch area or further along the fabrication cycle and into an assembly area. The
infeed conveyor for punching and drilling machines that handle angles, flats, small
channels and joists will normally be configured to handle 12 m long bars. There will
be a marking unit which carries a set of marking dyes that stamp an identification
mark on to the steel if required. There may be a number of hydraulic punch presses
each suitable for accepting up to three punching tools, and it is normal that the tool
holders are quick-change units. Typically, hydraulic presses have 1000 kN capacity.
The punch presses can form differently-shaped holes so that angles can be produced
with slots. Some machines produce the slot by a series of circular punching operations,
others have a single slot-shaped dye.
Once the material has passed through the punch presses, it is then positioned for
shearing.The hydraulic shear has a capacity of between 3000 and 5000 kN. Machines
which incorporate drilling facilities can have these positioned next to the punch
presses prior to the hydraulic shear. The output of the machine can be as high as a