TPT May 2009

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May 2009 34
Technology Update
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Hemming units are essentially portable roll
forming machines that form 180° hems on
the edges of a flat strip of metal. Hems are
primarily found on lighter gauge material to
either strengthen the profile and/or improve
safety, when handling.
Roll-Kraft, USA, has launched a new model
of hemming unit that can be designed and
built to suit almost any hem requirement.
Typically, the hems are formed before the
metal strip is introduced into the rollforming
mill or another forming process. Most
hems are small (to reduce the amount of
material required) and can be formed in
four stations.
Hemming units can be configured in
numerous ways. These configurations
include non-driven (pull-through), driven
(with overriding clutch or continuous drive),
mounted directly onto the existing roll
former base, freestanding (fabricated base),
variable product widths for ‘quick change’
(see figure 2), single or double hem, and
custom applications.
Roll-Kraft hemming units are constructed
using fabricated plate steel housing
assemblies, spur gear train (see figure
3), hardened tooling spindles (overhung),
adjustable top spindles with micrometer
dials, built-in material entry guide (see figure
1), hardened tool steel rollers, and optional
‘quick change’ width adjustment with digital
indicators (see figure 3).
Another advantage of integrating a Roll-
Kraft hemming unit into a rollforming system
is to save money. There are numerous
occasions when an existing rollforming mill
does not have enough forming stations
to produce a particular hemmed cross-
section. Instead of purchasing a new mill
or mill extension, a Roll-Kraft hemming unit
Launch of new portable hemming unit
 Figure 1 – Hemming unit (driven) with integrated
entry guides
 Figure 2 – Adjustable width hemming unit with
digital indicators
 Figure 3 – Powered hemming unit with spur
gears