Magnaflux Universal SW Series, Руководство по эксплуатации

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2.4 CURRENT CONSTANT CONTROL
During current flow, the strength of the magnetising
current is dependent on the electrical resistance of the
workpiece. The current strength defines the magnetic
field strength in the workpiece.
The constant current control regulates the voltage of
the magnetising circuits, depending on the current
flow at the time. The actual current value is maintained
during the entire magnetisation process in accordance
with the pre-selected set value.
2.5 CURRENT FLOW CONTROL
During magnetisation, the actual current value of the
magnetising current is constantly measured and com-
pared to the set value selected. If there is no current
flow, or too low a current, a current flow malfunction is
signaled.
The current flow control works in manual and automatic
operating modes but not in the intensity range of 0-10%
(the fault light will illuminate).
When experiencing a current flow malfunction, the
magnetisation cycle is repeated up to 3 times. If the
set value is not reached after the third attempt, a
malfunction is signaled and the machine is stopped.
2.6 TYPES OF MAGNETISING IN ACCORDANCE
WITH DIN EN ISO 9934-1
The types of magnetisation available for use depends
on the individual configuration of your machine
and its installed accessories. For more information,
please contact MAGNAFLUX GmbH.
DIN EN ISO 9934-1 (formerly DIN 54130) deals with
magnetic particle inspection in general, including all
types of magnetisation processes suitable for magne-
tising a workpiece. The most common magnetisation
methods are briefly described below
Axial current flux
• Magnetisation by current flux.
• Self-flux - the workpiece has direct contact and acts
like an electrical conductor.
• Generates a circular magnetic field around the
workpiece.
• Enables detection of longitudinal cracks.
Induction flux
• Magnetisation by current flux.
• Annular or tubular workpiece as secondary winding
(1 winding in short circuit) of a transformer.
• Generates a circular magnetic field around a work-
piece cross-section.
• Enables detection of longitudinal cracks
Yoke magnetising (stationary system)
• Magnetisation by magnetic field (field flux).
• Workpiece is placed within the magnetic field
between two electromagnetic yokes.
• Enables detection of transverse cracks.
Field flux with current-carrying conductor bar
• Magnetisation with current-carrying conductor
(auxiliary flux).
• Magnetising mandrel inside of tubular or circular
workpieces.
• Generates a circular magnetic field around the
conductor and the workpiece.
• Enables detection of longitudinal cracks.
Field flux with magnetising coil
• Magnetisation by magnetic field (field flux).
• Generates circular magnetic fields around the
conductor which combine to form a common
longitudinal field within the coil.
• Detection of longitudinal cracking.
2.7 DEMAGNETISING THE WORKPIECE
After testing for surface cracks with magnetic particle
inspection methods, residual magnetism remains in
the workpiece. Eliminating this residual magnetism
avoids negative effects during further processing or
when using the workpiece.
Decreasing the magnetic field intensity in the work-
piece can be achieved by using one of two methods:
• internal - magnetisation current is regulated against
zero along an exponential function to base e.
Demagnetisation is performed immediately after
magnetisation in the crack detection machine.
• external - demagnetisation is achieved by using an
external coil. The workpiece is continuously moved
out of the magnetic field.
Electronic demagnetising
Where the magnetisation was performed using
alternating current (AC), the workpieces must also
be demagnetised using AC. For that purpose, the
magnetising current is reduced along an e-function
until it reaches zero.
For demagnetising:
• a field with alternating polarity must be achieved
and
• the field intensity must be continuously reduced
until it is zero.
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