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Railway
axles which have been in service are routinely tested for surface
breaking cracks. One method of testing is the highly sensitive Magnetic
Particle Inspection technique which detects any fatigue cracks on
the axle.
Detection
of circumferential cracks on the wheelset axle
Uses
a single turn split coil to allow easy access between brake discs
Positioning
of coil along the axle is automatic, initiated by push button
Pendant
mounted controls for easy use
Magnetising
field strength up to 2400 Amps/Metre
Programmable
coil positioning to allow easy set-up for different axles, with
different disc positions
The
machine has two novel features. One is the magnetising procedure
and the other is the programmable control system.
Since
the axle is fitted with wheels and, possibly, other components the
use of a continuous rigid coil is not appropriate because the wheels
etc will not permit manipulation of the coil to the relevant position.
However a hinged split coil will allow traversing along the axle
to the required test positions, opening and withdrawing to avoid
the fitted components. Therefore the position of coil can be adjusted
to any accessible location on the axle including outside of the
wheels.
On
some axle types fittings such as brake discs are positioned closely
together restricting accessibility.
This problem is overcome by the use of a single turn 35mm x 35mm
solid copper coil. Whilst this solution might appear to be unorthodox,
provided the ampere-turns necessary to magnetise the axle sufficiently
can be achieved with a single turn, there is no advantage to multi-turn
coils. In this instance up to 4500 amps AC R.M.S. is passed through
the single turn giving 4500 ampere-turns. This would induce an applied
magnetic field of approximately 2400 A/M giving the required flux
density of 0.72 Tesla.
The
positioning of the coil along the axle is by press button switches
on a pendant. Through these is controlled the traverse of the coil
support carriage, via a rotating lead screw, driving the coil carriage
in lateral forward or reverse direction. Press buttons also advance
and close the coil and open and retract it. The operator can therefore
adjust the coil position and apply it to the axle visually. Safe
guards prevent movement of the coil carriage when the coil encircles
the axle.
The
pendant control also has press buttons for rotation of the wheelset
in the forward or reverse direction either with the coil in position
or when retracted. This facility permits viewing of the surfaces
for defect indications following magnetising and inking.
The
other novel feature is programmability of the coil position. The
standard Euromag microprocessor based control system allows the
selection and adjustment of the following magnetising parameters
by interactive display system by means of a single rotary control
and enter button in the interactive display system.
Magnetising
Current waveform, No. of amps required, Magnetising Mode (current
flow, encircling coil etc) duration of "shot" and no.
of "shots". Adjustment of the value of the option selected
is done by the same rotary control. The system display leads the
operator through the selection and adjustment procedure by menu
displayed on the screen.
The
value of the magnetising current is pre-selected, in that the current
to be applied to a particular mode is "entered" before
magnetising takes place. The system automatically adjusts to the
current to the preset value regardless of conditions.
Once
a set of parameters has been set it can be stored within the system
as a programme. Up to 100 such programmes can be stored. Additional
programmes can be held on P.C. disc.
Making
use of the above facility the soft-ware has been augmented so that
not only can the magnetising parameters required for each axle type
be stored and activated when required, but also the magnetising
coil positions can be stored as part of the axle type programme.
This
facility therefore will permit the composition of the programme,
identified by a simple numeric code, for a particular wheel set
type which not only sets up the equipment with the appropriate magnetising
parameters but also the pre-set correct positions for the magnetising
coil.
High
amperage current is supplied to the magnetising coil from a separate
power pack. The output from the main transformer is infinitely variable
and is regulated by thyristor controlled by the system. The system
also provides rapid demagnetisation from a value of magnetising
current plus 10%.
The
indicating medium, which is stored in the drain tray/reservoir,
is continuously recirculated to maintain the particles in the correct
suspension in the fluid. Application of the fluid to the axle is
by hand held hose.
The
equipment is supplied with a canopy to allow the inspection of the
axles for ultra-violet fluorescent indications in subdued light.
The canopy folds to allow wheelsets to be loaded from over-head.
To obtain this
information as an Adobe Acrobat document Click
Here.
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