Raytheon Beech Baron E55 - Page 170

Raytheon
Aircraft
Company
BARON
55
AND
58
SHOP
MANUAL
MA
GNETIC-PA
RTICLE INSPECTION
Magnetic-Particle
Inspection
is
a
method
for
locating
surface
and
subsurface
discontinuities in
ferromagnetic
materials
(i.e.
materials
capable
of
being
magnetized);
consequently,
non
ferromagnetic
materials
(such
as
aluminum
alloys,
magnesium
alloys,
copper
alloys,
lead,
titanium
alloys,
nickel base
alloys
and
many
stainless
steel
alloys)
cannot
be
inspected by
this method.
Magnetic-Particle
Inspection
is
based
upon
the
principle
that
any
discontinuities
lying
in
a
direction
generally
transverse to
the direction of the
magnetic
field
of the
part
magnetized
for the
test
will
cause a
leakage
field
to
be
formed
at
and
above the
surface
of
the
part.
The
presence
of the
leakage
field
denoting
the
discontinuity
is
detected
by
the
use
of
finely
divided
ferromagnetic particles
over
the
surface
of
the
part.
Some
of the
particles
are
magnetically gathered
and held
by
the
leakage
field
to
form
an
outline
indicating
the
location, size,
shape
and
extent
of
the
discontinuity.
In
general,
magnetic
particle
inspection
utilizes
a
variety
of
types
of
equipment
for
magnetization,
as
well
as
several
methods
for
application
of
ferromagnetic
particles
to
the
test
part.
Additionally,
the
ferromagnetic
particles
are
available
in
a
selection
of colors
(including fluorescent)
and
particle shapes.
Magnetic
particle inspections required by
this
manual
can
best be
accomplished
by
utilizing
the
wet
continuous
method
on
the standard
wet
horizontal
type
equipment,
with
either visible
or
fluorescent
magnetic
particles
suspended
in
a
petroleum
base vehicle
(normally kerosene).
Since
magnetic
particle
indications
are
best
obtained
when
the
discontinuity
lies
in
a
direction
transverse to
the
magnetic
field,
the
following
procedures
are
recommended for
optimum
detection of discontinuities in both
bolts and
nuts.
WARNING:
Improper
operation
of the
magnetic
particle inspection
because
of
faulty
equipment
or
untrained
operators
can
jeopardire
the
ainnrorthiness
of
parts
being inspected.
Minute
electrical
are
burns caused
during
inspection by
improper
operation
of
the
test
equipment
can
result
in
eventual
failure
of
the
part.
Bolts:
Inspection
of
a
bolt
is
accomplished by longitudinal magnetization
in
a
multi
turn
low-fill factor
coil
(i.e.
the
inner diameter
of the coil
greatly
exceeds the bolt
diameter).
For
proper
magnetization
the
bolt is
positioned
close
to
the
coil inside wall
with the bolt
length
perpendicular
to
the
winding
direction. The
magnetic particle
suspension
is
flowed
on
the bolt and the
appropriate
current
is
applied
to achieve
adequate
field
strength. Using
the described
I
procedure,
laboratory
testing
has
indicated thatthe
ampere
turn
values listed
in
Chart
2
provide
for
optimum
detection
of
discontinuities
perpendicular
to
the
bolt
axis.
Nuts:
Inspection
of
a
nut
is
accomplished by
circular
magnetization
on a
central
conductor
(usually
a
copper
rod)
the
approximate
size of the
nut
inside diameter. For
proper
magnetization,
the
central
conductor
bar
is
inserted
through
the
nut
and the bar is
positioned
between the heads
of
the
wet
horizontal
equipment.
The
magnetic
particle
suspension
is
flowed
on
the
nut
and
the
appropriate
current
is
applied through
the
central conductor
to
achieve
adequate
field
strength. Using
the
described
procedure,
laboratory testing
has indicated that the
amperage
values
listed in
Chart
3
provide
for
optimum
detection of discontinuities
parallel
to
the
nut
axis.
After
magnetic
particle
inspection,
the
parts
must
be
carefully demagnetized
and cleaned of the
ferromagnetic
particles.
Examine
parts
for
any
possible
evidence
of
electric
are
burn that
may
have occurred
during
the
inspection.
Page
222",%,
SECTION
3
Ena