-
GENERAL
Variation of percentages
of lamenar graphite in a ductile cast iron
significantly affects its
mechanical
properties and, for the purpose of a non
destructive control, it is related with a
remarkable
variation
of
the
propagation
velocity
and
attenuation
of
the
elastic
waves
through the material.
Other microstructural differences also determining
the mechanical
properties of the cast
iron (phase distribution within the matrix) do
not affect as much the propagation of
the elastic waves and, when non destructive
control
is required for this, eddy
current testing can reliably be used.
不
同的石墨形态影响铸铁的力学性能，
通过材料来测定不同的声速和弹性衰减，
通过一种无
无损坏方式来测定。
铸铁的不同显微组
织也决定了材料的机械性能，
并且在不影响波的传播
及不破坏组
织的前提下，涡流检测可以做到这一点
In
industrial
production
environments,
ultrasonic
testing
is
commonly
performed
for
nodularity control and,
acoustic velocity measurements can determine the
percentages of
laminar graphite with
the usually,
在工业产品领域中。
超声波检测技术经常用来测定球化率并且通常其声速值决定了石墨的分
布形
态
in practice,required
accuracy. Product quality requirement is specified
as an acceptable
acoustic velocity
range and suitable thresholds are defined not so
tight attending not only
to what it is
actually a critical percentage of laminar graphite
in a ductile iron (typically up
to
15%), but also to the significant intrinsic
heterogeneity of any cast part. In relation to
this,
在实际检测中，
要求精度，
产品质量通常是由声速范围值和一个合适的阀值来衡量，<
/p>
但也不
是一个严格规定，
它不仅作为在铸
铁中石墨形态分布的一个准确值通常为
15%
，
而且还作铸
铁中不均匀性性一个指标。
nodularity
control
of
components
is
mostly
required
as
a
single
spot
test
on
the
part
(defined
position) and, just in the case of few critical
components of large dimensions and
complex geometries, multiple spot tests
are specified.
Manual or
automatic in-line nodularity control in iron
foundries is usually carried out in the
as-cast
condition,may
be
after
some
heat
treatment
process but
before
any
machining
operation
if
required,
thus
on
parts
with
relatively
rough
surface
finishing
and
section
thickness that can vary up to
±
0,4 mm around its nominal thickness.
铸铁中手动或者自动的球化率控制是在铸铁条件下完成的，<
/p>
要在热处理工序之后，
机械加工
之前，要
求相对粗糙的表面处理后并且截面厚度在
±
0,4
mm
范围之内
Those
parts
come
dry
to
the
nodularity
control
station,
they
are
highly
susceptible
to
oxidation in contact with water based
liquids and, frequently, it is also required to
avoid the
presence of any liquid on
them before the next process stage or delivery.
要用这些干得部分来进行球化率检测，
因为他们碰上水或者其它液态后会被氧化，
并且在下
一个程序
进行之前避免这些液态在组织上面。
Ultrasonic
testing for measuring the acoustic velocity of a
material can be preformed in
through
transmission mode,
independent
of
the
actual
part
thickness
or,
in
pulse
echo
mode
providing the thickness of the part is known (well
assuming a minimum thickness
variation
around a given nominal value or, well having this
actual value out of a calliper or
similar).
超声波检测通过测量声速来完成，
或者单独厚度测量，
或者在脉冲回波模式下提供的厚度是
已知的
The
former, requires an immersion test with access
from the two sides of the part in just
parallel surfaces sections, and the
velocity value is obtained with a
precision
depending
on
the
TOF
measurement
resolution
of
the
ultrasonic
equipment
(also dependent on
the time base range set up) and the distance
between the two probes
used.
前者，
需要一个两个平行面的浸泡试
验，
声速值是通过
TOF
精密测量超声
仪器的分辨率，
以
及两个探头之间的距离来获得的
For
the
test,
a
minimum
of
mechanics
is
needed
either
for
manual
or
automatic
part
loading, as well specific software for
data processing into velocity
read-
outs. Immersion media use to be oil or water with
oxidation inhibitors and parts have
to
be dried or
检测时，
在自动或者手动的载荷下需
要一个最小的力学参数，
以及专门软件用来读出速度值，
油或者
抗氧化的液态，在检测完毕之后样件要保持干燥并且清除干净
cleaned after the test.
Ultrasonic
nodularity
control
in
pulse
echo
mode
does
not
present
access
to
the
part
constraints but the
size of the probe, it requires direct contact
between the probe and the
part
and
is
readily
available
for
manual
or
(with
a
minimum
of
mechanics)
automatic
inspection.
脉冲回波模式并不是限制球化率的因
素，
零件的尺寸和探头是关键，
在探头和零件之间直接
进行接触，可以在手动或者自动条件下完成
For measuring acoustic velocities with
this technique, the actual value of the thickness
of
the
part
under
the
ultrasonic
probe
is
needed
and
the
precision
of
the
measurement
depends
on
how
accurate
is
given
it
and
the
TOF
measurement
resolution
of
the
ultrasonic
equipment.
声速测量要用这个技术，
要获得一个准
确的厚度值，
探头必不可少，
精准的测量需要给一个
准确的值以及超声波的分辨率是多少
It is
quite conventional in practice to perform the
nodularity control of a given production
series in terms of apparent thickness
rather than velocities, for which it is used to
work
with tables of apparent thickness
thresholds for each given nominal part thickness.
在测定
Some ultrasonic instruments are
complemented with a calliper which, having access
to
both
sides of the part,
measures the actual thickness value and
gives it to the equipment, then
allowing the calculation of
the
acoustic velocity.
Attempts
to
implement
pulse
echo
systems
with
a
simultaneous
ultrasonic
thickness
measurement by
means of
an
additional
pair
of
angular
beam
probes
in
tandem
have
presented
some
practical
difficulties
because of the
larger area required on
the part to perform the test and the lack of
accuracy due to the