Note: Descriptions are shown in the official language in which they were submitted.
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_ETECTION OF FLAWS IN METAL MEMBERS
The present invention relates to a method for flaw
detection for metal members and, in particular, metal
blooms or billets such as of steel, aluminum or the like.
It is, of course, well known in the art that surace
flaws occur in the formation nf steel work pieces such as
blooms or billets, and many different attempts have been
made to detect these surface flaws for the purpose of
i eliminating them by grinding or the like. Indeed, many
of these methods are in commercial use today and have
proved to be quite successful. While successful, they
unfortunately also have drawbacks.
One method used for detecting surface flaws involves
the use of a magnetic field. Surface flaws are initially
filled with air, slag, oxides or the like, as a result o~
which the surface flaws, and notably cracks, will have a
poorer magnetic conductivity than the rest of the work
piece. There is thereby obtained a strong magnetic field
in a direction transverse to the cracks and this strong
' 20 magnetic field can be detected to indicate surface flaws.
o ~ e s c e~7 t
3~ In yet another known method, a flourescent magnetic
powder is distributed on the surface of the work piece.
The powder will tend to collect to a greater degree in
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the surf~ce flaws which can tken be exposed by ultraviolet
light. In still another method, the work piece is magnetized
by passing a current through it, after which it is covered
with a magnetically attractable powder including a coloring
agent which will melt and adhere to the billet upon heating~
The metal object is then heated to a sufficient intensity
to cause the coloring agent to adhere and, because of the
stronger magnetic attraction at the cracks, it will show up
the most at these locations. This process can be fully
automatic and is described in United States Patent No.
3,845,383.
; Other methods for detecting surface flaws are also
known and, in fact, the art is quite well developed.
However, there are disadvantages to all of the known prior
art processes. These involve one or more of a combination
of the process not being automatic or using up relatively
expensive materials, such as the magnetically attractable
compositions, or being inaccurate, or requiring the applica-
tion of a powder, dust or liquid which inherently creates
an undesirable environmental condition.
The applicant has now discovered that all of the fore-
going disadvantages of prior art processes can be overcome
by the relatively simple expedient of employing high
frequency heating and measuring the resulting temperature
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profile of th~ metal workpiece, suitably by recording
with an infrared camera. Surface flaws on blooms, billets
and the lik~ are characterized by sharp edges and other
irregularities in the surface, and these become much hotter
than the surrounding areas when subjected to high frequency
inductive heating. Because of this great difference in
temperature, a temperature profile can be developed which
will pinpoint the location of the surface flaws.
Because of the high heat conductivity of metal
materials, it is necessary to observe the temperature profile
either during the high frequency heating or immediately
thereafter, e.g., within no more than about 2-3 seconds.
For achieving this result, an infrared camera has been found
to be especially desirable. In fact, use of this apparatus
permits the process to be made fully automatic, including the
marking or subsequent grinding operation.
As a specific embodiment, the present invention
provides for a method of detecting surface flaws in a
workpiece comprising: (a) heating said workpiece using
a first induction heater; (b) scanning said workpiece
- immediately thereafter with a first infrared thermo-camera
for determining a first temperature profile of said workpiece;
~c) providing first temperature proile data from said
infrared thermo-camera, said data being in correspondence
with said first temperature profile; (d) feeding said first
temperature profile data to a data processor for controlling
grinding apparatus, said grinding apparatus being controlled
by said first temperature profile data for automatic grinding
of said workpiece in accordance with said first temperature
profile; (e) reheating said workpiece by use of a second
induction heater; (f) scanning said workpiece with a second
infrared thermo-camera immediately after said reheating for
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determining a second temperature profi].e of said workpiece;
(g) providing second temperature_profile data from said
second in~rared thermo-camera, said data being in accordance
with said second temperature profile; and (h) feeding said
second temperature profile data to said data processor for
automatic adjustment of the grinding apparatus.
These and other features of the present invention
may be more fully understood with re~erence to the Figure,
which shows a schematic of an apparatus which can be used
in the present invention.
In the Figure is shown a track 10, along with a
billet 12 is progressing in the direction of the arrow as
indicated thereon. In the picture as shown, the billet
passes through an induction heater 14 which operates at
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high frequency, preferably ab~ve about lO,OOO hertz~ P~tIoned
immediately downstream from the induction heater 14 is an
infrared thermo-camera 16 which scans the work piece and
forms a temperature profile. When the temperature across
the work piece is measured, there will be found an increase
in temperature adjacent surface irregularities, such as
cracks. The temperature profile will form a streaked
temperature pattern across the surface, and the surface
irregularities will be indicated by the fact that the
streaked pattern repeats itself. The data obtained from
the infrared camera can be recorded as a hard copy but is
preferably fed directly to a data processor 187 which in
turn controls downstream equipment 20, such as a marking
- pen or grinding equipment. In this way, the detected flaws
can be automatically marked or they can be automatically
ground out. Since the size~ shape and depth of the crack
will be discernible from the temperature profile~ the exact
grinding necessary to remove it can be determined by an
appropriate program. Obviously, the treated billet can
be subjected again to the flaw detection apparatus 14A,
16A to insure that the correct grinding has been effected
and, by appropriate feed back of data to the data processor
18, adjustments in the grinder 20 can be automatically made.
One of the most important advantages of the present
invention, in addition to those hereinbefore delineatedj is
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that the method can be used equally well with non-magnetic
metal work pieces. This is indeed a great advantage since
the magnetic processes are totally unsuitable for use with
non-ferrous materials, and these magnetic methods are the
most widely used today.
I~ will be understood that the claims are intended
to cover all changes and modifications of the preferred
embodiments of the invention, herein chosen for the purpose
of illustration, which do not constitute departures from
the spirit and scope of the invention.
