Note: Descriptions are shown in the official language in which they were submitted.
;~05~608
Metallqesellschaft AG Septe~oer 4, 1990
Reuterweg 14
6000 Frankfurt-on-Main 1
Case No. 90 00 91
Process of ~nalvzinn ~etal Particles
nEscRI~TIorl
T~is invention relates to a orocess for 3 clas6i-
fying analysis of a pnlydisperse bul~ ~aterial consisting of
various metal oarticles havino a oarticle size of 1 to 700 mm,
nreferably 10 to ~0 ~m, which riffsr in coroosition, ~!lith re-
ference to the relative concentrations of the ~ost freouentlv
occurrina ~etals, Illherein ret21 is removed at a detec'inn lo-
cation frorr a limited surfac~ oortion of each retal oarticle
hy ~eans of 2 oulsed laser to for~ 3 corresoon~inq 013sma,
oDtion211y aftsr the limited surf3ce oortion has oreviousl~
~een clean2d ~v means of a laser 3nr.~ the resultinn pl-s~a h3s
been r~oved, ora~eter~ined sn3ctral lines ~r soectrel line
rannzs ar3 filtered fro~ the lin3 so~ctru~ o~ the olosma, a
s~arac 3ristic valu2 is rleterrined ascorr1inn to en aloorith~
fro~ t~e radiant intensities at the lavel-nn-hs nF t~e s~-ctr21
: lin2s ~r soectr21 lin3 ranQes ~!~ich have 2e-n filter d out,
an~ z sortinn sional is nenerate~ in denen~-nce on the co~n~-
r~s3n ~f sairl -~aract-risti~ ~alue ~ith ore~-tsr~inon li~iti.o
values.
T~e use of 1~s3r_ in soectrD5coov oermi t3, i.a.,
a local soectroanalysis of ~a~erials in minule volunes or on
minute ,urf~c~ are2s bv means 2f a focused aser be--. The
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resulting plasma emits a line radi3tion of discrete sPectral
lineo, ~hich can be detected entirely or in oart b\/ means o~
a spectrometer-dlode array and can be analyzed b\y an optical
multichannel analyzer so that a aualitativa analysis of the
metal particle is available a fe~ milliseconds after the plas-
~a has been formed. That process has been d2scribed as a Laser-
Induced ereakdown Spectroscooy (LIP~) in the oeriodical ~O~CD
Electro-Optical Systems ~esign, ~lol. 14 (19~7), ~lo. 10, on
pages 35 to 41 and with use of a pulsed ~Id yar, or CC7 laser
has been used, inter alia, For the sortino of scraos consistino
oF ~etal oarticles differinc in co~nosition. The rate 3t l~hich
the ~etal oar'icles can bz 3nalvzed i9 limite~ only ~v the
repetition r~te of the laser, thD velocity of the resoonse of
the electriG ~etector and the velocity 3t !~lhich t~e ~etal oar-
ticles can be Fed to the ~easurinn location (oeria~icel "qpliea
Soectroscopv, ~lol. 41, 19r7, ~'o. 4, 03qes ~?7 to 57").
In an e~bodiment of such a orccos3 ~isclosed in
EP-~-u 753 S~3 at least 3C ~-tal particlas ~avinq a oarticle
size of 15 to a5 m~ oass throunh a detectinn location, at which
a oortion or the surface of -3ch metal ~article is cleane~ by
~eans of 3 oul3ed laser be2~, the resultlno nlasma is r-l~oven
~n~ t~e cleaned surf3se eortion is anain ecsod uDon 3y 3 pulse~
laser ~ea~. ~ rtain qredeter~in-~ uavalennt~q or l~levelannth
ranqes ara riltered ~ro~ the line rac'iatior -f th2 resultino
olas~a an~ ratio are detor~ine~ fram tho r-rient int-nsitizs
at 53i~ wa~/alennth9 nr I~JaVelan?ihs r3nOeS an~ are cn~roare~ ~Jith
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adjustable limiting values for the generation of a sorting
signal. In that process, Nd:YAG lasers operating in the
near infrared range or CO2 lasers operating in the
intermediate infrared range are employed and the pulsed
laser beam produced by such lasers is directly focused, as a
rule, on a point of the surface of the metal particle so
that the metal is melted and vaporized. The resulting
plasma may be contaminated by impurities which have been
removed from the combusted boundary zones. A decisive
disadvantage resides in that the contours of the surface and
the thickness of the metal particles vary so that -the laser
beam is not focused on a point of the surface, and as a
result, a constant energy density is not achieved on the
irradiated surface.
15 For this reason it is an object of the present
invention so to improve the process of the kind described
first hereinbe~ore that the plasmas which are produced emit
in addition to the physically inevitable white light only
the discrete spectral lines which are specific to the metal
particles and said plasmas can be produced to have
approximately the same intensity regardless of the thickness
of the metal particles.
According to the present invention, there is
provided a process for a classifying analysis of a
polydisperse bulk material consisting oE various metal
particles having a particle size of 1 to 200 mm, which
differ in composition, with reference to the relative
concentrations of the most frequently occurring metals,
wherein metal is removed at a detecting location from a
limited surface portion of each metal particle by means of a
pulsed laser to form a corresponding plasma, predetermined
spectral lines or spectral line ranges are filtered from the
line spectrum of the plasma, a characteristic value is
determined according to an algorithm from the radiant
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intensities at the wavelengths of the spectral lines or
spectral line ranges which have been filtered out, and a
sorting signal is generated in dependence on the comparison
of said characteristic value with predetermined limiting
values, characterized in that consecutive individual metal
particles are continuously transported on a line from a
feeding location through the measuring location and along a
fixed path to respective discharge locations and are
irradiated by an Excimer laser at the detecting location.
Preferably, the size of the various metal
particles is 10 to 80 mm, and the metal is removed at a
detecting location from a limited surface portion of each
metal particle by means of a pulsed laser to form a
corresponding plasma, optionally after the limited surface lS portion has previously been cleaned by means of a laser and
the resulting plasma has been removed.
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The Excimer la~er is an inert gas halide laser,
which oaerateS in the ultraviolet range l~ith a short oulse
length 3nd distinguishes by havin~ a large beam cross-section
in conjunction with a hiqh pulse energy and a plateaulike in-
tensity distribution and a high pulse-to-pulse stability.
Owing tn its relati\lely larne diverg2nce the laser beam can
be focussed to bave a relativaly large depth of field on a
large area so that the process by l~hich material is removed
can be adapted to the various surface contours and/or thick-
nesses of the metal particles 3nd a satisfactory analysis of
the metal particles is thus enabled. ~ompared to ather pulsed
lasers an Excimer 13ser has 31so the advantaae that the oro~er-
ties of its ~eam, oulse leneth, pulse enercy and, abovo all,
beam diveroence and, as a result, its focussability, are in-
dependent on its pulse rep~tition frequency. qecause enerny is
introducDd in a closely con,ined area into the ~aterial to be
removed, an action on the bound3ry zones will substantially be
avoided so that a cont3minaticn of the resultinq plas~as ~ill
he avoided too. ~ecauOe the ~xcimor laser s3nnot be fired in
air, the plasna also cannot 3 adversely affected by he plasma
which would form in air and it is not necessary to subtract
the sDectrum of an air olas~z rom the soectrum of the olas~a
of tha metal oarticlo.
The sDectral r-riation of the ]lasma orcduced by
means of an ~xcimer 13ser is 31most indepen~3nt of '~e work
Function oF the metals.
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Preferably each metal particle entering the
detecting location moves through an optical barrier and the
signal which is thus generated is used in an electronic
detector to control the Excimer laser.
To permit the laser to be fired in response to the
output signal of the electronic detector, the consecutive
metal particles are preferably spaced at least 0.75 mm
apart. A feeding at a higher velocity will require a larger
spacing of consecutive metal particles.
Preferably, the optical barrier consists of a
light beam, which is directed to a photocell and is used to
measure the length of each metal particle.
The optical barrier may alternatively consist of a
; laser beam or of a combination of a light beam and a laser
beam so that each metal particle can spatially be detected.
According to a preferred feature of the process,
spectral lines in -the wavelength range from 200 to 800 nm
are filtered from the spectrum amitted by the plasma.
Preferably, the pulse energy applied by the
Excimer laser to the metal particle amounts to 30 to 500 mJ.
Preferably, the pulse rate of the Excimer laser is
10 to 500 H~, preferably 100 to 150 Hz, and a consistant
quality of the laser beam is desirably ensured at different~
frequencies.
The analysis will be simplified if it covers only
a small number of spectral lines or a narrow range of
spectral lines. To this end the emitted spectral lines are
preferably filtered out
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during an interval of 0.2 to 5~ ~9, preFerably 1.5 to 50 ~U5,
after the laser pulse so that the backqround noise of the
plasma radiation L~ill distinctly be reduce~ and the spectra
can be more properly identified.
The invention will noL~ be explained in more de-
tail L~ith reFerence to an illustrative embadiment and an
associated drawing.
A conveyor belt 1 ~oving at a velocity of ~.5 m/s
is used to feed metal particles ~ having an averaoe oarticle
size of 30 mm and taken from a polydisoerse bulk scrap material
consisting, on an average, o,
65~ aluminum alloy scrao
12'- zinc alloy scrap
8r,~ copper 3110y scrao
7~6 brass scraa
7,; special steel scrao
1~ lead alioy 3srap
to a detecting location ~ fcr spectroanalysis. Each ~etal
particle 2 entering t~e det=cting locatian ~ is detected by
a light beam, L~hich i3 ~lres~ed to 3 ~hotocell, and ay a laser
beam, which comes for~ an ~ e laser 7 and is dirDcted by _
focusing lens 5 and a ~irror ~. The resulting output signals
ganerated by the photocell - and the ~e/r'e laser 7 ~re ssn-
vort-d to -l_ctronic sianal3 oy an el2ctronic detectar 3 and
both resulting sinnals 3re _~mbined and usod to tri~?er the
Excim2r laser 9. The la32r ,-am from ths 'xcimer las-r 9 is
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directed by a mlrror 10, the lens 5 and the mirror 5 onto the
metal particle 2. ~y the first laser pulse the metal particle
7 is cleaned on a portion of its surFace and the contaminated
plasma ~hich is thus produced i5 removed by an air stream. The
second plasma pulse applied to the cleaned surFace portion of
the metal particle 7 serves ta praduce the ~etal alasma, which
is analyzed by a spectral datector 11, which i9 nreceded by a
sp2ctral filter 12, ~hich filtars out only discrete soectrzl
lines or spectral line ranges during an interval of 20 U8 after
the laser pulse. The opening of the time windo~ of the spectral
detector 11 i9 controlled by the electronic rletector ~ hich
determines also measured values in a computzr-readable form.
~lumerical ratios are derived from said measured valuzs in 3
microprocessor 13 and are comaared ~ith precetermine~ limiting
values for a generation of siqnals, !~hich control a sorting
apparatus by means of an electronic triagering systam 14, that
is started by the outDut signal of the photo~2tector 4.
