Note: Descriptions are shown in the official language in which they were submitted.
115S~7'7
Background of the Invention
This invention is directed to a method for measur-
ing the thickness of a refractory in metallurgical apparatus,
and more particularly to measuring the thickness of a
refractory laid-up against the interior surface of the steel
shell of a metallurgical apparatus, for example a blast
furnace, electric arc furnace, basic oxygen furnace, etc.
The device used to measure the thickness of the refractory
is also described.
Apparatus, for example, metallurgical furnaces
and mobile hot metal transport, for example blast furnaces,
basic oxygen furnaces, electric arc furnaces, open hearth
furnaces, submarine ladles, stationary hot metal mixers,
glass refining furnaces, power house boilers and the like,
are constructed of a steel superstructure or steel shell
and a refractory supported by the superstructure or laid-up
against the interior surface of a steel shell. The refrac-
tory confines the heat and hostile atmosphere within the
apparatus and protects the surrounding environment and/or
steel superstructure and steel shell cr the apparatus.
~ ~55177
In recent years, much effort has been expended to
develop improved refractory. These efforts have resulted in
an increase in the life of the refractory and have increased
the length of furnace campaigns, i.e., the time a furnace is
5 in service before a reline of refractory is required. Such
efforts are continuing since the longer the time a furnace
is in operation the fewer relines are required and the lower
is the cost of producing molten metals in the furnace. Many
of these efforts have been directed to monitoring the wear
or erosion of the refractory so that timely repairs can be
made to the refractory to prolong the campaign of the furnace
and to prevent catastrophic failures of the refractory.
Several devices and methods for monitoring the wear
of the refractory in metallurgical furnaces are disclosed in
United States Patent No. 3,078,707 issued February 26, 1963
to Leo G. Weaver entitled "Thickness Gage for Blast Furnace
Wall", United States Patent No. 3,307,401 issued March 7, 1967
to George S. Bachman entitled "Element for Measurement of
Furnace Wall Thickness and Temperature", United States Patent
No. 3,532,797 issued October 6, 1970 to Hermann K. Lunig
entitled "Apparatus for Monitoring Thickness of Wall l:,ining
of Electric Arc ~urnace" and ~Jnited States Patent No.
3,512,413 issued May 19, 1970 to Otto VonKrusenstierna et al
entitled "Measuring Body Capable of Being Bullt Into the Wall
of a ~Iigh Temperature Furnace". All the monitoring devices
disclosed in the above patents are essentially thermocouples
having two dissimilar metals. The devices operate on the
principle of electrical resistance measurements and rely on the
discontinuity of an electric circuit. Bachman and Weaver use
~55:3 ~'7
l ................................... l
"ladder-llXe" de~ices extending through the thickne~s of the
refractory while Lunig and Krusenstlerna et al rely on a
¦plurallty of paired resistance wirea of ~arioua lengths
'llpo~itioned at varloua depths in the re~ractory thlcknes3.
5 li In actuality the monltorlng devices do not contlnuously
monltor the thlckne~s Or the rerractory ~n the sen~e that a
dlrect thickness measure~ent i~ made contlnuously. The
thicknes~ of the re~ractory is actually kno~n, or determined,
~ onlg at the ttme o~ a alsruptlon ln th~ electrlc circuit and
10 , is only appro~lmately knoNn when the c~rcult is agatn
completed,
l The prlor art device~ enumerated abo~e are limlted
l to ~easurln8 ~l~ed thlcXnea~es that are dependent upon the
l po~itlon o~ a partlcular wlre or loop ln the rerractory~
15 ~ m ese type~ Or devlces are also susceptible to bein8 ~shorted-
¦ out" by ~la~ penetration, breakage due to spalling Or the
¦ refractory, and detertoratlon o~ the sheath and in3ulatlng
¦ ~aterial placed b~twoen the ~lrea and tho ~heath. ~h~n,
too, th~ num~er Or r~rractory aurrace po~itlon~ or ~hlck-
ne3ses oP r~rractory ~hich can be measured by theae devlce~i8 ftn~te. For each new po~ltion, a separate wire or loop
mu~t be added to the monitor body.
Another method ~or meaauring the th~cknea~ and
l monitoring th~ wear Or the re~ractory i3 the u~e o~ 30urce~
251 Or low le~el radlation, l.e. radioactiYe i~otope~. A
~lurality o~ the sources ars embedded at predst~rmlned
locatlons in the rerractory duri~g reline. When a 90ur~e
_4-
,, .
1~55:1~7
1~ i
cea~es to emlt radiation, eroslon at tha~ location ~
¦ lndlcated. S~nce the actual erosl on is known only when
radiation cea3es~ ~t can be ~een that thl~ devlce and method
Il are slnllar to the other device~ and ~ethods in that the
5 ,I thlckness and ero~ion of the re~ractory 18 not known until
the ~ource disappears. Radiation type monitorlng i~ thu3
not really a continuous measurement system. Handling of the
radlolsotopes ~u~t furthermore be done by cpeclally tralned
l and llcensed per~onnel. I~ any isotopea remaln in the
10 1 rerractory a~ter a ~urnace campalgn, ~peclal care must be
taken by the licensed personnel to recoYer the 1sotopes.
Th~re ~s there~ore a need rOr an lne~pen~iYe,
safe, ~ubstantially continuous method ~or measurlng the
l thicknes~ o~ a re~ractory ln a metallurglcal apparatus
15 l particularly whlle the apparatu~ 18 ln service.
It 18 an obJe¢t o~ thls lnventlon to pro~lde a
method ror measurln~ the th~cXne~s o~ the refractory in a
metallur~ical apparatu3, ~or e~a~ple a blast ~urnace~ basic
~ oxy~en rurnace or electrlo rurnaae, etc. whersin at least
20 ~ on~ monitorlng device 1~ ~ositioned in a critical wear area
o~ the r~ractory lald-up against thc interior sur~ace Or
the steel shell Or the apparatu~ and the de~lce is connected
to an electronic instrumRnt which induces tlm~d pulse3 in
l the de~lce and records and display~ re~lected si~nals o~ the
25 l i~pulse~, whlch tisplay ls lndlcatl~a Or the length o~ the
¦ de~ice and thic~n~33 o~ the rerractory. I
¦ It i~ al~o an obJect Or thl3 ~n~entlon to p~o~ide
8 slmple monitor~ng de~lc~ suitable for w e with an electronlc
t l~S5~77
ln~trument whlch uses time-domaln rerlectometry technlques,
,l whereby the thlcknes~ of the refractory can be measured
either contlnuously cr lntermittently.
1~ Summar~ o~ the In~entlon
5 ! According to thi~ invention, there ~s pro~ided a
method ror meaæurin~ the thlckness Or a rerractory laid-up
agaln~t the ~nterlor sur~ace Or the steel shell o~ a metal-
lurglcal apparatus, ~or example, a blast furnace, an electrlc
I furnace~ a ba~lc oxy~en rurnace, etc. ~he met~od lncludes
the use Or at least one monltoring dev~ce lald-up in a
selected ¢ritlcal wear area Or the rurnace. The monitoring
device i3 comprlsed o~ a central metallic conductor and an
outer metallic sheath separated ~rom the conductor b~ a
pul~erulent clo~c-packed lnsulatlng materlal havln~ a deslrable
dielectrlc constant. Tho de~lce has two énds, a rree end
and a con~lnod end. The conflned end ma~ be con~lned ln a
Junctlon bos and be connected to an electrlcal connookor
moans attachod theroto or may be oonn~cted dlroctly to
~ the oleatrical connector means by whl¢h the de~icc is con-
nected to an electronic instrument which use~ tlme-doma n
re~loctometry t~chni~ue~ conrln-d ln a Ju~ctlon bo~,
an electrl¢al in~ulating packin~ o~ desired dlelectric
¢onstant may bo used to prevent dirt, dust or molsture
~ro~ ln~ress i~to the bos. Th~ devlce erodes at substan-
25 1 tlall~ t~e same rate as the r~ractory during ser~ce. In
Il the method Or the ln~entlon, the free end Or the devlce i~
¦~ pl~ced at a ~nown dl~tance ~rom the hot race o~ the refractory
¦ while the con~lned end, at~ached to an electrical connector
ll l
.
_~_
1~551.77
means, extends beyond the cold face of the refractory. The device isconnected by means of the electrical connector means to an electronic instru-
ment, for example a time-domain reflectometer (TDR) capable of generating
and sending stepped, timed voltages or pulses through the device and receiv-
ing reflected pulses or echoes which are visually displayed. The resultant
picture or signature of the reflected pulses is indicative of the length of
the monitoring device which in turn is indicative of the thickness of the
refractory.
More particularly, the present invention provides an improved
method for measuring the thickness of a refractory laid-up against the
interior surface of the steel shell of a metallurgical apparatus comprising:
(a) placing at least one monitoring device of predetermined
length comprised of a central metallic conductor coaxial with a metallic
sheath and spaced therefrom by a closely packed pulverulent refractory, the
device having a free end and a confined end, both being substantially flat
surfaces, the confined end being connected to an electrical connector means,
such that the free end is at a known predetermined distance from the hot face
of the refractory and the confined end extends a known distance beyond the
steel shell,
(b) connecting the confined end by means of the connector means
to an electronic instrument capable of generating and impressing fast-rise
timed pulses in the device and receiving and displaying pulaes reflected by
physical features of the device,
(c) ad~usting the length of the device on the display using
reflected pulses appearing as an inflection from the confined end as a
reference point, the reflected pulses along the length of the device appear-
ing as a substantially straight line and the reflected pulses from the free
end appearing as an inflection and showing the termination of the device,
(d) sending timed pulses through the device and displaying the
reflected pulses, and
(e) determining the thickness of the refractory from the length
of the straight line displayed on the instrument.
-7-
5~ 7~
Figures of the Invention
FIGURE 1 is an enlarged isometric view of the monitoring device
of the invention.
FIGURE 2 is a longitudinal view of the monitoring device of the
invention.
FIGURE 3 is a schematic diagram of a blast furnace showing a
plurality of the monitoring devices of the invention at several vertically
spaced critical wear areas in the refractory laid-up against the interior
surface of the steel shell of the furnace.
Preferred Embodiment of the Invention
According to the invention, there is provided a method for measur-
ing the thickness of a refractory which is laid-up against the interior
surface of the metallic shell of a metallurgical apparatus, for example a
blast furnace, basic oxygen furnace, electric arc furnace, etc.
In the method, at least one monitoring device is positioned at
a critical wear area in the refractory. The
~ '.1~ "
~ 7a-
115S.~7
de~lce ~ comprlQed o~ a central metalllc electrlcal con-
ductl~e conductor coaxlal wlth a metallic electrlcal conductlve
¦ ~heath and 3eparated thererrom ~y a clo~ely packed pul~erule~t
,l electrical ~n~ulatlng refractory. The de~lce ha3 two end~,
5 1 one free or exposed end and one con~ined end, each Or whlch
t 8 generally a rlat ~ur~ace. The con~ined end 1~ connected
to an electrlcal connectin~ means. The free end ls po31tioned
at a known di~tsnce rrom the hot race Or the re~ractory.
l Th~ hot race Or the rerractory 19 the race or sur~ace o~ the
10 1 rerractory ~hlch i8 oxpo~ed to the hotl hostlle environmer.t
in the apparatus. ~he devlcs e~tends appro~lmately per-
pendl¢ular to the hot race Or the re~ractory throu~h the
bo~y Or the refractory and the conrlned end extends a ~nown
l di~tance beyond the cold race ot the rerractory and the
e~terior surrace o~ the shell Or the apparatus. The cold
ra¢e Or the re~ractory 19 that ~a¢~ Or the rerractory whlch
1~ ~ubstantlally parallel to the hot race and ~paced thererrom
by the body Or the rerractory. The cold race i3 not actuall~
"cold" but sin¢e lt i8 the ~aco o~ th~ re~ractory ~urthe3t
rrom the en~lron~ont in th2 apparatu~ and ls protocted rrom
the hot en~lronment by the bulk o~ the r~rractory and other
re~ractory, lt iB ~enerally at a lower temperature than i5
the hot ~ace o~ the rerractory.
The con~i~ed end, 80 ¢alled becau~e lt may be
confined ln a ~unction bos, o~ t~e de~ice 18 connected to an
electronic instr~ent by mean~ o~ a coa~lal cable e~tendlng
rrom the ele¢trical connector moans to the ln~trument.
-8-
! . ...
~SS~Y7
The electronlc ln~tru~ent 18 a tl~e-domain re~lect-
ometer which uses pulse re~lectometry technlque~. The
ln~trument generate3 ultra-~ast rl~e time voltage step~ or
I pul3es whlch are propogated through the monitortng de~lce.
~ A portion Or the energy ln the pulses is re~lected back to
the instrument by phy~ical ~eatures Or the de~ice. ~he
re~lected energy i~ detected by the rerlectometer and is
~isually displayed on an oscillo~cope or cathode ray tube or
I llke display. The ~isual display may appear as an inflecSlon,
10 1 that 1~ either a rise or a ~all, or as a ~ubstantlally
~tralght l~ne. In the ln~entlon, the re~locted energy rrom
a rlr~t interSace ~h~ch i8 rormed by the capacltor comprlsed
the conductor and the ~heath and an alr separator in the
Junctlon box appear~ as an up~ard in~lectlon on the diaplay
and 1~ u~sd as a rererence ~oint ln d~termlnlng the length
Or the monltoring de~ice. All polnts along tho de~ice rrom
the con~lned end to the ~ree ~nd rerlect an equal ~ortion Or
the energ~ in the pul~os and thelr re~lection~ ar~ dl~played
a~ 8 ~trai~ht line. A portlon Or the onergy rerlected by a
~econd int~r~aco rormed by the rree end s~rra¢e Or ~he
dovice and the atmosphere in tho rurnace appears ~ither a~
an upward or downard ln~lection on the cathode ra~ tube but
~n either ca8e oho~ tho termlnation Or the monitoring
do~ic~. The strai~ht lin~ dlsplayed betw¢en the rir~t and
second ~nter~acc~ 1~ substantially the len~th of the
mnnltorin~ de~c~. The re~lection from the rr~e end sur~ace
o~ the ~onitor wil~ oc¢ur re~ardle~ o~ lt~ eleatrical
¢ondust~lt~, ~.e., the re~le~tion will occur ir the con-
ductor i9 el~ctrlcally insulated rrO~ coDpletaly 3hcrted or
,
! . .
..5~7
partlally qhorted to the shesth or the hot ~ace o~ the
refractory whlch conditlons adver~ely affect other type~ o~
two-wlre monitor3,
,I The prererred embodiment o~ t~e monltorln~ devlce
5 ¦ is ~hown in FIGURES 1 and 20 As shown ln FIGURE~ 1 and 2,
the monitorlng devlce 10 1~ o~ an~ predetermlned len~th,
¦ that 13, the monitoring devlce can be any length, for
e~ample, up to about 61 me~ers or more commensurate wlth the
l thlckne~s Or the refractory~ and the thlckness o~ the
10 1 3upportin~ structure Or the apparatu3 to be monitored. The
de~l¢e 18 comprl3ed Or a metalll¢ conductor 13 coa~ial wlth
a metalllc oheath 14 and 3eparated therefrom by a pulverulent
closely-packed insulatln~ re~ractory ~aterlal 15 ha~lng a
I known sultable dlelectrlc ¢onstant. ~he dlstan¢e between
15 ~ the conductor and ~heath 18 es~entlally the same the entl~e
length Or the devlce. The 3ultabllity Or the dlelectric
constant ~ dependent upon the relatl~e ~zes o~ th~ conductor
13 and the aheath 14 a~d the lmpedance neces~ary ror aorr~ct
l operation Or the partlcular electronlc in~trumont tnot
~hown) to ~hlch the de~ice 19 connected. The ~onltorlng
de~ice lO terminates ~n two generally rlat ~urrace~, Qnds ll
and 12. End 11 wlll herelnarter be re~erred to a~ the ~ree
or e~posed end and end 12 wlll hereinarter be re~rred to as
the con~lned end t~hown ln FI~U~E 2). A ~mall portlon l~a
~ the conduator 13 e~tends beyond end 12 Or the she~th 14
at conr~d end 12 and may bo separated ther$~ro~ by air
whlch ha~ a dlel~otric constant dirrerent ~rom the dlelectric
con~tant o~ the insulat~ng re~ractor~ matertal 15. The
--10--
S~7~
il conductor 13 and sheath 14 are 3ho~n aq bein6 ~enerally
I¦ clrcular ln cross-~ectton, however, the conductor and ~heath
may be o~ any sha~e in cross-section as long as ~-he dl~tance
Ij between the outer surface o~ the conductor and the lnner
5 1 ~ur~ace o~ the ~heath remains constant substantially the
entlre len~th of the devlce. I~ the dlstance between the
conductor and sheat~ should ~ary 31gnl~cantly, the lmpedance
the devlce wlll ~ary and ralse rerlections or echoe~ wlll
~ be created and appear on the electronic ln~trument. Minor
lO ~ dlscontinuitles along the device can be tolerated ~o long aQ
1 such di~continultles do not r~flect all the energy on the
¦ pul~es and are calibrated or accounted ~or ln readlng the
¦ d~3play on the electronlc lnstrument.
¦ The conrlned end 12 Or the monitorln~ device lO
15 ¦ may be contained in a Junctlon bo~ 16 o~ the ~hape ~hown.
5uch ~hape i9 ~hown by ~a~ o~ esample only, ~lnce other
type~ and 3hapes o~ ~unction boxes may be used. The Junctlon
bo~ 16 1~ Or a one-piece cast metal con~truction ror~in~ a
~ generally r~ctangularly ~ha~ed box 17 having an open top 17a
20 1 and integral end wall3 1~ and 19, ~ide walls 20 and 21, and
bottom 22. A cover plate Z3 i~ ~astened a~ shown to close
the bos. A bracket 24 havi~g an axial aperture (not shown)
acd a ~et screw 25 extending into the apert~rs ls ~astened
¦ to end w~ll 18 as 3hown. ~e aperture ln the bracket i~ I
25 ¦ aligned ~ith an aperturs tnst ~hown) ln end wall 18 whereby
¦ con~ined end 12 Or the ~onitor~ng de~Jice 10 can be in~erted
¦ t nto the bo~c 17 a3 shown . The monltor~ ng deYice 10 i3
irmly clzm~ed ln plac~ by tlghtenln~ ~et scre~r 25. A
.
5~
~I remale BNC connector 26 1R ~a~tened by approprla~e mean~ to
end ~all 19 wlth portlon~ 26a and 26b extendlng through
Il appropriate openings (not shown) ln the end wall 19 a~
,I shown. The conductor 13 and the ~heath are connected by any
~ell known means to connector 2~ a3 ~hown. A coa~ial cab~e
t~hown at 37 ln ~IGURE 3) ls attached to the co~nector 26
and co~ect~ the deYice 10 to a time-domaln re~l ectometer
(~hown dlagrammatlcally at 36 in FIGURE 3). The re~lecto-
l, meter can be a T~ktronik 1502TDR manufactured by Tektroni~5 Inc., ,
10 1 P.O.Bo~ 500, Beaverton, Oregon 97077, or suitable lnstrument
which csn be used with the de~ice of the lnrention to
measur~ the thickne~ and monitor the eros~on Or the re~ractory. 1
I~ lt 19 de~ired, con~ined end 12 may be connected directly
~ to the connector 26, wlthout belng con~ined ln Junctlon bo~
15 ~ 16 thereby simpllrying the ¢on~truction o~ the devlce 10
w~thout ad~er~ely a~re¢tlng lt8 accuracy.
l ~he ~unctlon box may be packed with an ele¢trically
l insulatlng m3terial ~not shown) havin3 a desired dtelectric
constant, rOr e~ampl~ ~illcone rubber produced by Dow Cornln~
CorporationJ Mldland, ~lchl~an 48640 and ~old commercially
a~ Silicone Rubber c}ear ~ealant prlor to placing th~ co~r
23 atop the bo2. The ~alant protec~s the conrlned ~nd and
electrlcal connectlons ln th~ bos rrom du~t, dirt and mol~ture.
¦ The bo~ may not aontaln an~ 3ealant ~o lon~; a3 the co~er 23
fitg tl~tly onto the bo;c to prevent the ~n~;re 3 0~ dlrt
dust or moisture. In the latter ca~e, air 1~ u~ed a~ t}le
¦1 insulatlng ~aterial arld the dlelect~ic con~taalt o~
¦¦ known. It i~ pre~erred to pack the box ~lth a sealant o~
~ the t~pe ment~ oned abo~re .
-12- ,
i177
.
I
As noted pre~iously, ~he end 12 may not be con-
~lned ln a ~unctlon bo~ but may be connected directl~ to an
electrlcal connector me n~, however it i9 prererred to
ll conrine the end 12 ln the ~unctlon bo~ 16.
5 1' The conductor 13 and sheath 14 are made from any
metal which w~ll be electrically conductl~e and wlll with-
stand the hostlle en~lronment pre~alent in metallurgical
apparatus, ~or e~ample a blsst rurnace, ba~ic o~ygen furnace
or an electrlc ~urnace. Materlal~ which can be u~ed are 304
10 1 grade stainless ~teel, lybdenum, lron, plat~nu~, tun~sten
¦ and nlckel-base allo~. Nlckel-ba~e alloys which contaln
mangane~e and aluminum or chromium or chromium and sillcon
and cobalt a~ described on pa~e~ 15 and 58-59, respectively,
in Ha~dbook Or Materlal $radenames by Zi~merman and ~avlne,
i5 l 1965, can be used as the ¢ondu¢tor in the de~ice. It 19
prererrod to use molybdenum rOr the conductor and 304 8rade
~talnless 3teel ~or the ~heath. The conductor may be sol~d
or hollow and may be about lO gage ln JiZo or may be larzer
~ in se~ere appllcatlon~ rsquirln~ more bod~ and 24 ~age or
20 ~ smaller in a~plications in which space i9 limited. However,
for practlcal ~urposes ~t i9 pre~erred that the size o~ the
conductor b~ wlthln a ran~e b~tween about 12 and 22 ~age.
In these speci~lcations all wlro sizes are American Wlre
¦ Ga~e.
$he re~ractory 15 can be any rerractory which 18
olectrlcally insulatl~e, 3uch a~ hi~h purlty alu~ina~ high
duty ~lreclay, mulllte, 3illimanite, ma~es~a, calcined
calc~um carbonate, calcined dolomite, calc~ned dolomitic
I" I
~13- .
iL~S 5 ~f77
llmestone, zirconia and the llke, ~o long as it ~9 com-
patlble with the re~ractory o~ the metallurgical apparatus.
It i3 pre~erred to u3e h~f&h purity alumina ln most applica-
l tlon~ but other refractories, such a3 ma~ne3ia or zlrconla
5 I may also be used.
The dlelectrlc constant o~ the refractory mu~t becompatlble with tho constructlon or the monltor de~ice and
the electrlcal characteristlcs Or the t~fme-domaln rerlect-
omoter. For esample, the impedance o~ the monltor device
10 ~ must be corre¢t ~or the TDR apparatus used. The impedance
¦ Or the monltor is dependent u70n the capacltance between the
conductor and the sheath. Capacltance 18 dependent ln turn
upon both the dlstance between the plate~ Or the capacitor,
the ~ize o~ the plates and the dlelectric matarial between
15 l the plates. Thu~, in ordor to ~rovlde any ~ivon capacitan¢e
the dleloctrlc constant o~ the re~ractory materlal must be
balanced agalnst the relative ~l~e Or the conductor 13 and
¦ the ¢onductl~o Jheath 14. Ver~ Jmall monltor dimen~lona may
¦ re~ulrc a rerractory havtng a dleloatric constant dl~similar
20 ¦ to that o~ a lar~or monltor in order to attain the most
¦ e~ectl~e i3pedance ~or the ~D~ apparatus usod. The ti~e
¦ domain re~lectomoter i8 not the e~clusi~o ~y~tom whlch can
¦ be u~ed ln tho ~n~ontton, howo~er, ~o prerer to use the time
¦ domain re~lectomoter ~lnce lt ls the ~implest and easlest
25 ¦ mean~ ~or tranJmltting and recording (dl~pla~lng) reflections
or echoes.
It 19 pre~erred that confined end 12 o~ thc
monltor lO e~tend beyond the refractory a si~nirica~t
,I -14-
. . .
i
;
l 1155177
¦ dl3tance since the constructlon of the monitor 18 heat
! reslstant and sturdy. Con~lned end 12 could be po~itioned
~ I .
~ub~tantlally at the cold ~ace Or the re~ractory, but this
I would re ult ln the ~unction box and connectlons belng
5 i exposed to both exce3~1ve heat and dirt. (A~ noted prevlou~ly,
i the cold face 1~ not really cold but in most ca~e3 relatlvely
cold when compared to the temperature o~ the hot face.) The
monltorlng devlce can ¢onvenlently extend beyond tAe 3hell
l o~ the apparatu~ to remote location~ snd can even be ben~
10 1 around curves to mcre acccssible le38 ri~orous or more
centrali~ed location~ wlthout inter~erlng wlth th~ reflected
i slgnals recei~ed there~rom. In such cases, the readlng of
! the length Or the ~onltor after rerractory wear ls merely
subtracted ~rom the ~nitlal readln~ o~ the len~th Or the
monltor to rlnd the e~tent o~ ro~ractory wear. Alternati~ely,
a dlscontlnuity can be introduced lnto the monitoring de~ice
at the cold ~ace o~ the re~ractory 80 that the exaet length
i Or the refractory can be d~rectly monitored at all time~.
~ Such a dlscontinu~by could cong~9t 0~ a si~nl~i¢ant crimp in
20 ¦ the ~heath or an ener~J refl~cting ~urface w~thin the
monito~, for example, a reflectlve surrace comprl~ed or the
inter~aae b~tween one diel~ctrlc material and another
tispo~ed ln the space between t~e conductor 13 and the outer
condu¢ti~e sheath 14. In one ~er~lon o~ ~uch a monltorln6
a5 device the ~lectrically ln~ulating rerractory matsrlal 15
could be arranged to be dis~osed between the conductor 13
and the 3heath 14 only ln the por~ion of the ~onitor extendin~
! ~r the hot face to the cold ~ace of the orlginsl re~r~ctory,
l Il
-15-
i
S~ ~ r- -. . .
55:1~7
while the conductor and the sheath extend farther beyond the
cold race of the re~ractory to 90me convenient locat~on with
11, only an alr dielectrlc between them. In thi3 lnstance,
,i however, the monitor must be made e~pecially ~or every
5 1 orlg~nal wall thlckness Or refractory ln whlch lt is to be
mounted. It is more conven~ent and e~lcient, therefore, to
orm monltorlng devlces havlng a con~enient length ar.d
subtract the len~th ~13ually dlsplayed upon the cathode ray
~ tube Or the TDR apparatu~ arter operatlon o~ the re~ractory
10 ~ apparatus rrom the orl~lnally di3played length at the
~nitlation Or operation to determine the thl¢knes~ o~ the
refractory.
To lllustrate the method of ~ea~urlng the thick-
ne~s and the ero~ion o~ the re~ractory lald-up against the
lnterlor surface Or the steel shell in a bla~t rurnace1 a
plurality or the monitoring devices 10 are ~ho~n in FIGURE 3
posltioned in the crltlcal wear areas Or the re~ractory 28
of the ~last rurnace 27. ~he monitorln~ de~ice~ lO are
posit~onod such that each Or t~e ex~ooed ~nd~ 11 are rlu3h
~lth tho hot race 28a Or the rerractory 28. The hot race Or
th~ r~ractory 19 that race ~hich i9 esposed to the hostile
envlronment ln the rurnace. The cold race 28b o f the
r~ractory 1~ ~arallal to the hot ~ace and iJ laid-up agaln~t
the interlor ~urrac~ Or the metallla ~hell Or the rurnace.
The devices 10 are po~ltloned ~ubstantially perpendicular to
the hot ~ace Or the rer~3ctory 28. The con~ned ~nds 12
e~tend beyond the outer sur~ace 35 Or the ~hell 30. me
re~ractory 28 ln the upper ~ack 31 of the ~urr.ace does not
_t 6-
l l~S5~77
generally fall durlng a campalgn because lt i3 exposed only
to abrasion ~au3ed ~ making contact wlth the raw ~aterial
used to produce molten iron as they are charged into the top
1 32 of the ~urnaco. T~e re~ractory ~n the upper tack 31 is
5 ¦ 3ub~ected to relatively low temperature3 and hence lt i~ not
es~ential to monitor the ero~lon o~ the re~ractory in this
area.
The re~ractory in the lower stack 33 and bosh 34,
I on the other hand, 18 expo~ed to e2cessl~ely hlgh t~-
peraturos, liquiSled sla~, mo}ten iron, a reducin~ atmosphere
and noxlou3 gase~ present in the rurnace en~ironment. The
rerractory can and does wear rapldly ln these critical wear
areas ~o several ~onitorlng devlces are posltioned at the
18.85 m~ter level identi~ied a~ A; at the 20.98 meter le~el
identlrled as B; and at the 23.11 meter level identlfied a3
C, aa 3hown ln PIGURE 3, and apaced 90~ a~art. Each o~ the
conr~ned ends may be connected ~equentially to a tlme-domain
rerlectomotor 36 by a coaxial e~ton~lon cablo 37.
~ Ea¢h o~ the monitoring de~iceo may be made rrom a
20 1 ~wa~eable assembly o~ a 20 8age molybdenu~ conductor po~i-
tioned in a prefired tube o~ ~lgh purlty alumina ha~inz an
outside diameter o~ 6.02 mm and an ln~ide dlameter o~ 1.96
m~ NhiCh i9 tnserted into a 304 ~rade ~ta~nles~ ~teol tubular
sheath ha~lng an outside diameter o~ 7.89g mm and a wall
thi¢~n~s~ Or 0-S35 ~. ~he a~sembly 1~ 3~aged do~n to a
de~ice whlch has an out3idc dlameter of 6.35 ~m. Durlnz the- ¦
l ~ragin~ o~eratlon, th~ prerired alumina tube ~ ~ rractured
i and broken lnto ma~y ~mall partlcle~ ~hlch are pressed lnto
¦¦ a elo~ely packed structure ae~arati~ the conductor and t~e
30 1¦ sheath.
, --17--
1155177
The mo~ltoring devlce can al~o ~e u~ed ln critlcal
wear areas, for example at the slag line in the refractory
~1 on the interlor ~urface of the ~teel ~hell o. a ~asic o~y~en
.,
,I furr.ace to monltor the ero~lon of the re~ractory. The
5 ¦ insulating refractory o~ the monltoring dev~ce in thi~ case
,¦ ca~ be a den3ely packed re~ractory other than alumina ~uch
mag~e~ia, or ca~ be alu~ina.
Since the monltorlng device 1~ lald-up wlthln the
, refractor~, it ls ~rotected rrom the hostile envlronment in
10 1 the ~urnace. A~ the refractory in the ~urnace erade3~ the
e~poaed end 11 o~ the monitoring device also erodes at
sub3tantially the ~ame rate as the re~ractory. The 103s in
length of the monitoring devlce 13 substantlally equ~l to
the los3 or the re~ractory i.e., the erosion or 1088 in
15 l thicknes~ Or the re~ractory. Slnce the original thic~ne~s
of the refractory and the poaition o~ expo~ed end 11 of the
monitoring device ln the re~ractory are ~nown, the thic~ness
o~ the re~ractory can be deduced at any time from the length
! Or the ~onitoring devlce ~i3ually displayed on the recording
instrument. Thi~ is acco~pllsh0d by ~ubtracting the di~played
length o~ the monitorlng device from the origlnal dl3played
¦ lenæ~h determlned along with a suitable callbratlon o~ the
recording lnstrument and in turn Rubtractln~ the difrerence
~ound ~rom the kno~n thlc~ne~ Or the orlginal re~ractory. I
25 ~ A monltorin~ device Or the lnventlon as sAown in
FI&~RE 2 ~as po~itioned e~perim~ntally ln a critical wear
l~ ar~a of a 170 ton electrlc rurnace du~ing re~lne o~ the
Il
l' l
-18-
.
' . r`. -
,
;
5S~77
furnace. The refractory o~ the rurnace wa~ comprl~ed Or
tar-bonded, tempered magnesia shapes hav~ng a th'cknes~ o4
Il 34.29 C2. The monitorlng device u~ed in the furnace was
,¦ 111.76 cm long and had a molybdenum conductor which ~as
5 ¦ O.737 mm in diameter, an alumlna refractory havlng a dl-
electrlc constant Or between 4.5 and 8.4 and a 3~4 ~tai~less
steel sheath havlng an tn~ide diameter Or 4.85 ~m and an
out~lde diameter o~ 6.35 mm. End 11 wa~ allgned ~lush wlth
l the hot ~ace o~ the refractory. ~nd 12 extended beyond the
steel shell o~ the ~urnace and wa3 co~nected to a TDR 1502,
~hich 18 a commerclally a~ailable time-domain reflectGmeter.
~he th~ck~ess of the refractory was measured and the eroslon
monitor~d durln~ the campaign Or the furnace. The actual
len~th Or the monitoring de~lce was 111.76 ¢m and the re~ractory
1~ thickness wa~ 34.2g cm, hence 77.47 lnches) Or the monitorin~
de~ice estended beyond the re~ractory through the shell of
the rurnace. The ~ignatur~ on the ~isual dlsplay of the
electronlc instrument was ad~usted to show the actual
thick~as3 34.29 ~m or tho r~ra~tory. During th~ ~urnace
ca~palgn a total o~ 126 heata, i.e., about 15.42x10 4 Xg
Or ~teel per heat produced ~rom one furnsce charge, o~ 3teel
~er~ rer1ned and the ~urnace taken out o~ servico for
reline. A partlal listing o~ the erosion Or t~e r~ractory
during the rurDac~ campaign i9 ~ho~n below:
M~aJured Calcu
Wall la~ed
~h~cknes~ ~onitor Wall
(Actual) Length Thlck~es~ i
~l (cm) (cm) ~cm)
3o At ~tart34,3 111.8 34.3
44 Heats ~ 99.7 22.2
104 ~eats 88.3 10.8
126 Heat35. 4 82. 6 5.1
.
1155177
I It can be ~een that the ~lnal actual thlcXne~s Or
the re~ractory was only about 3 mm thicker than that ~l~ually
recorded on the instrument.
¦ l~hile we have ~hown and deRcrlbed the use o~ the
5 11 monitorlng de~lce of the invention in metallurglcal furnaces
I which are comprl~ed Or a ~teel ~hell and a refractory laid-
u~ in the interlor of the ~hell to protect the 3hell ~rom
the hostlle en~ironment thereln, the ~onitorlng devlce can
also be used ln ap~aratus 3uch a~ open hearth furnacesg
~lass reflnlng furnaces, power hou~e boller~ moblle hot
metal trans~er car~ or 3ubmarlne ladles, hot metal mlxer~
and holdlng ladles and the like.
Ir it 1~ de~lrable to monltor the th~ckness of the
l rerractory ln a worklng ~urnace~ ap~ropriate ports 8ultable
15 l ror insertin~ the ~onitoring deYice Or the lnventlon can be
ormed ln the shell and refractory by drilling and de~ice
in~erted into the aperture ~o rormed
-20-
