CA1155177A - Method for measuring the thickness of a refractory in a metallurgical apparatus - Google Patents

Abstract

A METHOD FOR MEASURING THE THICKNESS OF A
REFRACTORY IN A METALLURGICAL APPARATUS

ABSTRACT OF THE DISCLOSURE

A method for measuring the thickness of a refrac-tory laid-up against the interior surface of the steel shell of a metallurgical apparatus wherein at least one monitoring device comprised of a metallic conductor coaxial with an outer metallic sheath and separated therefrom by a refractory having a desired dielectric constant and having a free end and an end confined in a junction box provided with elec-trical connecting means in a critical wear area of the apparatus such that the free end of the device is at a known distance from the hot face of the refractory and the confined end extends beyond the outer surface of the steel shell, connecting the device to an electronic time-domain reflectometer by electrical connecting means, generating and impressing timed pulses in the device, receiving reflections of the pulses and visually displaying them on a reflectometer, and measuring the length of the device appearing on the display as a straight line bounded by two inflections. The straight line is indicative of the thickness of the refractory.

Description

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.

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.

! . ...

~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 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 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--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 .

' . 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 .

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

Claims (26)

Claims

1. In 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 refrac-tory, 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 pulses reflected by physical features of the device, (c) adjusting 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 appearing 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 refrac-tory from the length of the straight line displayed on the instrument.

2. The method of claim 1 in which the central conductor in the monitor device is at least one metal taken from the group consisting of stainless steel, molybdenum, iron, platinum tungsten, and nickel base alloy containing manganese and aluminum and nickel base alloys containing chromium.

3. The method of claim 2 in which the electrical conductor is molybdenum.

4. The method of claim 1 in which the sheath of the device is at least one metal taken from the group consisting of stainless steel and molybdenum.

5. The method of claim 4 in which the conductor of the device is at least one metal taken grom the group consisting of metal base alloys containing chromium and molybdenum and the sheath of the device is stainless steel.

6. The method of claim 1 in which the electri-cally insulating refractory material of the device is at least one refractory taken from the group consisting of:
high purity alumina, mullite, sillimanite, chromite, lime, magnesia, calcined dolomite, silica and zirconia.

7. The method of claim 6 in which the electri-cally insulating refractory material of the device is high purity alumina.

8. The method of claim 6 in which the electri-cally insulating refractory material of the device is magnesia.

9. The method of claim 5 in which the electri-cally insulating refractory material of the device is high purity alumina.

10. The method of claim 5 in which the electri-cally insulating refractory material of the device is magnesia.

11. The method of claim 1 in which at least one of the monitoring devices is laid-up in the refractory in the interior of a blast furnace.

12. The method of claim 1, in which at least one of the monitoring devices is laid-up in the refractory in the interior of an electric furnace.

13. The method of claim 1, in which at least one of the monitoring devices is laid-up in the refractory in the interior of a basic oxygen furnace.

14. In 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 refrac-tory, the device having a free end and a confined end, both being substantially flat surfaces, the confined end is con-tained in a junction box packed with an insulating material having a desired dielectric constant and is connected to an electrical connector means attached to the junction box, the conductor and sheath being separated by a material having a known dielectric constant in the junction box and being separated by the refractory at the free end of the device, such that the free end is at a known predetermined distance from the hot face of the refractory end 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 pulses reflected by physical features of the device, (c) adjusting 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 appearing 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 refrac-tory from the length of the straight line displayed on the instrument.

The method of claim 14 in which the central conductor in the monitor device is at least one metal taken from the group consisting of stainless steel, molybdenum, iron, platinum, tungsten, and nickel base alloy containing manganese and aluminum and nickel base alloys containing chromium.

16. The method of claim 15 in which the electrical conductor is molybdenum.

17. The method of claim 14 in which the sheath of the device is at least one metal taken from the group consisting of stainless steel and molybdenum.

18. The method of claim 17 in which the conductor of the device is at least on metal taken from the group consisting of molybdenum and nickel base alloys containing chromium and the sheath of the device is stainless steel.

19. The method of claim 14 in which the electri-cally insulating refractory material of the device is at least on refractory taken from the group consisting of:
high purity alumina, mullite, sillimanite, chromite, lime, magnesia, calcined dolomite, silica and zirconia.

20. The method of claim 19 in which the electri-cally insulating refractory material of the device is high purity alumina.

21. The method of claim 19 in which the electri-cally insulating refractory material of the device is magnesia.

22. The method of claim 18 in which the electri-cally insulating refractory material of the device is high purity alumina.

23. The method of claim 18 in which the electri-cally insulating refractory material of the device is magnesia.

24. The method of claim 14 in which at least one of the monitoring devices is laid-up in the refractory in the interior of a blast furnace.

25. The method of claim 14 in which at least one of the monitoring devices is laid-up in the refractory in the interior of an electric furnace.

26. The method of claim 14 in which at least one of the monitoring devices is laid-up in the refractory in the interior of a basic oxygen furnace.