RECOMMENDED PROCEDURES FOR MECHANICAL ANALYSIS OF ROTARY KILNS
Mustafa Kamal Pasha
RECOMMENDED PROCEDURES FOR MECHANICAL ANALYSIS OF ROTARY KILNS TEXT AND ORIGINAL SKETCHES
SAFETY practicall guide for the This text is intended to serve as a practica operation and maintenance of rotary kilns and kiln drive drive systems. It is is not intended to be an instruction manual, and the procedures performed only by trained personnel discussed in this text are to be performed who are fully aware of the dangers involved with the equipment.
performed with all Any procedures presented in this text are to be performed barriers in place and fully operable. With the guards and safety barriers exception of ection !, "ear Alignment, removal of guards is not required to successfully utili#e these procedures.
All equipment must be operated and maintained according to applicable government safety and health laws and regulations such as $%A, &%A, generally recogni#ed industry standards, plant safety rules and regulations. All personnel must follow safe working practices and use good 'udgement. The installation, operation and maintenance of rotary kilns and potentiall unsafe conditions each associated equipment presents many potentia
of which could cause serious personal in'ury or death. but are not limited to the following(
These include
%igh Temperature &etal urfaces Avoid personal contact The flash point of liquids, gas may be exceeded %ot "ases and &aterial )ersonal contact can cause severe burns
*ethal +oltages )ersonal in'ury or death can result se lockout procedures %a#ardous -hemicals )ersonal contact can cause severe burns, death )oisonous &oving and otating &achinery )ersonal contact can cause hands, arms or legs to be caught in pinch points se guards and safety brakes
%eavy -omponents se proper procedures when lifting If components are dropped personal in'ury can result /ust /ust may be hot and0or caustic kin and eyes may be exposed se protective clothing
om1 ma'or safety concerns involving the kiln and associated equipment are listed below. 2. !ecause of the high temperatures, both the entire kiln must be treated as a temperatures generally range from a 72895-: up to about ;4456 78<=5-:. Ii
internal and external, dangerous area. kin low of about 34456 )ersonnel working on
piers or other locations where they can come into contact with the shell must be safety conscious to avoid inadvertent contact with the kiln which can result in severe burns. -aution should be taken to avoid heat prostration and dehydration which may be associated with long working periods near a hot kiln. <.
)ersonnel must be aware of the flash points of any lubricants, liquid, or solvents coming in contact with hot surfaces.
3.
-are must be taken in opening any inspection port. %ot dust from any kind of puffing can be blown in the operator>s face. )rotection for the face and eyes must be worn at these times.
8.
A lockout procedure should be used when performing any work on the equipment. ?.
@.
=.
/o not operate equipment unless all guards are in place.
!ecause rollers are ad'usted while the mechanism is in motion, personnel must exercise caution to avoid in'ury. Although the parts are rotating at relatively low speeds, danger does exist. )ersonnel must exercise particular caution in keeping themselves and their clothing well clear of the moving parts including tires, rollers and gears.
Improper or inadequate maintenance could result in personal in'ury, death, or property damage.
111
FOREWORD
The material in this book evolved gradually with the accumula tion of sketches which were prepared in order to clarify explanations of work to be done at times when language problems had to be overcome in various parts of the world. 6ield engineers and consultants who speciali#e in installation and maintenance problems cannot travel with equipment needed for the work. It is usually necessary to arrange for acquisition of precision test equipment from local sources and to prepare various 'igs and fixtures from material available at the plant site.
There are many ways to do the work described in this review of procedures for kiln survey and mechanical analysis. This work merely illustrates a few practical and simplified approaches. ome plant engineers and maintenance supervisors have followed up with custom madeB test equipment and fixtures designed for rapid setup for preventative maintenance test procedures to ensure maximum oper ating time for their rotary kiln7s:. There are no theoriesB contained in these descriptions of test procedures and the potential problems for operation and maintenance of a rotary kiln contained in this material. When certain long standing practices and0or recommendations are challenged, it is because for many years I have been called upon to rebuild equipment that broke down after components were set according to existing theories and misdirected logic. This text will call your attention to a few of the less obvious, often overlooked, problems encountered in kiln survey and mechanical analysis procedures for maintenance of a rotary kiln. After all, why should you have to learn the hard way.B
. ). -hapman
iv
ACKNOWLEDGEMENT
)reparing this material was similar to being in a longCdistance endurance race, with the final yardage also being an obstacle course.
It is important for me to acknowledge the support of many people as this material was being organi#ed, with special thanks to the people who became involved enough to keep it moving.
&any thanks to everyone for your encouragement and advice.
V
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Appropriate illustrations follow each chapter.
vi
A. PRESHUTDOWN ROCEDURES efer to Figure 1, for typical orientation and common terminology for reporting kiln details. In long distance telephone discussions and also in written descriptions of kiln problem #ones, the reporterB should clarify pier numbering sequence 7starting count at discharge end or at feed end: and should avoid local landmarks and0or compass directions when describing work areas for the kiln. 1 . ANAL YZE AND RECORD SHELL
CONDITION !efore a hot, onCstream kiln is shutdown for maintenance and realignment, observe the shell closely for indications of dis tortion and runout conditions. If runout is excessive, espe cially at feed or discharge ends, make arrangements for cutting the shell for realignment of the afkcted sections. ometimes certain #ones of the shellKincluding riding ring sectionsK are so badly distorted that new shell sections must be installed to eliminate the maintenance problems. In addition to observing kiln shell conditions, measure runout at predetermined test locations along the entire kiln length. se these measurements to plot graphic views of the crossC sectional shape of the shell at the various test locationsL also plot the plan views of the shell at test points 2;44 apart on the circumference. se the following procedure to measure and plot shell runout( a.
)repare a sturdy support stand for installation on the drive pier. This stand will be used to hold a piece of chalk in a steady position for marking a straight line around the circumference of the slowly rotating shell.
sually catwalks are too far from the kiln for service as testwork platforms.
&any kilns do not have walkways for closeCup inspection between support piers. A rigid work surface, within easy reaching distance of the kiln shell, is necessary for preparing reference lines and for obtaining actual test measurements. caffolds can be prepared for this work, but assembly and moving time must be considered. A selfCpropelled, hydraulically operated, telescoping, twoC man work basket is a convenient way to move between test points. As a third alternative, a small crane may be used to lift and hold a basketB for use as a twoC man work station. The basket must be secured against swinging or turning by attaching and anchoring at least two tag lines. b.
Although it can be extremely hot and uncomfortable, it is possible to measure and record the shell runout of an operating kiln. ince some kilns now rotate at speeds as high as 8 rpm, make arrangements for rotation at no more than 1 rpm during the testwork period at any single premarked test line. This lower speed reduces the poss ibility of misreading the fractional reference marks on a foot rule or scale. If the production department agrees to reduce kiln speed to 2 rpm while runout is measured at individual test lines, but returns to faster rotation speeds between tests, the control room must be advised when the test team is ready and also when it is finished at each test position. TwoCway 6.&. radios are useful for such contact.
c.
Predeer!"#e $e e%e# &' $e a#a()*"* & be +er'&r!ed, $e# !ar- $e *$e(( '&r e*"# a +&*""&#* a(&# *+a#* be/ee# "re *ec"&#* a#d a b&$ e#d* a* '&((&/*0
72: &easure the circumference of the shell at the refer ence line, then mark off 2< equal spaces around the shell. If the shell contains permanent fixtures 7man holes, thermocouples, etc.: that can be used as refer ence points for followCup work, select one of these items for marking the 4403@44 7or 2<(44 position: test line, as shown in F"re 2. This line is to be the index line for marking the entire length of the kiln shell. After marking position Eo. 2<, mark remaining space marks 72 through 22: as they come into position with rotation of the kiln.
)repare a combination support and slide surface for service as a fixed reference point for measuring and recording the shell dimensions at the twelve test stations on each test line. Arrange the slide surface perpendicular to the shell at whatever position is dictated by the final position of the work platform. )osition the end of the slide surface as close to the shell as possible after determining the approximate shell runout at that test point.
73: ecord the number and location of the line being tested and also indicate the twelve test points in vertical columns, 2 through @ and = through 2< for quick comparison of readings @ 2;44 apart 720=, <0;, etc.:. 78: &ove to each test line in turn and repeat the above measuring and recording procedure at each location. After all test lines have been processed, release the test team to other activities. CAUTION
When measuring runout of a hot kiln shell it is important to know that the runout is not influenced by a temporary warp condition such as will be found when the refractory lining and0or material coating is not equally thick, especially along longitudinal lines 2;45 apart in random #ones of the kiln. neven shell temperatures, resulting from varying insulation values of different thickness of the lining, will cause the kiln shell to form a temporary bowC shaped warp condition. hell temperature at the thin #one of lining will be relatively higher than at the heavily coated #ones. The hot side of the kiln shell will expand more than the relatively cool side. The hot side will form a convex lineKfor maximum plus runout—while the cool side @ 1800 away on the shell circumference will form a concave line, or maximum minus runout position. When recording shell runout, shell temperature 7s: at positions 2;45 apart must be considered for final
analysis
of the actual condition of the shell rotation relative to a true axis.
for
se infrared heat recording equipment, or use magnetCback dial type contact thermometers for veri fication of shell temperature at each test station around the shell at predetermined test lines. &easurement of a coldB kiln will not be influenced by unequal shell temperatures caused by condition of the lining, but it is important to consider the poss ibility of a temporary warp caused by sunlight or from ad'acent operational kilns. The side of the coldB kiln exposed to heat sources will be considerably warmer than the shadyB side and this imbalance will cause the shell to become bowCshaped enough for measurement of significant runout. hell temperature should be equali#ed prior to start of runout tests at idle kilns. d. Pre+are !a*er /&r- re+&r *$ee* '&((&/"# e#r"e*0
'&r
$e
72: $ne sheet for test figures and runout comparisons, and for converting as readB dimensions to relate to an average figure as though plus and minus values had been recorded by a dial indicator. See Figures 3 and 3A for a blank sheet and a filledCin example. 7<: $ne sheet 7to relate to the figure entry sheet: for plotting a crossCsectional view of the kiln shell in relation to a true circle, as shown in Figures 4 and 8A. 73: $ne sheet for plotting plan views of the shell profile as would be seen at points 2;44 apart with each rotational move of 345 of the kiln. See Figures 5 n! 5A. 78: )repare sufficient copies to cover all test points and the crossCsectional plot and to allow for probable layout errors when 'reparing the sheet for plotting the plan views. (5) Dnter dimensional data and plot approximate shell contours on appropriate work report sheets. With
8
dimensions now being transformed into graphic pat terns, the actual condition of the shell can be ana ly#ed to determine a plan of action for repair and0or realignment work. Eow it will be possible to decide whether or not to 72: replace any part of the shell, 7<: cut and realign the existing shell, or 73: to plan on realigning tire sections and support rollers for improved operation of the kiln. 2.
CHEC" TIRE AND SU##ORT ROLLER CONTACT SURFACE CONTOURS
If these faces are not flat, smooth and parallel to the axis of the shaft, arrange for an inCplace trueCup on the affected surfaces. Typically, tires and rollers in need of surface trueCup will also be peened outward past the side faces as shown in Figure $. These protrusions must be removed, and corners must be rounded at approximately MB radius.
NOTE TrueCup work on tire and roller surfaces should be done in advance of a planned kiln shutdown for realignment tests and ad'ustments. nless the kiln service crew is familiar with the procedure for recalculating support set points, and has access to original reference drawings, tire section misalignment may occur and cause serious maintenance roblems after the trueC up work is finished.
It is not enough to merely move individual rollers a distance equal to the amount removed from combined radii of tire and roller. The actual amount will vary according to original design, but will be somewhere in the range of 2.= to < units inward for each unit of 2 removed from combined radii of tire and roller. )erform trueCup work with a belt grinder arrangement to produce a smooth surface truly parallel to either the roller shaft axis or the kiln axis in the case of the tires. tandard machining procedures, if handled carefully, will produce surfaces that are parallel to the axis of the roller or tire, but unless the final cut is made with a broadCnose tool, the finish ?
will be slightly coarse and extra sensitive to roller skewing ad'ustments until the surface becomes smooth after a period of operation. 3.
O%SER&E SHELL AND TIRE TE'#ERATURES
&onitor shell and tire temperatures, at all pier positions, during various phases of operation. &aintain a log book and charts that will clearly indicate changing and potentially dangerous conditions.
The shell plate is heated from within by heat that bleeds through the refractory. The massive tires are cooled by ambient air and act as heat sinks on the relatively thin kiln shell. Temperature differences are taken into consideration for each tire position on the kiln. Allowance is made for the difference in expansion by machining the shell pads smaller than the bore of the tire. The smaller diameter shell will advance within the tire during every revolution of the kiln. ince the ambientCair cooled tire acts as a heat sink, heat from the shell is absorbed very slowly. If the shell is heated too rapidly in relation to the tire, it will 72: overexpand beyond the builtCin allowance for expansion, 7<: become choked within the partially expanded tire and 73: if the shell continues to overexpand after becoming choked inside the tire, it will bulge outward at both sides of the tire as shown in F"1re 4. The shell will be permanently deformed into what is referred to as a coke bottle shape, i.e. squee#ed in at the middle. After the tire is fully expanded and an insulating coating builds up on the refractory lining, the shell will cool down to its normal operating temperature. Along with contraction of the shell, excessive clearance will occur between shell pads and the bore of the tire as shown in 6igure =. As a result, the shell assumes an oval shape because there is now room for the sides of the shell to bulge out toward the tire to accommodate the top of the shell as it sags from its own unsupported weight. See F"1re 5.
The shell will now move into three distinct radius conditions during rotationL it is 72: approximately normal below the
hori#ontal centerline of the tire, 7<: somewhat flattened at the upper area of the tire, 73: pinched above the hori#ontal centerline at the points where shell contour changes from round to flattened. -ompressive forces are exerted on refrac tory linings at the pinch point on the upward moving side of the kiln and at the downward moving side of the kiln, as the shell moves into and through this configuration during rota tion. Tire and shell contours will also be slightly distorted at contact points on support rollers. Along with crushing the refractory lining, there is the inevitable extreme overheating of the shell plate under the tire. In addition to an overC expansion problem, the shell plate can become superCheated to the point where it becomes plastic enough to be hotCformed as its own weight forces it to mold itself inward on the tire during rotation. In cases where sections of refractory lining drop off in the area under the tire, additional hot spots can cause inward blisters 7flat spots: to form on the shell.
The above conditions can originate when the shell tempera ture is raised too rapidly when the kiln is started for the first time after original installation, or after being down for The conditions can also installation of new refractory. develop gradually as the refractory lining becomes increasingly thin. !y controlling shell temperature to avoid choking inside the tires and by establishing a routine schedule for recording shell and tire temperatures, increased temperature differentials provide advance warning of diminishing clearance between spacer pads and the tire and indicate the need to schedule a shutdown for refractory replacement work to avoid shell damage.
CAUTION When differential motion between tire and shell pads cannot be detected, there are two possible reasons for lockCup( Interference from a slug formation between a spacer pad the bore of the tire, where metals from one or both surfaces being gouged deeper and deeper to increase the si#e of the as it is drawn across the pad. The slug will eventually fall =
and are slug free
when it clears the trailing edge of the pad, but while it is enlarging itself, it will appear as if the tire is locked in position on the shell. N
The kiln shell has already expanded enough for spacer pads to be choked inside the tire. A typical reaction to this lockCup condition is to lubricate the bore of the tire to make contact surfaces slippery enough for differential rotation movement. Whether or not the bore of the tire should be lubricated at all 7except for application of dry graphite: is debatable. When differential movement cannot be detected, the underlying reason must be eliminatedL lubrication will not help. Gnowledge of shell and tire temperature differentials during normal operation of the kiln is valuable should it become necessary to prepare for shimming work, spacer pad replace ment or replacement of the entire tire section shell and pads. 4.
CHEC"
FOR
E(CESSI&E CLEARANCE %ET)EEN SHELL S#ACER #ADS AND %ORES OF THE TIRES Dxcess clearance is the space remaining between pads and the tire when the kiln is operating and in normally hot and expanded conditions. As mentioned previously, allowance was made for the greater expansion of the kiln shell within relatively cooler tires. With the outside diameter of the shell pads being somewhat less than the inside diameter of the tire, the shell rolls inside the tire as the kiln rotates. The distance the shell advances inside the tire is directly related to the difference in diameters 7A /:. /ifferential movement of kiln and tire indicated by the dimension between matchC marksKwill be referred to as creepBO. Total clearance and 7A/: can be determined in two ways when the shell is hot, without actually working on top of the shell for testing with feeler leaf gauges. 6Cree+7 "* &cca*"&#a(() 8a#d err&#e&1*()9 re'erred & a* 6*("++ae7. S"#ce $e r&a"# -"(# *$e(( "* $e dr":"# '&rce '&r r&a"&# &' $e (&&*e "re*, b) :"r1e &' /e"$ a#d 'r"c"&#, 6*("++ae7
*n
&cc1r /$e# *+acer +ad* a#d b&re* &' "re* are !ade *("++er) b)
"#r&d1c"&# &' $"$ (1br"c") rea*e. T$"* c&#d""&# "* 1#de*"rab(e *"#ce /"#d;b&r#e c&#a!"#a#* ca# c("# & $e rea*e a#d ca*e e%ce**":e /ear a "re a#d +ad
*r'ace*. Mea*1re!e# &' 6cree+7 "* #& acce+ab(e '&r ca(c1(a"&# &' 8AD9
/$e# $ere "* n+
d"''ere#"a( !&:e!e# e#$a#ced b) *+ec"a( (1br"ca"&# &' "re b&re* a#d +ad *r'ace*.
Dxcess clearance must be considered when planning for potential corrective work by shimming or by installation of overCsi#e shell spacer pads. a.
se the following procedure to obtain the difference in diameters 7*I/: between the shell and the tires( 72: )lace match marks at a pad surface or tire retainer block, and on the side face of the tireL then measure the distance between these marks after one or more revolutions of the kiln as shown in F"1re <. 7<: If the distance was measured after more than 2 revolution, divide the dimension by the number of revolutions to determine the average for 2. 73: /ifference in diameters ( /: can be determined by dividing travel per revolution by pi 73.282@:. Dxample(
PB 7measured: 4.<39B differ 4.=?4B Q 3.282@ ence in diameters 7*/: =
b.
=
se the following procedure to obtain clearance and creep of the kiln shell and tire( 72: ecord clearance and creep in chart form by placing a magnetCbacked tracing surface on the side face of a Then position a springCloaded pencil holder tire. 7mounted on a magnetic base: in an appropriate location for tracing shell movement patterns in rela tion to the tire through several revolutions of the kiln. The kiln must be stopped briey for mounting this test equipment. 7<: )lace the material on the shell and tire at the approximate bottom dead center position where the shell is normally fully seated inside the tire. )osition the pencil at the side of the tracing surface that trails the direction of rotationL the advancing shell carries the marker across the surface toward the upward moving side of the kiln. The initial point of contact of the marker becomes the bottom of the wave pattern that forms on the tracing surface. 9
73: As the tracer moves upward during rotation, the shell advances and moves away from the bore of the tireL the pencil draws a curving line on the chart surface. $n the downward moving side, after passing top dead center, the pattern reverses as the shell moves back into the bore of the tire. See F"re* 1= a#d bA. 78: /istance between start and stop points of individual waves is the distance the shell advanced inside the tire during one revolution of the shell. /istance between high and low peaks is the total clearance between shell pads and the tire at that test point. Rf the shell is distorted under the tire, the procedure should be repeated at points 945 apart around the shell. -learance, as recorded in this test, is not the actual difference in diameters 7A/:, since the shell ovality is included in the tracing. To determine actual 7A/:, divide the recorded clearance by S of pi 72.?=2:.
Dxample(
&easured, or recorded, clearance of PB 2.?=2 4.88=B A/. 4.8==B A/ 3.282@: 2.89;B travel per revolution.
=
=
4.=?4B Q H pi 7or
=
6or comparison( If travel, as measured in 8.a., would 4.88=B A/. have been 2SB, then 2.?B Q 3.282@ =
If this work is performed when the kiln is hot, A/, is the total excess clearance to be considered for alignment work or maintenance planning. If done when the kiln is cold, calculate the initial clearance required to satisfy shell and tire expansion factors. >.
RE#LACIN, #ADS AT
TIRE SECTIONS
If excess clearance, as determined in tep 8, is the result of wear on pad surfaces, and not from shell distortion, after the kiln is shut down install new pads but do not use pads at the original design thickness unless offCcenter rotation of the shell can be tolerated at the tire position being considered. 24
If eccentric rotation cannot be tolerated, as at a thrust tire which will affect girth gear runout and mesh condition at the drive pinion7s:, pads must not be as thick as the original nominal thickness. The original pad outside diameter was the result of machining oversi#e pads on a heavy shell section that was rolled, and braced internally, to certain tolerances for outC ofCroundness. )ads are not necessarily at uniform thickness around the circumference of the shell. This original condition may be further complicated by slight ovality of the shell.
se shim plates with thinner pads, if necessary, as shown in F"1re 11. )lace the shim plates between the pads and the shell to maintain the axis of the shell at the axis of the tire. hims may not be required in areas where original pads were less than the original theoretical design thickness. $.
USIN, SHI'S TO TE'#ORARILY FILL-IN E( ESSI&ELY LAR,E S#ACES %ET)EEN SHELL #ADS AND TIRES CAUTION This application is a temporary, expensive, emergency, band aidB procedure to be performed at shutdown. It is to be used as a stopgap measure to provide time in which to prepare and receive a replacement shell section.
If the shell plate is distorted into a +B or B shape, shim work will not be worth the effort, time or expense. If spacer pad surfaces are in reasonably good condition, and if shim thickness will be at least /16”, it may be feasible to plan for the work. After determining the actual A/ for the hot and expanded shell and tire, subtract 4.2
22
.
RE#LACIN, SHELL SECTIONS IN AREAS )HERE DISTORTION CAUSES #RO%LE'S
$bserve and replace the shell at shutdown when the following conditions are encountered(
a.
A shell which is wrinkled, blistered, or otherwise distorted from previous overheating caused by loss of refractory. This damage is often caused by kiln misalignment that had set up cyclic stress forces on the shell which, in turn, placed compressive forces on the lining. This condition is often associated with dog leg runout of the shell, with crossover being noted at one or more tire positions during rotation. See F"1re 12.
Actual shell runout profiles would be verified as previously described in tep 2, a through d.
b.
Dxtreme distortion of the shell under a tire with hot running excess clearance more than SB, and with the shell and spacer pads being too crooked for shims or pad replacement work.
c.
Along with b. above, spacer pad welds will probably break frequently and there will be scraps of temporary holdC down clamps and retainers. $riginal retainers for the tire will have broken off and been reset in any number of ways.
d.
6requent need to replace refractory at any tire section because of shell ovality related to excessive clearance between shell spacer pads and the bore of the tire 7as described previously in tep 8:.
e.
When narrow, bandCtype wrinkles 7bulges: appear on the kiln shellKusually near a tire sectionKand is further complicated by weld failure in the 'oint between the intermediate thickness plate section and the thinner plate forming the main span between the piers. This condition is usually the result of kiln shell mis alignment, either as a result of misplacement of support rollers or excessive clearance conditions at one or more tires. -yclic bending stress in the shell places compressive
2<
forces on the refractory, which eventually fails in the bending #one. The shell is then overheated in this exposed area and misalignment is selfCcorrected to some extent because the hot shell becomes deformed in the compression #one during rotation. Thermal stress at the stepCdown 'oint between intermediate and nominal thickness plates, with the heavier plate resisting the expansion of the lighter plate, sometimes leads to failure of the weld. The combination of shell distortion 7wrinkles: plus weld fail ure is usually less than oneChalf of the circumference of the shell. See F"1re 13. When narrow wrinkles develop in the shell downhill from, but close to the hot end tire, it is usually because the refractory lining became too thin and the shell became more flexible in the heavy stress #one. The weight of the unsupported end of the kiln causes cyclic bending at the stress point, where compression destroys two or more circles of refractory bricks. The shell then becomes superC heated where lining failed and the shell becomes wrinkled in reaction to the sagging end of the section. These wrinkles usually form around the full circumference of the shell and are sometimes accompanied by failure of the weld in the stepCdown 'oint at the intermediate and nominal thickness plates. Although it is possible to realign the end of the kiln shell and reweld the 'oint, the repair should be considered as being temporary. The heat affected shell should be replaced with a suitable length of new shell plate. 5.
CHEC" ,IRTH ,EAR ALI,N'ENT AND DRI&E #INION/S0 'ESHIN, CONDITION
This is not an allCout precision test conducted with precision test equipment. It is merely necessary to open inspection panels to permit visual observation of changing mesh condi tions during rotation of the kiln and to check on the position of the gear rims in relation to the ends of the pinion teeth. $ff center position of the gear centerline in relation to the axial centerline of the pinion usually is related to a problem at the thrust arrangement for the kiln. If the gear has moved far 23
enough off center at the pinion, it is highly probable that the rim of the gear has rubbed the panel of the gear guard and that the scuffing action has eliminated the pitch line reference points on the ends of the gear teeth. See F"re 1?. It is important to know the position of the girth gear in relation to the pinion7s:, especially if the kiln has been in the same operating position for a prlonged period of time. Wearing of tooth flanks will form step patterns so that if the kiln should change position and bring the high points of the gear teeth into mesh, the concentrated loading could lead to sudden failure of the gearing. "ear damage would prevent rotation of the kiln which, if hot, would become badly warped and with sufficient runout would destroy air seals and other components. See F"1re 15. In some cases a disk grinder can be used to smooth off ridges on tooth flanks. everse the gear and0or pinion if wear patterns are not acceptable for changing the operating position of the kiln. .
CHEC" CONDITION OF TIRE SIDE AND RETAINERS
FACES
6ull floatingB kilns are moved into proper operating position by ad'ustment of support rollers. These kilns have thrust tires which are intended to be in a position where there is no contact against either of the thrust rollers except when kiln operation and load conditions vary. oller skewing, when correct, causes the tire to move against retainers at the uphill side of the tire so that the retainers bear the thrust load for moving the kiln. In addition to thrust, retainers and side faces of tires are sub'ected to scuffing caused by the kiln shell advancing within the tire during rotation. When rollers are overCad'usted at any tire, there will be extremely high pressure on the retainersL eventually the retainers will wear down, but they will also cut into the side face of the tire. When this happens, the shell will lock into the tire at the underside of the kiln so that countermoves of the rollers will not move the tire away from the retainers, but the shell will continue to advance within the tire during rotation. See F"1re 1@.
28
When the support rollers are overCad'usted to the point where the kiln moves uphill to have the thrust tire hard against the upper thrust roller, that tire will touch the lower retainer arrangementL the downhill side face of the tire can become undercut when this condition becomes extreme. ince the kiln would continue to move uphill inside the thrust tire as the retainers and tire side face continue to wear away, the position of the girth gear in the pinion would change and lead to problems referred to previously in ;. efer to 6igure 2?.
NOTE -onditions described above will be reversed when the thrust tire moves hard against the lower thrust roller for continuous operation.
At plain tires, it may be possible to install oversi#e retainer blocks to eliminate the undercut tire condition, but at the thrust tire there may not be sufficient clearance for an oversi#e retainer to pass the top of the thrust roller. Alternate action would be required when there is a clearance problem at the thrust rollers. 12. GHEGK
POSITIONS OF
TIRES
ON
SUPPORT
AT ALL ROLLERS PIERS
ecord shell temperatures at various #ones on a routine basis to establish profiles through various phases of operation. ince refractory thickness and material coating will directly in fluence the amount of heat reaching the kiln shell, a tempera ture profile is valuable for determining the best operation position of the tires on each tire shell section. See F"1re 14.
When recording positions of tires on support rollers, check the following details for possible corrective work at individual tires( a.
b.
Is the tire against the uphill or downhill retainer arrange mentL and how much clearance exists at the other retainerU Where is the thrust tire in relation to upper or lower thrust rollersU
c.
Is there an excessive amount of clearance between the thrust tire and either of the retainer arrangementsU If so, did the kiln move uphill or downhill inside the tireU ee F"1re 1@.
This information is of special importance when shell section replacement is being consideredL complete details are required for accurate allowances for expansion of the shell from the thrust arrangement to all other .tire sections. 11. CHEC"
SHELL DISTORTION AT REIN FORCIN, RIN,S ON OLDER "ILNS FOR
$lder kilns may still have high, narrow reinforcing rings welded around the shell. If so, check both sides at each ring for distortion of the shell 7especially in the hot #one of the kiln:. These rings restrict the diametrical expansion of the shell and distortion is often accompanied by cracking of the shell along sides of the rings and sometimes directly under them. See F"1re 15. 1.
&ISUALLY CHEC" THR UST ROLLER ASSE'%LIES
If the thrust tire is touching and turning a thrust roller, rotation should be free and smooth with no overheating of the bushing or thrust disk. If rotation seems to be 'erkyB, or if scuff and scrape marks are seen on tapered contact faces of the tire and roller, it is a strong indication that the bushing and shaft are damaged and at least partially sei#ed. If the thrust roller appears to be tilted in relation to the equipment slope line, i.e. high toward the tire, extremely heavy kiln thrusting pressure probably has forced the roller shaft to wear into the longitudinal axis of the bushing thereby causing the tilted operating position. If a thrust roller rises up out of its housing during rotation, it is usually because the assembly is on the wrong side of the frame centerlineL it should be offCcenter at least 1/16F toward the downward moving side of the kiln. If the thrust assembly is actually on the correct side of the frame centerline, but still rises during rotation, it is probably because either uneven wear or field machining of support rollers shifted the kiln off
center toward its own downturning side, thus having the same effect as moving the roller in the wrong direction. ee 6igure 1< 1<;A. 13.
CHEC" HYDRAULIC THR UST ASSE'%LIES
Gilns with hydraulically operated thrust assemblies may have thrust arrangements on 2, <, or 3 piers depending upon the si#e of the kiln and the number of support piers. !y utili#ing a series of limit switches to control the start and stop sequence of the pump, the kiln should be moving uphill and downhill a distance of about 2CF
CHEC"
FOR
OIL
LEA"S AT SU##ORT ROLLER SHAFT SEALS
With the equipment set at a certain slope angle, oil leaks are found at the high side bearing assembly. $il escaping from the bearing travels down the shaft to the roller side wall and then to the rolling contact surface, where its lubricity cancels out the effectiveness of skewing ad'ustments and so increases the downhill gravitational thrust of the kiln.
The only time an oil leak is found at a low side bearing assembly is when the seal is bad and the oil reservoir is over filled. nder certain conditions, when a shaft seal is bad at a downhill bearing, dirt and0or rain water can work its way into the bearing housing. See F"re* 22 a#d 23.
2=
15.
CHEC" TE'#ERATURES OF THE ROLLER SHAFT AND THE %EARIN, HOUSIN, END #LATES
Typical support roller bearing lubricants start to break down at about 2;456. ometimes the shaft and bearing overheat because of overCskewing of the roller and occasionally because of sludge buildCup on the oil collector pockets for the bearing bushing.
If corrective ad'ustment of the roller does not relieve the overheating, or if application of a solvent 7for breaking up sludge: does not cool the bearings, set up an oil cooler with a circulating pump arrangement to continue operation until it is possible to shutdown the kiln. )henolic resin composition thrust washers, now being used in support roller assemblies, will disintegrate when they are overheated. This condition would result in damage at the end of the shaft and possibly result in damage to the oil dis tribution tray and oil elevator arrangement caused by inter ference at the opposite end of the shaft.
NOTE In addition to items listed in the preceding preshutdown considerations, the following rocedures are for total survey and analysis of most mechanical aspects of rotary kilns. Eot all of the items would be checked out as standard and routine procedures. Actual checkCout will be determined by the field engineer to suit maintenance problems reported by representa tives of the client.
