2. RECOMMENDED PROCEDURES
FOR MECHANICAL ANALYSIS
OF ROTARY KILNS
TEXT AND ORIGINAL SKETCHES
SAFETY
This text is intended to serve as a practical guide for the
operation and maintenance of rotary kilns and kiln drive systems. It is
not intended to be an instruction manual, and the procedures
discussed in this text are to be performed only by trained personnel
who are fully aware of the dangers involved with the equipment.
Any procedures presented in this text are to be performed with all
guards and safety barriers in place and fully operable. With the
exception of Section B, Gear Alignment, removal of guards is not
required to successfully utilize these procedures.
All equipment must be operated and maintained according to
applicable government safety and health laws and regulations such as
OSHA, MSHA, generally recognized industry standards, plant safety
rules and regulations. All personnel must follow safe working
practices and use good judgement.
The installation, operation and maintenance of rotary kilns and
associated equipment presents many potential unsafe conditions each
3. of which could cause serious personal injury or death. These include
but are not limited to the following:
High Temperature Metal Surfaces
Avoid personal contact
The flash point of liquids, gas may be exceeded
Hot Gases and Material
Personal contact can cause severe burns
Lethal Voltages
Personal injury or death can result
Use lockout procedures
Hazardous Chemicals
Personal contact can cause severe burns, death
Poisonous
Moving and Rotating Machinery
Personal contact can cause hands, arms or legs to be caught
in pinch points
Use guards and safety brakes
Heavy Components
Use proper procedures when lifting
If components are dropped personal injury can result
Dust
Dust may be hot and/or caustic
Skin and eyes may be exposed
Use protective clothing
Somç major safety concerns involving the kiln and associated
equipment are listed below.
1. Because of the high temperatures, both internal and external,
the entire kiln must be treated as a dangerous area. Skin
temperatures generally range from a low of about 300°F
(149°C) up to about 800°F (427°C). Personnel working on
Ii
4. 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.
Caution should be taken to avoid heat prostration and
dehydration which may be associated with long working
periods near a hot kiln.
2. Personnel must be aware of the flash points of any lubricants,
liquid, or solvents coming in contact with hot surfaces.
3. Care must be taken in opening any inspection port. Hot dust
from any kind of puffing can be blown in the operator’s face.
Protection for the face and eyes must be worn at these times.
4. A lockout procedure should be used when performing any
work on the equipment.
5. Do not operate equipment unless all guards are in place.
6. Because rollers are adjusted while the mechanism is in
motion, personnel must exercise caution to avoid injury.
Although the parts are rotating at relatively low speeds,
danger does exist. Personnel must exercise particular caution
in keeping themselves and their clothing well clear of the
moving parts including tires, rollers and gears.
7. Improper or inadequate maintenance could result in personal
injury, death, or property damage.
111
5. 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.
Field engineers and consultants who specialize 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 jigs 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. Some plant
engineers and maintenance supervisors have followed up with “custom
made” test equipment and fixtures designed for rapid setup for
preventative maintenance test procedures to ensure maximum oper
ating time for their rotary kiln(s).
There are no “theories” 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 and/or 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.”
R. P. Chapman
iv
6. ACKNOWLEDGEMENT
Preparing this material was similar to being in a long-distance
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 organized, with special thanks to the
people who became involved enough to keep it moving.
Many thanks to everyone for your encouragement and advice.
V
7. TABLE OF CONTENTS
PAGE
A. PRESHUTDOWN PROCEDURES 1
B. PRELIMINARY TEST PREPARATION PROCE
DURES 21
C. INITIAL SURVEY AND LAYOUT WORK 23
D. SCOPE OF LAYOUT AND TEST WORK 25
E. EXTERNAL ALIGNMENT TEST WORK 31
F. KILN TIRE SECTION REALIGNMENT BASED
UPON SURVEY WORK AND CALCULATIONS 37
G. INTERNAL (THROUGH CENTER) ALIGN
MENT TEST PROCEDURE 41
H. KILN ALIGNMENT QUICK CHECK 49
I.
J.
RESET AND ADJUST SUPPORT ROLLERS
ADJUSTMENT OF SUPPORT ROLLER ASSEM
BLIES FOR THRUST REQUIREMENTS
53
61
K. KILN ROLLER ASSEMBLY PROBLEMS 65
L. SUMMARY 81
Appropriate illustrations follow each chapter.
vi
8. A.
PRESHUTDOWN ROCEDURES
Refer 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 zones, the “reporter” should clarify pier numbering
sequence (starting count at discharge end or at feed end) and
should avoid local landmarks and/or compass directions when
describing work areas for the kiln.
1. ANAL YZE AND RECORD SHELL
CONDITION
Before a hot, on-stream 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.
Sometimes
certain zones of the shell—including riding ring sections—
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. Use these measurements to plot graphic views of
the cross- sectional shape of the shell at the various test
locations; also plot the plan views of the shell at test points
1800 apart on the circumference. Use the following
procedure to measure and plot shell runout:
a. Prepare 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.
Usually catwalks are too far from the kiln for service
as testwork platforms.
9. Many kilns do not have walkways for close-up 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. Scaffolds can be prepared for this work,
but assembly and moving time must be considered. A
self-propelled, hydraulically operated, telescoping, two-
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 “basket” for use as a two-
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.
Since some kilns now rotate at speeds as high as 4 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 1 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. Two-way F.M. radios are useful for such contact.
c. Predetermine the extent of the analysis to be performed, then
mark the shell for testing at positions along spans between tire
sections and at both ends as follows:
(1) Measure the circumference of the shell at the refer ence line,
then mark off 12 equal spaces around the shell. If the shell
contains permanent fixtures (man holes, thermocouples, etc.)
that can be used as refer ence points for follow-up work, select
one of these items for marking the 00/3600 (or 12:00
position) test line, as shown in Figure 2. This line is to be the
index line for marking the entire length of the kiln shell. After
marking position No. 12, mark remaining space marks (1 through
11) as they come into position with rotation of the kiln.
10. Prepare 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. Position the end of the slide surface as close
to the shell as possible after determining the approximate
shell runout at that test point.
(3) Record the number and location of the line being
tested and also indicate the twelve test points in
vertical columns, 1 through 6 and 7 through 12 for
quick comparison of readings @ 1800 apart (1/7,
2/8, etc.).
(4) Move 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 and/or material coating is
not equally thick, especially along longitudinal lines
180° apart in random zones of the kiln.
Uneven shell temperatures, resulting from varying
insulation values of different thickness of the lining,
will cause the kiln shell to form a temporary bow-
shaped warp condition. Shell temperature at the thin
zone of lining will be relatively higher than at the
heavily coated zones. The hot side of the kiln shell
will expand more than the relatively cool side. The
hot side will form a convex line—for 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 (s) at
positions 180° apart must be considered for final
11. analysis of the actual condition of the shell for
rotation relative to a true axis.
Use infrared heat recording equipment, or use
magnet-back dial type contact thermometers for veri
fication of shell temperature at each test station
around the shell at predetermined test lines.
Measurement of a “cold” 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
adjacent operational kilns. The side of the “cold”
kiln exposed to heat sources will be considerably
warmer than the “shady” side and this imbalance will
cause the shell to become bow-shaped enough for
measurement of significant runout. Shell temperature
should be equalized prior to start of runout tests at
idle kilns.
d. Prepare master work report sheets for the
following entries:
(1) One sheet for test figures and runout comparisons,
and for converting “as read” 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 filled-in example.
(2) One sheet (to relate to the figure entry sheet) for
plotting a cross-sectional view of the kiln shell in
relation to a true circle, as shown in Figures 4 and 4A.
(3) One sheet for plotting plan views of the shell profile
as would be seen at points 1800 apart with each
rotational move of 30° of the kiln. See Figures 5
and
5A.
(4) Prepare sufficient copies to cover all test points and
the cross-sectional plot and to allow for probable
layout errors when jreparing the sheet for plotting
the plan views.
(5) Enter dimensional data and plot approximate shell
contours on appropriate work report sheets. With
13. dimensions now being transformed into graphic pat
terns, the actual condition of the shell can be ana
lyzed to determine a plan of action for repair and/or
realignment work. Now it will be possible to decide
whether or not to (1) replace any part of the shell,
(2) cut and realign the existing shell, or (3) to plan
on realigning tire sections and support rollers for
improved operation of the kiln.
2. CHECK TIRE AND SUPPORT ROLLER
CONTACT SURFACE CONTOURS
If these faces are not flat, smooth and parallel to the axis of the
shaft, arrange for an in-place true-up on the affected surfaces.
Typically, tires and rollers in need of surface true-up will also
be peened outward past the side faces as shown in Figure
6. These protrusions must be removed, and corners must be
rounded at approximately ¼” radius.
NOTE
True-up work on tire and roller surfaces should be done in
advance of a planned kiln shutdown for realignment tests and
adjustments. Unless 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 true-
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 1.7 to 2 units
inward for each unit of 1 removed from combined radii of tire
and roller.
Perform true-up 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. Standard
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 broad-nose tool, the finish
5
14. will be slightly coarse and extra sensitive to roller skewing
adjustments until the surface becomes smooth after a period of
operation.
3. OBSERVE SHELL AND TIRE
TEMPERATURES
Monitor shell and tire temperatures, at all pier positions,
during various phases of operation. Maintain 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.
Since the ambient-air 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 (1) overexpand beyond
the built-in allowance for expansion, (2) become choked
within the partially expanded tire and (3) 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
Figure 7. The shell will be permanently deformed into what
is referred to as a coke bottle shape, i.e. squeezed 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 Figure 7. 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 Figure 8.
The shell will now move into three distinct radius conditions
during rotation; it is (1) approximately normal below the
15. horizontal centerline of the tire, (2) somewhat flattened at
the upper area of the tire, (3) pinched above the horizontal
centerline at the points where shell contour changes from
round to flattened. Compressive 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 over-
expansion problem, the shell plate can become super-heated to
the point where it becomes plastic enough to be hot-formed 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 (flat 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
installation of new refractory. The conditions can also
develop gradually as the refractory lining becomes increasingly
thin.
By 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 lock-up:
Interference from a slug formation between a spacer pad and
the bore of the tire, where metals from one or both surfaces are
being gouged deeper and deeper to increase the size of the slug
as it is drawn across the pad. The slug will eventually fall free
7
16. 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.
• The kiln shell has already expanded enough for spacer pads to
be choked inside the tire.
A typical reaction to this lock-up 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 (except for application of
dry graphite) is debatable. When differential movement
cannot be detected, the underlying reason must be eliminated;
lubrication will not help.
Knowledge 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. CHECK FOR EXCESSIVE CLEARANCE
BETWEEN SHELL SPACER PADS AND BORES
OF THE TIRES
Excess 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 (A D). Differential movement of kiln
and tire indicated by the dimension between match-
marks—will be referred to as “creep”*. Total clearance and
(AD) 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.
“Creep” is occasionally (and erroneously) referred to as “slippage”. Since the rotating
kiln shell is the driving force for rotation of the loose tires, by virtue of weight and
friction, “slippage” can occur when spacer pads and bores of tires are made slippery by
introduction of high lubricity grease. This condition is undesirable since wind-borne
contaminants can cling to the grease and cause excessive wear at tire and pad
surfaces.
Measurement of “creep” is not acceptable for calculation of (AD) when there ias ny
differential movement enhanced by special lubrication of tire bores and pad surfaces.
17. Excess clearance must be considered when planning for
potential corrective work by shimming or by installation of
over-size shell spacer pads.
a. Use the following procedure to obtain the difference in
diameters (LID) between the shell and the tires:
(1) Place match marks at a pad surface or tire retainer
block, and on the side face of the tire; then measure
the distance between these marks after one or more
revolutions of the kiln as shown in Figure 9.
(2) If the distance was measured after more than 1
revolution, divide the dimension by the number of
revolutions to determine the average for 1.
(3) Difference in diameters (I D) can be determined
by dividing travel per revolution by pi (3.1416).
Example:
¾” (measured) = 0.750” ÷ 3.1416 = 0.239” differ
ence in diameters (LD)
b. Use the following procedure to obtain clearance and creep
of the kiln shell and tire:
(1) Record clearance and creep in chart form by placing a
magnet-backed tracing surface on the side face of a
tire. Then position a spring-loaded pencil holder
(mounted 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 brieRy for mounting this
test equipment.
(2) Place the material on the shell and tire at the
approximate bottom dead center position where the
shell is normally fully seated inside the tire. Position
the pencil at the side of the tracing surface that trails
the direction of rotation; 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
18. (3) As the tracer moves upward during rotation, the shell
advances and moves away from the bore of the tire;
the pencil draws a curving line on the chart surface.
On the downward moving side, after passing top dead
center, the pattern reverses as the shell moves back
into the bore of the tire. See Figures 10 and bA.
(4) Distance between start and stop points of individual
waves is the distance the shell advanced inside the tire
during one revolution of the shell. Distance between
high and low peaks is the total clearance between
shell pads and the tire at that test point. [f the shell is
distorted under the tire, the procedure should be
repeated at points 90° apart around the shell.
Clearance, as recorded in this test, is not the actual
difference in diameters (AD), since the shell ovality
is included in the tracing. To determine actual
(AD), divide the recorded clearance by ½ of pi
(1.571).
Example:
Measured, or recorded, clearance of ¾” = 0.750” ÷
1.571 = 0.447” AD. AD 0.477” X pi (or
3.1416) = 1.498” travel per revolution.
For comparison: If travel, as measured in 4.a., would
have been 1½”, then 1.5” ÷ 3.1416 = 0.447” AD.
If this work is performed when the kiln is hot, AD, 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.
5. REPLACING PADS AT TIRE SECTIONS
If excess clearance, as determined in Step 4, 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 off-center rotation of the shell
can be tolerated at the tire position being considered.
10
19. If eccentric rotation cannot be tolerated, as at a thrust tire
which will affect girth gear runout and mesh condition at the
drive pinion(s), pads must not be as thick as the original
nominal thickness. The original pad outside diameter was the
result of machining oversize pads on a heavy shell section that
was rolled, and braced internally, to certain tolerances for out-
of-roundness. Pads 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.
Use shim plates with thinner pads, if necessary, as shown in
Figure 11. Place the shim plates between the pads and the
shell to maintain the axis of the shell at the axis of the tire.
Shims may not be required in areas where original pads were
less than the original theoretical design thickness.
6. USING SHIMS TO TEMPORARILY FILL-IN EX
ESSIVELY LARGE SPACES BETWEEN
SHELL PADS AND TIRES
CAUTION
This application is a temporary, expensive, emergency, “band
aid” 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 “V” or “U” 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 AD for the hot and expanded
shell and tire, subtract 0.125” from that figure to allow
clearance for final fit-up, then divide the remainder by 2 to
determine average shim thickness.
If excess clearance is further complicated by bulges or flat
spots on the shell plate, vary shim thickness upward or
downward in these areas, as required.
11
20. 7. REPLACING SHELL SECTIONS IN AREAS
WHERE DISTORTION CAUSES PROBLEMS
Observe 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 Figure 12.
Actual shell runout profiles would be verified as previously
described in Step 1, a through d.
b. Extreme distortion of the shell under a tire with hot
running excess clearance more than ½”, 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 hold-
down clamps and retainers. Original retainers for the tire
will have broken off and been reset in any number of ways.
d. Frequent 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 (as
described previously in Step 4).
e. When narrow, band-type wrinkles (bulges) appear on the
kiln shell—usually near a tire section—and is further
complicated by weld failure in the joint 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. Cyclic bending stress in the shell places compressive
12
21. forces on the refractory, which eventually fails in the
bending zone. The shell is then overheated in this exposed
area and misalignment is self-corrected to some extent
because the hot shell becomes deformed in the compression
zone during rotation. Thermal stress at the step-down
joint 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 (wrinkles) plus weld fail
ure is usually less than one-half of the circumference of the
shell. See Figure 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 zone. 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 super-
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 step-down joint at the intermediate and
nominal thickness plates. Although it is possible to realign
the end of the kiln shell and reweld the joint, the repair
should be considered as being temporary. The heat
affected shell should be replaced with a suitable length of
new shell plate.
8. CHECK GIRTH GEAR ALIGNMENT AND
DRIVE PINION(S) MESHING CONDITION
This is not an all-out 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. Off
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
13
22. 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 Figure 14.
It is important to know the position of the girth gear in
relation to the pinion(s), especially if the kiln has been in the
same operating position for a pràlonged 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. Gear 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 Figure 15. In some cases a disk grinder can
be used to smooth off ridges on tooth flanks.
Reverse the gear and/or pinion if wear patterns are not
acceptable for changing the operating position of the kiln.
9. CHECK CONDITION OF TIRE SIDE FACES
AND RETAINERS
“Full floating” kilns are moved into proper operating position
by adjustment 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. Roller 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 subjected to scuffing caused by the kiln shell
advancing within the tire during rotation. When rollers are
over-adjusted at any tire, there will be extremely high pressure
on the retainers; 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 Figure 16.
14
23. When the support rollers are over-adjusted 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
arrangement; the downhill side face of the tire can become
undercut when this condition becomes extreme. Since 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 8. Refer to Figure 15.
NOTE
Conditions 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 oversize retainer
blocks to eliminate the undercut tire condition, but at the
thrust tire there may not be sufficient clearance for an oversize
retainer to pass the top of the thrust roller. Alternate action
would be required when there is a clearance problem at the
thrust rollers.
10. GHEGK POSITIONS OF TIRES ON SUPPORT
ROLLERS AT ALL
PIERS
Record shell temperatures at various zones on a routine basis
to establish profiles through various phases of operation. Since
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 Figure 17.
When recording positions of tires on support rollers, check the
following details for possible corrective work at individual
tires:
a. Is the tire against the uphill or downhill retainer arrange
ment; and how much clearance exists at the other
retainer?
b. Where is the thrust tire in relation to upper or lower
thrust rollers?
24. c. Is there an excessive amount of clearance between the
thrust tire and either of the retainer arrangements? If so,
did the kiln move uphill or downhill inside the tire? See
Figure 16.
This information is of special importance when shell section
replacement is being considered; complete details are required
for accurate allowances for expansion of the shell from the
thrust arrangement to all other .tire sections.
11. CHECK FOR SHELL DISTORTION AT
REIN FORCING RINGS ON OLDER
KILNS
Older 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 (especially in the hot zone 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 Figure 18.
12. VISUALLY CHECK THR UST ROLLER ASSEMBLIES
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 “jerky”, 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 seized. 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 centerline; it should be off-center 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
25. center toward its own downturning side, thus having the same
effect as moving the roller in the wrong direction. See Figure
19 & 19-A.
13. CHECK HYDRAULIC THR UST ASSEMBLIES
Kilns with hydraulically operated thrust assemblies may have
thrust arrangements on 1, 2, or 3 piers depending upon the size
of the kiln and the number of support piers.
By utilizing 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 1-Y2” to 2” in continuous
cycles. Normally, support rollers are adjusted in neutral
positions with centerlines either parallel to the kiln centerline
or slightly skewed to relieve some of the gravitational thrust of
the kiln at the thrust roller(s). Since hydraulic thrust
arrangements generally do not have backup thrust rollers at
the uphill side of the tires, roller skewing must not, in itself,
cause the kiln to travel uphill. See Figures 20 and 21.
If drive amperage rises above normal, check support roller
assemblies for direction of shaft thrust. If one or more roller is
thrusting against the high bearing end plate and thrust
washer, the condition is forcing the kiln downhill and increas
ing the load on the thrust assembly.
14. CHECK FOR OIL LEAKS AT SUPPORT
ROLLER SHAFT SEALS
With the equipment set at a certain slope angle, oil leaks are
found at the high side bearing assembly. Oil 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 adjustments 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. Under certain conditions, when a shaft seal is bad at a
downhill bearing, dirt and/or rain water can work its way
into the bearing housing. See Figures 22 and 23.
17
26. 15. CHECK TEMPERATURES OF THE ROLLER
SHAFT AND THE BEARING HOUSING END
PLATES
Typical support roller bearing lubricants start to break down
at about 180°F. Sometimes the shaft and bearing overheat
because of over-skewing of the roller and occasionally because
of sludge build-up on the oil collector pockets for the bearing
bushing.
If corrective adjustment of the roller does not relieve the
overheating, or if application of a solvent (for 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.
Phenolic 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. Not
all of the items would be checked out as standard and routine
procedures. Actual check-out will be determined by the field
engineer to suit maintenance problems reported by representa
tives of the client.
