RECOMMENDED PROCEDURES

FOR MECHANICAL ANALYSIS OF

ROTARY KILNS

2012

Mustafa Kamal Pasha

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

of which could cause serious personal injury or death. These include but are not limited to the following:

High Temperature Metal Surfaces

Avoid personal contactThe 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 resultUse lockout procedures

Hazardous Chemicals

Personal contact can cause severe burns, deathPoisonous

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 liftingIf 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

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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.

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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

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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.

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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.

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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.

Sometimescertain zones of the shell—including riding ring sections—

areso 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.

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.

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 shellcircumference 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

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

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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

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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

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

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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 TIRESExcess 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 nydifferential movement enhanced by special lubrication of tire bores and pad surfaces.

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.

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(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 (or3.1416) = 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.

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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.

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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

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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

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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.

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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 SUPPORTROLLERS 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?

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 towardthe downward moving side of the kiln. If the thrust assemblyis 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. 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

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. Notall 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.