tires and ovality

Rotary Kiln Maintenance Rotary Kiln Maintenance SeminarSeminar

Tires and Ovality

Tires and OvalityTires and Ovality

� Tires and Tire Mounting� Tangential Suspension� Tire Clearances� Ovality� Tire Creep and Top Clearance� Correcting Ovality� Tire Pad and Stop Block Repairs� Tire Crack Repair

Tires and Tire MountingTires and Tire Mounting

Kiln Tire Support SystemKiln Tire Support System

Tires are mounted over support pads with machined O.D.’s. Precise clearances are maintained to allow for different rates of expansion between kiln tire and kiln shell.

Machined SurfaceMachined

Surface

Pads are not welded to the shell, but are trapped in place by guide bars. Stop blocks are welded on one side only, alternating from one side to the other.

Tire AttachmentTire Attachment

A loose stop ring is placed between the stop block and the tire. Wear takes place on the replaceable ring, not on the stop blocks.

Stop Ring

Stop Block

Guide Bars

Machined Support Pad

This shows a slightly different version of the floating pad, stop ring design.

Bolted Support PadsBolted Support Pads

Some FLS kilns have bolted support pads. Bolting avoids heavy welds which lead to shell cracks. The above arrangement uses a wear ring between stop blocks and tire.

Bolted Support PadsBolted Support Pads

This arrangement for smaller, light duty kilns uses stop blocks directly against the tire, i.e., without the use of wear rings.

On kilns without wear rings, when the blocks eventually wear down, they have to be cut off and new ones re-welded.

Tangential SuspensionTangential Suspension

The tire is fixed and does not creep inside the shell. Shell expansion is accommodated with a system of spring-loaded wedges.

Tangential suspension reduces ovality. Forces on the shell are tangent rather than radial.

Brackets are bolted onto the tire. “Dog bones” keep the tire in position. Wedges keep the brackets tight against the dog bones. Springs keep the wedges tight as dimensions change with heat expansion.

Tire Bracket

“Dog Bone”

Spring

Tire Bracket“Dog Bone”

Spring Rod

Wedge Retainer

A completed tire section ready for installation.

Wedges are held in position with retainer brackets bolted to the top of the “dog bones”.

The spring rod pushes the wedge in to maintain a tight fit between dog bones and brackets as the kiln shell expands and contracts.

As the wedges wear, the spring length increases. Periodically, check the distance and adjust the spring tension as required.

“Dog bones” are attached to the shell with heavy welds. Periodically inspect the welds for cracks.

Tire bolts are hydraulically tightened to specification.

Hydraulic Bolt Tensioning ToolHydraulic Bolt Tensioning Tool

Tire ClearanceTire Clearance

Tires are mounted over support pads with machined O.D.’s. Precise clearances are maintained to allow for different rates of expansion between kiln tire and kiln shell.

Machined Surface

It is necessary to have clearance between the tire support pads and tire I.D. to accommodate heat expansion of the shell. Cold clearance is typically 6-12 mm for a new kiln, depending on the location of the tire.

Normal Cold Clearance

The shell will heat up faster and expand more than the tire, and clearance will diminish. Normal hot running clearance should be from 0 to 3 mm (�”).

Normal Hot Running Clearance, 0-3 mm

Rate of ExpansionRate of Expansion

Example. A kiln shell with 5 meter (5000 mm) diameter at 20º C is heated to 320º C. The shell expands

5 meters x (320 - 20) = 15 mm100

Rule of Thumb

Expansion of Steel (approx):

1mm / Meter/ 100ºC

OvalityOvality

A kiln shell is not stiff enough to support its own weight. When placed on the ground it collapses to an oval shape.

OvalityOvality

When placed inside a rigid tire the shell’s deformation is reduced, but it will still collapse if there is any clearance present. The amount it collapses depends on the amount of clearance and on the stiffness of the shell.

Shell and Tire DeformationShell and Tire Deformation

Shell deformation also occurs because the tire is not absolutelyrigid. Due to elasticity of both shell and tire, the actual top clearance is 1.5 to 2 times the difference in diameter.

Perfectly Round

Shell and Tire

Deformed Shell and Tire

Difference in diameters

Actual Top Clearance

Ovality and Brick ProblemsOvality and Brick Problems

Kiln shell ovality causes continuous flexing of the brick lining as the kiln turns.

Excessive ovality will damage the refractory lining, typically with scattered spalling and single brick fall-out among otherwise undamaged areas.

Ovality Refractory DamageOvality Refractory Damage

Shell Cracks Due to OvalityShell Cracks Due to Ovality

Excessive ovality may cause longitudinal cracks in the shell beneath the tires.

Shell Cracks Due to OvalityShell Cracks Due to Ovality

This shell crack was caused by excessive ovality. The heavy welding used to attach the support pad was a contributing factor.

Definition of OvalityDefinition of Ovality

Absolute OvalityΑΑΑΑ = DH - DV

Relative Ovalityαααα = (DH – DV )/D

Different definitions of ovality are in use. This definition takes into account both shell and tire deformation. Ovality is usually expressed in percent.

Relative Ovality

αααα = 0

(shell is round)

Relative Ovality

αααα > 0

(shell is deformed)

Relative OvalityRelative Ovality

Ovality LimitsOvality Limits

Ovality as a function of kiln diameter. Exceeding these limits will cause refractory and shell problems.

Heating the kiln up too fast can result in bottle-necking (pinching) of the shell inside the tire. Excessive heating, i.e., after loss of refractory under the tire, will also cause bottlenecking.

Causes of Excessive OvalityCauses of Excessive Ovality

Because of its massive size, the tire will change temperature more slowly than the shell. If the kiln is heated up too fast the shell will become restricted inside the tire anddeformation will result.

After the shell becomes deformed and temperatures return to normal, there will be excessive running clearance and ovality, resulting in refractory damage.

Excessive Running Clearance

Causes of Excessive OvalityCauses of Excessive Ovality

Measuring OvalityMeasuring Ovality

The shell-test device measures the kiln shell’s actual radius of curvature during rotation. From this data the shell stresses can be precisely calculated.

Measuring OvalityMeasuring Ovality

Shell-test device

Ovality (%) = 4D²δδδδ x 100% 3dn

Ovality CalculationOvality Calculation

D = outside diameter of the shell at the test location (meters)

dn = nominal inside diameter of the shell (mm)

δ = δ/15, deflection measured from the shell test diagram (mm)

Sample Calculation

Tire #1, Station #1, Downhill

ovality (%) = 4D²δ x 100%3dn

ovality (%) = 4(3.727m)²(12mm/15) x 100%3(3657.60mm)

ovality (%) = 0.406%

OvalityOvality

Tire Creep and Top ClearanceTire Creep and Top Clearance

Because of the slight difference in diameter between the tire ID and shell (support pad) OD, the shell rolls inside the tire as the kiln turns. This gives the appearance that the shell is “creeping’ inside the tire.

CreepCreep

Place a chalk-mark on the tire and another right next to it on the shell. After one revolution, measure the distance between the two marks. This distance is the creep.

Measuring CreepMeasuring Creep

Creep is the difference in circumference. Therefore,

Measuring CreepMeasuring Creep

Creep ��

= Difference in Diameter

Top clearance depends on the difference in diameter and on the shell stiffness. The stiffness factor is normally between 1.5 and 2.0, depending on how thick the shell plate is.

Top ClearanceTop Clearance

Top Clearance = Difference in Diameter x Stiffness Factor

Measuring Creep and Top ClearanceMeasuring Creep and Top Clearance

Top clearance and creep can be measured with this simple device.

This is a data sheet of 5 kiln revolutions. The distance between waves is the creep. The height of the wave is the top clearance. Always record tire and shell temperatures and identifying data (kiln no., tire no., date).

Correcting OvalityCorrecting Ovality

Excessive clearance can be removed with the installation of shims beneath the support pads.

Shim thickness is calculated to give a hot running clearance of about 3 mm (�”).

ShimShim

If the kiln shell becomes deformed it is necessary to replace the tire section. Ovality can be reduced by installing temporary pads with filler plates, but bricks will never fit properly on the inside of the kiln shell.

Tire Pad and Stop Block RepairsTire Pad and Stop Block Repairs

Regularly inspect the supporting pads and stop blocks for weld cracks and repair at the next kiln stop. Waiting too long will only cause problems to compound.

Replace stop blocks when wear becomes excessive. Do not use shims as shown, as they probably won’t last.

Excessive stop block wear on the thrust tire is especially problematic since it can affect the gear’s position on the pinion.

Heavy welds directly on supporting pads frequently crack due to temperature fluctuations and fatigue stress. The floating pad design solves these problems.

Floating Tire Pad DesignFloating Tire Pad Design

Wear Ring InstallationWear Ring Installation

Wear Rings

Anti-Rotation

Wear Rings

Anti-Rotation

Wear Ring InstallationWear Ring Installation

Fractures at Shell PadsFractures at Shell Pads

Tire Crack RepairTire Crack Repair

Ultrasonic Inspection of TiresUltrasonic Inspection of Tires

Tire Repair WeldingTire Repair Welding

Tire Repair Welding

Tire Repair WeldingTire Repair Welding

tires and ovality

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