Shell Test

Shelltest

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Shelltest

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Kiln downtime causes § The following is a typical breakdown of the downtime

causes for a kiln: Frequency of shut-downs

Causes of shut-downs

80%

Brick lining failures

10%

Mechanical failures

6%

Electrical failures

4%

Others

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Radial deformation and its effect

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Creep / Relative movement (loose tires) To avoid permanent constriction of shell due to thermal expansion the shell and tire have different diameter

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Since the kiln is almost round, the nominal radial clearance is equal to the difference between its shell circumference and the inner tire circumference divided by π. This relationship can be used for a simple measurement. Sth = ∆U / π

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Plastic (permanent) deformation Shell constriction (restricted expansion) Buckling (local overheating) Crankshaft (excessive circunferential temp. difference) 6

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Shelltest- what for? § The shelltest device measures the kiln shell radial

elastic deformation.

§ One of the main results of this test is the ‘Ovality’ value,

which is compared against the recommended value.

§ In addition, thanks to the graphical representation of the

deformed kiln cross section, information can be obtained on: 4 4 4 4

Tire clearance Tire stiffness Roller adjustment (in some cases) Kiln deformation (crankshaft)

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Shelltest device

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Measurement principle §The kiln cross

section is rather elliptical §If the two axis (a and

b) are known, then ovality can be calculated §Or, with the

magnitude of the radial deformation δs 9

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Measurement principle

§ Through the Shelltest diagram, δs can be obtained, as

the maximum difference between sector height, magnified by a factor of 15.

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How to measure § Ovality has to be measured as close as possible to the

tire, on both sides of it (feed and discharge side). 4

Watch out with the heat shields, in case they obstruct the passage of the device!

§ As in the lead wire test, on each side of the tire, three

measurements have to be made (120° displacement). 4

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Each set of points (A, B and C) must be collinear and marked in a permanent way. A single diagram disk can be used for the three measurements (adjusting screw position has to be modified, to avoid overwriting curves). After each measurement, identify the resulting curve (A, B or C) . If the curve is not easily readable, remark it with a pencil). 11

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Form to be filled in for each diagram disk Lines are already drawn each mm on the disk, to easily determine δs Distance from the tire center to the actual measuring point

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How to measure- Tips and tricks § The disk face must always point at the same side of the

kiln (whether feed or discharge end). 4

This reference has to be kept in mind when looking at the curves

§ Be sure that the disk cannot rotate on its own (fasten it

with the small hole, which indicates as well the apex point of the shell) § After attaching the device to the shell, do not stand right

underneath! (it may drop on top of your head) § Let the device make a whole revolution, before pushing

the pencil in; check that the pencil touches the disk 13

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How to measure- Tips and tricks § After each measurement, cool down the magnetic base

with water (otherwise, it will lose its strenght) § Wear personal protective equipment, including gloves. § Do not forget to measure relative movement (creep) on

each tire.

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Calculating ovality It can be done graphically, or using the formula

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Calculating ovality

ω: relative ovality d: external diameter where the gauge is placed (mm) dn: nominal diameter of the section (mm) 16

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Calculating ovality § The graphic method is much easier § As the relative ovality limit values are given as a range,

it is not crucial to obtain a result with two decimal places.

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Evaluation of results-Ovality value § The following graph shows the adequate relative ovality

ranges, according to the kiln diameter § If the value falls within this range or below, no corrective

action is required (tire shimming)

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Evaluation of results-Graphically Case #1: § Low ovality §

low clearance (no flattening of the shell at the top)

§

no deformation at supporting areas

Result: Ideal situation – no actions rather than periodic monitoring needed 19

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Evaluation of results-Graphically Case #2: § High ovality §

excessive clearance (flattening of the shell at the top)

§ deformation at

supporting areas (soft tire)

Result: Roller adjustment required, as well as clearance decrease (tire shimming) 20

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