Note: Descriptions are shown in the official language in which they were submitted.
20~8~
HOLLOW SHELL DEFLECTION READING SYSTEM
TECHNICAL ~IELD
This invention is directed to a system for measuring
the local deflections taking place in the shell of a hollow
rotating body, and in particular, that of a rotary kiln; and
it lncludes a distance measuring and recordal apparatus for
such system.
BACKGROUND TO l'HE INVENTION
The operation and service life of the refractory lining
of a hot rotary kiln is heavily dependent upon the operating
characteristics of the steel shell of the kiln, in which the
lining is installed.
Hot rotary kilns, such as cement kilns and the like,
may be several hundred feet in length, having a comparatively
thin steel shell ranging from eight to twenty feet in
diameter, supported on a series of steel tires, carried upon
supporting rollers. The rollers in turn are mounted upon a
series of tall piers of sequentially diminishing height, which
provides the desired downslope between the inlet and the
outlet of the kiln.
The typical daily throughput of a cement kiln is
generally such that heavy financial penalties are incurred
when the kiln is inoperative; futhermore, the rebricking of
the refractory lining is prohibitively expensive. Thus, a
strong incentive exists to optimize the working conditions of
the kiln, to achieve maximum service life of the refractory
lining, and to minimize down time.
Owing to the conditions of operating at high
temperatures while revolving slowly about its polar axis, with
a dynamically varying load passing along its length, the kiln
shell has a series of pads interposed between the shell and
the tire, with a clearance provided between the pads and the
tire (when cold) to allow for differential thermal expansion
between shell and tire under normal operating conditions.
The refractory lining is generally installed within
2~2~0~
the shell of the kiln in a dry laid condition i.e. without
mortar, depending upon the arch principal to keep it locked in
a continuous arc.
Excessive flexing of the kiln shell in its rotation can
permit or induce flexing of the arch to the extent that the
arch fails, and collapses.
Dynamic changes of curvature of a kiln shell during its
operating rotation are affected by a number of factors:
1. The size of the supporting steel tires in regard to
their diameter, thickness and width.
2. The size of the supporting rollers in regard to
their diameter and width.
3. The axial spacing of the tires along the kiln.
4. The dead (self weight) loading and live loading
(moving charge), the latter being variable.
5. The operational radial clearance gap between the
tire and the shell.
6. The steady state temperatures of the shell and
respective supporting components.
7. The strength of the shell and its associated
components.
8. The alignment of the shell upon its supporting
rolls. .
The significance and effect of each of the above
factors can vary from kiln to kiln, and even from time to time
for the same kiln.
Measurement of kiln shell deflections, taken during
normal operations of the kiln, was taught by Kareby, in U.S.
Patent No. 2,676,867. This showed the use of a chordal beam,
physically secured to the exterior of the kiln shell at a
selected point, by way of a chain extending about the shell.
The beam carried a feeler or feeling member, providing contact
with the outer surface of the shell, and being responsive to
radial deflections of the shell surface, relative to the
secured chordal beam.
Relative movement of the feeler to the chordal beam was
`::
~2~
translated into movement of a recording member such as pen or
pencil against a drum mounted chart. Rotation of the chart
drum was provided by a hanging weight, so as to maintain the
chart drum rotationally static during its orbiting of the kiln
polar axis. The displacement of the recording member in
response to radial deflections of the kiln shell as it rotated
were translated by a mechanical linkage into repositioning of
the recording member in a polar direction, relative to the
chart drum, to thus give a trace upon the chart, proportional
to the extent of radial deflections of the shell and of the
feeler.
This early work was not without merit, but was subject
to mechanical inaccuracies, while the apparatus was difficult
to install and reposition on the kiln shell.
Subsequent work, along the same lines, carried out by
the HOLDERBANK company was based upon a mathematical
development published by G. R~SENBLAD "Radiale Deformation
von Drehofenmanteln" ZRG7 (1954) publication No. 4 wherein the
mathematical relationship between shell deformation, and shell .-
ovality is expressed as follows:
w = 2(a-b)
where a = major radius of shell
b = minor radius of shell.
and where d - extent of deformation = a-b
(i.e. the greatest difference between elipse radii)
From Rosenblad Wa = 2(a-b) = q' 3 d2/l . ~ m.m.
In the case oE kilns having diameter d less than 2
meters
3 / ~ [L + /l 2 (L/d) 2 + 7 / 2 4 (L/d)4 + l5/ (L/d) 6 ] 1 ~ 2
where d = kiln shell external diameter (meters)
L = Basic chordal length of measuring beam (one
meter)
~ = greatest deflection measurement (mm)
To enabl.e comparisons of ovality for kilns of
different diameters, the relative ovality Wr is used, wherein
the actual ovality is expressed as a percentage of the kiln
2~23~
internal diameter:
where Wr = Wa . 100 %
dn
dn being the kiln internal dlameter in meters.
It has been established in the past, in practice, that
to avoid an undue rate of kiln lining wear as a consequence of
kiln flexure, the ovality of the shell must stay below certain
limits. The limit on acceptable ovality increases with kiln
diameter.
Thus for kilns up to 3.5 meters diameter the upper
limit of relative ovality is approximately 0.3 %. Greater
values of ovality will lead to undue wear or the collapse of
the refractory arch.
For kilns of 6 meters diameter the upper safe limit of
ovality is approximately 0.5 %. In the past the Holderbank
organization relied upon an instrument known as the
"Shelltest" instrument. This comprises a one meter chordal
beam secured to the outer surface of the kiln shell, generally
by magnets, having a centre mounted feeler pin to contact the
shell surface below the centre of the beam, and a precision
gear transmission to multiply the displacement of the feeler
pin by a multiplying factor such as 15.
In the Shelltest instrument, a development of the
Kareby arrangement, a pencil marker is displaced laterally as
an output of the multiplier mechanism, and a graphic chart
carried upon a disk is provided to receive the pencil
markings, the chart being rotated by the rotation of the kiln,
under the influence of a stabilizing ballast weight.
The output of the prior art Shelltest instrument
comprises a so-called polar diagram, matched to the rotation
of the kiln shell and having a roughly circular trace, the
radial variations of which from a three inch base circle
represent the multiplied shell displacement.
In attempting to use diagrams such as those of Kareby
or the Shelltest system for purposes of calculating relative
ovalit~, it will be understood that inaccuracies arising from
. . . ~ ~ . ., -
--`` 2 0 ~
factors such as the width of the pencil trace can seriously
adversely affect the accuracy of the result, with consequent
inability to reliably determine whether or not kiln ovality
lies within or outside prescribed safe limits as referred to
above, to ensure the satisfactory service life of the
refractory lining.
The deficiencies of the prior instruments are
compounded by the fact that it is usual practlce to make three
characteristic deflection traces on each chart, with the
distinct possibility that the traces may partially overlap or
o~er-run each other, to further complicate the extraction of
accurate information therefrom. It should be born in mind
that the ovality measurements being made consist of radial
deviations of the polar trace from a theoretical line
representing the undeformed outer periphery of the shell. In
the case of Shelltest this is on a paper disc some 6 inches in
diameter.
The drawbacks of the later Shelltest prior art system,
in regard to accuracy are accentuated by the use of a
precision motion multiplying device, with its inherent
backlash, and vulnerability to general abuse and the adverse
effect of a high temperature environment and variation
therein, of the kiln.
Furthermore, the deflection measuring and multiplier
device, and the di.sc recording means therefor are expensive
and heavy, and have been known co dislodge the magnetic mounts
by which the 1-meter bridge adheres to the outer surface of
the shell.
SUMMARY OF THE INVENTION
The present invention provides a simple, reliable
system for directly and accurately measuring and recording the
radial deflections taking place in a rotatlng shell, such as a
kiln shell, enabling the provision of highly accurate graphs,
plotting radial shell deflection for the respective rotational
positions of the shell. --
2 ~
The apparatus o~ the system can be readily installed
and repositioned upon a kiln shell rotating at relatively high
speeds, under fully operational conditions for the kiln.
The present invention thus provides a method for
determining variations in the radial deflection of a
cylindrical shell during its rotation upon supporting rollers,
comprising the steps of securing a deflection sensor in spaced
relation from a surf~ce portion of the shell to directly
monitor variations in the distance of the surface of the shell
from the sensor, and recording the distance variation during
rotation of the shell.
The present invention further provides a method of
directly and accurately measuring radial deflections of a
rotating shell, to obtain an accurate graphic representation
of shell ovality.
The apparatus of the present system preferably includes
a deflection sensor comprising an electronic instrument having
a digital read-out, preferably used with a short beam
constituting an external chord of the shell, and recordal
means for recording the read-out values of the deflection
sensor during rotation of the shell.
In the preferred embodiment the short beam is secured
by magnetic mounting means in spac.ed relation upon the
periphery of the shell, the beam preferably also supporting a
data logger for recording the digital readout of the
electronic DTI.
With the preferred data logger/instrument combination
the variations in distance measured by the DTI are recorded at
selected time intervals, and stored in an on-golng basis for
later transfer to a computing device for subsequent
compilation.
The total readings, comprising as many as 42 sets of
data, with each set containing up to 100 readings, may be held
in the logger instrument. The data is provided in a form
suitable for being directly imported into a computer equipped
with a popular, standard spread sheet program such as LOTUS
2~2~
1-2-3 (T.M.), for ease of data manlpulation and for graphing.
The present method may be used with the shell in a
heated, operational condition.
The tabulated readings of DTI digital values can be
readily plotted as a graph or graphs, on a time basis. This
may be readily converted to a rotational basis, in terms of
the position of the shell. -
In the case of the high temperature kilns, a high
thermal gradient acting on the structure of the chordal bridge
or beam, may cause it to deform or bow, with a transient
deformation, as the beam heats up from an air ambient
condition towards the temperature of the shell.
Such transient thermal deformation distorts the value
of the DTI readings that are then obtained, as if the shell
had "pushed out".
By taking successive readings at 360 intervals, the
effect of the therma]. gradient can be readily detected,
graphically or statistically, and the DTI values
correspondingly corrected. AS the transient thermal effects
lie along a sensibly straight line curve, determination of the
curve, from readings taken 360 apart, enables offsetting
allowances to be accurately calculated and applied. This
thermal gradient correction is generally only of significance
for surface temperatures at about 700F or higher.
BRIEF DESCRIPTION OF THE DRAWINGS
Certain embodiments of the prior art, and of the pres-
ent invention are described by way of illustration, without
limitation of the invention to the illustrations thereof,
reference being made to the accompanying drawings, wherein:
Figure 1 is a side elevation showing a typical kiln
arrangement, to which the prior art and the present system is
applied;
Figure 2 is a side elevation of a prior art graphic
multiplier and polar diagram recorder;
Figure 3 is a prior art polar diagram as obtained from
20~Q~
the Figure 2 device;
Figure 4 is an ovality limit diagram showing the limits .
of acceptable ovality for a range of kiln diameters;
Figure 5 is an end view of a shell portion having an
apparatus for the deflection measuring and recordal system of
the present invention mounted upon a magnetically secured
chordal beam;
Figure 6 is a diagrammatic end view of a typical shell-
support roller arrangement;
Figure 7 is a plot of a normal ovality curve, on a base
of shell rotational positions;
Figures 8-12 are plots of particular eccentricity
curves for specific shell conditions;
Figure 13 is a plot of actual measurements from a kiln
shell, using the present invention; and,
Figure 14 is a plot similar to Figure 13~ for a kiln
shell, showing the transient effects of high thermal gradient
upon the beam.
BEST MODE OF THE CARRYING OUT THE INVENTION
Referring to Figure 1, a hot kiln 20, carried upon
piers 22, 24, 26 and 28 has tires 29 mounted upon pairs of
rollers 31 carried on the piers, for rotation of the shell 27
about its polar axis.
In Figure 2 the prior art "SHELLTEST" device 33 is
mounted upon a chordal bearn in a fashion similar to the pres-
ent invention. A body por~ion 34 secured to the supporting
beam (not shown) has a feeler pin 35 connecting with a mechan-
ical multiplier arrangementi to displace a recordal pencil 37
against a paper card 39 rnounted upon shaft 41, ballasted
upright durlng rotation of the shell by weight 43.
The feeler pin 35 bears against a portion 45 of the
kiln shell.
In operation, as the kiln portion 45 rotates, it is
deformed, causing the feeler pin 35 tc move, as with
deflection ~h. This translates into movement of the pencil 37
2~285~
g ,.
across card 39 by a distance M~h where M is a mechanical
multiplicant factor with a value such as 15. The shaft 41
being free to rotate, and being ballasted by weight 43 to
remain vertical, in the position shown, therefore rotates,
relative to the body portion 34, due to the circular
displacement of the body portion 34 with the rotating kiln.
This in turn draws the card 39 arcuately past the pencil 37,
so as to draw a trace.
Thus, referring to Figure 3, the prior art circular
card 39 has a polar deformation plot 41 drawi.ng thereon. The
actual deformation, as an ovality, is represented by the
difference in radii a and b, being one fifteenth of the
dimension represented on the card, when the multiplicand
factor M of the mechanism is 15.
It will be evident that an undue degree of accuracy is
required in order to extract deflection readings from the
polar diagrams that can provide qualitatively reliable values
of relative ovality, of sufficient accuracy to place reliance
therein in regard to the ovality limit diagram of Figure 4.
Referring to Figure 4, this empirical relation showing
the acceptable range of relative ovality, and its variance
with shell diameter has been established, and is generally
accepted as valid in the industry. . The median value of
acceptable relative ovality w ranges from about 0.3% to about
0.5%. Thus the shaded area of the figure represents a working
range of acceptable ovality. Ovality values lying above the
shaded area indicate undue clearances of the tire and undue
flexing of the shell, with an increased probability of failure
of the refractory lining.
Values of relative ovality lying below the shaded area
generally indicate inadequate clearances between tire and
shell, again with the probability of the occurrence of undue
wear of the refractory liner.
Referring to Figure 5, the apparatus 40 of the present
system is shown mounted on a portion of shell 17 of a kiln.
The apparatus 40 comprises a one meter bridge 42 having a DTI
2~2~
- 10 -
(Dial, Distance or Depth) Test Indicator 43 and data logger 44
mounted thereon.
Magnetic clamps 45 secure adjustable bridge supports
46 to the shell 27.
Adjustable clamps 48 facllitate setting of the bridge
42 in accordance with the diameter of shell 27, and may also
permit coarse adjustment for the DTI 43. The DTI 43 is a
precision electronic instrument, readily available in a number
of commercial models from many manufacturers, having a digital
readout that is connected to data logger 44.
The data logger 44 incorporates a timing clock, to
provide a time base for each recorded value of the read out
provided by DTI 43. Thus, each recorded value of deflection
has a corresponding recordal time, which is directly related
to the shell rotational position. The data storage facility
of the data logger enables the storing of total readings in
excess of 4000, for a full logging of a large kiln. These
accumulated values of defelection can be downloaded to a
computer, for handling by a standard spreadsheet such as LOTUS
1-2-3 (T.M.).
Figure 6 shows the typical arrangement of a shell 27, a
tire 29, and a pair of support rollers 31, with indication of
the salient points of the shell, as referred to in the
following description of Figure 7 through 12.
Thus, with the Top of Shell (Top Dead Centre or TDC) as
the location of the system apparatus ~0, upon rotation of the
system apparatus ~0 passes sequentially clockwise to the
3-o'clock position, over the right roller 31 to the Bottom
Dead Centre (BDC) position. From there past the left roller
31 to the 9-o'clock position, and from there, back to the TDC
starting location.
The arrangement, mass and interconnection of the
respective system components and their mode of mounting
enables the apparatus to be mounted and respositioned, even at
relatively high peripheral speeds, as high as 130 feet per
minute, on a 16-foot diameter kiln, for example, and under
2~2~
full operating conditions.
Figure 7 shows a so-called Normal Curve, wherein the
shell 27 is well centred on its rolls, and the relative
ovality is reasonably within limits.
Referring to the Figure 8 characteristic curve the
large spread of eccentricity values indicates either an unduly
heavily loaded pier (i.e. probable high live load) or an
undersized tire, or that the support rollers are holding the
kiln unduly high.
Figure 9 indicated the probability of an underloaded
pier (with adjacent piers probably overloaded).
Figure 10, showing a large spread of eccentricity
values is probably indicative of an excessive clearance gap
between tire 29 and shell 27.
Referring to Figure 11, the curves A and B are taken at
the same position along the shell, at the same "cross
section", but 180 apart from each other, on the shell
periphery, and indicate the shell to be bowed at this support.
In the case of Figure 12, the abrupt change in -
curvature is indicative of a crack in the shell plate.
The foregoing interpretations of the characteristic
curves yield rapidly available commentaries concerning the
kiln support and rotational system, and the rapid and totally
accurate eccentricity values may be used to accurately and
directly determine shell ovalities, in relation to the
acceptable ovality values of Figure 4.
A typical set of shell eccentricity values, as plotted
in Figure 13, and obtained from a test carried out on an
actual, operating kiln are given below.
A series of seventy two readings, taken at equal time
intervals representing one revolution of the shell are given,
for a total of six locations adjacent one of the shell tires.
The locations are located adjacent the tire for a
selected pier and the shell support bearings, being positioned
on the "uphill" and the "downhill" sides of the tire, and at
three such locations mutually located at 120 in~ervals, A, B,
C about the shell periphery.
- 2~28~
- 12 -
Kiln Diameter: 3,607 meters OD; 3.505 meters ID
Pier#4
Uphill Downhill
A B C A B C
%Oval0.500.26 0.32 0.50 0.32 0.32
Range1.010.53 0.65 1.02 0.65 0.65
MaxØ460.27 0.30 0.46 0.28 0.30
Min.-0.55-0.26 -0.35 -0.56 -0.36 -0.35
Maximum change in Dia.: 13.4 mm
at BDC: 10.7 mm
10.100.24 0.07 0.10 0.19 -0.03
20.210.26 0.09 0.190.23 -0.01
30.290.26 0.11 0.250.26 0.02
40.350.24 0.14 0.310.27 0.05
50.390.23 0.16 0.360.27 0.07
60.420.20 0.18 0.400.25 0.10
70.440.28 0.20 0.430.23 0.13
80.450.16 0.22 0.450.21 0.15
90.460.11 0.24 0.460.19 0.18
100.460.07 0.25 0.460.14 0.20
110.450.03 0.27 0.460.08 0.23
120.44-0.01 0.28 0.260.04 0.25
130.43-0.05 0.29 0.45-0.01 0.27
140.42-0.08 0.30 0.44-0.05 0.30
150.400.12 0.30 0.43-0.11 0.29
160.39-0.16 0.26 0.41-0.15 0.24
17 0.37 -0.19 0.200.39 -0.19 0.18
18 0.35 -0.21 0.160.36 -0.23 0.13
19 0.33 -0.24 0.100.34 -0.26 0.08
0.31 -0.25 0.050.32 -0.29 0.03
21 0.28 -0.26 0.010.29 -0.32 -0.02
22 0.26 -0.26 -0.040.25 -0.34 -0.02
23 0.23 -0.26 -0.030.21 -0.35 0.00
24 0.20 -0.25 -0.00 0.18 0.36 0.02
0.18 -0.24 0.04 0.15 -0.35 0.07
~2~
- 13 -
260.15-0.22 0.08 0.13 -0.34 0.11
270.13-0.19 0.120.11 -0.32 0.14
280.11-0.16 0.150.09 -0.29 0.16
290.09-0.12 0.160.09 -0.26 0.17
300.09-0.09 0.160.10 -0.23 0.18
310.10-0.04 0.160.12 -0.18 0.19
320.120.00 0.160.15 -0.14 0.20
330.170.04 0.160.20 -0.08 0.20
340.180.07 0.160.20 -0.03 0.20
350.180.11 0.160.20 0.02 0.20
360.170.15 0. lS0.190.06 0.19
370.150.18 0.140.17 0.11 0.18
380.130.21 0.130.16 0.15 0.16
390.110.23 0.120.14 0.19 0.15
400.090.25 0.100.11 0.22 0.13
410.060.26 0.090.08 0.25 0.11
420.030.27 0.070.05 0.28 0.09
43-0.010.27 0.060.00 0.29 0.07
44-0.040.25 0.040.04 0.29 0.05
45-0.070.23 0.02-0.07 0.29 0.02
46-0.100.19 -0.01-0.10 0.27 -0.01
47-0.130.14 -0.04-0.14 0.24 -0.04
48-0.170.07 -0.08-0.18 0.20 -0.08
49-0.200.02 -0.12-0.21 0.13 -0.13
50-0.24-0.02 -0.17-0.26 0.08 -0.18
51-0.28-0.05 -0.22--0.31 0.03 -0.24
52-0.33-0.08 -0.26-0.36 0.00 -0.29
53-0.38-0.11 -0.30-0.42 -0.03 -0.32
54-0.43-0.13 -0.33-0.47 -0.06 -0.34
55-0.48-0.14 -0.35-0.51 -0.09 -0.35
56-0.51-0.14 -0.35-0.54 -0.10 -0.34
57-0.54-0.14 -0.33-0.55 -0.11 -0.31
58-0.55-0.14 -0.31-0.56-0. ll -0.29
59-0.54-0.13 -0.29-0.54 -0.10 -0.26
60-0.52-0.11 -0.27-0.52 -0.08 -0.24
61-0.50-0.09 -0.25-0.50 -0.07 -0.23
- 14 -
62 -0.48-0.08 -0.25 -0.48-0.04 -0.23 -0.25*
63 --0.47-0.08 -0.25 -0.46-0.03 -0.22
64 -0.46-0.08 -0.26 -0.46-0.03 -0.23
65 -0.47-0.08 -0.26 -0.45-0.03 -0.24 -~
66 -0.48-0.07 -0.27 -0.46-0.04 -0.24
67 -0.50-0.06 -0.26 -0.47-0.05 -0.24
68 -0.50-0.03 -0.23 -0.48-0.05 -0.22
69 -0.490.00 -0.20 -0.47-0.02 -0.19
70 -0.440.04 -0.16 -0.440.01 -0.15
71 -0.390.08 -0.12 -0.330.05 -0.12
72 -0.270.11 -0.17 -0.180.09 -0.08
Average BDC
Ratio
0.37 0.30
0.75 0.80
0.35 *
-0.40
Delta Radius:
0.211 inches -
Ovality is defined, as referred to above, as being
twice the difference of major and minor radii of the
elliptically deformed section of the kiln.
Using the Rosenblad mathematical relationship to
determine ovality w
w = 2(a-b) = ~/3 X (OD/L) 2 X deflection (1j
The generic rela,tionship presented usually as a
percentage of kiln inside diameter, is expressed
% ovality = %w
= w x ~.00
ID
Where ID = Kiln inside diameter (= 3.353 meters)
a = Major ovality radius
b = Minor ovality radius
2 ~
L = Base Length (Bridge span) = 1 meter
This then yields plots on the Figure 4 ovality
acceptability chart, for the respective tire locations.
Referring to Figure 14, this relates to a deflection or
ovality plot for a single location, over the course of two
full revolutions of the kiln.
With a kiln temperature at or above 700F, the bridge
structure is sub~ect to a transient thermal gradient, causing
an exaggeration of the shell deflection readings, as can be
seen by the gradient of the line A-B. For stable thermal
conditions, with no distortion of the fixture bridge 42
(Figure S) the maximum deflections, both positive and
negative, should be constant, such that line A-B would
parallel the X-axis.
With the transient temperature effect thus plotted for
one station, correction factors may be applied to the
deflection or 'C' values, both for the Figure 14 graphs, and
for other plots taken at the other measurement stations,
upstream and downstream of the tire, and about the kiln
periphery, where the bridge is located at 120 intervals.
In addition to enabling corrections to be made to the
effects of thermal transients upon the apparatus of the
present invention, the precision of measurement also enables a
skilled practitioner to interpret from the readings much
significant information concerning various operating
conditions that are affecting the kiln.
Thus, at point D of Figure 14 the discontinuity
indicates displacement of the beam upon its mountings, the
beam having moved closer to the shell surface.
The point E denotes passage of the beam and DTI
instrument over the left support roller.
Point F represents "BDC", the Bottom Dead Centre
position.
Point G denotes passage of the beam and DTI instrument
over the right support roller.
Point H denotes the 3-o'clock location and point I the
2~2~
- 16 -
9-o'clock location.
The lines J, K and L may be regarded as typical
misalignment signatures, indicating that the kiln is
non-symetrically deformed at the subject pier support rollers,
due to lateral offset of the support rollers to one side,
relative to the kiln "ideal" axis. This is referred to as a
dog leg.
Thus it can be seen that the present system constitutes
a tool of very large potential, in the hands of a skilled
practitioner. furthermore, the results are substantially
repeatable, and it is contemplated that the interpretation
thereof probably also lends itself to computerization.
INDUSTRIAL APPLICABILITY
This apparatus and its method of use have worldwide
industrial applicability wherever kilns and like rotating
bodies, subject to deformation and wear, are in use.
