Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE I~VENTI O~
The present invention relates generally to a method
for manufacturing a stone roll, particularly a press roll, for
a paper machine and, more particularly, to such a method where-
in temperature-induced de1ections which occur in connection
with the operation of the stone roll are reduced or eliminated.
~ aturally occurring stone material and, in particu-
lar, grey granite, has been used for many years as the raw
material from which paper machine rolls are manufactured.
Since flawless blocks of ~rey granite which are sufficiently
large for the manufacture of paper machine rolls are not
easily obtained, attempts have been made to fina substitute
materials for granite. However, such attempts have failed to
produce a material which can replace and supplant the use of
stone material due to certain e~cellent properties found in
the latter. Thus, granite has in fact generally been regarded
as the best material from which to manufacture press rolls
having a hard surface for the reason, among others, that a
granite roll can be reconditioned and renewed without the
sur~ace properties thereof being changed.
As an example of the sizes of stone rolls to date,
the largest granite roll to applicants' knowledge which has
been supplied to date has a diameter of 16QQmm and a shell
surface lenyth of 9250mm and has been manufactured by Valmet
Oy of Finland, assignee of the instant application.
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The various constituents o~ the stone material of a
stone roll may be distributecl within the manufactured roll in
a non-uniform manner. This results in the coefficient of
thermal expansion of the material differing at different
points in the material. For this reason, the behavior of
the roll at various temperatures cannot always be predicted
with accuracy by calculations.
Indeed, in actual practice, it has been observed
that a stone roll, even when ground to absolute straightness
and finished to an ultimate gloss, will dev~lop deflections
which are extremely detrimental when the stone roll operates
as a press roll in a paper machine such, for example r as a
smooth-surface central roll in a "Sym-Press" (Trademark of
Valmet Oy), in conj~ction with which at least two press nips
are defined. Such deflections in the stone roll result in an
uneven distribution of the nip pressure in the press nips
which in turn manifest itself in a non-uIliform moisture pro-
file in the web being treated in the press.
SU~ lAFiY OF THE INVENTI (!N
It is an object o~ the present invention to provide
a new and improved method for manufacturiny a stone roll,
particularly a press roll, of a paper machine which eliminates
the drawbacks described above.
~ riefly, in accordance with thc present invention,
this object is achieved through the provision of a simple and
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efficient method for preventin~ deflections from occurrin~
during operation o~ the stone roll. To this end, the method
of the invention is characterized in that the cylindrical
shell of the stone roll is ground to its final shape ~t sub-
stantially the same temperature at which the stone roll will
operate in the paper machine.
DESCRIPTION OF THE DRA~INGS
A more complete appreciation of the present inven-
tion and many of the attendant advantages thereof will be
readily understood by reference to the following detailed
description when considered in connection with the accompa-
nying drawings in which:
FIG. 1 is an elevation view in section of a stone
roll of the type with which the present invention is concerned;
and
FIG. 2 is a graphical depiction illustrating the
deflection of a granite roll with respect to the surface
temperature thereof.
DESCRIPTIO~ OF THE PREFERRED E~QDIMENTS
Referrin~ now to the drawin~s, the structure of a
stone roll of the type which is suited for manufacture in
accordance with the method of the present invention i.s illus-
trated in Fi~. 1. In this connection, reference is made to
~ilmish Patent No. 57989 issued to the assi~nee of the present
application in which the structure and conventional method of
manufacture of the stone roll shown in Fig. 1 is disclosed.
The stone roll illustrated in Fig~ 1 comprises an
integral shell 10 formed of natural stone material such, for
example, as grey ~ranite. The shell 10 ~hus comprises a
one-piece granite cylinder in which a relatively large diameter
central bore 14 is formed. The diameter o bore 14 may for
instance be about 5~ of the diameter of the granite shell 10.
A tubular shaft 13 is situated within the bore 14 of
granite shell 10. Journal pins 12a and 12b are affixed within
respective ends o~ the tubular shaft 13 which carry bearing
elements lla and llb at their respective ends. As seen in
Fig. 1, end regions of the tubular shaft 13 extend beyond the
ends of the granite shell 10 and annular end flanges 15a and
15b are moun.ed on the shaft end regions between which the
granite shell 10 is clamped.
In order to center the granite shell 10 with respect
to the center line C~C of the roll shaft, annular grooves are
machined at the ends of the bore 1~ in which respective c~n-
terin~ rings 16 are itted whose inner parts engage the
outter surface of the tubular shaft 13.
In an investigation of the problems with which the
present invention is concerned, deflections of the stone roll
at room temperature and below room temperature were observed
with the roll removed from the paper machine. The temperature
was found to have a distinct influence on the deflection of
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the roll. Moreover, measurements of the deflections were con-
tinued with the stone roll installed in its operatin~ posi-
tion within the paper machine. More particularly, the initial
cleflection measurements were taken with the surface temper-
ature of the roll bein~ about ~20C which was substantially
e~ual to the ambient temperature. After starting the opera-
tion of the paper machine, the surface temperature of the roll
and the correspondin~ deflection thereof were measured every
12 hours durin~ the first two days of operation. The time
intervals between the measurements was thereafter increased
to 24 hours and measurements taken for one week. For the last
control measurement, the surface temperature of the roll had
stabilized at about ~53C and the roll deflection was about
0.25mm as measured at the center of the roll.
The results of the measurements described above are
graphically depicted in Fi~. ~ in which the values recited
above are noted. A so-called linear regression line has been
calculated for the deflection/temperature relationship observed
on the basis of the m~asured values and is illustrated iII Fi~.
by the dash-dot line and the equation of tYhich for the
particular roll e~amined is:
y - Q.0065~ ~ - 0.0848 + Q.0356
tYhere y is the ~eflection at the center of the roll in n~m and
x is the surface temp~rature of the roll in C.
~ eferrin~ to Fi~. 2, the curve portion desi~nated 1
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represents the phase of the tests durin~ which the stone roll
is cooling outdoors, the curve portion 2 represents ~he phase
wherein the stone roll is warming up in a room temperature
environment, and the curve portion 3 designates the test
phase wherein the stone roll is installed in the paper machine.
As noted above, the dash-dot line represents the regression
line havin~ the equation set ~orth above.
T t is noted that the coefficient of correlation r is
0.967168 and the percentage of explanation is 93.5. Under-
standing that there will be some difference between the sur-
face temperature of the roll and its average tem~erature
resulting from the thermal capacity of the roll, the deflec-
tion of the roll can be considered sukstantially entirely
dependent on the temperature and will be substantially linear
in the temperature range investigated.
As is known in the art, the outer sur~ace of the
stone roll is finished in a grinding machine in which the roll,
carried by its shaft, is rotated. The outer surface of the
roll is yround to a cylindrical shape using a suitable tool,
such as a grindin~ stone or a diamond with the surface rough-
ness being on ~he order o~ about 1.6~ m. The roll is there-
a~ter balanced in a known manner.
~ ccordin~ to the method of the invention, the stone
roll, i~e., the ~ranite roll in the case of the illustrated
embodiment, is heated in the roll grinding machine such, for
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example, by a water jet, substantially to the temperature at
which the roll will operate in the paper machine. For example,
i~ the roll is to be utilized in the press section of a paper
machine, a water jet may be directed onto the roll in the
grinding machine to elevate the te~perature of the roll to
that temperature at which the roll will operate in the press
section. The grinding of the roll to its final shape is
carried out in accordance with the invention at this temper-
ature, i.e., at a temperature corresponding to the operating
temperature of the roll. In this manner, a compensation for
the deviation in shape of the roll which would result from a
non-uniform thermal expansion of the stone material from which
the roll is constructed is achieved ~o that when the ground
roll is installed in the press section of the paper machine
no deflections will occur therein due to changes in temperature.
It is known that the normal operating temperature of
a stone roll in the press section of a paper machine is in the
range of about 35 to 40 C. In cases where the dewaterin~
action of the roll is boosted but through the provision of a
so-called steam box, such as that disclosed in U.S. Patent
4,163,688 assigned to the assignee of the instant application,
the operatin~ temperature of the stone roll will be in the
range of about 50 to 55C.
It has been ~ound in practice that the operating
temperature of a stone roll in its central region is slightly
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higher than the temperature in the region of the ends of the
stone roll. ln order to take this practical aspect into
account, the method of the present in~ention may be carried
out in a manner such that the grinding of the stone roll is
per~ormed with the central region thereof heated to a temp-
erature corresponding to the operating temperature of the
central region of the roll and with the end regions of the
roll heated to temperatures corresponding tc the operating
temperatures of these end regions when installed in the paper
machine. Such a temperature profile simulating the tempera-
ture profile of the roll during operation can be obtained
during grinding such, for example, as by utilizing water jet
apparatus from which a plurality of temperature-controlled
water jets are applied to appropriate regions o~ the stone
roll.
The temperature of the stone ~roll may be elevated
to the operating temperature during grinding in ways other
than that described above~ For e~ample, the stone roll can
be situated during grinding in a basin containing water whose
temperature is elevated in a controlled manner, the roll ro-
tating within the basin during grinding.
It is also understood t~lat the method of the inven-
tion may be utilized in connection with the manufacture of new
stone rolls as ~Yell as in connection with reconditionin~
existing rolls.
obviously, numerous modifications and variations of
the present invention are possible in the light of the above
teachings. It is therefore to be wlderstood that within the
scope of the claims appended hereto, the invention m~y be
practiced otherwise than as specifically disclosed herein.
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