TECHNICAL FIELD
The present invention relates to a method of supplying
lubricating oil in cold-rolling, more particularly relates to a method of supplying
lubricating oil by emulsion lubrication.
BACKGROUND ART
In cold-rolling of steel sheet, from the viewpoints of
stabilization of the rolling operation, the shape and surface quality of the product,
prevention of seizure, the roll lifetime, etc., it is necessary to maintain the
friction coefficient between the rolled material (steel sheet) and the work rolls
at a suitable value. To obtain a suitable friction coefficient, a lubricating oil
suitable for the grade, dimensions, and rolling conditions of the rolled sheet is
selected and supplied at the inlet side of the rolling stand to the rolled material
or rolls.
At the cold-rolling of a steel sheet, in general emulsion
lubrication is used. To obtain a suitable friction coefficient, a model is used
to control the emulsion supply rate or emulsion concentration.
As methods for controlling lubrication by a model, there
are:
- (1) The method of estimating and controlling the supply rate of the seizing
limit from a constant existing for each rolling condition, concentration, rolling
rate, etc. (for example, see
Japanese Patent Publication (Kokai) No. 2002-224731
),
- (2) The method of determining the positions of the lubricating oil supply nozzles
by considering the time required for oil-water separation at the time the lubricating
oil plates out on the steel sheet etc. (phase transition time) (for example, see
Japanese Patent Publication (Kokai)
No. 2000-094013
), etc.
In the past, it was not possible to estimate or measure
the oil film thickness at the time of emulsion lubrication. It was possible to arrange
an oil film thickness meter at the outlet side of the rolling stand to measure the
oil film thickness at the outlet side of the rolling stand, but it was not possible
to learn the oil film thickness directly under the roll bite at a certain time.
As a result, with the above conventional lubricating method, it was not possible
to obtain a suitable oil film thickness right under the roll bite and not possible
to control lubrication with a high precision.
Therefore, regarding the above method (1), since it is
for the prediction of the seizing limit, use is not possible at a low speed. There
is, therefore, room for improvement of the specific oil consumption in the low speed
region. Further, regarding the above method (2), phase transition time is required
for plateout of the emulsion lubricating oil. Setting the positions of the lubricating
oil supply ends considering the phase transition time is, it is true, effective,
but the method of determining the phase transition time is not fixed, therefore
there is the problem that the positions cannot be accurately determined.
SUMMARY OF THE INVENTION
The present invention has as its object to solve the above
problem and provide a method of supplying lubricating oil in cold-rolling enabling
high precision lubrication control.
- (1) A method of supplying lubricating oil in cold-rolling of the present invention
provides a method of supplying lubricating oil in cold-rolling by emulsion lubrication,
characterized by comprising: using "a constant (supply efficiency)" obtained under
conditions of a specific rolling rate, emulsion supply, emulsion concentration,
emulsion temperature, plateout length, rolled material width or roll barrel length,
rolling load, grade of the rolled material, and type of lubricating oil and "oil
film thickness" at the time of neat lubrication realized under the specific rolling
lubrication conditions to estimate "the oil film thickness" realized by emulsion
lubrication under the specific rolling lubrication conditions, and controlling at
least one of the emulsion supply, emulsion concentration, emulsion temperature,
and plateout length so that the estimated oil film thickness matches with the target
oil film thickness.
- (2) Another method of supplying lubricating oil of the present invention provides
a method of supplying lubricating oil in cold-rolling by emulsion lubrication, characterized
by comprising: detecting a load during rolling, an outlet side sheet speed, and
a roll speed, calculating in reverse a friction coefficient from an inlet side sheet
thickness, outlet side sheet thickness, load, outlet side sheet speed, and roll
speed obtained from a reduction schedule, storing in advance the relationship between
a constant (supply efficiency) obtained under conditions of a specific rolling rate,
emulsion supply, emulsion concentration, emulsion temperature, plateout length,
rolled material width or roll barrel length, rolling load, grade of rolled material,
and type of lubricating oil and the friction coefficient for each grade of rolled
material in a tabular form, finding the friction coefficient under the specific
rolling lubrication conditions from the supply efficiency, and controlling at least
one of the emulsion supply, emulsion concentration, emulsion temperature, and plateout
length so that the friction coefficient matches a target value.
- (3) Another method of supplying lubricating oil of the present invention provides
a method of supplying lubricating oil in cold-rolling by emulsion lubrication, characterized
by comprising: detecting an outlet side sheet speed and roll speed to calculate
a forward ratio, storing in advance the relationship between a constant (supply
efficiency) obtained under conditions of a specific rolling rate, emulsion supply,
emulsion concentration, emulsion temperature, plateout length, rolled material width
or roll barrel length, rolling load, grade of rolled material, and type of lubricating
oil and the friction coefficient for each grade of rolled material in a tabular
form, finding the forward ratio under the specific rolling lubrication conditions
from the supply efficiency, and controlling at least one of the emulsion supply,
emulsion concentration, emulsion temperature, and plateout length so that the forward
ratio matches with a target value.
- (4) A method of supplying lubricating oil of the (1), further comprising setting
an oil film thickness meter at the rolling stand outlet side, detecting a difference
between a measured value of the oil film thickness meter and a measured value of
the oil film thickness, periodically correcting the supply efficiency specified
by those rolling lubrication conditions, and, while doing so, estimating the oil
film thickness of the emulsion lubrication.
- (5) A method of supplying lubricating oil of the (1) to (4), further comprising
making the supply efficiency obtained under the specific rolling lubrication conditions
a function of the rolling rate, emulsion supply, emulsion concentration, emulsion
temperature, plateout length, rolled material width or roll barrel length, rolling
load, grade of rolled material, and type of lubricating oil.
- (6) A method of supplying lubricating oil of the (1) to (5), further comprising
making the supply efficiency:
where,
- &agr;:
- supply efficiency (function of rolling rate, emulsion supply, emulsion concentration,
plateout length, emulsion temperature, rolled material width or work roll barrel
length, rolling load, grade of rolled material, and type of lubricating oil)
- hemu:
- oil film thickness of emulsion lubrication realized under specific rolling lubrication
conditions
- hneat:
- oil film thickness of neat lubrication realized under specific rolling lubrication
conditions
The method of supplying lubricating oil of the present
invention uses the supply efficiency determined by specific rolling lubrication
conditions and the oil film thickness at the time of neat lubrication to estimate
the oil film thickness at the time of emulsion lubrication and control the emulsion
supply rate etc. based on this estimated oil film thickness.
The supply efficiency is a function of the rolling rate,
emulsion supply, emulsion concentration, plateout length, emulsion temperature,
rolled material width or roll barrel length, rolling load, grade of rolled material,
and type of lubricating oil, so the lubrication can be controlled with a high precision.
By high precision lubrication control, a suitable oil film
thickness without excess or shortage is formed directly under the roll bite, and
the friction coefficient between the rolled material and the work rolls is maintained
at a value suitable for the rolling conditions. As a result, it is possible to prevent
slip between the rolled material and work rolls and seizure of the rolled material
and perform stable rolling. Further, it is possible to reduce the rolling cost and
improve the product quality.
BRIEF DESCRIPTION OF THE DRAWINGS
- FIG. 1 is a view of an example of the relationship between the rolling rate
and supply efficiency when using the emulsion supply and emulsion concentration
as parameters.
- FIG. 2 is a view schematically showing an example of a rolling facility for
working the method of supplying lubricating oil of the present invention.
THE MOST PREFERRED EMBODIMENT
In the present invention, the supply efficiency obtained
under conditions of a specific rolling rate, emulsion supply, emulsion concentration,
plateout length, emulsion temperature, rolled material width, rolling load, grade
of rolled material, and type of lubricating oil and the oil film thickness at the
time of neat lubrication realized under the specific rolling lubrication conditions
are used to estimate the oil film thickness realized by emulsion lubrication under
the specific rolling conditions.
Further, at least one of the emulsion supply, emulsion
concentration, emulsion temperature, and plateout length is controlled so that the
estimated oil film thickness matches with a target oil film thickness.
Here, "specific" means specified for each of various rolling
lubrication conditions. The "plateout length" means the distance from the emulsion
supply position to the inlet of the roll bite enabling a sufficient time to be secured
for the lubricating oil in the emulsion supplied to the surface of the running steel
sheet to separate from the water and plate out on the surface of the steel sheet.
Further, it is possible to set the plateout length considering
the case of supplying lubricating oil to the rolls to be the same. The supply efficiency
can be calculated as a function of the rolling rate, emulsion supply, etc. by a
model. The supply efficiency can be determined, for example, as follows.
The oil film thickness introduced in the case of neat lubrication
under certain rolling conditions is designated by "hneat", while the oil film thickness
introduced in the case of emulsion lubrication (any concentration) under the same
rolling conditions is designated by "hemu". Under the same rolling lubrication conditions,
the oil film thickness at the time of neat lubrication is the maximum, so under
emulsion lubrication, the oil film thickness becomes smaller than that at neat lubrication.
Therefore, the supply efficiency &agr; is defined as hemu/hneat.
Here, "hemu" can be obtained by measuring the oil film
thickness during rolling. And, "hneat" may be measured in advance by conducting
actual neat lubrication experiments or may be calculated by lubrication theory etc.
In neat lubrication, along with the increase in the rolling
rate, the amount of oil introduced increases due to the wedge effect of the oil
and the friction coefficient falls. As opposed to this, in emulsion lubrication,
at the low speed region, the amount of oil introduced increases due to the wedge
effect of the lubricating oil, but when over a certain rolling rate, the lubrication
becomes insufficient, the oil film thickness is reduced, and the friction coefficient
increases.
If calculating the supply efficiency for each rolling rate
according to the definitions, the result becomes as shown in FIG. 1. The inventors
discovered that this curve differs depending on the emulsion supply rate, emulsion
concentration, plateout length, emulsion temperature, rolled material width or roll
barrel length, rolling load, grade of the rolled material, and type of the lubricating
oil, but if these rolling lubrication conditions are the same, becomes equal at
all times.
Therefore, by creating a model of the supply efficiency
in advance within the range of operation, it is possible to estimate the oil film
thickness directly under the roll bite at the time of emulsion lubrication through
this supply efficiency and the oil film thickness at the time of neat lubrication.
Therefore, if controlling the emulsion concentration or
emulsion supply so that the estimated oil film thickness matches with the target
value, it becomes possible to supply the lubricating oil without excess or shortage
under rolling lubrication conditions.
Further, the inventors discovered that it is possible to
estimate the supply efficiency from the rolling rate, emulsion supply, emulsion
concentration, plateout length, emulsion temperature, rolled material width or roll
barrel length, rolling load, grade of rolled material, and type of lubricating oil.
The equation for estimation of the supply efficiency may be set by fitting to the
values obtained by experiments by a suitable function.
The inventors confirmed that the supply efficiency can
be expressed by at least an exponential function for each of the low speed region
and high speed region. Any other function enabling suitable fitting may also be
used of course.
However, the low speed region and high speed region are
defined using the maximal value of the supply efficiency as a boundary. It is known
that &agr; can be estimated by a model equation, so this function (hemu =&agr;
x hneat) may be used to estimate the oil film thickness at the time of emulsion
lubrication from the oil film thickness at the time of neat lubrication (actually
measured or using values of fluid theory of lubrication) under conditions the same
as the lubricating oil supply conditions at the time of emulsion lubrication (emulsion
supply, emulsion concentration, emulsion temperature, and plateout length).
Therefore, it is possible to estimate the supply efficiency
on-line at all times, estimate the oil film thickness at the time of specific emulsion
lubrication, and thereby control the lubrication.
The simplest parameter as a control factor is the emulsion
supply rate. The number of lubrication tanks etc. may be used to change the emulsion
concentration. Similarly, the directions of the nozzles may be changed to change
the plateout length.
FIG. 2 is a view schematically showing an example of a
rolling facility for working the method of supplying lubricating oil of the present
invention. The rolling facility is for example comprised of five stands. FIG. 2
shows only one rolling stand 10 among them. The rolling stand 10 is a 4Hi rolling
stand provided with work rolls 12 and backup rolls 14.
The rolling facility is provided with emulsion tanks 20A
and 20B for storing the emulsion and a cooling water tank 40. The stored emulsion
is set in advance in type and concentration in accordance with the specific rolling
lubrication conditions since the type and/or concentration of the lubricating oil
differs.
The emulsion pipes 21A and 21B connected to the emulsion
tanks 20A and 20B have emulsion pumps 22A and 22B and emulsion flow rate adjustment
valves 23A and 23B attached to them. Further, the emulsion pipes 21A and 21B are
connected to a main pipe 25.
At the inlet side of the rolling stand 10, an emulsion
header 30 is arranged. The emulsion header 30 is provided with a plurality of emulsion
nozzles 34 via rotary joints 32 along the sheet width direction.
Each emulsion nozzle 34 is able to rotate by the rotary
joint 32 about an axis of rotation extending horizontally in the sheet width direction.
The emulsion nozzles 34 can be rotated to change the directions of spraying the
emulsion as shown by the broken lines and thereby adjust the plateout length.
The cooling water pipe 41 extending from the cooling water
tank 40 has a cooling water pump 42 and cooling water flow rate adjustment valve
43 attached to it. On the other hand, a cooling water header 45 is arranged at the
outlet side of the rolling stand 10. The cooling water header 45 has the cooling
water pipe 41 connected to it and has a plurality of cooling nozzles 46 attached
to it along the sheet width direction.
The rolling facility is provided with a lubrication control
apparatus 50 comprised of a computer. The lubrication control apparatus 50 stores
model equations of the rolling lubrication conditions and supply efficiency &agr;
and other data. The lubrication control apparatus 50 calculates the supply efficiency
&agr; by the model equations based on the given rolling lubrication conditions.
In the rolling facility configured as explained above,
if, for example, the emulsion EA is selected based on the rolling lubrication conditions
and supply efficiency &agr;, the emulsion pump 22A is driven and the emulsion
EA is sent from the emulsion tank 20A through the emulsion pipe 21A to the main
pipe 25. The operation signal from the lubrication control apparatus 50 may be used
to adjust the flow rate of the emulsion flow rate adjustment valve 23A.
At this time, the emulsion pump 22B is stopped and the
emulsion flow rate adjustment valve 23B is closed. The emulsion EA is supplied through
the main pipe 25, emulsion header 30, and rotary joints 32 from the emulsion nozzles
34 to the steel sheet 1 at the inlet side of the rolling stand. Further, the work
rolls 12 are cooled with cooling water sprinkled from the cooling water nozzles
46.
The rolling lubrication conditions change with each instant,
so if a new supply efficiency &agr; is calculated, for example it is possible
to leave the other conditions constant and change only the plateout length to change
the oil film thickness. The changed parameter is not limited to the plateout length
and may also be the emulsion supply rate or the emulsion temperature. Further, it
is also possible to change several of these parameters.
Further, if the rolling lubrication conditions change and
a new supply efficiency &agr; is set, the emulsion pump 22A is stopped and the
emulsion flow rate adjustment valve 23A is closed in some cases. Further, the emulsion
pump 21B is driven and the emulsion flow rate adjustment valve 23B is used to adjust
the flow rate of the emulsion EB.
The emulsion is supplied while switching from the emulsion
EA to the emulsion EB and changing the emulsion supply. Note that in this case,
the lubricating oil may be the same or different in type, and the emulsion supply
rate may be the same. Further, it is also possible to change the plateout length.
When periodically correcting the supply efficiency (learning
function), an oil film thickness meter 52 is set at the rolling stand outlet side.
The measured value detected by the oil film thickness meter is sent to the lubrication
control apparatus 50 where the difference between the measured value of the oil
film thickness meter and the estimated value of the oil film thickness was calculated.
Further, based on the detected difference, the supply efficiency under the rolling
lubrication conditions was periodically corrected while estimating the oil film
thickness of the emulsion lubrication.
Due to this, it is possible to further raise the precision
of the lubrication control. The period of the correction may be changed in any way
in accordance with the rolling lubrication conditions.
The supply efficiency &agr; is a parameter showing the
state of lubrication, so is directly correlated with the friction coefficient or
forward ratio. These friction coefficient and forward ratio are governed by how
much lubricating oil is introduced into the roll bite. The rate of oil introduced
is affected by the state of supply, that is, the emulsion concentration, supply
rate, plateout length, etc., so the relationship with the supply efficiency &agr;
is deep.
It is possible to investigate in advance the friction coefficient
or forward ratio and supply efficiency and calculate the supply efficiency from
the lubricating oil supply conditions to estimate the friction coefficient or forward
ratio. When the calculated friction coefficient or forward ratio does not match
the target value, it is possible to change the supply rate, plateout length, or
other parameters to obtain the target state of lubrication.
Therefore, in the present invention, it is possible to
detect the load during the rolling, outlet side sheet speed, and roll speed, calculate
in reverse the friction coefficient from the inlet side sheet thickness and outlet
side sheet thickness obtained from the reduction schedule and the above parameters,
store the relationship between the friction coefficient and the supply efficiency
for each grade of rolled material in advance in the form of a table, find the friction
coefficient under specific rolling conditions from the supply efficiency, and control
at least one of the emulsion supply, emulsion concentration, emulsion temperature,
and plateout length so that the friction coefficient matches with a target value.
Further, it is possible to detect the outlet side sheet
speed and roll speed to calculate the forward ratio, store the relationship between
the forward ratio and the supply efficiency for each grade of the rolled material
in advance in the form of a table, find the forward ratio under specific rolling
conditions from the supply efficiency, and control at least one of the emulsion
supply, emulsion concentration, emulsion temperature, and plateout length so that
the forward ratio matches with the target value.
However, even under the same lubricating oil supply conditions,
it is known that the friction coefficient or the forward ratio changes according
to the roll wear, the grade of the rolled material, etc. The roll wear should be
corrected by the number of tons of rolling of the rolled material from after roll-exchange.
The grades of the rolled material, for example, are classified by deformation resistance
to less than 350 MPa, 350 to 600 MPa, 600 to 800 MPa, 800 to 1200 MPa, and more
than 1200 MPa. There is no problem if storing the relationship between the friction
coefficient or forward ratio and supply efficiency for each in the form of a table.
The present invention is not limited to the above embodiments.
For example, the rolled material may also be, in addition to steel, titanium, aluminum,
magnesium, copper, or another metal and alloys of these metals.
There may also be three or more emulsion tanks. Further,
it is also possible to use a single tank for storing the lubricating oil and mix
the lubricating oil supplied out from the tank with heated water in the middle of
the pipe to prepare the emulsion.
In this case, it is also possible to change the mixing
ratio of the lubricating oil and heated water in accordance with the rolling lubrication
conditions and adjust the emulsion concentration and/or change the emulsion supply
rate.
EXAMPLES
A single stand 4Hi test mill was used to roll a coil. In
this experiment, palm oil was used as the base oil of lubricating oil (emulsion
concentration 2%, plateout length 0.3 m, supply rate 1 liter/min per side, sheet
width 50 mm) and the supply efficiency was calculated in advance in a preliminary
test in the range of conditions of the test. The rolling was performed by accelerating,
rolling at a constant 1500 mpm for 10 minutes, then decelerating and ending.
The present model was applied to a first coil (calculation
period of 1 second), whereby &agr; was between 0.11 to 0.23. The sheet was rolled
while changing the supply so that the estimated oil film thickness (current 0.38
to 0.48 µm) matched with the target oil film thickness. The target oil film
thickness was made an oil film thickness at the time of the limit of occurrence
of seizure flaws obtained by operation up to here. When using the present model,
rolling was possible without problems such as seizure flaws.
Even with ordinary rolling, the supply rate is changed
for each rolling rate, but this is rough control by table values. Therefore, the
rolling is not performed in the state close to the limit of seizure at all times
like in the present model.
If calculated by table values used in ordinary operation,
it is learned that the supply rate by the present experiment is 92% of ordinary
operation (after correction of sheet width). It could be confirmed by the present
model that the cost can be cut without any trouble.
Next, the supply efficiency was calculated during rolling
while conducting similar experiments. For verifying the precision of the supply
efficiency estimation model as well, the combination of the rolling conditions and
sheet thickness and width was changed to roll 23 coils. No rolling trouble occurred
for any coil including seizure flaws.
In the same way as the previous time, if compared with
the supply at the time of normal operation, in the present experiment, it could
be confirmed that the supply was 93% in normal operation. The effect could be confirmed
even in the case of estimating the supply efficiency during rolling.
INDUSTRIAL APPLICABILITY
As explained above, the present invention enables lubrication
control with a high precision in rolling control. Therefore, the present invention
is great in applicability in the ferrous metal industry.