FIELD OF INVENTION
The present invention relates to a method for evaluating industrial applicability of cold
rolling oil for steel mill. More particularly, the invention relates to a method for
evaluating industrial applicability providing data for all selective properties in a single
attempt in a systematic manner to judge whether new cold rolling oil can be used at a
given industrial mill.
The present invention also relates to comparing and evaluating performance of new
rolling oils at the pilot mill against reference curves eliminating the need of conducting
rolling with the oil-in-use. The present invention also relates to a method for diagnosing
deficiency in existing rolling oil and thereby making it possible to improve its quality.
BACKGROUND AND PRIOR ART
US3600931 teaches an apparatus for testing effectiveness of lubricants in rolling bore
friction applications where bearing balls are subjected to both roiling and sliding contact
with races. One of a pair of spaced curved bearing races of like radius are made
reciprocably pivotable about an axis distant from the races with respect to the race.
US3823599 discloses an apparatus for the evaluation of the lubricity of rolling oils and
the interaction of such oils with a variety of metal alloys employed in the construction of
rolls. The lubricant under test is applied to the region of frictional contact between the
roll and disc where the speed of the disc is controlled by applying torque to the disc. The
co-efficient of friction is determined by application of known load on roll of given length
and can be evaluated for various degrees of slipping velocity.
US Patent Application number US2004/0045356 teaches a method of determining the
thickness of a lubricant film disposed between two bodies by measuring and performing a
frequency spectrum analysis on a reflected or transmitted part of an ultrasound wave
propagated towards said film.
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In cold rolling of steed, interfaces between strip and work rolls are under immense
pressure and highly factional state. Unlike conventional sliding surfaces. friction is the
necessity of rolling process. Here, deformation energy is transmuted from rolls to the
strip through friction between rolls and strip. Friction has to be adequately high to ensure
traction in the roll bite and thus to avoid skidding phenomena. Contrarily, it also has to be
sufficiently low to limit the roll force to an acceptable level, to optimise mill motor power
requirement and to minimise shape and surface quality problems. Lubrication is therefore
introduced to reduce friction at the work roll-strip interfaces to an optimum level. This is
achieved by formation of lubricant films at the roll bite. Generally, the lubricant is
applied in the form of oil-in-water emulsion and thus it also seavenges heat, dirt and
wear-debris.
There are various kinds of cold rolling oils available in the market, whose constituents
vary in types and doses. There is no standard specification of these oils and selection of
the oil for a given mill is mostly decided on the merit of is performance. Most of the oil
manufacturers evaluate performance of the oil in terms of physico-chemical properties
and also use different types of tribological rigs for evaluating frictional and other
behaviour of cold rolling oils. These rigs do not simulate nailing condition properly. Most
of them even do not have plastic deformation at the lubricated contacts, which is a must
during rolling of steel strips. Also large numbers of experiments are required to be carried
out as each experiment may evaluate only one aspect of the oil's performance.
The other approach of evaluating performance of rolling oil, mostly followed by the
users, is to conduct industrial trial directly at the actual mill. This approach also has
limitations, particularly when the trial is not successful. In this case, there may be loss in
production, breakdown of mill components or deterioration of strip quality. Also, it may
not be possible to study the effect of various process conditions on the performance of
oil. In case more number of candidate oils are available for selecting the most promising
oil, there has to conduct trial with each rolling oil and thus it is a cumbersome exercise.
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The best way of simulating roiling condition in laboratory is possible only at pilot rolling
mill. It can be used to select the best performing oil from large number of new oils. It can
also be used for optimising oil's formulation based on its true performance. Effect of
various process conditions on the performance of oil can be studied separately. However,
there is no standard method available for evaluating industrial applicability of the cold
rolling oil even at the pilot rolling mill. In absence of any absolute or reference data,
performance of any new rolling oil is always compared with that of a rolling oil-in-use.
There is practice of evaluating performance of cold rolling oil in lerms of physico-
chemical properties using titration and other chemical methods. Some of these methods
belong to national/international standards of evaluating petroleum products. The
disadvantage of this practice is that none of the physico-chernical properties has direct
correlation with the actual performance of the oil at the industrial mill That is, knowing
physco-chemical properties of the oil no one can be certain about performance of the oil
at actual operation. It has been found that similar performance can be achieved by
appreciably different physico-chemical properties of the oil.
The other way of evaluating rolling oil is using some tribological rigs. This method also
has disadvantages. Firstly, most of these rigs do not simulate rolling conditions properly.
Some of the rigs have point contact, some have sliding conditions and most of them even
do not have plastic deformation of material. Secondly, these tigs evaluate individual
characteristics of the oil, say lubricity or emulsion behaviour, and do not evaluate all the
important characteristics at one go.
The third approach of evaluating performance of roiling oil is toconduct direct trial on the
industrial mill. Although this is the best way of evaluating merit of the oil, this too has
serious disadvantages. It carries huge risk of production loss, quality rejection, system
breakdown, etc. in case the trial is not successful due to inferior quality of rclling oil. It
does not provide good opportunity to optimise the oil formulation. It is difficult to study
the effect of individual process condition on performance of the oil by varying a
particular parameter. Further, when there are more than one candidate oils available,
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selecting the best one is a tedious and costly affair as industrial trial is required to be
tarried out with each oil.
Thus there is a need to provide a method for evaluating of the industrial applicability of
cold rolling oil, which will provide data for all key properties in a single run and a
method for comparing and evaluating performance of new rolling oils.
The present inventors have developed a melhod for evaluating industrial applicability of
cold rolling oils where surprisingly, the method gives a systematic and comprehensive
approach, of evaluating performance of a rolling, oil in single attempt to judge. whether it
can be used at a given mill or not. The present method is advantageous in terms of
providing comparison of performance of new rolling oils at the pilot mill eliminating the
need of conducting rolling with the oil-in-use by means of reference curves.
OBJECTS OF INVENTION
Thus it is an object of the present invention to provide a method for evaluating industrial
applicability of cold rolling oil, which is systematic in its approach.
Another object of the present invention is to provide reference curves to compare
performance of new rolling oils at the pilot mill eliminating the need of conducting
rolling with the oil-in-use.
Yet another object of the present invention is to provide a means for developing new
rolling oils and optimising its formulation.
The other object of the present invention is to provide a method for diagnosing deficiency
in existing oil and/or improving quality of rolling oil.
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SUMMARY OF INVENTION
Thus according 10 an aspect of the present invention there is provided a method for
evaluating industrial applicability of cold rolling oil for steel mill providing data for all
selective properties in a single attempt, said method comprising steps of:
(a) preparation of an emulsion of the oil at controlled pH, temperature, concentration;
(b) cold rolling of hot rolled strips at simulated reduction regime;
(c) evaluation of performance of the oil in said emulsion of step (a) in terms of
selective characteristics, selected from lubrication, thermal efficiency, emulsion
behaviour, ageing characteristics and the like
characterized in that the speed of the roiling is kept constant during said method of
evaluation.
According to another aspect of the invention there is also provided method of comparing
performance of new rolling oils eliminating the need of conducting rolling with the oil-
in-use by means of reference curves.
DETAILED DESCRIPTION OF THE INVENTION
This method of evaluation of industrial applicability of cold rolling oil is carried out by
preparing an emulsion of cold rolling oil in a tank at controlled plI, temperature and
concentration (1-5%).
Hot rolled pickled sheets are characterized in terms of their yield strength V5 cumulative
reduction ratio.
Cold rolling of the hot rolled sheets is carried out at simulated reduction regime
(reduction 10-50% per pass, number of pass 4-12).
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Rolling parameters like roll force, rolling speed, strip tension on two sides of the mill,
pass reduction, motor current, voltage, sheet temperature after rolling are recorded. Roll
force and strip tensions are measured using separate load cells. Speed is measured using a
tachometer. Pass reduction is measured as ratio of draft and initial thickness of
strip/sheet. Current and voltage are recorded using electrical signals. Sheet temperature
after rolling is measured using contact type pyrometer.
The surface quality of the rolled sheets/strip is studied in terms of sheet surface
reflectance and roughness of rolled sheets/strip. Strip surface roughness before and after
rolling is measured in transverse and longitudinal directions using conventional
roughness meter. Surface reflectance is evaluated using the tape test described below:
A blank adhesive tape is pasted over a white paper. Its reflectance is measured with a
reflectometer and set at 100.This is taken as a reference for the quantification of
cleanliness of rolled sheets. Subsequently, the tape is pasted over the rolled sheets and
after sometime it is removed and again pasted over the above white paper. During
removal of the tape from the rolled sheet it carries with it all the loose deposits over the
sheet. Reflectance of this tape is measured and compared with that of the above
reference.
The performance of the oil is evaluated in terms of lubrication characteristics, thermal
efficiency, cleanliness characteristics, emulsion behaviour and ageing characteristics-
Lubrication characteristics: Hot rolled pickled sheets (typical size of 2-3 mm x 100-180
mm x 250-350 mm) are rolled down to a minimum thickness in successive passes.
Rolling speed is kept constant throughout the test,.; Rolling parameters mentioned above
are recorded during rolling. These parameters are used as input date for a computer
model, which calculates friction coefficient at the roll bite. Lubrication characteristic is
measured in terms of friction coefficient minimum gauge rolled and total reduction
achieved in the fixed reduction schedule. Boundary lubrication characteristic of the oil is
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evaluated in terms of change in sheet surface roughness with increasing cumulative
reduction.
The effect of reduction, speed and roughness on lubrication are studied by varying these
parameters in the specified range.
Thermal efficiency: Thermal efficiency is evaluated by means of cooling efficiency of the
oil which is measured in terms of sheel temperature after rolling. Sheet temperature is
measured after each pass of rolling and maximum temperature versus reduction is plotted
to generate cooling curve.
Cleanliness characteristics: Cleanliness characteristics of the oil are evaluated in terms of
surface reflectance of rolled sheets measured by the scotch tape test.
Emulsion behaviour; Emulsion behaviour of the oil is evaluated in terms of ease of
emulsification, oil separation, foaming, colour, and odour. Ease of emulsification,
foaming, colour, and odour are studied qualitatively whereas oil separation value is
quantified.
Quantification is done as follows:
Emulsion samples are collected from the emulsion tank and spray header during rolling.
Oil % in the emulsion is measured by a chemical method in which emulsion is broken
into oil and water by adding acid into it and heating the emulsion for about 30 minutes.
The difference in oil % in the tank and at the spray header gives the value of oil
separation and thus the emulsion characteristics.
Ageing characteristics; Ageing characteristics of the oil is evaluated by comparing all the
above characteristics (lubrication, cooling, emulsion, and cleanliness) of the aged
emulsion with that of a fresh emulsion.
Aged emulsion is prepared as follows:
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The emulsion is contaminated by adding, tramp oil (10-50% of rolling oil in emulsion)
and iron fines (50-500ppm) and storing the emulsion for 6-10 weeks under intermittent
agitating conditions.
BRIEF DESRIPTION OF ACCOMPANYING FIGURES
Figure 1 illustrates Lubrication characteristics of oil at low reduction of the present
invention.
Figure 2 illustrates Lubrication characteristics of oil at high reduction of the present
invention.
Figure 3 illustrates Boundary lubrication characteristics of the present invention.
Figure 4 illustrates Cooling characteristics of the present invention.
Figure 5 illustrates Ageing characteristics of the present invention.
Figure 6 illustrates Validation of laboratory results of the present invention,
Figure 7 illustrates the process flow chart of the present invention.
DETAILED DESCRIPTION OF ACCOMPANYING FIGURES
The method thus tested is compared against reference curves (Fig. I- Fig.6) generated on
the basis of experience with development of various types of cold rolling oil over a
period of time.
Reference friction curves at low reduction (Fig.l)
Reference friction curve at high reduction (Fig.2)
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Reference for tooling efficiency (Fig.4)
Reference surface reftectance is over 90% .
Oil separation for stable oil is of the order of 10-15%, for metastable oil is 15-30% and
for unstable oil is over 30%.
Ageing characteristics are satisfactory if % deviation in any performance parameter of the
aged emulsion is within 10% when compared to the parameters of fresh emulsion.
This test method is applicable for a range of process conditions .The most preferred
conditions are pH of 5.0 to 8.0 depending upon the chemistry of the oil, temperature of
40ºC to 60°C depending upon oil quality and concentration range of 1-5%.
Based on the method formulation of rolling oil is optimized.
The present invention also provided a means for studying performance of the existing
rolling oil. Based on this study, deficiency in the current oil can be identified and
eliminated by suitable modifications in the formulation.
The results obtained are compared with the reference curves and are represented below
(Fig1-Fig.6)
Fig.l depicts lubrication characteristics of candidate oil evaluated at the pilot rolling mill
at low pass reduction (10-20%). Here lubricity of the candidate oil has been compared
with the two reference friction curves. Reference#] curve presents innovated set
reference friction data for superior frictional performance and Rcference#2 presents the
same for inferior frictional performance. As can be seen, the candidate oil is very close to
the Referenced 1 curve, which indicates that it possesses good lubricity at lower reduction
condition.
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Fig.2 depicls lubricity of candidate oil evaluated at the pilot rolling mill at high pass
reduction (20-50%). Here lubricity of the candidate oil has been compared with one
reference friction curve, closeness of which gives indication of satisfactory lubrication
characteristics at higher reduction condition.
Fig.3 depicts comparison of boundary lubrication characteristics of the two rolling oils,
which has been measured in terms of change in surface toughness of sheet samples after
rolling. The oil-2, which shows lesser reduction in surface roughness, is considered as
having better boundary lubrication property.
Fig,4 depicls comparison of cooling efficiency of the two rolling oils, which has been
measured in terms of sheet temperature immediately after rolling. The oil-2 is considered
to have better cooling efficiency compared to oil-1, as the maximum sheet temperature
with oil-2 is less than that with oil-1.
Fig.5 depicts comparison of lubrication performance of aged emulsion of a rolling oil
with that of its fresh emulsion. If deviation in corresponding friction coefficients in the
two states is within 10%, ageing characteristics of the oil with respect to lubricity is
considered satisfactory. Similarly comparative study of cooling, cleanliness and emulsion
behaviour can be made to evaluate complete ageing characteristics of the oil.
Fig.6 depicts validation of laboratory results on lubricity of the candidate oil by
evaluating lubricity of the oil under industrial condition at a Tandem Cold Mill. It can be
seen that the trend of friction data generated in laboratory is matching with that generated
under industrial condition. The difference in two values is not very high and thus
validates the laboratory results. Similar validation can be shown with respect to other
performance parameters of cooling and cleanliness characteristics.
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Figure 7 depicts the process flowchart for evaluating performance of the oil in terms of
lubrication characteristics, cooling efficiency, cleanliness characteristics, emulsion
behaviour, and ageing characteristics by comparing results with the reference data
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WE CLAIM
1. A method for evaluating industrial applicability of cold rolling oil for slect mill
providing data for all selective properties in a single attempt, said method
comprising steps of:
(a) preparation of an emulsion of the oil at controlled pH. temperature,
concentration;
(b) cold rolling of hot rolled strips at simulated reduction regime;
(c) evaluation of performance of the oil in said emulsion of step (a) in terms of
selective characteristics, selected from lubrication, thermal efficiency,
emulsion behaviour, ageing characteristics and the like
characterized in that the speed of the rolling is kept constant during said method of
evaluation.
2. Method as claimed in claim 1, wherein the lubrication characteristics of the oil are
evaluated in terms of friction characteristics, minimum gauge rolled, total
reduction, and change in strip surface roughness achieved in the simulated
reduction schedule.
3. Method as claimed in claim 1. wherein said thermal efficiency is evahiated by
means of cooling efficiency of oil measured in terms of maximum sheet
temperature after rolling.
4. Method as claimed in claim I; wherein the cleanliness characteristics of the oil are
evaluated in terms of surface reflectance of rolted sheet by the scotch tape test.
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5. Method as claimed in claim 1, wherein the emulsion behaviour of the oil is
evaluated in terms of ease of emulsification, oil separation, foaming, colour and
odour,
6. Method as claimed in claim I, wherein the ageing characteristics of the oil are
evaluated by comparing lubrication, cooling, emulsion, characteristics of the aged
emulsion with that of the fresh emulsion.
7. Method as claimed in claim 1. wherein said pH of the emulsion is in the range of
5.0-8.0.
8. Method as claimed in claim I, wherein said temperature of the emulsion is in the
range of 40°C-60 °C
9. Method as claimed in claim 1, wherein said concentration of the emulsion is in
the range of 1-5%.
10. Method for comparing performance of new rolling oils eliminating the need of
conducting rolling with the oil-in-use by means of reference curves.
Dated this 27th day of March, 2006.

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The present invention relates to a method for evaluating industrial applicability of cold
rolling oil for steel mill providing data for all selective properties in a single attempt. The
method comprises steps of preparation of an emulsion of the oil at controlled all,
temperature, concentration, cold rolling of hot rolled strips at simulated reduction regime and
evaluation of performance of the oil in said emulsion of step (a) in terms of selective
characteristics, selected from lubrication, thermal efficiency, emulsion behaviar ageing
characteristics and the like. The invention also relates to a method for comprising
performance of new rolling oils eliminating the need of conducting rolling with the oil-in-use
by means of reference curves.