Note: Descriptions are shown in the official language in which they were submitted.
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REUSE OF USED OIL IN A ROLLING MILL
Fiels of the invention
[0001] The present invention relates to a lubrication
method in a rolling mill. More particularly it relates to a
lubrication method using used oil, i.e. degraded and/or
contaminated oil.
State of the art
[0002] Cold-rolling mills consume a large amount of
oil for lubricating the contact between the rolls and the
product being rolled. The lubrication is carried out by
means of a mixture of water and oil called an emulsion,
typically comprising between 0.5 and 4% of oil in water.
[0003] The emulsion generally flows in a closed
circuit, as for example illustrated in documents
JP 56-041011, JP 6-246330 or in Fig. 1. Within the circuit,
the emulsion is collected, treated by means of filters and
oil skimmers and is then sent back to the rolling mill.
During use, fresh oil is mixed with the recycled emulsion
in order to maintain the oil concentration constant.
[0004] Over time, the emulsion degrades and/or is
contaminated by iron fines, by the presence of
micro-organisms, by the acid coming from the preliminary
pickling lines, by oils used in other portions of the
rolling mill, etc. Accordingly, a portion or the totality
of the emulsion must be emptied and stored in a waste tank
before it is subsequently treated in a specialized center.
This generates a significant amount of wastes. The wastes
from the lubrication method not only include the emptied
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emulsions but also the oily sludges that are deposited in
the filters, on the equipment, as well as the oil from the
filtration of skimmed oils.
[0005] Presently, used emulsions are generally de-
oiled in an emulsion-separation plant and/or dissociated
into oil and into water (see Fig. 1). During the storing of
the wastes, the used emulsions from the rolling may also be
mixed with other used emulsions used in any other step
occurring in the manufacturing of steel sheets. The
dissociated oils are then sent to a purification plant
where they are evaporated. These dissociated oils may be
mixed, before purification, with other used oils, used
during the manufacturing of steel sheets. These oils may
then be burnt, for example in blast the furnaces of a
steel-working plant.
[0006] The handling of these wastes and their
treatment generate costs that are highly significant and
that could be reduced by using again the wastes within the
rolling process, whether this is hot or cold rolling.
Aims of the invention
[0007] The present invention aims to provide a
solution that allows the reuse of the used emulsions, oily
sludges and used oils within the rolling process and, in
particular within the hot-rolling process.
[0008] It thus aims to reduce the amount of wastes
produced and the costs associated with their handling and
treatment.
Main characteristic elements of the invention
[0009] The present invention relates to a lubrication
method in a rolling mill by means of a lubricant comprising
used oil.
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[0010] According to particular embodiments of the
invention, the method comprises at least one or a suitable
combination of the following characteristics:
- said used oil stems from a waste or a mixture of wastes
from one or several of the steps occurring in the
manufacturing of a metal;
- said used oil at least partly stems from a waste coming
from a cold-rolling mill;
- said used oil is reused as a lubricant in a hot-rolling
mill;
- the waste comprises a used emulsion, an oily sludge or a
used oil;
- the used emulsion and the oily sludge are treated by
means of a separation technique to extract said used oil;
- said used oil is taken from a supernatant layer above the
aqueous phase of the used emulsion;
- the used oil taken from the supernatant layer above the
aqueous phase of the used emulsion is reused as a
lubricant in a hot-rolling mill without being subjected
to any purification treatment;
- the used emulsion is mixed with other wastes beforehand;
- the lubricant comprises a mixture of used oil and water;
- the mixture comprises an emulsifier;
- the lubricant comprises the used oil that is not mixed
with water;
- the waste stems from a lubrication process in a cold-
rolling mill or from a pickling process before the cold-
rolling mill;
- The result is a force reduction of the order of 30%
during the hot rolling of a steel sheet.
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Short description of the figures
[0011] Fig.1 schematically illustrates the complete
cycle of the emulsion, according to the state of the art,
in a cold-rolling mill.
[0012] Fig.2 illustrates the force reduction
resulting from the lubrication of a hot-rolling cage by
means of various lubricants including one reference and
those according to the invention.
Detailed description of the invention
[0013] The present invention relates to a method for
lubricating a rolling mill by means of a lubricant
comprising used oil, which will also be called waste oil.
Preferentially, the used oil according to the invention is
reused in a hot-rolling mill requiring a lower oil quality
than that of a cold-rolling mill. However, the present
invention does not exclude the reuse of waste oil in a
cold-rolling mill.
[0014] The expression used oil more particularly
designates an oil that is degraded and/or contaminated and
that, in this condition, no longer has the properties
required for optimum lubrication of a cold-rolling mill
even after filtration and provision of fresh oil. It thus
differs from a recycled emulsion/oil within a closed loop
such as described in documents JP 56-041011 and JP 6-246330
of the state of the art.
[0015] The expression used oil also includes
degraded and/or contaminated oil as defined above having
further been subjected to one or several treatments before
it is reused.
[0016] The degraded and/or contaminated nature of an
oil depends on the application field and is not easy to
define in a universal way. In the case of a cold-rolling
mill, the emulsion is thoroughly monitored. It may be
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decided to empty the emulsion on the basis of several
criteria which inter alia are a modification of the pH of
the emulsion, of the stability of the emulsion, of the size
= of the particles of the emulsion, of the viscosity of the
5 oil, of the rolling forces, etc. Each rolling mill has its
own operating window. Therefore, it is delicate to quantify
the wear of an oil without unduly limiting the scope of the
invention.
[0017] The used oil may stem from oily sludges, a
used emulsion, and/or, more simply, from a waste oil, all
three of which will be commonly called wastes. These wastes
may stem from a lubrication process of a cold-rolling mill
and/or from any other step occurring in the manufacturing
of a metal, and more particularly in the manufacturing of
steel sheets (pickling, winding, etc.). The present
invention also extends to the use of a used oil stemming
from other applications (French fry shops, change of oil
from engine, etc.). The used oil may thus be obtained from
a mixture of oils stemming from several sources of wastes.
[0018] The used oils may be extracted from sludges or
used emulsions by means of a separation techniques selected
according to the composition of the wastes and to the
amount of oil required for the application. More simply,
the separation may be carried out naturally within the tank
by destabilization of the emulsion at rest. Thus, in the
waste tank, the used oil will form a supernatant layer
above the aqueous phase and may be directly withdrawn.
[0019] As a non-limiting example, the lubrication
method according to the invention is illustrated below for
a hot-rolling mill but, as already mentioned, the method
according to the invention may also be implemented on a
cold-rolling mill.
[0020] Two used oils stemming from lubrication in an
industrial cold-rolling mill for steel sheets, and mixed
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with used preservation oils used on pickling lines, have
been tested in a pilot hot-rolling mill and compared with a
fresh reference oil. The tests related to the rolling of a
ferrous metal, namely steel. Both used oils were taken from
the upper layer which formed in the waste tank by
destabilization of the water/oil emulsion. They comprise
less than 0.5% of water and have not been subjected to any
purification treatment before reuse. Both used oils stem
from the same tank and have color variations (very dark
brown and dark brown versus very pale brown for fresh oil)
which express variations in compositions and/or in
concentrations of emulsifier within the layer in
suspension.
[0021] First of all, the emulsions were prepared with
a 1% concentration of oil by means of a mixer. The
properties of the oil and water mixture without or with
emulsifier were evaluated. The emulsifier concentration in
the mixtures comprising the latter, amounts to 2%. The
tests have shown that both used oils have different
capabilities of mixing into water. Thus, for a first used
oil, called o waste 1 , the mixing is carried out with
difficulty in the absence of an emulsifier, while in the
presence of an emulsifier, the mixing is carried out
properly. In the case of the second used oil, called
o waste 2 , good mixing properties are observed whether
with or without an emulsifier. In parallel, an emulsion
with 1% of fresh oil was prepared as a reference.
[0022] The prepared emulsions were sprayed on rolling
rolls with pressures of 3 and 7 bars giving an emulsion
flow rate of 3 L/min and 4.75 L/min, respectively.
[0023] Fig.2 illustrates the average percentage of
force reduction for the various emulsions tested relative
to a rolling test carried out without lubrication, moreover
everything else being equal. One observes a force reduction
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that may attain 30% with the used oil, called waste 1 ,
and may be greater than the one obtained with the reference
oil. It is further observed that the addition of emulsifier
tends to reduce the lubrication performances.
5 [0024] Additional tests were carried out with pure
used oil, i.e. not dispersed in water. The pure oil was
sprayed with flow rates of 10 and 20 L/min on rolling
rolls, according to the method described in document
WO 2009/046505 for example. The results of these tests are
also shown in Fig.2. A force reduction greater or equal to
30% is observed.
[0025] The present invention was illustrated for the
rolling of ferrous metals. The lubrication method according
to the invention using used oil may be extended to
lubrication within the scope of rolling of non-ferrous
metals.
