METHOD FOR LUBRICATING MILLING MATERIAL

PROCEDE DE LUBRIFICATION DE PRODUITS A LAMINER

English Abstract

Disclosed is a method for rolling milling material, especially for hot wide-
strip rolling in a finishing train or a continuous casting and rolling plant,
in which a lubricant is applied directly to the surface of the working rollers
or indirectly to the surface of the support rollers, the lubricant then being
transferred to the surface of the working rollers, before the milling material
is fed into the roller gap of a roll stand. A highly adhesive lubricant film
forms on the surface of the working roller, said lubricant film resulting in a
reduction of friction in the roller gap as an intermediate layer between the
roller and the milling material. According to the inventive method, the
lubricant is applied along the entire length of the milling material such that
the lubricating effect comes into play along the entire length of the milling
material.

French Abstract

L'invention concerne un procédé de laminage de produits, en particulier de laminage large bande, à chaud, dans un train finisseur ou dans une installation de laminage à coulée continue, procédé dans lequel un agent lubrifiant est appliqué directement sur la surface des cylindres de travail, ou indirectement, sur la surface des cylindres d'appui, avec transfert sur la surface des cylindres de travail, avant que le produit à laminer parvienne dans l'espace entre cylindres d'une cage de laminoir, de sorte qu'il se forme à la surface du cylindre de travail, un film lubrifiant adhérant fortement, lequel forme, dans l'espace entre cylindres, une couche intermédiaire entre le cylindre et le produit à laminer, entraînant ainsi une réduction de frottement. Le lubrifiant est appliqué sur toute la longueur du produit à laminer, de sorte que l'effet lubrifiant est actif sur toute la longueur du produit à laminer.

Claims

CLAIMS
1. Method for the rolling of rolling stock, especially for
the rolling of hot-rolled wide strip in a finishing train or a
continuous casting installation, in which a lubricant is applied
directly to the surface of the work rolls or indirectly to the
surface of the backup rolls and is then transferred to the
surface of the work rolls, before the rolling stock enters the
roll gap of a rolling stand, wherein a strongly adherent
lubricant film forms on the surface of the work rolls and leads
to reduction of friction in the roll gap as an intermediate
layer between the roll and the rolling stock, characterized by
the fact that the lubricant is applied over the entire length of
the rolling stock, and therefore the lubricating effect acts
over the entire length of the rolling stock.
2. Method in accordance with Claim 1, characterized by the
fact that a lubrication system that feeds lubricant from a
reservoir to the work rolls or backup rolls through lines and
nozzles is turned on 5-15 seconds before the rolling stock
enters the rolling stand.
3. Method in accordance with Claim 1, characterized by the
fact that the lubricant is applied in the second stand and in
each subsequent stand.

4. Method in accordance with Claim 1, characterized by the
fact that the lubricant is applied in the third stand and in
each subsequent stand.
5. Method in accordance with Claim 1, characterized by the
fact that the lubricant is applied in the second stand and in
each desired subsequent stand.
6. Method in accordance with Claim 1, characterized by the
fact that the lubricant is applied in the third stand and in
each desired subsequent stand.
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Description

CA 02547960 2006-06-02
METHOD FOR LUBRICATING MILLING MATERIAL
The invention concerns a method for the rolling of rolling
stock, especially for the rolling of hot-rolled wide strip in a
finishing train or a continuous casting installation, in which a
lubricant is applied directly to the surface of the work rolls
or indirectly to the surface of the backup rolls and is then
transferred to the surface of the work rolls, before the rolling
stock enters the roll gap of a rolling stand, wherein a strongly
adherent lubricant film forms on the surface of the work rolls
and leads to reduction of friction in the roll gap as an
intermediate layer between the roll and the rolling stock.
The use of roll gap lubrication in heavily loaded hot-
rolling finishing trains is well known. However, the
lubrication is turned on with some delay at the leading end of
the strip after the pass has started in the given stand and is
turned off a certain amount of time before the trailing end of
the strip exits the stand. Depending on the lubricating action,
a procedure of this type has an unfavorable effect on the
rolling process.
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CA 02547960 2006-06-02
DE 21 05 975 discloses a device for automatically feeding
oil to a hot-rolling mill stand through which rolling stock is
passing. The device comprises an oil spraying device for the
rolling stand, means for feeding oil to the spraying device,
means for initiating operation of the oil feed device shortly
after the leading end of the rolling stock passes through the
rolling stand, and means for terminating operation of the oil
feed device shortly before the trailing end of the rolling stock
reaches the rolling stand.
The document US 6,266,985 Bl describes a method in which a
lubricant is applied to the corners and ends of the rolling
stock that is to be hot-rolled.
DE 20 22 923 discloses a method and a device for applying a
lubricant to rolling stock in a hot-rolling strip mill, wherein
lubricant and atomizing air are delivered to several spray
nozzles in a four-high rolling stand equipped with two work
rolls and two backup rolls. The spray nozzles are arranged
across the width of at least one of the backup rolls. As soon
as the rolling stock enters the work rolls, the lubricant is
applied to the backup rolls, from which it is transferred to the
work rolls. The flow of lubricant and atomizing air to the
nozzles is cut off as soon as the rolling stock leaves the work
rolls.
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CA 02547960 2006-06-02
The starting time for the lubricant feed is the start of
the pass in the given stand. A disadvantage of this method and
this device is that a closed lubricant film must first form on
the surface of the backup roll and then be transferred to the
surface of the work roll in the gap between the backup roll and
work roll. From the work roll, the lubricant enters the roll
gap. It takes too much time for the lubricant to reach the
rolling stock (several seconds), depending on the peripheral
speed and diameter of the roll. In a method of this type and a
device of this type, the leading end of the strip is not
supplied with lubricant as it enters the roll gap, which
temporarily results in higher rolling forces.
Fundamentally, rolling is not possible without friction in
the roll gap, since sufficient friction is required to bite the
rolling stock and pull it through the roll gap. It is always
necessary to ensure that the so-called bite and pass conditions
are met_ With respect to the minimum required friction, the
bite condition, which describes the conditions at the leading
end of the rolling stock, is much more critical than the pass
condition. In the pass condition, the roll gap is completely
filled with rolling stock.
If one of the two conditions or both conditions are not
satisfied, slipping occurs, i.e., slip between the roll and the
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CA 02547960 2006-06-02
rolling stock.
In addition to the coefficient of friction, which describes
the friction itself, the bite angle and the rolling speed play a
role. The bite capacity decreases with increasing rolling
speed. With respect to the bite angle, which depends on the
thickness of the entering rolling stock, the relative thickness
reduction during rolling, and the diameter of the rolls, it can
be said that it must always be smaller than the friction angle
to allow slip-free rolling. With the usual draft distribution,
the bite angle in finishing trains decreases from the first to
the last stand. Accordingly, the greatest bite problems, mainly
slipping at the leading end of the rolling stock, occur in the
first finishing stand.
Since the bite condition at the leading end of the rolling
stock is more difficult to meet than the pass conditions in the
rolling stock, the roll gap lubrication is adjusted in such a
way that the lubrication is not turned on until after the
initial pass has started in the given stand and is turned off a
certain amount of time before the rolling stock exits the stand.
This allows the work rolls to continue rolling sufficiently long
for the lubricant present on the surface of the rolls to burn
off completely. In this way, the bite at the leading end of the
following piece of rolling stock is not jeopardized.
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CA 02547960 2006-06-02
As a result of the lubrication strategy described above,
two different load levels develop within the rolling stock,
provided that the prestrip or the thin slab enters the finishing
train with homogeneous properties over the length and without
speed-up: a high level at the leading end and the trailing end
of the rolling stock (without lubricating action) and a low
rolling force level in the remainder of the rolling stock
(active lubrication).
As a result of the reduction of the rolling force during
active lubrication, which can amount to 50'~ or more, there is a
change in the deflection of the work rolls. This simultaneously
results in a change in the state of flatness of the rolling
stock (prominent in the rear stands) and in the crown of the
rolling stock (prominent in the front stands).
However, if work roll bending is available as an adjusting
mechanism in the given stand, then in the case of large rolling
force reductions, the adjustment limits are more frequently
reached. The result is unstable travel of the rolling stock,
especially in the rolling of thin slabs.
It is customary to limit the rolling force reduction to a
value of about 20°,.
Therefore, the objective of the invention is to specify a
method for applying a lubricant to the surface of a work roll or

CA 02547960 2006-06-02
backup roll, which improves the rolling process, leads to a
reduction of roll wear, and lowers the power consumption of the
finishing train.
In accordance with the invention, this objective is
achieved by the characterizing features of Claim 1.
Advantageous refinements of the invention are specified in the
dependent claims.
If a lubrication system that feeds lubricant from a
reservoir to the work rolls or backup rolls through lines and
nozzles is turned on 5-15 seconds before the rolling stock
enters the rolling stand, all idle times in the lubrication
system are compensated, so that a closed lubricating film always
forms on the work roll even before the start of the pass.
The decisive advantage of the method of the invention is
that a constant level of rolling force for the given stand is
obtained over the entire length of the rolling stock, because
the lubrication is maintained over the entire length of the
rolling stock.
Due to the constancy of the rolling force, greater total
rolling force reductions can be achieved, for example, 40-50a;,
so that the loading of the rolling train is greatly reduced with
respect to wear and power consumption. In addition, the greater
rolling force reduction reduces work roll wear and thus
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CA 02547960 2006-06-02
increases the useful life of the rolls (service life).
The advantages of the method of the invention are thus:
-- constant rolling force level;
-- no change in the state of flatness related to the
rolling force;
-- no change in strip profile related to the rolling force;
-- since the forces at the leading end and the trailing end
of the rolling stock are also significantly reduced, stand
vibrations and roll damage can be even more effectively avoided;
-- this results in greater latitude for draft distributions
and thus optimized pass programs for rolling critical products;
-- since the state of flatness at the trailing end of the
rolling stock does not change due to the rolling force,
incorrect rolling of the leading end of the rolling stock can be
avoided.
A prerequisite for the use of the lubrication of the
invention is that the bite conditions at the leading end of the
rolling stock are ensured.
The application of the lubricant in accordance with the
invention in a finishing train or a continuous casting
installation is advantageously possible without restriction
starting with the second stand and for all subsequent stands.
Lubricant is generally not applied in the first finishing
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CA 02547960 2006-06-02
stand due to the great thickness of the rolling stock (large
bite angle). In accordance with the invention, in order already
to apply the lubricant in the second finishing stand, the
conditions existing in the given installation are taken into
consideration. These include, for example
-- the condition of the surface of the roll after grinding,
-- the work roll diameter,
-- the work roll material,
-- the entering strip thickness,
-- the relative reduction that is adjusted,
-- the surface condition of the entering rolling stock
(scale, temperature, roughness, material, etc.),
-- the lubricant used,
-- the amount of lubricant, and
-- the rolling speed.
If the bite angle is in the critical range, the lubricating
action at the leading end of the rolling stock is upwardly
limited by a smaller amount of lubricant or by a modified
lubricant, i.e., a lubricant with different properties.
When the method of the invention for applying lubricant to
a roll surface is used, it is advisable to use the pass program
model of the finishing train for this operation. In this
regard, at least a doubling of the adaptation matrix should be
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CA 02547960 2006-06-02
provided so as not to adversely affect the adapted operation
without roll gap lubrication. In physical models, the selection
of different sets of coefficients of friction -- for the
lubricated and unlubricated state -- is highly advantageous for
the startup, when new products are introduced, and for avoiding
high adaptation values.
Every change in friction is associated with a change in the
forward slip, i.e., with a change in mass flow or a disturbance
of mass flow. This type of disturbance must be stabilized by
the automatic control systems, which can lead to considerable
difficulties in critical thin strip rolling.
Another advantage of the method of the invention is that,
when constant lubrication is provided, constant forward slip is
achieved, which in turn results in constant mass flow.
In ferritic rolling, the roll gap lubrication is used to
have a favorable effect on the shear texture of the surface.
The application of the lubricant in accordance with the
invention produces a homogeneous surface texture over the whole
length of the rolled product.
To avoid time lags when the lubrication is turned on, the
lubrication system is provided with a closed-circulation line
with return to the lubricant tank and a switchable 3/2-way valve
before the lubricant mixer (for example, a static-tube mixer).
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