Lubrication – Lubricators – Roller
Reexamination Certificate
1999-08-19
2001-03-20
Bucci, David A. (Department: 3682)
Lubrication
Lubricators
Roller
C184S017000, C184S023000, C164S149000, C164S268000, C164S428000, C164S472000, C164S480000
Reexamination Certificate
active
06202792
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and a method for lubricating an edge dam in a twin-roll type strip casting machine, in which strips are continuously manufactured by supplying a metal melt into between a pair of casting rolls. More specifically, the present invention relates to an apparatus and a method for lubricating an edge dam in a twin-roll type strip casting machine, in which a continuous uniform lubrication boundary layer is formed on the friction face between the casting rolls and the edge dam, so that the wear of the edge dam refractory material can be reduced, and that the friction faces of the casting roll can be protected, thereby improving the performance and the durability of the machine.
2. Description of the Prior Art
Generally, as shown in
FIG. 1
, a twin-roll type strip casting machine
100
supplies a melt
122
from a tundish
110
through a melt supply nozzle
112
into between a pair of revolving casting rolls
120
, thereby directly manufacturing metal strips
130
of several mm.
Further, the casting rolls
120
are disposed in parallel with each other, and at both sides of the casting rolls, there are installed refractory plates called “edge dam
140
”. During the casting of the strips, the edge dams
140
prevent the spilling of the melt
122
from the casting rolls
120
. In order to prevent the edge dams
140
from being pushed backward by the pressure of melt
122
, hydraulic devices (not illustrated) support the back faces of the edge dams
140
.
The edge dams
140
which prevent the spilling of the melt
122
are subjected to wear due to the frictions between the edge dams
140
and the revolving rolls
120
. When the casting operation is carried out for a long time, the casting stability is aggravated due to an excessive wear of the edge dams
140
. Therefore it is a necessity to reduce the wear rate so as to extend the life expectancy of the casting machine.
Further, the casting rolls
120
are also subjected to wear due to the frictions with the edge dams
140
, with the result that the friction faces
125
of the casting rolls
120
are damaged. Such a damage of the casting rolls
120
accelerates the wearing of the refractory material
142
of the edge dams
140
. Therefore, the friction faces
125
of the casting rolls
120
need to be protected from wear.
The edge dam
140
is made of a refractory base material which has a high thermal shock resistance, a superior high temperature strength, and a low thermal deformation, such as mullite, fused silica, silicon carbide or the like. In addition, the friction face of the edge dam
140
is added with a ceramic layer
142
which has a high thermal shock resistance, a high corrosion resistance (against the melt), a high toughness, a good machinability and the like, such as Si
3
N
4
-BN composite, AlN-BN composite, SiC-BN composite or the like (refer to FIG.
2
). The ceramic layer
142
undergoes wear because it is closely contacted to the fast revolving casting rolls with a pressure of 2-4 Kg/cm
2
.
Generally, in the case where the composite material of the ceramic layer
142
is made to contain 40-60 vol % of BN, the wear rate is about 0.5 mm/min.
Therefore, if the casting operation is carried out for a long time, the wear becomes excessive, with the result that the casting stability is aggravated, and that the durability and life expectancy of the edge dam
140
are shortened.
If the hardness of the ceramic material of the ceramic layer
142
is high, although the wear rate is decreased, the friction face
125
of the casting roll
120
is damaged, giving a severe problem.
In this manner, there occur serious frictions between the ceramic layer
142
and the friction face
125
of the side of the casting rolls
120
. If the hardness or the wear resistance of the ceramic layer
142
is higher than that of the friction face
125
of the casting roll
120
, the wear of the edge dam
140
is small, but the wear of the friction face
125
of the casting roll
120
becomes high. In a worse case, pockmarks are formed on the casting rolls
120
, with the result that the edge portions of the manufactured strips
130
become defective, and that the melt is spilled from between the casting rolls
120
, these being a serious problem.
Therefore, Japanese Patent Gazette No. Hei-7-68352 proposes the following method. That is, a boron nitride composite ceramic layer which has a lubricating property and a proper wear resistance is attached on the portion of the edge dam
140
where frictions occur by being contacted with the casting roll
140
. In this manner, the ceramic layer
142
of the edge dam
140
, which has a low wear resistance in the relative terms, is made to be worn, thereby protecting the friction face
125
of the casting roll
120
, and preventing the spilling of the melt.
However, the edge dams
140
are supported continuously by means of springs or hydraulic cylinders (not illustrated) to make the edge dams
140
closely contact with the casting rolls
120
, and therefore, the wear of the ceramic layer
142
is increased too much after the elapse of casting time. Therefore, in the long run, the durability is aggravated owing to the increased wear.
Meanwhile, U.S. Pat. No. 5,201,362 discloses the following apparatus. That is, the closely contacting pressure of the edge dams
140
is controlled to a high level during the early casting stage, so that the wear of the ceramic layer
142
would be high in the early stage. However, when the casting is stabilized, the contacting pressure of the edge dams is lowered, and the contact force is controlled such that the wear rate should come into a proper range, thereby lowering the wear rate. In this method, after carrying out the casting for a long time, if the roughness of the friction face
125
of the casting rolls
120
becomes coarse, and if the physical properties of the ceramic material of the ceramic layer
142
are degraded at the high temperature, then the contacting pressure is lowered to obtain a decreased wear rate. In this manner, during the casting operation, an external force makes the edge dams
140
withdraw, and this withdrawing frequency is gradually increased. As a result, the quality of the edge portions of the metal strip
130
is degraded.
Meanwhile, in an attempt to overcome the damage of the casting rolls
120
and the excessive wear of the edge dams
140
, Japanese Patent Laid-open No. Hei-9-108788 discloses the following apparatus. That is, a solid lubricant such as sintered boron nitride (BN) which is manufactured by a hot pressing process is contacted to the friction face
125
of the casting roll
120
so as for the solid lubricant to be clad on the friction face
125
. The lubricant cladding layer acts as a lubricant on the friction face
125
, thereby preventing the wear of the casting rolls
120
and the edge dams
140
. However, if the surface of the friction face
125
is smooth (and not coarse), then the solid lubricant layer is hardly formed. On the other hand, if the surface of the friction face
125
is coarse, then the lubricant layer becomes too thick or the lubricating effect is decreased. Consequently, depending on the conditions of the surface of the friction face
125
, either the lubricant layer is not formed, or a non-uniform lubricant layer is formed, this being a problem.
SUMMARY OF THE INVENTION
The present invention is intended to overcome the above described disadvantages of the conventional techniques.
Therefore it is an object of the present invention to provide an apparatus and a method for lubricating edge dams of a twin-roll type strip casting machine, in which the casting rolls and the edge dams are protected from being wear-damaged, thereby improving the durability and life expectancy of the casting machine.
In achieving the above object, the apparatus for lubricating edge dams in a twin-roll type strip casting machine for reducing wear between the edge dams and casting rolls according to the present invention includes: a lubric
Cheong Han Nam
Choo Dong Kyun
Kang Tae Wook
Bucci David A.
Kim Chong H.
Pohang Iron & Steel Co. Ltd.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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