Disk roll exchanging apparatus for vertical piercing mill...

Details Disk roll exchanging apparatus for vertical piercing mill... Disk roll exchanging apparatus for vertical piercing mill...

2000-04-12

2001-07-31

Larson, Lowell A. (Department: 3725)

Metal deforming

By use of tool acting during relative rotation between tool...

During rotation of work

C072S238000

Reexamination Certificate

active

06266987

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The present invention relates to a disk roll exchanging apparatus for use in a vertical piercing mill used for manufacturing seamless steel tubes and to a disk roll exchanging method employed thereby, and more particularly to a disk roll exchanging apparatus which enables automatic exchange of disk rolls in accordance with a changeover schedule so as to reduce time for exchange and which is used in a vertical piercing mill suitable for flexible manufacture of a variety of differently-sized seamless steel tubes in small quantities, and to a disk roll exchanging method employed thereby.
BACKGROUND ART OF THE INVENTION
As a method of manufacturing seamless steel tubes under hot working conditions, the Mannesmann tube-making process is widely employed. In this tube-making process, a round billet heated to a high temperature is fed as a material to be rolled into a piercing mill (a so-called “piercer”), which pierces the axial center portion of the round billet to obtain a hollow shell. The thus-obtained hollow shell is fed, directly or as needed after undergoing an expansion or wall-thinning process in an elongator having the same structure as that of the piercing mill, into a subsequent elongating mill such as a plug mill, a mandrel mill, or the like so as to be elongated. Subsequently, the thus-elongated tube undergoes a finishing process provided by a stretch reducer for shape correction, a reeler for polishing, and a sizer for sizing, thereby becoming a seamless steel tube product.
FIG. 1
shows the material being pierced and an arrangement of piercing rolls and disk rolls in a piercing mill. Piercing rolls
2
,
2
are axisymmetrically arranged such that each of the piercing rolls
2
,
2
forms a predetermined cross angle and inclination angle with respect to the pass line X—X along which a round billet
1
serving as the material is rolled. Disk rolls
3
are arranged in proximity to and in a manner perpendicularly intersecting with the piercing rolls
2
such that the disk rolls
3
are opposed to one another with the round billet held in-between, and rotate independently of each other about respective shafts
4
. In the piercing mill with the piercing rolls
2
,
2
arranged as above, when the round billet
1
is fed along the pass line X—X in the direction indicated by the illustrated white arrow, the round billet
1
is caught between the piercing rolls
2
and is transferred along the pass line X—X while being rotated, during which the round billet
1
is pierced at its axial center portion by an unillustrated plug so as to become a hollow shell. During this piercing process, the disk rolls
3
follow the movement of the round billet
1
and rotate in the direction of the pass line X—X so as to prevent the round billet
1
from deflecting, to thereby establish smooth piercing.
In general, a piercing mill employing such a roll arrangement as shown in
FIG. 1
, in which a pair of piercing rolls are opposingly arranged in a vertical direction with a pass line running in-between, and a pair of disk rolls are opposingly arranged in a horizontal direction, is usually called a “vertical piercing mill.” In recent years, vertical piercing mills have widely been used in a seamless steel tube manufacturing process.
As described above, since piercing mill forces the high-temperature material between piercing rolls, the working surfaces of the piercing rolls are degraded with rolling time. Also, since disk rolls are in contact with the material during rolling, their surfaces unavoidably wear. Accordingly, the piercing rolls and the disk rolls must be replaced periodically. Particularly, exchanging disk rolls involves the steps of opening a mill housing and lifting the disk rolls up one after another for exchange through use of an overhead crane. Since exchanging a pair of disk rolls through use of an overhead crane takes a considerable amount of time, a reduction in the working ratio of the piercing mill is unavoidable.
Various improvements have been proposed for solving the above-described problem involved in disk roll exchange. For example, Japanese Patent Application Publication (kokoku) No. 63-64248 discloses the structure of a piercing mill which allows disk rolls to be replaced without use of an overhead crane. However, this proposed structure is only applicable to the case where a disk roll is supported in a cantilever manner on the driving shaft side. This cantilever-like support of a disk roll has the problem that the disk roll is not positioned in a sufficiently rigid manner during operation. That is, since the cantilever-like support of a disk roll involves a reduction in supporting rigidity, the disk roll may deflect from the material during piercing, resulting in the marking of scratches on the material surface.
By contrast, when a disk roll is supported at both ends of its shaft in order to secure a sufficient supporting rigidity for the disk roll, the structure of a supporting apparatus for a disk roll becomes complex. Thus, a disk roll exchanging apparatus applicable to such a complex supporting apparatus becomes large-scaled, resulting in a potential significant reduction in workability of disk roll exchange. This reduction in workability of disk roll exchange affects not only the working ratio of a piercing mill but also an overall efficiency of manufacture of seamless steel tubes, particularly when a continuous Mannesmann tube-making process is carried out for high efficiency production of seamless steel tubes as has been practiced in recent years.
SUMMARY OF THE INVENTION
In view of the above-described problems involved in disk roll exchanging work for a vertical piercing mill employed in a seamless steel tube manufacturing process, an object of the present invention is to provide a disk roll exchanging apparatus which enables automatic exchange of disk rolls by a simple structure and without reducing its workability even when the disk rolls are supported at both ends of their shaft, and which is used in a vertical piercing mill suitable for flexible manufacture of a variety of differently-sized seamless steel tubes in small quantities, as well as a disk roll exchanging method employed thereby.
The present invention provides (1) a disk roll exchanging apparatus for use in a vertical piercing mill and (2) a disk roll exchanging method employed by the apparatus, as shown in
FIGS. 3 and 4
, and described below. (1) A disk roll exchanging apparatus for use in a vertical piercing mill containing a pair of piercing rolls and a pair of disk rolls
3
in a mill housing such that the piercing rolls are opposingly arranged in a vertical direction with a pass line of the material to be rolled running in-between and that the disk rolls
3
are opposingly arranged in a manner perpendicularly intersecting with the piercing rolls, the disk roll exchanging apparatus comprising a pair of disk frames
6
each of which supports one of the disk rolls
3
and is located at the side of the mill housing and supported by a rotary shaft so that it can swing open away from the mill housing, a disk roll lifting device
12
for mounting the disk roll
3
to and demounting it from the opened disk frame
6
, and a horizontally moving device
18
for carrying and horizontally moving the disk roll lifting device
12
.
The disk roll
3
is integrally formed with a shaft
4
, and the shaft
4
is supported at both ends via chocks
10
and
11
. The disk roll lifting device
12
preferably has a structure capable of positioning the chocks
10
and
11
provided at both shaft ends and the disk roll
3
when the disk roll lifting device
12
supports the disk roll
3
. Also, the open position of the disk frame is preferably fixed to a constant position by open positioning means.
(2) A disk roll exchanging method for use in a vertical piercing mill containing a pair of piercing rolls and a pair of disk rolls
3
in a mill housing such that the piercing rolls are opposingly arranged in a vertical direction with a pass line of the material to be rolled running in-bet

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