1. Field of the Invention
This invention relates generally to rolling mills producing
long products such as rods and bars, and is concerned in particular with the provision
of an improved modular rolling mill.
2. Description of the Prior Art
Block-type rolling mills are known, as disclosed for example
U.S. Patent Nos. 4,537,055
. These serve primarily as finishing trains in rod rolling mills, and are
in widespread use throughout the world. Block type mills comprise a series of roll
stands arranged in sequence to roll an alternating oval/round pass sequence, with
the roll shafts of the round roll stands being staggered by 90° with respect
to the roll shafts of the oval roll stands in order to roll products in a twist
Typically, the roll stands having round and oval roll passes
are staggered on opposite sides of the mill pass line and are mechanically coupled
to respective parallel line shafts driven at different speeds by a common mill drive
connected to the line shafts by a differential gear box. Other known drive arrangements
for block type mills employ a single line shaft as disclosed for example in
U.S. Patent Nos. 3,587,277
, and chain drives, as disclosed in
U.S. Patent No. 4,129,023
Although block type mills are capable of rolling products
at high delivery speeds, e.g., 5.5mm rod at 120m/sec., their overall efficiency
is compromised by a lack of flexibility when changing from one product size to another.
For example, as shown in Figure 4, in a typical rolling
program for a ten stand block type mill, when all stands are operative, a feed size
having a 17mm diameter will be rolled into a finished product having a diameter
of 5.5 mm. In order to roll a finished product having a 7.0 mm diameter, roll stands
9 and 10 are rendered inoperative (a procedure commonly referred to as "dummying").
Progressively larger product sizes can be rolled by progressively dummying additional
roll stands, e.g., stands 7 and 8 to roll 8.5 mm rounds, stands 5 and 6 to roll
10.5 mm rounds, etc. Because the successive roll stands are integrally joined together,
in order to effect dummying, the work rolls must be removed and replaced with guides.
This is a labor intensive procedure, typically taking between 20-60 minutes to complete,
and occurring every 8 hours. If, conservatively speaking, one assumes an average
down time of 30 minutes for each dummying operation, with a mill operating 300 days
per year at a rate of 60 tons/hr, the lost production can amount to upwards of 27,000
In order to achieve improved efficiencies, modular mills
have been developed, as disclosed for example in
U.S. Patent Nos. 5,595,083
. These mills employ multiple motors driving gear boxes detachably coupled
to pairs of successive rolling units. The rolling units each include roll stands
with oval and round roll passes, and are interchangeable and rapidly shiftable onto
and off of the mill pass line to thereby accommodate the rolling of different product
sizes. Although mechanically sound and advantageously flexible, as compared to block
type mills, such modular arrangements are relatively complex and expensive, both
to purchase and subsequently to maintain.
The objective of the present invention is to provide an
improved modular rolling mill that overcomes or at least substantially mitigates
the disadvantages associated with conventional modular and block type mills.
SUMMARY OF THE INVENTION
In accordance with the present invention, a modular rolling
mill comprises a plurality of separate rolling units arranged along a mill pass
line. Each rolling unit includes at least two pairs of work rolls defining oval
and round roll passes and carried on roll shafts that are staggered 90° with
respect to each other. The rolling units contain intermediate drive trains configured
to connect the roll shafts to parallel input shafts projecting to a first side of
the pass line from the respective rolling units.
A single driven line shaft is parallel to and on the first
side of the pass line. Output shafts are mechanically coupled to the line shaft
by bevel gear sets. The output shafts project laterally from the line shaft towards
the pass line and are connected by couplings to the input shafts of the rolling
units. The couplings are separable to accommodate ready removal of the rolling units
to an opposite second side of the pass line.
The line shaft is advantageously subdivided into segments
coupled to the input shafts by the bevel gear sets, with clutches joining the shaft
segments. The clutches are alternatively adjustable to either connect or disconnect
the respective joined shaft segments.
Since only one line shaft is employed to drive all of the
rolling units, it may be directly coupled to the mill motor without having to interpose
a differential gear box.
These and other features and advantages of the present
invention will now be described in further detail with reference to the accompanying
BRIEF DESCRIPTION OF THE DRAWINGS
- Figure 1 is a schematic plan view of a modular rolling mill in accordance with
the present invention;
- Figure 2 is a schematic illustration of the intermediate drive train contained
in the rolling units;
- Figure 3 illustrates the relationship of the gears in a four gear cluster incorporated
in the intermediate drive train; and
- Figure 4 is an illustration of an exemplary rolling program.
With reference to Figure 1, a modular rolling mill in accordance
with the present invention comprises a plurality of separate rolling units 10 arranged
along a mill pass line "P." The direction of rolling is indicated by arrow 12. Each
rolling unit has at least two pairs of work rolls 14, 14 and 16, 16 configured to
define oval and round roll passes. The rolls of each successive pair are staggered
by 90° to effect twist-free rolling of long products, e.g., bars, rods, and
With reference additionally to Figures 2 and 3, it will
be seen that the work rolls are mounted on roll shafts 18, and that intermediate
drive trains are contained within the rolling units to mechanically couple the roll
shafts to input shafts 20. The input shafts are parallel and project to a first
side "A" of the pass line. The intermediate drive trains include gears 22 on the
roll shafts meshing with intermeshed gears 24 on shafts 26, with one of the shafts
26 connected by a bevel gear set 28 to a shaft 30. The shafts 30 carry gears 32
meshing with a gear 34 on the input shaft 20.
Although not shown, it will be understood that as an alternative
to this arrangement, the intermediate drive trains could be configured to drive
each pair of work rolls 14, 14 and 16, 16 with separate input shafts 20.
A line shaft 36 extends along the first side A in parallel
relationship to the pass line P. The line shaft is directly coupled to and driven
by a drive motor 38 located at the entry end of the mill.
The line shaft 30 may be continuous, but preferably it
is subdivided into segments 36' joined by clutches 40. Each line shaft segment 36'
is coupled to an output shaft 42 by a bevel gear set 44. The output shafts 42 are
parallel and project laterally from the line shaft towards the pass line. The clutches
40 are alternatively adjustable to mechanically connect or disconnect the respective
line shaft segments.
Couplings 46 connect each output shaft 42 to a respective
input shaft 20. The couplings are separable to accommodate removal of the rolling
units to the second opposite side "B" of the pass line. A network of tracks 48 on
side B is arranged to receive and convey rolling units removed from the pass line.
A rolling unit is shown in broken lines at 10' in its removed position from the
Preferably, the rolling units 10 are identical and thus
readily interchangeable one for the other. Each rolling unit can be readily removed
from the pass line and replaced by a guide.. The guide may comprise part of a protective
cover, as disclosed for example in
U.S. Patent No. 5,247,820
In light of the foregoing, it will now be understood by
those skilled in the art that the modular mill concept of the present invention
offers significant advantages over conventional block and modular mills. For example,
the ability to rapidly remove rolling units from the pass line is conservatively
estimated to reduce mill down time by approximately 67%. Thus, for the exemplary
rolling operation previously described, this can amount to an annual increase in
production of 18,000 tons/yr. The use of a single driven line shaft, and the elimination
of costly gear units between the line shaft and the mill drive motor, makes possible
significant savings in capital investment as well as in subsequent maintenance costs
over the life of the mill.
With regard to maintenance, it is important to note that
all of the gears, shafts, and associated bearings of the intermediate drive trains
are contained in the rolling units 10, and are thus accessible for periodic maintenance
when the rolling units are removed from the mill pass line, without having to interrupt
continued operation of the mill. Likewise, the bevel gear sets 44 of dummyed rolling
units can be de-clutched from the line shaft 36 and also subjected to periodic maintenance,
again while the remainder of the mill continues in operation.