1. Field of the Invention
This invention relates generally to hot rolling mills of the type
producing bar and rod products, and is concerned in particular with improvements
in the pinch roll units and associated controls employed to propel and/or retard
the movement of such products at various places along the mill pass line.
2. The Prior Art
Pinch roll units are conventionally employed in rod mills to propel
smaller diameter products through water boxes, and to propel larger diameter products
through the laying heads. Alternatively, pinch roll units can be employed to retard
and brake the movement of bar products being directed to cooling beds, and to prevent
the tail ends of rod products from accelerating after they leave the last mill stand
and before they arrive at the laying heads.
Pinch roll closure must be precisely timed to achieve the desired
function, and the pinching force and torque exerted by the pinch rolls must be carefully
controlled and coordinated to avoid marking the product. Marking can result from
excessive pinching force, or by an imbalance of pinching force and driving torque
resulting in slippage of the rolls against the product surface.
Conventional pinch roll units employ electric motors to drive the
pinch rolls, and pneumatically driven linear actuators to open and close the pinch
rolls. The latter have proven to be problematical due to fluctuations in the pressure
of compressed air normally available in rolling mills, and the relatively slow reaction
times attributable largely to solenoid valve dead times, cylinder closing times,
and the stroke distance of the pistons. Such problems are particularly acute in
high speed rolling environments, e.g., in rod mills where product delivery speeds
now routinely exceed 100m/sec.
The principal objective of the present invention is to eliminate or
at least significantly minimize the above described problems by replacing the conventional
pneumatically driven linear actuators with more reliable faster acting electrically
driven closure mechanisms.
SUMMARY OF THE INVENTION
According to claim 1, a pinch roll unit for either propelling or retarding
a product moving along the pass line of a rolling mill comprises: a pair of levers
mounted for rotation about parallel first axes; roll shafts carried by said levers,
each roll shaft being journalled for rotation about a second axis parallel to the
first axis of its respective lever; pinch rolls carried by said roll shafts, said
pinch rolls defining a gap there between for receiving said product; an electrically
powered first motor; linkage means for mechanically coupling said first motor to
said levers, said first motor being operable via said linkage means to rotate said
levers about said first axes and to move said pinch rolls between open positions
spaced from said product, and close positions contacting and gripping said product
there between; and an electrically powered second motor for rotatably driving said
Preferably, said linkage means comprises a disc crank driven by said
first motor for rotation about a third axis parallel to said first and second axes,
and a pair of link members, each link member being pivotally coupled at opposite
ends to said disc crank and to a respective one of said levers.
Accordingly to another embodiment, the pinch roll unit further comprises
detector means for generating a signal indicative of the presence of said product
at a location along said pass line preceding the gap defined between said pinch
rolls, and control means responsive to said signal for operating said first motor
to move said pinch rolls between said open and closed positions by rotating said
levers about said first axes.
Preferably, said control means is additionally operative to control
the pressure exerted by said pinch rolls on the product.
Preferably, the pressure exerted by the pinch rolls on the product
is controlled by varying the torque exerted by said first motor.
Preferably, said control means is additionally operative to control
the speed at which said pinch rolls are driven by said second motor.
According to another preferred embodiment, said first motor is a servo
Preferably, said control means is additionally operative for a given
product size, to determine a pre-touch position for said pinch rolls between said
open and closed positions, and to memorize said pre-touch position for subsequent
reuse with products of the same size.
Preferably, said control means is additionally operative to change
said pre-touch position in response to changes in said product size.
The invention further provides the following method: In a rolling
mill in which hot rolled products are directed along a pass line between pinch rolls,
and the pinch rolls are opened and closed by an electrically powered servo motor,
a method of controlling the operation of said pinch rolls, said method comprising:
detecting the arrival and speed of a product at a location along the pass line in
advance of said pinch rolls; based on the results of step 1, determining whether
the product size has changed from a preceding size to a new size; based on the results
of step 2: if the product size has changed: setting the current limit to be applied
to the servo motor to achieve a predetermined pinch roll pressure on the product;
energizing the servo motor to move the pinch rolls slowly from fully open positions
to closed positions in contact with the product to effect said predetermined pinch
roll pressure; determining and storing an interim setting for the servo motor at
which the pinch rolls are moved from, said fully open positions to pre-touch positions
spaced a short distance from the product; or if the product size has not changed:
energizing the servo motor in accordance with a previously stored interim setting
to move the pinch rolls rapidly from said fully open positions to the resulting
pre-touch positions; setting the current limit to be applied to the servo motor
to achieve a predetermined pinch roll pressure on the product; moving the pinch
rolls slowly from the pre-touch positions into contact with the product to effect
said predetermined pinch roll pressure on the product; determining and storing an
updated interim setting for the servo motor; awaiting a pinch roll open command;
and energizing the servo motor to return the pinch rolls to their fully open positions.
A pinch roll unit in accordance with the present invention operates either to propel
or retard a product moving along the pass line of a rolling mill. The pinch roll
unit includes a pair of levers mounted for rotation about parallel first axes. Roll
shafts are carried by the levers. Each roll shaft is journalled for rotation about
a second axis parallel to the first axis of its respective lever. Pinch rolls are
carried by the roll shafts, and are spaced one from the other to define a gap for
receiving the product being processed by the mill.
An electrically powered first motor is operable via intermediate linkage
to rotate the levers in opposite directions about their first axes, and to thereby
adjust the pinch rolls between open positions spaced from the product, and closed
positions contacting and gripping the product there between. An electrically powered
second motor rotatably drives the pinch rolls. Advantageously, the first motor is
a servo motor driving a disc crank for rotation about a third axis parallel to the
first and second axes, with link members mechanically connecting the disc crank
to the levers carrying the roll shafts.
Preferably, the pinch roll unit operates in conjunction with a detector,
e.g., a hot metal detector, which generates a signal indicative of the presence
of the product at a location along the pass line preceding the gap defmed by the
pinch rolls. A control system operates in response to the detector signal to operate
the first motor precisely and to adjust the pinch rolls between their open and closed
positions. The control system is also preferably operable to control the pressure
exerted by the pinch rolls on the product. Advantageously, this pressure control
is achieved by varying the torque exerted by the first motor.
These and other features and advantages of the present invention will
now be described in greater detail with reference to the accompanying drawings,
BRIEF DESCRIPTION OF THE DRAWINGS
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
- Figure 1
- is a schematic depiction of the delivery end of a rod mill equipped with pinch
roll units in accordance with the present invention;
- Figure 2
- is a horizontal sectional view taken through one of the pinch roll units shown
in Figure 1;
- Figure 3
- is a vertical sectional view taken along line 3-3 of Figure 2;
- Figure 4
- is a schematic diagram of the system for controlling the pinching sequence of
each pinch roll unit; and
- Figure 5
- is a flow-chart describing a typical pinching sequence.
With reference initially to Figure 1, an exemplary delivery end of
a high speed rod mill is shown comprising a finishing block 10 of the type disclosed,
for example, in U.S. Patent No. Re. 28, 107. The hot rolled rod is propelled from
the finishing block along the mill pass line PL at speeds typically exceeding 100m/sec.
The rod is cooled sequentially in water boxes, 12, 14 and 16 before being directed
to a laying head 18. The laying head forms the rod into a continuous series of rings
20 which are deposited in an offset pattern on a cooling conveyor 22. The cooling
conveyor delivers the rings to a reforming station (not shown) for collection into
Pinch roll units 24 and 26 in accordance with the present invention
are positioned along the mill pass line PL. Pinch roll unit 24 serves mainly in
a driving mode to propel the product forwardly and to insure its passage through
the last water box 16. Pinch roll unit 26 operates in either a breaking mode to
slow the tail ends of smaller diameter products, which exhibit a tendency to speed
up after they leave the finishing block 10, or in a driving mode to push larger
diameter slower moving products through the laying head 18. With reference additionally
to Figures 2 and 3, it will be seen that pinch roll units 24, 26 in accordance with
the present invention each include a housing 28 in which a pair of levers 30a, 30b
are mounted for rotation about parallel first axes A1. Roll shafts 32a,
32b are carried by the levers 30a, 30b, with each roll shaft being journalled for
rotation about a second axis A2 parallel to the first axis A1
of its respective lever. Pinch rolls 34 are carried by the roll shafts and are spaced
one from the other to define a gap there between for receiving a product moving
along the mill pass line PL.
An electrically powered first motor 36 operates via a planetary gear
unit 38 to rotate a disc crank 40 about a third axis A3 parallel to the
first and second axes A1, A2. Link members 42 are pivotally
connected at opposite ends as at 44 to the disc crank 40 and as at 46 respectively
to ears projecting from the levers 30a, 30b.
The disc crank 40 and link members 42 serve as a linkage for mechanically
coupling the motor 36 and its gear unit 38 to the levers 30a, 30b, with the motor
being operable via that linkage to rotate the levers about their respective first
axes A1 and to thereby adjust the pinch rolls 34 between open positions
spaced from a product moving along the mill pass line, and closed positions contacting
and gripping the product.
The roll shafts 32a, 32b are provided with toothed segments 48 meshing
with intermeshed drive gears 50a, 50b carried on drive shafts 52a, 52b. Drive shaft
52a is coupled as at 54 to an electrically powered second motor 56. Motor 56 serves
as the means for driving the pinch rolls 34.
With reference additionally to Figure 4, it will be seen that the
first and second motors 36, 56 of the pinch roll units 24, 26 are controlled by
a programmable logic controller (PLC) which operates in response to a product speed
signal 58 generated by the mill control system, and by control signals 60, 62, 64
respectively generated by a hot metal detector (HMD-1) at the exit end of the finishing
block 10, and by hot metal detectors (HMD-2) immediately preceding the pinch roll
units 24, 26. The signal 58 representative of product speed enables the PLC to determine
the time of product travel from one location to the next along the pass line, e.g.,
between a hot metal detector and its associated pinch roll unit. Changes in product
speed are also indicative of changes in the size of the product being rolled.
The signals generated by the hot metal detectors are indicative of
the passage of front and tail ends at their respective locations along the pass
Figure 5 depicts the process of controlling a front end pinch sequence
for one of the pinch roll units. The process begins by determining whether motor
56 is operating to drive the pinch rolls 34 (Step 66). If the pinch rolls are not
being driven, the process is aborted (Step 68). If the pinch rolls are being driven,
the system then determines if the servo motor 36 has been enabled (Step 70). If
the servo motor has not been enabled, the process is aborted. If the servo motor
is enabled, the system then awaits a pinching command (Step 72) to be supplied by
the PLC in response to a front end presence signal 60 received from the hot metal
detector HMD-1. Based on an analysis of the product speed signal 58, the system
then determines whether the product size has changed (Step 74). If the product size
has changed, the system awaits the arrival of the front end at HMD-2 (Step 76).
Upon arrival of the front end at that location, the system sets the current limit
for the servo motor 36 (Step 78), which determines the maximum pinch pressure to
be applied to the product by the pinch rolls 34. The servo motor is then operated
to slowly move the pinch rolls 34 into contact with the product and to increase
the current to the preset limit (Step 80). After a prescribed delay, e.g., 5 seconds
(Step 82), the system determines a pre-touch position for the pinch rolls (Step
84), which is a short distance from contact with the product surface, e.g., 2mm
from contact. The system then awaits an open command from the mill control system
(Step 86), before signaling the servo motor to move the pinch rolls to their fully
open positions (Step 88).
If the product size has not changed (Step 74), the system then moves
the pinch rolls to the previously determined pre-touch position (Step 90). The system
then awaits the arrival of the front end at HMD-2 (Step 92), after which the current
limit for the servo motor 36 is set (Step 94), and the servo motor is energized
to rapidly move the pinch rolls 34 from their pre-touch position into contact with
the product followed by a current increase to the preset limit (Step 96). The system
then cycles through the remainder of steps 84 to 88.
It will be understood by those skilled in the art that the similar
routines are provided for pinching the tail ends of products, or when circumstances
dictate, for pinching the entire product length.
The present invention provides numerous advantages over pneumatically
actuated pinch roll units and control systems currently being employed. For example,
the fast reaction times of the servo motors 36 makes it possible to locate the HMD-2
detectors close to the pinch roll units and to pinch the product within a meter
of the head end passing through the pinch roll units. By contrast, when employing
the slower reacting pneumatically actuated systems, the hot metal detectors must
be positioned well in advance of the pinch roll units, usually before the finishing
block 10. The torque limiting capabilities of the servo motors 36 and the speed
controls of the drive motors 56 can be electronically coupled to properly balance
pinch roll torque and pinching force during product acceleration and deceleration,
thus avoiding surface marking of the product, Pre-touch positions of the pinch rolls
can be memorized and used repeatedly for the same product sizes. The electrically
driven system for effecting pinching sequences is more rigid than the conventional
pneumatically controlled systems, which, because of the compressibility of air,
suffer from uncontrollable variations in pinching force as product dimensions change.