Hot mill hydraulic direct roll drive

Abstract

 A rolling mill capable of forming a hot, continuously cast metallic strand into a strip with a large bite and with one pass uses only two small diameter rolls, each mounted for rotation in a pair of chock blocks and each having a comparatively narrow, enlarged diameter working portion. An hydraulic motor that produces a large torque at a low rotational speed with good control rotates each roll. The motors are coupled to their associated rolls directly.

Description

[0001] This invention relates in general to a rolling mill for strand and strip metal products. More specifically, it relates to a hydraulic drive system for the rolls of a two high, small roll diameter mill where the drive system provides a high torque at a low speed to produce a large reduction without slippage.

[0002] A wide variety of mill stands are known for hot and cold rolling metals. Where there is a large separating force between the working rolls, whether due to a large reduction and/or to the nature of the material being rolled, there are a number of inherent design problems. One is that the rolls work against a separation force that is sufficiently large to bend or even to deform the rolls depending on the diameter, length and material of the roll as well as the nature of the material, its temperature, and the reduction ratio. The diameter of the roll is also important because for a given "bite" (thickness reduction of the product entering the mill) the "bite ratio" (roll diameter over bite) is an important factor in determining when slippage will occur between the rolls and the product. As low a ratio as possible is desired to minimize roll size (and therefore roll cost) and/or maximize bite. Typical bite ratios for mills currently in use are in the range of 50:1 to 100:1. Another consideration is that larger diameter rolls produce a greater speed, however, the attendant separation force is also larger. Ideally, the roll design should produce the desired spread with the minimal separation force. Heretofore, in order to deal with large separation forces (e.g., in excess of 45,359 kg/stand (100,000 lbs/stand), it has been necessary to use a four high mill, that is, one with two working rolls and two "back up" rolls that provide mechanical support for the working rolls. Such mills are also characterised by a quite heavy, expensive frame that can accommodate all four rolls and resist the large forces generated by the rolling. U.S.-A-3,103,138; U.S.-A-3,391,557; U.S.-A-3,550,413 and U.S.-A-3,568,484 are exemplary of such four high mill stands. While certain mills produce a high reduction by passing the product through the mill multiple times, this is not possible in a continuous, on-line casting and rolling operation. (For example, rolling operations with twenty passes are not uncommon).

[0003] The torque and speed of rotation of the rolls are important in producing a high reduction without slippage. More specifically, in order to hot roll copper and brass strand with a large bite (e.g., in excess of 2.54 cms (1 inch) and a low bite ratio (e.g., 7:1), the drive system for the working rolls must have a comparatively high torque (typically in excess of 1356 Nm (1,000 ft-lbs.) to achieve a large bite and a comparatively low speed (typically less than 400 rpm) to couple the rolling mill speed to that of the caster. In addition, it is necessary to vary these parameters depending on the particular product being run and other factors such as the roll diameter. Heretofore mill stands requiring a variable high torque at a low speed have used electric motors with a reducing gear train. This arrangement provides the required operating characteristics, but it is a costly system that takes up a large amount of space compared to the mill itself. Moreover, applicant is not aware of any commercially available direct drive trains for rolling mills that can produce thousands of Nm (ft-lbs) of torque. Further, known drive trains with many components are not "stiff". As a result, the drive system is not closely responsive to servo changes in the drive input. Indeed no known rolling mill is designed to utilise a highly responsive direct drive. The drive train of the present system is a directly coupled hydrostatic drive commonly used in large earth moving equipment.

[0004] Torque requirements are also interrelated with other design factors such as roll diameter and anticipated separation forces and thus, size and cost of the mill, the gauge of the rolled product and friction. Heretofore, the lower rolling force of small diameter rolls and their ability to roll thin gauge products has generally been balanced against offsetting considerations through the .use of back-up rolls. If two rolls are used where substantial separation forces are produced, prior art mills have used costly, massive rolls with very large diameters, e.g., 61 to 91 cm (two to three feet). Heretofore, high reduction rolling using unsupported (two high) small diameter rolls (less than at least 30.5 cm (one foot) in diameter) has not been commercially practical. U.S.-A-4,218,907 describes a two high mill which provides operating characteristics only achievable previously with four high mills. However, this two high mill requires a special bearing assembly which supports the rolls over all or most of their length.

[0005] It is therefore a principal object of this invention to provide a drive for the working rolls of a rolling mill that produces a high quality narrow strip from a continuously cast hot metallic strand where the mill is only two high and uses small diameter rolls yet is capable of producing a high reduction with precisely controlled dimensions and profile of the rolled strip product. Another significant object of the invention is to provide such a drive characterised by a variable high torque, low speed drive for the rolls that does not require an electric motor or reducing gears.

[0006] Yet another object of the invention is to provide a drive that is compact and relatively cost effective as compared to known electric drives.

[0007] Still another object of the invention is to provide a drive that is readily engaged to or disengaged from the working rolls to facilitate roll changes.

[0008] A drive system according to the present invention is particularly adapted to use in conjunction with a hot .rolling mill that receives continuously cast, hot metallic strand, particularly strands of copper and copper alloys, and produces a high quality narrow strip with precisely controlled dimensions, profile and camber and with a high reduction. The mill has only two working rolls with a comparatively small diameter, each mounted for rotation in chock blocks. One roll is fixed and the other roll and its chock blocks are movable vertically under the control of a pair of hydraulic cylinders to vary the gap between the rolls. For copper and brass, this mill can produce a bite in excess of 2.54 cm (one inch) and approaching 5.1 cm (two inches) and bite ratios of as low as 5:1 without slippage.

[0009] Each roll is driven independently by an hydraulic motor that can develop a large variable torque at a low rotational speed. There is a direct coupling between the motor and the roll. The rolls and the motor preferably have mating couplings that bolt to one another. The motors are preferably of the radial piston type with a swashplate in the pump power supply to adjust the speed. In the preferred form, the rolls also propel the strand or strip.

[0010] An embodiment of the invention will now be described by way of example, reference being made to the accompanying drawings, in which:-

Fig. 1 is a highly simplified top plan view of a tandem hot rolling mill operation according to the present invention;

Fig. 2 is a more detailed top plan view, with portion broken away, of the three mill stands shown in Fig. 1;

Fig. 3 is a view in side elevation of the mill stands shown in Fig. 2;

Fig. 4 is a top plan view of the first mill stand shown in Figs. 1-3 with frame portions, rotary brushes, entrance and exit guides, and gauges removed for clarity;

Fig. 5 is a view in front elevation of the mill stand shown in Fig. 4;

Fig. 6 is a detailed view in front elevation of the rolls and their associated chock blocks shown in Figs. 4 and 5 with the right lower chock block shown in vertical section;

Fig. 7 is a view in side elevation of the chock blocks shown in Fig. 6; and

Fig. 8 is a highly simplified view in side elevation showing the action of the rolls of the first mill stand to effect a very high reduction of an incoming cast rod into a narrow strip.

[0011] Fig. 1 shows a tandem hot rolling line 12 that receives a continuously cast metallic strand 14 and reduces it to a narrow strip 16 of accurately controlled width and gauge. While this line can hot roll a wide variety of metals and strands having a variety of cross-sectional shapes, it will be described herein with respect to its preferred use, the continuous hot rolling of copper and copper alloy rod having a circular cross section into a narrow strip. This rod is preferably supplied directly from a continuous casting operation of the type described in U.S.-A-4,211,270 and U.S.-A-4,301,857, the disclosures of which are incorporated herein by reference. This rod leaves the caster red hot and advancing at speeds that are usually in the range of 76.2 to 762 cm/min (cpm) (30 to 300 inches per minute (ipm)) depending on the diameter of the rod being cast and the desired production line speed.

[0012] The line 12 includes first, second and third hot rolling mill stands 18, 20 and 22, respectively. Each stand is preceded by a gas-fired reheating furnace 24 that raises the temperature of the strand 14 or strip 16 to the desired rolling temperature, typically 760°C (1400°F). The separation between adjacent mill stands is sufficiently short that the strip will not cool substantially (or require excessively long reheating furnaces), but long enough that the speed and gap controls on each stand are able to adjust without adversely affecting the strip, e.g., causing unstable plastic flow. After the strip leaves the third stand 22 it is cooled in a closely coupled quench tank 26 to control oxidation. A gauge area including a laser width gauge 28 and an X-ray thickness gauge 30 follow the quench tank. Each of these instruments generates a measurement signal that is used to control the operation of the line 12. Width gauges 28 are also mounted at the exit of the last mill stand to provide an immediate measure of the width of the strip 16 as it leaves the mill. Each mill also preferably has a two- colour infrared pyrometer (not shown) mounted to measure the temperature of the strip as it enters the mill. The line terminates with a shear 36 and a spooler 38. The shear is used primarily to remove portions of strip that do not meet set tolerances, for example, the initial portion of a strip when the line starts up before the rolls have fully adjusted to a steady state operating condition. The spooler 38 collects the strip 16 in an even, level wound coil on a core.

[0013] With particular reference to Figs. 2-5, each rolling mill stand 18, 20 and 22 has substantially the same construction. (Like parts are identified with the same reference number, but common parts associated specifically with the second mill are noted with a prime (') and parts associated with the third mill are noted with a double prime ("). Unprimed numbers refer to parts of the first mill stands which will be described in detail.) The mill stand 18 is organised around a frame assembly 40 formed primarily of steel I-beams in a generally rectangular array around the passline 16a of the strip 16. Two rolls 42,42 are each mounted in associated chock blocks 44,44 for rotation. An hydraulic motor 46 that receives a supply of pressurized hydraulic fluid from an hydraulic power supply 47 drives each of the rolls 42,42. Hydraulic cylinders 48,48 acting through rods 48a,48a and the upper chock blocks 44,44 position the upper roll and apply the necessary downward force to offset the separation force generated by rolling the strip. The cylinders 48 are capable of operating with applied fluid pressures of 246 _kg/cm² (3,500 psi) to generate downward forces of 31752 kg (70,000 lbs) per cylinder or 63500 kg (140,000 lbs.) per stand. The cylinders also preferably include a standard, commercial distance measuring device which can measure vertical movement of the rods 48a. An internal ultrasonic device with a resolution of 0.00254 mm (0.0001 inch) is preferred. The cylinders 48,48 are each controlled independently to vary the profile of the strip 16.

[0014] The frame has a base member 40a formed of a pair of beams 40 a(1) aligned generally parallel to the strip and a pair of cross beams 40a(2) aligned generally transverse to the strip. The beams 40a(1) are located generally under the hydraulic motors 46,46 and the beams 40a(2) support the overlying components of the mill, but are spaced to allow clearance for the rolls and their mountings. The cross beams 40a(2) support a movable motor mounting plate 50 and a fixed motor mounting plate 52. The movable plate 50 is supported on a pneumatic cylinder 54 that counterbalances the motor so that there are approximately equal loads on the cylinders 48,48. Upper and lower C-shaped mounting brackets 56 and 58 are secured to the inner face of the plate 50. Each of these brackets supports a vertically oriented slide shaft 60 journalled in an associated pillow block 62 which in turn is mounted on a vertical side frame member 40b. The slide shafts guide the vertical movement of the upper motor. Since the motor mounting plate 52 is fixed to the beams 40a(2),40a(2), the associated hydraulic motor 46 mounted on its outer face and the lower roll 42 driven by this motor do not move vertically during operation (except for a very small deflection due to the separation forces). A spline coupling 80 between the motor 46 and its associated roll 42 is designed to accommodate this deflection.

[0015] With reference principally to Fig. 6, the rolls 42 of the present invention are characterised by a relatively narrow central working portion 42a having an enlarged diameter as compared to neck portions 42b,42b journalled in bearing assemblies 70 mounted in each chock block 44. However, the diameter of even this "enlarged" working portion 42a is small, less than 30.5 cm (a foot) and typically 12.7 to 17.8 cm (five to seven inches), as compared to conventional two high rolls used in "break down" mills where there is a substantial reduction in the thickness of the product being rolled and there are large separation forces.

[0016] A significant feature of the present invention is that each roll 42 is driven independently by one of the hydraulic motors 46. There is therefore no gearing or other power transmission coupling which is usually employed to transmit power from one driven roll to another slave roll or rolls. Another feature is that the motors are coupled directly to the rolls through the spline coupling assembly 80 including a "roll half" 80a found integrally with one end of each roll and mating "motor half" 80b mounted on the drive shaft 46a of the motor. To connect the motor to the roll, the coupling halves 80a and 80b are simply mated and bolted to one another. This coupling avoids transmission power losses and greatly reduces the bulk, complexity and cost of the roll drive. It also allows rolls to be changed easily. Using this direct drive, the "stiffness" of the drive train is substantially increased. This makes both rolls 42,42 more responsive to servo changes in the drive. Also, the comparatively few components in the roll drive produces drives for the two rolls 42,42 that are more closely matched in stiffness than conventional prior art drives.

[0017] This coupling is possible due to the use of hydraulic motors that provide a high torque (in excess of 1356 Nm (1,000 ft.-lbs.)) at a low rpm (less than 400, and often less than 100). The hydraulic motors 46,46 are preferably the radial piston type with adjustment in the speed output provided by a swashplate in the hydraulic power supply 47. With this arrangement, the pressure across the motor can be varied to maintain the rolled strip at a constant speed. This drive system provides a precise and responsive control over the power supplied to the rolls 42,42 to produce a high torque rotation at a controlled uniform speed. For the first mill stand 18, the motors 46,46 preferably operate at 263.6 kg/cm² (3,750 psi) pressure (281 kg/em² (4,000 psi,) peak) to produce a required total torque of 16948 Nm (12,500 ft-lbs) (23524 Nm (17,350 ft-lbs,) peak) at speeds less than 50 rpm. The reduction and spreading at the second and third stands are less and therefore they have lower requirements. Since the strip is moving faster after each reduction, the speed requirement of the motors goes up in each successive millstand. The second stand 20 preferably utilises motors 46',46' of the same type as the motors 46,46 but ones which produce a required total output torque of 8813 Nm (6,500 ft-lbs) (11199 Nm (8,260 ft-lbs,) peak). The motors 46",46" of the third mill stand preferably have a required total output torque of 3390 Nm (2,500 ft-lbs) (3525 Nm (2,600 ft-lbs,) peak).

[0018] In operation the line 12 continuously hot rolls a metallic strand 14 into a strip 16 (Fig. 8) having a highly uniform configuration and a recrystallised grain pattern. The line preferably operates to roll copper or copper alloy rod into narrow strips. In addition to rolling the strand or strip, each mill, and in particular the first mill 18, act as drives for the strand or strip.

[0019] There has been described a novel drive system particularly useful in a two high hot rolling mill with small diameter rolls that can produce a narrow strip of copper or copper alloys from a continuously cast strand. The rolling is characterised by a large bite with only one pass in each mill stand. The drive system, utilising hydraulic motors coupled directly to the associated rolls, produces a high torque at a low rotational speed and with good control. Also, this drive system is compact, less costly than conventional electric motor drives and facilitates the rapid disengagement of the rolls from the drive to facilitate their replacement.

[0020] While the invention has been described with reference to its preferred embodiment, it will be understood that various variations and modifications will occur to those skilled in the art from the foregoing detailed description and the accompanying drawings. Such variations and modifications are intended to fall within the scope of the appended claims.

Claims

1. In a hot rolling mill that includes a frame, a pair of small diameter rolls rotatably mounted in the frame, and means urging the rolls toward one another to produce a large reduction of a metallic strand into a narrow strip, the improvement comprising drive means for rotating said rolls about their longitudinal axes comprising

an hydraulic motor associated with each of said rolls that produces a high torque output at a controlled uniform speed, and

means for directly coupling said hydraulic motors with the associated one of said rolls.

2. Improved drive means according to claim 1 characterised in that said hydraulic motors are radial piston motors and include an hydraulic power supply with an adjustable swashplate to control said rotation.

3. Improved drive means according to claim 1 or 2 characterised in that said high torque is in excess of 1356 Nm (1,000 ft/lbs) and said controlled uniform speed is less than 400 rpm.

4. Improved drive means according to claim 1, 2 or 3 characterised in that said direct coupling means comprises a coupling secured to each said drive shaft,

a mating coupling secured to one end of each said roll, and

means for securing said couplings in said mating relationship.

Drawing