Claims:We Claim
1. A servo mechanism (400) for a coiler (100) of a hot strip mill, said coiler (100) having a top pinch roller (110) and a bottom pinch roller (120) arranged to define a gap (130) therebetween, a pair of supports (140) arranged at ends of said top pinch roller (110) for supporting said top pinch roller (110), and a top pinch roller housing (160) mounted on each support (140), said servo mechanism (400) coupled to each end of said top pinch roller (110), and configured to displace said end of said top pinch roller (110) to adjust said gap (130), said servo mechanism (400) comprising:
a servo valve;
a servo cylinder (410) coupled to said servo valve;
a piston rod assembly having a piston rod (420) extending downwardly from said servo cylinder (410), said piston rod assembly configured to be displaced in a vertical direction, thereby displacing said top pinch roller housing (160) and said end of said top pinch roller (110);
a retract cylinder housing (430) configured to receive said piston rod (420), said retract cylinder housing (430) received in said top pinch roller housing (160); and
a lock ring (450) disposed in said retract cylinder housing (430) and mounted on said piston rod (420), said lock ring (450) extending outwardly in radial direction with respect to said piston rod (420), said lock ring (450) configured to restrict displacement of said piston rod assembly with respect to said retract cylinder housing (430).
2. The servo mechanism (400) as claimed in claim 1, wherein said piston rod (420) has a groove configured to receive said lock ring (450).
3. The servo mechanism (400) as claimed in claim 1, wherein said lock ring (450) includes two split half-rings.
4. The servo mechanism (400) as claimed in claim 1, wherein said mechanism (400) includes a lock plate (470) connected at a bottom surface of said retract cylinder housing (430) and configured to lock said piston rod assembly with said retract cylinder housing (430).
5. The servo mechanism (400) as claimed in claim 1, wherein said mechanism (400) includes a bush (480) disposed between said piston rod (420) and an inner surface of said retract cylinder housing (430).
6. The servo mechanism (400) as claimed in claim 1, wherein said retract cylinder housing (430) is secured in said top pinch roller housing (160) via a plurality of fasteners and a circular plate arranged on a top surface of said retract cylinder housing (430) and said top pinch roller housing (160).
Dated this 30th day of March, 2021.

FOR STEEL AUTHORITY OF INDIA LIMITED
By their Agent

(GIRISH VIJAYANAND SHETY)
Agent No. IN/PA/1022
KRISHNA & SAURASTRI ASSOCIATES LLP , Description:FORM 2

The Patents Act, 1970
(39 of 1970)

&

The Patents Rules, 2003

Complete Specification
[See Section 10, Rule 13]

A MODIFIED SERVO CYLINDER FOR A COILER TOP PINCH ROLL IN HOT STRIP MILL

STEEL AUTHORITY OF INDIA LIMITED, WHOSE ADDRESS IS RESEARCH AND DEVELOPMENT CENTRE FOR IRON AND STEEL, DORANDA, RANCHI – 834002, JHARKHAND, INDIA.

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

TECHNICAL FIELD OF THE INVENTION
The present invention relates to the field of servo mechanisms for coilers used in hot strip mills.
BACKGROUND OF THE INVENTION
A coiler us used in a hot strip mill to coil hot metal strips. The coiler has two pinch rollers, viz., a top pinch roller and a bottom pinch roller. The rollers are arranged to define a gap therebetween. A hot rolled metal strip is passed through the gap for coiling purposes. The rollers are independently rotated using motors and gear mechanisms. To adjust the gap between the rollers, a servo mechanism is mounted on each end of the top pinch roller. The servo mechanism has a servo cylinder, a piston rod extending downwardly form the servo cylinder, and a retract cylinder housing receiving the piston rod. The retract cylinder housing is received in a pinch roller housing mounted on each support of the top pinch roller. The piston rod is secured to the retract cylinder housing via a lock plate attached at the bottom of the retract cylinder housing. In normal mode of operation, the servo mechanism is operated simultaneously such that both ends of the top pinch roller are either lowered or raised simultaneously. In a skew mode, the servo mechanisms are operated independently, wherein either ends of the top pinch roller is lowered or raised independently. However, in skew mode, the piston rod is subjected to stresses due to uneven lowering or raising of the ends of the top pinch roller. This exerts shearing force on bolts of the lock.
Due to the extreme force, the bolts of the lock plate may fail resulting in ejection of the piston rod form the retract cylinder housing. As such, the coiler stops working. This is results in increase in machine down time and hampers the production of coiled strips. Further, the bearings of the coiler and the piston rod may get severely damaged. Replacement of the bearings or the piston rod adds to the maintenance cost.
Therefore, there is felt a need of a servo mechanism for a coiler of a hot strip mill that alleviates the aforementioned drawbacks of conventional servo mechanisms.
SUMMARY OF THE INVENTION
The present invention envisages a servo mechanism for a coiler of a hot strip mill. The coiler has a top pinch roller and a bottom pinch roller arranged to define a gap therebetween. A pair of supports is arranged at ends of the top pinch roller for supporting the top pinch roller. A top pinch roller housing is mounted on each support. The servo mechanism is coupled to each end of the top pinch roller and is configured to displace the end of the top pinch roller to adjust the gap between the top pinch roller and the bottom pinch roller. Each servo mechanism comprising a servo valve, a servo cylinder, a piston rod assembly, a retract cylinder housing, a lock ring, and a lock plate. The servo cylinder is coupled to the servo valve. The piston rod assembly has a piston rod extending downwardly from the servo cylinder and a piston extending downwardly from a bottom end of the piston rod. The piston rod assembly is configured to be displaced in a vertical direction, thereby displacing the pinch roller housing and the end of the pinch roller. The retract cylinder housing is configured to receive the piston rod and the piston. The retract cylinder housing is received in the top pinch roller housing. The lock ring is disposed in the retract cylinder housing and mounted on the piston rod. The lock ring extends outwardly in radial direction with respect to the piston rod. The lock ring is configured to restrict displacement of the piston rod assembly with respect to the retract cylinder housing.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
A servo mechanism for a coiler of a hot strip mill, of the present invention will be described with reference to accompanying drawings, in which:
Figure 1 illustrates a schematic view of a coiler of a hot strip mill;
Figure 2 illustrates a schematic view of conventional servo mechanism; and
Figure 3 illustrates a schematic view of a servo mechanism, in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Although specific terms are used in the following description for sake of clarity, these terms are intended to refer only to particular structure of the invention selected for illustration in the drawings, and are not intended to define or limit the scope of the invention.
References in the specification to “one embodiment” or “an embodiment” mean that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.
The present invention provides a servo mechanism for a coiler of a hot strip mill.
An arrangement of a coiler is shown in figure 1. A coiler 100 comprises a top pinch roller 110 and a bottom pinch roller 120. The rollers 110, 120 are arranged so that a gap 130 is defined between the top pinch roller 110 and the bottom pinch roller 120. A hot metal strip is passed through the gap 130 for coiling of the metal strip. A pair of supports 140 is arranged at the ends of the top pinch roller 110 for rotatably supporting the top pinch roller 110. Bearings are used between the shaft of the top pinch roller 110 and the supports 140 for facilitating rotation of the top pinch roller 110. A pair of supports 150 is arranged at the ends of the bottom pinch roller 120 for rotatably supporting the bottom pinch roller 120. The rollers 110, 120 are rotated using a motor and a gear mechanism. The rollers 110, 120 can be rotated synchronously or independently. A top pinch roller housing 160 is mounted on each support 140.
A servo mechanism 200 is coupled to each end of the top pinch roller 110, and is configured displace the end of the top pinch roller 110 to adjust the gap 130 between the top pinch roller 110 and the bottom pinch roller 120.
A conventional servo mechanism 300 is shown in figure 2. The mechanism 300 includes a servo valve, a servo cylinder housing 310, a piston rod 320 extending downwardly from the servo cylinder housing 310, a retract cylinder housing 330 for receiving the piston rod 320. The retract cylinder housing 330 is received in the pinch roller housing 160. The piston rod 320 is secured to the retract cylinder housing 330 using a lock plate 340. The lock plate 340 is fastened to the piston rod 320 using fasteners.
In skew mode operation, uneven forces are applied on the piston rod 320 and the lock plate 340 which results in failure of the fasteners of the lock plate 340. Due to this, the piston rod 320 may come out of the retract cylinder housing 330 and cause failure of the coiler 100.
The present invention envisages a servo mechanism that alleviates the aforementioned drawbacks of conventional servo mechanisms.
The servo mechanism of the present invention is now described with reference to figure 3.
Referring to figure 3, a servo mechanism 400 in accordance with an embodiment of the present invention is shown.
The mechanism 400 is coupled to each end of the top pinch roller 110 and is configured to displace the end of the top pinch roller 110 to adjust the gap 130 between the top pinch roller 110 and the bottom pinch roller 120.
The mechanism 400 comprises a servo valve and a servo cylinder 410 coupled to the servo valve. The servo valve controls the amount of hydraulic fluid entering into the servo cylinder 410. The servo valve is a computerized control valve.
The mechanism 400 comprises a piston rod assembly having a piston rod 420 extending downwardly from the servo cylinder 410. The piston rod assembly is configured to be displaced in a vertical direction, thereby displacing the pinch roller housing 160 and the end of the top pinch roller 110. The servo valve controls the flow of the hydraulic fluid in the servo cylinder 410 to control the displacement of the piston rod 420.
The mechanism 400 comprises a retract cylinder housing 430 configured to receive the piston rod 420. The retract cylinder housing 430 is received in the top pinch roller housing 160. The retract cylinder housing 430 is secured in the top pinch roller housing 160 via a plurality of fasteners and a circular plate arranged on a top surface of the retract cylinder housing 430 and the top pinch roller housing 160.
In an embodiment, the retract cylinder housing 430 includes a piston 440 circumscribing the piton rod 420 as shown in figure 3.
The mechanism 400 comprises a lock ring 450 disposed in the retract cylinder housing 430. The lock ring 450 is mounted on the piston rod 420. More specifically, the lock ring 450 is mounted on a portion of the piston rod 420 within the retract cylinder housing 430. The shape and size of the lock ring 450 is such that the lock ring 450 extends outwardly in radial direction with respect to the piston rod 420. The lock ring 450 is configured to restrict displacement of the piston rod 420 assembly with respect to the retract cylinder housing 430. In an embodiment, the piston rod 420 has a groove configured thereon to receive the lock ring 450. The lock ring 450 fits in the groove and extends out of the groove in radial direction of the piston rod 420. In an embodiment, wherein the retract cylinder housing 430 includes the piston 440, the groove is configured on the piston rod 420 below the piston 440.
The outer diameter of the lock ring 450 is more than the outer diameter of the piston rod 420. In case of the piston 440, the outer diameter of the lock ring 450 is equal to the outer diameter of the piston 440. The inner diameter of the lock ring 450 is equal to the diameter of the piston rod 420 in the groove portion.
In an embodiment, the lock ring 450 includes two split half rings. The half rings are easy to install on the piston rod 420.
To mount the lock ring 450, initially, the piston rod 420 is separated from the retract cylinder housing 430. Further, the groove is configured on the piston rod 420 at appropriate location. In case the retract cylinder housing 430 has the piston 440 in it, the groove is configured on the portion of the piston rod 420 below the piston 440. In case the retract cylinder housing 430 does not include the piston 440, the groove is configured on the piston rod 420 just below a covering plate 460 of the retract cylinder housing 430 such that the lock ring 450 abuts the bottom surface of the covering plate 460. Two half-rings are then mounted in the groove of the piston rod 420. Further, the assembly of the piston rod 420 and the lock ring 450 is disposed in the retract cylinder housing 430. The covering plate 460 is then fastened to the retract cylinder housing 430 such that the movement of the piston rod 420 is restricted.
The mechanism 400 comprises a lock plate 470 connected at a bottom surface of the retract cylinder housing 430 and configured to lock the piston rod assembly with the retract cylinder housing 430.
A bush 480 is disposed between the piston rod 420 and an inner surface of the retract cylinder housing 430.
In an operative configuration, a hot metal strip is passed through the gap 130 between the top pinch roller 110 and the bottom pinch roller 120 for coiling. The servo mechanism 400 is actuated to adjust the gap 130. The servo valve controls the flow of the hydraulic fluid into the servo cylinder 410 to displace the piston rod 420. The piston rod 420 displaces the assembly of the retract cylinder housing 430, the top pinch roller housing 160, the support 140, and the end of the top pinch roller 110 to which the servo mechanism 400 is attached. During the loading, the lock ring 450 prevents the displacement of the piston rod 420 within the retract cylinder housing 430 as the lock ring 450 is restricted against the piston 440 or the covering plate 460. Even if the bolts in the lock plate 340 fails, the lock ring 450 prevents the piston rod 420 from ejecting out of the retract cylinder housing 430.
The servo mechanism 400 prevents the down time or stoppage of the coiler 100. Thus, efficiency of the coiler and thereby production of coiled metal strips is improved. Further, the servo mechanism 400 also prevents the failure of the pinch roller bearings and the piston rod resulting in savings in maintenance cost and overall operational cost.
The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others, skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.
LIST OF REFERENCE NUMERALS
100 – Coiler
110 – Top pinch roller
120 – Bottom pinch roller
130 – Gap
140 – Support for top pinch roller
150 – Support for bottom pinch roller
160 – Top pinch roller housing
200 – Servo mechanism
300 – Conventional servo mechanism
310 – Servo cylinder housing
320 – Piston rod
330 – Retract cylinder housing
340 – Lock plate
400 – Servo mechanism
410 – Servo cylinder
420 – Piston rod
430 – Retract cylinder housing
440 – Piston
450 – Lock ring
460 – Covering plate
470 – Lock plate
480 – Bush