Metal deforming – By use of roller or roller-like tool-element – Comprising tool movable relative to stationary work-portion...
Reexamination Certificate
1999-12-23
2001-07-10
Butler, Rodney A. (Department: 3725)
Metal deforming
By use of roller or roller-like tool-element
Comprising tool movable relative to stationary work-portion...
Reexamination Certificate
active
06257040
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for controlling a hydraulic rotary and feed drive for rotating and feeding tubes in a cold pilger rolling mill for producing tubes in which a rolling stand of the cold pilger rolling mill moves back and forth in the rolling direction via a crank drive, the rolls of the rolling stand being of a tapered design and rolling over the rolling stock with an alternating sense of rotation as the rolling stand moves back and forth, the rolling stand occasionally releasing the tube so that the tube can be rotated and fed to a new position by the hydraulic rotary and feed drive as a function of the position of the crankshaft of the rolling stand, and the rotation and feeding of the tube being performed by hydraulic motors controlled by a pressure medium and assigned to the rotary and feed drive members acting on the tube.
2. Description of the Related Art
In the 1960s, movements of rotary and feed drives for a tube during the execution of a cold pilger rolling method were represented hydromechanically. That is, cam plates were used to move control pistons of the valves of hydraulic motors. This mechanically complicated type of valve drive led to frequent failures. Furthermore, frequent pipe line breakages occurred because of very hard braking ramps.
In the cold pilger rolling mills of the 1990s, a very complicated servo-hydraulic path control has been used to track the rotary and feed movement otherwise produced purely mechanically with cam plate drives. This system operates reliably but has disadvantages with regard to production costs and maintenance. For example, the servo valves used in these systems are specialized products and therefore have long delivery times. Accordingly, when one of these valves becomes inoperable and requires replacement in the case of damage, the cold pilger rolling mill is inoperable or at least not optimally operable until the new valve can be delivered. To alleviate this concern, the servo valves may be stored as spare parts. However, the servo valves require regular cleaning of preservatives and renewing of the preservatives to maintain operability. Accordingly, a high maintenance cost is associated with storing the valves.
In addition, the complicated control path of these drives has the effect that it is difficult to locate faults when they occur. Well trained experts who can clarify whether there is a malfunction in the servo hydraulics, in the control or in the mechanism are required to trouble shoot the faults. Such highly qualified personnel are not available in many mills and must be summoned from, for example, a regional service center.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide a method for controlling a rotary and feed drive for a cold pilger rolling mill that is reliable, maintenance-friendly and cost-effective.
To achieve the object, it is proposed according to the invention that a control method according to an embodiment of the invention includes controlling a pressure medium feed for each hydraulic motor in a rotary and feed drive for a cold pilger rolling mill by a proportional valve which is opened for a time interval proportional to a length of a path required for the drive member to be moved by the hydraulic motor.
The control according to the invention is performed using a logic which is easy to understand and implemented with simple components. The complicated path control of the prior art is replaced by stipulating a time interval during which a control valve must remain open to effect a corresponding amount of movement. This system is a cost-effective solution for the existing problem in that there is a low maintenance outlay and no exceptional maintenance staff demands are required.
In a refined embodiment of the invention, the movement executed by each drive member or hydraulic motor is measured and compared with a stored desired value. The time intervals for the valve opening are then corrected in response to any deviation determined between the measured and the desired values.
The reliability and accuracy achievable by the control system according to the present invention allow the simple control system to operate a cold pilger rolling mill of the generic type. The cold pilger rolling mill may be operated with a simple control loop, without the demanding control requirement of the prior art systems. In addition, faults in the system are easily located because the previously complicated path control of the servo valves is eliminated.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.
REFERENCES:
patent: 4037444 (1977-07-01), Ledebur et al.
patent: 4562713 (1986-01-01), Kondoh
patent: 5419173 (1995-05-01), Baensch et al.
patent: 5921128 (1999-07-01), Stinnertz et al.
Baensch Michael
Ernhardt Wolfgang
Gromada Bernhard
Holler Ernst
Mattes Horst
Butler Rodney A.
Cohen & Pontani, Lieberman & Pavane
SMS Demag AG
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