Expansible chamber devices – With linkage or transmission having relatively movable members
Reexamination Certificate
2001-06-15
2003-11-04
Look, Edward K. (Department: 3745)
Expansible chamber devices
With linkage or transmission having relatively movable members
C403S079000
Reexamination Certificate
active
06640691
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a bearing system that accommodates angular movements occurring during the operation of a linear actuator, and more particularly to such a bearing system utilizing annular, non-spherical bearing surfaces, allowing motion about three mutually perpendicular axes during the operation of a linear actuator in a lifting structure for a ladle that contains liquid steel in a continuous casting installation.
2. Background of Invention
In the continuous casting of steel, molten steel is transferred to a continuous caster by ladles weighing typically from 200 to 400 tons, which includes the molten steel. The temperature of the molten steel is critical to the casting process, and so it is imperative that a ladle is tapped for the casting process according to a schedule established to prevent the cooling of the molten steel below a desired casting temperature and to avoid the need to return the molten steel to the steel making furnace for reprocessing and the consequential stoppage of the casting process. An unplanned stoppage of the casting process not only results in a consequential production loss but also in additional operating costs to restart the continuous casting process. The complex process of continuous casting begins at the caster, where molten steel flows from a ladle into a tundish, and then into one or more continuous casting molds. Maintaining a steady flow of molten steel into the continuous casting mold is essential, so as not to disturb the delicate balance of cooling, containment of a liquid steel core in the newly formed solid shell, and casting speed required for proper solidification. The volume of liquid in the tundish is selected to maintain an operating level unaffected by minor fluctuations in the liquid flows formed by the floating out of impurities of slag and the flow of molten steel into the mold. Another factor affecting the volume of liquid steel contained in the tundish is the need to accommodate a momentary interruption of the flow of molten steel from one ladle to allow the sequencing of ladles to the caster and reestablish a flow of molten steel from a second ladle.
A typical sequencing of ladles is started by first increasing the flow of molten steel from a first ladle slightly before the ladle is empty to raise the liquid steel level in the tundish slightly above an operating level. When the flow from the ladle changes from molten steel to slag, the slag flow is detected and a slidegate is immediately closed to stop the flow of slag. A pouring tube is disconnected from the ladle nozzle and the ladle is moved away from the casting position. At the same time a second ladle is brought into cast position and a pouring tube is connected to the ladle nozzle of the second ladle whereupon opening of the slidegate initiates the flow of steel into the tundish. The entire sequence, from the stoppage of the flow of molten steel in one ladle to the establishment of a flow of molten steel in a replacement ladle, must be completed before the liquid level in the tundish has been depleted to a certain critical level, below which the quality of the cast steel strand is adversely affected. The sequence of changing the supply of molten steel from one ladle to another is normally accomplished within a very safe time margin. There are instances where reliance on the safe time margin is necessary such as, for example, when the ladle nozzle of the second ladle fails to open due to the freezing of steel in the pouring channel of the ladle exit port. It is a customary practice to use an oxygen lance, which is consumed in the process to remelt the solidified steel in the ladle exit port and start the flow of steel. The pouring channel is sometimes blocked by a large column of solidified steel, in which event it is necessary to raise the ladle to a greater elevation above the tundish to allow greater access to the ladle exit port for the continuous feeding of an elongated oxygen lance which is consumed while remelting the column of solidified steel.
To allow more time for the variable time-consuming use of the oxygen lance, designers have tried to decrease the time needed for other functions such handling of the pouring tube and, in particular, for movement of the ladles. Two typical devices employed in the efficient exchange of ladles are a ladle car and a ladle turret, both of which may employ an actuator for lifting a ladle. A ladle used to supply steel to the tundish of a continuous caster normally has two separate structures for supporting the ladle. The first structure is a pair of trunnions extending from the ladle along a horizontal axis. They are located above the center of gravity of the ladle and are engaged by the J-hooks of a hot-metal crane to transport the ladle to the caster. The second structure is a pair of elongated horizontal seats located below the trunnions. The seats are used for supporting the ladle on a ladle car, ladle turret or stationary stand. The transfer of a ladle from the hot metal crane to a ladle car, ladle turret or stationary stand normally occurs with impact loading on the elements of the support system in the ladle car, ladle turret or stationary stand. A lifting mechanism on the ladle car or turret normally includes means to stabilize the ladle supports and thus also the ladle against tilting during the lifting travel. In addition to sustaining the vertical loading, the lifting mechanism also receives lateral loading due to incidents of positing and negative accelerations due to the movements of the ladle. The vertical and lateral loads on the lifting mechanism produce critical structural deflections that must be considered in the design of the bearing elements of the lifting mechanism.
Electro-mechanical lifting of a ladle on a ladle car, ladle turret or stationary stand has been widely used in the past and provides that each of the two ladle seats is supported on a lifting bridge. The lifting bridges are supported at each end on screw jacks. The four screw jacks are synchronized and driven by universal spindle shafts and gearboxes by one electric motor. The electromechanical lifting system is very reliable for a short lifting distance at a slow speed, but to move a ladle over an extended lifting distance at a faster speed requires heavy-duty ball screw jacks, which are not commercially available. The special nature of the ball screw jacks is very costly in terms of both initial equipment and maintenance. The use of hydraulically powered actuators for lifting a ladle has been employed as a direct replacement of the electromechanical system. The overall structure of the mechanism is very similar and essentially involves replacing each screw jack and associated drive components with a hydraulic cylinder. Synchronization of the four hydraulic cylinders when controlled within the hydraulic system is susceptible to wear of system components and leakage of hydraulic fluid. An improved control system includes the use of an electronic feedback and position controls, but integration of the control system is costly and requires adherence to a strict maintenance schedule.
A third method of lifting a ladle on a car or turret is a combination of hydraulic actuation with mechanical synchronization. This method is chosen for the purpose of illustrating and describing the present invention hereinafter. The mechanical synchronization is accomplished by the use of two parallelogram linkages, one positioned in each of two vertical and parallel planes containing support points for the elongated horizontal seats of the ladle. A rigid frame is used to tie the upper links of the two parallelogram linkages together so that a single hydraulic cylinder positioned near the center of the rigid frame provides the lifting force. One end of each upper link is supported at a stationary point by a bearing on each side of the vertical support structure of the ladle car or turret. The lower link of each parallelogram linkage serves to stabi
Leslie Michael
Look Edward K.
Poff Clifford A.
SMS Demag Inc.
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