US3025579A

US3025579A - Continuous casting of metals

Info

Publication number: US3025579A
Application number: US820744A
Authority: US
Inventors: Littlewood Geoffrey
Original assignee: British Iron and Steel Research Association BISRA
Current assignee: British Iron and Steel Research Association BISRA
Priority date: 1958-06-17
Filing date: 1959-06-16
Publication date: 1962-03-20
Anticipated expiration: 1979-03-20

Description

March 20, 1962 INVENTOR.

Geoffrey Litflewood ATTO RNEY United States Patent Ofifice 3,025,579 Patented Mar. 20, 1962 3,025,579 CONTINUOUS CASTING OF METALS Geoffrey iiittlewood, Sheffield, England, assignor to The British iron and Steel Research Association, London,

England Filed June 16, 1959, Ser. No. 820,744 Claims priority, application Great Britain June 17, 1958 1 Claim. ((11. 22--57.2)

This invention relates to improvements in continuous casting apparatus.

US. Patent 2,815,551 describes a system of moving the mold used for continuously casting steel in such a manner so as to prevent or minimize the effects of friction between the mold and the ingot. In this specification the mold is water cooled and open at both ends and is used to solidify or partly solidify the liquid metal which is poured in at one end and withdrawn as a solid or partly solidified casting or ingot at the other end.

Frictional forces acting at or near the meniscus level in the mold often cause transverse tears in the ingot skin, and said patent describes several methods of overcoming this tearing. One of these methods consists of supporting the mold on springs, so that when the ingot adheres to the mold wall, the mold is moved downwardly with the ingot and against the restoring force of the springs. When the mold has travelled a short distance, a force is exerted on the mold to move the-mold in the direction of ingot withdrawal at a speed in excess of that of the ingot, so that the friction causing the sticking is overcome by compressing the ingot skin, so inhibiting transverse ruptures. This force is produced by mechanical or pneumatic means.

In the present application the compressive releasing force is applied by hydraulic means. Hydraulic means are preferred because they can produce a superimposed mold movement of uniform speed and almost instantaneous acceleration, and thereby fully inhibit transverse ruptures of the ingot skin.

In accordance with the present invention, apparatus for preventing tearing in ingots being cast by continuous casting molds comprises a hydraulic system regulated by a control system which causes operation of the hydraulic system when sticking occurs, to move the mold faster than, and in the same direction as, the withdrawal of the ingot, and springs or like means being arranged, when permitted by the control system, to act upon the mold to return the mold to its original position after the mold has passed through a predetermined distance.

The invention will be more readily understood by way of example from the following description, reference being made to the accompanying drawing which is a part sectional and part diagrammatical view of the apparatus.

A stream of molten metal, as indicated at 11, is poured into the open upper end of a water cooled mold 13 from suitable molten metal delivery means (not shown) with the casting or ingot 12 formed in the mold withdrawn downwardly from the open lower end thereof by a withdrawal mechanism (not shown). The rate of molten metal delivery to and the rate of ingot withdrawal from the continuous casting mold 13 are coordinated for the proper solidification of the molten metal.

A platform 14 is attached to the mold 13 and is connected at each end to a hydraulic means for lowering the platform 14 and mold 13 when sticking of the ingot occurs. Only one such means is shown in the drawing and, as there illustrated, comprises a piston rod 15 secured to the platform 14 and attached to a piston 16 located in a cylinder 17 which contains a spring 18 and a fluid 19, acting on opposite sides of the piston 16. The fluid 19 is continuously pumped into the cylinder 17 by a pump 22 from a storage tank 27 through a metering valve 23 in a delivery tube 24 and is discharged through an electromagnetic valve 25 in a second delivery tube 26 to a storage tank 27, the latter tube 26 being of larger bore than the tube 24. The piston 16 is mounted on the spring 18, thereby supporting the mold 13.

Above and below the platform are two spaced limit switches, such as micro-switches 2S and 29 respectively. Switch 28, while operated by contact with the platform 14 prevents the valve 25 from closing, but on becoming inoperative through downward movement of the platform 14 (breaking contact with switch 28) causes the valve 25 to close, resulting in an immediate build up of pressure until the switch 29 is contacted by the platform 14 moving downwardly and causes the valve 25 to reopen.

When sticking of the ingot 12 to the mold 13 occurs, the mold 13 is drawn downward a short distance by the ingot 12, which is being withdrawn by the withdrawal mechanism. Movement of the mold 13 and hence the platform 14, causes the switch 28 to close the valve 25 which then prevents flow of the fluid 19 from the cylinder 17. The downward movement of the piston 16 is initiated by movement of the platform 14 and mold 13 as caused by adhesion between the ingot and the mold wall. As soon as the contact between switch 28 and the platform 14 is broken, closing the valve 25, the hydraulic fluid entering the cylinder 17 will force the piston 16 downward at a rate dependent upon the flow regulating position of the metering valve 23. In accordance with the invention, the rate of flow through the tube 24 will be suflicient to force the piston 16 in a downward direction at a greater rate than that caused by adhesion of the ingot to the wall of the mold. Thus the mold will also move downward at a greater rate than the ingot to break the adhesion therebetween.

The piston 16 moves downward under the force exerted by the hydraulic fluid and compresses the spring 18 until the switch 29 reopens the valve 25. With the release of fluid from the cylinder 17 through the line 26, the piston with platform 14 and mold 13 thereon will rise to its upper position with the platform again in its usual position in contact with switch 28. When the friction between the ingot and the mold again rises the cycle will be repeated. The storage tank 27 provides a means for containing excess fluid until such time as it is again required. The flow rate through the metering valve 23 may be kept in adjustment manually, or automatically in coordination with the ingot withdrawal speed by well known electrical or mechanical means.

It will be understood that the apparatus described should be duplicated in order that the vertical movement of the mold is maintained coaxial with respect to the ingot. However, it will also be understood the apparatus may be applied by connecting one end of a lever to the piston 16 and attaching the other end of the lever to the mold 13, in which case only one cylinder would be necessary.

Alternatively, the use of springs such as 18 may be dispensed with by admitting a continuous flow of hydraulic fluid through the lower chamber of cylinder 17, maintaining sufficient pressure therein just to hold the mold in its uppermost position. Upon the friction level rising between mold and ingot, the mold will be moved downward and so trip limit switches which will simultaneously: (1) Stop fluid entering the lower chamber of cylinder 17, (2) Stop fluid leaving the top chamber 19. Thus the mold will be forced down at a rate proportional to the the rate of flow of fluid which is controlled by valve 23.

After travelling a certain distance, the valve 25 is opened allowing fluid to flow out of chamber 19, and simultaneously fluid is re-admitted to the lower chamber to force the mold to its uppermost position.

In such a system, whereby the relative speeds of mold and ingot are not of great importance, so long as the downward speed ofthe mold exceeds that of the ingot, the operating fluid may conveniently be compressed air and the system may be run from any available supply of compressed air.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form and mode of operation of the invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is:

In apparatus for the continuous casting of metal having an upright open ended mold and means for delivering molten metal to the upper end and withdrawing an ingot from the lower end of said mold, the combination comprising means guiding said mold for vertical movement in coaxial relationship to the withdrawn ingot including a closed cylinder, a piston in said cylinder arranged to support said mold, spring means for supporting said piston in said cylinder, conduit means for continu ously delivering a hydraulic fluid to said cylinder, a second conduit means of greater flow area than said first conduit means for the, discharge of said hydraulic fluid from said cylinder, a cut-off valve in said second conduit means, and valve operating means for closing said valve when said mold initially moves downwardly from an upper position against said spring means in response to an increase in friction between said mold and ingot, said valve operating means closing said valve to force said mold downwardly at a substantially uniform rate greater than the Withdrawal rate of said ingot, under the influence of the incoming flow of said hydraulic fluid, said valve operating means being arranged to open said valve after a predetermined downward movement of said mold to release hydraulic fluid from said cylinder at a flow rate greater than said fluid delivering rate and thereby causing said mold to return to its said upper position at a substantially uniform rate under the influence of said spring means.

References Cited in the file of this patent UNITED STATES PATENTS 1,743,367 Maybach Jan. 14, 1930 2,815,551 Hessenberg et al. Dec. 10, 1957 FOREIGN PATENTS 776,285 Great Britain June 5, 1957