US3047915A - Apparatus for continuous casting of steel - Google Patents

Description

Aug. 7, 1962 D. A. BARNARD ETAL APPARATUS FOR CONTINUOUS CASTING OF STEEL Filed June 9, 1960 United States Patent ()fifice 3,047,915 Patented Aug. 7, 1962 3,047,915 APPARATUS FOR CONTKNUOUS CASTING OF STEEL Dennis Arthur Barnard and Alfred Nossiter, Stockton-on- Tees, England, assignors to Head, Wrightson 8: Company Limited, Thornahy-on-Tees, England, a company of the United Kingdom Filed June 9, 1960, Ser. No. 34,994

Claims priority, application Great Britain June 11, 1959 4 Claims. (Cl. 22-57.2)

This invention relates to apparatus for the continuous casting of metal billets and more especially to casting of metals having a high melting point, e.g. iron, steel.

The continuous casting of steel, by means of a vertical, bottomless water cooled mould, from which the molten metal, as it solidified into the billet, is withdrawn by passage between pinch rolls, by which the rate of withdrawal and lowering of the billet is controlled, gives rise to certain difficulties in practice.

A frequent cause of trouble in such a process is ruptureof the billet in or below the mould, allowing the liquid steel interior to escape. Such ruptures, it has been found, are caused by excessive friction between billet and mould, or less frequently by remelting of the initial billet skin.

We have nowdiscovered that by retarding the speed of casting whenever the friction forces tend to rise above a preset level, and by increasing the speed when the friction forces tend to fall below this level, the billet will be cast under a more or less uniform tension.

According to the present invention therefore, in the continuous casting of metal billets in a bottomless mould in which the mould is statically supported in relation to the draw-off rolls for the billet, the draw-01f speed is so controlled that it is dependent upon the frictional drag between the mould and billet.

In order to practice this invention it is necessary to measure the friction between the billet and mould and according to a further feature of the invention the mould apparatus comprises means such as a load cell arrangement for measuring the resistance in an axial direction of the mould due to the pull exerted through the draw-01f rolls on the billet.

Preferably the mould is supported so that it is capable of displacement in a plane at right angles or substantially at right angles to the axis of the billet. By this means the billet and mould have a limited free horizontal movement, and any horizontal thrust between billet and mould is minimized.

During normal operation the entire mould assembly is static, and the load cells continuously meter the vertical drag on the mould caused by friction between billet and mould. Any rise in this friction force above a preset value increases the output signal from the load cells; this signal is amplified and used via a speed controller to slow down 'the motor driving the pinch rolls. Should the friction force decrease below the preset value the casting speed is correspondingly raised.

The invention is illustrated in the accompanying drawings which is a diagrammatic view of .a vertical bottomless water cooled mould from which the billet is withdrawn by pinch rolls controlled by means for speeding up and slowing down the rate of movement of the billet in accordance with the invention.

In the drawing there is shown a vertical bottomless mould A having a water jacket I provided with an inlet and outlet for the circulation of water, the mould having a central chamber C, into which the molten metal is poured and from which the billet is withdrawn through its open bottom. On leaving the mould, the billet passes between guide rollers R and since for some distance below the mould the billet interior is still liquid, as is well known, cooling water sprays (not shown) are directed over the billet in this region to substantially solidify the billet before it is subjected to the pinch roll pressure. The rate of withdrawal of the molten metal as it solidifies into the billet B is controlled by operating means, as shown pinch rolls P, these rolls being driven from a pinch drive variable speed motor M through a fixed reduction gear box G.

Unless the rate of withdrawal of the billet B by the pinch rolls P is controlled rupture of the billet in and below the mould may take place. It has, however, been found in accordance with this invention that by retarding the speed of casting, whenever the friction forces tend to rise above a preset level, and by increasing the speed when the friction forces tend to fall below this level, the billet can be cast under a more or less uniform tension.

Accordingly for this purpose, the mould A is supported by a series of load cells 1 of which there are conveniently 3 at apart and which are placed in a position on the underside where they support the dead weight of the mould and the billet. These load cells are connected in an electric circuit 2 having an amplifier 1' by which the signals from the load cells are amplified and transmitted to a speed controller S thence fed to the variable speed motor N driving the gear box N. It will be appreciated, therefore, that the load cells 1 measure the resistance in an axial direction of the mould due to the pull exerted on the billet by the draw off rolls P.

In order to minimize an horizontal thrust between the billet B and the mould A provision is made for supporting the mould so as to permit a limited but free movement in a horizontal plane. For this purpose the load cells 1 are statically supported by .a main plate 5 which is superimposed on two laterally movable plates 6 and 7 each provided with two sets of rolls 8, 9, whose axes are arranged in directions at right angles to one another so that the two plates 6 and 7 are capable of movement in parallel horizontal planes in directions at right angles to one another. Thus the plates 6 and 7 and the rolls provide a two way roller action so as to permit of freedom of movement of the mould in a plane at right angles to the axis of the billet. A similar result would be obtained by making use of a single support plate 6 mounted on balls to support the plate 5 carrying the load cells.

As stated above the signal from the load cells is amplified and used via the speed controller to slow down the motor driving the pinch rolls when the friction is excessive. Should the friction force decrease below the present value the casting speed is correspondingly raised.

It may happen on occasion that the friction force abnormally rises too rapidly for the speed control unit to respond in time to prevent rupture. To overcome this difficulty, means may be provided for agitating the mould.

The agitating means may consist of any suitable device for imparting oscillating motion to the mould and conveniently this is done by connecting an oscillatory device to the main platform or base plate 7 so that the entire mould assembly can be subjected to an up and down oscillatory motion, which is in a direction parallel to the axis of the billet. Oscillatory motion is imparted to the mould by means of a cam 10 driven by means of a magnetically operated clutch 11 from a second variable speed motor 12 through a fixed reduction gear box 13. The outer circuit from the amplifier 1' which passes to the speed controller S is also connected to the motor 12 so that the speed of the latter is controlled in a fixed ratio to the main motor by the same speed controller thus ensuring that motion of the oscillating unit bears a direct relation to the casting speed.

In the embodiment illustrated the cam shaft 14 driving the cam 10 from the magnetic clutch, which comes into operation at the upper preset friction, incorporates two rotary switches 15, 16. Switch 15 is open circuited for 355 degrees of rotation and switch 16 for 5 degrees only, the opening and closing positions being symmetrically disposed about the upper cam position as indicated on the drawing. Excessive output from the load cells operates through a relay 1% to close a third switch 17. This switch 17 energizes the clutch relay 19 via rotary switch 15. Rotation of the drive commences, the clutch being energised for the remainder of the revolution by switch 16. When friction (and load cell output) falls to a safe level relay 18 no longer being operative opens the switch 17, switch 15 becomes dead, and the camshaft completes its current cycle until switch 16 also becomes dead with the cam in its upper position.

It will be obvious that as an alternative to the arrangement shown having a variable speed motor M it is possible to make use of an infinitely variable gear change speed box in place of the fixed reduction gear box G. In this case instead of two separate variable speed motors a single constant speed motor provides the drive both for the pinch rolls and to the cam, the speed controller controlling the gear box ratio and hence the speeds of casting and oscillation.

In the context the casting speed refers to the speed of billet withdrawal and not to the speed of pouring.

What we claim is:

1. Apparatus for continuously casting metal billets comprising a bottomless mould into which the metal is poured; means supporting said mould and maintaining it against substantial vertical movement; variable speed operating means for continuously and uninterruptedly pulling the billet metal through said mould and out through the bottom end thereof; means for measuring the frictional drag between said mould and the billet being drawn through said mould; and means controlled by said measuring means for maintaining substantially constant speed operation of said operating means when said measuring means measures a predetermined frictional drag and for decreasing and increasing the speed of operation of said operating means respectively in response to increasing and decreasing the frictional drag from said predetermined frictional drag.

2. Apparatus for continuously casting metal billets comprising a bottomless mould into which the metal is poured; means supporting said mould and maintaining it against substantial vertical movement; variable speed operating means for continuously and uninterruptedly pulling the billet metal through said mould and out through the bottom end thereof; means for measuring the frictional drag between said mould and the billet being drawn through said mould; means controlled by said measuring means for maintaining substantially constant speed operation of said operating means when said measuring means measures a predetermined frictional drag and for decreasing and increasing the speed of operation of said operating means respectively in response to increasing and decreasing the frictional drag from said predetermined frictional drag; and means for agitating said mould in response to an abnormal increase in the frictional drag.

3. Apparatus for continuous casting of metal billets comprising a bottomless mould into which the metal is poured; pinch rolls positioned to engage and draw-off the cast billet on leaving the bottom end of the mould; support means including a series of load cells for statically supporting the mould; means for signalling any variation in load on said load cells due to a rise or fall in friction between the mould and billet when being drawn-off; control means for effecting an increase or decrease in the speed of the pinch rolls; and means for transmitting a signal to the control means proportional to any such rise or fall in load.

4. Apparatus for continuous casting of metal billets comprising a bottomless mould into which the metal is poured; pinch rolls positioned to engage and draw-off the cast billet on leaving the bottom end of the mould; a platform having a number of load cells by which the mould is statically supported in relation to the pinch rolls; means mounting the platform so as to permit of limited displacement at right angles to the axis of the billet; control means for effecting an increase or decrease in the speed of the pinch rolls; and signalling means for transferring signals proportional to any rise or fall in load recorded by the load cells to the said control means for speeding up or slowing down said pinch rolls.

References Cited in the file of this patent UNITED STATES PATENTS 2,814,843 Savage et al. Dec. 3, 1957

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