US3817313A

US3817313A - A method of continuously casting metal

Info

Publication number: US3817313A
Application number: US00218804A
Authority: US
Inventors: P Gamble; J Marsh
Original assignee: Davy Ashmore Ltd
Current assignee: Davy Ashmore Ltd
Priority date: 1971-01-19
Filing date: 1972-01-18
Publication date: 1974-06-18
Anticipated expiration: 1991-06-18
Also published as: FR2122516B1; GB1380582A; FR2122516A1; IT946673B; DE2202134A1

Abstract

In a continuous casting process the casting is intermittently withdrawn from a stationary horizontal mould by the action of at least one pair of pinch rolls which engage the casting and at least one of the rolls is driven. After each withdrawal phase a push-back force is applied to the casting by the pinch rolls to urge the casting back towards the mould. The push-back force is sufficiently large to allow the casting to contract back towards the mould but it is insufficiently large to cause displacement of the casting at the inlet end of the mould. Apparatus of the invention includes means for driving the pinch rolls in the direction to withdraw the casting from the mould and means by which the drive means is energised after each withdrawal phase to rotate the pinch roll in the opposite direction of rotation to apply a limited push-back force to a casting engageable by the pinch roll. Both pinch rolls are preferably driven in which case they are driven by separate drive means which may be hydraulic motors.

Description

[ A METHOD OF CONTINUOUSLY CASTING METAL [75] Inventors: Peter Charles David Gamble,

Wootton; John Marsh, Putnoe, both of England [73] Assignee: Davy-Ashmore Limited, London,

England [22] Filed: Jan. 18, 1972 [21] Appl. No.: 218,804

[30} Foreign Application Priority Data Jan. 19, 1971 Great Britain 2536/71 [52] US. Cl. 164/83, 164/260 [51] Int. Cl B22d 11/02 [58] Field of Search 164/82, 83, 260

[56] References Cited UNITED STATES PATENTS 3,354,936 ll/l967 Atkin 164/82 3,545,528 12/1970 Chang 3,669,176 l/l972 Krall et a1. 164/83 X FOREIGN PATENTS OR APPLICATIONS 1,087,026 10/1967 Great Britain 164/83 June 18, 1974 Primary Examiner-R. Spencer Annear Attorney, Agent, or Firm-Morton, Bernard, Brown, Roberts & Sutherland [57 ABSTRACT In a continuous casting process the casting is intermittently withdrawn from a stationary horizontal mould by the action of at least one pair of pinch rolls which engage the casting and at least one of the rolls is driven. After each withdrawal phase a push-back force is applied to the casting by the pinch rolls to urge the casting back towards the mould. The push-back force is sufficiently large to allow the casting to contract back towards the mould but it is insufficiently large to cause displacement of the casting at the inlet end of the mould.

Apparatus of the invention includes means for driving the pinch rolls in the direction to withdraw the casting from the mould and means by which the drive means is energised after each withdrawal phase to rotate the pinch roll in the opposite direction of rotation to apply a limited push-back force to a casting engageable by the pinch roll. Both pinch rolls are preferably driven in which case they are driven by separate drive means which may be hydraulic motors.

5 Claims, 4 Drawing Figures PATENTEDJUM m 333173313 same ur 2' I Displacement V Qg laccml I A METHOD OF CONTINUOUSLY CASTING METAL This invention relates to a method of, and apparatus for, the continuous casting of metals, particularly steel.

Continuous casting consists essentially of allowing molten metal stored in a container, usually in the form of a tundish, to flow through a mould and for the metal to be cooled sufficiently in the mould for the casting leaving the mould to retain the cross sectional shape of the mould. The casting is usually withdrawn from the mould by means of one or more pairs of pinch rolls which engage opposite sides of the casting and at least one roll of each pair is driven.

In the past, vertical continuous casting machines have been used, but the capital and operating costs of the continuous casting process are reduced if the mould is horizontally aligned and the casting is withdrawn horizontally. It has also been found that with horizontal continuous casting apparatus it is necessary for the mould to be fixed relative to the tundish and for the inlet end of the mould to be sealed to the outlet of the tundish. Additionally oxidation of the metal stream flowing into the mould is prevented. If a straight through" system of tundish outlet and mould is employed, i.e., a system where the cross section of the outlet of the tundish and the cross section of the mould are the same, it has been found that the operation of the apparatus is only possible by the use of graphite at least at the tundish end of the mould. Use of graphite in the mould precludes the casting of metals in which graphite is soluble, for example steel. To overcome this difficulty it has been proposed to introduce at least one refractory apertured component which is not soluble in the metal being cast between the outlet of the tundish and the inlet of the mould, with the component having a smaller aperture than the bore of the mould. The component thus provides an obstruction at the entrance to the mould and the tundish and mould system is then no longer of the straight through type.

To attain high casting speeds, continuous withdrawal from a stationary horizontal mould is not possible since any breaks in the solidifying skin resulting from sticking in the mould do not heal sufficiently quickly and solidified metal is left behind in the mould. This condition frequently leads to rupture of the skin outside the mould and a break out of molten metal. This difficulty can sometimes be overcome by withdrawing the casting with an intermittent motion using the pinch rolls. When a pull:pause withdrawal cycle was employed with the above described non-straight-through system of tundish outlet and mould, it was found that circumferential hot tears occurred in a cyclic manner on the surface of the casting. It was discovered that the reason for this is that during each withdrawal part of the cycle, metal flows into the mould and solidifies against the mould wall up to the refractory component. The molten metal also solidifies against the part of the solid skin which was in contact with the refractory component on the previous cycle. Between these two solidified portions the thickness of the skin is a minimum and is therefore a point of weakness between the two parts of the skin. During the pause part of the withdrawal cycle, contraction of the casting causes this point of weakness to open up and form a hot tear.

It has been proposed in British Pat. Specification 1,087,026 to withdraw metal from a body of molten metal through a continuous casting mould, cooling the withdrawn metal within the mould to effect solidification thereof as it is being withdrawn, reversing the direction of rotation of supporting rollers to reverse the direction of movement of the cooled casting so as to reintroduce it at least partially into the mould and then withdrawing the solidified casting further by movement in the original direction. This method of pulling the casting and pushing it back into the mould can only be employed in a straight-through system of mould and tundish and its use with apparatus having an obstruction at the mould inlet is not possible. If it was attempted to push the casting back into the mould, the casting would abut against the obstruction and either force it from its seating with the mould or the thin skin adjacent the obstruction would be forced against the obstruction and cause the skin to be wrinkled thus producing a casting of poor surface finish.

According to a first aspect of the present invention in a method of continuously casting metal, the casting is intermittently withdrawn from a stationary horizontal mould by the action of at least one pair of pinch rolls engaging the casting and with at least one of each pair being driven, and after each withdrawal phase a push back force is applied to the casting by the pinch rolls to urge the casting back towards the mould. the push back force being sufficiently large to allow the casting to contract back towards the mould but insufficiently large to cause displacement of the casting at the inlet end of the mould.

According to a second aspect of the invention, continuous casting apparatus includes a stationary horizontal mould, at least one pair of pinch rolls engageable with a casting produced in the mould, drive means for one of the rolls of each pair and means by which the drive means is intermittently energised to rotate the pinch roll in the direction to withdraw the casting from the mould and means by which the drive means is energised after each withdrawal phase to rotate the pinch roll in the opposite direction of rotation to apply a limited push-back force to a casting engageable by the pinch roll.

Both pinch rolls of each pair may be driven in which case they are driven by separate drive means. The drive means for each roll may be a hydraulic motor.

In order that the invention may be more readily understood it will now be described, by way of example only, with reference to the accompanying drawings in which FIG. 1 is a side elevation, partly in section of continuous casting apparatus,

FIG. 2 is a diagrammatic hydraulic circuit for withdrawal apparatus of the continuous casting apparatus, and

FIGS. 3A and 3B are time/displacement graphs at the portion of a casting engaged by a pair of pinch rolls and e at the inlet end of the continuous casting mould respectively.

FIG. 1 illustrates the mould tundish arrangement of a horizontal continuous casting apparatus. A continuous casting mould, particularly suitable for casting steel, comprises a tubular upper sleeve I surrounded by but spaced from a steel jacket 2, but alternatively the mould may be made entirely of copper. Liquid coolant is arranged to flow between the sleeve and the jacket in order to cool the mould. The sleeve 1 defines the mould passage 3 which is arranged with its longitudinal axis horizontal.

At the inlet end of the mould passage there is provided a refractory body 4, conveniently of silicon nitride when casting steel. The body is in the form of an apertured plate and its surrounds and abuts against the inlet end of the passage with a portion 5 of the body projecting inwardly of the mould passage. A refractory feed tube which constitutes the outlet nozzle from the tundish 11 is sealed by means of conventional refractory cement to the body 4 to prevent leakage between the nozzle and the plate. The mould-tundish is thus not of the straight-through type because the plate 4 projects into the mould passage.

A casting produced in the mould passes from the open end of the mould through a secondary cooling zone and is gripped by at least one pair of pinch rolls (not shown in FIG. 1) located on the side of the secondary cooling zone which is away from the mould. The pinch rolls are thus spaced at some distance from the mould. At least one of the pinch rolls is driven but preferably both rolls of each pair are driven.

The withdrawal of the casting from the mould comprises repeating withdrawal cycles each consisting of a pull phase followed by a push phase during which a limited force is applied to the casting to urge it towards the mould. During the push phase only movement of the casting equivalent to the contraction of the casting is permitted and the casting is not forced back into the mould. There is therefore no movement of the casting at the inlet end of the mould and consequently there is no danger of the plate 4 being forced off its seating at the entrance to the mould. Furthermore the thin skin of the castng at the inlet end of the mould is not wrinkled due to movement of the casting at the inlet end of the mould.

Referring now to FIG. 3, FIG. 3A illustrates a time/- displacement graph for a portion of the casting situated between the pinch rolls. It can be seen that during the pull phase A the casting is displaced longitudinally in the direction away from the mould and during the push back phase B the casting moves back for a short distance towards the mould. This push back of the casting is brought about by applying a limited reverse torque to the pinch rolls to allow the casting to move back to compensate for contraction of the length of casting between the mould and the pinch rolls. It can be seen however from FIG. 38 that the casting is not forced back into the mould because the displacement/time graph at the inlet end of the mould shows that this part of the casting does not move back relative to the mould. During pull phase A the casting is withdrawn in the direction out of the mould but during the time interval B it is not displaced back relative to the mould.

A hydraulic circuit for controlling a pair of hydraulic motors driving a pair of pinch rolls is illustrated in FIG. 2. A pair of pinch rolls 20, 21 are connected to a pair of

hydraulic drive motors

22, 23 respectively. The motors are connected in series between a pair of

fluid lines

24, 25. Alternatively the motors could be connected in parallel. The fluid lines 24, 25 are connected to respective parts on a fluid control valve 26. Three further fluid lines 27, 28 and 29 are connected to the control valve and the valve is provided with a spool which can be displaced by solenoids. The spool of the valve 26 is connected mechanically to the spool of a by-pass valve 30 which is connected across the lines 27, 28. A pump 31 having a relief valve 32 in shunt with it is connected across the fluid lines 27, 28 and a backing pump 33 is connected to supply hydraulic fluid from a reservoir 34 to the inlet of the pump 31. A further pump 35 is connected to draw hydraulic liquid from the reservoir 34 and supply it through a check valve 36, and a flow control valve 37 to the line 29. A by-pass valve 38 is connected in parallel with the valve 37 and an adjustable pressure relief valve 39 is connected between the outlet of the pump 35 and the reservoir 34.

In use all the pumps are energised continuously. To apply a withdrawal pull to the casting the spool of the valve 26 is adjusted to the position in which fluid supplied on the line 27 by the pump 31 is passed to the

motors

22 and 23. The by-pass valve 30 is closed and fluid supplied to the valve 26 by the pump 35 is passed through the valve and returned to the line 28. The motors are thus rotated in the direction to withdraw the casting from the mould. At the end of the pull phase the valve 26 is switched so that fluid supplied on the line 29 is supplied to the motors but in the direction to rotate them in the opposite direction. The pressure and quantity of fluid supplied to the motors is limited by the

valves

39 and 37. The by-pass valve 30 is opened so that fluid pumped by the pump 3! passes through the by-pass 30 and is not supplied to the motors.

The by-pass valve 38 may be opened to increase the speed of rotation of the motors in the reverse direction when it is necessary to drive a dummy bar up to the mould before casting commences.

As an alternative to a hydraulic drive, the pinch rolls could be driven electrically. The two drive motors would then be electric motors and the torque limited push back may be brought about by using eddy current couplings and adjusting the current in the coupling circuit. A variable resistor in the power supply to the eddy current coupling circuit enables control of the current to be effected.

We claim:

1. A method of continuously casting metal utilizing a mould having a tundish for holding molten metal, a horizontally disposed mould passage, and a feed nozzle through which the molten metal flows to the mould passage inlet to pass through and solidify within the mould passage, the feed nozzle having a cross-section adjacent the mould passage inlet smaller than the crosssection of the mould passage; said method comprising the steps of passing molten metal from the tundish through the feed nozzle to the mould passage inlet; passing the metal through the mould passage while cooling the metal to cause the metal to form a casting; gripping a portion of the casting outside the mould passage between at least one pair of pinch rolls with at least one roll being driven by a hydraulic motor; intermittently applying hydraulic fluid under pressure from a source through a first pressure relief valve to the hydraulic motor to drive at least one roll to withdraw the casting from the mould passage in a withdrawal phase of a distance less than the length of the mould passage; after each withdrawal phase applying hydraulic fluid under pressure from a source through a second pressure relief valve to the hydraulic motor to drive at least one roll to apply to the casting a push-back force; and controlling the second pressure relief valve to limit maximum pressure of the hydraulic fluid to a pressure which limits the push-back force to a value less than a maximum value which is sufficient to allow the casting to contract in the direction back toward the mould passage but insufficient to cause the portion of the casting engaging the mould passage inlet to be displaced relative thereto.

2. A method as claimed in claim 1 in which the rolldriving steps include driving both rolls of at least one pair of pinch rolls.

3. A method as claimed in claim 1 in which the roll driving steps include driving one roll from a first hydraulic motor and driving another roll from a second hydraulic motor.

4. A method as claimed in claim 1 in which the roll driving steps include supplying fluid under pressure from a first pump to the hydraulic motor to drive at least one roll to withdraw the casting and supplying fluid under pressure from a second pump to the hydraulic motor to drive at least one roll to apply the push-back force to the casting.

5. A method as claimed in claim 4 in which the first roll driving step includes placing a control valve in a first valve position, supplying fluid from the first pump through the control valve to the hydraulic motor, placing the control valve in a second valve position, and supplying fluid from the second pump through the control valve to the hydraulic motor.

Claims

1. A method of continuously casting metal utilizing a mould having a tundish for holding molten metal, a horizontally disposed mould passage, and a feed nozzle through which the molten metal flows to the mould passage inlet to pass through and solidify within the mould passage, the feed nozzle having a cross-section adjacent the mould passage inlet smaller than the cross-section of the mould passage; said method comprising the steps of passing molten metal from the tundish through the feed nozzle to the mould passage inlet; passing the metal through the mould passage while cooling the metal to cause the metal to form a casting; gripping a portion of the casting outside the mould passage between at least one pair of pinch rolls with at least one roll being driven by a hydraulic motor; intermittently applying hydraulic fluid under pressure from a source through a first pressure relief valve to the hydraulic motor to drive at least one roll to withdraw the casting from the mould passage in a withdrawal phase of a distance less than the length of the mould passage; after each withdrawal phase applying hydraulic fluid under pressure from a source through a second pressure relief valve to the hydraulic motor to drive at least one roll to apply to the casting a push-back force; and controlling the second pressure relief valve to limit maximum pressure of the hydraulic fluid to a pressure which limits the push-back force to a value less than a maximum value which is sufficient to allow the casting to contract in the direction back toward the mould passage but insufficient to cause the portion of the casting engaging the mould passage inlet to be displaced relative thereto.

2. A method as claimed in claim 1 in which the roll-driving steps include driving both rolls of at least one pair of pinch rolls.