EP0790873B1

EP0790873B1 - Tundish impact pad

Info

Publication number: EP0790873B1
Application number: EP95934731A
Authority: EP
Inventors: Donald Richard Zacharias
Original assignee: Foseco International Ltd
Current assignee: Foseco International Ltd
Priority date: 1994-11-09
Filing date: 1995-10-24
Publication date: 1998-06-03
Anticipated expiration: 2015-10-24
Also published as: MX9703352A; TW321615B; JP4007429B2; DK0790873T3; DE69502838T2; JP2000505728A; CA2162551A1; FI971968A; AU692622B2; FI110312B; CN1171752A; AU3704395A; BR9509706A; CA2162551C; ES2104525T3; CN1069243C; WO1996014951A1; TR199501393A2; FI971968A0; DE69502838D1

Abstract

A tundish impact pad (20) to reduce turbulence in the tundish comprises a body of refractory material capable of withstanding contact with molten steel in a tundish (10), the body comprising a base (22) having an impact surface (24), an outer sidewall (26, 40) extending upwardly from the impact surface (24), a top surface (32) connected to the sidewall (26, 40) and defining an opening (30) therein, in which the top surface (32) has an inner annular portion (42) substantially parallel to the impact surface (24), and the sidewall (26, 40) has an interior face (28) which is substantially perpendicular to the impact surface (24) and wherein a substantially right angle corner (28A) is provided between the sidewall (28) and the impact surface (24) and a substantially right angle corner is provided between the sidewall (28) and the top surface inner annular portion (42).

Description

This invention relates to a tundish impact pad, i.e. a pad of erosion resistant material positioned on the floor of a tundish to receive the incoming stream of molten metal poured into the tundish from a ladle.

U.S. patent 5169591 discloses an impact pad for a tundish for continuous casting of steel that comprises a base, a peripheral top surface and a discontinuous sidewall extending between the base and the peripheral top surface, the sidewall having an undercut inner surface, which may be curvilinear.

U.S. patent 5358551 discloses an impact pad which comprises a base, a sidewall extending around the base, the sidewall having an inner surface having a portion which extends inwardly and upwardly. That inner surface may be concave.

U.S. patent 4776570 discloses a ladle stream breaker in the form of a closed box into which the ladle stream is directed via a pouring tube. The box has apertured walls through which the stream flows out of the box as a series of sub-streams each flowing perpendicularly to and impinging against a wall of a tundish.

Whereas the aforesaid devices are designed to reduce turbulence in the tundish, we have surprisingly found that improved turbulence reduction can be achieved by providing an impact pad with internal corners defined between its base, its peripheral wall and its upper surface. Thus, we have now found that it can be advantageous to provide such internal corners and that improvements in the reduction of surface turbulence, minimisation of slag entrainment, prevention of break-up of tundish flux cover, reoxidation of the molten steel and ensuring a proper flow path of the steel within the tundish, may be achieved.

Accordingly, in one aspect, the invention provides a tundish impact pad comprising a body of refractory material capable of withstanding contact with molten steel in a tundish; the body comprising a base having an impact surface, an outer sidewall extending upwardly from the impact surface, a top surface connected to the sidewall, an opening being defined in the top surface, which opening provides open access for molten steel to and from the impact surface; the top surface having an inner annular portion substantially parallel to the impact surface, and the sidewall having a continuous interior face which is substantially perpendicular to the impact surface and wherein a substantially right angle corner is provided between the sidewall and the impact surface and a substantially right angle corner is provided between the sidewall and the top surface inner annular portion.

Molten steel entering through the opening and contacting the impact surface flows outwardly then is turned inwardly by the sidewall interior face and then flows out of the opening.

Preferably, the sidewall is endless, i.e. it extends continuously around the impact surface.

Preferably, the opening is non-uniform in that it has a long dimension and a short dimension perpendicular to the long dimension. Thus, it may be, for example, rectangular or oval.

The top outer surface of the pad may conveniently also be parallel to the impact surface.

The impact pads of the present invention uniformly disperse the flow of incoming steel rather than merely redirecting it.

Since the steel flow can be dispersed over a larger area than if a circular or other uniform configuration were used, the result is more uniformly surface directed flow while maintaining the benefits of reduced splash and turbulence. Also due to the non-uniform configuration of the impact pad it presents a larger "target" to the incoming steel than a similar width uniform shaped pad (e.g. circular or square), with the desired results obtained even if the steel stream is imperfectly aligned with the centre of the impact pad.

The invention is particularly useful in providing improved residence time distribution parameters in the poured molten steel. It can also be of reduced cost due to its simplified internal chamber shapes and may be of reduced overall size relative to known impact pads.

The impact pads according to the present invention are formed of a refractory composition which is capable of withstanding continuous contact with molten metal, in particular, molten steel such as used in continuous casting operations. Usually a standard medium-to-high alumina monolithic refractory, with an alumina content in the range of about 55 to 85% by weight is desirable. Where a basic refractory is preferred because of steel chemistry, it is preferred that a magnesia based monolithic refractory be utilised, with MgO in the range of about 58 to 93% by weight.

In another aspect the invention provides a tundish for holding a volume of molten steel and having a floor and side walls enclosing a region of impact and a drain, an impact pad of the present invention being provided on the floor of the tundish in the region of impact.

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a side cross-sectional view of a tundish including an impact pad of the invention disposed on the floor of the tundish;

Figure 2 is a top plan view of the impact pad of Figure 1, which illustrates where the cross-section of Figure 1 is taken (along line I to I);

Figure 3 is a cross-section along line III to III of Figure 2; and

Figure 4 is an enlarged sectional view of a portion of the impact pad of Figure 3.

In Figure 1, a conventional tundish 10 is shown and includes an inner lining 12 and a pair of well blocks or outlets 14 to allow molten metal (typically steel) from a bath 16 contained in the tundish 10 to continuously exit the tundish 10 and enter moulds (not shown) which form metal castings. As is also conventional, a ladle shroud 18 or like tundish filling device, is positioned above the tundish 10 and continuously directs a stream of molten metal into the tundish 10. A tundish impact pad 20 constructed according to the present invention is placed generally centrally on the floor 15 of the tundish 10.

As seen in Figures 1 to 4, the tundish impact pad 20 is preferably rectangular in shape and is positioned with its longer sides parallel to the longitudinal axis of the tundish. The pad includes a base 22 having a planar, horizontal, impact surface 24. The pad 20 further includes an endless, annular

outer sidewall

26, 40 having an inner wall face surface 28. The impact pad 20 also has a top surface 32 parallel to the impact surface 24 and connected to the

sidewall

26, 40 and defining a non-uniform opening 30 therein. By "non-uniform" it is meant that the opening 30 is not circular or square; rather it has a long dimension 30' (see Figure 2) and a short dimension 30'' substantially perpendicular to the long dimension 30'.

As seen in all of Figures 1 through 4, the interior face 28 of the sidewall extends upwardly substantially at right angles to the impact surface 24 around the entire periphery thereof. The continuous nature of the inner surface 28 is perhaps seen most clearly in Figure 2, being shown in dotted line therein.

As shown in Figures 3 and 4, the sidewall 28, with impact surface 24 and underside portion 42 of top surface 32, provides two

sharp corners

28A and 28B respectively, which corners also extend continuously around the inside of the impact pad.

As seen in Figure 1, the outer sidewall 26 may be tapered inwardly from the top surface 32 toward the base 22, defining ears 27 at opposite ends. The ears 27 facilitate connection of the impact pad 20 to the base or floor 15 of the tundish when certain types of tundishes are utilised. Alternatively, the impact pad 20 may merely be mounted in a conventional manner on the bottom of the tundish.

It is also noted that the bottom portion of the top surface 32 has annular portions 39, 42 (see Figure 3) thereof, which lie parallel to the impact surface 24. This annular, overhang surface 42 facilitates proper directing of the molten steel during filling of the tundish 10. Note that the long dimension 30' of the opening 30 is positioned aligned with the long dimension of the tundish (the dimension between the outlets 14, as seen in Figure 1), whereas the short dimension 30'' of the opening 30 is aligned with the short dimension of the tundish 10.

The outer sidewall portions 40, rather than being tapered inwardly like the sidewall portions 26, preferably taper very slightly (e.g. 2 to 5°) outwardly, as seen in Figure 3. Alternatively, straight sides may be provided for both

walls

26, 40 and straight sidewalls 26 may or may not contain ears 27.

The refractory material of which the impact pad 20 is made must be capable of withstanding continuous contact with molten steel during the entire use cycle of the tundish 10. It must have adequate refractoriness normally available from a standard medium-to-high alumina monolithic refractory. For example, an alumina content in the range of about 55 to 85% may be utilised. Where a basic refractory is preferred because of the steel chemistry, typically an MgO-based monolithic refractory, with MgO in the range of about 58 to 93% is preferred.

While it is preferred that the impact pad 20 be rectangular in shape, as illustrated in Figures 1 through 4, other non-uniform configurations can also be provided. For example, an oval impact pad may be utilised, or another type of multi-sided polygon configuration, as long as there is an opening with a long dimension which is aligned with the long dimension of the tundish 10 and a short dimension aligned with the short dimension of the tundish 10.

In use of the tundish pad 20 illustrated in Figure 1, molten steel flowing in the path 34 from a location disposed above the pad 20 strikes the impact surface 24 and then moves radially outwardly as illustrated by arrows 35. When the steel impacts the inner face 28 of the sidewall, it is directed inwardly then upwardly, flowing as illustrated at 36 in Figure 1 and ultimately being dispersed generally radially outwardly as indicated by

arrows

37, 38 in Figure 1. This minimises turbulence on the surface of the bath 16 and helps direct slag and other impurities away from the stream 34.

It is not essential that the corners shown in dotted line in plan in Figure 2 be radiused as shown and the corners may, if desired, be right-angled.

If desired, small corner fillets may be present in the right-angle corners between the sidewall and the impact surface and/or the top surface inner annular portion.

Claims

A tundish impact pad (20) comprising a body of refractory material capable of withstanding contact with molten steel in a tundish (10), the body comprising a base (22) having an impact surface (24), an outer sidewall (26, 40) extending upwardly from the impact surface (24), a top surface (32) connected to the sidewall (26, 40), an opening (30) being defined in the top surface, which opening provides open access for molten steel to and from the impact surface (24), the top surface (32) having an inner annular portion (42) substantially parallel to the impact surface (24), and the sidewall (26, 40) having a continuous interior face (28) which is substantially perpendicular to the impact surface (24) and wherein a substantially right angle corner (28A) is provided between the sidewall (28) and the impact surface (24) and a substantially right angle corner (28B) is provided between the sidewall (28) and the top surface inner annular portion (42).
A tundish impact pad according to Claim 1, wherein the opening (30) has a long dimension (30') and a short dimension (30'') perpendicular to the long dimension.
A tundish impact pad according to Claim 2, wherein the opening (30) is rectangular or oval.
A tundish impact pad according to Claim 1, 2, or 3, wherein the top outer surface (32) of the pad is parallel to the impact surface (24).
A tundish impact pad according to any preceding claim, whereinthe sidewall (26.40) is endless.
A tundish impact pad according to any preceding claim, wherein the pad (20) is a monolithic refractory having an alumina content of from 55% to 85% by weight.
A tundish impact pad according to any one of Claims 1 to 5, wherein the pad (20) is a monolithic refractory comprising magnesia and containing from 58% to 93% by weight of magnesia.
A tundish (10) for holding a volume of molten steel (16) and having a floor (15) and sidewalls (12) enclosing a region of impact and a drain (14), wherein the tundish (10) contains an impact pad (20) as claimed in any preceding claim on the floor (15) in the region of impact.
A tundish according to Claim 8, wherein the impact pad (20) has an opening (30) to receive a stream of molten metal, the opening (30) having a long dimension (30') and a short dimension (30'') perpendicular to the long dimension (30') and the long dimension (30') of the opening (30) is aligned with the long dimension of the tundish.