GB2236837A

GB2236837A - Tap hole closure

Info

Publication number: GB2236837A
Application number: GB9021871A
Authority: GB
Inventors: Owen Eastwood
Original assignee: Monocon International Ltd
Current assignee: Monocon International Ltd
Priority date: 1989-10-11
Filing date: 1990-10-09
Publication date: 1991-04-17
Anticipated expiration: 2010-10-09
Also published as: GB8922863D0; GB9021871D0; GB2236837B

Abstract

A closure device to throttle the flow of molten metal from a furnace tap hole during tapping and indicate approach of the slag/metal interface to the tap hole comprises a refractory body 1 of elliptical transverse cross-section, longitudinally tapered such that the major axis of the ellipse towards one end 4 of the body 1 is greater than the diameter of a tap hole for which it is intended and the major axis of the ellipse towards the other end 5 of the body 1 is smaller than the diameter of the tap hole for which it is intended, and at any point of contact of the component with the tap hole, the minor axis of the body 1 is less than the diameter of the tap hole. In use the device floats at the slag/metal interface, and is located in the tap hole by tail 2. <IMAGE>

Description

TAP HOLE CLOSURE MEANS This invention relates to furnace tap hole closure means.

In steelmaking a layer of slag is present on the surface of the body of molten metal, and two important criteria need to be observed. One is that the maximum amount of useable metal should be tapped from the furnace, and the other that the slag should be retained within it for subsequent disposal.

Historically considerable reliance was placed on the skill of the operative, who watched molten metal flowing from the tap hole until the first signs of slag were detected, and when the tap hole was closed. This however has the result that slag would emerge from the tap hole, to a greater or a lesser degree dependent on the skill of the operative.

To avoid this, it has long been known to employ a refractory component in the form of a body of a density such that when desposited in a furnace above the tap hole it floats at the slag/metal interface and during tapping is drawn down by the vortex created in the molten steel until it locates in the mouth of the tap hole to close it. Slag balls or floats, as they are frequently referred to, are reasonably efficient in the prevention of slag being entrained in the molten metal flowing through the tap hole, but inevitably result in a proportion of useable metal also being retained within the furnace. As a means of reducing the quantity of retained metal, it is also known to groove the periphery of the ball.

Modified constructions of an elongate and tapered configuration have been evolved, so-called darts, to improve the surety that the component would locate properly in a tap hole, but with the same disadvantage that a proportion of useable metal is retained in the furnace.

This has led to the development of slag darts that when located in a tap hole do not shut the tap hole but which reduce the flow of metal to a significant degree. The situation here is that the throttling of the full flow of metal emerging from the tap hole is instantly recognisable as indicating that slag is now approaching the tap hole, and when the operative can watch the much reduced flow more easily to detect the first signs of slag and then terminate tapping ensuring that substantially all the useable metal is removed from the furnace and any entrained slag is minimal.

Thus it is known to provide darts of irregular transverse cross-section, and to provide darts of circular cross-section with a number of longitudinal grooves, but with attendant noticeably increased costs of production.

It is the object of the invention to provide a refractory component to serve as a dart that avoids those disadvantages mentioned above.

According to the present invention, a furnace tap hole closure means comprises a refractory body of elliptical transverse cross-section, said body being longitudinally tapered such that the major axis of the ellipse towards one end of the component is greater than the diameter of a tap hole for which it is intended and the major axis of the ellipse towards the other end of the component is smaller than the diameter of the tap hole for which it is intended, and at any point of contact of the component with the tap hole, the minor axis of the component is less than the diameter of the tap hole.

According to a further feature of the invention, a furnace tap hole closure means comprises a body having in transverse section a major and a minor axis, and being externally tapered along its length, the relationship between the major and minor axes being such that at any point along the length of the body the area of the cross-section at that point is not less than 65% of the area of a circle of a diameter equal to the length of the major axis at that point.

Thus, with the closure means located in a tap hole a maximum of 35% of the area of the tap hole is available for the flow of molten metal around the closure means and through the tap hole, to provide a major throttling effect as the closure means locates in the tap hole. Preferably the size relationship between the major and minor axes of the closure means is such as to provide between 8% and 3% of the tap hole area free to permit the passage of molten metal. Further preferably the free area is between 18% and 2%; and still further preferably is between 16% and 17%.

The external walls of the component may be straight, but are preferably curved, and further preferably flat faces are provided at each end of the body. A connecting means may be provided extending from the larger flat face at one end of the body to enable the closure means to be disconnectably attached to loading means for placing the closure means in a furnace, and a tail may be provided extending from the smaller flat face to lend assistance to the correct location of the closure means in a tap hole.

By being of regular cross-sectional shape, and by avoiding the need to provide grooves in its periphery, but at the same time by providing an ability to provide close control over the free area of a tap hole through which the molten metal can pass, the closure means of the invention constitutes a notable and cost effective advance over the known art.

One embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an elevation in the direction of the minor axis of a tap hole closure device according to the invention; Figure 2 is an elevation of the device of Figure 1 in the direction of its major axis; and Figure 3 is a plan view of the device of Figure 1.

In the drawings, a tap hole closure device comprises a body 1 attached to an elongate tail 2 of circular section, and with an upwardly extending rod 3 for the attachment of the device to an appropriate means for placement of the device in a furnace.

The body 1 and tail 2 are of an appropriate refractory material, and of a density such that the body l floats at the slag/metal interface, with the tail extending down into the molten metal.

As is shown in the drawings, the body 1 is of elliptical cross-section, and of progressively reducing cross-sectional area from its upper surface 4 to its lower surface 5, and such that the length of the major axis at the surface 4 is greater than the diameter of a tap hole for which the device is intended, and the length of the major axis at the face 5 is less than the diameter of that tap hole, and additionally, the length of the minor axis at the point of contact on the device with the tap hole is less than the diameter of that tap hole.

Thus, in use, and after the manner of the closure devices of the prior art, the closure device of the invention progresses down the furnace during tapping until the tail 3 engages in the tap hole to centralise the body 1 on the tap hole axis, and continues to fall until the body 1 engages in the tap hole.

By virtue of its elliptical shape and the size relationships as between the major and minor axes of the body and the diameter of the tap hole, the tap hole is not closed completely by the closure device, but a major throttling of the flow of molten metal through the tap hole is created, and to a degree dictated by free unblocked area between the sides of the closure device and the mouth of the tap hole.

Preferably, those size relationships are such as to leave a total unblocked area of between 8% and 3% of the tap hole cross-sectional area.

A throttling of the flow of molten metal through the tap hole of this magnitude is instantly recognisable by a furnace operative who can then watch the further reduced flow until the first signs of slag emerging through the tap hole, and when tapping is terminated. Consequently, there is maximised the degree of extraction of usable metal from the furnace, and there is minimised the degree of slag emerging from the furnace. The slag then remaining in the furnace is disposed of in conventional manner.

The body depicted in the drawings shows the reduction in area to be provided by a convex outer shape, but it will be understood that the same effect is achieved by a body that is a frustrum of an elliptical cone.

Claims

1. A furnace tap hole closure means comprising a refractory body of elliptical transverse cross-section, said body being longitudinally tapered such that the major axis of the ellipse towards one end of the component is greater than the diameter of a tap hole for which it is intended and the major axis of the ellipse towards the other end of the component is smaller than the diameter of the tap hole for which it is intended, and at any point of contact of the component with the tap hole, the minor axis of the component is less than the diameter of the tap hole.

2. A furnace tap hole closure means as in Claim 1, wherein the longitudinal taper is formed by a convex outer surface of the body extending from its larger to its smaller end.

3. A furnace tap hole closure means as in Claim 1, wherein the longitudinal taper is provided by the body being a frustrum of an elliptical cone.

4. A furnace tap hole closure means as in any of Claims 1 to 3, wherein the relationship between the major and minor axes of the body is such that at any point along the length of the body the area of the cross-section at that point is not less than 65% of the area of a circle of a diameter equal to the length of the major axis at that point.

5. A furnace tap hole closure means as in Claim 4, wherein the size relationship between the major and minor axes of the closure means is such as to provide between 8% and 3% of the tap hole area free to permit the passage of molten metal.

6. A furnace tap hole closure means as in any of Claims 1 to 5, wherein flat faces are provided at each end of the body.

7. A furnace tap hole closure means as in any of Claims 1 to 5, wherein a connecting means is provided at the larger end of the body, to be disconnectably attached to loading means for placing the closure means in a furnace.

8. A furnace tap hole closure means as in any of Claims 1 to 7, wherein a tail is provided extending from the smaller end of the body to lend assistance to the correct location of the closure means in a tap hole.