GB2254274A

GB2254274A - Stopper for controlling metal flow from a vessel and delivering gas

Info

Publication number: GB2254274A
Application number: GB9207457A
Authority: GB
Inventors: Stephen John Lee; William Donnelly Muir
Original assignee: Thor Ceramics Ltd
Current assignee: Thor Ceramics Ltd
Priority date: 1991-04-06
Filing date: 1992-04-06
Publication date: 1992-10-07
Anticipated expiration: 2012-04-06
Also published as: GB9207457D0; GB9107281D0; GB2254274B

Abstract

A monoblock stopper 1 which is adapted to deliver gas during pouring of moulting metal comprising a stopper body having an internal gas chamber 3 and an exit gas port 7, a bore 6 connecting the chamber 3 to the exit port 7 of the stopper, wherein a portion of the bore is formed using a sacrificial void former to provide restricted slit-form path which offers a predetermined resistance to flow to maintain a positive gas pressure within the stopper. The former is preferably tubular having opposed cut-outs so that when the former is consumed on firing the stopper after pressing, two opposed arcuate slit restrictions (9, Fig 3) are formed. Sloping wall 4 about the bore inlet acts to divert debris away from the inlet. <IMAGE>

Description

STOPPER This invention relates to a monoblock stopper rod used to control the flow of molten metal from a discharge nozzle in a holding vessel during metal teeming.

In continuous casting processes the use of Argon injected down the stopper rod has been shown to have significant benefits on the quality of steel being cast and various systems have been developed to ensure an accurate measured flow of Argon gas is supplied to the stopper. Problems have been encountered with sealing such systems and ensuring that the Argon follows its intended path and is not wasted. An improved stopper which has proved to be successful in meeting many of these problems is disclosed in EP-A-0 179 837.

However, even given such valuable improvements, there is a need to address other problems. One such problem is apparent due to the effect during pouring of large volumes of melt of metal flowing past the nose of a stopper through the outlet nozzle. A negative pressure can be generated at the stopper tip which can be transmitted through the gas discharge port into the body of the stopper and back to the supply pipework where it may exploit any inadequate joints causing air entrainment into the Argon stream with significant detriment to the quality of the steel being cast.

Various solutions have been proposed to eliminate this risk which involve restricting the gas flow within the stopper thereby seeking to create a positive pressure at the stopper tip. For example, a simple restriction in the feed pipe pressed into the stopper body to provide control is known. At the required pressure, the orifice size of the feed pipe was found to be between 0.2-0.5mm in diameter and, as such, extremely sensitive to blockage by debris in the Argon gas stream thereby causing loss of flow. It is also known to insert a permeable plug or nose section into the stopper to provide the required restriction to flow and to pressurise the stopper tip.However, these systems suffer from the problem of changes in the permeable characteristics of the refractory materials with during the operational life of the stopper and susceptibility to the rapid temperature increase during casting and have found limited use.

The present invention aims to overcome or at least mitigate the above problems associated with the prior art stoppers.

According to one aspect of the present invention, there is provided a monoblock stopper which is adapted to deliver gas during pouring of molten metal comprising a stopper body having an internal chamber and an exit port, a bore connecting the chamber to the exit port of the stopper, wherein a portion of the bore is formed using a sacrificial void former to provide a restricted slit-form path which offers a predetermined resistance to flow and tends to maintain a positive gas pressure within the stopper.

Preferably, the slit-form path is formed by a tubular sacrificial void former having portions of the wall thereof cut away to allow penetration of particulate refractory ceramic material during formation of the stopper body which is otherwise formed. in a manner known per se, and fired, whereupon the sacrificial void former is consumed to leave a void of the desired shape and characteristics . Conveniently a pair of slits will be formed which are arcuate and have an effective diameter similar to the diameter of the bore.

Preferably also, the floor of the chamber is inclined radially about the bore to divert any debris collecting in the chamber away from the bore.

An embodiment of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is an axial section through a stopper according to one aspect of the present invention; Figure 2 is a cross sectional view on the line A-A of Figure 1, and Figure 3 is a cross sectional view on the line 3-B of Figure 1.

Referring now to the Figures, Figure 1 shows an axial section through a stopper 1 according to one aspect of the present invention.

The stopper has a stopper body portion 2 which is formed by methods generally known per se e.g. by isostatic pressing of particulate materials and bonding agents, using arbors to provide the body with a chamber 3 into which Argon gas is fed by a conventional Argon gas supply.

In this embodiment, the floor region 4 of the chamber 3 is inclined upwardly from its periphery towards the centre which is provided with an opening 5. The opening 5 leads into an axial bore 6 through the stopper body 2 which ends in an exit port 7 at the lower end of the stopper 1. The diameter of the bore 6 is preferably about 6 mm, but may be of any suitable diameter for the conditions required.

intermediate within the bore 6, a restriction 8 is formed which reduces the cross section of the bore 6 to two arcuate slits 9 as shown in Figure 3. The-length and effective diameter of the arcuate slits 9 can be varied to any required dimensions.

In use, Argon gas is fed into the chamber 3 of the stopper body 2 by a conventional system as known in the art. As the opening 5 of the bore 6 is raised from the floor 4 of the chamber 3, any debris in the Argon gas streak falling down through the chamber 3 is diverted outwards away from the bore and trapped in a catchment area at the outer periphery of the floor 4 of the chamber 3 and is thus prevented from entering the opening 5 of the bore 6 and thus avoids blocking the bore.

As the Argon gas flows through the bore 6 and the arcuate slits 9, a frictional resistance is created by the surfaces of the arcuate slits. Varying the diameter of the agate slits allows different resistances to be create and hence allows predetermined control of the resultant internal pressure in the system for any set of castin conditions.

Te arcuate slits are not affected by changes in dimension during casting and the flow resistance therefore remains constant. Furthermore, due to the configuration of the floor 4 of the chamber 3, there is minimal likelihood of blockage of the arcuate slits 9 ensuring a consistent predetermined resistance to flow and hence internal pressure is maintained.

The twin arcuate slits, feed and exit ports are typically manufactured according to the invention by incorporating a shaped sacrificial former into the pressing mould, packing in the required refractory material around it and isostatically pressing to form the resultant monoblock stopper.

For a given set of flow operating conditions of steel flow rate, gas supply pressure and gas flow rate, the sacrificial former can be designed to give a specific resistance to flow and thus generate the required internal pressure thereby delimiting the risk of air ingress into the argon feed supply line and significantly increasing both the cast steel quality and the operating-efficiency.

The table below shows the effect of changes in slit length and depth on the back pressure generated within the stopper for a standard gas flow: inlet Pressure 2 BAR, Flow Rate 20 1/mien Slit Length (mm) Slit Depth (mm) Back Pressure (BAR) 9 20 0.8 9 30 0.9 13.5 20 0.6 18 40 0.2 This table shows that by controlling the slit lengths and depths, a significant alteration to the back pressure is possible allowing a good match to individual casting conditions.

Although the slits have been described throughout as arcuate, it is to be appreciated that the slits may be of any confirlration, this being a result of the confiGlration of the sacrificial former used during manufacture of the stopper.

Claims

1. A monoblock stopper which is adapted to deliver gas during pouring o- molten metal comprising a stopper body having an internal chamber and an exit port, a bore connecting the chamber to the exit port of the stopper, wherein a portion of the bore is formed using a sacrificial void former to provide a restricted slit-form path which offers a predetermined resistance to flow to maintain a positive gas pressure within the stopper.

2. A stopper according to claim 1, wherein the slit-form path is formed by a tubular sacrificial void former having portions of the wall thereof cut away to allow penetration of particulate refractory ceramic material during formation of the stopper body, whereupon the sacrificial void former is consumed to leave a void of the desired shape and characteristics.

3. A stopper according to claim 1 or 2, wherein a pair of slits is formed which are arcuate and have an effective diameter similar to the diameter of the bore.

4. A stopper according to any one of the previous claims, wherein che floor of the chamber is inclined radially about the bore to divert any debris collecting in the chamber away from the bore.

5. A monoblock stopper substantially as hereinbefore described with reference to and as shown in the accompanying drawings.