DESCRIPTION

This inventiqn relates to monoblock one-piece pouring stoppers which are used as valve closures to control the outflow of molten . metal through bottom pouring nozzles- in foundry ladles or tun dishes in the iron and steel industry. Each monoblock pouring stopper is made from a refractory material such as graphitized alumina or clay graphite.

These stoppers have been made in 2 pieces i. e. an extruded clay graphite body with a screwed on nose cap, which could have a different composition to improve ^' wear resistance. In use the nose caps wear quickly due to erosion by the pressure of the outflowing melt through the nozzle of the tun dish or ladle and it has been proposed to improve the wear characteristics of the nose cap by the addition of fused or calcined alumina to the refractory ix formula. Another type of monoblock pouring stopper has been developed- which is formed in one-piece by an isostatic pressing of graphitized alumina.

However the effective life of this stopper is also shortened by erosion at the tip of the stopper. This necessitates removal of the stopper and reshaping and grinding of the tip in order to provide a good mating seal with the . pouring nozzle in a ladle or tun dish.

In the modern continuous casting plants this interruption in production not only wastes time but also fuel due to the cooling to allow removal of the stopper and subsequent reheating required to attain operating temperatures when the stopper is replaced. It is an object of the present invention to obviate or mitigate the aforesaid "disadvantages.

According to the present invention there is provided a one-piece monoblock pouring stopper having a nose portion comprising a high refractory material selected from calcined alumina, fused alumina, magnesite and zirconia. The most preferred high refractory additive material is stabilised or unstabilised zirconia. . .

Further according to the present inventipn there is provided a method of manufacturing a one-piece monoblock pouring stopper comprising charging a mould with a refractory material and a bonding agent to a level short of the full capacity of the mould and filling the remaining volume with a higher refractory material selected from calcined alumina, fused alumina, magnesite and zirconia, together with a bonding agent, compressing the contents of the mould, firing the compressed contents to form a monolithic structure and shaping the monolithic structure to form a one-piece monoblock stopper.

Preferably the mould is an isostatic pressing mould and compression of the contents thereof is effected by an isostatic pressing apparatus. Most preferably, the method comprises charging the isostatic pressing mould with graphitized alumina bonded with a -foundry type resin to a level short of the full capacity of the mould and filling the remaining volume with a mix of zirconia and a foundry . resin -as bonding agent. A preferred embodiment of this invention will now be described by way of example with reference to the accompanying drawing in which a monoblock stopper is illustrated mounted in an operational position above a pouring nozzle of a tun-dish.

A one-piece monoblock pouring stopper according to this embodiment of the invention is formed by a high intensity mixing of graphite and alumina powder together with foundry resin as bonding agent to for a homogeneous mix and charging the mix

A graded batch of zirconia together with a phenolic resin bonding agent, optionally including other minor ingredients such as graphite, is blended in a high intensity mixer to form a homogeneous blend and the blend is added to the mould to fill the remaining volume.

The mould is sealed and immersed in water and subjected to isostatic pressing. The ^" compressed contents of the mould are then fired to form a monolithic structure which can then be shaped to form a one-piece monoblock stopper provided with an integral armoured nose portion of zirconia which is more highly resistant to erosion. Thus such a stopper has an extended working life.

In use a one-piece monoblock stopper 1 having an armoured nose portion 2 is fixed by conventional means to a cross arm control member 3 above the pouring nozzle 4 of a tun dish 5.

By raising or lowering of the control member 3 the armoured nose portion 2 of the stopper 1 increases or reduces the outflow volume of molten metal 6 through the pouring nozzle 4 into a continuous casting mould 7 wherein the molten metal begins to solidify to a mass 8 suitable for subsequent rolling.

The aperture 9 , which allows the optional step of inj ection of argon gas through the- stopper into the metal , may not be present in other embodiments so as to leave a thick solid armoured nose . This solid coating is advantageous in cases of severe wear.