GB2282091A

GB2282091A - Parting material

Info

Publication number: GB2282091A
Application number: GB9418556A
Authority: GB
Inventors: Samuel Alexander Franklin; Derek Edward Capes
Original assignee: British Steel PLC
Current assignee: British Steel PLC
Priority date: 1993-09-22
Filing date: 1994-09-15
Publication date: 1995-03-29
Also published as: GB9418556D0; GB9319549D0

Abstract

Used magnesia-carbon or alumina-carbon refractory bricks are crushed and screened then mixed with bentonite and high-alumina cement. This mixture can be wet-gunned onto metallurgical vessels to act as a parting material.

Description

WEAK MATERIAL This invention relates to weak materials, often called parting materials. Particularly it relates to materials for use in metallurgical applications where, for example, slag or hot liquid metal solidifies in contact with the vessel lining during the metallurgical process, or after it has finished, and the solidified material needs to be removed. To be able to remove this material without damage to the vessels a sacrificial parting layer is often applied by wet "gunning" a granular material onto the appropriate part of the vessel before the process starts. This parting material dries into a weak material sufficient to withstand the metallurgical process but which will easily part or fracture at the end to allow the slag or metal adherent thereto to be broken away from the containing vessel without damaging the permanent lining ofthe vessel.

The invention is of particular interest in that it uses recycled materials; it employs a particular sort of refractory material after it has been scrapped from its primary use.

The changes within the refractory material during its initial use are such that it becomes extremely suitable for use as a component of a parting material.

According to the present invention there is provided a parting material manufactured from crushed used carbon-bonded refractory material. The refractory material may be magnesia-carbon or alumina-carbon material. The parting material may also include a sticking agent such as bentonite, and high alumina cement and there may be up to 10% bentonite and 5-15% of high alumina cement added to said crushed bricks (by weight). The used crushed refractory bricks may be screened and the screen may be a 5mm screen. The powders may be premixed and may be formed into a slurry with water before use or may be wet gunned with water added at the gun nozzle.

The invention will now be described by way of example.

Magnesia-carbon bricks are a common refractory of the wider carbon-bonded refractory class, and are typically manufactured by mixing magnesia particles and graphite flakes with a binder which may either be pitch or a phenolic resin. Other additives may be employed in small quantities according the proprietary manufacturer of ofthese bricks.

These refractory bricks are fired to a low temperature, usually about 300"C, to set the bond. In use the brick is subjected to much higher temperatures and the binder decomposes. This produces a carbon char together with gases. The carbon char is strong enough to hold the brick together but it is essentially inert. The result is that, once the bricks have been scrapped, they can be crushed and the carbon char is broken leaving it surrounding the magnesia particles. These particles will no longer adhere.

The used magnesia-carbon bricks (of any shape ) are crushed, screened and mixed, typically in a ratio of 75-95 parts of crushed bricks and up to 10 parts bentonite as a sticking agent and 5-15 parts of high alumina cement, all by weight. The material is stored as a mixed powder or used immediately. It is gunned in a standard manner onto the metallurgical vessels where it is required and water is added, again in a conventional manner, at the nozzle during the gunning process.

The high alumina cement forms a matrix but the magnesia particles are surrounded by the carbon char and this does not adhere to the high alumina cement and thus prevents the development of a strong gunned body.

It has been found that the strength of the gunning material thus produced is useful in many applications, and provides a way of reusing old refractories before they are finally waste.

The process may also use alumina-carbon bricks, which work in a similar manner.

Claims

1. A parting material manufactured from crushed used carbon-bonded refractory material.

2. A parting material as claimed in claim 1 in which the refractory material is a magnesia-carbon or alumina-carbon material.

3. A parting material as claimed in claim 1 or 2 including a sticking agent.

4. A parting material as claimed in claim 3 where the sticking material is bentonite.

5. A parting material as claimed in claim 4 containing up to 10% bentonite by weight.

6. A parting material as claimed in any preceding claim including high alumina cement.

7. A parting material as claimed in claim 6 containing between 5% and 15% of high alumina cement by weight.

8. A parting material as claimed in any preceding claim in which the refractory material has been screened.

9. A parting material as claimed in claim 8 in which the screen is a 5mm screen.

10. A parting material as claimed in any preceding claim which, prior to use, is mixed into a slurry with water.

11. A parting material as claimed in any of claims 1 to 10 which, in use, is wet gunned with water being added at the gun nozzle.