GB2115341A

GB2115341A - Refractory tube

Info

Publication number: GB2115341A
Application number: GB08236189A
Authority: GB
Inventors: Jean Pierre Luc; Jean Claude Constant
Original assignee: Foseco Trading AG
Current assignee: Foseco Trading AG
Priority date: 1982-01-07
Filing date: 1982-12-20
Publication date: 1983-09-07
Also published as: JPS58175617A; FR2519287A1; DE3300036A1; GB2115341B

Abstract

A method of making a refractory tube comprises feeding an aqueous slurry of refractory filler and binder into an annular cavity. A mandrel located within the cavity provides the core and water from the slurry is extracted via the mandrel to form a damp tubular article. The damp product is separated from the mandrel and heated to dry and cause the binder to set. The refractory tube thus formed may be used to contain a stream of molten steel flowing from a ladle into a tundish during continuous casting.

Description

SPECIFICATION Production of refractory tubes The invention concerns the production of refractory tubes, especially tubes to surround a stream of molten steel flowing from a ladle into a tundish in continuous casting.

According to the invention a method of making a refractory tube comprises feeding an aqueous slurry of refractory filler and binder into a generally annular cavity via an end of the cavity, extracting water, via a mandrel providing the inner surface of the cavity, from the slurry in the cavity thereby forming a damp tubular product in the cavity, separating the mandrel from the tubular product and heating the tubular product to dry it and to set the binder.

By use of the method, refractory tubes having advantageous properties can readily be made. In particular, advantageous combinations of refractory and other properties, e.g.

mechanical strength, resistance to thermal shock and heat insulation, can be achieved.

In the method, the outer surface of the generally annular cavity may be provided by a tubular member, which may be unitary or formed of a number of separable parts, forming a part of the apparatus used. In this case, after the damp tubular product has been formed in the cavity, both the mandrel and the tubular members are separated from the damp tubular product. The tubular member may be permeable to water and water extracted through it from the slurry via the mandrel.

It is greatly preferred that the refractory tube should be provided with metallic reinforcement. This can be achieved by first making the refractory tube and then providing metallic reinforcement around it e.g. by fitting the refractory tube into a metallic sleeve.

However, in accordance with the invention, it is much preferred to form the refractory tube in contact with the metallic reinforcement.

Accordingly, it is preferred to position a metallic reinforcing member or members, preferably a sleeve, in the generally annular cavity or, preferably, at the periphery of the cavity.

The reinforcing sleeve is preferably continuous but it may be perforated and, if it is perforated, the perforations may be such as to permit outward dewatering through it. In any event, perforations in the sleeve can heip to secure the sleeve to the refractory tube. As indicated above, the sleeve is preferably at the periphery of the generally annular cavity and it may be adjacent to an external tubular member forming a part of the apparatus used.

However, if the sleeve is able to withstand the pressures used in feeding the slurry to the cavity and dewatering it, an external member is not needed. In cases where the pressures could not be withstood by the reinforcing sleeve desired in the product, the sleeve is surrounded by support means, e.g. a tubular member, to prevent undue distortion of the sleeve, said member may consist of a plurality of separable parts e.g. half-sections.

The aqueous slurry used in the method comprises, as indicated above, a refractory filler and a binder. The filler may be, for example, calcined magnesite, especially deadburnt magnesite, silica or calcined bauxite or a mixture of two or more refractory fillers. The binder may be organic and/or inorganic.

Examples of suitable organic binders include starch and resins e.g. urea-formaldehyde and phenol-formaldehyde resins whilst silicates e.g. sodium silicates are examples of suitable inorganic binders.

The slurry may contain additional ingredients for particular purposes e.g sintering aids to enhance the strength of the tube at high temperatures, suspension aids, pH control additives and fibres. Organic fibres can be used for example, to aid suspension of other solids in the slurry whilst inorganic fibres can be used for example, to enhance the strength of the tube at high temperatures.

The solid content of the slurry may be in the range of from 50-75% by weight, and typically, is about 60% by weight.

The slurry may be fed to the generally annular cavity from a holding vessel having means for agitating the slurry. To convey the slurry to the cavity under pressure a pump may be used, e.g. a centrifugal pump able to produce pressures typically in the range of up to 6 bar. Alternatively, higher pressure pumps able to produce pressures well in excess of 7 bar may be used. Instead of pumping the slurry into the cavity, the slurry may be fed from a pressure vessel to the cavity by use of a top pressure on the slurry in the pressure vessel. In any event, a sub-atmospheric pressure e.g. a pressure which may be as low as 110 mm of mercury may be applied to the mandrel to cause or aid introduction of the slurry into the cavity and to cause or aid dewatering through the mandrel.

As stated above, the slurry is fed into the cavity via an end of the cavity e.g. via an inlet port or ports located in one end of the cavity.

In cases where the slurry is fed to the cavity by pumping, once the cavity has been filled, air pressure may be applied to aid dewatering.

If the slurry is to be dewatered outwardly, as well as inwardly through the mandrel, then the outward dewatering can be aided by application of a vacuum at the outer dewatering surface.

After the slurry has been dewatered, the mandrel is, as stated above, separated from the tubular product e.g. by a shock force and subsequent application of a load to overcome the frictional forces. For this purposes it is greatly preferred that the mandrel should taper slightly. if the slurry is dewatered out wardly as well as inwardly, after dewatering is complete the tubular product is also separated from the outward dewatering surface forming part of the apparatus e.g. by separating the parts of that surface where it is provided by a number of parts.

The method of the invention can be used to produce tubes having a variety of shapes. The cross section of the tube is not necessarily circular nor is it necessarily the same along the length of the tube nor is the internal shape necessarily the same as the external one. An end of the tube may be specially contoured to mate with a component with which the tube is to be used.

The invention is further described with reference to the accompanying diagrammatic drawing which is a longitudinal section through one form of apparatus for carrying out the method of the invention.

The apparatus comprises a generally cylindrical mandrel 1 positioned in a generally cylindrical steel sleeve 2 to define a generally annular cavity 3 between the mandrel and the sleeve. The mandrel 1 has a perforated surface to permit an aqueous slurry of refractory filler and binder in the cavity 3 to be dewatered through the mandrel.

At each end of the sleeve 2 there is a support collar 4 and at one end of the sleeve a cap 5 is fitted. In the cap 5 there are inlet ports 6 for introducing a slurry into the cavity 3. The inlet ports 6 are connected to individual slurry supply pipes 7 and 7' which in turn are connected to the main slurry supply pipe 8 provided with valves 9 and 1 4. At the opposite end of the sleeve 2 is an effluent collection chamber 10 provided with an outlet pipe 11.

Slurry supply pipe 8 is connected to a pressurisable slurry reservoir 1 2 at a point along the pipe between valve 9 and the individual slurry supply pipe 7. The reservoir 1 2 is provided with valve 1 3.

In use of the apparatus the slurry is fed e.g.

by pumping, with valves 1 3 and 1 4 closed, to the cavity 3 and dewatered through the mandrel 1. After the cavity has initially been filled with the slurry, the valve 9 may be closed and, if required, further slurry supplied from pressurised slurry reservoir 1 2 on opening valve 1 3 with valve 1 4 closed. Excess slurry can be returned to a holding tank (not shown) by applying an air pressure through the reservoir 12 with the valve 9 closed and valve 14 open. Subsequntly closing valve 14, the air pressure can be maintained to assist dewater ing and/or dewatering can be aided by apply ing a vacuum within the mandrel 1.

When dewatering is complete, the mandrel 1 is separated from the damp tubular product formed in the cavity 3 and that product re moved together with the sleeve 2 which pro vides an external reinforcement for the tubular product. The product is then heated to dry it and to set the binder.

If it is desired to feed the slurry to the cavity at a pressure higher than that which the sleeve 2 could withstand by itself, the apparatus additionally comprises a tubular support member encasing the sleeve 2 and shown by chain-dotted lines 1 5. In this case there are no distinct support collars 4, these being replaced by the ends of the tubular support member. Similarly, the cap 5 and chamber 10 may be integral with the support member which itself may consist of a plurality of parts.

Whilst the sleeve 2 is shown in the drawing as having a smooth surface, it may have integral projections to aid keying to the bonded refractory part of the tubular product.

An example of the solids composition of a slurry useful in the method of the invention is as follow: Ingredient % by weight deadburnt magnesite 86.1 silica 5 phenol4ormaldehyde resin 3.9 blast furnace slag 2.8 boric acid 1.8 glass fibre 0.36 suspension aid 0.04 Tubes made by the method of the invention form a part of the invention.

Claims

1. A method of forming a refractory tube comprising refractory filler material and binder characterised in that an aqueous slurry of refractory filler and binder is fed into a generally annular cavity via an end of the cavity, water is extracted, via a mandrel providing the inner surface of the cavity, from the slurry in the cavity to form a damp tubular product in the cavity, the mandrel is separated from the tubular product and the tubular product is heated to dry it and to cause the binder to set.

2. A method according to claim 1 charac terised in that the outer surface of the generally annular cavity is provided by a tubular member.

3. A method according to claim 2 charac terised in that the tubular member is formed of a plurality of separable parts.

4. A method according to any of claims 1 to 3 characterised in that a reinforcing mem ber is located in the generally annular cavity prior to feeding the aqueous slurry to the cavity.

5. A method according to claim 4 charac terised in that the reinforcing member is lo cated at the periphery of the generally annular cavity.

6. A method according to claim 4 or claim 5 characterised in that the reinforcing member is in the form of a sleeve.

7. A method according to any of claims 4 to 6 characterised in that the reinforcing member is surrounded by supporting means.

8. A method according to any of claims 1 to 7 characterised in that the solids content of the aqueous slurry is in the range of 50 to 75% by weight.

9. A method according to any of claims 1 to 8 characterised in that the aqueous slurry is fed to the generally annular cavity at a super-atmospheric pressure.

1 0. A method according to any of claims 1 to 9 characterised in that a sub-atmospheric pressure is applied within the mandrel.

11. A method of forming a refractory tube substantially as herein described with reference to the drawing.