GB2226021A

GB2226021A - Refractory mortars and refractory cements

Info

Publication number: GB2226021A
Application number: GB8928666A
Authority: GB
Inventors: Georges Wernert
Original assignee: Didier Werke AG
Current assignee: Didier Werke AG
Priority date: 1988-12-19
Filing date: 1989-12-19
Publication date: 1990-06-20
Anticipated expiration: 2009-12-19
Also published as: IT1238352B; IT8948667A1; FR2640618B1; DE3842691A1; FR2640618A1; ES2018448A6; GB2226021B; NL8903063A; BE1003552A3; IT8948667A0; GB8928666D0; DE3842691C2

Description

I-- - 1 REFRACTORY MORTARS AND REFRACTORY CEMENTS The invention relates to

refractory mortar or refractory cement of the type which includes a conventional refractory material, clay and a temporary bonding agent.

so-called refractory mortars or refractory cements are used for connecting refractory moulded components, e.g., refractory bricks, and particularly for the installation of gas permeable moulded components, such as gas flushing bricks, gas flushing plugs and sleeves in vessels or particularly molten steel.

containers for molten metals, Such gas flushing bricks and plugs are described in, for instance, EP-Bl-0021861 and US-A-3330645.

Refractory mortars or cements previously used for the installation of such refractory components included, inter alia, at least one A1203containing, granular refractory material, clay and a temporary bonding agent. These known refractory mortars or cements have, however, the disadvantage that refractory components secured with them in metallurgical vessels could only be.disassembled or removed with difficulty since the mortar or cement became so solidified and ceramically sintered by the action of high temperature, e.g. of the order of 1 5000C in the case of molten steel, that the components could only be broken out with the application of high mechanical forces, e.g. by means of a compressed air hammer.

DE-C2-2747636 discloses refractory compositions which 1 2 are stable in storage and are used for lining vessels for liquid steel or iron and are based on fired, granular dolomite and contain 1 to 6 wtA of natural triglyceride oil and 2 to 6 wtA of dry, inorganic, ground bonding agent. These refractory compositions are, however, not suitable as refractory mortars or cements, particularly for the installation of sleevest gas flushing bricks or gas flushing plugs in metallurgical vessels.

It is the object of the present invention to provide a refractory mortar or refractory cement which hardens less but nevertheless produces a satisfactory seal at the high temperatures, e.g. 15000C, to which it can be heated when used in a metallurgical vessel so that when a gas flushing brick or plug is broken out lower mechanical forces than previously are required in order to break the connection between the nozzle brick and the gas flushing brick or plug so that a complete or partial sheet metal sheathing of the gas flushing brick or plug or of the sleeve is no longer necessary but nevertheless a reliable fit is ensured.

In accordance with the present invention there is provided a refractory mortar or cement including a refractory material having a specific surface area of less than 1.5m2/9, clay and a temporary bonding agent comprising 3 to 15 wt.%, with respect to all the components, of at least one drying oil.

In a preferred embodiment the refractory mortar or cement contains 6 to 12 wtA drying oil, linseed oil or boiled linseed oil being particularly preferred.

n ii 3 However, other drying oils can also be used, for instance wood oils, petrilla oil, soya oil and fish oil or dehydrated castor oils, i.e. oils which by reason of the presence of unsaturated fatty acids take up oxygen from the air and dry to form a relatively hard, elastic layer.

The refactory material used in the refractory mortar or cement in accordance with the invention has a specific surface area of less than 1. 5m2/g, preferably of less than 1.0m2/g (measured in accordance with the BET method). The refractory material can be an individual material or a mixture of materials.

The refractory materials are preferably A1203containing materials, particularly preferably tabular alumina or mullite pellets. When using tabular alumina a higher temperature limit of application, i.e. maximum permitted use temperature, of the refractory mortar or cement may be achieved. When using mullite pellets a so-called "ballbearing effect" is produced, i.e. when using such a refractory mortar or cement for inserting sleeves or flushing bricks into a corresponding opening they may be easily "screwed in".

in a further preferred embodiment a portion of the refractory materials can be replaced by Cr203 (chromium oxide, green) or a chromium-magnesia ore or a magnesiachromium ore whereby an improved slag resistance can be achieved. Cr203 of pigment grade is preferably used, i.e. with a grain size between 0.1pm and 15pm, whereby the amount Of Cr203 advantageously does not exceed 2 wtA with respect to all the refactory materials.

1 c 4 The same applies when using magnesia-chromium ores or chromium-magnesia oresp whereby the Cr203 content of the refractory material mixture should also not exceed 2 wt.%.

In a further preferred embodiment polyacrylonitrile fibres are added, usually in an amount between 0.05 and 1 wt.% with respect to all the components. The addition of such polyacrylonitrile f ibres produces -a standardising agent effect and an improved workability of the refractory mortar or cement when installing e.g. sleeves or gas flushing bricks in the openings provided for them.

As mentioned above, the refractory mortar or cement in accordance with the invention may include an Al 203containing refractory material, preferably tabular alumina, i.e. highly pure, dense A1203. However, corundum or fused alumina can also be used. The proportion of the A1203- containing refractory material is commonly at least 80 wt.% with respect to all the components of the refractory mortar or cement.

In a further preferred embodiment the refractory mortar or cement in accordance with the invention contains one or more of Zr02. ZrS'04 (zirconium sand), MgO and S'02 (quartz sand) as refractory materials.

The range of grain sizes of the refractory material(s) is commonly such that the upper grain size is 90pm and advantageously 44 p M.

The refractory mortar or cement in accordance with the 1 1 invention further contains a clay component which is commonly 1 to 5 wt. % and pref erably 1 to 3 wt. % with respect to all the components.

In a preferred embodiment the clay in the refractory mortar or cement in accordance with the invention is a laminar clay or plasticising clayp particularly bentonite, the amount of the bentonite preferably being 1 to 3 wt.% and particularly preferably 1.5 to 2.5 wt.% The invention also embraces the use of refractory mortar or cement in accordance with the invention for securing sleeves, gas flushing bricks or gas flushing plugs in vessels for molten metals.

The reference made herein to "with respect to the components" relates to the actual components of the refractory mortar or cement, i.e. refractory materials, clay and the temporary bonding agent in the form of the drying oil. The refractory mortar or cement in accordance with the invention is prepared with water for use in order to achieve a suitable consistency. This water does however not count as one of the actual components.

As described above, it has surprisingly been found that the refractory mortars or cements in accordance with the invention are suitable particularly as a joint filling material for the installation of sleeves, gas flushing bricks or gas flushing plugs in vessels or containers for molten metals, particularly molten steel, since they harden substantially less strongly than previously known refractory mortars or cements i 6 which contain no drying oil. After the cement has been used, i.e. after it has been subjected to high temperature in a metallurgical vessel, the "used" refractory mortar or cement forms a somewhat porous, crumbly mass so that it is sufficient, for instance when removing gas flushing bricks and plugs, to knock the brick or plug out of the nozzle brick surrounding it with gentle hammer blows, and the used refractory mortar or cement easily crumbles away.

The invention will be described in more detail with reference to the accompanying Figure, which shows a standard system with a replaceable flushing plug and ceramic sleeve, as is used for the introduction of gasesf e.g. argon or nitrogen, into steel pouring ladles.

In the Figure, the portions of the ladle bottom, in which a nozzle brick 2 with a frusto-conical opening is mortared, is indicated by 1. Set in this nozzle brick 2 is the gas permeable gas flushing plug 3. The joint 4 between the opening in the nozzle brick 2 and the gas flushing plug 3 is filled with a refractory mortar or cement in accordance with the invention. The gas flushing plug 3 is secured to the outer surface of the ladle bottom 1 by means of a conventional bayonet connector 5, which is only shown in part, and is connected to a gas supply pipe 6 through which the flushing or purging gas is introduced.

The refractory cement, which was used to install the plug 3, comprised the following components which were mixed together in an intimate mixing process to form an 1 C, 7 easily workable cement which smeared well during use:

parts by wt. tabular alumina (A1203) 1.5 parts by wt. bentonite 10 parts by wt. boiled linseed oil This cement was brought to the necessary consistency, i.e. viscosity, with 8.5 parts by wt. water.

This refractory cement had not only better workability, i.e. a good lubricant action, but the assembly was also facilitated by the fact that this cement remained workable for a relatively long time and fitting, i.e. exact alignment of the gas flushing plug, was possible for a relatively long period of time.

Furthermore, this refractory cement had the advantage of higher strength at lower temperatures due to the cross-linking of the linseed oil. Also, when in "use", i.e. when subjected to high temperature, no ceramic bonding occurred which permitted an easier disassembly and enabled adhering cement residues on the frustoconical opening in the nozzle brick to be easily removed.

it can, however, be necessary with a refractory mortar or cement in accordance with the invention to exclude as much as possible the access of atmospheric oxygen at elevated temperatures, since otherwise premature erosion could occur with the consequence of increasing porosity with reduced gas-tightness and ultimately reducing mechanical strength.

A gas flushing plug or gas flushing brick or a sleeve i c 8 which is used together with the refractory mortar or cement in accordance with the invention thus advantageously has on that side. at which free air access is possible, e.g. a sheet metal jacket which prevents such access of atmospheric oxygen.

When using a refractory mortar or cement in accordance with the invention it can be advantageous to apply a protective layer of a less porous refractory cement to the tip side of a gas flushing plug, i.e. to that side which later comes in contact with the liquid metal, in order to delay access of the metal to the refractory mortar or cement.

Such a protective later is designated 7 in the drawing.

The refractory mortar or cement in accordance with the invention can further contain conventional additives known per se, particularly suspension stabilisers, standardising agents, surface active substances, gelling agents, etc.

The following table gives the composition of further refractory mortars or refractory cements in accordance with the invention, the amount of water to be added also being shown.

t 1 9 Composition (kg) TABLE I II III IV V vi Tabular alumina, A1203 95% finer than 0.044mm Bentonite Linseed oil Water Cr203. green (Pigment grade:0.1-10um) PAN-fibres, Length 0.4-0.5mm Mullite pellets Standardising agent PAN - Polyacrylonitrile 16 16 16 16 16 0.3 0.3 0.3 0.3 0.3 2.0 2.3 2.0 2.0 2.0 1.7 2.0 1.7 1.7 1.7 16 0.3 2.0 1.7 0.2 0.2 - 0.1 0.05 - 0.05 0.02 - C

Claims

CLAIMS'

1. A refractory mortar or cement including a refractory material having a specific surface area of less than 1.5m2/g, clay and a temporary bonding agent comprising 3 to 15 wt.%, with respect to all the components, of at least one drying oil.

2. A mortar or cement as claimed in claim 1 which contains 6 to 12 wtA drying oil.

3. A mortar or cement as claimed in claim 1 or claim 2 in which the drying oil is linseed oil or boiled linseed oil.

4. A mortar or cement as claimed in any one of the preceding claims in which the specific surface area of the refractory material is less than 1. 0m2/g.

5. A mortar or cement as claimed in any one of the preceding claims in which the refractory material is an A1203-containing material.

6. A mortar or cement as claimed in claim 5 in which the refractory material is tabular alumina.

7. A mortar or cement as claimed in any one of claims 1 to 4 in which the refractory material includes one or more of Zr021 ZrS'04 (zirconium sand), MgO, Cr203. S'02 and mullite pellets.

8. A mortar or cement as claimed in any one of the preceding claims which contains polyacrylonitrile 1 fibres in an amount of between 0.05 and 1 wt.%, with respect to all the components.

9. A mortar or cement as claimed in any one of the preceding claims in which the clay is present in an amount of 1 to 5 wt.%, with respect to all the components.

10. A mortar or cement as claimed in claim 9 in which the clay is a plasticising clay.

11. A mortar or cement as claimed in claim 10 in which the plasticising clay is bentonite.

12. A mortar or cement as claimed in claim 11 which contains 1 to 3 wtA bentonite.

13. The use of refractory mortar or cement as claimed in any one of the preceding claims for securing sleeves, gas flushing bricks or gas flushing plugs in vessels for molten metals.

14. A refractory mortar or cement as claimed in any one of claims 1 to 12 substantially as specifically herein described, or disclosed in the accompanying Table.

piibaishedI990 at The Patent Office. State House. 66 711-IighHolborn. London WCIR4TP Further copies maybe obtained fro m. The Patent Office Sales Branch, St Mary Cray. Orpington. Kent BRS 3RD. Printed by Mulvilex techniques Itd. St Mary Cray. Kent- Con 18'