GB2216117A

GB2216117A - Refractory compositions or cements

Info

Publication number: GB2216117A
Application number: GB8904515A
Authority: GB
Inventors: Guenter Wieland
Original assignee: Didier Werke AG
Current assignee: Didier Werke AG
Priority date: 1988-03-01
Filing date: 1989-02-28
Publication date: 1989-10-04
Anticipated expiration: 2009-02-28
Also published as: GB8904515D0; DE3806554A1; FR2628097B1; FR2628097A1; GB2216117B; AT398205B; DE3806554C2; BE1003691A5; ATA46489A

Description

2216117 REFRACTORY COMPOSITIONS OR CEMENTS The invention relates to

refractory compositions or cements of the type which contain conventional refractory materials and organic materials comprising a free fatty acid as a temporary bonding agent and optionally other conventional components.

It is known to add fatty oils or fat as a temporary bonding agent to refractory compositions or cements. However, these function only as a consequence of their oily consistency,, whereby when such compositions or cements are subsequently used, i.e. when they are heated up, they form a cohesive carbon structure and also other organic carbon- containing materials as a consequence of their thermal decomposition. DE- B-1471297 discloses unfired or fired materials based on magnesium oxide (MgO) which can be used when constructing vessels such as furnaces for melting metals.

Such known refractory materials based on MgO contain 0.1 to 15 wt.% of at least one aliphatic hydroxytricarboxylic acid or a salt or an ester of such an acid, e.g. citric acid or its salts. By virtue of the use of such hydroxytricarboxylic acids or salts or esters thereof, which are preferably water soluble, a setting mixture, that is to say a mixture similar to cement, is obtained. The magnesium oxide material should be plastic and finely divided; dead-fired magnesite is referred to as an example. DE-B-1 257051 discloses a refractory ramming mixture which is bonded by means of a non-aqueous, carbon-containing bonding agent in the form of an unsaturated, flowable pitch which is obtained as a residue when distilling 2 vegetable oils to remove the fatty acids. Such residual pitches are termed fatty acid pitches, i.e. such pitches still contain unsaturated fatty acids and have an acid number of 30 to 60. The ref ractory materials used with these fatty acid pitches can also be basic aggregates, e.g. dolomite, dead-fired magnesite, hard-fired calcium oxide or mixtures thereof. DE-B-1274489 further discloses a temporary bonding agent for ceramically bonded, basic refractory materials, the bonding agent comprising a mixture of a medium and/or hard pitch and a fatty acid pitch, the fatty acid pitch advantageously having an acid number of 20 to 40. Only dead-fired materials are used as the basic, conventional refractory materials in both DE-B- 1257051 and also DE-B-1274489. In DE-A-2119668 a fatty acid pitch is also used as a temporary bonding agent, though in this case granulated phosphorus pentoxide, P205, is additionally used. If magnesite is used as the refractory material in this specification then dead-fired magnesite is used.

It is the object of the present invention to provide a refractory composition or cement which may be stored, i.e. remain processable and particularly plastic, for a prolonged period of time, but which after use, e.g. as a stamping composition or a moulding composition or as cement for pointing brickwork, retain the shape given to it and when used, i.e. when heated, produce a crack-free lining without joints which has a high resistance to slag attack and crack formation.

It has now been found that long chain fatty acids in conjunction with reactive MgO constitute a temporary bonding agent whose use results in such properties.

The properties of the composition or cement thereby 3 1 obtained are achieved whilst it is processed and whilst it is used. i.e. after being heated up or fired in use.

A refractory composition or cement of the type referred to above solves the aforementioned object when it contains one or more long chain fatty acids comprising 8 or more carbon atoms in conjunction with reactive MgO as the temporary bonding agent.

The reactive MgO can be caustically fired MgO andlor finely ground magnesia and/or dolomite sintered powder.

The fatty acid is preferably liquid and is preferably an unsaturated fatty acid, e.g. an oleic or linoleic acid.

In a further preferred embodiment the refractory composition or cement additionally contains an extender. Examples of suitable extenders are mineral oils, fatty oils, stand oil, heating oil, lecithin, bitumen, tar oil (anthracene oil), tar, pitch or wax, particularly soft wax. By virtue of using an extender the plasticity of the composition or cement in accordance with the invention can be selected at will. Furthermore, when using the composition or cement, i.e. when it is heated and the organic components in it are decomposed, a higher percentage of carbon is produced in the decomposition of the organic components which can be advantageous for certain applications.

The composition or cement in accordance with the invention preferably contains at least 0.5 wt.% of the fatty acid and at least 0.2 wtA of the reactive MgO, in each case with respect to the weight of the entire mixture of refractory materials. temporary bonding agent and optionally other conventional components.

Such optional conventional components can be e.g.

4 surface-active materials, materials producing a chemical bond such as monoaluminium phosphate or fibrous components such as mineral f ibres or carbon fibres. A further optional component is also very finely divided, i.e. pulverulent, refractory material, e.g. alumina, bauxite dust or Cr203 (green).

The amount of fatty acid is preferably 1.0 to 8 wt.% and the amount of the reactive MgO 0.2 to 4 wt.% with respect to the weight of the entire mixture in each case. If an amount of 8 wt.% of fatty acid and 4 wt.% of the reactive MgO is exceeded there is in general no increase of the advantageous properties as regards the processing and when using the composition or cement. It is of course, however, also possible for is the conventional refractory material to comprise active, optionally granulated, caustic MgO so that the preferred upper limit of 4 wt.% of the reactive MgO can be simply exceeded. Refractory compositions or cements which contain MgO as the conventional refractory material are particularly preferred. This MgO refractory material is advantageously a dead-burned magnesite or dolomite.

The compositions and cements in accordance with the invention are preferably used as ramming compositions for lining furnaces but may also be used as slinger compositions, casting compositions or vibration compositions. They can also be further processed into briquettes, e.g. by extrusion. In the same mannner refractory bricks can also be produced from them.

The long chain organic fatty acids used in the refractory compositions or cements in accordance with the invention have carbon numbers above 8, preferably above 12. They can be individual fatty acids or the commercially available fatty acid mixtures. in general the fatty acids do not have carbon numbers higher than 30. It is particularly preferred that unsaturated fatty acids are used since these are liquid at normal temperature; examples of such acids are oleic acid, linoleic acid and linolenic acid, i.e. fatty acids with 18 carbon atoms. If the f atty acids are not liquid they can be used in a mixture with other liquid, usually unsaturated, fatty acids or they can - be dissolved in an organic solvent, e.g. mineral oil. A different suitable organic solvent can optionally also be used, e.g. an alcohol, such as ethanol, or chlorohydrocarbons.

The reactive MgO used in the refractory composition or cement in accordance with the invention in conjunction with the fatty acid is preferably a relatively finely divided material, i. e. it usually has a grain size below 0.5 mm and advantageously below 0.2 MM. It is however also possible to use powdery reactive MgO, i.e. with a grain size below 0.09 mm and preferably of 0.044 mm.

it has now been found that when mixing e.g. pure oleic acid,, which constitutes a thin liquid, with reactive MgO a viscous sticky product is obtained which constitutes the temporary bonding agent in the compositions or cements in accordance with the invention. It is therefore assumed that a chemical reaction occurs between the fatty acid and the reactive MgO. It is not known whether water is liberated or whether the water itself remains bonded in such a chemical reaction. However, no disadvantageous properties have been determined, such as a gradual 6 destruction of ramming bodies, e.g. dolomite ramming bodies, bonded with a temporary bonding agent in accordance with the invention. The product of the reaction of the fatty acid and the reactive MgO, which constitutes a viscous, sticky mass, is thus probably responsible for the advantageous properties both in the processing and also in the use of the refractory compositions and cements produced with it.

The refractory materials contained in the refractory composition or cement in accordance with the invention may be conventional refractory materials, preferably basic refractory materials. Examples of such materials are fired dolomite, fired magnesite, fired lime or mixtures thereof. However, other is refractory materials, such as chromite, aluminium oxide, silicates or silicon dioxide (quartz) can also be used as the refractory materials or as an admixture to the aforementioned basic refractory materials.

The term "conventional refractory materials" used herein embraces refractory materials of the usual sizes, the maximum grain size commonly being 12 mm and advantageously 6 mm. However, the term "conventional refractory materials" also embraces a certain proportion of very finely divided materials, such as pulverulent materials, which proportion may be up to 40% by weight of the refractory materials. The invention will be described in more detail with reference to the following examples. Example 1 30 This example relates to a furnace chamber ramming composition. 65 parts by weight of a dead-burned magnesite with a grain size of 0.2 to 4 mm and 35 parts by weight pulverulent, dead-burned sinter magnesite 7 with a grain size of up to 0.09 mm were mixed in a mixer together with 0. 3 parts by weight of a reactive MgO with a maximum grain size of 0.1 mm. A liquid mixture of 1.8 parts by weight oleic acid. 1.2 parts by weight mineral oil and 0.8 parts by weight stand oil were added and mixed in a mixer at ambient temperature of about 220C for 15 minutes. A crumbly ramming composition was obtained which had a storage life of more than four weeks and could be easily used for ramming a furnace chamber. After heating the rammed lining no cracks could be detected in it.

Example 2

The procedure of example 1 was repeated but a mixture of 0.8 parts by weight oleic acid and 1.9 parts is by weight lecithin was used as the liquid component. The ramming composition thus obtained was particularly well suited to the production of wall components.

Example 3

A ramming composition was produced in accordance with the procedure of example 1 from 50 parts by weight granulated dolomite sinter with a grain size of 0.5 to 4 mm,, 20 parts by weight pulverulent sinter dolomite with a maximum grain size of 0.2 mm and 0.5 parts by weight reactive MgO with a maximum grain size of 0.1 mm and a liquid mixture of 3 parts by weight oleic acid, 0.5 parts by weight lecithin and 0.8 parts by weight stand oil. This composition was an excellent ramming composition for ladles.

Example 4

100 parts by weight reactive MgO with a grain size of 0 to 4 mm were mixed in a mixer with 9 parts by weight bonding tar and 5 parts by weight oleic acid which resulted in a crumbly composition which was used 8 to produce briquettes on a roll press. These briquettes were very suitable for advantageously regulating both chemically and physically the slags which are present in vessels for producing steel.

Example 5

A mixture. which was initially in the form of a slurry, was produced from 65 parts by weight of a deadburned magnesite with a grain size of 0. 2 to 4 mm and 35 parts by weight pulverulent dead-burned sinter magnesite with a grain size of up to 0.09 mm, 0.5 parts by weight of a reactive MgO with a maximum grain size of 0.1 mm, 3.5 parts by weight oleic acid, 3.5 parts by weight soft wax, 2.3 parts by weight tar and 2 parts by weight pitch. After about two days this mixture was of pasty consistency. This mixture can be used in hot furnaces as a pouring composition to be liquefied in the heat. Example 6 The procedure of example 5 was repeated and the following mixture was used:

parts by weight of the mixture of dead-burned magnesite of differing grain sizes, 0.3 parts by weight reactive MgO with a maximum grain size of 0.1 mm, 2 parts by weight of oleic acid, 3.5 parts by weight of the bonding tar used in example 5, 2 parts by weight of the hard pitch used in example 5 and 5 parts by weight bitumen. This mixture was initially of slurry consistency and was solidified after two days into a cement. This cement could also be used in the repair of hot furnaces as a pouring composition which liquefies in the heat.

Example 7 parts by weight sinter dolomite with a grain 9 size of 0 - 7 mm were mixed with 9% bitumen and 5% oleic acid and 1% reactive MgO in a mixer to produce a crumbly composition which was suitable for manufacturing briquettes on a roll press. These briquettes were used successfully for repairing worn portions of a converter. e.g. the scrap impact point.

Example 8 parts by weight of a mixture of dead-burned magnesite of differing grain sizes were thoroughly mixed in a mixer at 200C with 0.4 parts by weight reactive MgO, 2 parts by weight soot. 1 part by weight viscous mineral oil and 2 parts by weight oleic acid. This mixture could be pressed into shaped bricks on a press. The shaped bricks could be used with or without post-treatment, such as tempering, for the lining of metallurgical vessels.

1,

Claims

1 A refractory composition or cement comprising a mixture of refractory material and a long chain fatty acid having at least 8 carbon atoms in conjunction with reactive MgO as a temporary bonding agent.

2. A composition or cement as claimed in claim 1 in which the reactive MgO is caustically fired MgO and/or finely ground magnesia and/or dolomite sinter dust.

3. A composition or cement as claimed in claim 1 or claim 2 in which the fatty acid is a liquid.

4. A composition or cement as claimed in any one of claims 1 to 3 in which the fatty acid is unsaturated.

5. A composition or cement as claimed in any one of the preceding claims which additionally contains an extender.

6. A composition or cement in which the extender is a mineral oil.

7. A composition or cement as claimed in any one of the preceding claims which contains at least 0.5 wt.% of the fatty acid and at least 0.2 wt.% of the reactive MgO, in each case with respect to the weight of the entire mixture.

8. A composition or cement as claimed in claim 7 which contains 1.0 to 8 wt.% of the fatty acid and 0.2 to 4 wt.% of the reactive MgO, in each case with 4 respect to the weight of the entire mixture.

9. The use of a composition or cement as claimed in any one of the preceding claims as a stamping composition. a slinger composition, a moulding composition, for producing briquettes, a pouring composition or a vibration composition.

10. The use of a composition or cement as claimed in any one of claims 1 to 8 for producing refractory bricks.

11. A refractory composition or cement substantially as described in any one of the accompanying Examples.

1 Published 1989 at The Patent Office, State House, 65-71 High Holborn, London WC1R 4TP. Purthe copies maybe obtained from Me Patent Office. Wes Branch, St Mary Cray, Orpington, Kent BRS 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con. 1187