Metallurgical apparatus – Linings
Reexamination Certificate
2000-06-01
2003-11-11
Kastler, Scott (Department: 1742)
Metallurgical apparatus
Linings
C501S101000, C501S099000, C264S030000, C266S286000
Reexamination Certificate
active
06645425
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a batch, in particular for the production of a refractory shaped body as described in the preamble of claim
1
, to a refractory shaped body in accordance with the preamble of claim
29
, and to a process for producing the shaped body in accordance with the preamble of claim
31
.
In the iron and steelmaking industry, the reaction and transport vessels used are brick-lined with refractory materials or lined with ramming compounds. Vessels of this nature are, in particular, converters, such as basic oxygen furnaces or bottom-blowing converters, in which crude steel is obtained from pig iron. Furthermore, steel casting ladles and treatment ladles for secondary metallurgical processes (steel refining), and also downstream units in the steel casting system, are provided with a similar refractory lining.
In this case, steel casting ladles, for example, may both be lined with a high alumina content and have an alkaline lining based on MgO or dolomite.
In particular in converters, but also in steel ladles, it is customary to use linings in which the refractory material has a high content of a carbon carrier. This carbon carrier may be in the form of synthetic resins of any type, tar or pitch or graphite or mixtures of these constituents.
The functions of the carbon carriers are complex. However, the essential function of the carbon is to minimize slagging of the shaped bodies by reducing the wettability of the surface and, in addition, closing open pores.
In use, refractory shaped bodies of this nature become worn due to various operations carried out.
One wear mechanism is that relatively thin surface layers of the shaped body which have been infiltrated by slag wear away through dissolution, abrasion and spalling. This is known as thermochemical wear.
Thermomechanical wear, which takes place as a result of spalling of unchanged brick regions because of excessive thermomechanical stresses is also known.
In addition, carbon-containing shaped bodies also become worn as a result of decarburization of the layers on the hot side.
MgO is one of the most frequently used refractory raw materials.
Shaped bodies based on MgO are generally distinguished by a high refractory quality and a very good ability to withstand slags, in particular highly alkaline slags, i.e. they exhibit considerable advantages against thermochemical stresses. Drawbacks which can be mentioned in particular with regard to the thermal shock behavior is the relatively high coefficient of thermal expansion of MgO and its high modulus of elasticity. Furthermore, MgO has a relatively high thermal conductivity.
For refractory shaped bodies or refractory batches which have a high carbon carrier content as “slag inhibitor”, in particular pitch-bonded shaped bodies, in particular based on magnesite, are known. These magnesite bricks, or alternatively dolomite bricks, can be produced with tar or pitch bonding. To enable pitch-containing binders to be used, these coarse-grained magnesite sinter mixtures are preheated to approximately 100° C. and higher as early as in the silo and are mixed in the hot state with pitch and any carbon additives and, if appropriate, crosslinking substances, in heatable mixers. After the shaped bodies have been pressed, they undergo heat treatment in a tempering furnace at approx. 300° C. The tempering increases the strength of the bricks and significantly reduces the susceptibility to spalling through the release of highly volatile hydrocarbons, in particular in the heat-up phase of the converter. With batches of this nature, it is ensured, inter alia, that raw materials with the lowest possible iron oxide and silicate content and a low boron content, a high sinter density and with large crystals (periclase) are used.
To increase the carbon content, and, in addition, to achieve an increase in the thermal conductivity, so that the heat can be dissipated more quickly in particular to water-cooled outside walls, it is known for refractory raw materials to be mixed with graphite and provided with resin or pitch bonding.
Furthermore, unfired shaped bodies, i.e. shaped bodies which have not been produced with a ceramic bond, but only from the bonding tar, are known, and shaped bodies which, in addition to the refractory oxide component (for example magnesite), contain a continuous bond formed by graphite platelets have been developed. Further developments envisaged using carbon in the form of soot, resulting in a longer service life of the shaped bodies. It has emerged that if relatively large amounts of graphite are used, synthetic resins (resol resins, novolak resins) are particularly suitable as binders for shaped bodies of this nature.
Therefore, working on the basis of tar-bonded sintered dolomite or magnesite bricks, pitch-bonded or resin-bonded two-component bricks have been developed which, with regard to the chemical resistance, combine the advantages of the refractory oxides and of the graphite.
In general, shaped bodies with resin bonding and graphite are produced by mixing the components in the cold state, shaping them under a high pressure and then hardening them at approximately 200° C. The hardening mechanisms depend, inter alia, on whether a one-component resin (resol resin) or a two-component resin with a hardener (novolak resins) is being used.
The resin content is usually between 2 and 5%, the graphite content may be between approximately 7 and 20%, with around 15% perhaps being regarded as customary.
To improve the service properties of carbon-containing bricks, it is additionally possible to add antioxidants, in particular in the form of metals, such as Al, Mg or Si.
In addition to the wear mechanisms which have already been described, during operation of the converter, steel scrap is added to the pig iron and is then melted down. This steel scrap is introduced into the converter, falls into the converter and in the process imposes considerable loads, in particular as a result of direct impact on the refractory lining. Furthermore, it is possible that mechanical wear may take place through stresses caused by temperature changes during heating or reheating after significant cooling, and this wear makes its presence felt by spalling. Furthermore, wear is caused by erosion in the area of power flows, for example at the pig iron impact point (casting jet impact and in nozzle regions).
The refractory lining is also subjected to substantial wear in other areas of steelmaking and steel processing, in particular in metallurgical ladles, especially also in the casting jet impact region. The service life of the units described is substantially determined by the wear at these principle points of loading.
To improve the mechanical resistance of such refractory linings, in particular refractory shaped bodies, it is proposed, in DE 196 43 111 A1, to introduce reinforcement bodies into the shaped bodies during production, which reinforcement bodies are to make the shaped body better able to withstand impact loads. The reinforcement bodies are to comprise in particular wire elements made from steel with a high heat resistance; an approximate Z shape of these elements is proposed as a particular embodiment.
Tests have shown, that reinforcement with steel wire of this nature, and also reinforcement with steel fibers in the form of a steel wool which is incorporated in the shaped body, do not enable such mechanical improvements to take place. On the one hand, it is not possible to compress the material which has been mixed with pieces of steel wire to the desired and required level of compaction. On the other hand, pressing results in an undesirable formation of compressed layers, in particular when using steel wool, and the inhomogeneities observed occur as early as during mixing. The steel reinforcement elements are drawn steel wires which are substantially elastically deformed in the brick during the pressing operation, i.e. the energy of deformation is stored so that after pressing, the brick is driven outwards again by the restoring forces in the
Bartha Peter
Jansen Helge
Wienand Hans
Goodman & Teitelbaum, Esqs.
Kastler Scott
Refractechnik Holding GmbH
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