MXPA99010558A - Castable refractory compositions - Google Patents

Abstract

The invention relates to a method for producing refractory compositions and more particularly to a method for producing castable refractory compositions which comprises combining appropriate quantities of bulk particulate refractory aggregates substantially without pre-mixing;separately adding to the aggregate system an appropriate quantity of a pre-blended binder composition;mixing the aggregate system and the pre-blended binder composition in a mixer;and discharging the refractory composition from the mixer.

Description

MOLDING REFRACTORY COMPOSITIONS DESCRIPTIVE MEMORY This invention relates to refractory and other compositions, and more particularly, to castable refractory compositions comprising refractory aggregates in particles and binder components. Compositions for isopression are also within the scope of the present invention. Moldable refractory compositions comprising refractory particulate aggregates and binder components are used in the metallurgical, cement, petrochemical and glass industries for the production of furnace and bucket coatings, punts or drinking troughs, pouring nozzles and other heat resistant applications. In general, manufacturers produce moldable refractory compositions far away from end-user facilities. In a conventional process for producing a castable refractory composition, the raw materials either bulk, in intermediate volume containers or bags on pallets including refractory particulate aggregates and binder components, are introduced to a mixer, which usually has around from one to two tons of capacity. With the exception of pallets, which can be reused, the packaging of raw materials is subsequently discarded frequently, especially when it comes to small paper or plastic bags. Normally, the packaging of raw materials is discarded by burying or incinerating it; Both procedures are expensive, and the first is subject to taxes established by the State. However, residues of refractory particulate materials in the packaging also produce waste and, therefore, a reduction in this and the volume of redundant packaging that is required to be disposed of would be extremely convenient. In general, the loading of raw materials discharged is subject to a thorough mixing operation in the mixer for 5-20 minutes, depending on the composition, to produce a homogeneous composition. The energy consumption of the mixer is considerable and is added to the costs of the product. Finally, the composition is discharged from the mixer and repacked in bags of 25 kg, 250 kg, 500 kg, 1000 kg, or 2000 kg, as necessary, and after having undergone extensive quality control tests, It is transported to the end user's facilities. Upon arrival at the end user's premises, the various types of bags are broken open, and the contents are discharged into a second mixer. The bags can be discarded once more, with the concomitant waste problems mentioned above, and the composition is subjected to a further mixture in the second mixer, during which process, water is added to the mixed composition. Then, the moldable composition is discharged from the mixer to transport it, or pump it, to the place where the casting coating is formed in situ. From the above description it will be apparent that there are several inherent difficulties in the present method for the manufacture of moldable refractory compositions. In addition to the waste problems represented by the two sets of discarded bags, it is necessary to mix the entire composition on two separate occasions in large mixers that have a substantial energy consumption. Once the aggregates are mixed with the binder, it is important that the composition remains dry until needed, otherwise the binder may deteriorate the homogeneous cure of the final mixtures. Originally, it is for this reason that the smaller bags of the composition could be used frequently, so that, if a bag develops a leak during storage or transportation, allowing the entry of water, only a small amount of water is damaged. the composition. However, an unrelated matter at all is that it costs a considerable amount of money to keep the ovens isolated while the repairs are being made. Furnace operators plan upgrades and repairs to the furnace and connected equipment, in a meticulous way, so that the time during which the furnace is not in operation can be reduced. A repair is the change of the lining of outlets, drinking fountains, ovens and ladle coverings, etc., and for the supplier of refractory compositions, which usually has the responsibility of supervising the repair, this means that it can allow little time for the item to be repaired is cooled before the repair has to be made, so the freshly molded refractory composition will cure and harden before the kiln restarts online; therefore, time is the essential. In addition, by casting the refractory compositions into still very hot components that have just left the line, the rate of cure of the composition is very fast inevitably. Although this in itself is not a problem, it means that when there are limits between a casting and a subsequent casting, weak lines can develop in the limit, giving as a possible result cracks or other defects in the refractory lining. The answer to these problems is to strain in large volumes very quickly; in this way, kiln operators can be provided with a large two-ton mixer and some mobile baskets or hoppers of the same capacity so that they can discharge the mixed composition into the baskets, one immediately after the other. Therefore, perhaps three or four baskets may be filled, one after the other, so that each can be discharged in rapid succession, providing, at bottom, a continuous distribution. Meanwhile, the mixer is mixing one more load, which can be ready to be emptied into the first hopper or hopper (already empty), before having discharged the third boot. In this way, perhaps up to sixteen tons of refractory compositions can be squeezed almost at the same time. However, the loading, addition of water, mixing and discharging of the mixers takes relatively long time, and this element is the difficulty in the process. Finally, the speed of the cycle is reduced to its slowest component, and the quasi-continuous casting is reduced to casting by load. Since it is the objective to have a continuous cycle of loading, mixing and unloading, for the casting process to be continuous, it is necessary to accelerate the mixing procedure. This precludes the use of small bags of composition, only for the time required to empty the bags in the mixer. In this way, it is an object of the invention to overcome the aforementioned problems or at least mitigate their effects. In accordance with the present invention, the above difficulties are overcome by a novel method in which the binder composition is combined in a separate step before mixing with the particulate refractory materials (hereinafter referred to as the aggregate system). In a first aspect, the present invention provides a method for producing castable refractory compositions comprising the composition of a system of aggregates of appropriate quantities of refractory aggregate in bulk particles, basically without premixing, adding separately to the aggregate system an appropriate amount of a pre-blended binder composition, the transportation of the aggregate system to an installation site, the mixing at the installation site of the aggregate system and the pre-blended binder composition with water in a blender and the discharge of the refractory composition from the blender. Said method produces numerous advantages. In a preferred embodiment of the invention, the components of the aggregate system are purchased in accordance with the specification of particle size and chemical composition guaranteed in reusable intermediate volume containers. Preferably, the pre-binder is added in a quantity by weight to the aggregate components, and the combined materials are transported to the user's site in the intermediate volume container that originally contains one of the aggregate components; this has the advantage of providing at least two reusable intermediate volume containers, one containing the material sent to the user's site, and one available for another use. In this specification, the term "castable refractory composition" is defined as a precursor comprising particulate refractory materials, and a binder composition, which, when combined with water in suitable proportions, preferably in the mixer, can be discharged, transported and squeezed in. in situ to form the desired refractory figure.

The components of the aggregate system comprise refractory aggregates in the appropriate amounts, and generally comprise a first and second aggregate components, for example, the first comprising alumina and the second comprising silicon carbide. The first component, alumina powder, is preferably present in an amount of 10 to 90% the total composition by weight, and preferably has a typical particle size scale of 100 to 12,500 microns. The second component, silicon carbide, is preferably present in the composition in an amount of 5 to 90% of the total composition by weight, and preferably has a typical particle size scale of 5 to 2000 microns. In each case, the particle size distribution is controlled within a specified scale. Other components of the aggregate system can be used as a total or partial replacement of the alumina and silicon carbide components, but there will always be at least two components; alternatives may include, for example, andalusite, calcined bauxite, quianite, sillimanite, chamottes, concreted or fused alumina-spinel, magnesia, concreted or fused, zirconium and zirconia. The required particle size distribution of the aggregate components can be achieved, for example, by the combination or assembly of specific fractions of particulate refractory materials in the desired proportions. Preferably, this operation is carried out by the suppliers of aggregate components that will assemble the correct combination of particles to satisfy a specific particle size distribution objective, and pack them into a container of intermediate volume of specific capacity and type. An important aspect of the present invention is that the parts of the components of the binder composition are combined separately before loading with the aggregate system. The components of the binder composition may comprise, for example, reactive alumina, fine silicon carbide, ultrafine silica powder, clays, cements with high alumina content and hydratable alumina. Preferably, the binder composition comprises from 5 to 35% of the total refractory composition by weight. The above proportions of materials refer to dry weight, and do not include the water that is added to produce the final castable refractory composition. The amount of water added may be up to about 10% by weight, but preferably it is from 5 to 5.5% by weight, based on the total dry weight of the composition. In the preferred embodiments, the invention allows the entire composition to be mixed only once, using a mixer located in the facilities of the end user. In addition, it has been found that the time required for blending so far is less than originally required at the site, when mixing water with the premixed aggregate and the binder composition. In other words, substantial energy savings can be made at the location site of the suppliers of the refractory compositions, avoiding mixing there, whose saved costs can be passed on to the final customer. Another important advantage of the present invention is that the pre-blended binder and aggregate have very poor flow properties, due to the finer particles that fill the spaces between the large particles and agglutinate all together; this is, of course, very desirable in the final casting product, but not when efforts are made to transfer the packaging components to the mixer by solid flow. Thus, an important aspect of the present invention provides a package of materials for producing formable refractory products, the materials comprising, in appropriate relative amounts, substantially unmixed layers of at least the first and second compositions. Preferably, said product is moldable and the first and second compositions comprise aggregate components. Preferably, said package includes a layer of a pre-blended binder composition in an appropriate amount with respect to said aggregate components. Preferably, the binder is between the first and second composition layers.

The components are in amounts ready to be mixed with water to form said moldable refractory composition. This placement has two particular advantages. First, since there is no substantial mixing between the layers, each layer is separated and therefore flows relatively easily. This effect is improved if the first and second components graduate themselves in sublayers. This placement allows a complete and fast unloading of the package, leaving it relatively clean to reuse it later. Secondly, if the binder is between the two layers of aggregates, it is protected from two main sources of moisture ingress, namely, the open top of the package, and the lower part of the package that is sensitive to perforations and filtration. water that is on the ground. Of course, it does not matter if the aggregates get a little wet, as long as the binder stays dry. Since the binder is the finest powder, it is usually the one that sticks to the walls of the packaging, etc .; however, the aggregate seated on the binder has the effect of purifying the package when leaving it, taking with it basically all traces of the binder. An additional advantage of this placement is the security it offers against deliberate attempts by others to determine the composition of the product being supplied. The precise compositions of the aggregate components, and the binder compositions, not to mention the total composition in the final product, are sometimes very well kept trade secrets. By providing the components in segregated layers in the delivery package, an attempt to discern this information can not be made successfully by simply taking a small sample as a means to establish the content of the entire package. Furthermore, the present invention finds application with isopresionizable refractory compositions, such as alumina / graphite, which can be formed by isostatic pressure on alumina-graphite pieces, ie, wherein the first and second compositions include alumina and graphite. The graphite can be found in a layer between the layers of alumina. In a preferred embodiment of a moldable product, the components of the aggregate system, which each have the required particle size distribution, are delivered to the manufacturer in reusable packaging, which preferably comprises, for example, a mini-volume bag. Preferably, the alumina aggregate is delivered in an extra-large minivolume sack that has u? size such that there is sufficient volume for the silicon carbide and binder composition to be added to the bag; This avoids the use of paper sacks for the components, lightening the waste problem, and reducing the loss of components when removing them from the bags. Of the components of the composition discharged in the minivolume sack, only the binder composition will have been subjected to a previous combination; however, the components will be accurately weighed in the mini-volume bag, so that they are present in the specified proportions. Then, the mini-volume bag, or other suitable package, can be delivered to the end user. At the end-user's facilities, the mini-volume bag is discharged directly into the mixer, and the entire refractory composition mixed for the first and only time. Given the unmixed nature of the components, the discharge of the bag is rapid. Water is then added to the mixer and the castable refractory composition is discharged and processed in the usual manner. The energy consumption is reduced, as mentioned above, since the binder represents only 5 to 35% by weight, almost always 20% of the final mixture, and this is the only component that undergoes a previous combination. A further advantage is that the quality control test of the components can be substantially reduced in the new method, since each ton of binder will almost always produce 5 tons of final moldable composition. In fact, this last point is of particular importance, since until now, samples of binders and mixed aggregates, in practice, can only be subjected to one test for every three to six tons produced, depending on the size of the load, ( which represents 15-33% of test speed), so the quality could not be fully guaranteed. However, with the present method, the supplier of aggregates supplies the aggregates in a guaranteed composition that has been guaranteed quality separately. The supplier of refractory compositions only needs to deal with the binder for which a single filler, which almost always comprises 10 to 20% by weight of the final composition, will almost always be sufficient for, say, six tons of final product; therefore, the premixed binder test represents 100% quality assurance. The method according to the invention also allows the reuse of packages to be introduced, whereby the problem of disposal of unwanted packaging materials is reduced; Above all, there is less handling of raw material and therefore the waste / spillage of raw materials is reduced. The number of weight operations can also be reduced and above all load accuracy can be improved in this way. Although it is common for the manufacturer to supply the refractory composition to the end user in ready-to-mix reusable volume containers, it would be possible for the aggregate system and the combined binder composition to be delivered to the end user separately and unloaded in a mixer at the facility of the end user. Furthermore, the present invention relates to isopression compositions, such as alumina / graphite, which can be pressed into pieces of alumina-graphite. In the same way, the advantages of the present invention can be perceived with said compositions.

A comparison between the conventional process method and a method according to the invention is illustrated, by way of example, in the accompanying flow diagrams, in which: Diagram 1 is a schematic representation of a conventional method for producing compositions moldable refractory; and Diagram 2 is a schematic representation of a method for producing castable refractory compositions according to the invention. In diagrams 1 and 2, the essential difference between the two procedures is the mixing station 12 in diagram 1 applies to all materials, since the same station 12 'in diagram 2 only refers to the combination of the binder. In addition, there is an additional entry 14 in diagram 2, in which previously weighted aggregates, certified by the supplier to adhere to the predetermined specifications, are supplied directly to the charging station 16. The invention is described in more detail in further, by way of example, with reference to the accompanying drawing, in which there is a section through a mini-volume bag showing the formation of layers of the materials contained therein. In the drawing, a mini-volume bag 16 comprises a reinforced cloth bag having handles 18 and a discharge opening 20. The opening 20 is controlled by a knot 22. In the bag there are three layers of material: a first layer 24 of a first component of aggregates, such as alumina; a second layer 26 of a binder composition; and, a third layer 28 of a second component of aggregates, such as silicon carbide. The binder layer 26 is a precombined homogenous composition, as described below; however, the aggregate layers 24 and 28 may be laminated according to the different components without substantially intermixing. At any time, there is little or no intermixing between the three layers, different from the marginal mixture and in mutual settlement at the respective limits. It is important that there is no opportunity for mutual packaging of the various components, so that the smaller particles of the components do not fill or pack the interstices between the larger particles. An embodiment of the invention will be illustrated below by the following examples: EXAMPLE 1 This example describes the production of a castable refractory composition by a method according to the invention.

Preparation of the binder The component parts of a binder composition comprising ultrafine alumina powder, silicon carbide powder, high alumina cements, clay and deflocculants are introduced to a suitable blender with the ability to produce a large charge. The packaging is discarded from the binding ingredients. At the end of the mixing cycle, the binder composition is discharged from the mixer into suitable containers or packages that may include reusable elements. At this stage, a sample of the binder composition is taken and combined with the correct proportion of the aggregate system to provide a complete mix for the quality control test in the laboratory. The physical properties of the final composition are then determined and compared with the definition or specification of the product.

Preparation of the aggregate system 1.0 tons of alumina aggregate are placed on a scale of average particle size 12500 to 100 microns in a mini-volume sack with a total capacity of 2.0 tons. 0.6 tons of silicon carbide aggregate from particle size scale 2000 to 5 microns are placed in a 1.0 tonne capacity mini-volume sack. Additional aggregate materials, for example, concreted or fused alumina-spinel can be added to bring the aggregate system to the desired specification. Alternatively, the concreted or fused alumina-spinel aggregates can replace the alumina component wholly or in part. In any case, the components of each aggregate are added separately so that, in each bag, the aggregates are in sublayers inside the bag. 0.4 tons of blended binder composition are added to the minivolume bag containing the alumina aggregate component, followed by 0.6 tons of the silicon carbide aggregate component, to produce a package of layered components. Of course, pouring the silicon carbide component into sublayers in the alumina bag results in some mixing, but not enough to homogenize that component. Then, the bag is sealed to be transported to the end user's installation site. At the end user's facilities, the entire content of the minivan bag is discharged into a mixer with a capacity of 2 tons. By virtue of the formation of layers of the components, the discharge takes around 15 seconds, as opposed to around 30 seconds with mixed components; In addition, the discharge is clean, allowing the bag to be used again. The components are mixed for 2 minutes in the mixer, while almost always 100 liters of water are added, and, after mixing more for about 4 minutes to distribute the water homogeneously throughout the composition, the castable refractory composition is discharge in suitable conveyor systems to take them to the area where the moldable composition will be installed.

EXAMPLES A to D Three more examples (A, B and C) were prepared to compare them with a fourth example (D), premixed in a conventional manner. All examples A to D have identical compositions, and each example A to C was mixed dry to reduce the time before mixing with water. The following results table was obtained: PICTURE Example A represents a mixing time equivalent to the conventional D example, since Example D will have been premixed for about six minutes at the supplier's facilities of the refractory compositions before delivering them to the installation site. The example 'C, however, shows that the reduction of the dry mixing step to no more than what is conventionally done, prior to the addition of water, has no fundamental effect on the physical and dry properties of the final product compared to Example D, despite having made the mixture reduced.

Claims (20)

NOVELTY OF THE INVENTION CLAIMS

1. - A method for producing castable refractory compositions, which consists of: combining a system of aggregates of appropriate quantities of refractory aggregates into bulk particles basically without premixing; adding separately to the aggregate system an appropriate amount of a pre-blended binder composition basically without mixing with the aggregate system; transport from the aggregate system and the binder to an installation site; mix at the installation site of the aggregate system and the pre-blended binder composition with water in a mixer; and discharging the refractory composition from the mixer.

2. A method according to claim 1, further characterized in that the aggregate system and the binder composition are transported in a reusable bulk container.

3. A method according to claim 2, further characterized in that the reusable container is a bag of minivolumen.

4. A method according to claim 1, further characterized in that the aggregate system and the pre-blended binder composition are discharged directly to the mixer and mixed therein.

5. A method according to any of the preceding claims, further characterized in that the aggregate system comprises the first and second components.

6. A method according to claim 5, further characterized in that the first and second components are alumina and silicon carbide, respectively.

7. A method according to claim 5 or 6, when dependent on claim 3, further characterized in that the first component of aggregates is delivered in said extra-large mini-volume bag having a size that allows sufficient volume for the second component of aggregates and the binder composition that will be added to the bag.

8. A method according to any of the preceding claims, substantially as described in the examples.

9. A method according to any of the preceding claims, substantially as described above in the present invention.

10. A package of materials for producing formable refractory products, the package comprising a container and at least two of: a) a binder composition; b) a first component of aggregates; and c) a second component of aggregates, wherein at least two materials are layered in said container. 1.

A package according to claim 10, further characterized in that the product is moldable and the first and second compositions comprise aggregate components.

12. A package according to claim 1, further characterized in that the package includes a layer of a pre-blended binder composition, in an appropriate amount with respect to the aggregate components.

13. A package according to claim 12, further characterized in that the binder is in a layer between the first and second layers of composition, so that the binder is at least partially protected from moisture ingress in the package from any of the sides of the first and second layers of composition from the binder layer.

14. A package according to any of claims 1 to 13, further characterized in that the first composition is alumina, and the second component is silicon carbide.

15. A package according to any of claims 1 to 13 further characterized in that the first composition is alumina and the second component is alumina-spinel.

16. - A package according to any of claims 1 to 13, further characterized in that the first and second components are the same.

17. A package according to claim 10, further characterized in that the product is isopresionable, and the first and second compositions include alumina and graphite.

18. A package substantially as previously described in the present invention with reference to the examples.

19. A package according to claim 13, further characterized in that the product is isopresionable, and the first and second compositions include alumina and graphite.

20. A package substantially as described above in the present invention with reference to the examples.