RU163018U1 - Smelting crucible for induction installation - Google Patents

Abstract

A melting crucible for an induction installation, consisting of three layers made of ceramic material, the inner and outer layers of which are made by plasma spraying, and the middle layer placed between them is made in the form of a printed lining, the thickness of which is 0.05-0.30 the inner diameter of the crucible characterized in that the middle layer is made of periclase-based ceramic material, while in the area of the lower part of the crucible, the lining of the middle layer is formed by backfilling, compaction and heating until the sintering mass Which comprises periclase and boric acid at the following content of the fractions and components, in wt. %: periclase: particles of a fraction of 2 mm 49-51 particles of a fraction of 1 mm 44-47boric acid 3-6, and in the area of the upper part of the crucible, the lining of the middle layer is formed by backfilling and compaction of the packing mass, which contains periclase and kaolin wool, with the following fractions and components, in wt.%: periclase: particles of a fraction of 1 mm 49-51 particles of a fraction of 0.08 mm 34-38 kaolin wool 12-16, while the height of the lower part of the printed lining of the middle layer is 0.4-0.6 depth of the crucible.

Description

The utility model relates to metallurgy, in particular to the structural elements of crucible pot furnaces, namely: replaceable multilayer crucibles containing refractory ceramics, which are intended for heating, holding and casting a melt of high-temperature metals, which are melted in induction plants at temperatures above 1600 ° C, for example, metals of the platinum group, namely: palladium and its alloys.

During the operation of such a crucible, the metal placed in it undergoes a state of melting, in which the crucible is heated to a high temperature from the metal. Then, after the hot metal is melted and cast, a cold metal charge is loaded into the crucible, from which the crucible is cooled. So the crucible is subjected to thermal cyclic loads. This is further complicated by the fact that the heating of the crucible with the metal to a high temperature in induction plants is carried out for a very short time and occurs from the inside of the crucible. The water flowing through the inductor cools the crucible from the outside. Thus, a high temperature gradient occurs along the wall thickness of the crucible.

In addition, induction mixing, ensuring the uniformity of the structure of the melted metal, at the same time causes a strong corrosion and erosion effect on the refractory walls of the crucible, subjecting them to severe wear.

All this leads to a breakthrough of the smelted metal to the inductor of the melting plants and the output of their system.

One of the main tasks is the creation of a crucible for induction plants, capable of resisting sharp thermal shocks for a long time when obtaining pure high-temperature metals.

Known melting crucibles for induction plants, consisting of three layers, the inner and middle layers of which are made of ceramic material, and the outer one is made of metal (AS USSR No. 665190, IPC F27B 14/10, pp. 21.11.1977, Op. 30.05.1979, A.S. USSR No. 1499081, IPC F27D 11/06, P. 26.10.1987, Op. 07.09.1989).

However, the presence of the middle layer of known crucibles in the form of a filling of ceramic material allows only partially compensate for the mismatch of the temperature expansion coefficients of the ceramic of the inner layer and the metal of the outer layer, which leads to its fairly rapid destruction. In addition, when transporting the crucible, both empty and with the melt, the crucible receives compressive forces from the grips of the transporting means. This does not allow such crucibles to withstand a large number of heating and cooling prior to their destruction and to obtain high-purity metals with the required yield.

Also known are crucibles for induction plants, consisting of three or more layers made of ceramic material (Chinese patent No. 103604294 (A), IPC F27B 14/10, c. 10.30.2013, op. 26.02.2014, Chinese patent No. 103673601 ( A), IPC F27B 14/10, app. 11/14/2013, op. March 26, 2014), the inner layer of which is made sintered and dense, and the layer next to the center of the crucible is bulk, during alternation of which a multilayer crucible is formed . In the well-known crucibles, the layers are made of one - to prevent contamination of one type of ceramic by another, and of different ceramic materials, but in any embodiment, bulk layers reduce stresses arising in the sintered layers. This prevents the general destruction of crucibles during cyclic processes of their heating and cooling. However, known crucibles are formed without taking into account properties that may be desirable in its various places, for example, be different in height.

Crucibles for induction installations are also known (USSR AS No. 1019202, IPC F27B 14/10, F27D 1/14, c. 07.01.1981, op. 05.23.1983, Belarus patent No. 10816, IPC F27D 23 / 00, z. 12.28.1999, op. 30.06.2008), consisting of layers made of ceramic material. The service life of these crucibles - the number of heating and cooling cycles to failure, is formed by creating their layers with different properties: internal - with low porosity and wettability, and external - with higher porosity for thermal insulation of the crucible. The presence of the middle layer of high-strength refractory material allows the crucible to acquire increased resistance to thermal shock. However, it is possible that the insufficient level of porosity of one layer and the strength of the other layer does not allow the formation of a melting crucible with high long-term resistance to thermal shock during operation to produce large volumes of high-purity metal.

Also known is a melting crucible (Japanese Patent Laid-Open No. 20144024740 (A), IPC F27B 14/10, 3.30.07.2012, op. 06.02.2014) - a sintered ceramic body that contains finely and coarse-grained magnesite, while small magnesite crystals are located between its large crystals. This helps to increase the coefficient of thermal expansion of the ceramic material, thereby increasing its resistance to thermal shocks. However, it is possible that the selection of the used amount and size of magnesite fractions is not optimal for achieving the required number of heating and cooling cycles of the crucible without its destruction and obtaining a sufficient amount of high-purity metal.

Also known is a melting crucible for induction installations (AS USSR No. 349863, IPC F27B 14/10, c. 06.17.1969, op. 04.09.1972), consisting of three layers made of ceramic material based on magnesite, having high refractoriness, the middle layer, located between the inner and outer layers along the entire height of the crucible, contains boric acid. She in the process of manufacturing the lining of the crucible contributes to its hardening by the manifestation of its sintering properties. However, it is possible that the large thermal expansion inherent in magnesite, without rigorous selection of its fractions, leads to the formation of cracks and contamination of the molten metal.

Known crucibles have structural features and materials that can solve the problem of increasing the operational resource and increasing the volume of smelting of high-purity metals by maintaining the shape of the crucibles by, for example, creating a depreciation of their layers in the radial direction.

However, if we take into account that various properties that are manifested during their operation are desirable in different places of the ceramic product, then we can cite well-known crucibles whose properties are different in their height.

So, the crucible of the induction unit (USSR AS No. 1013724, IPC F27D 1/16, c. 06.26.1981, op. 04.23.1983), formed of a ceramic material in which the upper part of the inner layer is made of the main refractory material, and the lower part of this layer is made of acid refractory material. The presence of a composite lining along the height of the crucible eliminates the detrimental effect of the main slag induced in the crucible on the acid lining, which increases the service life - the life of the crucible, and ensures the purity of the melted metal.

Known crucible is designed for melting steel and cast iron, where the formation of slag. However, such a device is not in demand for the melting of palladium, during which slag is not induced, due to the fact that the palladium metal is not able to oxidize.

Also known is the melting crucible of an induction furnace (USSR AS No. 739948, IPC F27D 11/06, c. 12.06.1978, op. 20.11.2005), consisting of three or more layers made of ceramic material, in the outer layer of which a graphite ring is located in the plane of the upper coil of the inductor. Such a ring helps to reduce tensile stresses in the upper part of the crucible, increases its reliability and durability under cyclic thermal loads and ensures the purity of the melted metal.

However, the use of a known crucible with a ring of a material such as graphite does not make it possible to melt metals such as palladium in the crucible due to the formation of brittle palladium carbides with graphite, which enter the metal and render it unusable.

Also known is a melting crucible made of ceramic material, placed in an induction installation (RF patent No. 2282806, IPC F27B 14/06, dated 12.05.2005, op. 27.08.2006), in the upper part equipped with insulating ceramic cylinders around the perimeter crucible, fixed with a metal rope. The initiation of additional compression stresses improves the efficiency of the crucible.

In the middle part along the height of the crucible, its thermal expansion is restrained by a rigid metal band and locks. However, the rigidity of the structural elements of the crucible does not fully reduce the tensile stresses in the crucible to a level that excludes its destruction and penetration of its material into the melt. The service life of the crucible and the volume of melted high-purity metal do not reach the required values.

Also known is a melting crucible of an induction installation (USSR AS No. 616506, IPC F27B 14/04, October 7, 1975, op. 07/25/1975), consisting of three layers made of ceramic material. The multilayer crucible contains an inner layer of refractory oxides, on the outer surface of which a middle layer of refractory oxides is formed by plasma spraying. This is followed by an outer layer of refractory packing material. In the upper part of the crucible there is a ring, which is a reinforcing structural element and at the same time carries a protective function for the crucible during chill casting of molten metal.

The middle layer obtained by plasma spraying of refractory oxides on the inner layer, strengthens it, while at the same time merging with it. This leads to the propagation of cracks that arise in the inner - working layer through the layer formed by the plasma, to the penetration of metal into them, which reduces its quality and the number of melts before the destruction of the crucible.

The closest to the claimed utility model for the combination of essential features (prototype) is a crucible for induction installation (RF patent for utility model No. 114765, IPC F27B 14/10, z. 08/25/2011, op. 10.04.2012), consisting of three layers made of ceramic material, the inner and outer layers of which are made by plasma spraying, and the middle layer placed between them is made in the form of a printed lining, the thickness of which is 0.05 ÷ 0.30 the inner diameter of the crucible.

The known crucible is made of periclase, but its specific fractions and possible additives are not specified, while layers of such an indeterminate composition are evenly distributed over the entire surface of the crucible without taking into account that various properties may be desirable at different places in the ceramic product.

Known crucible is suitable for melting platinum group metals, including palladium and its alloys. However, the uncertainty of the fractional and component composition of the ceramic material of the crucible and the lack of its structural features aimed at optimizing the functioning of the crucible taking into account the depth of the melting space, which is essential for induction heating, does not allow to achieve the required operational resource - the required number of melts before the destruction of the crucible. Moreover, the known crucible does not provide a high yield of products - high-purity platinum metals, for example, palladium with a purity of 99.95 wt. %, the main component due to cracking of the crucible and the ingress of its material into the melt.

The problem to which the claimed utility model is directed is to increase the crucible's service life while increasing the yield — a high-purity palladium metal.

The goal is achieved due to the technical result - to prevent cracking of the crucible, by lining it with a composite height of the crucible, with properties desirable for each of these zones: durable - in the lower part of the crucible and insulating - in the upper.

The problem is achieved in that in the known melting crucible for induction installation, consisting of three layers made of ceramic material, the inner and outer layers of which are made by plasma spraying, and the middle layer placed between them is made in the form of a printed lining, the thickness of which is 0, 05 ÷ 0.30 of the inner diameter of the crucible, according to a utility model, the middle layer is made of ceramic material based on periclase, the lining of which in the zone of the lower part of the crucible is formed by filling , Sealing and heating to sintering stuffing mass which contains periclase and boric acid at the following content of the fractions and components, in wt. %:

periclase:

particles of fraction 2 mm - 49 ÷ 51,

particles of fraction 1 mm - 44 ÷ 47,

boric acid 3 ÷ 6,

and in the area of the upper part of the crucible, the lining of the middle layer is formed by backfilling and compaction of the packing mass, which contains periclase and kaolin wool at the following content of fraction and components, in mass. %:

periclase:

particles of fraction 1 mm - 49 ÷ 51,

particles of a fraction of 0.08 mm - 34 ÷ 38,

kaolin wool 12 ÷ 16,

however, the height of the printed lining of the middle layer in the zone of the lower part of the crucible is 0.4-0.6 depth of the crucible.

The proposed crucible has a middle layer made on the basis of periclase, a highly refractory ceramic material that has a high coefficient of thermal expansion among oxides and low thermal conductivity. Moreover, such properties of periclase are usually equally manifested throughout the height of the crucible.

However, based on the fact that the peculiarity of induction melting plants is that the ratio of the dimensions of the depth of the melting space to the surface of the metal mirror is much larger than in other melting furnaces, the higher specific pressure of the liquid metal column leads to increased wear of the lining in the lower zone of the crucible.

In addition, the crucible must be mechanically strong enough to withstand mechanical shocks in the lower zone of the crucible when loading a solid metal charge.

At the same time, the lining of the crucible undergoes erosion under the conditions of induction mixing of the metal, and to a greater extent in the lower zone of the crucible - near its bottom, due to gushing mixing of the metal upon impact of its directed flows to the bottom under the influence of induced eddy currents.

As a result, a lining mass containing periclase and a sintering agent, boric acid, was selected as the lining material in the area of the bottom of the crucible, which is a substance that contributes to better bonding of the particles of the lining mass heated before fusion. The introduction of a sintering additive into the middle stuffed layer of the crucible in the zone of its lower part promotes the formation of a monolithic heat-resistant frame, which tightly covers the inner layer of the crucible and prevents the opening of cracks that occur in the inner layer of the crucible during operation of the device. Thus, the crucible in its lower part is durable, able to withstand mechanical and thermal stresses.

Due to the fact that the metal inside the crucible in an alternating magnetic field heats up to very high temperatures, and the inductor placed outside the crucible is cooled by water of usually room temperature, a large temperature gradient arises between the inner and outer layers of the crucible, which causes thermal stresses in the crucible, which lead to it cracking. The crucible must have low thermal conductivity to provide thermal insulation and reduce heat loss. At the same time, the total thickness of the layers of the crucible should be as small as possible, since as it increases, the electrical characteristic of the induction installation worsens. As a result of this, in order not to increase such thickness over the entire depth of the crucible, the insulating part of the middle layer of the crucible is formed only in its upper part. This reduces the temperature gradient, thermal stresses and eliminates cracking of the crucible. In the lower part of the crucible, the presence of temperature stresses does not entail the destruction of the strong sintered monolithic structure of ceramics, therefore, a heat-insulating additive in the middle layer of the lower part of the crucible is not required. The introduction of kaolin wool into the middle layer in the upper part of the crucible allows you to keep it in bulk, not sintered, during the entire period of operation of the crucible. The presence of such a buffer layer compensates for the thermal expansion of the inner layer and significantly reduces the tensile stresses perceived by the outer layer. This prevents the formation of through cracks and the penetration of liquid metal to the turns of the inductor.

The ranges of ratios of fractions and components in the inner layer of the crucible in the area of its upper and lower parts are due to experimentally found conditions for achieving a technical result.

So, the low content of sintering additives is less than 3 wt. %, in the middle layer of the zone of the lower part of the crucible leads to insufficient density of the material of this layer, to the penetration of molten metal through cracks in the inner layer of the crucible into the printed middle layer. The content of sintering additives is more than 6 wt. % does not improve the sintering of the middle layer, but leads to a copious release of water vapor upon decomposition of an increased amount of boric acid upon heating of the crucible. Due to the fact that the moisture evaporating from the lining of the furnace increases in volume many times, this leads to cracking of the layers and destruction of the crucible. Low content - less than 12 wt. % of the heat-insulating material in the packed layer in the zone of the upper part of the crucible leads to heating of this part of the crucible and, as a result, to cracking and destruction of the outer layer.

The content of thermal insulation material is more than 16 wt. % does not allow to obtain a dense metal-impermeable printed lining, increases the cracking of the layers and reduces the resistance of the crucible - its operational life.

Also experimentally determined is the range of relations of the height of the printed lining in the zone of the lower part of the crucible to its depth, corresponding to the achievement of the technical result. Reducing the height of the printed lining with sintering additive less than 0.4 from the depth of the crucible leads to the penetration of the melt into the printed layer through cracks in the inner layer.

An increase in the height of the packing layer with a sintering additive of more than 0.6 crucible depth leads to overheating and cracking of the outer layer.

The proposed device is a design in which the claimed combination of materials, composite along the depth of the crucible, of the lining of the middle layer, the form of the outer and inner layers is plasma-ceramic, and the middle layer is printed, the relative sizes of the structural elements allow you to create a new high-quality product with a high service life during repeated loading processes and melting of high temperature platinum metal - high purity palladium.

Distinctive from the closest analogue (prototype) features of the claimed utility model are significant as they affect the achievement of a technical result.

Distinctive features of the claimed utility model are functionally not independent: quantitative or indicate the relative position of the device parts, the search for such signs is carried out without interruption from those functionally independent signs to which they relate without interruption from the object as a whole.

The set of essential features of the claimed utility model is not known at the prior art, therefore it is new.

The drawing shows the proposed device: a front view of the device with a cut along its central longitudinal axis, where:

1 - the inner layer of the crucible,

2 - the outer layer of the crucible,

3 - the middle layer of the crucible in the zone of its lower part,

4 - the middle layer of the crucible in the area of its upper part,

5 - collar.

Information confirming the possibility of implementing a utility model to obtain the specified result is contained in the description of the device in statics and the method of its manufacture.

The melting crucible for the induction installation consists of three layers made of ceramic material. The inner layer 1 and the outer layer 2 are made by plasma spraying. Located between layers 1 and 2, the middle layer is made in the form of a printed lining, the thickness of which is 0.05 ÷ 0.30 of the inner diameter of the crucible. The middle layer is made of periclase-based ceramic material. At the same time, in the zone of the lower part of the crucible, the lining 3 of the middle layer is formed by filling, compaction, and heating to sintering the packing mass, which contains periclase and a sintering additive in the form of boric acid. In the area of the upper part of the crucible, the lining 4 of its middle layer is formed by filling and compacting the packed mass, which contains periclase and a heat-insulating additive in the form of kaolin wool. The compositions of the packed mass of the middle layer with phases and components for the lower and upper zone of the crucible are shown in table 1, columns 3 and 5, respectively. Moreover, the height of the printed lining 3 of the middle layer of the crucible in the zone of its lower part is 0.6 depth of the crucible.

In addition, the crucible is equipped with a collar 5 for sealing the middle layer to prevent it from spilling during casting of the melt.

To obtain the inventive device with a volume of 0.75 l, the packed masses for the composite lining of the middle layer of the crucible, the composition of which is shown in table 1, was prepared in a twin-shaft mixer of the SL / 10Z brand with Z-shaped blades. The packed mass with a sintering additive for the middle layer of the lower part of the crucible was mixed for 6 minutes. The stuffed mass with a heat-insulating additive for the middle layer in the zone of the upper part of the crucible was mixed for 50 minutes. Mixing was carried out with a change in the direction of rotation of the mixer blades to obtain a homogeneous packing mass without separate fragments of kaolin wool.

The packing mass for the collar was prepared with the same composition and using the same technology as for the middle layer of the crucible in its upper part.

To create the inventive device, the inner and outer layers of the multilayer crucible were made by plasma spraying of grade 15A electrocorundum onto removable mandrels, creating voluminous thin-walled products in the form of single-layer crucibles. Then, the smaller (diameter 70 mm, height 90 mm) obtained plasma-ceramic crucible to create the inner layer of the multilayer crucible was centered on a relatively larger plasma-ceramic crucible (104 mm in diameter and 103 mm high), formed to obtain the outer layer of the multilayer melting crucible. Following this, the lower part of the gap between the plasma-ceramic crucibles was filled with a packed mass of different fractions of periclase, in which 2.0 mm particles were 50.0 wt. % and particles with a size of 1.0 mm amounted to 47.0 wt. %, and another component, boric acid, was 3.0 wt. % The gap was filled approximately to the middle of the wall of the inner crucible, using approximately 500 g of stuffed mass, which was then compacted on a vibrating table of grade VI - 101B with a plate rammer.

The upper part of the gap between single-layer plasma-ceramic crucibles, forming layers of a multilayer melting crucible, was filled with a pre-homogenized packing mass containing periclase of different fractions, in which 1.0 mm particles were 50 wt. % and particles with a size of 0.08 mm - 38.0 wt. %, and another component - kaolin wool, was 12 wt. % Such a packing mass was compacted on the indicated vibration table, while filling and compaction of the packing mass was repeated until it reached the upper edge of the wall of the outer plasma-ceramic crucible - the upper edge of the outer layer of the multilayer melting crucible. At the same time, the thickness of the middle stuffed layer, taking into account the thicknesses of the inner and outer layers - 2 mm each, was 13 mm. Therefore, its ratio with the inner diameter of the crucible was 0.18, that is, included in the claimed range. The sealing of the middle layer of the melting crucible - forming the collar, was carried out from the specified packing mass, suitable for forming the middle layer of the melting crucible in the area of its upper part, with the addition of liquid glass with a density of 1.3 g / cm ³ , brought to a pasty state. Then the collar was pierced with a rod in 10 places for the release of water vapor, which subsequently forms when the crucible is heated and the boric acid decomposes. Subsequently, the melting crucible was dried for 6 hours at 200 ° C. The final formation of the middle layer of the crucible was carried out during the trial - the first melting. In this case, the melting crucible was placed in the inductor of the installation, loaded with metal - palladium, and heated with overheating at 100 ° C from its melting point - 1552 ° C for 40 minutes.

At the same time, the packed mass of the middle layer in the zone of the lower part of the crucible containing the sintering additive turned into a monolith tightly covering the inner layer of the crucible. It was sufficiently heat-resistant and prevented the opening of cracks that sometimes formed in the inner layer of the crucible as a result of cyclic temperature changes from heating during the melting of the metal to cooling when loading the charge.

The temperature of the outer layer of the crucible, which was approximately taken as the temperature of the middle layer of the crucible, was also measured with a AKIP 9309 laser thermometer. This temperature in the lower zone of the crucible was 900 ° C, and in the zone of the upper part of the crucible it was 600 ° C; therefore, at the same melt temperature along the depth of the crucible, the thermal conductivity of the middle layer in the zone of the upper part of the crucible was 30–35% lower than its thermal conductivity in the zone of the lower parts of the crucible.

Tests of the claimed device were conducted on the induction installation IPU 100-8-10 in the conditions of URALINTECH CJSC, in which the crucible showed a high service life, namely: it withstood 20 melts without breaking and melting in it was stopped only due to the lack of metal. The yield is Pd - 1 grade palladium with a palladium mass fraction of 99.95% according to GOST 31291-2005 and amounted to 99.6%. Tests of other similar melting crucibles for an induction installation with a capacity of also 0.75 L with different contents of fractions and components in the packed mass and different ratios of the structural elements of the devices both at the declared ranges of values (claimed crucibles) and beyond (experimental crucibles) were also conducted. ) The data are listed in table 1.

In addition, we provide comparative data for the claimed and known devices used in the indicated induction installation at CJSC URALINTECH. The inner and outer layers of all crucibles are made by plasma spraying from corundum. The data are listed in table 2. From this table it is seen that the inventive melting crucible has a high service life - the number of melts before the destruction of the crucible of known devices was 4 ÷ 8, while only before the planned stop of the melting program of the inventive crucible, in the absence of it destruction, amounted to 22. However, it can be argued that the resistance of the new melting crucible has increased by more than 5 times.

So, when fusing the same volume of palladium, for example 3400 kg, using known crucibles, 113 were used, and the number of claimed crucibles was 20 pcs. Given the cost of manufacturing one crucible with a capacity of 0.75 liters, amounting to 1.8 thousand rubles, the savings on all crucibles is more than 167 thousand rubles.

In addition, the volume and cost of processing poor waste in the form of a lining of spent crucibles for the extraction of precious metals, such as palladium, decreased by 5 times.

At the same time, the yield is high-purity, expensive and scarce palladium with its content of 99.95 wt. % in metal, increased from 98.6% when melting in a known crucible to 99.6% in the proposed.

Claims (1)

A melting crucible for an induction installation, consisting of three layers made of ceramic material, the inner and outer layers of which are made by plasma spraying, and the middle layer placed between them is made in the form of a printed lining, the thickness of which is 0.05-0.30 the inner diameter of the crucible characterized in that the middle layer is made of periclase-based ceramic material, while in the area of the lower part of the crucible, the lining of the middle layer is formed by backfilling, compaction and heating until the packed mass is sintered sy, which contains periclase and boric acid, with the following content of fractions and components, in wt. %: periclase: particles of fraction 2 mm 49-51 particles of fraction 1 mm 44-47 boric acid 3-6, and in the area of the upper part of the crucible, the lining of the middle layer is formed by backfilling and compaction of the packed mass, which contains periclase and kaolin wool, in the following fractions and components, in wt.%: periclase: particles of fraction 1 mm 49-51 particles of a fraction of 0.08 mm 34-38 kaolin wool 12-16, the height of the lower part of the printed lining of the middle layer is 0.4-0.6 depth of the crucible.

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