CN113149698A - Magnesium oxide ceramic core with good dissolution collapsibility and preparation method thereof - Google Patents
Magnesium oxide ceramic core with good dissolution collapsibility and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a magnesium oxide ceramic core with good dissolution collapsibility and a preparation method thereof, wherein the magnesium oxide ceramic core is mainly prepared from 80-100 parts by weight of magnesium oxide, 3-15 parts by weight of calcium carbonate and 1-3 parts by weight of wood powder. The method comprises the following steps: weighing and mixing the magnesium oxide, the calcium carbonate and the wood powder according to a certain proportion, adding tung oil, grinding uniformly, pressing and molding the mixed powder, demoulding to prepare a green body, and heating and sintering the pressed green body according to a certain sintering program to obtain the magnesium oxide ceramic core. The magnesium oxide ceramic core prepared by adopting calcium carbonate as a mineralizer and wood powder as a pore-forming agent has good room-temperature bending strength and excellent dissolution collapsibility, and in addition, the sintering temperature and the addition amount of calcium carbonate can be adjusted according to the requirements on the performance of the core in the actual use process, so that the use performance of the core is met.
Description
Technical Field
The invention belongs to a precision casting material and a preparation method thereof, and particularly relates to a magnesium oxide ceramic core with good dissolution collapsibility and a preparation method thereof.
Background
The development of the aviation industry has greatly promoted the development of investment precision casting technology, and particularly, in the application of high-temperature alloy, titanium alloy, aluminum alloy, alloy steel and other materials, the development of large-scale, complicated, integrated and light-weight machine parts is promoted. Compared with the traditional solidification forming manufacturing process, the complex part formed by the near-net-shape investment precision casting technology has the advantages of high dimensional precision, low surface roughness and the like, and can be used for producing complex thin-wall parts and complex inner cavity structure castings.
The inner cavity of the traditional investment casting is mainly prepared by applying fusible pattern materials, coating refractory materials, sanding a module and the like together with the appearance. Along with the development of large-scale, complicated and integrated machine parts, the inner cavity structure of the parts tends to be more precise and complicated, and the process methods have certain limitations, so that a special ceramic core is required to be adopted to form the inner cavity of the casting. The properties of the ceramic core directly affect the dimensional accuracy, yield, and manufacturing cost of parts, and thus research and development of the ceramic core have been receiving attention. In recent years, around the research and development of precision castings for high-end power machinery, ceramic cores for high-temperature alloy production are researched and applied more, and the more mature domestic application is silicon-based ceramic cores. However, when the use temperature exceeds 1550 ℃, the core is easy to deform, and the silicon oxide is easy to react with elements in the alloy steel, so that defects are formed on the surface of a casting, the core release performance is seriously influenced, and the application of the core in cast steel is limited.
In common refractory materials, the affinity of magnesium to oxygen is far greater than that of alloy elements in steel, a ceramic core prepared from the common refractory materials cannot react with the elements in the steel at high temperature, and in addition, the magnesium oxide ceramic core can be dissolved in phosphoric acid solution and acetic acid solution, and slight corrosion of the magnesium oxide ceramic core can be ignored in the actual production process of alloy steel castings, so that the magnesium oxide ceramic core has important application value for manufacturing complex thin-wall stainless steel and alloy steel castings. At present, the magnesium oxide ceramic core for alloy steel has the main problems that: when the sintering temperature is low, the strength of the mold core is low, and the mold core is easy to break during casting; when the sintering temperature is high, the dissolution rate of the mold core is slow, and the mold core is not easy to strip.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to provide a magnesia ceramic core with good dissolution collapsibility; the second purpose of the invention is to provide a preparation method of the magnesia ceramic core.
The technical scheme is as follows: the magnesium oxide ceramic core with good dissolution collapsibility is mainly prepared from 80-100 parts by weight of magnesium oxide, 3-15 parts by weight of calcium carbonate and 1-3 parts by weight of wood powder.
Further, a preferred magnesia ceramic core is made mainly of 90 parts by weight of magnesia, 5 parts by weight of calcium carbonate and 2 parts by weight of wood flour.
In the magnesia ceramic core, calcium carbonate is used as a raw material, and on the one hand, the calcium carbonate is decomposed at high temperature to form CO2And (3) escaping gas to increase the porosity of the ceramic core, enabling the core removing liquid to enter the core through the air holes, corroding the connection part of particles, disconnecting the connection between the particles and dispersing the ceramic core. The higher the porosity is, the easier the core removing liquid enters the interior of the ceramic core, and the higher the porosity is, the more the dissolution collapsibility of the ceramic core can be effectively increased. On the other hand, calcium carbonate is decomposed at high temperature to form calcium oxide, magnesium oxide and calcium oxide do not react at high temperature, and no new phase is generated, so that calcium carbonate serving as a mineralizer in sintering prevents the formation of a mineral phase which is difficult to dissolve, forms the directional mineralization effect, and does not generate redundant new phase, so that the calcium carbonate is compared with the traditional calcium oxideMagnesium oxide cores, products made using calcium carbonate have good dissolution collapsibility. By adopting the wood powder, on one hand, the wood powder can be used as a pore-forming agent to be removed at high temperature, no redundant residue is left in a matrix after removal, and the porosity of the ceramic core is improved; on the other hand, in the high-temperature sintering process, the wood powder decomposition product can slow down the decomposition of calcium carbonate, reduce the decomposition speed of calcium carbonate and avoid the generation of defects such as surface bubbling and the like in the sintering process.
Further, the granularity of the magnesium oxide is 200-400 meshes; the granularity of the calcium carbonate is 400-600 meshes, and the granularity of the wood powder is 200-400 meshes. The size and the shape of each raw material particle determine the size and the shape of pores inside the ceramic core, and different sizes also influence the mixing uniformity among different raw materials and influence the uniform distribution of the pores, so that the particle sizes of the calcium carbonate and the wood powder need to be strictly controlled. Too large granularity easily causes the gas pocket size too big, can seal when high temperature sintering, causes the reduction of permeability, and the granularity undersize can not play the effect of pore-forming, influences the dissolution collapsibility of core.
The invention also provides a preparation method of the magnesium oxide ceramic core with good dissolution collapsibility, which comprises the following steps:
(1) respectively drying magnesium oxide, calcium carbonate and wood powder, mixing in proportion, and then ball-milling to obtain a mixture;
(2) adding tung oil into the mixture, and uniformly grinding;
(3) pressing and molding the ground mixture, and demolding to obtain a green body;
(4) and sintering the pressed green body to obtain the magnesium oxide ceramic core.
Further, in the step (1), the ball milling speed is 250-300 r/min, and the ball milling time is 1.5-2 h. The mixing degree of the magnesium oxide, the calcium carbonate and the wood powder can be improved by the ball milling mode, and the core particles can be broken by the over-high ball milling rotating speed, so that the property of the base material is changed.
Further, in the step (2), the mass ratio of the tung oil to the mixture is 2-4: 100. compared with the traditional binder (such as polyvinyl alcohol), the core powder has the advantages that a layer of flexible film can be formed on the surface of particles, the strength of a blank body is improved, the core powder can be effectively inhibited from hydration reaction, the effect of preventing moisture absorption and denaturation of the core is achieved, and the preservation of the core green body is facilitated.
Further, in the step (3), the pressure is controlled to be 4-6 Mpa during the compression molding process, and the pressure maintaining time is 90-120 s.
Further, in the step (4), the sintering temperature is 1250-1500 ℃, and the sintering time is 0.5-2 h. The sintering temperature must be strictly controlled in order not to crack the green body during sintering. In addition, it is necessary to maintain the temperature at which the additives are removed for a sufficiently long time in view of the convenience of removing various organic additives.
Further, in the step (1), the drying temperature is 100-110 ℃, and the drying time is 1-3 h.
Has the advantages that: compared with the prior art, the invention has the following remarkable advantages: the magnesium oxide ceramic core prepared by adopting calcium carbonate as a mineralizer and wood powder as a pore-forming agent has good room-temperature bending strength and excellent dissolution collapsibility, and in addition, the sintering temperature and the addition amount of calcium carbonate can be adjusted according to the requirements on the performance of the core in the actual use process, so that the use performance of the core is met.
Drawings
FIG. 1 is a binary phase diagram of MgO-CaO material used in the ceramic core of the present invention;
FIG. 2 is a graph showing the relationship between the bending strength of the core and the addition amount of calcium carbonate;
FIG. 3 is a graph of core shrinkage versus calcium carbonate addition;
FIG. 4 is an SEM image of a cross section of a sintered core at 1400 ℃ with 5 parts by weight calcium carbonate added;
FIG. 5 is an SEM image of a cross section of a core sintered at 1340 ℃ with the addition of 5 parts by weight of wood flour;
FIG. 6 is an SEM image of a cross section of a core sintered at 1340 ℃ using 150 mesh magnesium oxide.
Detailed Description
The technical solution of the present invention is further described in detail with reference to the accompanying drawings and examples.
In the following examples, bending strength of samples is measured by a microcomputer-controlled electronic universal tester, mass of the cores before and after dissolution is measured by a weighing method, and loss rate of core dissolution mass is calculated.
Example 1
(1) Weighing a certain amount of magnesium oxide, calcium carbonate and wood powder, wherein 80 parts by weight of magnesium oxide powder, 3 parts by weight of calcium carbonate powder and 1 part by weight of wood powder; the granularity of the magnesium oxide powder is 400 meshes, the granularity of the calcium carbonate powder is 400 meshes, and the granularity of the wood powder is 200 meshes;
(2) putting the weighed powder into a drying oven, and drying at the temperature of 100 ℃ for 3 h;
(3) putting the dried raw materials into a ball milling tank of a planetary ball mill, and carrying out ball milling for 1.5h at the rotating speed of 250 r/min;
(4) preparing 2 parts by weight of tung oil, putting the mixture into a mortar, adding the tung oil, and uniformly grinding;
(5) placing the uniformly ground mixture into a die, maintaining the pressure for 90 s under the pressure of 6MPa, demoulding and taking out a green body;
(6) and (3) placing the pressed green body into a box furnace, and sintering at 1500 ℃ for 0.5h according to a set sintering curve to obtain the core, wherein the bending strength is 20MPa, and the mass loss rate of the acetic acid dissolved core is 45% in 10 h.
Referring to fig. 1, only mutually solid-dissolved phases exist in the core, at 1700 ℃, MgO can be solid-dissolved with about 1.8wt.% CaO, and CaO can be solid-dissolved with about 2.6wt.% MgO, so that a refractory mineral phase is not generated, and the high temperature resistance of the core is not affected.
Example 2
(1) Weighing a certain amount of magnesium oxide, calcium carbonate and wood powder, wherein 90 parts by weight of magnesium oxide powder, 5 parts by weight of calcium carbonate powder and 1 part by weight of wood powder; the granularity of the magnesium oxide powder is 400 meshes, the granularity of the calcium carbonate powder is 600 meshes, and the granularity of the wood powder is 200 meshes;
(2) putting the weighed powder into a drying oven, and drying at the temperature of 100 ℃ for 1 h;
(3) putting the dried raw materials into a ball milling tank of a planetary ball mill, and carrying out ball milling for 1.5h at the rotating speed of 300 r/min;
(4) preparing 4 parts by weight of tung oil, putting the mixture into a mortar, adding the tung oil, and uniformly grinding;
(5) placing the uniformly ground mixture into a die, maintaining the pressure for 100s under the pressure of 5MPa, demoulding and taking out a green body;
(6) and (3) placing the pressed green body into a box furnace, sintering for 2h at 1340 ℃ according to a set sintering curve to obtain a core, wherein the bending strength is 16MPa, and the mass loss rate of the 10h acetic acid-soluble core is 50%.
Example 3
(1) Weighing a certain amount of magnesium oxide, calcium carbonate and wood powder, wherein 85 parts by weight of magnesium oxide powder, 10 parts by weight of calcium carbonate powder and 2 parts by weight of wood powder; the granularity of the magnesium oxide powder is 270 meshes, the granularity of the calcium carbonate powder is 600 meshes, and the granularity of the wood powder is 400 meshes;
(2) putting the weighed powder into a drying oven, and drying at the temperature of 110 ℃ for 2 h;
(3) putting the dried raw materials into a ball milling tank of a planetary ball mill, and carrying out ball milling for 2 hours at the rotating speed of 280 r/min;
(4) preparing 4 parts by weight of tung oil, putting the mixture into a mortar, adding the tung oil, and uniformly grinding;
(5) placing the uniformly ground mixture into a mold, maintaining the pressure for 120s under the pressure of 4MPa, demolding and taking out a green body;
(6) and (3) placing the pressed green body into a box furnace, and sintering at 1400 ℃ for 0.5h according to a set sintering curve to obtain the core, wherein the bending strength is 16MPa, and the mass loss rate of the 10h acetic acid dissolved core is 55%.
Example 4
(1) Weighing a certain amount of magnesium oxide, calcium carbonate and wood powder, wherein 95 parts by weight of magnesium oxide powder, 10 parts by weight of calcium carbonate powder and 3 parts by weight of wood powder are weighed; the granularity of the magnesium oxide powder is 270 meshes, the granularity of the calcium carbonate powder is 500 meshes, and the granularity of the wood powder is 270 meshes;
(2) putting the weighed powder into a drying oven, and drying at the temperature of 110 ℃ for 1 h;
(3) putting the dried raw materials into a ball milling tank of a planetary ball mill, and carrying out ball milling for 1.5h at the rotating speed of 300 r/min;
(4) preparing 3 parts by weight of tung oil, putting the mixture into a mortar, adding the tung oil, and uniformly grinding;
(5) placing the uniformly ground mixture into a mold, maintaining the pressure for 120s under the pressure of 6MPa, and then demoulding to take out a green body;
(6) and (3) placing the pressed green body into a box furnace, and sintering at 1300 ℃ for 0.5h according to a set sintering curve to obtain the core, wherein the bending strength is 12MPa, and the mass loss rate of the 10h acetic acid dissolved core is 68%.
Example 5
(1) Weighing a certain amount of magnesium oxide, calcium carbonate and wood powder, wherein 100 parts by weight of magnesium oxide powder, 15 parts by weight of calcium carbonate powder and 3 parts by weight of wood powder are weighed; the granularity of the magnesium oxide powder is 200 meshes, the granularity of the calcium carbonate powder is 400 meshes, and the granularity of the wood powder is 400 meshes;
(2) putting the weighed powder into a drying oven, and drying at the temperature of 105 ℃ for 2 h;
(3) putting the dried raw materials into a ball milling tank of a planetary ball mill, and carrying out ball milling for 1.5h at the rotating speed of 250 r/min;
(4) preparing 2 parts by weight of tung oil, putting the mixture into a mortar, adding the tung oil, and uniformly grinding;
(5) placing the uniformly ground mixture into a mold, maintaining the pressure for 120s under the pressure of 4MPa, demolding and taking out a green body;
(6) and (3) placing the pressed green body into a box furnace, and sintering at 1250 ℃ for 0.5h according to a set sintering curve to obtain the mold core, wherein the bending strength is 6MPa, and the mass loss rate of the acetic acid dissolved mold core is 75% in 10 h.
Comparative example 1
The influence of the content of the raw material calcium carbonate on the performance of the ceramic core is studied, and the specific process is the same as that in example 2, except that 20 parts by weight of calcium carbonate is added, so that the bending strength of the core is 7.92MPa, and the mass loss rate of the 10-hour acetic acid-soluble core is 90%. The calcium carbonate content therefore directly affects the properties of the ceramic core, the flexural strength decreasing with increasing calcium carbonate content relative to 16Mpa in example 2.
See FIG. 2, 5 parts by weight of CaCO3Ceramic core performanceThe bending strength is almost unchanged at different sintering temperatures, and the higher the content of the added calcium carbonate is, the more sensitive the bending strength is along with the change of the sintering temperature, and the more unstable the performance is. Referring to FIG. 3, when the ceramic core is subjected to thermal shock of molten metal over 1500 ℃ during casting, the surface temperature of the core can reach 1400 ℃ and 5 parts by weight of CaCO3The smaller the shrinkage change of the ceramic core is, the more stable the performance is, and the quality of the casting can be ensured. Referring to FIG. 4, 5 parts by weight of CaCO was added for sintering at 1400 deg.C3The SEM picture of the ceramic core shows that a large number of small protrusion structures grow on the surface of the particles, the structures are probably generated due to the synergistic effect of wood powder and calcium carbonate, the small protrusions consume atomic surface energy increased by the increase of sintering temperature, and the performance of the ceramic core can be stabilized.
Comparative example 2
The influence of the content of the raw material calcium carbonate on the performance of the ceramic core is studied, and the specific process is the same as that in example 2, except that 5 parts by weight of wood flour is added. The bending strength of the obtained core is 6MPa, and the mass loss rate of the core dissolved in acetic acid for 10h is 90%. The content of wood flour therefore directly affects the properties of the ceramic core, the flexural strength decreasing with increasing content of wood flour relative to 16Mpa in example 2. As can be seen from FIG. 5, the addition of excessive wood powder can form large holes in the core after sintering, greatly affecting the performance of the core, reducing the strength, and breaking the core during casting.
Comparative example 3
The specific process for studying the influence of the mesh number of the magnesium oxide on the performance of the ceramic core is the same as that in example 2, except that the 150-mesh magnesium oxide is added. The bending strength of the obtained core is 6MPa, and the mass loss rate of the core dissolved in acetic acid within 10h is 45%. Therefore, the mesh size of the raw material magnesia directly affects the performance of the ceramic core, and the flexural strength decreases with decreasing mesh size of the magnesia (the larger the mesh size, the smaller the particle size) relative to 16MPa in example 2.
The larger the particle volume, the lower the specific surface energy, and sintering under the same conditions, the more difficult the particle volume is to sinter. Referring to fig. 6, it is apparent that the core is formed by stacking large particles, fine particles are filled in the large particles, large gaps exist between the large particles, and the sintering degree of the core is low. The larger the powder particles are, the wider the gap generated by particle accumulation is, the slower the atom migration fills the gap during sintering, the performance of the core is greatly influenced, the bending strength is low, and the core is easy to break during casting.
Claims (10)
1. A magnesia ceramic core with good dissolution collapsibility, characterized in that: the magnesium oxide-calcium carbonate-wood composite material is mainly prepared from 80-100 parts by weight of magnesium oxide, 3-15 parts by weight of calcium carbonate and 1-3 parts by weight of wood powder.
2. The magnesia ceramic core with good dissolution collapsibility of claim 1, wherein: is mainly made of 90 parts by weight of magnesium oxide, 5 parts by weight of calcium carbonate and 2 parts by weight of wood flour.
3. The magnesium oxide ceramic core with good solution collapsibility according to claim 1 or 2, wherein: the particle size of the magnesium oxide is 200-400 meshes.
4. The magnesium oxide ceramic core with good solution collapsibility according to claim 1 or 2, wherein: the granularity of the calcium carbonate is 400-600 meshes, and the granularity of the wood powder is 200-400 meshes.
5. The method for producing a magnesium oxide ceramic core with good solution collapsibility according to any one of claims 1-2, comprising the steps of:
(1) respectively drying magnesium oxide, calcium carbonate and wood powder, mixing in proportion, and then ball-milling to obtain a mixture;
(2) adding tung oil into the mixture, and uniformly grinding;
(3) pressing and molding the ground mixture, and demolding to obtain a green body;
(4) and sintering the pressed green body to obtain the magnesium oxide ceramic core.
6. The method for preparing a magnesia ceramic core having good solution collapsibility as claimed in claim 5, wherein: in the step (1), the ball milling speed is 250-300 r/min, and the ball milling time is 1.5-2 h.
7. The method for preparing a magnesia ceramic core having good solution collapsibility as claimed in claim 5, wherein: in the step (2), the mass ratio of the tung oil to the mixture is 2-4: 100.
8. the method for preparing a magnesia ceramic core having good solution collapsibility as claimed in claim 5, wherein: in the step (3), the pressure is controlled to be 4-6 Mpa in the compression molding process, and the pressure maintaining time is 90-120 s.
9. The method for preparing a magnesia ceramic core having good solution collapsibility as claimed in claim 5, wherein: in the step (4), the sintering temperature is 1250-1500 ℃, and the sintering time is 0.5-2 h.
10. The method for preparing a magnesia ceramic core having good solution collapsibility as claimed in claim 5, wherein: in the step (1), the drying temperature is 100-110 ℃, and the drying time is 1-3 h.
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| CN116496100A (en) * | 2023-04-18 | 2023-07-28 | 东南大学 | Hollow magnesium-based ceramic core and preparation method and application thereof |
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Application publication date: 20210723 |