阅读说明：本技术 一种钛铝合金熔模精密铸造用高退让模壳及其制备方法 (High-yield formwork for titanium-aluminum alloy precision investment casting and preparation method thereof ) 是由 冯港雯 范李鹏 徐信锋 姬艳硕 王宝兵 张旭亮 杨剑 于 2021-01-15 设计创作，主要内容包括：本发明公开了一种钛铝合金熔模精密铸造用高退让模壳制备方法；所述方法为：在熔模精密铸造型壳制备的沾浆和挂砂过程中加入木屑粉、木屑和棉线,木屑粉、木屑和棉线在型壳焙烧过程中充分燃烧,形成均匀孔隙,进而提高型壳的透气性和退让性；具体地,是在熔模精密铸造型壳制备的涂料配制和型壳涂挂过程中,将棉线均匀缠绕于前层型壳表面,采用含有木屑的背层耐火涂料进行沾浆,采用混有木屑的耐火砂进行挂砂。本发明通过在型壳制备时制备含木屑粉的耐火涂料、混有木屑的耐火砂,并于型壳表面均匀缠绕棉线,有效地提高了型壳的透气性和退让性,降低了钛铝合金铸件在凝固过程中的开裂倾向,最终提高了钛铝合金铸件合格率。(The invention discloses a preparation method of a high-yield formwork for titanium-aluminum alloy precision investment casting; the method comprises the following steps: adding sawdust powder, sawdust and cotton threads in the slurry dipping and sand hanging processes of investment precision casting shell preparation, wherein the sawdust powder, the sawdust and the cotton threads are fully combusted in the shell roasting process to form uniform pores, so that the air permeability and the deformability of the shell are improved; specifically, in the process of preparing a coating and hanging the shell prepared by precision investment casting of the shell, cotton threads are uniformly wound on the surface of a front-layer shell, a back-layer refractory coating containing wood chips is adopted for dipping, and refractory sand mixed with the wood chips is adopted for hanging sand. According to the invention, the fireproof coating containing the sawdust powder and the fireproof sand mixed with the sawdust are prepared during the preparation of the shell, and the cotton threads are uniformly wound on the surface of the shell, so that the air permeability and the deformability of the shell are effectively improved, the cracking tendency of the titanium-aluminum alloy casting in the solidification process is reduced, and the qualification rate of the titanium-aluminum alloy casting is finally improved.)

1. A preparation method of a high-yield formwork for precision casting of a titanium-aluminum alloy investment is characterized by comprising the following steps:

step S1: adding a pretreatment composition during the preparation of the precision casting shell;

step S2: the pretreatment composition is co-fired with the shell to provide uniform porosity in the final shell.

2. The method of claim 1, wherein in step S1, the pretreatment composition includes sawdust powder, sawdust, and cotton threads.

3. The method for preparing the high-yield formwork for titanium-aluminum alloy investment precision casting according to claim 1 or 2, wherein the step S1 specifically comprises the following steps:

winding cotton threads in the pretreatment composition on the surface of a front-layer shell in the processes of preparing a coating prepared by precision investment casting of the shell and hanging sand;

after winding is finished, adopting a back layer fireproof coating containing wood dust powder in the pretreatment composition to carry out slurry dipping on the surface of the front layer shell;

after the slurry is attached, the refractory sand containing wood chips in the pretreatment composition is used for sand hanging.

4. The method for preparing the high-yield formwork for titanium-aluminum alloy investment precision casting according to claim 3, wherein the particle size of the wood dust is 60-100 meshes; the particle size of the sawdust is 40-60 meshes; the diameter of the cotton thread is 0.3 mm-1.2 mm; when winding, the distance between the cotton threads is 5 mm-20 mm.

5. The method of claim 3, wherein the cotton threads are uniformly wound onto the surface of the mold shell after the previous shell is prepared and dried.

6. The method for preparing a high-yield formwork for titanium-aluminum alloy investment precision casting according to claim 3, wherein the back layer refractory coating comprises zircon powder, silica sol, sawdust powder, a defoaming agent and a wetting agent, wherein the defoaming agent is n-butyl alcohol, and the wetting agent is fatty alcohol-polyoxyethylene ether.

7. The method of claim 3, wherein the refractory backing layer coating comprises from about 3 to about 5 coating layers.

8. The method for preparing the high-yield formwork for titanium-aluminum alloy investment precision casting according to claim 3, wherein the step S2 comprises the following steps: and (2) fully combusting the pretreatment composition and the shell in the shell roasting process so as to enable the final shell to have uniform pores, wherein the roasting process conditions are as follows: and (3) heating the roasting furnace to 250-350 ℃ in the atmospheric environment, preserving the heat for 1-2 h, heating the roasting furnace to 900-1050 ℃, preserving the heat for 2-2.5 h, cooling the roasting furnace to below 500 ℃ along with the furnace, and discharging the roasting furnace. .

9. The high-yield formwork for titanium-aluminum alloy investment precision casting is characterized in that the high-yield formwork for titanium-aluminum alloy investment precision casting is prepared by the preparation method of the high-yield formwork for titanium-aluminum alloy investment precision casting according to any one of claims 1 to 8.

10. The high-yield formwork shell for titanium-aluminum alloy investment casting according to claim 9, wherein the shell of the high-yield formwork shell for titanium-aluminum alloy investment casting has pores with a porosity of 6-10%, and the air permeability reaches 13-16cm⁴The deformability reaches 0.35-0.4mm per gram per minute. .

Technical Field

The invention relates to a method for preparing a mold shell for precision investment casting, in particular to a method for preparing a high-yield mold shell for precision investment casting of titanium-aluminum alloy, and belongs to the technical field of precision investment casting of titanium-aluminum alloy.

Background

The aluminum content in the titanium-aluminum alloy (also called titanium-aluminum based intermetallic compound) reaches about 50 percent, and compared with the conventional titanium alloy, the titanium-aluminum alloy has the excellent performances of small density, high specific strength and specific elastic modulus, strong high-temperature oxidation resistance and creep resistance and the like, and has become the development target of novel aviation and aerospace materials. Through continuous research, at present, scholars at home and abroad develop third-generation and fourth-generation titanium-aluminum alloys, and research is being carried out on fourth-generation and even fifth-generation titanium-aluminum alloys with higher heat-resisting temperature.

Because the titanium-aluminum alloy has low room temperature plasticity and the implementation difficulty of plastic forming methods such as forging, rolling and the like is high, and investment precision casting is an ideal forming method for producing large complex structural parts with low cost, the adoption of a low-cost net forming casting technology is the most possible method for manufacturing titanium-aluminum alloy components used in the fields of aviation, aerospace and the like.

At present, the oxide ceramic shell for precision investment casting of titanium-aluminum alloy is generally the same as the conventional titanium alloy, and most of the surface layer shells are yttrium sol + Y₂O₃Powder + Y₂O₃Sand or zirconium sol + ZrO₂Powder + ZrO₂The back layer of the sand system ceramic shell is selected from silica sol, zircon powder and mullite system ceramic shell.

The titanium-aluminum alloy has high smelting and pouring temperature, a liquid-solid phase region is narrow (50-100 ℃), the heat conduction of the alloy is fast, and the density is low, so the filling and feeding capabilities are poor; in addition, the titanium-aluminum alloy has large solidification shrinkage and poor plasticity, and when the deformability of the shell is poor, the contraction of the casting is hindered, and the casting is easy to crack or even break, so that the casting is scrapped.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a high-yield formwork for titanium-aluminum alloy investment precision casting and a preparation method thereof, so as to solve the problem of cracking of a casting in the titanium-aluminum alloy investment precision casting process. According to the invention, cotton threads, sawdust powder and sawdust are added in the traditional preparation process of the investment precision casting back layer shell, and the cotton threads, the sawdust powder and the sawdust in the shell are combusted to form gaps in the roasting process of the shell, so that the air permeability and the deformability of the shell are improved, the cracks of the investment precision casting titanium-aluminum alloy casting are effectively controlled, and the qualified rate of the casting is finally improved.

In order to achieve the purpose, the invention is realized by the following technical scheme:

in a first aspect, the invention provides a method for preparing a high-yield formwork for precision casting of a titanium-aluminum alloy investment, which comprises the following steps:

step S1: adding a pretreatment composition during the preparation of the precision casting shell;

step S2: the pretreatment composition is co-fired with the shell to provide uniform porosity in the final shell.

Preferably, in the step S1, the pretreatment composition includes sawdust powder, sawdust, and cotton threads.

Preferably, the step S1 specifically includes the following steps:

winding cotton threads in the pretreatment composition on the surface of a front-layer shell in the processes of preparing a coating prepared by precision investment casting of the shell and hanging sand;

after winding is finished, carrying out slurry coating on the surface of the front-layer shell by adopting a back-layer fire-resistant coating containing wood dust powder in the pretreatment composition;

after the slurry coating is finished, the refractory sand containing the wood chips in the pretreatment composition is used for sand coating.

Preferably, the particle size of the wood dust powder is 60-100 meshes; the particle size of the sawdust is 40-60 meshes; the diameter of the cotton thread is 0.3 meshes to 1.2 mm; when winding, the distance between the cotton threads is 5 mm-20 mm.

The particle size of the wood dust is preferably 60-100 meshes, because when the wood dust particles are too small, the purposes of increasing the shell porosity, improving the shell air permeability and deformability cannot be achieved, and the wood dust in the coating material floats upwards due to too large particles.

More preferably, the mass percentage of the wood dust is 0.5-2% of the total weight of the refractory slurry, because: the purposes of increasing the porosity of the shell and improving the air permeability and deformability of the shell cannot be achieved due to too low mass percentage; and the mass percentage is too high, so that on one hand, sawdust powder in the coating floats upwards, and on the other hand, the shell strength is too low and is easy to crack and break.

Preferably, the particle size of the wood chips is 40-60 meshes, because when the wood chip particles are too small to achieve the purposes of increasing the shell porosity, improving the shell permeability and deformability, too large particles can cause too large amount of gas generated in single voids of the shell, so that the shell is cracked and broken in the roasting process.

More preferably, the mass percentage of the wood chips is 0.5-2% of the weight of the refractory sand, when the mass percentage is too low, the purposes of increasing the shell porosity and improving the shell permeability and deformability cannot be achieved, and when the mass percentage is too high, the shell porosity is too high, the gas evolution is too large, the shell strength is too low, and the shell is cracked and broken in the roasting process.

The refractory sand includes wood chips and mullite sand.

Preferably, the diameter of the cotton thread is 0.3 mm-1.2 mm, because the wet strength of the shell is insufficient due to the thin cotton thread, and the aims of increasing the porosity of the shell and improving the air permeability and deformability of the shell cannot be achieved; too thick cotton thread results in too high void ratio and too large gas evolution of the shell, and further results in too low strength of the shell, so that the shell is cracked and broken in the roasting process.

Preferably, the cotton thread is wound on the surface of the oxide shell after the previous shell slurry is dried; the winding is uniform winding, and the number of layers wound each time is a single layer.

Preferably, the distance between the winding cotton threads is 5mm to 20mm because: the too narrow winding width of the cotton thread and the too large porosity of the shell after roasting can cause the low strength of the shell after roasting, and the shell is easy to be cracked in the using process. Conversely, if the winding width is too wide, the dry strength of the shell is not reduced and the deformability is not improved.

Preferably, when the cotton thread in the pretreatment composition is wound on the surface of the former shell, the cotton thread is uniformly wound on the surface of the shell after the former shell is prepared and dried.

Preferably, the refractory coating comprises zircon powder, silica sol, wood chip powder, a defoaming agent and a wetting agent, wherein the defoaming agent is n-butyl alcohol, and the wetting agent is fatty alcohol-polyoxyethylene ether.

Preferably, the powder-to-liquid ratio of zircon powder to silica sol in the refractory slurry is 1.7-2.2: the wood dust, the n-butyl alcohol serving as a defoaming agent and the fatty alcohol-polyoxyethylene ether serving as a wetting agent respectively account for 0.5-2%, 0.01-0.03% and 0.02-0.05% in mass percentage;

preferably, the viscosity of the back layer fireproof coating is 10-25 s, a proper amount of silica sol can be added when the viscosity is too high, and a proper amount of zircon powder can be added when the viscosity is too low;

preferably, the backing layer fire resistant coating is prepared by: adding silica sol liquid, adding a wetting agent fatty alcohol-polyoxyethylene enzyme, stirring, adding zircon powder and wood dust powder in corresponding amount, stirring for a period of time, adding, and adding n-butyl alcohol serving as a defoaming agent after the viscosity reaches the standard.

The shell preparation process comprises a surface layer refractory coating, a transition layer refractory coating and a back layer refractory coating, and the scheme aims at improvement of the back layer refractory coating.

Preferably, the number of coating layers of the back layer fireproof coating is 3-5. This is because: the wet strength of the investment shell can be improved by winding cotton threads, so that the coating layer number can be properly reduced compared with the traditional titanium alloy investment shell, but the shell with too few coating layer number has lower strength and is easy to crack in the casting process; too many coating layers can lead to poor deformability of the shell on the one hand, and can lead to too heavy shell, increased operation difficulty and poor air permeability of the shell on the other hand;

preferably, the specific steps of step S2 are: roasting the mould shell containing the pretreatment composition, wherein the pretreatment composition is sufficiently burnt in the roasting process so as to enable the final mould shell to have uniform pores, and the burning process conditions are as follows: and (3) heating the roasting furnace to 250-350 ℃ in the atmospheric environment, preserving the heat for 1-2 h, heating the roasting furnace to 900-1050 ℃, preserving the heat for 2-2.5 h, cooling the roasting furnace to below 500 ℃ along with the furnace, and discharging the roasting furnace. After roasting, the sawdust powder, the sawdust and the cotton threads are fully combusted, uniform gaps are formed in the shell, and the air permeability and the deformability of the shell are improved.

In a second aspect, the invention provides a high-yield formwork for titanium-aluminum alloy investment precision casting, which is prepared by adopting the preparation method for the high-yield formwork for titanium-aluminum alloy investment precision casting.

Preferably, the shell of the high-yield die shell for titanium-aluminum alloy investment precision casting has pores with the porosity of 6-10%, and the air permeability reaches 13-16cm⁴The deformability reaches 0.35-0.4mm per gram per minute. .

The air permeability and the deformability of the formwork prepared by the method for preparing the high-deformability formwork for titanium-aluminum alloy investment precision casting are greatly improved, and especially compared with the prior art, cotton threads, sawdust powder and sawdust can be added in the traditional investment precision casting formwork preparation process, gaps are formed by combustion of the cotton threads, the sawdust powder and the sawdust in the high-temperature roasting process, and the air permeability and the deformability of the formwork are improved. Therefore, the method is simple to operate, can obtain higher performance improvement by simple transformation on the original production line, is low in transformation cost, and saves economic cost.

Compared with the traditional titanium alloy shell manufacturing process, the invention has the beneficial effects that:

1. because the surface of each layer of shell is wound by cotton threads, the wet strength of the shell prepared by the method is 5% higher than that of the shell prepared by the traditional method, and the shell can not be broken due to continuous turning and transfer in the preparation process.

2. Because the sawdust powder, the sawdust and the cotton threads in the shell are burnt to leave gaps in the roasting process, the dry strength of the shell is reduced, and the air permeability and the deformability are improved; compared with the dry strength of the shell prepared by the traditional method, the dry strength of the shell prepared by the method is reduced by 22 percent, and the air permeability and the deformability are respectively improved by more than 30 percent and 25 percent.

3. The porosity of the titanium-aluminum alloy investment shell prepared by the method is obviously higher than that of the investment shell prepared by the traditional method, the higher porosity improves the air permeability and the deformability of the shell, reduces the heat conduction of the shell, reduces the solidification rate of the titanium-aluminum alloy casting in the solidification process, reduces the stress concentration phenomenon, further effectively reduces the cracking tendency of the titanium-aluminum alloy casting, and improves the casting quality.

Drawings

FIG. 1 is a flow chart of a conventional process for preparing a titanium alloy precision casting mold shell.

Detailed Description

The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.

Example 1

The process for preparing the high-yield mold shell for titanium aluminum alloy investment precision casting of example 1 can refer to the conventional titanium alloy shell-making process of fig. 1, but unlike the conventional titanium alloy shell-making process, in the process of fig. 1, the pretreatment composition is added in example 1, so that the pretreatment composition is co-fired with the mold shell, so that the finally prepared mold shell has uniform pores therein.

The preparation method of the high-yield formwork for titanium-aluminum alloy precision investment casting comprises the following steps:

step S1: adding a pretreatment composition during the preparation of the precision casting shell;

step S2: the pretreatment composition is co-fired with the shell to provide uniform porosity in the final shell.

Specifically, in step S1, during the coating preparation and sanding process for investment precision casting shell preparation, cotton threads in the pretreatment composition are wound on the surface of the previous shell;

after winding is finished, carrying out slurry coating on the surface of the front-layer shell by adopting a back-layer fire-resistant coating containing wood dust powder in the pretreatment composition;

after the slurry coating is finished, the refractory sand containing the wood chips in the pretreatment composition is used for sand coating.

In step S2, the pretreatment composition is sufficiently combusted with the shell during shell firing to provide uniform porosity in the final shell, wherein the combustion process conditions are: and (3) heating the roasting furnace to 250-350 ℃ in the atmospheric environment, preserving the heat for 1-2 h, heating the roasting furnace to 900-1050 ℃, preserving the heat for 2-2.5 h, cooling the roasting furnace to below 500 ℃ along with the furnace, and discharging the roasting furnace.

The preparation method for the pretreatment composition of example 1 is as follows:

1.1 preparation of a Back layer flame-resistant coating containing sawdust powder

The back layer fireproof coating comprises zircon powder, silica sol, wood chip powder, n-butyl alcohol serving as an antifoaming agent and fatty alcohol-polyoxyethylene ether serving as a wetting agent, wherein the particle size of the wood chip powder is 60-100 meshes, the wood chip powder accounts for 1% of the total weight of the back layer fireproof coating, the ratio of the coating powder to the coating liquid is 2:1, the antifoaming agent accounts for 0.02% of the total weight of the back layer fireproof coating, and the wetting agent accounts for 0.03% of the total weight of the back layer fireproof coating.

The preparation process comprises the following steps: adding silica sol glue solution and wetting agent fatty alcohol-polyoxyethylene ether into a stirring barrel, adding zircon powder and sawdust powder after stirring, adding defoamer n-butyl alcohol after uniformly stirring, testing the viscosity of the coating after stirring for 24 hours to ensure that the viscosity is 10-25 s, adding a proper amount of silica sol when the viscosity is too high, and adding a proper amount of zircon powder when the viscosity is too low.

1.2 preparation of refractory Sand containing sawdust

The refractory sand comprises mullite sand and wood chips, wherein the particle size of the wood chips is 40-60 meshes, and the mass ratio of the wood chips to the mullite sand is 1: 99.

The preparation process comprises the following steps: and weighing the mullite sand and the sawdust according to a proportion, putting the mullite sand and the sawdust into a turnover type stirring barrel together, and stirring until the mullite sand and the sawdust are uniformly stirred to obtain the required refractory sand.

1.3 winding cotton thread on the surface of the shell

Before each layer of back shell is prepared, cotton threads with the diameter of 1mm are uniformly wound on the surface of the former layer of shell, the distance between the cotton threads during winding is determined according to the shape of the actual shell, the thread spacing is 5-20 mm (of course, in some other preferred embodiments, the thread spacing can also be set to be 5-15 mm), and after winding is finished, the next layer of shell is subjected to slurry dipping, sand hanging and drying.

1.4 Shell baking and testing

And roasting the shell after dewaxing is finished, wherein the wood chips are carbonized and combusted at the temperature of 300 ℃ for 1.5 hours and at the temperature of 960 ℃ for 2.5 hours, and wood chip powder, wood chips and cotton threads in the shell are fully combusted after roasting, so that uniform pores are formed in the shell.

Testing the formed shell on a standard table tennis mould shell sample by adopting a shell air permeability tester, wherein the testing temperature is room temperature; and testing the standard three-point bending test formwork sample by using a universal material testing machine.

From the test results, it was found that the uniformly distributed pores significantly improved the air permeability and the deformability of the shell, so that the porosity of example 1 reached 6-10% and the air permeability reached 13-16cm⁴The deformability reaches 0.35-0.4mm per g/min, and compared with the prior art, the air permeability of the embodiment is improved by 32% and the deformability is improved by 26%.

It should be noted that the prior art in the protection scope of the present invention is not limited to the examples given in the present application, and all the prior art which is not inconsistent with the technical scheme of the present invention, including but not limited to the prior patent documents, the prior publications and the like, can be included in the protection scope of the present invention.

In addition, the combination of the features in the present application is not limited to the combination described in the claims of the present application or the combination described in the embodiments, and all the features described in the present application may be freely combined or combined in any manner unless contradictory to each other.

The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.