Preparation method for improving performance of high-specific-gravity tungsten alloy spray granulation powder

Abstract

The invention relates to a preparation method for improving the performance of high-specific-gravity tungsten alloy spray granulation powder. The preparation method comprises the following steps that S1, powder is weighed and mixed; s2, performing cold isostatic pressing to form a blank, crushing and sieving; s3, preparing a binder; s4, ball-milling slurry: mixing a binder and the sieved powder to form slurry with the solid content of 60-75wt.%, and carrying out ball-milling; and S5, performing spray granulation to obtain powder. Compared with the prior art, the prepared high-specific-gravity tungsten alloy spray granulation powder is good in flowability and high in apparent density, the uniformity, stability and dimensional precision of a compression molding blank can be improved, the equipment blocking risk is low, and the production efficiency is high.

Description

Technical Field

[0001] The invention relates to the technical field of powder metallurgy, and in particular to a preparation method for improving the performance of high-density tungsten alloy spray granulation powder. Background Art

[0002] High-density tungsten alloy is an alloy material with tungsten as the base material (content ≥85wt.%) and nickel, iron, copper, etc. as the main bonding phase. It has the advantages of high density, high strength, good toughness, and strong radiation absorption ability. It is widely used in national defense, aerospace, medical equipment and other fields, such as kinetic energy damage units, gyroscope outer rotors, radiation protection shielding materials, etc.

[0003] High-density tungsten alloy has a high melting point, and its preparation generally adopts powder metallurgy process. Compression molding is an important part of the powder metallurgy process. The uniformity, stability and dimensional accuracy of compression molding are closely related to the performance of the powder. Good compression molding performance requires the powder to have good fluidity and high bulk density. Therefore, it is usually necessary to granulate the powder to improve its comprehensive performance. The traditional sieving granulation process has the disadvantages of irregular powder morphology, poor uniformity, and low production efficiency. The powder produced by the spray granulation process has good sphericity, high concentration of particle size distribution, and is suitable for large-scale production. The traditional spray granulation process is as follows: Figure 1 As shown in the figure, the high-density tungsten alloy powder prepared by mixing powder - preparing binder - ball grinding slurry - spray granulation has insufficient fluidity and low bulk density, which seriously affects the uniformity, stability and dimensional accuracy of compression molding.

[0004] Patent CN202110447943 discloses a forming agent suitable for spray granulation of high-density tungsten alloy powder, as well as its preparation method and application. Polyvinyl alcohol, polyethylene glycol, stearic acid, propylene glycol block polyether and sodium polycarboxylate aqueous solution are used as binders. The performance of the spray granulation powder is significantly improved, but the high solid content of the slurry can easily cause equipment blockage and reduce production efficiency; and there are many types of binders, which is not conducive to subsequent degreasing.

[0005] Therefore, it is necessary to improve the existing high-density tungsten alloy spray granulation preparation method. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a preparation method for improving the performance of high-density tungsten alloy spray granulation powder in response to the above technical status quo, thereby improving the fluidity and bulk density of the spray granulation powder.

[0007] The technical solution adopted by the present invention to solve the above technical problems is: a preparation method for improving the performance of high-density tungsten alloy spray granulation powder, characterized by comprising the following steps:

[0008] S1. Weigh and mix powders;

[0009] S2, cold isostatically pressing the powder into billets, crushing and screening;

[0010] S3, prepare adhesive;

[0011] S4. Ball milling slurry: Mix the binder and the sieved powder to form a slurry with a solid content of 60-75 wt.%, and perform ball milling;

[0012] S5. Spray granulation to obtain powder.

[0013] Preferably, the weight percentage of the tungsten powder in step S1 is ≥90 wt.%, and the powder mixing time is 8 to 12 hours to ensure that the powders are evenly mixed.

[0014] Preferably, the powder in step S1 comprises the following components: tungsten ≥ 90 wt.%, nickel 3.5-7 wt.%, iron 1.2-2.9 wt.%, and the remainder being manganese and cobalt.

[0015] Preferably, in step S2, the cold isostatic pressing pressure is 120-200 MPa, the holding time is 10-30 minutes, and the crushed powder is vibrated and sieved to a mesh size of 500-2000. If the cold isostatic pressing pressure is lower than 120 MPa and the holding time is less than 10 minutes, the density of the pressed blank is low, and the powder performance after spray granulation is not significantly improved; if the cold isostatic pressing pressure is higher than 200 MPa and the holding time is longer than 30 minutes, the powder is severely deformed, which is not conducive to molding; if the mesh size is higher than 2000, the crushed powder is difficult to sieve, resulting in low production efficiency; if the mesh size is lower than 500, the sieved crushed powder is coarse, and spray granulation is meaningless.

[0016] Preferably, the binder in step S3 is a mixed solution of polyvinyl alcohol (PVA1788) and polyethylene glycol (PEG 6000) in deionized water, with the mass ratio of PVA to PEG being 1:1 to 3:1, and the total mass of PVA and PEG accounting for 0.8 to 2 wt.% of the powder. The binder is a mixed solution of polyvinyl alcohol and polyethylene glycol in deionized water: its simple composition facilitates degreasing and has high production efficiency. PVA and PEG are stirred and dissolved in deionized water at 90°C to 95°C and 60°C to 70°C, respectively. After complete dissolution, the mixture is uniformly mixed and cooled to room temperature to obtain a mixed solution of polyvinyl alcohol and polyethylene glycol in deionized water. PVA and PEG are commonly used binders and can also serve as dispersants. PVA has a relatively high hardness at room temperature. Adding an appropriate proportion of PEG can improve the powder's plasticity and reduce compression molding pressure. If the amount of PVA added is less than the amount of PEG, the spray granulation powder has poor moldability. If the amount of PEG added is less than 1 / 3 of the amount of PVA, the compression molding pressure is relatively high. If the total mass fraction of PVA and PEG is lower than 0.8% of the powder, the spray granulation powder has poor formability; if the total mass fraction of PVA and PEG is higher than 2% of the powder, it is not conducive to subsequent degreasing.

[0017] In order to fully stir the sieved crushed powder and the water-soluble binder, avoid powder agglomeration and stratification, and obtain a uniform slurry, preferably, in step S4, the binder and the sieved powder are mixed into a slurry, the ball milling time is 8 to 12 hours, the ball mill frequency is 20 to 40 Hz, and the ball-to-material mass ratio is 1:2 to 2:3.

[0018] Preferably, in step S5, the peristaltic pump speed is 60-100 rpm, the centrifugal atomizer frequency is 50-120 Hz, the inlet air temperature is 150-190°C, and the outlet air temperature is 100-120°C. If the peristaltic pump speed is too low, the feeding speed is slow, the slurry is prone to sedimentation in the pipeline, and even clogs the atomizer; if the speed is too high, the feeding speed is fast, and the slurry atomization is incomplete. If the atomizer frequency is too low, the droplet size is large and the moisture content is high, and it is easy to stick to the inner wall of the atomization tower; if the atomizer frequency is too high, the atomized particles are small in size, and the granulation powder performance is poor. If the inlet and outlet air temperatures are too low, the atomization effect is poor, the particles have a high moisture content, and they are easy to stick to the inner wall of the equipment; if the inlet and outlet air temperatures are too high, the droplets are prone to expansion, deformation, and rupture, and the granulation powder performance is poor.

[0019] Compared with the existing technology, the advantages of the present invention are: the initial loose density of the powder is improved by cold isostatic pressing into a blank and then crushing pretreatment. After spray granulation, the powder has good fluidity and high loose density, which is beneficial to improving the uniformity, stability and dimensional accuracy of the compression molding. In addition, the solid content of the slurry is 60-75wt.%, the solid content is moderate, and the risk of clogging is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the traditional spray granulation process;

[0021] Figure 2 This is a schematic diagram of the spray granulation process of the present invention;

[0022] Figure 3 This is a scanning electron microscope image of the spray granulation powder of Example 4. DETAILED DESCRIPTION

[0023] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

[0024] Example 1

[0025] like Figure 2 As shown, a preparation method for improving the performance of high-density tungsten alloy spray granulation powder includes the following steps:

[0026] S1. Weigh and mix the powders: tungsten, nickel, and iron at 93 wt.%, 5 wt.%, and 1.9 wt.%, with the remainder being manganese and cobalt. Place the prepared powders in a mixing tank and mix for 8 hours.

[0027] S2. Cold isostatic pressing and crushing: put the powder bag into the cold isostatic press, apply a pressure of 150 MPa, hold the pressure for 18 minutes, then take out the blank for crushing and pass through a 1800 mesh sieve.

[0028] S3. Prepare the binder: Prepare the binder at a mass ratio of PVA to PEG of 2:1, with the total mass of PVA and PEG accounting for 1.2 wt.% of the powder. Stir and dissolve PVA in deionized water at 95°C and PEG in deionized water at 62°C. After complete dissolution, mix well and cool to room temperature.

[0029] S4. Ball milling slurry: Mix the prepared binder and powder into a slurry with a solid content of 65 wt.%, ball milling time of 10 h, ball mill frequency of 25 Hz, and a ball-to-powder ratio of 1:2.

[0030] S5. Spray granulation: After the inlet air temperature stabilizes at 150°C, the peristaltic pump sends the slurry in the ball mill into the atomizing tower for spray granulation. The peristaltic pump speed is 90 rpm, the centrifugal atomizer frequency is 90 Hz, and the outlet air temperature is 103°C.

[0031] Example 2

[0032] A preparation method for improving the performance of high-density tungsten alloy spray granulation powder comprises the following steps:

[0033] S1. Weigh and mix the powders: Weigh the ingredients to a ratio of 93 wt.% for tungsten, 5 wt.% for nickel, and 1.9 wt.% for iron, with the remainder being manganese and cobalt. Place the prepared powders in a mixing tank and mix for 8 hours.

[0034] S2. Cold isostatic pressing and crushing: put the powder bag into the cold isostatic press, apply a pressure of 165MPa, hold the pressure for 15min, then take out the blank for crushing and pass through a 1800 mesh sieve.

[0035] S3. Prepare the binder: Prepare the binder at a mass ratio of PVA to PEG of 2:1, with the total mass of PVA and PEG accounting for 1.2 wt.% of the powder. Stir and dissolve PVA in deionized water at 93°C and PEG in deionized water at 68°C. After complete dissolution, mix well and cool to room temperature.

[0036] S4. Ball milling slurry: Mix the prepared binder and powder into a slurry with a solid content of 65 wt.%, ball milling time of 12 h, ball mill frequency of 25 Hz, and a ball-to-powder ratio of 1:2.

[0037] S5. Spray granulation: After the inlet air temperature stabilizes at 150°C, the peristaltic pump sends the slurry in the ball mill into the atomization tower for granulation. The peristaltic pump speed is 90 rpm, the centrifugal atomizer frequency is 90 Hz, and the outlet air temperature is 103°C.

[0038] Example 3

[0039] A preparation method for improving the performance of high-density tungsten alloy spray granulation powder comprises the following steps:

[0040] S1. Weigh and mix powders: Weigh the ingredients so that the tungsten, nickel, and iron contents are 95 wt.%, 3.5 wt.%, and 1.4 wt.%, respectively, with the remainder being manganese and cobalt. Place the prepared powders into a mixing tank and mix for 10 hours.

[0041] S2. Cold isostatic pressing and crushing: put the powder bag into the cold isostatic press, apply a pressure of 180 MPa, hold the pressure for 20 minutes, then take out the blank for crushing and pass through a 1800 mesh sieve.

[0042] S3. Prepare the binder: Prepare the binder at a mass ratio of PVA to PEG of 3:1, with the total mass of PVA and PEG accounting for 1.8 wt.% of the powder. Stir and dissolve PVA in deionized water at 95°C and PEG in deionized water at 60°C. After complete dissolution, mix well and cool to room temperature.

[0043] S4. Ball milling slurry: Mix the prepared binder and powder into a slurry with a solid content of 70 wt.%, ball milling time of 10 h, ball mill frequency of 30 Hz, and a ball-to-powder ratio of 2:3.

[0044] S5. Spray granulation: After the inlet air temperature stabilizes at 160°C, the peristaltic pump sends the slurry in the ball mill into the atomization tower for granulation. The peristaltic pump speed is 90 rpm, the centrifugal atomizer frequency is 80 Hz, and the outlet air temperature is 108°C.

[0045] Example 4

[0046] A preparation method for improving the performance of high-density tungsten alloy spray granulation powder comprises the following steps:

[0047] S1. Weigh and mix powders: Weigh the ingredients so that the tungsten, nickel, and iron contents are 95 wt.%, 3.5 wt.%, and 1.4 wt.%, respectively, with the remainder being manganese and cobalt. Place the prepared powders into a mixing tank and mix for 10 hours.

[0048] S2. Cold isostatic pressing and crushing: put the powder bag into the cold isostatic press, apply a pressure of 195 MPa, hold the pressure for 20 minutes, then take out the blank for crushing and pass through a 1800 mesh sieve.

[0049] S3. Prepare the binder: Prepare the binder at a mass ratio of PVA to PEG of 3:1, with the total mass of PVA and PEG accounting for 2 wt.% of the powder mass. Stir and dissolve PVA in deionized water at 93°C and PEG in deionized water at 67°C. After complete dissolution, mix well and cool to room temperature.

[0050] S4. Ball milling slurry: Mix the prepared binder and powder into a slurry with a solid content of 75 wt.%, ball milling time of 10 h, ball mill frequency of 30 Hz, and a ball-to-powder ratio of 2:3.

[0051] S5. Spray granulation: After the inlet air temperature stabilizes at 155°C, the peristaltic pump sends the slurry in the ball mill into the atomization tower for granulation. The peristaltic pump speed is 90 rpm, the centrifugal atomizer frequency is 80 Hz, and the outlet air temperature is 106°C. The obtained powder is shown in the scanning electron microscope image. Figure 3 .

[0052] Comparative Example 1

[0053] The difference between this comparative example and Example 1 is that cold isostatic pressing and crushing and screening were not performed, and the remaining process parameters and operating steps were the same as those in Example 1.

[0054] Comparative Example 2

[0055] The difference between this comparative example and Example 3 is that cold isostatic pressing and crushing and screening were not performed, and the remaining process parameters and operating steps were the same as those in Example 3.

[0056] Table 1 Performance parameters of spray granulation powders of Examples 1 to 4 and Comparative Examples 1 to 2

[0057] Flowability (s / 50g) <![CDATA[松装密度(g / cm 3 )]]> Example 1 26.5 3.7 Example 2 25.1 3.8 Example 3 23.4 4.1 Example 4 22.3 4.2 Comparative Example 1 35.6 2.5 Comparative Example 2 31.4 3.0

[0058] Table 1 shows that the spray-granulated powders of Examples 1-4 all had shorter flow times and greater apparent densities than the comparative examples. Therefore, cold isostatic pressing followed by crushing pretreatment results in spray-granulated powders with improved flowability and higher apparent density, which is beneficial for improving the uniformity, stability, and dimensional accuracy of the blanks subsequently produced by compression molding.

Claims

1. A method for improving the performance of high-density tungsten alloy spray granulation powder, characterized by: The following steps are involved: S1. Weigh and mix powders; S2, cold isostatically pressing the powder into billets, crushing and screening; S3, prepare adhesive; S4. Ball milling slurry: Mix the binder and the sieved powder to form a slurry with a solid content of 60-75 wt.%, and perform ball milling; S5. Spray granulation to obtain powder.

2. The method for improving the performance of high-density tungsten alloy spray granulation powder according to claim 1, wherein: The weight percentage of tungsten powder in the powder material of step S1 is ≥90 wt.%, and the powder mixing time is 8 to 12 hours.

3. The method for improving the performance of high-density tungsten alloy spray granulation powder according to claim 2, wherein: The powder material of step S1 comprises the following components: tungsten ≥90 wt.%, nickel 3.5-7 wt.%, iron 1.2-2.9 wt.%, and the remainder being manganese and cobalt.

4. The method for improving the performance of high-density tungsten alloy spray granulation powder according to claim 1, characterized in that: In step S2, the cold isostatic pressing pressure is 120-200 MPa, the pressure holding time is 10-30 minutes, and the crushed powder is vibrated and sieved with 500-2000 mesh.

5. The method for improving the performance of high-density tungsten alloy spray granulation powder according to claim 1, characterized in that: The binder in step S3 is a mixed solution of polyvinyl alcohol and polyethylene glycol in deionized water.

6. The method for improving the performance of high-density tungsten alloy spray granulation powder according to claim 5, characterized in that: The mass ratio of polyvinyl alcohol to polyethylene glycol is 1:1 to 3:1, and the total mass of the polyvinyl alcohol and polyethylene glycol is 0.8 to 2 wt.% of the powder.

7. The method for improving the performance of high-density tungsten alloy spray granulation powder according to claim 5, characterized in that: The step S4 is: stirring and dissolving polyvinyl alcohol and polyethylene glycol in deionized water at 90° C. to 95° C. and 60° C. to 70° C. respectively, mixing them uniformly after they are completely dissolved and cooling them to room temperature.

8. The method for improving the performance of high-density tungsten alloy spray granulation powder according to claim 1, characterized in that: In step S4, the ball milling time is 8 to 12 hours, the ball mill frequency is 20 to 40 Hz, and the ball-to-material mass ratio is 1:2 to 2:

3.

9. The method for improving the performance of high-density tungsten alloy spray granulation powder according to claim 1, characterized in that: In step S5, the rotation speed of the peristaltic pump is 60-100 rpm, the frequency of the centrifugal atomizer is 50-120 Hz, the inlet air temperature is 150-190° C., and the outlet air temperature is 100-120° C.

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