A balance block and a method of manufacturing the same

Abstract

The present application belongs to the technical field of balance block, and discloses a balance block and a preparation method thereof. The balance block is prepared from balance block alloy powder raw materials. In the present application, the addition of nano-Fe3O4 sintering aid in the balance block alloy powder can obviously improve the sintering performance of the alloy material, and improve the density and tensile strength of the balance block.

Description

Technical Field

[0001] This invention belongs to the field of balance blocks, specifically relating to a balance block and its preparation method. Background Technology

[0002] To meet the requirements of high-performance rotors, compressor balance blocks generally need to possess non-magnetic or low-magnetic properties, high density, precise mass, and good mechanical properties. Currently, the main processes for manufacturing balance blocks include powder metallurgy and casting. Compared to traditional casting processes, powder metallurgy offers numerous advantages such as high efficiency, high material utilization, simple manufacturing process, and environmental friendliness, and is therefore widely used in various compressor components. To meet the performance requirements of balance blocks, the density of powder metallurgy-prepared balance blocks is crucial; excessively low density makes it difficult to meet the mechanical, mass, and volume requirements of the balance block.

[0003] Currently, adding a certain amount of copper is commonly used to improve sintering density and compressibility. However, increasing the amount of copper added will inevitably increase production costs. Furthermore, copper has a lower melting point than conventional sintering temperatures, and a liquid phase exists during the sintering process. As a result, the shape and size of the resulting equilibrium block are difficult to control. Therefore, the amount of copper used should be minimized.

[0004] Therefore, it is still necessary to develop a new alloy powder process for balance blocks in order to overcome the shortcomings of current powder metallurgy preparation of balance blocks. Summary of the Invention

[0005] In view of the shortcomings of the existing powder metallurgy preparation of balance blocks, such as low density and poor mechanical properties, the present invention will provide a high-density balance block by pre-preparing an alloy powder for balance blocks to improve the sintering performance of the alloy.

[0006] To achieve the above objectives, the following technical solutions are specifically included:

[0007] An alloy powder for a balance block includes a pre-alloyed powder, copper powder, a sintering aid, and a lubricant;

[0008] The pre-alloyed powder comprises the following components in weight percentage: C 0.5-2%, Ni 0-2%, Mn 10-25%, Si 0.1-1%, P 0-0.9%, with the balance being Fe and unavoidable impurities;

[0009] The sintering aid is nano-ferric oxide and / or silane coupling agent modified nano-ferric oxide, wherein the average particle size of the nano-ferric oxide is 10-1000 nm.

[0010] The nano-ferric oxide has a mass percentage content of 0.2-1% in the alloy powder for the balance block, and the copper powder has a mass percentage content of 2-11% in the alloy powder for the balance block.

[0011] Nano-ferric oxide possesses the characteristics of nanomaterials, particularly its high surface energy, high activity, good dispersibility, and fluidity. It can be used as an activating agent in the sintering process of alloy powders for balance blocks, improving the sintering performance of the alloy powder, reducing porosity, and promoting improved pore distribution and densification, thereby achieving high densification and high tensile strength in the balance blocks. This is because, under the reducing atmosphere during the sintering process, nano-ferric oxide is reduced to new, highly active, tiny Fe atoms, which have a certain activating effect on sintering. Simultaneously, Fe atoms with variable valence exist within the ferric oxide. 3+ and Fe 2+ Its own reversible reduction-oxidation process also plays a certain role in sintering. Its activity is higher than that of ferric oxide. In addition, a small amount of H2O is generated during the reversible reduction-oxidation process, but it is easily reduced in a reducing atmosphere during sintering, which increases the atomic activity and also plays a role in activating sintering to a certain extent.

[0012] Furthermore, although iron(III) oxide is magnetic, its addition is in small amounts, and the subsequent sintering temperature is higher than its Curie temperature, which can convert it to paramagnetism. Relatively speaking, the magnetism becomes weaker, and it has little impact on the overall magnetism of the balance block. Therefore, the final balance block still maintains a magnetism of less than 0.15 mT, which fully meets the requirements of non-magnetic or extremely low magnetism of the balance block.

[0013] The activity of nano-Fe3O4 is related to its particle size. Particles larger than 1000 nm have relatively low activity and little effect on activation and sintering. If the particle size is too small, such as less than 10 nm, the surface activity is too high, making it unstable in the air environment and prone to oxidation, deactivation, and agglomeration. This increases the difficulty of the powder mixing process, resulting in severe agglomeration and uneven dispersion, which weakens its activation and sintering effect. In addition, the larger the particle size, the higher the cost, which is not conducive to conventional production.

[0014] In a preferred embodiment of the present invention, the average particle size of the nano-ferric oxide is 50-500 nm.

[0015] Within the aforementioned particle size range, the balanced block exhibits superior tensile strength and densification.

[0016] In a preferred embodiment of the present invention, the nano-ferric oxide has a mass percentage content of 0.4-0.8% in the alloy powder for the balance block.

[0017] If the content of nano-Fe3O4 is too low, it will not be able to mix effectively with the alloy powder, and its influence on the alloy powder will be insufficient, failing to improve the sintering activity. If the content is too high, the surface of nano-Fe3O4 is generally rough. If it exceeds a certain amount, the compatibility between the alloy powder and nano-Fe3O4 particles will not be high. At the same time, if the activity of the powder is too high, the agglomeration phenomenon will be serious, resulting in poor powder dispersion and uniformity, which will significantly reduce its sintering aid effect.

[0018] Within the aforementioned content range, the balance block exhibits higher tensile strength and density.

[0019] In a preferred embodiment of the present invention, the copper powder has a mass percentage content of 5-10% in the alloy powder for the balance block.

[0020] Copper has a relatively low melting point (1083℃). During high-temperature sintering, it forms a liquid phase, filling the pores between particles and significantly improving the densification of the alloy, thus increasing the tensile strength of the equilibrium block within a certain range. When the copper content is low, only a portion of the alloy undergoes transient liquid phase sintering during sintering, which has little effect on alloy diffusion and densification. Within a certain range, the density gradually increases with the increase of copper powder content. However, if this range is exceeded, excessive copper has little effect on the degree of densification, pore filling, and rearrangement. Excessive copper phase not only affects the shape but also leads to a decrease in the mechanical properties of the alloy.

[0021] Mn and C are the main elements for forming non-magnetic, room-temperature stable austenite. In this invention, the content of C is 0.5-2% and Mn is 10-25%. Within the above content range, a balance block with non-magnetic or low magnetic properties and good mechanical properties can be obtained.

[0022] Ni is an element that expands the non-magnetic, room-temperature stable austenite. It can be omitted or added, but it is preferable to add 2% or less Ni. Ni can stabilize the austenite that is transformed after heat treatment and has a certain effect on improving the mechanical properties of the balance block. However, its content should not be too high, otherwise it will cause the mechanical properties of the balance block to drop sharply. Si can reduce the oxygen content in the alloy, so that the balance block has the characteristic of low oxygen content. However, too low a silicon content will not achieve the purpose of reducing oxygen content, and it should not be too high either, otherwise it will cause the mechanical properties of the balance block to drop sharply. It is preferable to add 1% or less Si.

[0023] Lubricant can play a role in lubrication and bonding. It is better to add less than or equal to 1% lubricant. If there is too little lubricant, it will not be able to lubricate the alloy powder sufficiently. If there is too much lubricant, it will lead to too much organic matter between the alloy powder. During high-temperature sintering, it will cause too many pores inside the balance block and reduce the density of the balance block.

[0024] In a preferred embodiment of the present invention, the lubricant is at least one of hydrocarbons, fatty acids, fatty acid amides, esters, alcohols, and metal soaps.

[0025] As a further preferred embodiment of the present invention, the lubricant is at least one of liquid paraffin, paraffin-based wax powder, and zinc stearate.

[0026] In a preferred embodiment of the present invention, the lubricant has a mass percentage content of 0.1-1% in the alloy powder for the balance block.

[0027] In a preferred embodiment of the present invention, the nano-ferric oxide is nano-ferric oxide modified with a silane coupling agent.

[0028] As a preferred embodiment of the present invention, the preparation method of the silane coupling agent modified nano-iron oxide includes the following steps: dispersing nano-iron oxide in ethanol, adding silane coupling agent under stirring to carry out modification reaction, separating solid and liquid after reaction, and drying the solid to obtain silane coupling agent modified nano-iron oxide.

[0029] In a preferred embodiment of the present invention, the temperature of the modification reaction is 50-80°C, and the time of the modification reaction is 1-12 hours.

[0030] In a preferred embodiment of the present invention, the drying is vacuum drying.

[0031] In a preferred embodiment of the present invention, the ratio of nano-ferric oxide to ethanol is 1g:100mL.

[0032] Modifying nano-Fe3O4 using silane coupling agents can reduce the surface roughness of nano-Fe3O4, improve its fluidity, stability, and dispersibility, and facilitate the mixing effect of alloy powder, resulting in a tighter internal connection of the alloy powder and better filling of the gaps between alloy particles. During the sintering process, the silane coupling agent, acting as a protective layer, decomposes and volatilizes first, leaving behind more active nano-Fe3O4, which can significantly improve the degree of alloy sintering. At the same time, in the subsequent high-temperature sintering process, the copper liquid phase will also cooperate to fill the pore structure, thereby comprehensively improving the density and tensile strength of the equilibrium block.

[0033] In a preferred embodiment of the present invention, the silane coupling agent accounts for 0.2-1% of the mass of nano-ferric oxide.

[0034] If the silane coupling agent content is too low, it will not modify the surface of nano-Fe3O4; if the silane coupling agent content is too high, there will be too much silane coupling agent loaded on the surface of nano-Fe3O4. Since silane coupling agent is easy to decompose at high temperature, it will produce gas, which will increase the porosity of the alloy. This will prevent subsequent alloy diffusion (including copper liquid phase) from filling a large number of pore structures in time, resulting in a decrease in the density and mechanical properties of the alloy.

[0035] In a preferred embodiment of the present invention, the silane coupling agent includes at least one of KH550 (γ-aminopropyltriethoxysilane), KH560 (γ-glycidoxypropyltrimethoxysilane), and KH570 (γ-methacryloyloxypropyltrimethoxysilane).

[0036] The above are all commonly used silane coupling agents in the field, with low cost. Among them, KH570 is better for modifying nano-ferric oxide.

[0037] A method for preparing a balance block includes the following steps:

[0038] (1) Press the uniformly mixed balance block with alloy powder to obtain a green blank;

[0039] (2) The green embryo is pre-fired in a reducing atmosphere and then sintered. After cooling, the balance block is obtained. The pre-fired temperature is 500-700℃ and the pre-fired time is 0.5-1.5h.

[0040] Pre-sintering before green compact sintering not only decomposes the silane coupling agent and lubricant in the organic components at high temperatures, but also facilitates the filling of pores formed by the sintering of organic components by the copper liquid phase during subsequent high-temperature sintering, improving the densification of the alloy. Furthermore, pre-treatment at this temperature range can reduce internal thermal stress and stress brittleness in the green compact, thereby improving the mechanical properties of the alloy. During the pre-treatment stage, the temperature should not be too low, otherwise incomplete sintering of the organic components will result in poor diffusion and pore filling in the subsequent alloy process; conversely, the temperature should not be too high, as this will also lead to high thermal stress and fail to achieve the effect of reducing internal stress brittleness in the alloy.

[0041] In a preferred embodiment of the present invention, the sintering temperature is 1100-1250℃ and the sintering time is 0.5-1h.

[0042] If the sintering temperature is too low, it will not reach the melting point of copper or the liquidus line, thus failing to function as copper powder. If the temperature is too high, it may approach the liquidus line of the alloy, which is detrimental to the densification of the alloy and the improvement of its mechanical properties.

[0043] In a preferred embodiment of the present invention, the pre-alloyed powder is prepared by conventional powder metallurgy methods, such as high-pressure spray powder preparation.

[0044] In a preferred embodiment of the present invention, both the mixing and the pressing are carried out in an inert gas atmosphere, which can minimize the oxidation of the alloy powder.

[0045] In a preferred embodiment of the present invention, the pressing pressure is 600-1200 MPa.

[0046] In a preferred embodiment of the present invention, the reducing atmosphere includes at least one of a hydrogen atmosphere and a decomposed ammonia atmosphere.

[0047] Compared with the prior art, the present invention has the following beneficial effects: the addition of nano-ferric oxide sintering aid to the alloy powder for balance blocks can significantly improve the sintering performance of the alloy material and increase the density and tensile strength of the balance block. Detailed Implementation

[0048] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below through specific embodiments.

[0049] Nano-ferric oxide and nano-ferric oxide are both commercially available.

[0050] Examples 1-19 and Comparative Examples 1-13

[0051] (1) The preparation method of pre-alloyed powder includes the following steps:

[0052] The pre-alloyed powder was prepared with a total mass of 100% as the raw material. The specific components and contents were: C 1.5%, Ni 1.2%, Mn 20%, Si≤1%, P≤0.9%, with the balance being Fe and unavoidable impurities. The mixture was smelted in a melting furnace. The above-mentioned mixed molten liquid was then sprayed at high temperature using a high-pressure water atomization device to produce powder alloy material. The high-pressure water pressure was 30MPa. The resulting pre-alloyed powder was then obtained.

[0053] (2) Under a nitrogen atmosphere, pre-alloy powder, electrolytic copper powder, sintering aid and 1% zinc stearate lubricant are mixed in a powder mixer for 2 hours to obtain alloy powder for balance blocks. The alloy powder for balance blocks is pressed into a conventional balance block shape to form a green blank. The thickness of the green blank is about 16 mm, and the pressing pressure is 600-1200 MPa.

[0054] (3) The green embryo is pre-fired in an atmosphere of decomposed ammonia (N2:H2=1:3), then sintered at high temperature, and naturally cooled to obtain a balance block. The heating rate is 15-20℃ / min.

[0055] The preparation method of silane coupling agent modified iron(III) oxide includes the following steps:

[0056] Nano-iron oxide was dispersed in ethanol (based on a nano-iron oxide:ethanol ratio of 1g:100mL), and a silane coupling agent was added under stirring and at 65°C to carry out a modification reaction. After the reaction, the solid and liquid were separated, and the solid was dried under vacuum to obtain silane coupling agent modified nano-iron oxide.

[0057] The component content and process parameters mentioned above are detailed in Table 1, where the content of copper powder, sintering aid and lubricant is calculated with the total alloy powder used for balance blocks as 100%.

[0058] Table 1

[0059]

[0060]

[0061] Comparative Example 13

[0062] Compared to Example 2, an equal amount of ferric oxide with an average particle size of 100 nm was used as a substitute.

[0063] Balance block test method:

[0064] (1) The density of the pressed green body and the sintered body was measured in accordance with GB / T 5163-2006 "Determination of density, porosity and oil content of sintered metal materials with permeability", the principle of which is Archimedes' water displacement method.

[0065] (2) The tensile strength of the balance block was tested at room temperature according to GB / T228.1-2021;

[0066] (3) Magnetism: Use a gaussmeter to detect magnetism.

[0067] Table 2

[0068]

[0069]

[0070] The balance block of this invention has a tensile strength > 500 MPa, an elongation > 5%, a magnetic field ≤ 0.15 mT, and a density ≥ 7.2 g / cm³. 3 .

[0071] Examples 1-4 and Comparative Examples 1, 12-13 show that adding nano-ferric oxide with an average particle size of 10-1000 nm can promote sintering and improve the density and tensile strength of the sintered balance block. The average particle size is more preferably 50-500 nm. Moreover, compared with nano-ferric oxide, nano-ferric oxide has a better sintering-promoting effect.

[0072] As can be seen from Examples 2, 5-7 and Comparative Examples 2-3, if the content of nano-ferric oxide is too low, it is insufficient to effectively mix with the alloy powder, resulting in insufficient influence on the alloy powder and failing to improve sintering activity. If the content is too high, the surface of nano-ferric oxide is generally rough, and if it exceeds a certain amount, the compatibility between the alloy powder and nano-ferric oxide particles is not high. At the same time, the activity of the powder is too high, and the agglomeration phenomenon is serious, resulting in poor powder dispersion and uniformity, which significantly reduces its sintering aid effect. In addition, since nano-ferric oxide itself is an oxide, it can also have a cutting effect on the matrix, resulting in a decrease in mechanical properties. Therefore, the content of nano-ferric oxide is preferably 0.2-1%, more preferably 0.4-0.8%.

[0073] As can be seen from Examples 2, 8-9 and Comparative Examples 4-5, when the copper content is low, only a portion of the alloy undergoes transient liquid phase sintering during sintering, which has little effect on alloy diffusion and densification. Within a certain range, the density gradually increases with the increase of copper powder content. However, if the above range is exceeded, excessive copper has little effect on the degree of densification, pore filling, and rearrangement. In fact, excessive copper phase leads to a decrease in the mechanical properties of the alloy.

[0074] Examples 2, 10-15, and Comparative Example 6 show that modifying nano-Fe3O4 with a silane coupling agent can reduce the surface roughness of nano-Fe3O4, improve its fluidity, stability, and dispersibility, and facilitate the mixing effect of the alloy powder, resulting in a tighter internal connection of the alloy powder and better filling of the gaps between alloy particles. During the sintering process, the silane coupling agent, acting as a protective layer, decomposes and volatilizes first, leaving behind more active nano-Fe3O4, which significantly improves the degree of alloy sintering. Simultaneously, in the subsequent high-temperature sintering process, the copper liquid phase also cooperates to fill the pore structure, thereby comprehensively improving the density and tensile strength of the equilibrium block. However, excessive silane coupling agent content, resulting in too much silane coupling agent loaded on the surface of nano-Fe3O4, can lead to increased alloy porosity due to the easy high-temperature decomposition of the silane coupling agent, which generates gas. This prevents subsequent alloy diffusion (including the copper liquid phase) from filling a large number of pores in time, leading to a decrease in the density and mechanical properties of the alloy. Therefore, the preferred silane coupling agent content is 0.2-1%.

[0075] As demonstrated in Examples 2, 16-17, and Comparative Examples 7-9, pre-sintering before green compact sintering not only decomposes the silane coupling agent and lubricant in the organic components at high temperatures, but also facilitates the filling of pores formed by the sintering of organic components by the copper liquid phase during subsequent high-temperature sintering, thus improving the densification of the alloy. Furthermore, pre-treatment at this temperature range can reduce the internal thermal stress and stress brittleness of the green compact, thereby improving the mechanical properties of the alloy. During the pre-treatment stage, the temperature should not be too low, otherwise incomplete sintering of the organic components will result in poor subsequent alloy diffusion and pore filling; conversely, the temperature should not be too high, as this will also lead to high thermal stress and fail to reduce the internal stress brittleness of the alloy. Therefore, the preferred pre-sintering temperature is 500-700℃.

[0076] As can be seen from Examples 2, 18-19 and Comparative Examples 10-11, the preferred sintering temperature is 1100-1250℃, and the sintering time is 0.5-1h. Otherwise, if the sintering temperature is too low, the melting point of copper will not be reached, and the liquidus line will not be reached, so that it will not play the role of copper powder. If the temperature is too high, it may approach the liquidus line of the alloy, which is not conducive to the densification of the alloy and the improvement of mechanical properties, that is, it will lead to over-sintering.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a balance block, characterized in that, Includes the following steps: (1) The uniformly mixed balance block is pressed with alloy powder to obtain a green blank; the alloy powder used for the balance block includes pre-alloy powder, copper powder, sintering aid and lubricant; The pre-alloyed powder comprises the following components in weight percentage: C 0.5-2%, Ni 0-2%, Mn 10-25%, Si 0.1-1%, P 0-0.9%, with the balance being Fe and unavoidable impurities; The sintering aid is nano-ferric oxide and / or silane coupling agent modified nano-ferric oxide, wherein the average particle size of the nano-ferric oxide is 10-1000 nm. The nano-ferric oxide contains 0.2-1% by mass in the alloy powder for the balance block, and the copper powder contains 2-11% by mass in the alloy powder for the balance block; the silane coupling agent accounts for 0.2-1% of the mass of the nano-ferric oxide. The preparation method of the silane coupling agent modified nano-Fe3O4 includes the following steps: dispersing nano-Fe3O4 in ethanol, adding silane coupling agent under stirring to carry out modification reaction, separating solid and liquid after reaction, and drying the solid to obtain silane coupling agent modified nano-Fe3O4. (2) The green embryo is pre-fired in a reducing atmosphere and then sintered. After cooling, the balance block is obtained. The pre-fired temperature is 500-700℃ and the pre-fired time is 0.5-1.5h.

2. The method for preparing the balance block as described in claim 1, characterized in that, Includes at least one of the following ACs: A. The average particle size of the nano-iron oxide is 50-500 nm; B. The mass percentage of the nano-ferric oxide in the alloy powder used for the balance block is 0.4-0.8%; C. The copper powder accounts for 5-10% of the mass percentage of the alloy powder used in the balance block.

3. The method for preparing the balance block as described in claim 1, characterized in that, The lubricant is at least one of hydrocarbons, fatty acids, fatty acid amides, esters, alcohols, and metal soaps; the lubricant has a mass percentage content of 0.1-1% in the alloy powder for the balance block.

4. The method for preparing the balance block as described in claim 1, characterized in that, The temperature of the modification reaction is 50-80℃, and the time of the modification reaction is 1-12h.

5. The method for preparing the balance block as described in claim 1, characterized in that, The silane coupling agent includes at least one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane.

6. The method for preparing the balance block as described in claim 1, characterized in that, The sintering temperature is 1100-1250℃, and the sintering time is 0.5-1h; the mixing and pressing are both carried out in an inert gas atmosphere; the pressing pressure is 600-1200MPa; the reducing atmosphere includes at least one of hydrogen atmosphere and decomposed ammonia atmosphere.

7. The balance block prepared by the method of any one of claims 1-6.

Images