A high-density non-magnetic compressor balance block and its preparation method

Abstract

This invention relates to a high-density non-magnetic compressor balance block and its preparation method. The high-density non-magnetic compressor balance block is prepared by a sintering process, and its composition is: 0.3-0.8% C, 13-18% Mn, 4-6% Pb, with the remainder being Fe. The density of the high-density non-magnetic compressor balance block is 7.8 g / cm³. 3 The above-mentioned magnetic induction intensity is below 0.05mT. The preparation process is as follows: 1) Prepare raw material powders of C, Mn, Pb and Fe according to the composition; 2) Place the raw materials in a planetary ball mill and perform low-energy ball milling to obtain mixed powder; 3) Press the mixed powder into a compact; 4) Sinter the compact to obtain a high-density non-magnetic compressor balance block.

Description

Technical Field

[0001] This invention relates to a high-density non-magnetic compressor balance block and its preparation method. The high-density non-magnetic compressor balance block of this invention has high density and is non-magnetic, which is beneficial to reducing the volume of the balance block and realizing the miniaturization of the compressor. Background Technology

[0002] In refrigeration equipment compressors, counterweights are common components. Due to the centrifugal force acting on the compressor crankshaft during rotation, the compressor may become unbalanced during operation. To adjust the dynamic balance of the crankshaft during rotation, counterweights (i.e., counterweights) need to be installed on the crankshaft. This can greatly reduce vibration and noise during compressor operation, prevent the crankshaft from operating under stress imbalance conditions, and improve the crankshaft's lifespan.

[0003] The balance weight needs to be made of non-magnetic material to avoid interfering with the motor's magnetic field. Previously, balance weights were typically made of copper because of its high density, which facilitated compressor miniaturization; however, copper was relatively expensive. Later, inexpensive high-manganese steel was gradually adopted as a substitute for copper. High-manganese steel is an austenitic single-phase steel with non-magnetic properties. Balance weights made from high-manganese steel can be produced using two methods: melting and casting, and powder metallurgy. The melting and casting method produces a higher material density, reaching 7.7 g / cm³. 3 However, the preparation process is relatively complex, energy-intensive, and polluting, and cannot be formed in one step, making subsequent processing more complicated. Powder metallurgy can directly form balance block materials in one step, and the process is relatively simple. The preparation process is energy-saving and environmentally friendly, but the density of its materials is lower than that of the melting and casting method, which is not conducive to the miniaturization of compressors.

[0004] Therefore, the present invention provides a high-density non-magnetic balance block prepared by powder metallurgy process. Summary of the Invention

[0005] The present invention aims to solve the technical problems faced by the prior art as mentioned in the background section. The present invention provides a high-density non-magnetic balance block, which is prepared by powder metallurgy (sintering) method. It has high density and non-magnetic properties, which is beneficial to reducing the volume of the balance block and realizing the miniaturization of the compressor. In addition, the balance block has a uniform density distribution, which can reduce vibration and noise during the operation of the compressor.

[0006] The present invention solves the technical problem and achieves the corresponding technical effect through the following technical solutions.

[0007] This invention provides a high-density non-magnetic compressor balance block, characterized in that the high-density non-magnetic compressor balance block is prepared by a sintering process, and its composition is: 0.3-0.8% C, 13-18% Mn, 4-6% Pb, with the remainder being Fe, and the density of the high-density non-magnetic compressor balance block is 7.8 g / cm³. 3 Above, the magnetic induction intensity is below 0.05mT.

[0008] The high-density non-magnetic compressor balance block provided by this invention has a room-temperature austenitic single-phase structure, so it exhibits non-magnetic properties and is suitable for use as a compressor balance block material.

[0009] The density of the high-density non-magnetic compressor balance block of this invention is 7.8 g / cm³. 3 The above-mentioned optimal values ​​can reach 7.9 g / cm³. 3 In particular, when the Pb content is close to the upper limit of 6% and the Mn addition is around the lower limit of 13%, the density of the high-density compressor balance block of the present invention can reach 7.95 g / cm³. 3 In summary, under the premise of the same mass, the volume of the compressor balance block has been reduced, which is beneficial to the miniaturization of the compressor.

[0010] C and Mn are elements that ensure the compressor balance block of this invention has a room-temperature austenitic structure. Both can improve hardenability and room-temperature stability of austenite, ensuring a single-phase room-temperature austenitic structure, thereby guaranteeing the non-magnetic properties of the compressor balance block. C and Mn are also important elements for ensuring the mechanical properties of the compressor balance block. In this invention, the amount of C added is controlled at 0.3-0.8%, and the amount of Mn added is controlled at 13-18%. Under the premise of ensuring room-temperature austenite stability, the lower the amount of C and Mn added, the better. The lower the content of both, the more beneficial it is to improve the density of the compressor balance block.

[0011] Pb is one of the key improvements of this invention over the traditional high-manganese steel composition. Pb has a high density, reaching 11.34 g / cm³. 3Furthermore, Pb has a very low melting point of approximately 327.5℃ and a boiling point of approximately 1750℃. In traditional technical concepts, except in certain special steels (such as free-cutting steel), Pb is generally considered an impurity element that leads to the deterioration of steel performance and is therefore restricted from addition. However, in practical work, it has been found that for counterweights, their main function during operation is weight distribution, with the primary requirement being non-magnetic properties and very low requirements for mechanical properties. Based on this, the inventors of this invention broke through the constraints of traditional understanding and boldly experimented with using Pb as an additive in counterweight steel. This sacrificed some mechanical properties of the steel in exchange for increased density in high-manganese steel; that is, some mechanical properties unimportant to the counterweight were given up, while the density of the counterweight, crucial for the miniaturization of compressors, was increased.

[0012] The advantages of adding Pb in this invention are at least reflected in the following two aspects: First, Pb has a very high element density, and appropriate addition of Pb is beneficial to improving the density of the balance block material, thereby realizing the miniaturization of the compressor; Second, Pb has a very low melting point, and it has already melted within the sintering temperature range of high manganese steel (about 1100℃). Molten Pb forms a liquid phase during the sintering process, which is beneficial to the diffusion of other powders, can promote the connection and growth of the sintering neck, and can effectively fill the pores, thereby improving the density of the balance block.

[0013] In other words, the high-manganese steel with a certain amount of Pb added in this invention must be prepared by sintering. This is because the melting temperature of traditional high-manganese steel is close to the boiling point of Pb, which is easily volatilized and toxic. The sintering temperature is much lower than the boiling point of Pb. Therefore, from the perspectives of Pb yield and environmental friendliness, powder metallurgy process is required to prepare the balance block of this invention.

[0014] In this invention, to ensure that the compressor balance block has high density and that the mechanical strength remains within an acceptable range, the Pb content is 4-6%. Excessive Pb addition results in significant damage to mechanical properties, affecting the reliability of the compressor; conversely, insufficient Pb addition leads to inadequate density enhancement.

[0015] By controlling the addition amounts of C, Mn, and Pb, the compressor balance block of the present invention has a content of at least 7.8 g / cm³. 3 With a density of less than 0.05 mT, a magnetic induction intensity of more than 380 MPa, a tensile strength of more than 300 MPa at room temperature, and an elongation of more than 4.5%, the density of the compressor balance block is increased while taking into account the mechanical and magnetic properties of the compressor balance block, which is beneficial to the miniaturization of the compressor.

[0016] The high-density non-magnetic compressor balance block of the present invention is prepared by powder metallurgy process, the preparation steps of which include: 1) preparing raw material powders of C, Mn, Pb and Fe according to the composition; 2) placing the raw materials in a planetary ball mill for low-energy ball milling to obtain mixed powder; 3) pressing the mixed powder into a compact; 4) sintering the compact to obtain the high-density non-magnetic compressor balance block.

[0017] The raw material powders of C, Mn, Pb, and Fe are preferably elemental raw material powders, and the particle size of each elemental raw material powder is controlled within 20-50 μm.

[0018] While increasing the density of the balance block in a non-magnetic compressor, it is equally important to obtain a uniform density distribution. A uniform density distribution of the balance block can effectively avoid vibration and noise during the operation of the compressor, and also helps to improve the lifespan of the balance block and the compressor.

[0019] The Pb element intentionally added in this invention has a relatively soft texture. Therefore, the ball milling process parameters need to be strictly controlled during the preparation of the mixed powder to avoid cold welding of Pb powder with other raw material powders. Because Pb is soft, once cold welding occurs, Pb will coat the surface of the other powders. As ball milling progresses, this cold welding effect will increase exponentially, like a snowball rolling downhill, eventually leading to agglomeration of the mixed powder. This cold welding and agglomeration will cause an imbalance in the distribution of Pb in the mixed powder. Furthermore, this imbalance will also result in an uneven increase in density due to Pb during sintering, ultimately affecting the uniformity of the density distribution of the compressor balance block and causing imbalance during compressor operation.

[0020] Therefore, the preparation of the compressor balance block of the present invention must employ low-energy ball milling and a wet milling process with the addition of a process control agent during the mixing stage. For example, deionized water or anhydrous ethanol can be used. Furthermore, the amount of process control agent added during wet milling should not be less than 45% of the total weight of the raw material powder. If the amount of process control agent added is too small, the mixture after ball milling will exhibit agglomeration, affecting the density distribution of the compressor balance block. Additionally, the ball milling method suitable for the raw material composition of the present invention is low-energy ball milling. High-energy ball milling introduces excessive energy, resulting in significant cold welding and unavoidable agglomeration. Therefore, the compressor balance block of the present invention containing increased Pb must be mixed using low-energy ball milling, with the ball milling speed controlled at 20-40 r / min and the ball milling time controlled at 2-5 h. Excessive ball milling speed or excessively long ball milling time will lead to powder cold welding and agglomeration problems.

[0021] After wet milling, the mixed powder is dried, and then pressed into a compact under a pressure of 800-1500MPa. After pressing, it is sintered at a temperature of 1050-1250℃ for 1.5-3.0h.

[0022] The compressor balance block of the present invention prepared by the above method has a content of at least 7.8 g / cm³. 3 Its density is below 0.05 mT, its density distribution is uniform, and the density difference between different parts is no greater than 0.05 g / cm³. 3 Although the addition of Pb leads to a deterioration in performance, its room temperature mechanical properties still meet the requirements of tensile strength above 380 MPa, yield strength above 300 MPa, and elongation above 4.5%, which fully meets the mechanical performance requirements of the compressor balance block.

[0023] As another objective of this invention, the present invention also provides a preparation process for the aforementioned high-density non-magnetic balance block, specifically including: 1) preparing C, Mn, Pb, and Fe raw material powders according to their composition; 2) placing the raw materials in a planetary ball mill for low-energy ball milling to obtain a mixed powder; 3) pressing the mixed powder into a compact; 4) sintering the compact to obtain a high-density non-magnetic compressor balance block. The low-energy ball milling is wet milling, and the amount of process control agent added is not less than 45% of the total weight of the raw material powder, for example, 55%, 65%, 75%, etc.; the ball milling speed is 20-40 r / min, and the milling time is 2-5 h; preferably, the ball-to-powder ratio is controlled at 1-8:1. After wet milling, the mixed powder is dried and then pressed into a compact. The pressing pressure is 800-1500 MPa, and the compact is then sintered. The sintering temperature is controlled at 1050-1250℃, and the sintering time is 1.5-3.0 h.

[0024] As described above, the technical solution of the present invention has the following technical advancements.

[0025] Based on the actual operating conditions of compressor balance blocks, the inventors of this invention comprehensively weighed the density and mechanical properties of steel, and intentionally added a certain amount of Pb to the traditional high-manganese steel balance block, breaking through the traditional perception of Pb as an impurity. This sacrifice of some mechanical properties of the steel in exchange for increased density of the high-manganese steel, meaning some mechanical properties unimportant to the balance block are given up to improve the balance block density, which is crucial for compressor miniaturization. Pb has a high density, and appropriate addition of Pb is beneficial for increasing the density of the balance block material, thereby achieving compressor miniaturization. Pb also has a low melting point, melting within the sintering temperature range of high-manganese steel (approximately 1100℃). Molten Pb forms a liquid phase during sintering, which facilitates the diffusion of other powders, promotes the connection and growth of the sintering neck, and effectively fills pores, thus improving the density of the balance block. To accommodate the addition of Pb, this invention specifically employs low-energy ball milling and wet milling to prepare the mixed powder. By controlling the ball milling speed and time, as well as the amount of process control agent added, the invention avoids the formation of cold welds in the soft Pb and other element powders, preventing agglomeration. This ensures that the compressor balance block has a uniform density distribution, guaranteeing stable compressor operation, low noise, and minimal vibration.

[0026] The compressor balance block of the present invention has a content of at least 7.8 g / cm³. 3 Its density is below 0.05 mT, its density distribution is uniform, and the density difference between different parts is no greater than 0.05 g / cm³. 3 Although the addition of Pb leads to a deterioration in performance, its room temperature mechanical properties still meet the requirements of tensile strength above 380 MPa, yield strength above 300 MPa, and elongation above 4.5%, which fully meets the mechanical performance requirements of the compressor balance block. Detailed Implementation

[0027] To enable those skilled in the art to fully understand the technical solution and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0028] Experimental Example 1.

[0029] The compressor balance block was designed and prepared according to the composition in Table 1. The specific process included: 1) Preparing elemental powders of C, Mn, Pb, and Fe according to the composition, with the particle size controlled between 20-50 μm; 2) Placing the raw materials in a planetary ball mill, adding anhydrous ethanol as a process control agent to the ball mill jar, with the amount of anhydrous ethanol added being 50% of the total weight of the raw material powder, using ZrO2 grinding balls with a diameter of 5 mm, and the ratio of the weight of the ZrO2 grinding balls to the total weight of the raw material powder being 2:1, and ball milling for 3 hours at 30 r / min; 3) After ball milling, a mixed powder was obtained, which was dried at 110℃, and then the dried mixed powder was pressed into a compact under a pressure of 1000 MPa; 4) The compact was sintered at 1130℃ for 2.5 hours to obtain a sample with a diameter of 30 cm and a height of 15 cm.

[0030] The sample density was tested, and the magnetic induction intensity of the sample was measured using a gaussmeter. The specific test results are shown in Table 1. The tensile strength, yield strength and elongation of the sample were measured according to the national standard GB / T228.1-2021. The specific test results are shown in Table 2.

[0031] Table 1. Composition (Fe balance), density, and magnetic induction intensity of each compressor balance block.

[0032]

[0033] Table 2 Mechanical properties of the balance blocks of each compressor.

[0034]

[0035] As shown in Table 1, the magnetic induction intensity of all samples is below 0.05 mT, which meets the non-magnetic requirement of this invention. However, regarding density: samples with Pb content within the range required by this invention (sample numbers 1-8) meet the density requirements of this invention; sample number 11 has the highest Pb content and also the highest density; sample number 9 has a low Pb content, and samples 10 and 12 have no Pb added. Reducing or omitting Pb content lowers the density from the perspective of raw material composition. Furthermore, too low or no Pb content leads to insufficient liquid phase during sintering, which is not conducive to powder diffusion, resulting in poor connection and growth of the sintering neck, and inability to effectively fill pores. Therefore, samples 9, 10, and 12 do not meet the density requirements of this invention.

[0036] As can be seen from Table 2, samples with Pb content within the range required by this invention (samples 1-8) have mechanical properties that meet the requirements of this invention; samples with low Pb content or no Pb added (samples 9, 10, 12) have better mechanical properties, but such mechanical properties are far from excessive for the balance block material, and cannot reflect the value of the high mechanical properties of the compressor balance block in actual compressor applications; the Pb content of sample 11 is too high, and its mechanical properties deteriorate sharply, failing to meet the requirements of this invention.

[0037] In summary, it can be confirmed that samples 1-8 that meet the composition requirements of this invention can meet the requirements of the invention in terms of density, magnetic properties, and mechanical properties, while samples 9-11 that do not meet the composition requirements of this invention cannot meet the requirements of this invention in terms of density or mechanical properties.

[0038] Experimental Example 2.

[0039] Raw material powders were prepared according to the following composition: C: 0.45%, Mn: 15.7%, Pb: 5.0%, with the balance being Fe. All raw material powders were selected as elemental powders, with particle sizes controlled between 20-50 μm. The raw materials were placed in a planetary ball mill. Anhydrous ethanol was used as the process control agent in this process control scheme. ZrO2 grinding balls with a diameter of 4 mm were used, with a ZrO2 grinding ball weight to raw material powder weight ratio of 2:1. The process control agent dosage, ball milling speed, and ball milling time are shown in Table 3. After ball milling, a mixed powder was obtained and dried at 100℃. The dried mixed powder was then pressed into a compact under a pressure of 1050 MPa. The compact was sintered at 1200℃ for 2 hours to obtain a compressor balance block sample with dimensions of 30 cm long, 20 cm wide, and 10 cm thick.

[0040] The overall density of the obtained sample was measured and denoted as ρ0. Then, six cubic sample blocks with sides of 4cm were randomly cut from different parts of the sample, and their densities were measured and denoted as ρ1, ρ2, ρ4, ρ5, and ρ6, respectively. The maximum difference between ρ1, ρ2, ρ4, ρ5, and ρ6 was denoted as Δρ. max Record the test results in Table 4, in g / cm³. 3 .

[0041] Table 3. Ball milling process parameters for each compressor balance block.

[0042]

[0043] Table 4. Densities of each sample, in g / cm³ 3 .

[0044]

[0045] For example, the amount of process control agent added in sample number 1302 was relatively small, although its overall density was still within the range of 7.8 g / cm³ of the present invention. 3 However, compared to sample number 1301, it still shows a certain decrease, and the density difference between different parts reaches a maximum of 0.29 g / cm³. 3 The analysis suggests that the insufficient addition of process control agent led to some degree of Pb powder cold welding and agglomeration, resulting in uneven Pb distribution in the mixed powder. Pb was concentrated in some areas and scarce in others. Consequently, some areas could not obtain sufficient liquid phase during sintering, resulting in poor powder diffusion conditions, insufficient powder sintering neck bonding and growth, and inadequate pore filling. This led to a decreasing overall density. Furthermore, due to Pb cold welding and agglomeration, Pb accumulated in some areas, resulting in poor density uniformity of the sample.

[0046] Similarly, samples 1303, 1304, and 1307 also exhibited Pb cold welding or agglomeration due to excessively high ball milling speed, excessively long ball milling time leading to excessive ball milling energy, or the lack of process control agents causing a significant amount of ball milling energy to be transferred to the mixed powder. As a result, the overall density of the materials decreased to varying degrees, and the density uniformity of the samples was poor, failing to meet the requirements of this invention. The reasons for these phenomena are the same as those for sample 1302 mentioned above.

[0047] The ball milling speed or milling time of samples 1305 and 1306 was too low, which resulted in Pb not being evenly distributed. In the sintered billet, Pb was concentrated in some local areas and depleted in others. Therefore, some areas could not obtain enough liquid phase during the sintering process, resulting in poor powder diffusion conditions, insufficient powder sintering neck connection and growth, and insufficient filling of pores. This led to a downward trend in overall density, and the uneven distribution of Pb resulted in poor density uniformity of the samples.

[0048] Sample No. 1301, with appropriate process control agent dosage, ball milling speed, and ball milling time, ultimately produced a material with a high overall density of 7.8 g / cm³. 3 The above conditions are met, and the density distribution is uniform, with the density difference between different parts not exceeding 0.05 g / cm³. 3 The overall density and density distribution uniformity both meet the requirements of this invention.

[0049] In summary, it can be confirmed that by controlling the amount of process control agent added, the ball mill speed, and the ball milling time within a reasonable range during the ball milling process, high-density compressor balance block material with uniform density distribution can be obtained.

Claims

1. A high density non-magnetic compressor balance block, characterized by, The high-density non-magnetic compressor balance block is prepared by a sintering process, and its composition is: 0.3-0.8% of C, 13-18% of Mn, 4-6% of Pb, and the rest is Fe, and the density of the high-density non-magnetic compressor balance block is 7.8 g / cm 3 Above, the magnetic induction intensity is 0.05 mT or less; The high-density non-magnetic compressor balance block is prepared by the following process: 1) preparing C, Mn, Pb and Fe raw material powder according to the composition; 2) placing the raw material in a planetary ball mill to perform low-energy ball milling to obtain mixed powder; 3) forming a compact from the mixed powder; 4) sintering the compact to obtain the high-density non-magnetic compressor balance block; The low-energy ball milling is wet milling, the amount of wet milling process control agent added is not less than 45% of the total weight of the raw material powder, and the ball milling speed of the low-energy ball milling is 20-40 r / min, and the ball milling time is 2-5 h.

2. A high density non-magnetic compressor balance block according to claim 1, wherein, The high-density non-magnetic compressor balance block has an austenitic single-phase structure at room temperature.

3. A high density non-magnetic compressor balance block according to claim 1, wherein, The compact forming pressure is 800-1500 MPa, the sintering temperature is controlled at 1050-1250 DEG C, and the sintering time is 1.5-3.0 h.

4. The method of making a high density non-magnetic compressor balance as defined in claim 1, wherein, The method comprises the following steps: 1) preparing C, Mn, Pb and Fe raw material powder according to the composition; 2) placing the raw material in a planetary ball mill to perform low-energy ball milling to obtain mixed powder; 3) forming a compact from the mixed powder; 4) sintering the compact to obtain the high-density non-magnetic compressor balance block; The low-energy ball milling is wet milling, the amount of wet milling process control agent added is not less than 45% of the total weight of the raw material powder, and the ball milling speed of the low-energy ball milling is 20-40 r / min, and the ball milling time is 2-5 h.

5. The method of making a high density non-magnetic compressor balance as set forth in Claim 4, wherein, The mixed powder is dried after the wet milling, and then compact forming is performed.

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