A copper alloy for low-lead pressure reducing valve body and a method for manufacturing the same

Abstract

The application discloses a copper alloy for a low-lead pressure reducing valve body and a preparation method thereof, relates to the technical field of alloys, and comprises the following components: 0.5-1 wt% of tin, 0.01-0.05 wt% of phosphorus, 0.4-0.8 wt% of lead, 0.1-0.5 wt% of manganese, 0.05-0.5 wt% of iron, 1-1.4 wt% of molybdenum, 0.5-1.5 wt% of bismuth, 0.1-0.4 wt% of silicon, and the balance of inevitable impurity elements and copper; the application utilizes molybdenum powder modified by mercapto to form a coordination effect with lead elements in a melt, to stably adsorb free lead on the surface of molybdenum powder particles, to be uniformly distributed in the copper alloy, and to be kept in a solid state in the copper alloy mixed melt by the molybdenum powder, so that the lead cannot be extruded to cause segregation migration in the copper alloy mixed melt solidification process, the formation of a lead-rich area in the inner wall of the valve body is significantly reduced, the uniformity of lead in the copper alloy mixed melt is ensured, and the risk of lead dissolution and precipitation in a water medium in the service process of the valve body is further reduced.

Description

Technical Field

[0001] This invention relates to the field of alloys, and more particularly to a copper alloy for a low-lead pressure reducing valve body and a method for preparing the same. Background Technology

[0002] Leaded brass is an extremely important and widely used complex brass, possessing excellent machinability and wear resistance. It is commonly used as a valve body material. On one hand, lead is almost insoluble in copper alloys and exists as dispersed particles, playing a self-lubricating and chip-breaking role during machining, thus significantly improving the alloy's machinability and casting performance. On the other hand, lead particles can provide lubrication at the friction interface, helping to improve the valve body's wear resistance and sealing performance during opening and closing. Traditional lead-copper alloys have long been widely used in the valve manufacturing industry. However, lead is toxic. For the preparation of low-lead pressure-reducing valve bodies using lead-copper alloys, the lead content needs to be controlled below 0.8% to be suitable for use in pressure-reducing valves in water.

[0003] For low-lead pressure reducing valves, on the one hand, the standard electrode potential of lead in copper alloys is lower than that of copper. Lead often exists as an anode phase in the copper matrix and easily forms micro-batteries with the copper matrix. When in contact with water, lead will first dissolve and precipitate. After lead ions enter the water, they will cause drinking water pollution, and long-term use may cause serious health hazards. On the other hand, lead has a melting point of 327℃. During the casting process, lead has a low melting point and migrates to the surface when the copper alloy solidifies. This results in the lead concentration on the inner wall of the valve body being much higher than the internal lead concentration. After the valve body comes into contact with water, the water flow will wash away the inner wall of the valve body and damage the inner surface layer, further leading to a large amount of lead coming into contact with the water.

[0004] Therefore, it is necessary to design a copper alloy for low-lead pressure reducing valve bodies and its preparation method to solve the above-mentioned technical problems. Summary of the Invention

[0005] This invention overcomes the shortcomings of the prior art and provides a copper alloy for low-lead pressure reducing valve bodies and a method for preparing the same.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for preparing a copper alloy for a low-lead pressure reducing valve body, comprising the following steps:

[0007] Step S1: Heat copper to a molten state, and add tin, phosphorus, lead, manganese, iron, bismuth and silicon in sequence according to the proportion and mix them evenly to obtain a copper alloy mixed melt;

[0008] Step S2: Take molybdenum powder and modify it with mercapto to obtain mercapto-modified molybdenum powder, and then perform sulfidation treatment;

[0009] Step S3: Gradually cool the copper alloy molten mixture to a semi-solid state, and add sulfidated molybdenum powder in proportion and mix evenly to adsorb lead in the copper alloy molten mixture.

[0010] Step S4: Pour and cool the copper alloy molten mixture from step S3 to obtain the valve body.

[0011] In a preferred embodiment of the present invention, the composition of the copper alloy mixed melt includes: 0.5-1 wt% tin, 0.01-0.05 wt% phosphorus, 0.4-0.8 wt% lead, 0.1-0.5 wt% manganese, 0.05-0.5 wt% iron, 1-1.4 wt% molybdenum, 0.5-1.5 wt% bismuth, 0.1-0.4 wt% silicon, with the balance being unavoidable impurity elements and copper;

[0012] The content of impurity elements is 0-1 wt%.

[0013] In a preferred embodiment of the present invention, step S1 includes the following sub-steps:

[0014] Step S11: Heat copper to 1050-1150°C at a rate of 10-15°C / min, and hold for 10-15 minutes until the copper is completely liquefied;

[0015] Step S12: Add tin, phosphorus, lead, manganese and iron to the molten copper solution in sequence and stir electromagnetically for 20 to 30 minutes.

[0016] In a preferred embodiment of the present invention, in step S2, the particle size of the molybdenum powder is 1-5 μm.

[0017] In a preferred embodiment of the present invention, step S2 includes the following sub-steps:

[0018] Step S21: Immerse molybdenum powder in pickling solution at a liquid-to-solid ratio of 10-12:1 and sonicate at 60-80°C for 25-30 minutes.

[0019] Step S22: Take a mixed solution of 3-mercaptopropyltrimethoxysilane and ethanol, and add acetic acid to adjust the pH to 4-4.5;

[0020] Step S23: Dry the acid-washed molybdenum powder and add it to the mixed solution. React at 60-70℃ for 5-6 hours to immobilize thiol groups on the surface of the molybdenum powder.

[0021] Step S24: Dry the reacted molybdenum powder under vacuum at 75-80℃ for 10-15 min to obtain mercapto-modified molybdenum powder;

[0022] Step S25: Pass argon gas through the mercapto-modified molybdenum powder and heat treat it at 500-800℃ for 30-120 min to form a molybdenum sulfide coating on the surface of the molybdenum powder, thus obtaining molybdenum sulfide powder.

[0023] In a preferred embodiment of the present invention, in step S21, the pickling solution includes: H2SO4 with a concentration of 96-98%, HNO3 with a concentration of 60-68%, and H2O, wherein the mass ratio of H2SO4, HNO3, and H2O is 3-4:1:1.

[0024] In a preferred embodiment of the present invention, the 3-mercaptopropyltrimethoxysilane and ethanol are mixed in a mass ratio of 1:9 to 10.

[0025] The mass ratio of the molybdenum powder to the mixed solution is 1:5 to 7.

[0026] In a preferred embodiment of the present invention, in step S3, the copper alloy molten mixture is cooled to 800-900°C at a rate of 5-10°C / min to a semi-solid state;

[0027] Add molybdenum sulfide powder to the copper alloy molten mixture, stir at 100-200 rpm for 10-15 minutes, maintain the temperature at 800-900℃, and let stand for 5-8 minutes.

[0028] In a preferred embodiment of the present invention, in step S4, after the pouring is completed, the temperature is reduced to room temperature at a rate of 10-15°C / min.

[0029] A copper alloy for use in low-lead pressure reducing valve bodies comprises: 0.5–1 wt% tin, 0.01–0.05 wt% phosphorus, 0.4–0.8 wt% lead, 0.1–0.5 wt% manganese, 0.05–0.5 wt% iron, 1–1.4 wt% molybdenum, 0.5–1.5 wt% bismuth, 0.1–0.4 wt% silicon, with the balance being unavoidable impurity elements and copper.

[0030] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0031] (1) The present invention provides a method for preparing copper alloy for low-lead pressure reducing valve body. Molybdenum sulfide powder is used to coordinate with lead in the melt, and free lead is stably adsorbed on the surface of molybdenum powder particles, and then uniformly distributed in copper alloy. The molybdenum powder is kept solid in the copper alloy mixed melt, so that lead will not be squeezed and segregated during the solidification of the copper alloy mixed melt. This significantly reduces the formation of lead-rich area on the inner wall of the valve body, ensures the uniformity of lead in the copper alloy mixed melt, and further reduces the risk of lead dissolution and leaching in water medium during valve body service.

[0032] (2) This invention provides a method for preparing a copper alloy for a low-lead pressure reducing valve body. By cooling the melt to a semi-solid state, liquid lead is forced to be squeezed into the interdendritic region to form a lamellar structure, which reacts with the surface of molybdenum powder forming a molybdenum sulfide coating to form a Pb-S / Pb-Mo-S complex state and chemically fixes the free lead on the surface of the molybdenum powder, significantly reducing the chemical freeness of lead. This allows free lead in the copper alloy melt to be captured in time and exist in a complex / bonded form, reducing the risk of dissolution caused by lead entering the parent phase or surface in a soluble form from the source. This invention directly changes the chemical form of lead by forming chemical bonds, significantly reducing the lead dissolution rate during the service of the valve body, improving the environmental safety of the water supply system, and eliminating its harm to water quality while retaining lead to improve processing and lubrication performance.

[0033] (3) The present invention provides a method for preparing copper alloy for low-lead pressure reducing valve body. High melting point molybdenum is used as carrier, so that molybdenum remains solid in the melt and acts as the anchoring phase for lead, adsorbing and fixing free lead. Solid and dispersed molybdenum particles will not be squeezed out by the liquid phase or migrate with the low melting point phase during solidification, so that the adsorbed lead is buried with the parent phase along with the molybdenum particles instead of agglomerating at the grain boundary or casting surface, avoiding the segregation of lead at the end of solidification and enrichment in the inner cavity and surface layer, which leads to the formation of high concentration lead peaks on the inner wall. This scheme ensures that lead is uniformly dispersed in the matrix by using molybdenum as carrier, which improves the uniformity and surface density of copper alloy material, reduces the risk of embrittlement, porosity and early failure caused by local lead enrichment, thereby improving the mechanical stability and service life of valve body. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a flowchart of a preferred embodiment of the present invention for preparing a copper alloy for a low-lead pressure reducing valve body. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0038] like Figure 1 As shown, a method for preparing a copper alloy for a low-lead pressure reducing valve body includes the following steps:

[0039] Step S1: Heat copper to a molten state, and add tin, phosphorus, lead, manganese, iron, bismuth and silicon in sequence according to the proportion and mix them evenly to obtain a copper alloy mixed melt;

[0040] Step S2: Take molybdenum powder and modify it with mercapto to obtain mercapto-modified molybdenum powder, and then perform sulfidation treatment;

[0041] Step S3: Gradually cool the copper alloy molten mixture to a semi-solid state, and add sulfidated molybdenum powder in proportion and mix evenly to adsorb lead in the copper alloy molten mixture; wherein, a large amount of copper solid phase skeleton has been precipitated in the semi-solid melt, while the remaining liquid phase is rich in low melting point elements such as lead and fills the dendrite gaps.

[0042] Step S4: Pour and cool the copper alloy molten mixture from step S3 to obtain the valve body.

[0043] By utilizing the coordination between molybdenum sulfide powder and lead in the melt, free lead is stably adsorbed on the surface of molybdenum powder particles, and then uniformly distributed in the copper alloy.

[0044] Furthermore, by keeping molybdenum powder in the copper alloy melt, lead is prevented from being squeezed and segregating during the solidification process of the copper alloy melt. This significantly reduces the formation of lead-rich zones on the inner wall of the valve body, ensures the uniformity of lead in the copper alloy melt, and further reduces the risk of lead dissolution and leaching in the water medium during valve body service.

[0045] In this invention, the composition of the copper alloy mixed melt includes: 0.5-1 wt% tin, 0.01-0.05 wt% phosphorus, 0.4-0.8 wt% lead, 0.1-0.5 wt% manganese, 0.05-0.5 wt% iron, 1-1.4 wt% molybdenum, 0.5-1.5 wt% bismuth, 0.1-0.4 wt% silicon, with the balance being unavoidable impurity elements and copper;

[0046] The content of impurity elements is 0-1 wt%.

[0047] By adding bismuth and silicon to a copper alloy melt, bismuth tends to agglomerate at grain boundaries, forming local atomic clusters. Since the atomic radius of bismuth is significantly larger than that of iron or copper, its presence at grain boundaries leads to lattice distortion, increases the grain boundary energy barrier, and hinders grain boundary migration. Silicon can form high-melting-point compounds to pin grain boundaries, i.e., achieve the pinning effect. This is mainly because grain boundary migration requires overcoming an energy barrier, and the agglomeration of bismuth increases the barrier height, thus inhibiting grain boundary movement.

[0048] Lead tends to diffuse along grain boundaries at high temperatures, so the addition of bismuth inhibits lead migration.

[0049] In this invention, step S1 includes the following sub-steps:

[0050] Step S11: Heat copper to 1050-1150°C at a rate of 10-15°C / min, and hold for 10-15 minutes until the copper is completely liquefied;

[0051] Step S12: Add tin, phosphorus, lead, manganese and iron to the molten copper solution in sequence and stir electromagnetically for 20 to 30 minutes.

[0052] In step S1, the copper is heated at a rate of 10-15°C / min until the entire metal is liquidized and reaches 1050-1150°C, and then held at that temperature for 10-15 min.

[0053] The easily soluble tin, which has little impact on the melt, is added in sequence, followed by the phosphorus-containing Cu-P master alloy, then lead, and finally the iron-manganese master alloy.

[0054] Tin is readily soluble in copper and contributes to fluidity and lubrication. Adding it first can improve the viscosity / lubricity of the melt, making it easier to disperse subsequent elements.

[0055] Phosphorus is easily oxidized and forms intermetallic compounds with copper. To prevent phosphorus loss and the generation of free phosphorus gas, the Cu-P main alloy is added in batches in small amounts and stirred rapidly, so that phosphorus enters the melt in a stable main alloy form.

[0056] Because lead has a low melting point, is volatile and prone to splashing, it should be added in the form of small particles, strips or lead balls under the conditions of stable mother liquor temperature and good stirring, and should be sealed or protected with a covering agent as soon as possible after addition.

[0057] Finally, the iron-manganese main alloy is added.

[0058] Considering that lead is insoluble in copper alloys and that the surface energy of lead is typically lower than that of the copper matrix, when the temperature rises, lead atoms gain sufficient kinetic energy to overcome lattice constraints and transition from a solid state to a quasi-liquid state or a highly mobile state. At this point, lead atom vibrations intensify, increasing vacancy defects and providing channels for diffusion. Therefore, to prevent lead from migrating and causing uneven distribution within the copper alloy, molybdenum powder needs to undergo sulfidation treatment to adsorb lead into the molten copper alloy. Specifically:

[0059] Step S2 includes the following sub-steps:

[0060] Step S21: Immerse molybdenum powder in pickling solution at a liquid-to-solid ratio of 10-12:1 and treat with ultrasound at 60-80℃ for 25-30 minutes. The particle size of the molybdenum powder is 1-5 μm.

[0061] The pickling solution includes: H2SO4 with a concentration of 96-98%, HNO3 with a concentration of 60-68%, and H2O, wherein the mass ratio of H2SO4, HNO3, and H2O is 3-4:1:1;

[0062] The molybdenum powder was treated with pickling solution. On the one hand, the oxide layer and impurities on the surface of the molybdenum powder were removed to expose the fresh metal surface. On the other hand, the surface was activated by ultrasound to generate a large number of reactive sites, which laid the foundation for subsequent functionalization modification.

[0063] Step S22: Take a mixed solution of 3-mercaptopropyltrimethoxysilane and ethanol, wherein the 3-mercaptopropyltrimethoxysilane and ethanol are mixed in a mass ratio of 1:9 to 10, and acetic acid is added to adjust the pH to 4 to 4.5.

[0064] Step S23: Dry the acid-washed molybdenum powder and add it to the mixed solution. React at 60-70℃ for 5-6 hours to immobilize thiol groups on the surface of the molybdenum powder.

[0065] Step S24: Dry the reacted molybdenum powder under vacuum at 75-80℃ for 10-15 min to obtain mercapto-modified molybdenum powder;

[0066] Step S25: Pass argon gas through the mercapto-modified molybdenum powder and heat treat it at 500-800℃ for 30-120 min to form a molybdenum sulfide coating on the surface of the molybdenum powder, thus obtaining molybdenum sulfide powder.

[0067] The trimethoxy group in the 3-mercaptopropyltrimethoxysilane molecule can undergo a condensation reaction with the hydroxyl sites on the surface of molybdenum powder after hydrolysis, forming a stable -Si-O-Mo- bond. At the same time, the -SH thiol group at the other end is exposed on the particle surface, resulting in thiol-modified molybdenum powder.

[0068] Considering that the organic thiol functional group itself cannot survive at the high temperature of copper alloy smelting, but it is the best precursor to achieve highly uniform molecular-level dispersion of sulfur on the surface of molybdenum powder, in order to improve the dispersion uniformity of sulfur on the surface of molybdenum powder, the molybdenum powder is modified by thiol group, and the modified molybdenum powder is subjected to sulfidation treatment.

[0069] In this process, because the molybdenum powder is directly sulfided, the sulfur element will mainly exist in the form of physical adsorption or local reaction, resulting in a very uneven distribution and easy agglomeration, which greatly reduces the effective reaction area.

[0070] One end of the 3-mercaptopropyltrimethoxysilane molecule is a siloxane group that can form covalent bonds with the oxides on the surface of molybdenum powder, and the other end is a mercapto group (-SH). Through molecular self-assembly, it will be immobilized on the surface of molybdenum powder, thereby pinning sulfur atoms to the surface with a density of molecular spacing, ensuring that the distribution of the active sites of the molybdenum sulfide formed subsequently is extremely uniform and without any dead corners of agglomeration.

[0071] By modifying molybdenum powder with 3-mercaptopropyltrimethoxysilane, the problem of sulfur powder easily falling off can be avoided, and the bonding strength between sulfur and molybdenum powder can be improved.

[0072] When heated to 500–800°C in an inert atmosphere (such as argon), the organic thiol chain decomposes and carbonizes, but its sulfur atoms undergo a solid-phase reaction with the molybdenum substrate to generate a strong, stable, and high-temperature resistant molybdenum sulfide coating. This coating can then react fully with lead and has a high melting point, allowing it to remain solid in the copper alloy melt. Consequently, it can combine with lead in subsequent processes and distribute it evenly.

[0073] In this invention, the mass ratio of molybdenum powder to the mixed solution is 1:5 to 7.

[0074] In step S3, the copper alloy molten mixture is cooled to 800-900°C at a rate of 5-10°C / min to achieve a semi-solid state.

[0075] Add molybdenum sulfide powder to the copper alloy molten mixture, stir at 100-200 rpm for 10-15 minutes, maintain the temperature at 800-900℃, and let stand for 5-8 minutes.

[0076] By slowly cooling the melt to 800-900℃, at this temperature, the copper dendrites that solidify first form a framework, and the liquid lead is squeezed into the interdendritic region. Due to the modification effect of Bi / Si on the grain boundaries, the lead cannot shrink into spheres and can only be forced to spread along the grain boundaries, eventually forming a continuous or semi-continuous sheet-like or network-like structure.

[0077] Flake lead has a larger specific surface area, providing more contact sites for sulfur vacancies in molybdenum sulfide, promoting the formation of Pb-S-Mo bonds, enhancing the bond density, and thus enhancing the strength of Pb-S-Mo bonds. This effectively inhibits lead migration and dissolution, while also allowing lead to achieve uniform dispersion along with the uniform dispersion of molybdenum sulfide powder.

[0078] It should be noted that the layered structure of molybdenum sulfide powder exposes a large number of unsaturated sulfur atoms, forming highly active sulfur vacancies. The ionic radius of lead is highly compatible with the lattice size of sulfur vacancies, allowing it to embed into vacancies and form strong covalent bonds. Copper, iron, and other metals, due to their smaller size or lower charge density, have significantly weaker bonding stability than lead.

[0079] Under the high temperature environment of the melt, sulfur on the surface of molybdenum sulfide powder and lead form a stable cyclic complex Pb-Mo-S through chelation. Other metals are difficult to form a similar stable structure due to differences in electronic layer structure. Therefore, when molybdenum sulfide powder is added to copper alloy melt, it will preferentially combine with lead.

[0080] When molybdenum sulfide powder is added to copper alloy melt, the free lead in the melt is preferentially anchored by the thiol groups on the surface of the molybdenum powder, forming Pb-Mo-S coordination bonds and binding firmly. This prevents the lead from migrating or segregating freely in the form of droplets or particles, but instead it adheres to the surface of the molybdenum powder and is evenly distributed in the melt along with the molybdenum powder.

[0081] In step S3, the specific operation is to add molybdenum sulfide powder to the melt in batches and slowly to avoid local temperature fluctuations or powder agglomeration caused by adding a large amount at once. The process of adding molybdenum sulfide powder is completed within the first 1 / 3 to 1 / 2 of the entire stirring cycle so that there is enough time for mixing and reaction.

[0082] After adding molybdenum sulfide powder to the melt, the melt is stirred to fully disperse the molybdenum powder, prevent sedimentation or agglomeration, and promote the contact and chemical reaction / coordination between the thiol surface and the free lead in the melt.

[0083] It should be noted that forming a Pb-Mo-S complex and chemically fixing free lead on the surface of molybdenum powder significantly reduces the chemical freeness of lead, allowing free lead in the copper alloy melt to be captured in time and exist in a complex / bonded form, thereby reducing the risk of dissolution caused by lead entering the parent phase or surface in a soluble form from the source.

[0084] By forming chemical bonds to directly change the chemical form of lead, the leaching rate of lead during valve body service is significantly reduced, improving the environmental safety of water supply systems, and eliminating its harm to water quality while retaining lead to improve processing and lubrication performance.

[0085] In this invention, in step S4, the copper alloy molten mixture from step S3 is cast into a valve body shape. After casting, it is cooled to room temperature at a rate of 10-15°C / min to obtain a low-lead pressure reducing valve body.

[0086] It is worth mentioning that high-melting-point molybdenum is used as a carrier, so that molybdenum remains solid in the melt and acts as an anchoring phase for lead, adsorbing and fixing free lead. The solid and dispersed molybdenum particles will not be squeezed out by the liquid phase or migrate with the low-melting-point phase during solidification. This allows the adsorbed lead to be embedded in the parent phase along with the molybdenum particles instead of accumulating at the grain boundaries or casting surface, avoiding the segregation of lead in the late solidification stage and its enrichment in the inner cavity and surface, which would lead to the formation of high-concentration lead peaks on the inner wall.

[0087] Using molybdenum as a carrier ensures that lead is uniformly dispersed in the matrix, which improves the uniformity and surface density of copper alloy materials, reduces the risk of embrittlement, porosity and early failure caused by local lead enrichment, and thus improves the mechanical stability and service life of the valve body.

[0088] This invention introduces phosphorus into the melt by adding a Cu-P master alloy. During the solidification of the copper matrix, phosphorus can form tiny phosphide particles (such as Cu3P) as heterogeneous nuclei. These particles provide preferential deposition sites before dendrite formation, accelerate local solidification, thereby increasing the nucleus density and achieving fine crystallization.

[0089] A copper alloy for use in low-lead pressure reducing valve bodies comprises: 0.5–1 wt% tin, 0.01–0.05 wt% phosphorus, 0.4–0.8 wt% lead, 0.1–0.5 wt% manganese, 0.05–0.5 wt% iron, 1–1.4 wt% molybdenum, 0.5–1.5 wt% bismuth, 0.1–0.4 wt% silicon, with the balance being unavoidable impurity elements and copper.

[0090] Example 1:

[0091] A. Heat copper to 1150℃ at a rate of 15℃ / min and hold for 10min until the copper is completely liquefied. Then, add 1wt% tin, 0.05wt% phosphorus, 0.6wt% lead, 0.5wt% manganese, 0.5wt% iron, 1wt% bismuth, and 0.3wt% silicon to the molten copper solution in sequence and stir electromagnetically for 20min.

[0092] B. Take 1 wt% of molybdenum powder with a particle size of 1-5 μm, immerse the molybdenum powder in pickling solution at a liquid-to-solid ratio of 10:1, and ultrasonically treat it at 60℃ for 25 min. The pickling solution includes 98% H2SO4, 68% HNO3 and H2O, wherein the mass ratio of H2SO4, HNO3 and H2O is 3:1:1.

[0093] Take a mixed solution of 3-mercaptopropyltrimethoxysilane and ethanol in a mass ratio of 1:9-10, and add acetic acid to adjust the pH to 4-4.5. Dry the acid-washed molybdenum powder at 80℃ and add it to the mixed solution. React at 60℃ for 5 hours. Dry the reacted molybdenum powder under vacuum at 80℃ for 15 minutes to obtain mercapto-modified molybdenum powder.

[0094] C. The mercapto-modified molybdenum powder is passed through argon gas and heat-treated at 600℃ for 60 min to form a molybdenum sulfide coating on the surface of the molybdenum powder, thus obtaining molybdenum sulfide powder. The powder is then mixed with copper alloy melt and stirred at 100 rpm for 15 min. The temperature is then reduced to 850℃ at a rate of 8℃ / min and allowed to stand for 5 min.

[0095] D. Cast the copper alloy molten mixture from step C and cool it to room temperature at a rate of 10℃ / min to obtain the valve body.

[0096] Example 2:

[0097] Similar to Example 1, except that the proportion of molybdenum powder is changed;

[0098] A. Heat copper to 1150℃ at a rate of 15℃ / min and hold for 10min until the copper is completely liquefied. Then, add 1wt% tin, 0.05wt% phosphorus, 0.6wt% lead, 0.5wt% manganese, 0.5wt% iron, 1wt% bismuth, and 0.3wt% silicon to the molten copper solution in sequence and stir electromagnetically for 20min.

[0099] B. Take 1.1 wt% of molybdenum powder with a particle size of 1-5 μm, immerse the molybdenum powder in pickling solution at a liquid-to-solid ratio of 10:1, and ultrasonically treat it at 60℃ for 25 min. The pickling solution includes 98% H2SO4, 68% HNO3 and H2O, wherein the mass ratio of H2SO4, HNO3 and H2O is 3:1:1.

[0100] Take a mixed solution of 3-mercaptopropyltrimethoxysilane and ethanol in a mass ratio of 1:9-10, and add acetic acid to adjust the pH to 4-4.5. Dry the acid-washed molybdenum powder at 80℃ and add it to the mixed solution. React at 60℃ for 5 hours. Dry the reacted molybdenum powder under vacuum at 80℃ for 15 minutes to obtain mercapto-modified molybdenum powder.

[0101] C. The mercapto-modified molybdenum powder is passed through argon gas and heat-treated at 600℃ for 60 min to form a molybdenum sulfide coating on the surface of the molybdenum powder, thus obtaining molybdenum sulfide powder. The powder is then mixed with copper alloy melt and stirred at 100 rpm for 15 min. The temperature is then reduced to 850℃ at a rate of 8℃ / min and allowed to stand for 5 min.

[0102] D. Cast the copper alloy molten mixture from step C and cool it to room temperature at a rate of 10℃ / min to obtain the valve body.

[0103] Example 3:

[0104] Similar to Example 1, except that the proportion of molybdenum powder is changed;

[0105] A. Heat copper to 1150℃ at a rate of 15℃ / min and hold for 10min until the copper is completely liquefied. Then, add 1wt% tin, 0.05wt% phosphorus, 0.6wt% lead, 0.5wt% manganese, 0.5wt% iron, 1wt% bismuth, and 0.3wt% silicon to the molten copper solution in sequence and stir electromagnetically for 20min.

[0106] B. Take 1.2wt% of molybdenum powder with a particle size of 1-5μm, immerse the molybdenum powder in pickling solution at a liquid-to-solid ratio of 10:1, and ultrasonically treat it at 60℃ for 25min. The pickling solution includes 98% H2SO4, 68% HNO3 and H2O, wherein the mass ratio of H2SO4, HNO3 and H2O is 3:1:1.

[0107] Take a mixed solution of 3-mercaptopropyltrimethoxysilane and ethanol in a mass ratio of 1:9-10, and add acetic acid to adjust the pH to 4-4.5. Dry the acid-washed molybdenum powder at 80℃ and add it to the mixed solution. React at 60℃ for 5 hours. Dry the reacted molybdenum powder under vacuum at 80℃ for 15 minutes to obtain mercapto-modified molybdenum powder.

[0108] C. The mercapto-modified molybdenum powder is passed through argon gas and heat-treated at 600℃ for 60 min to form a molybdenum sulfide coating on the surface of the molybdenum powder, thus obtaining molybdenum sulfide powder. The powder is then mixed with copper alloy melt and stirred at 100 rpm for 15 min. The temperature is then reduced to 850℃ at a rate of 8℃ / min and allowed to stand for 5 min.

[0109] D. Cast the copper alloy molten mixture from step C and cool it to room temperature at a rate of 10℃ / min to obtain the valve body.

[0110] Example 4:

[0111] Similar to Example 1, except that the proportion of molybdenum powder is changed;

[0112] A. Heat copper to 1150℃ at a rate of 15℃ / min and hold for 10min until the copper is completely liquefied. Then, add 1wt% tin, 0.05wt% phosphorus, 0.6wt% lead, 0.5wt% manganese, 0.5wt% iron, 1wt% bismuth, and 0.3wt% silicon to the molten copper solution in sequence and stir electromagnetically for 20min.

[0113] B. Take 1.3wt% of molybdenum powder with a particle size of 1-5μm, immerse the molybdenum powder in pickling solution at a liquid-to-solid ratio of 10:1, and ultrasonically treat it at 60℃ for 25min. The pickling solution includes 98% H2SO4, 68% HNO3 and H2O, wherein the mass ratio of H2SO4, HNO3 and H2O is 3:1:1.

[0114] Take a mixed solution of 3-mercaptopropyltrimethoxysilane and ethanol in a mass ratio of 1:9-10, and add acetic acid to adjust the pH to 4-4.5. Dry the acid-washed molybdenum powder at 80℃ and add it to the mixed solution. React at 60℃ for 5 hours. Dry the reacted molybdenum powder under vacuum at 80℃ for 15 minutes to obtain mercapto-modified molybdenum powder.

[0115] C. The mercapto-modified molybdenum powder is passed through argon gas and heat-treated at 600℃ for 60 min to form a molybdenum sulfide coating on the surface of the molybdenum powder, thus obtaining molybdenum sulfide powder. The powder is then mixed with copper alloy melt and stirred at 100 rpm for 15 min. The temperature is then reduced to 850℃ at a rate of 8℃ / min and allowed to stand for 5 min.

[0116] D. Cast the copper alloy molten mixture from step C and cool it to room temperature at a rate of 10℃ / min to obtain the valve body.

[0117] Example 5:

[0118] Similar to Example 1, except that the proportion of molybdenum powder is changed;

[0119] A. Heat copper to 1150℃ at a rate of 15℃ / min and hold for 10min until the copper is completely liquefied. Then, add 1wt% tin, 0.05wt% phosphorus, 0.6wt% lead, 0.5wt% manganese, 0.5wt% iron, 1wt% bismuth, and 0.3wt% silicon to the molten copper solution in sequence and stir electromagnetically for 20min.

[0120] B. Take 1.4 wt% molybdenum powder with a particle size of 1-5 μm, immerse the molybdenum powder in pickling solution at a liquid-to-solid ratio of 10:1, and ultrasonically treat it at 60℃ for 25 min. The pickling solution includes 98% H2SO4, 68% HNO3 and H2O, wherein the mass ratio of H2SO4, HNO3 and H2O is 3:1:1.

[0121] Take a mixed solution of 3-mercaptopropyltrimethoxysilane and ethanol in a mass ratio of 1:9-10, and add acetic acid to adjust the pH to 4-4.5. Dry the acid-washed molybdenum powder at 80℃ and add it to the mixed solution. React at 60℃ for 5 hours. Dry the reacted molybdenum powder under vacuum at 80℃ for 15 minutes to obtain mercapto-modified molybdenum powder.

[0122] C. The mercapto-modified molybdenum powder is passed through argon gas and heat-treated at 600℃ for 60 min to form a molybdenum sulfide coating on the surface of the molybdenum powder, thus obtaining molybdenum sulfide powder. The powder is then mixed with copper alloy melt and stirred at 100 rpm for 15 min. The temperature is then reduced to 850℃ at a rate of 8℃ / min and allowed to stand for 5 min.

[0123] D. Cast the copper alloy molten mixture from step C and cool it to room temperature at a rate of 10℃ / min to obtain the valve body.

[0124] Comparative Example 1:

[0125] Similar to Example 1, except that no modification treatment was applied to the molybdenum powder;

[0126] A. Heat copper to 1150℃ at a rate of 15℃ / min and hold for 10min until the copper is completely liquefied. Then, add 1wt% tin, 0.05wt% phosphorus, 0.6wt% lead, 0.5wt% manganese, 0.5wt% iron, 1.3wt% molybdenum powder, 1wt% bismuth, and 0.3wt% silicon to the molten copper solution in sequence and stir electromagnetically for 20min to obtain a copper alloy mixed melt.

[0127] B. Pour the copper alloy molten mixture from step A and cool it to room temperature at a rate of 10℃ / min to obtain the valve body.

[0128] Performance testing:

[0129] 1. Lead distribution uniformity test: The valve body is cut open along the axis, and chip samples are drilled in the central layer and inner layer. Three points are taken in each area, and the lead content is determined by ICP-OES.

[0130] 2. Lead leaching test: Refer to GB / T 8464-2023 "Threaded Valves of Iron, Copper and Stainless Steel", place the valve body in deionized water with pH=7.0±0.2, maintain the water temperature at 25℃, and let it stand for 19 days. Take the valve body on the 3rd, 11th and 19th days to test the lead leaching.

[0131] The valve bodies obtained in Examples 1 to 5 and Comparative Example 1 were subjected to lead distribution uniformity testing and lead leaching amount testing, as shown in Table 1.

[0132] Table 1:

[0133]

[0134] Comparing Examples 1 to 5 and Comparative Example 1, it can be seen that as the content of molybdenum powder increases, the distribution of lead in the melt becomes more uniform. This is mainly because, by adding molybdenum sulfide powder with a solidified surface to the melt, the free lead in the melt is preferentially anchored by the -S on the surface of the molybdenum powder, forming a Pb-S / Pb-Mo-S complex state and chemically fixing the free lead on the surface of the molybdenum powder. This significantly reduces the chemical freeness of lead, allowing free lead in the copper alloy melt to be captured in time and exist in a complex / bonded form. Combined with high-melting-point molybdenum as a carrier, molybdenum remains solid in the melt and acts as an anchoring phase for lead. The solid and dispersed molybdenum particles will not be squeezed out by the liquid phase or migrate with the low-melting-point phase during solidification, thus ensuring the uniformity of lead distribution.

[0135] However, when the molybdenum powder content is too high, it will reduce the uniformity of lead in the melt. Excessive molybdenum powder is more likely to cause local agglomeration or form large inclusions at high temperatures, causing some adsorbed lead to form aggregates that can be released by mechanical disturbance.

[0136] Meanwhile, as the molybdenum powder content increases, the lead leaching decreases. This is mainly because the lead is evenly distributed and does not accumulate on the surface of the valve body. The surface is supported by molybdenum sulfide powder added to the melt, which forms a stable coordination with lead in the high-temperature melt, creating a Pb-S / Pb-Mo-S complex state and chemically fixing the free lead on the surface of the molybdenum powder. This significantly reduces the chemical leaching degree of lead, allowing free lead in the copper alloy melt to be captured in time and exist in a complex / bonded form, thereby reducing the risk of dissolution caused by lead entering the parent phase or surface in a soluble form from the source.

[0137] In summary, comparing Examples 1 to 5 and Comparative Example 1, it can be concluded that Example 4 is the optimal solution of the present invention.

[0138] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing a copper alloy for a low-lead pressure reducing valve body, characterized in that, Includes the following steps: Step S1: Heat copper to a molten state, and add tin, phosphorus, lead, manganese, iron, bismuth and silicon in sequence according to the proportion and mix them evenly to obtain a copper alloy mixed melt; Step S2: Take molybdenum powder and modify it with mercapto to obtain mercapto-modified molybdenum powder, and then perform sulfidation treatment; Step S3: Gradually cool the copper alloy molten mixture to a semi-solid state, and add sulfidated molybdenum powder in proportion and mix evenly to adsorb lead in the copper alloy molten mixture. Step S4: Pour and cool the copper alloy molten mixture from step S3 to obtain the valve body.

2. The method for preparing a copper alloy for a low-lead pressure reducing valve body according to claim 1, characterized in that: The composition of the copper alloy mixed melt includes: 0.5–1 wt% tin, 0.01–0.05 wt% phosphorus, 0.4–0.8 wt% lead, 0.1–0.5 wt% manganese, 0.05–0.5 wt% iron, 1–1.4 wt% molybdenum, 0.5–1.5 wt% bismuth, 0.1–0.4 wt% silicon, with the balance being unavoidable impurity elements and copper; The content of impurity elements is 0-1 wt%.

3. The method for preparing a copper alloy for a low-lead pressure reducing valve body according to claim 1, characterized in that: Step S1 includes the following sub-steps: Step S11: Heat copper to 1050-1150°C at a rate of 10-15°C / min, and hold for 10-15 minutes until the copper is completely liquefied; Step S12: Add tin, phosphorus, lead, manganese, iron, bismuth and silicon to the molten copper solution in sequence and stir electromagnetically for 20 to 30 minutes.

4. The method for preparing a copper alloy for a low-lead pressure reducing valve body according to claim 1, characterized in that: In step S2, the particle size of the molybdenum powder is 1–5 μm.

5. The method for preparing a copper alloy for a low-lead pressure reducing valve body according to claim 1, characterized in that: Step S2 includes the following sub-steps: Step S21: Immerse molybdenum powder in pickling solution at a liquid-to-solid ratio of 10-12:1 and treat with ultrasound at 60-80℃ for 25-30 minutes. Step S22: Take a mixed solution of 3-mercaptopropyltrimethoxysilane and ethanol, and add acetic acid to adjust the pH to 4-4.5; Step S23: Dry the acid-washed molybdenum powder and add it to the mixed solution. React at 60-70℃ for 5-6 hours to immobilize thiol groups on the surface of the molybdenum powder. Step S24: Dry the reacted molybdenum powder under vacuum at 75-80℃ for 10-15 min to obtain mercapto-modified molybdenum powder; Step S25: Pass argon gas through the mercapto-modified molybdenum powder and heat treat it at 500-800℃ for 30-120 min to form a molybdenum sulfide coating on the surface of the molybdenum powder, thus obtaining molybdenum sulfide powder.

6. The method for preparing a copper alloy for a low-lead pressure reducing valve body according to claim 5, characterized in that: In step S21, the pickling solution includes: H2SO4 with a concentration of 96-98%, HNO3 with a concentration of 60-68%, and H2O, wherein the mass ratio of H2SO4, HNO3, and H2O is 3-4:1:

1.

7. The method for preparing a copper alloy for a low-lead pressure reducing valve body according to claim 5, characterized in that: The 3-mercaptopropyltrimethoxysilane is mixed with ethanol in a mass ratio of 1:9 to 10. The mass ratio of the molybdenum powder to the mixed solution is 1:5 to 7.

8. The method for preparing a copper alloy for a low-lead pressure reducing valve body according to claim 1, characterized in that: In step S3, the copper alloy molten mixture is cooled to 800-900°C at a rate of 5-10°C / min to achieve a semi-solid state. Add molybdenum sulfide powder to the copper alloy molten mixture, stir at 100-200 rpm for 10-15 minutes, maintain the temperature at 800-900℃, and let stand for 5-8 minutes.

9. The method for preparing a copper alloy for a low-lead pressure reducing valve body according to claim 1, characterized in that: In step S4, after the pouring is completed, the temperature is reduced to room temperature at a rate of 10-15℃ / min.

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