Manufacturing method of high-density low-color K platinum jewelry casting

Abstract

The invention discloses a manufacturing method of a high-density low-color K platinum jewelry casting. The manufacturing method comprises the steps that S1, alloy components are prepared; s2, a cast tree structure is designed; s3, casting process; wherein the alloy components comprise 5%-14% of nickel, 34%-48% of copper, 6%-14% of zinc, 0.1%-1% of tin, 0.05%-0.5% of silicon, 0.03%-0.2% of rare earth and the balance of gold; the tree casting structure adopts a casting-waterline-tree core-sprue base four-stage communication structure; according to the manufacturing method, alloy components and the process are optimally combined, the alloy melting point is reduced, the solidification and crystallization interval is shortened, the metal fluidity is improved, the casting tree structure is optimized, and the negative pressure / pressurization / vibration composite mode is adopted, so that the molten metal feeding capacity is improved, shrinkage porosity and air holes are reduced, and the casting density is improved; under the condition that the alloy does not contain precious metal elements except gold, the material cost is reduced, and high cost performance is embodied.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of precious metal jewelry manufacturing, and particularly relates to a production method of high-density low-carat K white gold jewelry casting, which is used for improving the density of the casting and improving the surface quality. BACKGROUND

[0002] White K gold has similar color to platinum gold, but the strength and hardness are obviously higher than that of platinum gold, and is suitable for inlaying gemstones, and thus becomes a widely used gold alloy material. With more and more attention paid to fashion and decoration of jewelry, low-carat K gold materials of 9K-10K are welcomed by the market. Because of the complex structure and various styles of jewelry, most of the jewelry is formed by casting. Compared with other casting forming processes, the gypsum mold precision casting process has the characteristics of wide adaptability to product structure and batch, high dimensional accuracy, good surface quality, and convenient cleaning, and thus the gypsum mold precision casting process becomes the main way of forming K gold jewelry.

[0003] The basic process of gypsum mold precision casting K gold jewelry is as follows: jewelry wax molds are assembled into a tree, and then the tree is embedded with casting powder slurry, and after dewaxing and baking, a high-temperature casting mold is prepared; then a gold alloy material is melted, and the molten metal is poured into the cavity of the high-temperature casting mold by means of vacuum suction casting or centrifugal casting, and a jewelry casting is obtained after condensation. The casting is polished, combined and welded, inlaid, polished, and electroplated, and finally a jewelry product is prepared.

[0004] K white gold jewelry generally needs to be highly polished to obtain a mirror effect, and then surface electroplating treatment is performed, and 10 times magnifying glass is often used for quality inspection in production, which puts forward a high requirement on the surface quality of the jewelry casting. Many castings with high-quality surfaces in the field of industrial or art casting can only be classified as defective products with surface defects according to the quality standard of jewelry products. The density of the casting has the greatest impact on the surface quality, and when the casting has defects such as porosity and pores, the surface brightness will be seriously affected.

[0005] The factors affecting the density of jewelry castings are multifaceted, covering metal materials, mold materials, casting equipment, casting processes, and so on. Compared with yellow K gold and red K gold, the production difficulty of white K gold jewelry is significantly increased, which is closely related to the material properties of existing K white. Since gold itself is yellow, in order to make its alloy white, it needs to add bleaching elements. Nickel and palladium are strong bleaching elements of gold, but the price of palladium is too high, so K white gold widely uses nickel as the main bleaching element. The melting point of nickel is relatively high, the tendency of gettering is relatively large, the fluidity is poor, and the gold content of low-carat K gold is relatively low, so a large amount of non-precious metals need to be added to the material. If the alloy material design is not good, the material melting point is high, the crystallization temperature range is wide, the casting performance is poor, and defects such as shrinkage, porosity, and inclusions are prone to occur during casting, resulting in poor casting density, insufficient strength, and surface flaws, which seriously affect the subsequent processing and product quality. In terms of mold materials, gypsum mold has good mold performance, fine surface, and good collapse performance, and has almost become a necessary material for gold and silver jewelry casting. However, the air permeability, thermal conductivity and thermal stability of gypsum mold are poor, and the problem of coarse grains is prone to occur during casting, which increases the tendency of casting porosity. In terms of casting methods, there are mainly two categories at present. One is to use a fire gun to melt and combine with vacuum suction casting, which belongs to the traditional melting method. The quality of the castings depends largely on the experience of the operators, and quality fluctuations are prone to occur. The other is to use induction melting combined with automatic pouring, including centrifugal pouring and vacuum suction casting. The quality stability is relatively improved, but it still cannot fully solve the problem of poor density of low-carat K white gold jewelry casting.

[0006] So far, there are few reports on the casting technology of K white gold jewelry, and the relevance of solving the problem of K white gold jewelry casting density is not great, and the research on low fineness K white gold is even less. For example, Chinese patent CN101255507 discloses a rare earth containing multi-component white gold alloy, the composition of which is: Au 75-76%, Ni 5-10%, Zn 2-5%, Cu 10-16%, La 0-0.2%, Ce 0-0.2%, Y 0-0.2%, Co 0-0.3%, B 0-0.1%, Si 0-0.05%, In 0-0.05%. Chinese patent CN201910782463.0 discloses a white gold alloy, the mass percentage of which is: 75wt% gold, 1-2wt% silicon, 16-17wt% copper, 3.5-4.5wt% zinc and 2.5-3.5wt% nickel. Chinese patent CN105369047B discloses a white gold alloy for high-temperature enamel jewelry, the composition of which is: 75.0-75.5wt% gold, 7.0-8.0wt% nickel, 3.0-4.0wt% silver, 9.5-10.5wt% copper, 3.0-3.5wt% zinc, 0.3-0.8wt% palladium, 0.01-0.03wt% silicon, 0.008-0.02wt% scandium, and other unavoidable impurities. Chinese patent CN108823454A discloses a 18K white gold material and processing technology for jewelry material with wear resistance and no nickel allergy, the chemical composition of the alloy is: Ca0.8-1.0wt%, Re0.2-0.4wt%, Fe0.6-1.4wt%, Ge2.0-3.0wt%, In8.0-10.0wt%, Ag10.0-12.0wt%, the balance is gold. The above materials belong to 18K gold, which is very different from the properties of low fineness K gold, and the key innovation points of the technology are also far from the present application. Chinese patent CN105420531B discloses a nickel-free white gold alloy for high-temperature enamel jewelry and a preparation method thereof, the composition of which is: 33.3-33.5wt% gold, 56.0-58.0wt% silver, 3.0-5.0wt% copper, 4.0-6.0wt% zinc, 0.2-0.4wt% palladium, 0.02-0.05wt% silicon, 0.008-0.02wt% scandium, 0.0005-0.001wt% boron, and other unavoidable impurities. The technology is aimed at low fineness K gold, but mainly focuses on how to meet the requirements of firing high-temperature enamel, containing a large amount of precious metals other than gold.

[0007] Jewelry casting is generally one type of many, in order to benefit from the filling of liquid metal, improve the metal yield and the utilization rate of gypsum casting, the wax pattern of the casting is generally connected to the straight runner (tree core) in the form of an inverted umbrella, the design of the casting tree structure and the pouring system has a great influence on the quality of the casting. The traditional method is mainly based on experience, and the production quality often fluctuates, and the problem of poor casting density is common. Around how to improve the pouring and filling process of metal, there are only a few research reports. For example, Chinese patent CN201510234567X discloses a stepped pouring system for jewelry precision casting, which adopts a multi-stage stepped runner design of main runner + branch cross runner + buffer pool, the cross runner cross section is trapezoidal structure, reducing metal liquid turbulence, the pouring gate and the connecting part of the casting are provided with an arc transition to avoid hot spots. However, its runner structure is not conducive to the smooth flow of liquid metal. Chinese CN201820678901.5 discloses a centrifugal pouring system for jewelry casting, which links the pouring system with the centrifuge, the rotation speed is 300-500 rpm, the main runner is designed as a spiral tapered structure, and the centrifugal force is used for shrinkage, and the casting layout is radially symmetrically distributed (casting tree structure), but the specific structure design of the casting tree is vague, and it is for the centrifugal pouring mode, and the problem to be solved is the filling completeness of complex hollow jewelry, which deviates greatly from the present application. Chinese patent number CN201710891234.8 discloses a multi-directional branch casting tree structure and a 3D printing wax mold preparation method, which connects the branch wax mold through buckles, the branch angle is 15°-45°, avoids mutual interference of liquid metal, and automatically generates the casting tree layout combined with the topological optimization algorithm, which solves the problems of wax mold assembly efficiency and metal utilization rate. Chinese patent CN202010456789.1 discloses a bionic casting tree structure suitable for precious metal jewelry, which simulates the design of pouring channels in the form of tree branch fractal structure, the main runner diameter and branch runner are in the golden ratio (1:0.618), the decreasing end is provided with a spherical liquid storage bag, and the dynamic shrinkage has a certain effect on reducing shrinkage defects, but the setting of the spherical liquid storage bag is difficult to be accepted by production, and the runner structure and proportion are not suitable for low-karat K white gold.

[0008] The jewelry structure is relatively fine, and it is difficult to use conventional gravity casting molding. It needs to use external forces such as negative pressure and centrifugal force to improve the filling effect, but they are still insufficient in improving the complete filling and density of the casting. Therefore, the industry has carried out related research on improving jewelry casting methods. For example, Chinese patent CN201510789012.3 discloses a vacuum suction casting device and method for precious metal jewelry. It uses a double vacuum system, the melting chamber (10-2Pa) and the casting chamber (10-1Pa) are independently controlled, and the inclined suction casting is used. The casting mold is inclined by 15°-30°, the metal liquid fills along the wall surface smoothly, and the infrared temperature feedback adjusts the suction casting speed (50-100mm / s) in real time. This method has certain benefits for reducing casting pores, but inclined suction casting is not conducive to filling and density uniformity. Chinese patent CN202010234567.8 discloses a vacuum suction casting-centrifugal composite process for multi-hole hollow jewelry. It first fills the main structure by vacuum suction casting, then starts the centrifuge (400rpm) to supplement the details, and pre-installs a ceramic fiber filter in the mold to reduce oxide inclusions. This technology solves the problem of incomplete filling of hollow jewelry, not the improvement of the density of the casting. Patent CN201710123456.X discloses a gas pressure-differential pressure composite pressurizing device for jewelry precision casting. It uses two-stage pressurization, first 0.3MPa gas pressure pre-tightening, then differential pressure (0.5MPa) rapid filling, and built-in micro pressure sensor in the mold, dynamic adjustment of the pressurization curve. It solves the problem of filling of complex inlay jewelry, and does not use gypsum mold.

[0009] In summary, there is no technical solution in the prior art that is specifically aimed at the casting and improvement of the density of low-carat K white gold jewelry. SUMMARY

[0010] In order to overcome the shortcomings of the prior art, the present application provides a method for making high-density low-carat K white gold jewelry casting, which combines alloy composition and process optimization to reduce alloy melting point, reduce solidification interval, and improve metal fluidity. By optimizing the structure of the casting tree and using negative pressure / pressure / vibration composite mode, the metal liquid feeding capacity is improved, the shrinkage and pores are reduced, and the density of the casting is improved. The alloy does not contain noble metal elements other than gold (contains gold), which reduces the material cost and reflects high cost performance.

[0011] The application adopts the following technical solutions:

[0012] A method for making high-density low-carat K white gold jewelry casting, comprising the following preparation steps:

[0013] S1: preparing alloy composition

[0014] The alloy composition comprises the following components by mass percentage:

[0015] Nickel 5% to 14%, copper 34% to 48%, zinc 6% to 14%, tin 0.1% to 1%, silicon 0.05% to 0.5%, rare earth 0.03% to 0.2%, the rest is gold, and inevitable impurity elements;

[0016] In the above material, the nickel is pure nickel with a content of 99.95wt% and above, the copper is pure copper with a content of 99.95wt% and above, the zinc is pure zinc with a content of 99.95wt% and above, and the tin is pure tin with a content of 99.95wt% and above.

[0017] S2: Casting tree structure design

[0018] The casting tree structure adopts a four-level communication structure of casting-moat-tree core-gate pocket;

[0019] S3: Casting process

[0020] The casting equipment includes a melting machine, a power supply system, a PLC system, a vacuum system, a water cooling system, a protective gas station system, a compressed air system, and a vibration table;

[0021] The metal furnace charge is put into a graphite crucible, then the smelting chamber is vacuumed to 10-100 Pa, industrial pure argon is filled to 0.06-0.09 MPa, heating and smelting are performed, and the temperature of the metal liquid is accurately controlled through a thermocouple;

[0022] The calcined gypsum mold is loaded on the loading table of the casting chamber, a heat-resistant gasket is placed on the top surface of the mold, the bottom cylinder is started to lift the mold and press it tightly onto the bottom plate of the smelting chamber to form a sealed space of the casting chamber, the casting chamber is vacuumed to 10-100 Pa before pouring; the pouring temperature of the metal liquid is controlled to be 30-100℃ higher than the liquidus temperature of the alloy, after the pouring temperature is reached, the crucible plug rod is lifted, the metal liquid is poured into the gate pocket of the mold, and under the action of vacuum negative pressure, the metal liquid is smoothly filled into each mold cavity; within 1-5s after pouring, the vibration table is started, the vibration frequency is set to 50-100Hz, the amplitude is set to 0.1-0.3mm, and the vibration duration is set to 15-45s; 2-10s after pouring, solidification pressurization is started to forcibly press the metal liquid into the hot spot area.

[0023] Further, in step S1, the gold is divided into 9K and 10K, the gold content of 9K is controlled to be 37.5%-37.8%, and the gold content of 10K is controlled to be 41.7%-42.0%.

[0024] Further, in step S1, the total content of the inevitable impurity elements does not exceed 0.1%.

[0025] Further, in step S1, the rare earth is one or more of cerium, yttrium, lanthanum, neodymium, and gadolinium.

[0026] In the above materials, cerium is pure cerium with a content of 99.95wt% or above, yttrium is pure yttrium with a content of 99.95wt% or above, lanthanum is pure lanthanum with a content of 99.95wt% or above, neodymium is pure neodymium with a content of 99.95wt% or above, and gadolinium is pure gadolinium with a content of 99.95wt% or above.

[0027] Further, in step S1, the liquidus temperature of the alloy is not more than 1020℃, and the solidification crystallization interval is not more than 60℃.

[0028] Further, in step S2, the diameter of the water line is 1.3-2.5 times the maximum thickness of the casting, the diameter of the core is 1.5-3 times the diameter of the water line, and the diameter of the sprue nest is 2-5 times the diameter of the core.

[0029] Further, in step S2, according to the structure of the casting product, the specifications, connection positions, number and water inlet mode of the water lines are determined. Specifically, the water lines are divided into main water lines and branch water lines, the main water lines are connected at the thickest hot spots of the casting, and each branch water line is arranged at a residual hot spot or a slender part of the casting, and each branch water line converges to the main water line.

[0030] Further, in step S2, the total cross-sectional area of each branch water line is 1.2-1.8 times the cross-sectional area of the main water line.

[0031] Further, in step S2, the core is provided with a taper of 5-8°, and 10-15mm of the core at both ends is left without being connected to the water line. The connection of the water line to the core is arranged in a spiral and uniformly distributed, the step distance of the spiral is controlled to be 10-15mm, the distance between the castings is not less than 2.5mm, and the included angle between the water line and the core is controlled to be 30-60° and the distance is 8-15mm.

[0032] Further, in step S2, the sprue nest is designed to be hemispherical, a buffer cone is arranged at the bottom of the sprue nest, the lower diameter of the sprue nest is matched with the large end diameter of the core, the upper diameter of the sprue nest is 1.5-2.5 times the large end diameter of the core, and the taper angle is 90-120°.

[0033] Further, in step S3, the inner diameter of the gasket is 10-20mm larger than the diameter of the sprue nest, and the outer diameter is 5-10mm smaller than the inner diameter of the casting steel ring.

[0034] Further, in step S3, for a conventional casting with a relatively simple structure, the pressurizing pressure is set to be 0.2-0.3MPa, and the pressurizing duration is 50-100s; for a casting with a complex hot spot, the pressurizing is set to be segmented, first pressurizing at a pressure of 0.1-0.2MPa for 10-20s, and then continuously pressurizing at a pressure of 0.25-0.3MPa for 50-120s.

[0035] Compared with the prior art, the present application has the beneficial effects that:

[0036] The manufacturing method of the present application reduces the alloy melting point, reduces the solidification crystallization interval, improves the metal fluidity by optimizing the alloy composition and process, improves the metal liquid feeding capacity, reduces the shrinkage and porosity, and improves the casting density by optimizing the casting tree structure and adopting the negative pressure / pressurization / vibration combination, so that the material cost is reduced without the noble metal elements except gold in the alloy, and high cost performance is embodied. BRIEF DESCRIPTION OF DRAWINGS

[0037] Fig. 1 A casting surface profile graph for Example 1;

[0038] Fig. 2 A surface line roughness graph for Example 1;

[0039] Fig. 3 A casting surface profile graph for Comparative Example 1;

[0040] Fig. 4 A surface line roughness graph for Comparative Example 1. DETAILED DESCRIPTION

[0041] The present application aims to provide a high-density casting method for low-color K white platinum jewelry, which reduces the alloy melting point, reduces the solidification crystallization interval, and improves the metal fluidity by optimizing the alloy composition and process; improves the metal liquid feeding capacity, reduces the shrinkage and porosity, and improves the casting density by optimizing the casting tree structure and adopting the negative pressure / pressurization / vibration combination. The alloy does not contain noble metal elements except gold, which reduces the material cost and embodies high cost performance.

[0042] To achieve the above object, the present application provides the following technical scheme:

[0043] 1. Alloy composition optimization

[0044] (1) Gold, which is the base element of the alloy, is controlled at 37.5% to 37.8% for 9K and 41.7% to 42.0% for 10K to ensure the color of the material and avoid the loss of enterprises caused by too high color.

[0045] (2) Nickel, which is a bleaching element of gold, is controlled at 5% to 14% to increase the risk of nickel allergy and affect the casting performance of the material when too high, and the whiteness of the alloy is not enough when too low.

[0046] (3) Copper, which has good combination with gold, improves the mechanical properties of the alloy, and is controlled at 34% to 48%.

[0047] (4) Zinc, which has good combination with gold, improves the casting performance of the alloy, and is controlled at 6% to 14%.

[0048] (6) Tin, improve the corrosion resistance of the alloy, control the content of 0.1-1%.

[0049] (7) Silicon, improve the casting performance of the alloy, control the content of 0.05-0.5%.

[0050] (8) Rare earth, as grain refiner and refining agent, refine the alloy structure, improve the metallurgical quality and casting performance. One or more of cerium, lanthanum, yttrium, gadolinium, neodymium and other elements can be used, and the content is controlled to be 0.03-0.2%.

[0051] By optimizing the composition, the liquidus temperature of the alloy is controlled within 1020℃, the solidification crystallization interval is not more than 60℃, the alloy has good fluidity, which is beneficial to realize the layer-by-layer solidification mode, and the alloy contains grain refiner, so that the crystal growth competitiveness can be reduced, the grain refinement degree can be improved, and the density of the casting can be improved.

[0052] 2. Casting tree structure design

[0053] In order to improve the casting yield and production efficiency, and reduce the production cost, the jewelry wax parts must be welded on the straight sprue rod (tree core) one by one through the water line to form a tree-shaped wax mold. The structure design of the casting tree has a great influence on the filling and shrinkage process of the metal liquid. The structure of the casting tree in the prior art is arbitrary and the proportion is unreasonable. The wax tree structure is innovatively designed as follows:

[0054] (1) In order to keep the shrinkage channel of the casting tree system, a four-stage communication structure of casting--water line--tree core--sprue nest is adopted, the equivalent thickness of each component is increased according to the ratio, the diameter of the water line is 1.3-2.5 times the maximum thickness of the casting, the diameter of the tree core is 1.5-3 times the diameter of the water line, and the diameter of the sprue nest is 2-5 times the diameter of the tree core.

[0055] (2) Connection of water line and casting. According to the structure of the casting product, the specification, connection position, number and water inlet mode of the water line are determined. The ring, earring, link and other castings with basically uniform wall thickness prefer to use single water line. The castings with large volume such as bracelet, pendant and fine castings of flower silk adopt 2 or more branch water lines, and all branch water lines are collected into the main water line, and the total cross-sectional area of all branch water lines is controlled to be 1.2-1.8 times the cross-sectional area of the main water line. The castings with uneven wall thickness, multiple thermal nodes and local fine structure are set in the mode of main branch water line + auxiliary branch water line, the main branch water line is connected at the thickest thermal node, and the branch water lines are respectively set at the remaining thermal nodes or fine structures.

[0056] (3) The tree core is provided with a taper of 5-8°, and 10-15mm of the tree core is left at both ends without being connected with the water line. The tapered tree core rapidly forms a negative pressure zone at the initial pouring stage, which is helpful for the metal liquid to flow into each part of the casting mold rapidly, beneficial to the filling of the metal liquid and the discharge of gas and inclusions, and can also make the top of the tree core solidify later, thereby improving the permanent feeding effect.

[0057] (4) The connection between the water line and the tree core is preferentially provided in a spiral uniform distribution, the step distance of the spiral is determined according to the product structure and is controlled to be 10-15mm, and the step distance of the thick-walled casting is preferentially taken as a large value. The distance between the castings is not less than 2.5mm, so as to avoid mutual shielding and heat accumulation. The included angle between the water line and the tree core is controlled to be 30-60°, and the distance is 8-15mm, so as to improve the metal liquid filling speed and uniformity and ensure the feeding. The connection between the water line and the tree core should be smoothly transitioned to avoid dead angle and turbulence.

[0058] (5) The sprue nest is designed to be hemispherical, and compared with the traditional conical structure, the hemispherical sprue nest has obvious advantages in the aspects of metal liquid flow stability, elimination of turbulent bubbles, isolation of impurities and the like. The sprue nest is provided with a buffer cone at the bottom, the lower opening diameter of the buffer cone is matched with the large end diameter of the tree core, the upper opening diameter is 1.5-2.5 times of the large end diameter of the tree core, and the taper angle is 90-120°.

[0059] (6) The large end of the tree core is located directly below the sprue nest, and the connection between the tree core and the buffer cone of the sprue nest should be smoothly transitioned to avoid dead angle and turbulence.

[0060] 3. Casting process

[0061] The content of base metal in low-carat K white gold is high, and the casting performance of the metal liquid is generally not as good as that of high-carat gold alloy, and the grain in the gypsum mold casting tends to be coarse, which is not conducive to the density of the casting. In order to improve the filling performance of the metal liquid and the density of the casting, the present application adopts a linkage casting process of vacuum protection melting + negative pressure suction casting + solidification pressurization + vibration crystallization.

[0062] (1) The casting equipment is composed of a melting and casting machine, a power system, a PLC system, a vacuum system, a water cooling system, a protective gas station system, a compressed air system, a vibration table and the like. The melting and casting machine includes a melting chamber and a casting chamber, and is installed and fastened on the vibration table through a rubber damping pad. The PLC system is combined with the power system, and the remaining systems are separately provided, and the whole equipment is formed through pipelines to complete the links of metal melting in a protective atmosphere, automatic pouring, solidification pressurization and vibration crystallization.

[0063] (2) After the metal charge is put into the graphite crucible, the melting chamber is vacuumed to 10-100Pa, then industrial pure argon is filled to 0.06-0.09MPa, the metal charge is melted by induction heating, and the temperature of the metal liquid is accurately controlled through a thermocouple.

[0064] (3) The baked gypsum mold is loaded on the loading table of the casting chamber, a heat-resistant gasket is placed on the top surface of the mold, the inner diameter of the gasket is 10-20 mm larger than the diameter of the sprue hole, and the outer diameter of the gasket is 5-10 mm smaller than the inner diameter of the mold ring, the bottom cylinder is started to lift the mold and press it onto the bottom plate of the melting chamber to form a closed space of the casting chamber. The casting chamber is vacuumized to 10-100 Pa.

[0065] (4) According to the structure of the casting, the pouring temperature of the molten metal is controlled to be 30-100 ℃ higher than the liquidus temperature of the alloy. After the pouring temperature is reached, the crucible plug rod is lifted, the molten metal is poured into the sprue hole of the mold, and under the action of vacuum negative pressure, the molten metal is smoothly filled into each mold cavity.

[0066] (5) The vibration table is started within 1-5 s after pouring, the vibration frequency is set to 50-100 Hz, and the amplitude is set to 0.1-0.3 mm. The shear force generated by vibration breaks the dendrites formed in the early stage of solidification, forming more crystal cores, thereby refining the grains. However, if the vibration time is too long, it will interfere with the surface quality of the casting, causing the surface roughness to increase. Setting the vibration duration to 15-45 s can achieve good results.

[0067] (6) The solidification pressurization is started 2-10 s after pouring. Under the action of pressure, the molten metal overcomes the resistance along the way and is forced to press into the hot spot area, providing more feeding for the solidification shrinkage of the casting. If the pressurization time is too early, it is easy to cause the molten metal to splash, resulting in oxidation inclusions in the casting; if the pressurization time is too late, the molten metal feeding channel is blocked, and the effect of enhancing feeding cannot be achieved. For conventional castings with relatively simple structure, a section pressurization mode is set, and the pressurization pressure is set to 0.2-0.3 MPa, and the pressurization duration is set to 50-100 s. For castings with complex hot spots, a segmented pressurization mode is preferred, first pressurized at a pressure of 0.1-0.2 MPa for 10-20 s, and then pressurized at a pressure of 0.25-0.3 MPa for 50-120 s.

[0068] In the following, the application will be further described in conjunction with specific embodiments. It should be noted that the embodiments described below or the technical features thereof can be combined in any manner to form new embodiments without conflict.

[0069] Example 1

[0070] 1. Alloy composition design

[0071] This embodiment is to cast a 9K white ring, and the alloy material composition is: gold 37.6%, nickel 6.24%, copper 46.3%, zinc 9.34%, silicon 0.14%, tin 0.31%, and yttrium 0.07%.

[0072] 2. Casting structure design

[0073] (1) In order to keep the feeding channel of the casting tree system, the four-stage communication structure of ring-water line-tree core-gate pocket is adopted. The diameter of the water line is 1.7 times of the thickness of the casting, the diameter of the tree core is 2.9 times of the diameter of the water line, and the diameter of the gate pocket is 4 times of the diameter of the tree core.

[0074] (2) The connection of the single water line with the casting is adopted.

[0075] (3) The tree core is provided with a taper of 6°, and 12 mm of the tree core at both ends is not connected with the water line.

[0076] (4) The connection of the water line and the tree core is provided with spiral uniform distribution, and the step distance of the spiral is controlled to be 12 mm. The distance between the castings is not less than 2.5 mm. The included angle between the water line and the tree core is controlled to be 45-55°, and the distance is 10-12 mm. The connection of the water line and the tree core is smooth transition.

[0077] (5) The gate pocket is designed to be hemispherical, and a buffer cone is arranged at the bottom of the gate pocket. The lower diameter of the buffer cone matches the large end diameter of the tree core, the upper diameter of the buffer cone is 1.8 times of the large end diameter of the tree core, and the taper angle is 90°.

[0078] (6) The large end of the tree core is located directly below the gate pocket, and the connection of the tree core and the buffer cone of the gate pocket is smooth transition.

[0079] 3. Casting process

[0080] (1) The casting equipment is composed of a melting and casting machine, a power system, a PLC system, a vacuum system, a water cooling system, a protective gas station system, a compressed air system, a vibration table and the like. The melting and casting machine includes a melting chamber and a casting chamber, which are tightly fixed on the vibration table. The PLC system is combined with the power system, and the remaining systems are separately arranged to form the whole equipment through pipelines, so as to complete the links of metal melting, automatic pouring, secondary pressurization and vibration crystallization under a protective atmosphere.

[0081] (2) After the metal charge is put into the graphite crucible, the melting chamber is vacuumized to 30-40 Pa, then industrial pure argon is filled to 0.07-0.08 MPa, the metal charge is melted by induction heating, and the temperature of the metal liquid is accurately controlled by a thermocouple.

[0082] (3) The calcined gypsum mold is loaded on the loading table of the casting chamber, a heat-resistant gasket is placed on the top surface of the mold, the inner diameter of the gasket is 12-15 mm larger than the diameter of the gate pocket, the outer diameter of the gasket is 6-8 mm smaller than the inner diameter of the mold ring, a bottom air cylinder is started to lift the mold and press it tightly onto the bottom plate of the melting chamber, thereby forming a sealed space of the casting chamber. The casting chamber is vacuumized to 40-50 Pa.

[0083] (4) The pouring temperature of the molten metal is 60°C higher than the liquidus temperature of the alloy. After the pouring temperature is reached, the crucible plug rod is lifted, the molten metal is poured into the pouring well of the mold, and under the action of vacuum negative pressure, it is filled into the mold cavity of each casting.

[0084] (5) 2s after pouring, the vibration table is started. The vibration frequency is 80Hz, the amplitude is 0.15-0.2mm, and the vibration duration is 25s.

[0085] (6) 4s after pouring, the solidification pressurization is started. The pressurization pressure is set to 0.28Mpa, and the pressurization time is 70s.

[0086] Through detection, the implementation effect of the embodiment is:

[0087] By optimizing the alloy formula, the material of the embodiment has good fluidity, which is beneficial to realize the layer-by-layer solidification mode, and the alloy contains an antioxidant and a grain refiner, which can reduce oxidation during smelting and casting, form a large number of heterogeneous cores, and refine the grain structure. By optimizing the structure design of the casting tree, the molten metal can be smoothly filled into the mold, reducing the problems of gas entrainment and inclusions caused by turbulence, which is beneficial to the floating and discharge of gas and inclusions; at the same time, the force and the supplementing channel from the pouring well to the core to the water line to the casting provide conditions for the solidification shrinkage compensation of the casting. Through the comprehensive measures of protective atmosphere smelting, negative pressure suction casting, solidification pressurization and vibration crystallization, the problem of air absorption and oxidation during smelting can be effectively reduced. By precisely controlling the vibration crystallization time and vibration process conditions of the casting, the shear force generated by vibration breaks the dendrites formed in the early stage of solidification, forms more crystallization cores, avoids the problems of interference with the filling process caused by vibration too early or too long duration, and avoids the problems of too few crystallization cores caused by vibration too late or too short duration. By precisely controlling the start and duration of secondary pressurization, the problems of metal liquid splashing and oxidation inclusions caused by pressurization too early, and the problem of pressurization failure caused by pressurization too late are avoided.

[0088] The conventional 9K white material and negative pressure suction casting process are used to cast a ring casting, and the implementation effects of the two are compared as shown in Table 1, and the surface roughness of the castings is compared as shown in Figs. 1-4

[0089] Compared with Comparative Example 1, the alloy material, casting tree structure design and smelting process are comprehensively improved in the embodiment, which significantly improves the density, surface roughness and microstructure of the 9K white gold jewelry casting, thereby obtaining a high-brightness surface effect.

[0090] Table 1

[0091]

[0092] ​

[0093] Example 2

[0094] 1. Alloy composition design

[0095] This example is a cast 10K pendant, the alloy material composition is: gold 41.8%, nickel 6.98%, copper 39.11%, zinc 11.64%, silicon 0.15%, tin 0.2%, cerium 0.06%, lanthanum 0.06%.

[0096] 2. Casting tree structure design

[0097] (1) In order to keep the feeding channel of the casting tree system, a four-stage connected structure of ring-water line-tree core-gate pocket is adopted. The diameter of the water line is 2 times the thickness of the casting, the diameter of the tree core is 2.6 times the diameter of the water line, and the diameter of the gate pocket is 3.5 times the diameter of the tree core.

[0098] (2) Three branch water lines are adopted to connect with the casting, all branch water lines converge to the main water line, and the total cross-sectional area of all branch water lines is controlled to be 1.4 times the cross-sectional area of the main water line.

[0099] (3) The tree core is set to have a taper of 7°, and 11 mm of the tree core at both ends is left without connecting water lines.

[0100] (4) The connection between the water line and the tree core is set to be spiral and uniformly distributed, and the spiral step is controlled to be 14 mm. The spacing between castings is not less than 3.5 mm. The included angle between the water line and the tree core is controlled to be 50-60°, and the distance is 13-14 mm. The connection between the water line and the tree core is smooth transition.

[0101] (5) The gate pocket is designed to be hemispherical, and a buffer cone is set at the bottom of the gate pocket. The lower diameter of the buffer cone matches the large end diameter of the tree core, the upper diameter is 2 times the large end diameter of the tree core, and the taper angle is 100°.

[0102] (6) The large end of the tree core is located directly below the gate pocket, and the connection between the tree core and the buffer cone of the gate pocket is smooth transition.

[0103] 3. Casting process

[0104] (1) The casting equipment is composed of a melting and casting machine, a power system, a PLC system, a vacuum system, a water cooling system, a protective gas station system, a compressed air system, a vibration table and other parts. The melting and casting machine includes a melting chamber and a casting chamber, which are installed and fastened on the vibration table. The PLC system is combined with the power system, and the remaining systems are separately set up to form the whole equipment through pipelines, which completes the links of metal melting, automatic pouring, secondary pressurization and vibration crystallization under protective atmosphere.

[0105] (2) After the metal charge is put into the graphite crucible, the smelting chamber is vacuumed to 50-60 Pa, then industrial pure argon is filled to 0.06-0.07 MPa, the metal charge is melted by induction heating, and the temperature of the molten metal is precisely controlled by a thermocouple.

[0106] (3) The calcined gypsum mold is loaded on the loading table of the casting chamber, a heat-resistant gasket is placed on the top surface of the mold, the inner diameter of the gasket is 15-17 mm larger than the diameter of the sprue hole, and the outer diameter is 5-7 mm smaller than the inner diameter of the mold ring, the bottom cylinder is started to lift the mold, and the mold is pressed onto the bottom plate of the smelting chamber to form a sealed space of the casting chamber. The casting chamber is vacuumed to 20-30 Pa.

[0107] (4) The pouring temperature of the molten metal is controlled to be 50℃ higher than the liquidus temperature of the alloy. After the pouring temperature is reached, the crucible plug rod is lifted, the molten metal is poured into the sprue hole of the mold, and under the action of vacuum negative pressure, it is filled into the mold cavity of each casting.

[0108] (5) 3s after pouring, the vibration table is started. The vibration frequency is 60 Hz, the amplitude is 0.12-0.14 mm, and the vibration duration is 35s.

[0109] (6) 6s after pouring, the solidification pressurization is started. Two-stage pressurization mode is set, first pressurized at 0.12-0.15 MPa for 15s, then pressurized at 0.29 MPa for 25s.

[0110] Through detection, the implementation effect of the embodiment is:

[0111] By optimizing the alloy formula, the material of the embodiment has good fluidity, which is beneficial to realize the layer-by-layer solidification mode, and the alloy contains an antioxidant and a grain refiner, which can reduce oxidation during smelting and casting, form a large number of heterogeneous cores, and refine the grain structure. By optimizing the design of the casting tree structure, the molten metal can be smoothly filled, reducing the problems of gas entrainment and inclusions caused by turbulence, which is beneficial to the floating and discharge of gas and inclusions; at the same time, the force and the holding from the sprue hole---the tree core---the water line---the feeding channel of the casting provide conditions for the solidification shrinkage compensation of the casting. Through the comprehensive measures of protective atmosphere smelting, negative pressure suction casting, solidification pressurization, and vibration crystallization, the problem of air absorption and oxidation during smelting can be effectively reduced. By precisely controlling the vibration crystallization time and vibration process conditions of the casting, the shear force generated by vibration breaks the dendrites formed in the early stage of solidification, forming more crystallization cores, avoiding the problems of interference with the filling process caused by premature vibration or long duration on the surface solidification of the casting, and avoiding the problems of few crystallization cores caused by late vibration or short duration. By precisely controlling the start and duration of the second pressurization, the problems of metal liquid splashing and oxidation inclusions caused by early pressurization, and the problems of pressurization failure caused by late pressurization are avoided.

[0112] The 10K white pendant cast in this example has a liquidus temperature of 984°C and a crystallization interval of 51°C. The average grain size is 80 μm, the surface roughness Ra of the casting is 1.964 μm, and the density reaches 98.5%.

[0113] Example 3

[0114] 1. Alloy composition design

[0115] This example is a 10K white gold bracelet, and the chemical composition is: gold 42%, copper 34.22%, zinc 14.5%, nickel 8.7%, silicon 0.23%, tin 0.26%, lanthanum 0.04%, and yttrium 0.05%.

[0116] 2. Casting tree structure design

[0117] (1) In order to keep the casting tree system with feeding channels, a four-stage communication structure of casting-water line-tree core-gate pocket is adopted. The diameter of the water line is 1.8 times the maximum thickness of the casting, the diameter of the tree core is 3 times the diameter of the water line, and the diameter of the gate pocket is 4 times the diameter of the tree core.

[0118] (2) Two main branch water lines are used to connect the two ends of the bracelet, two auxiliary branch water lines are used to connect the middle part of the bracelet, and all branch water lines are collected into the main water line. The total cross-sectional area of all branch water lines is controlled to be 1.6 times the cross-sectional area of the main water line.

[0119] (3) The tree core is provided with a taper of 8°, and 15 mm of the tree core at both ends is left without connecting water lines.

[0120] (4) The connection between the water line and the tree core is set to be uniformly distributed in a spiral form, and the spiral step is controlled to be 15 mm. The casting spacing is not less than 4 mm. The included angle between the water line and the tree core is controlled to be 40-45°, and the distance is 8-10 mm. The connection between the water line and the tree core should be smooth transition.

[0121] (5) The gate pocket is designed to be hemispherical, and a buffer cone is provided at the bottom of the gate pocket. The lower diameter of the buffer cone matches the large end diameter of the tree core, the upper diameter is 2.5 times the large end diameter of the tree core, and the taper angle is 120°.

[0122] (6) The large end of the tree core is located directly below the gate pocket, and the connection between the tree core and the buffer cone of the gate pocket is smooth transition.

[0123] 3. Casting process

[0124] (1) The casting equipment is composed of a melting and casting machine, a power system, a PLC system, a vacuum system, a water cooling system, a protective gas station system, a compressed air system, a vibration table and the like. The melting and casting machine includes a melting chamber and a casting chamber, which are installed and fastened on the vibration table through rubber damping pads. The PLC system is combined with the power system, and the remaining systems are separately arranged to form the entire equipment through pipelines, so as to complete the steps of melting, automatic pouring, solidification and pressurization and vibration crystallization of metal under a protective atmosphere.

[0125] (2) After the metal charge is put into the graphite crucible, the melting chamber is vacuumized to 10-20 Pa, and then industrial pure argon is filled to 0.06-0.07 MPa. The metal charge is melted by induction heating, and the temperature of the metal liquid is accurately controlled by a thermocouple.

[0126] (3) The calcined gypsum mold is loaded on the loading table of the casting chamber, and a heat-resistant gasket is placed on the top surface of the mold. The inner diameter of the gasket is 16 mm larger than the diameter of the sprue hole, and the outer diameter is 7 mm smaller than the inner diameter of the mold steel ring. The bottom cylinder is started to lift the mold and press it tightly onto the bottom plate of the melting chamber, forming a sealed space in the casting chamber. The casting chamber is vacuumized to 10-20 Pa.

[0127] (4) The pouring temperature of the metal liquid is controlled to be 40°C higher than the liquidus temperature of the alloy. After the pouring temperature is reached, the crucible plug rod is lifted, and the metal liquid is poured into the sprue hole of the mold. Under the action of vacuum negative pressure, the metal liquid is smoothly filled into the mold cavity.

[0128] (5) The vibration table is started within 4 seconds after pouring, the vibration frequency is set to 70 Hz, the vibration amplitude is set to 0.10-0.15 mm, and the vibration duration is set to 45 seconds.

[0129] (6) The solidification and pressurization are started 8 seconds after pouring. The pressurization is divided into two stages, first at 0.13 MPa for 18 seconds, and then at 0.29 MPa for 72 seconds.

[0130] Through detection, the implementation effect of the embodiment is:

[0131] By optimizing the alloy formula, the material of the embodiment has good fluidity, which is conducive to realizing the layer-by-layer solidification mode, and the alloy contains an antioxidant and a grain refiner, which can reduce oxidation during smelting and casting, form a large number of heterogeneous cores, and refine the grain structure. By optimizing the structure design of the casting tree, the metal liquid can be smoothly filled, the problems of gas entrainment and inclusions caused by turbulence can be reduced, and the floating and discharge of gas and inclusions are facilitated; at the same time, the force and the holding from the gate nest---the core---the water line---the feeding channel of the casting provide conditions for the solidification shrinkage compensation of the casting. Through the comprehensive measures of protective atmosphere smelting, negative pressure suction casting, solidification pressurization and vibration crystallization, the problem of air absorption and oxidation during smelting can be effectively reduced. By precisely controlling the vibration crystallization time and vibration process conditions of the casting, the shear force generated by vibration breaks the dendrites formed in the early stage of solidification, forms more crystallization cores, avoids the problems of interference with the filling process caused by vibration too early or too long duration, and avoids the problems of too late vibration or too short duration. By precisely controlling the start and duration of secondary pressurization, the problems of metal liquid splashing and oxidation inclusions caused by pressurization too early, and the problems of pressurization failure caused by pressurization too late are avoided.

[0132] The 10K platinum bracelet cast by the embodiment has a liquidus temperature of 975℃ and a crystallization interval of 57℃. The average grain size is 70μm, the surface roughness Ra of the casting is 1.873μm, and the density reaches 98.6%.

[0133] The above-mentioned embodiments are only preferred embodiments of the present application, and cannot be used to limit the scope of protection of the present application. Any non-essential changes and replacements made by those skilled in the art on the basis of the present application are within the scope of protection of the present application.

Claims

1. A method of making a high-density, low-karat white gold jewelry casting, characterized in that, The preparation steps include: S1: preparing alloy components The alloy components include the following components with mass percentage: 5% to 14% of nickel, 34% to 48% of copper, 6% to 14% of zinc, 0.1% to 1% of tin, 0.05% to 0.5% of silicon, 0.03% to 0.2% of rare earth, the rest being gold, and inevitable impurity elements; S2: design of tree structure of casting The tree structure of casting adopts four-stage communication structure of casting- water line- tree core- gate pocket; S3: casting process The casting equipment includes a melting and casting machine, a power supply system, a PLC system, a vacuum system, a water cooling system, a protective gas station system, a compressed air system and a vibration table; The metal furnace charge is put into a graphite crucible, then the smelting chamber is vacuumed to 10 to 100 Pa, and then industrial pure argon is filled to 0.06 to 0.09 MPa to heat and smelt, and the temperature of the metal liquid is precisely controlled through a thermocouple; The roasted gypsum mold is loaded on the loading table of the casting chamber, a heat-resistant gasket is placed on the top surface of the mold, the bottom cylinder is started to lift the mold and press it tightly onto the bottom plate of the smelting chamber to form a closed space of the casting chamber, the casting chamber is vacuumed to 10 to 100 Pa before pouring, the pouring temperature of the metal liquid is controlled to be 30 to 100 ℃ higher than the liquidus temperature of the alloy, after the pouring temperature is reached, the crucible plug rod is lifted, the metal liquid is poured into the gate pocket of the mold, and under the action of vacuum negative pressure, the metal liquid is smoothly filled into each mold cavity; within 1 to 5 seconds after pouring, the vibration table is started, the vibration frequency is set to 50 to 100 Hz, the amplitude is set to 0.1 to 0.3 mm, and the vibration duration is set to 15 to 45 seconds; 2 to 10 seconds after pouring, solidification pressurization is started to forcibly press the metal liquid into the hot spot area.

2. The method of making a high-density, low-karat white gold jewelry casting according to claim 1, wherein, In step S1, the gold is divided into 9K and 10K, the gold content of 9K is controlled to be 37.5% to 37.8%, and the gold content of 10K is controlled to be 41.7% to 42.0%.

3. The method of making a high-density, low-karat white gold jewelry casting according to claim 1, wherein, In step S1, the rare earth is one or more of cerium, yttrium, lanthanum, neodymium and gadolinium.

4. The method of making a high-density, low-karat white gold jewelry casting according to claim 1, wherein, In step S1, the liquidus temperature of the alloy is not more than 1020 ℃, and the solidification crystallization interval is not more than 60 ℃.

5. The method of making a high-density, low-karat white gold jewelry casting according to claim 1, wherein, In step S2, the diameter of the water line is 1.3 to 2.5 times the maximum thickness of the casting, the diameter of the tree core is 1.5 to 3 times the diameter of the water line, and the diameter of the gate pocket is 2 to 5 times the diameter of the tree core.

6. The method of making a high-density, low-karat white gold jewelry casting according to claim 1, wherein, In step S2, the water line is divided into a main water line and branch water lines, the main water line is connected at the thickest hot spot of the casting, each branch water line is arranged at a residual hot spot or a slender part of the casting, and the branch water lines converge to the main water line.

7. The method of making a high-density, low-karat white gold jewelry casting according to claim 6, wherein, In step S2, the total cross-sectional area of the branch water lines is 1.2 to 1.8 times the cross-sectional area of the main water line.

8. The method of making a high-density, low-karat white gold jewelry casting according to claim 1, wherein, In step S2, the tree core is provided with a taper of 5 to 8°, 10 to 15 mm of the tree core at both ends is left without being connected to the water line, the connection of the water line and the tree core is provided in a spiral and uniformly distributed, the step distance of the spiral is controlled to be 10 to 15 mm, the distance between the castings is not less than 2.5 mm, and the included angle between the water line and the tree core is controlled to be 30 to 60° and the distance is 8 to 15 mm.

9. The method of making a high-density, low-karat white gold jewelry casting according to claim 1, wherein, In step S2, the gate pocket is designed as a semi-sphere, the bottom of the gate pocket is provided with a buffer cone, the lower opening diameter of the gate pocket is matched with the big end diameter of the core, the upper opening diameter of the gate pocket is 1.5-2.5 times of the big end diameter of the core, and the cone angle is 90-120°.

10. The method of making a high-density, low-karat white gold jewelry casting according to claim 1, wherein, In step S3, for the conventional castings with relatively simple structure, the pressurizing pressure is set as 0.2-0.3 MPa, and the pressurizing duration is 50-100 s; for the castings with complex hot spots, the segmented pressurizing is set, i.e. first pressurizing under the pressure of 0.1-0.2 MPa for 10-20 s, and then continuously pressurizing under the pressure of 0.25-0.3 MPa for 50-120 s.

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