Method for full-component stepwise recycling of precision casting waste shell

Abstract

The application discloses a kind of precision casting waste shell full component stepwise recycling method, belong to foundry solid waste resource regeneration technical field.The method includes grinding, stepwise screening, rough magnetic separation, metal purification, stepwise magnetic separation iron removal, fine grinding and screening grading steps, utilize the particle size difference of metal and mullite sand to realize physical separation, output high-purity metal reverberatory material, regenerated zircon sand and regenerated mullite sand;Fine material under screen is removed iron by stepwise magnetic separation and fine grinding, and different particle size specifications of refractory composite powder are prepared.Full process is operated in full closed and negative pressure state, equipped with bag dust removal system and PLC centralized control system, without any high-temperature calcination link, without involving metal heating melting, full-temperature dry method physical operation, without using water, without producing waste water.Active SiO2Retention is 8.3 times of calcination process, and total energy consumption is only 27.7% of calcination process.

Description

Technical Field

[0001] This invention relates to the field of resource recycling and circular economy technology of casting solid waste, and more specifically to a method for the tiered recycling of all components of precision casting waste shells. Background Technology

[0002] Precision casting, especially the precision casting process that uses silica sol, water glass or ethyl silicate as binders, is widely used in the forming of metal materials such as stainless steel, carbon steel, alloy steel, cast steel, special steel and high temperature alloy. It is the core process for the production of key components such as high-end valves, pipe fittings, pump bodies, medical devices, ship parts, automotive parts, aerospace parts and so on.

[0003] Precision casting mold shells typically consist of a face layer and a back layer. The face layer is in direct contact with the molten metal, and depending on the casting metal, the face layer material is mainly zircon powder or white fused alumina powder. Zircon powder is used for high-end castings such as stainless steel and alloy steel, offering good anti-sand adhesion properties; white fused alumina powder is used for castings such as carbon steel and cast steel, offering high refractoriness and lower cost. The back layer is usually made of mullite. The face and back layers are coated layer by layer with binders such as silica sol, water glass, or ethyl silicate to form the mold shell.

[0004] After dewaxing and firing, the shell is poured with molten metal at 1500-1600℃. During this high-temperature thermal history, a series of beneficial material science transformations are completed inside the shell: the mullite phase tends to stabilize, zircon or corundum completes lattice restructuring, amorphous active silica generated by the decomposition of silica sol or ethyl silicate uniformly coats the surface of aggregate particles, sodium silicate glass phase generated by the decomposition of water glass coats the surface of aggregate particles, and low-melting-point impurities are selectively vitrified or volatilized.

[0005] During the casting process, a large number of waste shells are generated for every ton of qualified precision castings produced. These waste shells are composed of expensive mullite sand and zircon powder (or white corundum powder) with the help of a binder. They have withstood the high-temperature thermal shock of molten metal at 1500-1600℃ during pouring and are essentially a high-quality refractory material that has been modified by high temperature.

[0006] Current waste shell recycling technologies generally employ a process route of "crushing and grinding → high-temperature secondary calcination". This approach has the following fundamental flaws:

[0007] Firstly, subjecting raw materials that have already undergone high-temperature molten metal to secondary calcination is a thermodynamic waste of energy. Furthermore, high-temperature calcination irreversibly destroys the active silica components generated by the decomposition of the binder, leading to a reduction in the activity of the recycled products.

[0008] Secondly, in the conventional "grinding and then sorting" iron removal process, the waste shell contains metal fragments and iron oxide scale. During grinding, the refined ferromagnetic impurities will be embedded in the surface of non-magnetic particles under mechanical force, forming a "mechanical alloying" contamination layer that is difficult to separate, resulting in low iron removal efficiency and high iron content in the recycled product.

[0009] Third, existing technologies have a single method for treating waste shells, and do not perform tiered separation and differentiated utilization of materials of different particle sizes and compositions in the waste shells, resulting in the failure to effectively recover high-value components (such as zircon sand and metal remelting materials).

[0010] Fourth, existing waste shell recycling processes generally neglect dust pollution, have low automation levels, rely on manual operation, have unstable process parameters, and result in large fluctuations in product quality.

[0011] Chinese invention patent application CN106825111A discloses a method for graded regeneration and recovery of mullite and zircon sand from precision casting waste shells. The steps are: crushing → dry screening → flotation. This method uses a wet process, requires flotation reagents, generates chemical waste liquid, and cannot retain the active silica component in the waste shell.

[0012] Therefore, there is an urgent need to develop a method for regenerating precision casting waste shells that does not require high-temperature calcination, generates no wastewater, allows for the cascade utilization of all components, and is environmentally friendly. Summary of the Invention

[0013] In view of this, the present invention provides a method for the full-component tiered recycling of precision casting waste shells. This method achieves the full-component tiered separation and recycling of metals, zircon sand, recycled mullite sand, and refractory composite powders in the waste shells under ambient temperature dry conditions through a combination of grinding, tiered sieving, coarse magnetic separation, tiered magnetic separation for iron removal, and fine grinding.

[0014] To achieve the above objectives, the present invention adopts the following technical solution: A method for the full-component cascade recycling of precision casting waste shells includes the following steps: Step 1, Grinding: The collected precision casting waste shells are sent to grinding equipment for grinding. The waste shells are formed by coating layers of silica sol, water glass, ethyl silicate or other precision casting binders as binders, zircon powder, white corundum powder or a mixture of zircon powder and white corundum powder as surface materials, and mullite as back material. After dewaxing and firing, molten metal at 1400℃-1700℃ is poured in. After the casting cools, the waste shells are removed.

[0015] Preferably, the molten metal includes, but is not limited to: stainless steel (including 304, 316, 304L, 316L, 321, 310S, 2205 duplex stainless steel, 17-4PH precipitation hardening stainless steel), carbon steel (including 20# carbon steel, 45# carbon steel, ZG230-450 cast carbon steel), cast steel (including various grades of cast carbon steel and cast alloy steel), alloy steel (including 42CrMo, 35CrMo, 40Cr, 20CrMnTi), special steel (including H13 mold steel, Cr12MoV mold steel, 1Cr18Ni9Ti heat-resistant steel, wear-resistant steel, high-speed steel), high-temperature alloys (including nickel-based high-temperature alloys, cobalt-based high-temperature alloys) and other metal materials that require precision casting.

[0016] The waste shell contains residual steel from the gate, flash, and other metal remnants. This step and all subsequent steps are carried out at room temperature, without involving the heating or melting of any metal, and without the use of any high-temperature calcination kilns.

[0017] The waste shell has the following characteristics due to the differences in adhesive system and surface material: Silica sol + zircon powder surface waste shell: Silica sol decomposes into amorphous active silica at high temperatures above 1400℃, which uniformly coats the surface of mullite and zircon powder particles, forming a reactive nanoscale coating layer.

[0018] Silica sol + white fused alumina surface waste shell: Amorphous active silica generated from the decomposition of silica sol is uniformly coated on the surface of mullite and white fused alumina particles, forming a reactive nanoscale coating layer.

[0019] Waste shell of water glass + zircon powder surface layer: Water glass decomposes and loses water at high temperatures above 1400℃, generating sodium silicate glass phase. Most of the Na2O has volatilized or reacted with mullite and zircon to form a stable aluminosilicate glass phase.

[0020] Water glass + white fused alumina surface waste shell: Sodium silicate glass phase generated from the decomposition of water glass is wrapped around the surface of mullite and white fused alumina particles.

[0021] Ethyl silicate waste shell: Ethyl silicate decomposes at high temperature to generate amorphous silica, which uniformly coats the surface of aggregate particles.

[0022] The grinding equipment is a fully enclosed structure, with sealed connections at both the inlet and outlet, and is connected to the bag filter dust collection system via a sealed pipeline. The main equipment is equipped with soundproof covers or silencers to control workshop noise levels to no more than 85 decibels. The grinding equipment can be independently selected from any one of the following or any combination thereof: Ball mills (including dry ball mills, wet ball mills, continuous ball mills, intermittent ball mills, overflow ball mills, grate ball mills, and planetary ball mills), rod mills, Raymond mills (suspended roller mills), vertical mills, tower mills, ring roller mills, vibratory mills, stirred mills, sand mills, mechanical impact crushers, hammer mills, autogenous mills, semi-autogenous mills, disc mills, and any other equipment that crushes and refines materials by means of mechanical force through impact, compression, shearing, or grinding.

[0023] Ball mills are preferred. When using a ball mill, the inner wall of the mill cylinder is lined with wear-resistant plates, made of any one of high-manganese steel, chromium-molybdenum alloy steel, or alumina ceramic. The grinding media are steel balls, with the following diameter ratio: large balls (40-60mm) accounting for 20%-30%, medium balls (25-40mm) accounting for 40%-50%, and small balls (15-25mm) accounting for 20%-30%. The large balls are mainly responsible for impact crushing, while the medium and small balls are responsible for grinding and refining.

[0024] The ball milling process parameters are as follows: ball-to-material ratio of 2:1 to 4:1, ball loading rate of 35% to 45% of the effective volume of the ball mill cylinder, and ball milling speed of 65% to 80% of the critical speed. Due to the high brittleness of silica sol waste shells, the ball milling time is preferably 15-25 minutes; due to the high toughness of water glass waste shells, the ball milling time is preferably 25-40 minutes. The endpoint of ball milling is determined by sampling and sieving; when the proportion of material passing through the target cut-off sieve reaches 90% or more, the ball milling has reached its endpoint. If this is not achieved, the ball milling should be extended by 5 minutes each time, followed by retesting.

[0025] During ball milling, a cooling device is installed on the outside of the mill cylinder to control the milling temperature to not exceed 80℃, preventing changes in the surface properties of the material due to overheating or premature sintering of active silica. The temperature of the ball mill cylinder is monitored in real time by thermocouples, and the temperature signal is connected to the PLC control system. When the temperature exceeds 80℃, the PLC automatically issues an alarm signal and increases the cooling water flow.

[0026] Dust collection configuration for the grinding equipment: A dust suction hood is installed above the feed inlet of the grinding equipment, and a sealed dust collection interface is installed at the connection between the discharge outlet and the screw conveyor. Negative pressure sealing devices are installed at the bearing seats at both ends of the cylinder. All the above dust collection points are connected to the bag filter dust collection system through sealed pipes. The air volume of the feed inlet dust suction hood is adjusted by an air volume regulating valve, and the air volume signal is fed back to the PLC control system. The dust-laden gas generated during the grinding process is purified by the bag filter dust collection system before being discharged in compliance with standards, and the collected dust is recycled for production.

[0027] Step 2, tiered screening: The ground material is fed into a screening device via a fully enclosed screw conveyor for multi-stage screening. The screening device can be any one of the following: a fully enclosed linear vibrating screen, circular vibrating screen, rotary vibrating screen, gyratory screen, drum screen, or probability screen, with a vibration frequency of 960-1450 times / minute and an amplitude of 3-6mm. The screen body is covered by a sealed casing made of 304 stainless steel, and each connection surface is equipped with sealing strips.

[0028] The screen is made of 304 or 316 stainless steel woven mesh, with a screen inclination angle of 10°-20°. Each screen is equipped with a bouncing ball cleaning device or an ultrasonic cleaning device to prevent fine mullite powder from clogging the screen holes. A tensioning device is installed under the screen to ensure that the screen does not loosen during long-term use. When the screen needs to be replaced, the screen body is equipped with a quick-opening maintenance door, and a sealing strip is installed between the maintenance door and the screen body. After the screening equipment is switched to "maintenance mode" via the PLC control system, the equipment controller is locked and cannot be started. After maintenance is completed, authorized personnel can enter a password on the touch screen to unlock "maintenance mode" before normal production can be resumed.

[0029] The significant particle size difference between metal and mullite after grinding is utilized to achieve physical separation through sieves of different mesh sizes. Metal, due to its good toughness and high ductility, is not easily ground and remains on the sieve with a larger particle size; mullite, due to its high brittleness and hardness, is ground into fine particles and passes through the sieve as the undersize material.

[0030] The screening process employs a multi-stage adjustable screen combination, which can be flexibly adjusted according to differences in waste shell source, metal content, and particle size distribution. The basic screen combination includes: 14 mesh (1.18mm aperture), 23 mesh (0.71mm), 36 mesh (0.425mm), 46 mesh (0.355mm), and 60 mesh (0.25mm). Depending on actual production needs, the number of screen stages can be increased or decreased, adding intermediate screens such as 10 mesh, 20 mesh, 24 mesh, 30 mesh, 50 mesh, 70 mesh, 80 mesh, and 100 mesh. The critical cutoff point for screening can be flexibly selected between 40 and 100 mesh: when the metal particles in the waste shell are relatively coarse or a coarser particle size is required for regenerated mulberry sand, the cutoff point can be selected between 40 and 50 mesh; when the metal particles in the waste shell are relatively fine or a finer particle size is required for regenerated mulberry sand, the cutoff point can be selected between 80 and 100 mesh. This invention is described with 60 mesh as the preferred cutoff point, but the scope of protection is not limited to 60 mesh. Any cutoff point selected between 40 mesh and 100 mesh falls within the scope of protection of this invention.

[0031] Screening efficiency ≥95%, meaning the mass percentage of the target particle size in the material passing through the cut-off mesh sieve is ≥95%. The material passing through each level of sieve is collected separately through fully enclosed chutes or pipelines, awaiting entry into the coarse magnetic separation process.

[0032] The material passing through the cut-off mesh sieve is temporarily stored in a storage tank via a fully enclosed screw conveyor. The storage tank is equipped with a moisture-proof breather valve and a level gauge (ultrasonic or radar level gauge), with the level signal connected to a PLC control system. A vibrating discharge device is installed at the bottom of the storage tank to prevent powder bridging and blockage. The material passing through the cut-off mesh sieve (e.g., with a cut-off point of 60 mesh, meaning passing through a 60-mesh sieve with a particle size ≤0.25mm) is fine mullite powder, primarily composed of mullite, and containing a small amount of zircon (when the surface layer is zircon powder) or a small amount of corundum (when the surface layer is white corundum), with a particle size range from the cut-off mesh to 200 mesh. This material is recycled mullite.

[0033] This recycled mullite has withstood the high temperatures of molten metal (1400℃-1700℃) during casting, exhibiting complete mineral phase stability, excellent volume stability, and extremely low loss on ignition. For recycled mullite derived from silica sol waste, the particle surface is coated with active amorphous silica; for recycled mullite derived from water glass waste, the particle surface is coated with a stable aluminosilicate glass phase. The performance of recycled mullite from all sources is superior to that of untreated virgin mullite powder.

[0034] The quality indicators for recycled mullite are as follows: particle size between the cut-off mesh and 200 mesh; Al2O3 content 40%-55% (zircon powder layer) or 50%-70% (white fused alumina layer); SiO2 content 35%-50% (zircon powder layer) or 20%-35% (white fused alumina layer); Fe2O3 content ≤1.0%; loss on ignition ≤0.5%; and moisture content ≤0.3%. Samples of each batch of product are taken and tested for the above indicators; only those that pass the tests can be shipped out or proceed to the next step.

[0035] Uses of recycled mulley sand include, but are not limited to: Sand for molding and core making of cast steel parts (including carbon steel, alloy steel, and stainless steel castings); backing sand for precision casting; filling sand for lost foam casting; filling sand for V-process casting; resin sand regeneration substitute sand; clay sand substitute sand; original coated sand; substitute material for recycled silica sand for casting; refractory aggregates; refractory castable aggregates; refractory ramming aggregates; refractory plastic aggregates; ladle drainage sand; lean raw materials for building ceramic blanks (including lean materials for ceramic tile blanks, rock slab blanks, large slab blanks, and thin slab blanks); lean raw materials for daily-use ceramics and sanitary ceramics blanks; high-grade mortar aggregates for construction; wear-resistant flooring aggregates; and other industrial fields requiring mullite or corundum refractory aggregates.

[0036] Step 3, Coarse Magnetic Separation: All the material collected by the various screens in Step 2 is fed into a coarse magnetic separator via a fully enclosed screw conveyor for magnetic separation. The coarse magnetic separator can be any one of a single-drum magnetic separator, a double-drum magnetic separator, a suspended iron remover, or a magnetic drum, with a magnetic field strength ranging from 1000 to 3000 Gauss, preferably 1500 to 2500 Gauss. This step is performed at room temperature and does not involve any heating process.

[0037] The purpose of coarse magnetic separation is to further separate and remove iron oxide scale, iron powder, weakly magnetic stainless steel fragments, and residual mullite powder adhering to the surface of the metal particles on the sieve, thereby improving the purity of the metal remelting material. After coarse magnetic separation, the metal purity of the material on 14-mesh to 46-mesh sieves increases from ≥90% to ≥95%, and the metal purity of the material on 60-mesh sieves increases from ≥85% to ≥90%.

[0038] The ferromagnetic impurities (iron oxide scale, iron powder, weakly magnetic stainless steel shavings) removed by coarse magnetic separation are collected in an iron storage silo and can be sold to metal smelters as chromium-nickel iron powder.

[0039] Metal purification: The metal particles obtained from the coarse magnetic separation in step three are fed into a wet ball mill for secondary ball milling. The ball-to-material ratio is 2:1 to 3:1, the ball loading rate is 35%-40% of the effective volume of the mill, the ball mill speed is 70% of the critical speed, the ball milling time is 10-15 minutes, the grinding concentration is 60%-65%, and the grinding media are steel balls (15-25mm in diameter). Through the impact and grinding action of the ball mill, the residual mullite and zircon sand adhering to the surface of the metal particles are peeled off and released.

[0040] The ball-milled material is then fed into a wet shaking table (gravity separator), utilizing the metal (density approximately 7.8 g / cm³). 3 Zircon sand (density approximately 4.6 g / cm³) 3 Gravity separation was performed based on the density difference between the sand and mullite (density approximately 2.8 g / cm³). The bed slope was 1.8°-2.8°, the flushing frequency was 320-400 times / minute, and the lateral water flow rate was 0.9-1.3 m³ / min. 3 The feed concentration is 60%-65% per hour. The heavy-duty belt of the shaking table collects high-purity metal particles (purity ≥98%), which are then dehydrated and dried for sale as stainless steel remelting material. These particles can be returned to AOD furnaces, medium-frequency furnaces, electric arc furnaces, induction furnaces, and other smelting equipment for remelting. The medium-duty belt of the shaking table collects zircon sand, which is then dehydrated and dried for sale as recycled zircon sand. The light-duty belt of the shaking table collects fine mullite powder, which flows with the water into a settling tank. After sedimentation and dehydration, it is mixed with 60-mesh sieve material for further processing. The recycling of this metal remelting material is not within the scope of this method; this method only involves room-temperature physical separation and magnetic separation, and does not involve the heating and melting of the metal.

[0041] Dust collection configuration for coarse magnetic separation: The feed inlet of the coarse magnetic separator is equipped with a sealed feeding device that is tightly connected to the discharge port of the oversize material from the upstream screening equipment. Both the magnetic material discharge port and the non-magnetic material discharge port are equipped with sealed interfaces and are tightly connected to downstream equipment via pipelines. A dust collection hood is installed throughout the equipment or the operating area, and the dust collection hood is connected to the bag filter system via pipelines.

[0042] Dust collection configuration for vibrating screens: The dust collection points of the screening equipment include: a dust collection pipe interface on the top of the sealed cover of the screen body; auxiliary dust collection branch pipes in the transition area between each level of screen; and a sealed dust collection interface at the connection between the discharge chute of the oversize material and the storage silo. All of the above dust collection points are connected to the bag filter dust collection system through sealed pipes. Each branch pipe is equipped with an airflow regulating valve, and the airflow signal is fed back to the PLC control system. The collected dust mainly consists of mullite and zircon (or corundum) ultrafine powder (-200 mesh), which is returned to the grinding equipment through a closed loop to participate in subsequent grinding, or directly mixed with the undersize material for the next step of processing.

[0043] Steps one through three involve no chemical treatment or high-temperature calcination; the physical separation of the metal from the mullite and the purification of the metal are achieved solely through mechanical grinding, cascade sieving, and coarse magnetic separation.

[0044] Step four, stepped magnetic separation for iron removal: The material undersize from the sieve produced in step two is fed into a magnetic separation unit for at least one stage of magnetic separation to remove iron. This magnetic separation is completed before the fine grinding step. This step is performed at room temperature and does not involve any heating process.

[0045] Ferromagnetic impurities in precision casting waste shells possess unique magnetic characteristics. During the pouring of molten metal at temperatures above 1400℃, trace amounts of fine metal fragments remaining in the undersize sieves undergo severe oxidation due to prolonged exposure to the high-temperature environment. This oxidation forms a black oxide film primarily composed of magnetite (Fe3O4) and ferric oxide (Fe2O3), which itself exhibits strong ferromagnetism. Simultaneously, the high-temperature oxidation induces a phase transformation in the metal surface structure, further enhancing the overall magnetism of the metal fragments. Testing has shown that approximately 99% or more of the residual metal fragments in the undersize sieves from various waste shell sources possess magnetic properties that allow them to be effectively attracted by a magnetic field.

[0046] By placing magnetic separation before fine grinding, all ferromagnetic impurities are deeply removed before the new surface of the particles is formed, thus fundamentally avoiding the defects of mechanical alloying contamination of iron in the process of grinding before separation.

[0047] The magnetic separation and iron removal unit adopts a two-stage stepped magnetic separation configuration: First-stage coarse magnetic separation: A drum magnetic separator is used, independently selected from single-drum, double-drum, or triple-drum magnetic separators. The magnetic field strength ranges from 1000 to 5000 Gauss, preferably 1500 to 4000 Gauss. The magnetic field is uniformly distributed on the drum surface. The material is evenly distributed on the drum surface by a vibrating feeder, with the feed thickness controlled at 5-15 mm. Magnetic materials are adsorbed on the drum surface and fall off as the drum rotates to the non-magnetic zone, while non-magnetic materials fall freely, achieving continuous separation.

[0048] The second stage of fine magnetic separation employs a high-intensity magnetic roller separator or a drawer-type high-intensity magnetic rod box. The surface magnetic induction intensity ranges from 6000 to 15000 Gauss, preferably 8000 to 12000 Gauss. The high-intensity magnetic roller separator uses a high-gradient magnetic field design, and the magnetic field intensity on the surface of the magnetic roller can reach over 15000 Gauss.

[0049] When the magnetic field strength of the selected magnetic separation is 8000-12000 Gauss, the Fe2O3 content of the product is controlled at 0.5%-1.5%, which is suitable for lost foam casting coatings and cast iron coatings. When the magnetic field strength of the selected magnetic separation is increased to 12000-15000 Gauss, the Fe2O3 content of the product is controlled at 0.2%-0.5%, which is suitable for alcohol-based coatings for carbon steel / cast steel and back coatings for stainless steel castings.

[0050] The aforementioned graded control of iron content is all completed under normal temperature dry conditions, without the need for acid washing or high-temperature treatment. By adjusting the magnetic separation parameters, flexible switching between different quality grades of products can be achieved, enabling this invention to serve multi-level market demands, from refractory materials to high-end coatings, using the same set of equipment and processes.

[0051] The magnetic separation device in the magnetic separation and iron removal unit is independently selected from any one or any combination of a single-roller magnetic separator, a double-roller magnetic separator, a triple-roller magnetic separator, a single-roller high-intensity magnetic roller separator, a double-roller high-intensity magnetic roller separator, a drawer-type magnetic rod box, a suspended iron separator, a magnetic drum, an eddy current separator, an electromagnetic iron separator, and a permanent magnet iron separator. The number of magnetic separation stages can be flexibly selected according to the content of ferromagnetic impurities in the undersize material. When the iron content is less than 1%, only one stage of magnetic separation can be used; when the iron content is between 1% and 5%, two stages of magnetic separation are used; and when the iron content is greater than 5%, three stages of magnetic separation are used.

[0052] Step four involves the dust removal configuration of the magnetic separator: The feed inlet of the drum-type magnetic separator is equipped with a sealed feeding device that is tightly connected to the discharge outlet of the front-end storage tank. The feeding device uses a star-shaped discharge valve. Both the magnetic material discharge outlet and the non-magnetic material discharge outlet are equipped with sealed interfaces and are tightly connected to downstream equipment via pipelines. The high-intensity magnetic roller separator is entirely equipped with a sealed casing, and the top of the casing has a dust collection pipeline interface that connects to the bag filter dust collection system. The drawer-type magnetic rod box has a fully enclosed structure, and both the inlet and outlet are equipped with sealed flange interfaces. The collected ferromagnetic impurities are temporarily stored in an iron storage silo via a fully enclosed screw conveyor.

[0053] Step 5, Fine Grinding: The clean material after iron removal by magnetic separation in Step 4 is fed into a fine grinding device and ground to the target particle size at room temperature. The fine grinding device is a fully enclosed structure, with sealed connections at both the inlet and outlet, and is connected to the bag filter system via a sealed pipeline. The main equipment is equipped with soundproof covers or silencers.

[0054] To further improve the particle morphology of the product and enhance coating performance, this invention also provides the following particle morphology optimization scheme. This scheme is an optional step, and its activation can be flexibly selected according to the customer's requirements for the particle morphology of the product: The finely ground powder is fed into an air jet mill for particle shaping. High-speed airflow causes the particles to collide and rub against each other, removing sharp edges and making the particles more spherical. After air jet milling, the sphericity of the product particles is significantly improved.

[0055] The technical effects of improved particle morphology include: when used in coatings, it can effectively reduce internal stress in the coating and reduce the risk of drying cracking; when used in lost foam coatings, it can improve the air permeability and uniformity of the coating; when used in polishing abrasives, it can reduce surface scratches on the workpiece and improve the polishing effect.

[0056] The particle shaping process uses a purely physical method without introducing any chemical additives, which is consistent with the technical route of this invention, which is entirely free of chemical additives.

[0057] The fine grinding equipment is independently selected from any one of the following equipment or any combination thereof: Dry ball mills (including continuous ball mills, intermittent ball mills, overflow ball mills, grate ball mills, planetary ball mills), Raymond mills (suspended roller mills), vertical mills, tower mills, ring roller mills, vibratory mills, stirred mills, sand mills, air jet mills, disc mills, colloid mills, and any other equipment that grinds materials to a target particle size at room temperature by mechanical force.

[0058] Raymond mills are preferred. When using Raymond mills, the process parameters are: 3 to 5 grinding rollers, main machine speed of 120 to 180 rpm, and adjustable classifier speed to control the output particle size. The Raymond mill system operates under full negative pressure in a closed system, with a built-in classifier, integrating grinding and classification. It eliminates the need for separate sieving equipment to obtain finished powder with uniform particle size and concentrated distribution.

[0059] When the classifier speed is set to 120-150 r / min, the output particle size is 150-200 mesh, suitable for producing powder for lost foam coatings, with a daily capacity of approximately 35-45 tons. When the classifier speed is set to 180-240 r / min, the output particle size is 200-300 mesh, suitable for producing powder for alcohol-based coatings, with a daily capacity of approximately 25-35 tons. When the classifier speed is set to 240-300 r / min, the output particle size is finer than 325 mesh, suitable for producing powder for 3D printing or electronic materials, with a daily capacity of approximately 15-20 tons.

[0060] When using a dry ball mill, the process parameters are as follows: ball-to-material ratio of 3:1 to 5:1, ball loading rate of 40% to 50% of the effective volume of the mill cylinder, mill speed of 70% to 85% of the critical speed, milling time of 30 to 120 minutes, and grinding media of any one of steel balls, alumina balls, or zirconium balls. A cooling device is installed on the outside of the mill cylinder during the milling process to control the milling temperature to not exceed 80℃. The temperature of the mill cylinder is monitored in real time by thermocouples, and the temperature signal is connected to the PLC control system.

[0061] The two fine grinding methods can be flexibly selected based on the actual production scale, product particle size requirements, and customers' differentiated needs for powder activity. When high powder activity is required, dry ball mill grinding is preferred to leverage its mechanochemical activation effect; when pursuing large-scale continuous production and particle size uniformity, Raymond mill grinding is preferred. A combined process of "first coarse grinding to 100-150 mesh using Raymond mill, then fine grinding to the target particle size using dry ball mill" can also be adopted.

[0062] The target granularity is precisely determined based on the application area of ​​the final product: When used in alcohol-based casting coatings: Grind until all particles pass through a 200-mesh standard sieve (i.e., finer than 200 mesh, particle size ≤ 74 μm). The preferred particle size distribution, by mass percentage, is: 200-230 mesh (74μm-63μm) accounts for 15%-25%, providing skeletal support and preventing the coating from drying shrinkage and cracking; 230-270 mesh (63μm-53μm) accounts for 25%-35%, filling the gaps between coarse powders and improving the density of the coating; 270-325 mesh (53μm-45μm) accounts for 25%-35%, and is further filled to form a continuous dense layer; 325 mesh with finer particles (≤45μm) accounts for 10%-20%, improving suspension and brushability, and preferentially sintering at high temperature to form a closed layer.

[0063] When used in lost foam coatings: Grind to 150-200 mesh (particle size 100μm-74μm). The preferred particle size distribution, by mass percentage, is: 150-170 mesh (100μm-90μm) accounts for 10%-20%, forming a breathable channel framework; 170-200 mesh (90μm-74μm) accounts for 45%-55%, constituting the main body of the coating; 200-270 mesh (74μm-53μm) accounts for 20%-30%, filling the gaps to ensure strength; 270 mesh with finer particles (≤53μm) accounts for 5%-10%, and is preferentially sintered at high temperature to form a local sealing layer.

[0064] When higher requirements are placed on the air permeability of lost foam coatings, the mass ratio of the coarse aggregate (150-170 mesh) can be increased to 20%-25%. When customers have higher requirements on surface finish, the mass ratio of the fine filler (200-270 mesh) can be increased to 30%-35%.

[0065] When used in ceramic blanks: Grind to 200 to 325 mesh (74μm-45μm).

[0066] When used for 3D printing ceramic materials: Grind until all particles pass through a 325-mesh standard sieve (≤45μm).

[0067] When used as a filler in electronic ceramics: Grind until all particles pass through a 400-mesh standard sieve (≤38μm), or further pulverize to the micron level (D50≤5μm) using airflow.

[0068] Step Six, Sieving and Grading: When dry ball milling is used in Step Five, the ground powder is fed into sieving equipment for particle size classification via a fully enclosed screw conveyor or pneumatic conveying pipeline. A 200-mesh standard sieve is used when preparing powder for alcohol-based coatings; a 150-mesh standard sieve is used when preparing powder for lost foam coatings. The material exceeding the sieve is returned to the fine grinding equipment through a closed loop for further grinding, while the material below the sieve enters the next process. When Raymond milling is used in Step Five, particle size control is already achieved through its built-in classifier, so this sieving step is not required. For ultrafine powders used in 3D printing or electronic materials, an air classifier can be used for precision classification.

[0069] Dust collection configuration for screening: The screening equipment is a fully enclosed structure, with a sealed cover over the screen body. The top of the cover has a dust collection pipe interface that connects to the bag filter system. Both the oversize and undersize material outlets are equipped with sealed interfaces and connected via sealed pipes. The air classifier system operates under full negative pressure and a closed-loop system.

[0070] In the baghouse dust collection system for fine grinding and sieving processes, the ultrafine powder collected by the dust collector is separately collected to a dedicated storage silo through independent sealed pipes and ash discharge valves, without mixing with coarse powder. The particle size range of this ultrafine powder is finer than 325 mesh (≤45μm), and some can reach below 800 mesh (≤18μm), making it a high-quality raw material for producing high-end fine polished micro powder.

[0071] The collected ultrafine powder is graded and utilized according to its particle size distribution: 325-400 mesh (45μm-38μm), suitable for fine sandblasting abrasives and coarse polishing abrasives; 400-600 mesh (38μm-23μm), suitable for medium polishing abrasives and precision polishing powders; 600-800 mesh (23μm-18μm), suitable for fine polishing abrasives and automotive polishing wax fillers; Abrasives with a mesh size of 800 or less (≤18μm) are suitable for mirror polishing and optical glass polishing.

[0072] This ultrafine powder was originally collected by a bag filter dust collection system, and in conventional processes, it is often mixed back into the finished product or directly discarded. This invention collects and utilizes it separately, without the need for additional raw material input, to produce high-value-added fine polished micro powder, extending the product line, realizing the resource utilization of all components, and generating no secondary solid waste.

[0073] Step 7, Finished Product Packaging: The qualified powder is fed into the finished product packaging unit for sealing. The finished product packaging machine's outlet is equipped with a sealing bag clamping device. The packaging bags are woven bags or ton bags lined with plastic film. For ultrafine powders or powders used in electronic materials, vacuum packaging or nitrogen-filled packaging is employed. The packaging process is completed in a completely enclosed state. The top of the packaging machine is equipped with a dust collection pipe interface connected to a bag filter system. The finished product warehouse is equipped with ventilation and moisture-proof facilities, with the temperature controlled between 5-35℃ and the relative humidity controlled below 60%.

[0074] The applications of the produced refractory composite powder include, but are not limited to: In the field of casting coatings: lost foam casting coatings (including water-based lost foam coatings and alcohol-based lost foam coatings), alcohol-based casting coatings (including precision casting alcohol-based coatings and sand casting alcohol-based coatings), V-process casting coatings, centrifugal casting coatings, metal mold casting coatings, sand casting coatings, precision casting backing and transition layer coatings, casting protective slag, and covering agents.

[0075] In the field of unshaped refractory materials: refractory castables, refractory ramming mixes, refractory plastics, refractory spraying materials, refractory coatings, ladle castables and ladle lining repair materials, tundish coatings and tundish slag weirs, high-temperature sealing materials and high-temperature adhesives, refractory precast components, ceramic kiln furniture materials (including saggers, kiln shelves, supports, pushers, ceramic rollers), kiln repair materials, and kiln lining materials.

[0076] In the field of refractory bricks: high alumina bricks, mullite bricks, zircon bricks, corundum bricks, and composite refractory bricks.

[0077] In the ceramics industry: raw materials for building ceramic bodies (including ceramic tile bodies, slab bodies, large slab bodies, thin slab bodies, polished tile bodies, glazed tile bodies, and antique tile bodies), raw materials for daily-use ceramic bodies (including tableware ceramics, teaware ceramics, and art ceramic bodies), raw materials for sanitary ceramic bodies (including sanitary ware ceramics, squat toilets, and toilet bodies), raw materials for special ceramic bodies (including wear-resistant ceramics, corrosion-resistant ceramics, and insulating ceramic bodies), raw materials for ceramic glazes (including transparent glazes, opaque glazes, matte glazes, and crystalline glazes), ceramic membrane support materials, and refractory fiber products.

[0078] Additive manufacturing (3D printing) field: mullite-based or corundum-based powder materials for ceramic 3D printing, photopolymerization ceramic slurry fillers, powder bed fusion printing ceramic fillers, and binder jet printing ceramic fillers.

[0079] In the field of electronic materials: epoxy molding compound fillers, fillers for ceramic substrates, fillers for electronic packaging materials, fillers for low dielectric constant composite materials, and fillers for high-frequency and high-speed copper-clad laminates.

[0080] In the field of fine chemical fillers: high-grade building coating fillers, industrial anti-corrosion coating fillers, polypropylene (PP) reinforced fillers, polyethylene (PE) reinforced fillers, polyvinyl chloride (PVC) reinforced fillers, silicone rubber heat-resistant fillers, fluororubber heat-resistant fillers, and epoxy resin fillers.

[0081] Abrasives: fine sandblasting abrasives, precision polishing powders, abrasives for grinding pastes, and abrasives for polishing optical glass.

[0082] Friction materials: brake pad friction materials, clutch disc friction materials, high-speed rail braking friction materials.

[0083] Environmental protection field: industrial wastewater treatment filter media, biological filter packing, heavy metal ion adsorption carrier, and oily wastewater treatment filter media.

[0084] Other high-tech fields: metal matrix composite reinforcing phases (including aluminum matrix composites and magnesium matrix composite reinforcing phases), high-temperature lubricating materials, catalyst carriers, high-temperature heat insulation materials, high-temperature anti-corrosion coating fillers, wear-resistant flooring fillers, and other high-temperature engineering materials and high-tech fields that require aluminum-silica, corundum, or zirconium-containing refractory powders.

[0085] End-to-end baghouse dust collection system: The baghouse dust collection system is a pulse jet baghouse dust collector. The dust collector parameters are: filtration area of ​​200m², filter bag material of polyester needle-punched felt, filtration velocity of 0.8-1.0m / min, pulse jet pressure of 0.5MPa, automatic pulse jet cleaning cycle of once every 30-60 minutes, and dust removal efficiency of ≥99.9%.

[0086] The baghouse dust collection system is connected to the dust collection ports of all dust-generating equipment throughout the entire process via sealed pipes, maintaining the entire production system under negative pressure. All collected dust is reused in production. The entire production system achieves zero dust discharge and zero waste.

[0087] Environmental protection measures during equipment maintenance: All major equipment is equipped with quick-opening maintenance doors, and sealing strips are installed between the maintenance doors and the equipment body. Before maintenance, close the feed valves and discharge valves at the front and rear ends of the equipment. Allow the bag filter system to continue running for 5-10 minutes to remove residual dust from the equipment before opening the maintenance doors. The bag filter system will remain operational during maintenance.

[0088] Electrical automation control system (PLC centralized control system): The start-up and shutdown of all equipment in the entire process, the monitoring of operating parameters, the dust removal control of the bag filter system, and the differential pressure monitoring are all realized through a PLC centralized control system.

[0089] (1) Control host: Siemens S7-1200 series or Mitsubishi FX5U series PLC controller is adopted, and analog input / output modules, digital input / output modules and communication modules are configured. The PLC controller communicates with the controllers, frequency converters and touch screens of each device through PROFINET or CC-Link industrial bus.

[0090] (2) Human-Machine Interface: Equipped with a touch screen of 10 inches or larger, installed on the central control cabinet panel. The touch screen can display the real-time operating status of each piece of equipment, ball mill speed, ball mill current, ball mill cylinder temperature, vibrating screen vibration frequency, vibrating screen amplitude, magnetic separator magnetic field strength, Raymond mill main unit speed, Raymond mill classifier speed, bag filter inlet and outlet pressure difference, bag filter cleaning cycle, air volume at each dust collection point, and material level in the storage tank, etc. The touch screen has a main screen, sub-screens for each section, parameter setting screen, alarm record screen, and historical data screen.

[0091] (3) Variable frequency control: The main equipment such as ball mill, vibrating screen, Raymond mill, screw conveyor, and fan are all equipped with frequency converters. The frequency converters communicate with the PLC controller through PROFINET or CC-Link bus to realize stepless adjustment of equipment speed or air volume.

[0092] (4) Sensor configuration: Ball mill cylinder temperature sensor: Uses a K-type thermocouple. When the temperature exceeds 80℃, the PLC will automatically issue an audible and visual alarm.

[0093] Differential pressure sensors at the inlet and outlet of the bag filter: A micro differential pressure transmitter is used. When the differential pressure exceeds the limit, the cleaning frequency is automatically increased and an alarm is triggered.

[0094] Storage tank level gauge: Ultrasonic or radar level gauges are used.

[0095] Air volume sensors for each dust collection branch pipe: thermal anemometers or Pitot tube anemometers are used, with feedback to regulate the air volume control valve.

[0096] (5) Interlocking control logic: Start-up sequence: bag filter dust collection system → screening equipment → grinding equipment → magnetic separation equipment → feeding equipment.

[0097] Stop sequence: feeding equipment → magnetic separation equipment → grinding equipment → screening equipment → bag filter dust collection system (delay 5-10 minutes).

[0098] Emergency Stop: Press the emergency stop button, and all equipment will stop operating immediately.

[0099] Fault Interlock: If any equipment fails and stops, the upstream equipment will automatically stop feeding.

[0100] (6) Remote monitoring and alarm function: Equipped with an Ethernet communication interface, it can be remotely accessed via computer or mobile APP to view equipment status, process parameters and historical alarms in real time. Alarm information is automatically pushed in case of failure.

[0101] (7) Data recording and quality traceability: Automatically record the process parameters of each batch of production and keep them for no less than 12 months.

[0102] (8) Maintenance Safety Mode: Switch the maintenance equipment to "Maintenance Mode" via the touchscreen. The equipment controller will be locked and cannot be started. An authorized password is required to unlock it.

[0103] Furthermore, the entire process of the method is a physical operation at room temperature, without the use of water, without the generation of wastewater, and without the installation of any high-temperature calcining kilns, heat treatment furnaces, hot air furnaces, or hot air devices.

[0104] Furthermore, the metal materials collected by cascade screening and coarse magnetic separation, as well as the ferromagnetic impurities collected by magnetic separation, all contain valence metal elements and can be used as recycled materials in metal smelting after being briquetted.

[0105] The refractory composite powder finally obtained by this invention has the following chemical composition: Zircon powder surface layer source: Al2O3 content 40%-55%, SiO2 content 35%-50%, ZrO2 content 3%-8%, Fe2O3 content ≤0.5%, CaO content ≤0.5%, MgO content ≤0.5%, total K2O+Na2O content: silica sol waste shell source ≤1.0%, water glass waste shell source ≤2.0%, TiO2 content 0.5%-2%, loss on ignition ≤0.5%.

[0106] Because the zircon powder content in the surface layer of precision casting waste shells naturally fluctuates due to differences in foundry processes, the ZrO2 content of different batches of waste shells may vary between 3% and 8%. This invention achieves differentiated utilization through the following grading system: Each batch of products was sampled before packaging, and the ZrO2 content was detected using X-ray fluorescence spectrometry. The products were then categorized according to the following standards: When the ZrO2 content is 6%-8%, the ratio of mullite to zircon powder is about 7:3. The product is positioned as a high zirconium type anti-adhesion sand aggregate, which is suitable for high-end cast steel coatings with high requirements for anti-adhesion sand performance. When the ZrO2 content is 4%-6%, the ratio of mullite to zircon powder is about 8:2. The product is positioned as a standard anti-sticking sand aggregate, which is suitable for general carbon steel / cast steel coatings. When the ZrO2 content is 3%-4%, the ratio of mullite to zircon powder is about 9:1. The product is positioned as an economical aggregate and is suitable for gray iron / ductile iron coatings and general refractory materials. When the ZrO2 content is ≤3%, the ratio of mullite to zircon powder is approximately 95:5. The product is positioned as a general refractory aggregate and is suitable for unshaped refractory materials such as ramming mixes and castables.

[0107] The zirconium content of the same batch of products fluctuates within ±0.5%. The grading information is marked on the packaging bag and the accompanying inspection report. This grading system ensures that batches with high zirconium content are used for high-end coatings, while batches with low zirconium content are used for ordinary refractory materials, maximizing the utilization of resource value.

[0108] Sources of white fused alumina surface layer: Al2O3 content 55%-75%, SiO2 content 20%-35%, Fe2O3 content ≤0.5%, CaO content ≤0.5%, MgO content ≤0.5%, total K2O+Na2O content: silica sol waste shell source ≤1.0%, water glass waste shell source ≤2.0%, loss on ignition ≤0.5%.

[0109] As can be seen from the above technical solution, compared with the prior art, the present invention has the following technical effects: (1) Comprehensive coverage of binder systems and surface materials: It is applicable to silica sol, water glass, ethyl silicate and other precision casting binder systems, and covers two mainstream surface materials: zircon powder and white corundum.

[0110] The refractory composite powder prepared by this invention, based on its process characteristics of room temperature physical purification, has a product purity suitable for auxiliary materials such as backing sand for precision casting, aggregates for lost foam coatings, aggregates for alcohol-based coatings (carbon steel, cast steel, cast iron parts), and aggregates for unshaped refractory materials.

[0111] It should be noted that the surface layer of precision casting is in direct contact with molten steel, requiring extremely high purity of the aggregate, necessitating the use of pure zircon powder (ZrO2 ≥ 65%) or high-purity corundum powder (Al2O3 ≥ 95%). This area is outside the application scope of the product of this invention. The core of this invention lies in covering the market for auxiliary materials such as backing layers, coatings, and refractory materials, which are used in the largest quantities in precision casting, with extremely low cost and zero-emission environmental advantages, rather than pursuing the ultimate purity at the surface layer level.

[0112] (2) Full-process stepped iron removal: The first step of coarse magnetic separation is combined with the second step of stepped magnetic separation to form an iron removal system that runs through the entire process. The Fe2O3 content of the recycled product is ≤0.5%.

[0113] (3) Full-component tiered recycling: The waste shell is divided into high-purity metal remelting material (purity ≥ 98%), recycled zircon sand, recycled mullite sand and various specifications of refractory composite powder, etc., to achieve zero solid waste discharge.

[0114] (4) Complete elimination of calcination process: no heating throughout the process, complete preservation of active silica components in waste shell, active SiO2 retention rate ≥95%.

[0115] (5) Dry process throughout: No water is used, no wastewater is generated, and no flotation reagents are used.

[0116] (6) Fully enclosed green and environmentally friendly production: dust removal efficiency ≥99.9%, workshop dust concentration ≤10mg / m³ 3 .

[0117] (7) Product particle size is precise and controllable: By adjusting the speed of the Raymond mill classifier, the output particle size can be precisely controlled within the range of 100-1000 mesh.

[0118] (8) The entire process adopts a normal-temperature physical treatment process, completely eliminating the high-temperature calcination stage and eliminating the need for thermal equipment such as kilns, heat treatment furnaces, and hot air systems. The entire process adheres to the principle of "zero chemical addition," eliminating the use of chemical agents and the generation of waste liquid; relying on a fully enclosed negative pressure production system, near-zero dust emissions are achieved (dust removal efficiency ≥99.9%). Through full-component cascade recycling technology, simultaneous zero discharge of solid waste and wastewater is achieved. This technical approach realizes green and low-carbon full-quantity resource recycling. Detailed Implementation

[0119] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0120] Example 1: Full-process production of alcohol-based coating powder (1) Collect 1000kg of stainless steel silica sol 304 precision casting waste shell, containing about 8% stainless steel residue.

[0121] (2) Ball milling: The ball is fed into a fully enclosed ball mill with a high-manganese steel liner on the inner wall of the cylinder. The ball diameter ratio is 25% for 40-60mm, 45% for 25-40mm, and 20% for 15-25mm. The ball-to-material ratio is 3:1, the ball loading rate is 40%, and the rotation speed is 72% of the critical speed. The ball milling time is 25 minutes. During the ball milling process, the external cooling device of the cylinder controls the temperature to not exceed 80℃. Sampling and sieving are performed. If the mass of the material passing through the 60-mesh sieve is 92%, the ball milling has reached its endpoint.

[0122] (3) Step-by-step screening: After ball milling, the material is fed into a linear vibrating screen and passes through 14-mesh, 23-mesh, 36-mesh, 46-mesh, and 60-mesh screens in sequence. Oversize material collection: approximately 25 kg from the 14-mesh screen (96% stainless steel purity), approximately 18 kg from the 23-mesh screen (95% purity), approximately 15 kg from the 36-mesh screen (94% purity), approximately 12 kg from the 46-mesh screen (92% purity), and approximately 10 kg from the 60-mesh screen (87% purity), totaling approximately 80 kg. Undersize material from the 60-mesh screen: approximately 920 kg.

[0123] (4) Coarse magnetic separation: 80kg of the sieve material is fed into a single-drum magnetic separator with a magnetic field strength of 2000 Gauss. About 5kg of ferromagnetic impurities are extracted, and about 75kg of metal particles are extracted after magnetic separation.

[0124] (5) Metal purification: 75 kg of metal particles are fed into a wet ball mill with a ball-to-material ratio of 2.5:1, a grinding concentration of 60%, and a grinding time of 12 minutes. The material after ball milling is fed into a wet shaking table with a table slope of 2.2°, a frequency of 360 times / minute, and a water supply of 1.1 L / min. Approximately 72 kg of high-purity stainless steel particles (purity ≥98%) are collected in the heavy phase, approximately 2 kg of zircon sand is collected in the medium phase, and fine mullite powder from the light phase is recycled into a sedimentation tank with the water flow.

[0125] (6) Cascade magnetic separation: 920 kg of 60-mesh undersize material is fed into a two-stage magnetic separator. The first stage is a drum magnetic separator with a speed of 3500 gauss, and the second stage is a high-intensity magnetic roller separator with a speed of 12000 gauss. Approximately 15 kg of ferromagnetic impurities are collected. The net material after magnetic separation is approximately 905 kg.

[0126] (7) Fine grinding: 905 kg of clean material is fed into the Raymond mill. The main machine rotates at 150 rpm, the classifier rotates at 200 rpm, and the output is 200-300 mesh. The finely ground powder is then sent to the air jet mill for particle shaping. The daily production capacity is about 30 tons. The Raymond mill system operates under full negative pressure in a closed system.

[0127] (8) Finished product packaging: The finished product is collected by a cyclone collector, sealed and packaged to obtain about 900 kg of refractory composite powder for alcohol-based coatings.

[0128] Table 1. Product test results of Example 1

[0129] It is used as an alcohol-based casting coating, resulting in a dense, non-porous coating that dries without cracking and leaves castings with a smooth, sand-free surface.

[0130] Example 2: Performing only the first step produces regenerated mullite. The steps are the same as (1) to (3) of Example 1. Approximately 920 kg of the material passing through the 60-mesh sieve is sold directly as recycled mullite sand. It can be used for core making of cast steel parts, backing sand for precision casting, filling sand for lost foam casting, refractory aggregate, etc.

[0131] Example 3: Preparation of powder for lost foam coating using Raymond mill Based on (1) to (6) of Example 1, the Raymond mill classifier speed was adjusted to 140 rpm, and the output material was 150-200 mesh, yielding approximately 900 kg of refractory composite powder for lost foam coating. When used in lost foam coating, the coating has high strength, good air permeability, does not scorch during casting, and the surface of the casting is smooth and free of sand adhesion.

[0132] Example 4: Comparative Experiment of the Invention and Calcination Process 500 kg of material from the same batch, passing through a 60-mesh sieve, was divided into two groups, A and B. Group A was processed according to the process of this invention (no calcination at room temperature), while Group B was processed according to the traditional process (calcination at 1000℃ for 2 hours). The comparison results are shown in Table 2.

[0133] Table 2 Comparison results between the present invention and the calcination process

[0134] The comparative results show that the present invention is significantly superior to the traditional calcination process in terms of the retention of active components (2.5% vs 0.3%, which is 8.3 times that of the calcination process), iron removal effect and product quality, and the total energy consumption is only 27.7% of that of the calcination process.

[0135] Example 5: Effect of Fe2O3 content on coating performance Four groups of samples with Fe2O3 contents of 0.2%, 0.5%, 1.0%, and 2.0% were prepared to create alcohol-based coatings, which were then cast into 304 stainless steel test blocks. The results are shown in Table 3.

[0136] Table 3. Effect of Fe2O3 content on coating performance

[0137] The results show that the coating performance is excellent when the Fe2O3 content is ≤0.5%, and significantly deteriorates when the Fe2O3 content is >1.0%. The product of this invention has an Fe2O3 content of 0.25%, which is within the excellent range.

[0138] Example 6: Effect of Raymond Mill Classifier Rotation Speed ​​on Discharge Particle Size A Raymond mill was used with a main unit speed of 150 rpm. The effects of different classifier speeds on the output particle size and product application were investigated. The results are shown in Table 4.

[0139] Table 4. Comparison of Classifier Rotation Speed, Discharge Particle Size, and Applications

[0140] Example 7: Effect of different particle size distributions on lost foam coatings The effects of different particle size distributions on the air permeability of lost foam coatings and the surface quality of castings were investigated, and the results are shown in Table 5.

[0141] Table 5. Effect of different particle size distributions on lost foam coatings

[0142] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0143] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for the tiered recycling of all components of precision casting waste shells, characterized in that, Includes the following steps: Step 1, Grinding: The precision casting waste shell is sent into a fully enclosed grinding equipment for room temperature grinding to obtain the grinding product; The waste shell is made by coating layers of silica sol, water glass or ethyl silicate as binders, zircon powder, white corundum powder or a mixture of zircon powder and white corundum powder as surface material, and mullite as back material. After dewaxing and baking, molten metal at 1400℃-1700℃ is poured in. After the casting cools, the waste shell is removed. Step 2, cascade sieving: The ground product is subjected to multi-stage cascade sieving through a fully enclosed sieving device, utilizing the size difference between metal particles and mullite particles to achieve physical separation; the sieving adopts a multi-stage adjustable screen combination, with the basic screen combination including 14 mesh, 23 mesh, 36 mesh, 46 mesh and 60 mesh, and the cutoff point is selected between 40 mesh and 100 mesh; the material under the cutoff mesh is recycled mullite, and the materials over the various mesh sizes are combined and then proceed to Step 3; Step 3, coarse magnetic separation: Send all the oversize material obtained in step 2 into a coarse magnetic separator and perform magnetic separation at room temperature to remove ferromagnetic impurities adhering to the surface of the metal particles and improve the purity of the metal particles. Step 4, stepped magnetic separation for iron removal: The undersize material obtained in Step 2 is fed into the magnetic separation unit for iron removal. At least one step of stepped magnetic separation is performed before fine grinding to remove residual ferromagnetic impurities from the undersize material and obtain clean material. Step 5, fine grinding: The clean material obtained in step 4 is fed into a fully enclosed fine grinding equipment and ground to the target particle size at room temperature. The finely ground powder is then fed into an air jet mill for particle shaping. Step Six: Sieving, Grading and Packaging of Finished Product: The powder product obtained in Step Five is classified by particle size, and the qualified powder is sealed and packaged to obtain the finished refractory composite powder product.

2. The method for the full-component tiered recycling of precision casting waste shells according to claim 1, characterized in that, The molten metal mentioned in step one includes one or more of the following: stainless steel, carbon steel, cast steel, alloy steel, special steel, and high-temperature alloy; The grinding equipment is equipped with sealing connection devices at both the inlet and outlet, and is connected to the bag dust collection system in a sealed manner through pipelines. The grinding equipment is independently selected from any one or any combination of ball mill, rod mill, Raymond mill, vertical mill, tower mill, ring roller mill, vibratory mill, stirred mill, sand mill, mechanical impact crusher, hammer mill, autogenous mill, semi-autogenous mill, or disc mill.

3. The method for the full-component tiered recycling of precision casting waste shells according to claim 2, characterized in that, The grinding equipment is a ball mill; the inner wall of the ball mill cylinder is equipped with wear-resistant liners, the material of which is independently selected from high manganese steel, chromium-molybdenum alloy steel or alumina ceramic; the grinding media are steel balls, which include large balls with a diameter of 40-60mm, medium balls with a diameter of 25-40mm and small balls with a diameter of 15-25mm, with large balls accounting for 20%-30% of the total mass of the steel balls, medium balls accounting for 40%-50%, and small balls accounting for 20%-30%; the ball-to-material ratio is (2-4):1, the ball loading rate is 35%-45% of the effective volume of the ball mill cylinder, and the ball mill speed is 65%-80% of the critical speed.

4. The method for the full-component tiered recycling of precision casting waste shells according to claim 1, characterized in that, The screening equipment mentioned in step two is any one of the following: a fully enclosed linear vibrating screen, a circular vibrating screen, a rotary vibrating screen, a swing screen, a drum screen, or a probability screen. The vibration frequency is 960-1450 times / minute, and the amplitude is 3-6mm. The screen body is covered by a sealed cover made of 304 stainless steel, and each connection surface is equipped with a sealing strip.

5. The method for the full-component tiered recycling of precision casting waste shells according to claim 1, characterized in that, The coarse magnetic separation equipment mentioned in step three is any one of a single-drum magnetic separator, a double-drum magnetic separator, a suspended iron remover, or a magnetic drum, with a magnetic field strength range of 1000-3000 Gauss. This step is carried out at room temperature.

6. The method for the full-component tiered recycling of precision casting waste shells according to claim 1, characterized in that, Step 3 also includes metal purification: the metal particles after coarse magnetic separation are fed into a wet ball mill for secondary ball milling, and then the ball-milled material is fed into a wet shaking table to perform gravity separation by utilizing the density difference of the metals; The ball-to-material ratio is (2-3):1, the ball loading rate is 35%-40% of the effective volume of the cylinder, the ball mill speed is 70% of the critical speed, the ball milling time is 10-15 minutes, the grinding concentration is 60%-65%, and the grinding media are steel balls with a diameter of 15-25mm. The wet shaking table has a surface slope of 1.8°-2.8°, a stroke frequency of 320-400 strokes / minute, and a transverse water flow rate of 0.9-1.3m³. 3 / h, feed concentration 60%-65%.

7. A method for the full-component tiered recycling of precision casting waste shells according to claim 1, characterized in that, In step four, the magnetic separation adopts a two-stage stepped magnetic separation configuration: the first stage of coarse magnetic separation uses a drum magnetic separator with a magnetic field strength of 1000-3000 Gauss; the second stage of fine magnetic separation uses a strong magnetic roller separator or a drawer-type strong magnetic rod box with a surface magnetic induction intensity of 3000-12000 Gauss.

8. A method for the full-component tiered recycling of precision casting waste shells according to claim 1, characterized in that, In step five, the fine grinding equipment is independently selected from any one of the following equipment or any combination thereof: Dry ball mill, Raymond mill, vertical mill, tower mill, ring roller mill, vibratory mill, stirred mill, sand mill, air jet mill, disc mill, colloid mill.

9. The application of recycled mullite sand obtained by the method of full-component tiered recycling of precision casting waste shells as described in any one of claims 1-8 in the molding and core-making sand of cast steel parts, backing sand for precision casting, filling sand for lost foam casting, filling sand for V-process casting, resin sand recycled substitute sand, clay sand substitute sand, original coated sand, substitute material for recycled silica sand for casting, refractory aggregate, refractory castable aggregate, refractory ramming aggregate, refractory plastic aggregate, ladle drainage sand, lean raw material for building ceramic blanks, lean raw material for daily ceramic and sanitary ceramic blanks, high-grade mortar aggregate for building, wear-resistant flooring aggregate, and other industrial fields that require mullite or corundum refractory aggregates.

10. The refractory composite powder prepared by the method of full-component cascade recycling of precision casting waste shells as described in any one of claims 1-8 is used in casting coatings, unshaped refractory materials, refractory bricks, ceramics industry, additive manufacturing, electronic materials, fine chemical fillers, abrasives, friction materials, environmental protection, and high-tech fields.

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