Self-sharpening gas quenching steel slag sand blasting abrasive material and preparation method and cyclic application method thereof

Abstract

The invention discloses a self-sharpening gas quenching steel slag sand blasting abrasive material as well as a preparation method and a cyclic application method thereof. The preparation method comprises the following steps: S1, controlling the alkalinity CaO / SiO of liquid steel slag at the temperature of 1600 DEG C or above to be 1.88-2.08; the liquid steel slag is drained to a gas quenching device, and impact granulation is conducted through high-speed airflow sprayed out of a Laval nozzle; the gas quenching pressure is controlled to be 0.25 to 0.40 MPa, and the Mach number of a spray hole is controlled to be 1.2 to 1.6; and S2, cooling and solidifying the granulated slag drops, and collecting to obtain the self-sharpening gas quenching steel slag sand blasting abrasive. The invention relates to the technical field of industrial solid waste resource utilization and surface treatment. According to the self-sharpening gas quenching steel slag sand blasting grinding material and the preparation method and the cyclic application method thereof, the stability problem is solved, more importantly, enrichment of a high-hardness and wear-resistant iron-containing phase in slag at the edge of slag particles is promoted, a unique hard shell-soft core structure is formed, and self sharpening of the grinding material under impact is achieved.

Description

Technical Field

[0001] This invention relates to the field of industrial solid waste resource utilization and surface treatment technology, specifically to a self-sharpening gas-quenched steel slag blasting abrasive and its preparation and recycling methods. Background Technology

[0002] Steel slag is a major solid waste generated during the steel smelting process, accounting for approximately 10%-15% of crude steel production. Taking China as an example, the annual output of steel slag is enormous, but the comprehensive utilization rate has long been at a low level (about 30%). The large stockpiles of steel slag not only encroach on land resources, but the heavy metal elements in it are also more likely to pose potential ecological risks to soil and groundwater bodies under rainwater leaching, which has become one of the key problems restricting the green development of the steel industry.

[0003] Currently, the mainstream treatment processes for steel slag include hot quenching and hot pouring. While these methods can stabilize the steel slag, they generally suffer from high water consumption, long processing cycles, and failure to recover waste heat. More importantly, the steel slag products obtained by wet processing have low activity, uneven particle size, and high free calcium oxide (f-CaO) content (usually above 3%), resulting in poor volume stability, which severely restricts its high-value-added resource utilization. Such steel slag is mostly used in low-value-added fields such as road construction and backfilling, or requires secondary processing such as crushing and grinding before further use, resulting in unsatisfactory economic and resource efficiency.

[0004] In the surface treatment industry, sandblasting (shot peening) is a key pretreatment process widely used for rust removal, cleaning, roughening, and strengthening (such as improving fatigue strength) of workpiece surfaces. The core consumable material for this process is abrasive. Currently, commonly used abrasives mainly include: Metal abrasives (such as cast steel shot and steel wire cut shot): have good toughness and long service life, but are expensive and are prone to iron contamination (embedded in the matrix) when processing soft metals such as copper and aluminum.

[0005] Natural mineral abrasives (such as quartz sand and olivine): are relatively inexpensive, but generally have low hardness, high breakage rate, and short service life. Furthermore, quartz sand generates serious silica dust hazards during sandblasting, endangering the health of operators.

[0006] Artificial non-metallic abrasives (such as brown fused alumina, white fused alumina, and silicon carbide) have high hardness and strong cutting ability, but they also suffer from high prices and performance issues. In particular, they are relatively brittle and prone to pulverization under high-speed impact, resulting in limited service life per use, high consumption, and high overall cost.

[0007] In addition, whether natural or artificial abrasives, their production process requires the extraction of natural resources or the consumption of large amounts of energy (such as the preparation of corundum by electrofusion, which requires temperatures above 2000℃), and they face resource constraints and carbon emission pressures.

[0008] To address these issues, researchers have begun exploring the use of industrial solid waste as an alternative to traditional abrasives. Steel slag, due to its high-hardness silicate minerals and iron oxides, has shown potential as a sandblasting abrasive. Current research has attempted to use slowly cooled steel slag, after simple crushing and screening, as an abrasive. However, this method has significant drawbacks: Poor performance: Slow-cooled steel slag minerals crystallize fully, with high f-CaO content, and the risk of volume stability has not been fundamentally resolved; its particle morphology is mostly irregular and angular, which causes severe wear on sandblasting equipment (such as nozzles and pipelines); and its internal microstructure is uneven, with poor toughness, weak impact crushing ability, and short cycle service life.

[0009] The process is rough: simple crushing and screening cannot accurately control the particle size distribution and sphericity of the abrasive, resulting in unstable sandblasting effect and difficulty in controlling the surface quality of the workpiece after sandblasting.

[0010] Poor self-sharpening properties: Irregularly shaped crushed particles are mostly broken as a whole during the impact process, making it difficult to form an ideal new sharp cutting edge. The self-sharpening effect is not obvious, and the cleaning efficiency decreases rapidly with the increase of the number of uses.

[0011] Gas-quenched steel slag is produced by quenching and crushing liquid steel slag using a high-pressure gas jet. Studies on the basic properties of gas-quenched steel slag show that it meets the performance requirements for use as abrasive in sandblasting and even exceeds national standards in some aspects. Therefore, it has the potential to be used as abrasive in sandblasting.

[0012] Therefore, this invention proposes a self-sharpening gas-quenched steel slag blasting abrasive, its preparation method, and its recycling method to solve the aforementioned problems. Summary of the Invention

[0013] To address the shortcomings of existing technologies, this invention provides a self-sharpening gas-quenched steel slag blasting abrasive, its preparation method, and its recycling method, thus solving the problems mentioned in the background section.

[0014] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a self-sharpening gas-quenched steel slag blasting abrasive, specifically comprising the following steps: S1. The basicity (CaO / SiO2) of the liquid steel slag at a temperature above 1600℃ is controlled at 1.88-2.08; the liquid steel slag is diverted to an air quenching device and impacted and granulated by high-speed airflow from a Laval nozzle; the air quenching pressure is controlled at 0.25-0.40MPa and the nozzle Mach number is controlled at 1.2-1.6. S2. The granulated slag droplets are cooled and solidified, and collected to obtain self-sharpening gas-quenched steel slag blasting abrasive.

[0015] A self-sharpening gas-quenched steel slag blasting abrasive can be prepared according to the above preparation method.

[0016] A method for recycling self-sharpening gas-quenched steel slag blasting abrasive involves mixing self-sharpening gas-quenched steel slag blasting abrasive of different particle sizes in a certain proportion to obtain a mixed abrasive; using the mixed abrasive for sandblasting the surface of a workpiece; recovering the abrasive after sandblasting, sieving to remove powder, and then adding a small amount of new abrasive for continued recycling; when the average particle size of the abrasive decreases significantly or its performance no longer meets the requirements, the waste abrasive is magnetically separated to recover the iron-rich components. Beneficial effects

[0017] This invention provides a self-sharpening gas-quenched steel slag blasting abrasive, its preparation method, and its recycling method. Compared with the prior art, it has the following advantages: (1) The self-sharpening gas-quenched steel slag blasting abrasive and its preparation and recycling methods, source conditioning and self-sharpening structure design: It is clearly pointed out that gas-quenched steel slag microspheres with the basicity (CaO / SiO2) of liquid steel slag controlled in the range of 1.88-2.08 not only have a large output and controllable product quality, but also reduce the f-CaO content (which can be reduced to below 1.85%, far exceeding the national standard requirement of <4%), solving the stability problem. More importantly, it promotes the enrichment of high-hardness, wear-resistant iron-containing phases (such as magnesium iron spinel and magnetite) in the slag at the edge of the slag particles, forming a unique "hard shell-soft core" structure. This structure is the fundamental reason why the abrasive can "self-sharpen" under impact.

[0018] Amorphous phase control: Through gas quenching and rapid cooling, a large number of amorphous phases (glassy phases) are formed in the slag, which together form a composite structure with the precipitated crystalline phases, jointly determining the overall toughness and crushing behavior of the abrasive.

[0019] Precise control of gas quenching granulation: The key processes for obtaining gas-quenched steel slag microspheres with high sphericity and high bead formation rate were identified, which together ensured that the slag droplets obtained the best cooling rate and flight trajectory, thereby forming spherical abrasives with uniform particle size and controllable defects.

[0020] Based on its self-sharpening properties, different particle sizes are actively mixed and used in a specific ratio. The small particles in the abrasive are responsible for the initial cutting, while the large particles are continuously self-sharpened and broken during recycling, replenishing the medium and small particles. This allows the entire abrasive system to automatically maintain stable cutting ability and service life during the recycling process.

[0021] Recycling and enrichment of valuable elements: This study revealed that after repeated sandblasting, the easily grindable components of the abrasive are consumed, and the wear-resistant iron-containing minerals (such as spinel) in the tailings are further enriched. This not only extends the life of the abrasive but also makes the waste abrasive a high-quality raw material that is easy to recover iron resources through magnetic separation, realizing the full-process resource utilization of "abrasive utilization - tailings value-added". Attached Figure Description

[0022] Figure 1 This is a physical image of the steel slag gas quenching bead forming system of the present invention; Figure 2 This is a schematic diagram of the steel slag gas quenching bead formation process of the present invention; Figure 3 This is a schematic diagram of the parameters for the steel slag gas quenching bead formation test scheme in this invention; Figure 4 This is a schematic diagram illustrating the effect of gas quenching pressure on gas quenching granulation in this invention. Figure 5 This is a schematic diagram illustrating the effect of nozzle Mach number on gas quenching granulation in this invention. Figure 6 A schematic diagram illustrating the effect of slag discharge temperature on gas quenching granulation. Figure 7 This is a schematic diagram of the particle size classification of gas-quenched steel slag in this invention; Figure 8 This is a schematic diagram of the apparent morphology of gas-quenched steel slag in this invention; Figure 9 This is a schematic diagram of the apparent density of air-quenched steel slag in this invention; Figure 10 This is a schematic diagram of the Vickers hardness of air-quenched steel slag in this invention; Figure 11 This is a schematic diagram of the hysteresis loop of gas-quenched steel slag in this invention; Figure 12 This is a schematic diagram of the f-CaO content in the gas-quenched steel slag of the present invention; Figure 13 This is a schematic diagram of the weight loss rate of gas-quenched steel slag under different corrosive environments in this invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Please see Figure 1-2 The present invention provides the following technical solution: a self-sharpening gas-quenched steel slag blasting abrasive, wherein the abrasive is composed of steel slag microspheres prepared by gas quenching; the chemical composition of the steel slag microspheres contains less than 2.0% free calcium oxide (f-CaO) by mass; the steel slag microspheres contain magnesium iron spinel and / or magnetite phases enriched in the particle edge region, and the interior is mainly composed of silicate amorphous phase, forming a "shell-core" structure; the Vickers hardness of the abrasive is not less than 600 HV.

[0025] A method for preparing a self-sharpening gas-quenched steel slag blasting abrasive specifically includes the following steps: S1. The basicity (CaO / SiO2) of the liquid steel slag at a temperature above 1600℃ is controlled at 1.88-2.08; the liquid steel slag is diverted to an air quenching device and impacted and granulated by high-speed airflow from a Laval nozzle; the air quenching pressure is controlled at 0.25-0.40MPa and the nozzle Mach number is controlled at 1.2-1.6. S2. The granulated slag droplets are cooled and solidified, and the steel slag abrasive is collected.

[0026] A method for recycling self-sharpening gas-quenched steel slag blasting abrasive involves mixing gas-quenched steel slag abrasives of different particle sizes in a specific ratio, wherein particles with a diameter of 0.5-1.0 mm account for no less than 80%; applying the mixed abrasive to the surface of a workpiece for blasting; recovering the abrasive after blasting, sieving to remove powder, and then replenishing it with a small amount of new abrasive for continued recycling; when the average particle size of the abrasive decreases significantly or its performance no longer meets requirements, the waste abrasive is magnetically separated to recover its iron-rich components.

[0027] like Figure 2 As shown, liquid slag at a certain temperature is poured out, and the gas quenching and beading system is activated to form beads through gas quenching. The steel slag gas quenching system mainly includes: a small electric arc furnace, a microsphere collection chamber, a control system, a dust removal system, and a gas injection system. This system is fully automated, capable of automatic heating, automatic pouring, and automatic gas injection, and is safe, stable, and highly efficient.

[0028] like Figure 3 and Figure 4 As shown, the key experimental steps for the gas quenching and bead formation test of steel slag are as follows: Equipment inspection: A thorough check of each critical component of the equipment was conducted to ensure safety. Key areas of inspection included furnace lining thickness, graphite crucible thickness, graphite electrode length, circulating cooling water, tilting system, gas injection device, and temperature measurement system. After the molten steel slag reaches the predetermined temperature (1600℃), the graphite electrode rises to the top of the furnace, then the power is cut off, heating is stopped, and the automatic tilting device is activated to pour the molten steel slag along the slag discharge port into the slag flow trough. The furnace body tilts at a uniform speed to ensure a stable flow rate of the molten steel slag. The slag discharge process must be rapid to avoid excessive temperature drop in the molten slag. Gas quenching into beads: Set the nozzle type and blowing pressure of the gas quenching into beads system. Before slag discharge, turn on the gas quenching system. The liquid slag flows from the top of the slag trough to the bottom of the slag trough and falls freely through the flow hole at the bottom of the slag trough. High-pressure blowing gas is injected vertically at high speed into the free-falling slag flow, and the liquid slag gas quenching into beads officially begins. In the slag bead collection process, the downward-flowing liquid slag is subjected to the lateral aerodynamic force of the gas, breaking the liquid slag flow into countless small droplets. These droplets fly in parabolic arcs at a certain speed in different directions and are injected into the microbead collection chamber. During the flight, the steel slag droplets shrink into spheres and rapidly cool down, eventually falling into the microbead collection chamber to form solid microbeads. The microbeads in the collection chamber are then collected for subsequent testing and use.

[0029] The experiment used air as the quenching medium. A gas compressor compressed and pressurized the air to provide a preset pressure. For a given pipe cross-sectional area, the greater the gas pressure and flow rate, the greater the quenching kinetic energy received by the liquid steel slag. Figure 4 and Figure 6 It can be seen that the gas quenching pressure improves both the gas quenching rate and the bead formation rate of steel slag. When the gas quenching pressure increases from 0.25 MPa to 0.35 MPa, the gas quenching rate of steel slag increases from 75% to 81%, an increase of 8%, and the bead formation rate increases from 76.2% to 81.3%, an increase of 6.7%. When the liquid slag is subjected to a greater energy impact, the liquid slag flow is more easily broken up, and the slag droplets travel farther, which is beneficial for the shrinkage and balling of liquid slag droplets and rapid cooling. Although the continuous increase of pressure within a certain range is beneficial to improving the bead formation effect of gas quenching, in the experiment, it was difficult to obtain a stable pressure for a long time when the pressure exceeded 0.35 MPa, and the higher the pressure, the greater the gas quenching noise.

[0030] Reference Figure 5 The Mach number of the nozzle orifice has a certain effect on improving the gas quenching rate and bead formation rate of steel slag. When the Mach number is 1.0, 1.4, and 1.6, the gas quenching rates of steel slag are 73.3%, 78.3%, and 79.8%, respectively. When the Mach number increases from 1.0 to 1.4, the gas quenching rate of steel slag increases from 73.3% to 78.3%, an increase of 7%. When the Mach number increases from 1.4 to 1.6, the gas quenching rate of steel slag increases from 78.3% to 79.8%, an increase of only 2%. As the Mach number further increases, the effect of improving the gas quenching rate of steel slag weakens. With the increase of Mach number, the gas ejected from the nozzle has strong impact kinetic energy, and the liquid slag is broken into smaller droplets, which are more likely to shrink into spheres, improving the bead formation rate. When Ma=1.6, the maximum gas quenching bead formation rate of steel slag is 84.3%.

[0031] Reference Figure 6When the slag discharge temperature was 1500℃, the slag gas quenching was not smooth and was terminated prematurely. Based on the liquid slag temperature drop characteristics described earlier, although this temperature met the gas quenching temperature range, it was found in actual operation that the slag became sticky after cooling. The sticky liquid slag had poor fluidity, and when it flowed to the end of the slag chute orifice, the flow rate was too slow. The liquid slag in the slag chute failed to flow out of the orifice in time for gas quenching and instead overflowed directly from the upper end of the slag chute, preventing further gas quenching. When the molten slag temperature was 1550℃, the liquid slag fluidity improved, and gas quenching could proceed normally, with liquid slag beads successfully entering the slag bead collection chamber. However, slag overflow from the slag chute still occurred in the later stages of gas quenching, resulting in a slag gas quenching rate of only 59% and a bead formation rate of 71.9%. When the slag discharge temperatures were 1600℃ and 1650℃, the slag gas quenching rates were 78.3% and 83.4%, respectively, with bead formation rates of 84.5% and 82.5%, respectively. The above demonstrates that increasing the slag discharge temperature significantly improves the beading effect of steel slag during gas quenching, especially below 1600℃. With increasing slag discharge temperature, both the gas quenching rate and the beading rate of the steel slag rapidly increase. The higher slag discharge temperature raises the superheat temperature of the liquid slag, effectively improving its fluidity and expanding the temperature range within which the steel slag can be gas quenched, thus improving the beading effect. From 1600℃ to 1650℃, the improvement in the beading effect is not significant, showing almost no change. However, heating the steel slag from 1600℃ to 1650℃ during the experiment requires more energy and takes longer, which is not economically viable. Therefore, in this experiment, the slag discharge temperature was set at 1600℃ to ensure the beading effect while maintaining low energy consumption.

[0032] Taking into account the gas quenching effect of steel slag, experimental conditions and energy consumption, the optimal gas quenching bead formation conditions are: gas quenching pressure 0.30-0.35MPa, nozzle Mach number 1.4-1.6, slag discharge temperature ≥1600℃, the gas quenching rate and bead formation rate of steel slag can both reach 80%.

[0033] Reference Figure 7 According to the national standard for sandblasting abrasives GB / T17850.11-2011, abrasive particle size is divided into six grades, which can be reasonably configured according to specific application scenarios. Standard sieves are used to screen air-quenched steel slag, classifying it into six particle size grades. The distribution of the proportion of air-quenched steel slag of each particle size is shown in the figure. The particle size of conventional sandblasting abrasives is usually less than 2.8 mm.

[0034] Reference Figure 8 Only 6.07% of the gas-quenched steel slag has a particle size greater than 2.8 mm, while the proportion of commonly used abrasive particles is 93.93%, of which 18.98% have a particle size less than 0.5 mm, 44.33% have a particle size of 0.5-1 mm, and 20.06% have a particle size of 1-1.4 mm.

[0035] Reference Figure 9 Comparing (b), (c), and (d), it can be seen that although most of the gas-quenched steel slag is spherical, some did not completely form closed spheres during the gas quenching process, resulting in defects such as holes and pits. As shown in Figures (d) and (e), due to the large number of phases present in the gas-quenched steel slag, and the different shrinkage rates of each phase, the surface of the gas-quenched steel slag is not very smooth. During the gas quenching process, affected by factors such as the viscosity and surface tension of the molten slag, small particles adhere together to form particle clusters, as shown in Figure (f).

[0036] Reference Figure 10 The proportion of air-quenched steel slag with Vickers hardness values ​​ranging from 600 to 1000 HV is relatively large, and its overall hardness is higher than the hardness value of glass slides (520.13 HV). That is, the hardness value of air-quenched steel slag is higher than Mohs hardness level 6, which meets the national standard requirements.

[0037] Reference Figure 11 The maximum magnetization of the two particle sizes of gas-quenched steel slag differed significantly. The maximum magnetization of the 0.5–1 mm and 2–2.8 mm particle sizes was approximately ±0.7 emu / g and ±0.3 emu / g, respectively, and the area enclosed by the hysteresis loop of the 0.5–1 mm particle size was larger than that of the 2–2.8 mm particle size. Analysis of the maximum magnetization and hysteresis loop characteristics indicates that under the action of an applied magnetic field, the gas-quenched steel slag exhibits a higher magnetization capacity with increasing magnetic field strength, and the smaller particle size sample shows a stronger magnetic response. During demagnetization, the magnetization of both types of slag decreased rapidly as the external field weakened, exhibiting typical soft magnetic material characteristics.

[0038] Reference Figure 12 The average f-CaO content in gas-quenched steel slag is shown in the figure. During the slow cooling process of the molten steel slag, CaO has ample time to precipitate and aggregate. Furthermore, due to the gradual cooling process, CaO is unlikely to fully react with the silicate phase to form stable calcium silicate minerals (such as C2S and C3S), resulting in a large amount of unreacted CaO remaining in the slag in a free state. In addition, the sufficient crystal growth under slow cooling conditions is conducive to the stable existence of f-CaO crystals. Therefore, the slow cooling process inhibits the solid solution and transformation of CaO mineral phases, ultimately leading to a significant increase in f-CaO content. The f-CaO content of remelted, slowly cooled steel slag is 2.775%, while the f-CaO content of gas-quenched steel slag is between 1.12% and 1.61%, which is at a relatively low level. The f-CaO content increases with increasing particle size, and the smaller the particle size, the higher the cooling rate, indicating that a higher cooling rate has an inhibitory effect on the formation of f-CaO.

[0039] Reference Figure 13The weight loss rate of gas-quenched steel slag was highest in acidic environments, averaging 1.78%, while the average weight loss rates in alkaline and neutral environments were 0.47% and 0.23%, respectively, indicating the weakest resistance to acidic environments. This is because gas-quenched steel slag contains a relatively high amount of alkaline substances. Although amorphous substances constitute a large proportion (over 95%) of the slag after rapid quenching, small amounts of minerals and metallic iron are also present. These substances react with the acidic solution... The reaction enters the solution, causing significant weight loss in the gas-quenched steel slag. In alkaline and near-neutral environments, the gas-quenched steel slag can react with... The amount of reacting substances is relatively small, so the losses are all relatively small.

[0040] Furthermore, any content not described in detail in this specification is existing technology known to those skilled in the art.

[0041] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0042] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a self-sharpening gas-quenched steel slag blasting abrasive, characterized in that: Specifically, the following steps are included: S1. The basicity (CaO / SiO2) of the liquid steel slag at a temperature above 1600℃ is controlled at 1.88-2.08; the liquid steel slag is diverted to an air quenching device and impacted and granulated by high-speed airflow from a Laval nozzle; the air quenching pressure is controlled at 0.25-0.40MPa and the nozzle Mach number is controlled at 1.2-1.

6. S2. The granulated slag droplets are cooled and solidified, and collected to obtain self-sharpening gas-quenched steel slag blasting abrasive.

2. A self-sharpening gas-quenched steel slag blasting abrasive prepared by the preparation method according to claim 1, wherein the abrasive is composed of steel slag microspheres prepared by gas quenching, wherein the mass content of free calcium oxide f-CaO in the chemical composition of the steel slag microspheres is less than 2.0%, wherein the steel slag microspheres contain magnesium iron spinel and / or magnetite phases enriched in the particle edge region, and the interior is mainly composed of silicate amorphous phase, forming a "shell-core" structure, and the Vickers hardness of the abrasive is not less than 600 HV.

3. A method for the cyclic application of the self-sharpening gas-quenched steel slag blasting abrasive as described in claim 2, characterized in that: The self-sharpening gas-quenched steel slag abrasive of different particle sizes is mixed in a certain proportion to obtain a mixed abrasive; the mixed abrasive is used for sandblasting the surface of the workpiece; after sandblasting, the abrasive is recovered, the powder is removed by sieving, and a small amount of new abrasive is added for continued recycling; when the average particle size of the abrasive is significantly reduced or the performance does not meet the requirements, the waste abrasive is magnetically separated to recover the iron-rich component.

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