Wet process reverse grading process for superfine and ultralight hollow glass beads

Abstract

The invention discloses a wet reverse grading process for superfine and ultralight hollow glass beads, and belongs to the technical field of superfine and ultralight powder screening. Comprising the following steps: step 1, mixing superfine and ultralight hollow glass beads to be graded with water to prepare slurry; 2, conveying the slurry, maintaining the slurry below a screen immersed in water, and stirring and dispersing the slurry in the area; enabling the hollow glass beads with the particle size smaller than the aperture of the screen mesh to upwards penetrate through the screen mesh; and 3, fine powder located above the screen and coarse powder located below the screen are collected respectively, dewatering and drying are conducted in sequence, and graded products are obtained. The buoyancy of water is used as core power, the characteristics of the superfine and ultralight hollow glass beads are fully matched, accurate classification can be achieved on the premise that the intact structure and performance of the beads are guaranteed, modification can be synchronously completed or the effect is improved through circulation classification, and a practical and reliable technical scheme is provided for high-end application of the hollow glass beads.

Description

Technical Field

[0001] This invention belongs to the field of ultrafine and ultralight powder sieving technology, specifically, it relates to a wet reverse classification process for ultrafine and ultralight hollow glass microspheres. Background Technology

[0002] Hollow glass microspheres are micron-sized, hollow, spherical inorganic non-metallic materials filled with inert gas. They are characterized by low density, high strength, low thermal conductivity, and chemical stability. The true density of commercially available hollow glass microspheres typically ranges from 0.1 to 0.7 g / cm³. 3 The particle size distribution ranges from approximately 10 to 300 μm. In recent years, with the rapid development of downstream application technologies, higher and more refined requirements have been placed on the performance of hollow glass microspheres. Industrially produced hollow glass microspheres typically exhibit a broad unimodal normal particle size distribution, but different application fields have drastically different specific requirements for their particle size distribution: for example, in paints and coatings, different spraying processes have strict limitations on the maximum particle size of the added powder; in solid buoyancy materials, to balance buoyancy and mechanical properties, microspheres with smaller particle sizes need to be selected at the same density; in thermal insulation composite materials, to achieve the best lightweight effect, microspheres of different particle sizes need to be precisely graded according to the close packing theory. Therefore, efficient, high-precision, and non-destructive grading of hollow glass microspheres is an indispensable prerequisite for meeting these high-end applications.

[0003] Currently, the main mature methods for classifying hollow glass microspheres in the industry include rotary vibratory sieving and cyclone sieving.

[0004] Vibratory sieving technology (as described in patent CN101530845A) is a traditional dry sieving method. Its principle relies primarily on the powder's own gravity; through the periodic vibration of the screen box, the material undergoes a jumping motion on the screen surface, allowing particles smaller than the screen aperture to pass through and become the undersize, while larger particles are discharged as the oversize. However, hollow glass microspheres have extremely low density. When used for fine sieving of 300 mesh or larger (aperture approximately 50 μm and below), the microspheres easily adhere to the screen mesh due to static electricity, adsorption, and other reasons, leading to severe screen clogging. Even with the aid of an ultrasonic screen cleaning device, the sieving efficiency remains very low, especially for sieving with even lower density or higher mesh sizes. Here, sieving efficiency is defined as the percentage of the mass of the target particle size powder obtained after sieving relative to the total mass of the target particle size powder in the raw material.

[0005] Cyclone sieving technology (such as that represented by patent CN101108380A) improves sieving capacity to a certain extent. This method uses compressed air to atomize and fluidize the powder on the sieve surface, and forces fine particles through the synergistic effect of negative pressure and gravity. Its sieving effect is superior to that of a vibrating sieve, achieving sieving of meshes above 400 mesh. However, a significant drawback of this method is that the high-speed airflow causes frequent collisions between the microspheres and the sieve with high energy, easily leading to structural damage and breakage of the hollow glass microspheres (see...). Figure 1 This alters the screen's density and performance integrity; at the same time, intense friction significantly shortens the screen's lifespan.

[0006] In addition, some wet classification schemes have emerged in existing technologies (such as CN119588502A and CN213103254U), which use water as a medium to disperse microspheres, alleviating the problems of screen clogging and dust. However, these wet technologies generally adopt a "forward sieving" mode, in which the slurry is located above the screen, and the particles are forced downward through the screen holes by gravity or external force. This method fails to fully utilize the characteristic that the density of hollow glass microspheres is much lower than that of water, and fails to effectively convert the buoyancy of water into the main driving force for the target microspheres to pass through the screen. Therefore, there is still considerable room for improvement in classification efficiency and accuracy, and it fails to fundamentally solve the industry problems of low screening efficiency and potential damage of fine particles.

[0007] In summary, developing a sieving method that can efficiently and accurately classify microspheres while completely avoiding mechanical damage to ultrafine and ultralight hollow glass microspheres has become a key technological bottleneck that urgently needs to be overcome in this field. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a wet reverse grading process for ultrafine and ultralight hollow glass microspheres.

[0009] The objective of this invention can be achieved through the following technical solutions: A wet reverse grading process for ultrafine, ultralight hollow glass microspheres includes the following steps: Step 1: Prepare slurry: Mix the ultrafine and ultralight hollow glass microspheres to be graded with water to prepare a slurry of 5-10 wt%. Step 2: Buoyancy screening: The slurry is conveyed and maintained below a screen submerged in water, while the slurry is stirred and dispersed in this area; hollow glass microspheres with a particle size smaller than the screen aperture pass upward through the screen. In this step, the entire screening system is placed in water, with the screen submerged below the water level. The hollow glass microsphere slurry is conveyed to the area below the screen via a conveying device and fully dispersed by a stirring device. Because the surface of the unmodified hollow glass microspheres is hydrophilic, the microspheres disperse very well in water. Under the influence of buoyancy, the water carries the fine powder of hollow glass microspheres smaller than the screen aperture onto the screen, achieving separation of ultralight powder particles by size. Buoyancy is the main driving force for screening; the microspheres in water are simultaneously subjected to a downward force of their own weight G and an upward force of buoyancy F. The force analysis is shown in [link to force analysis]. Figure 2 When the size of the microspheres is constant, the buoyant force F is a constant value. The lower the density, the greater the upward net force. Therefore, hollow glass microspheres with lower density have better effects. If wet modification of hollow glass microspheres is required, a modifier can be added to the water, and the modification can be completed during the sieving process.

[0010] Step 3: Collection and post-processing: Collect the fine powder above the sieve and the coarse powder below the sieve, and dehydrate and dry them in sequence to obtain the graded product.

[0011] In a more optimized manner, if the powder is not completely screened, a cyclic classification step may be included: the coarse powder collected below the screen in step 3 is reconstituted into a slurry with a mass fraction of 5-10 wt%, and returned to step 2 for cyclic classification until the target fine powder is completely screened.

[0012] Ideally, the modifier is a silane coupling agent.

[0013] Ideally, the mesh size of the screen is 400 mesh or higher.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention employs a wet reverse sieving design, using the buoyancy of water as the core driving force for microsphere classification. Combined with the hydrophilic properties of the microspheres themselves, this ensures excellent dispersion of the microspheres in water, effectively avoiding screen clogging common in traditional sieving processes and ensuring smooth classification. Simultaneously, the buoyancy-driven classification method ensures gentle stress on the microspheres during sieving, preventing damage to the hollow structure of the microspheres caused by high-speed collisions or severe friction, thus protecting the structural integrity of the product. The process allows for the re-slurrying and recycling of the coarse powder remaining after sieving, further optimizing the sufficiency of classification and enhancing the practicality of the process. Furthermore, this process allows for the simultaneous addition of modifiers during sieving to achieve wet modification, eliminating the need for additional modification steps, simplifying the production process, and reducing operational complexity. The overall process design is scientifically sound and highly adaptable to the classification of ultrafine, ultralight hollow glass microspheres, especially those with a mesh size of 400 or larger, achieving precise, gentle, and efficient classification results, providing a stable and reliable material basis for subsequent applications. Attached Figure Description

[0015] The invention will now be further described with reference to the accompanying drawings.

[0016] Figure 1 This is a diagram showing the broken state of hollow glass microspheres after sieving by a cyclone screen. Figure 2 A schematic diagram illustrating the force analysis of ultrafine, ultralight hollow glass microspheres in water; Figure 3 This is a flow chart of the wet reverse grading process for ultrafine and ultralight hollow glass microspheres in an embodiment of the present invention. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1: A wet reverse classification process for ultrafine and ultralight hollow glass microspheres, comprising the following steps (process flow as follows) Figure 3 (as shown) Basic parameters of ultrafine and ultralight hollow glass microspheres to be graded: Model 46P8000; True density 0.46 g / cm³ 3 Particle size distribution: D50 = 20.1 μm, D90 = 42.5 μm; Powder content at 500 mesh: 80.2%; Step 1: Prepare slurry: Take the 46P8000 hollow glass microspheres to be graded, mix them with deionized water, stir evenly, and prepare a slurry with a mass fraction of 10wt%. Step 2: Buoyancy Screening: Use a 500-mesh screen and place the entire screening system in deionized water, ensuring the screen is completely submerged. Use a pump to deliver the prepared slurry to the area below the screen, while simultaneously starting the mixing equipment to continuously stir and disperse the slurry to prevent micro-bead aggregation. Under the action of buoyancy, fine powder with a particle size smaller than the 500-mesh screen aperture will pass upward through the screen, while coarse powder with a particle size larger than the screen aperture will remain below the screen. Step 3: Collection and post-processing: The fine powder slurry above the screen and the coarse powder slurry below the screen are collected separately by scraper. The two slurries are then introduced into filter bags and dehydrated by centrifugal dewatering machine. After being placed in a drying oven, they are dried at 80°C for 4 hours to obtain the graded fine powder product and coarse powder by-product.

[0019] A vibrating sieve was used to screen the ultrafine and ultralight hollow glass microspheres to be classified. A cyclone sieve was used to screen the ultrafine and ultralight hollow glass microspheres to be classified. The specific screening data obtained are shown in Table 1: Table 1 As shown in Table 1, when the wet reverse grading process was used to grade 46P8000 hollow glass microspheres to a 500-mesh size in this embodiment, the true density of the microspheres remained at 0.46 g / cm³. 3 No breakage was observed, and the screening efficiency reached 92%.

[0020] In contrast, when using a traditional vibrating screen for classification under the same conditions, severe screen clogging occurred, resulting in a screening efficiency of only 23%. Although no microspheres were broken, the separation effect was extremely poor. However, when using a cyclone screen for classification under the same conditions, the screening efficiency reached 86%, but hollow glass microspheres broke, and the density of the fine powder increased to 0.51 g / cm³. 3 This disrupts the original structure of the microspheres.

[0021] Example 2: A wet reverse classification process for ultrafine and ultralight hollow glass microspheres, comprising the following steps (process flow as follows) Figure 3 (as shown) Basic parameters of ultrafine, ultralight hollow glass microspheres to be graded: Model: 32P3500; True density: 0.32 g / cm³ 3 Particle size distribution: D50=28.2μm, D90=50.2μm; Powder content at 400 mesh: 72.3%; Step 1: Prepare slurry: Take the 32P3500 hollow glass microspheres to be graded, mix them with deionized water, stir evenly, and prepare a slurry with a mass fraction of 8wt%. Step 2: Buoyancy Screening: Select a 400-mesh screen and place the screening system in deionized water, ensuring the screen is completely submerged; add modifier KH560 to the water at a rate of 1% of the microsphere mass; use a pump to transport the slurry to the area below the screen, start the mixing equipment to disperse the slurry, and use buoyancy to drive fine powder particles smaller than the 400-mesh screen to float through the screen, while coarse powder remains below the screen; Step 3: Collection and post-processing: The fine powder slurry above the screen and the coarse powder slurry below the screen are collected by scraper, filtered by filter bag, centrifuged and dehydrated (3000 r / min, 15 min), and dried at 100℃ for 3 hours to obtain the graded fine powder product and unmodified coarse powder.

[0022] A vibrating sieve was used to screen the ultrafine and ultralight hollow glass microspheres to be classified. A cyclone sieve was used to screen the ultrafine and ultralight hollow glass microspheres to be classified. The specific screening data obtained are shown in Table 2: Table 2 As shown in Table 2, when the wet reverse grading process was used to grade 32P3500 hollow glass microspheres to 400 mesh in this embodiment, the true density of the microspheres remained at 0.32 g / cm³. 3 No breakage was observed, and the screening efficiency reached 94%.

[0023] In contrast, when using a traditional vibrating screen for classification under the same conditions, severe screen clogging occurred, resulting in a screening efficiency of only 18%. Although no microspheres were broken, the separation effect was extremely poor. However, when using a cyclone screen for classification under the same conditions, the screening efficiency reached 88%, but hollow glass microspheres broke, and the density of the fine powder increased to 0.36 g / cm³. 3 This disrupts the original structure of the microspheres.

[0024] Example 3: A wet reverse classification process for ultrafine and ultralight hollow glass microspheres, comprising the following steps (process flow as follows) Figure 3 (as shown) Basic parameters of ultrafine, ultralight hollow glass microspheres to be graded: Model: 15P500; True density: 0.15 g / cm³ 3 Particle size distribution: D50=40.6μm, D90=67.5μm; Powder content at 400 mesh: 49.5%; Step 1: Prepare slurry: Take the 15P500 hollow glass microspheres to be graded, mix them with deionized water, stir and disperse them to prepare a slurry with a mass fraction of 5wt%. Step 2: Buoyancy screening: Select a 400-mesh screen, place the screening system in water, and submerge the screen; transport the slurry to the bottom of the screen, start the stirring equipment to continuously disperse it, avoid the agglomeration of ultrafine particles, and use buoyancy to make fine powder with a particle size smaller than the 400-mesh screen pass through the screen and float to the surface, while coarse powder remains at the bottom of the screen. Step 3: Collection and post-processing: Collect the fine powder slurry on the sieve and the coarse powder slurry under the sieve separately by scraping, collect them by filter bag, centrifuge (2800 r / min, 20 min), and dry at 90℃ for 5 hours to obtain primary fine powder product and coarse powder.

[0025] A vibrating sieve was used to screen the ultrafine and ultralight hollow glass microspheres to be classified. A cyclone sieve was used to screen the ultrafine and ultralight hollow glass microspheres to be classified. The specific screening data obtained are shown in Table 3: Table 3 As shown in Table 3, when the wet reverse grading process was used to grade 15P500 hollow glass microspheres at a mesh size of 400, the true density of the microspheres remained at 0.15 g / cm³. 3No breakage was observed, and the screening efficiency reached 95%.

[0026] In contrast, when using a traditional vibrating screen for classification under the same conditions, severe screen clogging occurred, resulting in a screening efficiency of only 10%. Although no microspheres were broken, the separation effect was extremely poor. However, when using a cyclone screen for classification under the same conditions, the screening efficiency reached 83%, but hollow glass microspheres broke, and the density of the fine powder increased to 0.21 g / cm³. 3 This disrupts the original structure of the microspheres.

[0027] In summary, the wet reverse grading process of this invention utilizes the buoyancy of water as its core driving force, perfectly suited to the characteristics of ultrafine and ultralight hollow glass microspheres. It overcomes the clogging problem of traditional vibrating screens and avoids the microsphere breakage issue caused by cyclone screens. This process achieves a sieving efficiency of 92%-95%, enabling precise grading while preserving the integrity of the microsphere structure and performance. It also allows for simultaneous modification or improved efficiency through cyclic grading, providing a practical and reliable technical solution for high-end applications of hollow glass microspheres.

[0028] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0029] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A wet reverse grading process for ultrafine, ultralight hollow glass microspheres, characterized in that, Includes the following steps: Step 1: Prepare slurry: Mix the ultrafine and ultralight hollow glass microspheres to be graded with water to prepare a slurry of 5-10 wt%. Step 2: Buoyancy screening: The slurry is conveyed and maintained below a screen submerged in water, while the slurry is stirred and dispersed in this area; Hollow glass microspheres with a particle size smaller than the sieve mesh size are allowed to pass upward through the sieve mesh; Step 3: Collection and post-processing: Collect the fine powder above the sieve and the coarse powder below the sieve, and dehydrate and dry them in sequence to obtain the graded product.

2. The wet reverse grading process for ultrafine, ultralight hollow glass microspheres according to claim 1, characterized in that, It may also include a cyclic classification step: the coarse powder collected below the screen in step 3 is reconstituted into a slurry with a mass fraction of 5-10 wt%, and returned to step 2 for cyclic classification.

3. The wet reverse grading process for ultrafine, ultralight hollow glass microspheres according to claim 1, characterized in that, In step 2, a modifier is added to the water.

4. The wet reverse grading process for ultrafine, ultralight hollow glass microspheres according to claim 3, characterized in that, The modifier is a silane coupling agent.

5. The wet reverse grading process for ultrafine, ultralight hollow glass microspheres according to claim 1, characterized in that, The mesh size of the sieve is 400 mesh or higher.

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