A ceramic grinding ball using gamma alumina and its preparation method

Abstract

This invention relates to a method for preparing ceramic grinding balls using gamma-alumina, comprising the steps of: pre-grinding, flocculation, pre-firing, coarse grinding, molding, drying, and sintering. The beneficial effects of this invention are: pre-grinding and pre-firing of γ-Al₂O₃, silica, talc, calcium carbonate, and lanthanum oxide reduce the high fineness requirements of the molded powder, resulting in a finer powder; solid solution strengthening of alumina crystals forms a LaAlO₃ solid solution structure, improving mechanical properties; and increasing B... ₂ O ₆ Zn ₃ While providing a glassy phase to lower the temperature required for pre-firing, it can also adsorb free Na in the Al2O3 structure. + To avoid the formation of sodium peraluminate, which affects the final conversion rate of the corundum phase, and to avoid the formation of β-Al2O3, the time for subsequent sintering and densification can be saved. The particles are further finely ground by air jet mill, which enables the spherical blanks to grow rapidly, reduces the difficulty of granulation, saves the time for aging and homogenization, and effectively improves the forming performance of the powder.

Description

Technical Field

[0001] This invention belongs to the field of ceramic industry technology, and particularly relates to a ceramic grinding ball using gamma alumina and its preparation method. Background Technology

[0002] Currently, vertical stirred milling is widely used in secondary grinding and ultrafine grinding. The surface grinding mechanism of the grinding media affects the wear of the grinding media itself and the overall grinding efficiency in high-energy-density working environments.

[0003] More seriously, during the grinding process of large-sized grinding media, most of the grinding beads will develop pits on their surface, and these pits will expand outwards, causing a large amount of the grinding media surface layer to fall off. This results in an uneven surface on the entire grinding bead, causing the unit energy consumption of the grinding bead to gradually increase from a stable state to an exponential increase. Consequently, the power of the grinding equipment drops significantly, thereby reducing the energy utilization rate.

[0004] In addition, fine particles are more prone to self-aggregation during the molding process, and their high specific surface area makes it easy for powder and even ball blanks to adhere to the machine wall, resulting in insufficient rolling and phenomena such as tail beads, out-of-roundness, and core-bound broken balls. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a ceramic grinding ball using gamma alumina and its preparation method.

[0006] A ceramic grinding ball using gamma alumina is composed of the following components: 88-95 wt% γ-Al2O3, 0.5-3 wt% SiO2, 0.5-2 wt% talc, 0.5-2 wt% CaCO3, 0.5-3 wt% B2O6Zn3 and 0.5-2 wt% La2O3.

[0007] The preparation method of this ceramic grinding ball using gamma alumina includes the following steps:

[0008] Step 1, Pre-grinding: Weigh the components according to the proportions of each component in the ceramic grinding ball with gamma alumina as described above, mix them thoroughly to obtain a mixture, and then add the mixture to the ball mill and wet grind with water.

[0009] Step 2, Flocculation: Add flocculant to the slurry obtained from wet grinding in Step 1, and continue wet grinding and stirring in the ball mill for 10-15 minutes to allow the fine particles in the slurry to initially agglomerate, reduce the difficulty of subsequent filter pressing, reduce the possibility of filter breakage, and improve the filter pressing quality.

[0010] Step 3, Filtration: Pump the slurry obtained from ball milling in step 2 into a filter press for dewatering. Control the moisture content of the filter cake obtained from dewatering to 15-30 wt% so that the filter cake has the strength to successfully complete the filtration and sintering process.

[0011] Step 4, Pre-firing: The filter cake is pre-firing at a heating rate of 3-6℃ / min until it reaches 1100-1250℃. The fired filter cake is then held at this temperature for 60-120 minutes. This process can reduce the impact of crystal transformation on subsequent forming and sintering. During the γ-Al2O3 phase transformation, La2O3 can fill the vacant tetrahedral structure in the γ-Al2O3 structure, forming solid solution strengthening. It can also reduce the formation of θ-Al2O3 (monoclinic phase) and avoid excessive growth of internal grains in γ-Al2O3. The increased adsorption effect of B2O6Zn3 on Na can improve the phase transformation rate of the corundum phase and avoid the formation of β-Al2O3.

[0012] Step 5, Coarse Grinding: Use a crusher to crush the low-temperature fired filter cake to a particle size of 3-5 mm, and then use an air jet mill to further grind the particles until the powder D98 fineness is 40-80 μm. After eliminating the static electricity of the powder, collect the ground powder. The advantages of coarse grinding of the filter cake before fine grinding are: it helps to improve the forming performance of the powder itself, and the air jet milling process introduces fewer impurities compared with the conventional ball milling dry grinding process. The temperature of the powder obtained is lower than that of conventional flash drying or spray drying, resulting in better homogenization of the powder, saving aging time and shortening the production cycle.

[0013] Step 6, Shaping: The pre-made spherical seed crystals are put into the rolling mill. While the rolling mill is rotating, water is sprayed in and the powder obtained from the previous crushing and grinding step is added. The powder and the spherical seed crystals are fully bonded and grown to obtain spherical seed crystals with a diameter of 0.36-230 mm. The amount of water sprayed in is such that the moisture content of the grown spherical seed crystals is 13-15 wt% to avoid the spherical seed crystals becoming too dry and losing their roundness or becoming too moist and having a core.

[0014] Step 7, Drying and Sintering: Dry the spherical blanks obtained in Step 6 at 80-120℃ until the moisture content of the blanks reaches 0-1wt% to prevent internal defects from occurring during sintering; then place the blanks into a kiln for drying, heating them to 1350-1450℃ at a rate of 4-6℃ / min, and then holding them at that temperature for 60-100min to obtain ceramic grinding balls with a diameter of 0.3-200mm.

[0015] Preferably, the output fineness of the ball mill during wet grinding with water in step 1 is 5-10 μm.

[0016] As a preferred option: the filter cake obtained by the initial low-temperature calcination in step 4 has a grain size of 0.05 to 2 μm. The grains in the filter cake have been homogenized with the remaining phases, and the alumina grains have been nano-sized.

[0017] Preferably, the flocculant added in step 2 accounts for 0.01 to 0.05 wt% of the total weight of the slurry obtained from wet milling. The flocculant is composed of 75 to 85 wt% polyacrylamide, 5 to 15 wt% chitosan, 5 to 10 wt% fatty acids, and 3 to 5 wt% carboxymethyl cellulose.

[0018] Preferably, the sprayed slurry in step 6 consists of 0.5-1 wt% polyacrylol and 99-99.5 wt% water.

[0019] Preferably, the added polyacrylol has a molecular weight of 80,000 to 150,000 da.

[0020] The beneficial effects of this invention are:

[0021] This invention involves pre-grinding and pre-sintering γ-Al₂O₃, silica, talc, calcium carbonate, and lanthanum oxide to reduce the high fineness requirements of the shaped powder and obtain a coarser powder. While relaxing the ultrafine requirements of pre-grinding, pre-sintering allows La₂O₃ to fill the vacant tetrahedral structure in the γ-Al₂O₃ structure during the phase transformation, enabling solid solution reaction between lanthanum oxide and γ-Al₂O₃ during the phase transition at higher temperatures. This solid solution strengthening of the alumina crystal results in a solid solution structure, LaAlO₃. The Al in the solid solution structure LaAlO₃... 3+ Distributed in octahedral voids, it is more stable than in tetrahedral void structures, thus improving mechanical properties;

[0022] The glassy phase formed at high temperatures in the alumina-silica-magnesium oxide-calcium oxide system of the formulation facilitates ion transfer during sintering; the added B2O6Zn3 not only provides the glassy phase to lower the required pre-sintering temperature, but also adsorbs free Na in the Al2O3 structure. + To avoid the formation of sodium peraluminate which affects the final conversion rate of the corundum phase and to prevent the formation of β-Al2O3, pre-calcination treatment can obtain α-Al2O3 particles with intact size of 0.05-2μm, and pre-combining them with the remaining raw materials, which can save time for subsequent sintering densification.

[0023] This invention employs an air jet mill for further fine grinding of particles, while crushing and air jet milling coarsely grind the material into granules. Dry compressed air causes intense collisions between materials, homogenizing the powder's composition during the air jet milling process. High-temperature drying and high-speed collisions make the powder more porous, reducing the binding force between particles. Therefore, an electrostatic elimination process is introduced to eliminate the charge on the particles, reducing the repulsive force between powder particles. The coarse powder particles are more easily dispersed and adhere to each spherical blank during the forming process, allowing for rapid spherical growth and reducing granulation difficulty. Compared to conventional methods, it eliminates the need for aging and homogenization time, effectively improving the powder's forming performance. The overall production process is shorter than that required for conventional ceramic products. The product of this invention has small grains, a dense structure, high hardness, and good wear resistance. During high-speed self-polishing, the pits do not easily spread outwards, preventing large-area surface peeling, effectively improving the abrasive stability and impact resistance of the grinding media. Detailed Implementation

[0024] The present invention will be further described below with reference to embodiments. The description of the embodiments below is only for the purpose of helping to understand the present invention. It should be noted that those skilled in the art can make several modifications to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0025] Example 1

[0026] A method for preparing impact-resistant ceramic grinding balls using γ-Al2O3 includes the following steps:

[0027] Pre-grinding: The components were mixed in a specific ratio, including 92 wt% γ-Al₂O₃, 3 wt% silica, 2 wt% talc, 1 wt% calcium carbonate, 0.5 wt% zinc borate, and 0.5 wt% lanthanum oxide. The mixture was then added to a ball mill and wet-milled with water. The D98 fineness of the slurry after wet milling was measured to be 7.32 μm.

[0028] Flocculation: Add flocculant to the ground slurry and continue ball milling for 12 minutes. The amount of flocculant added is 0.02 wt% of the slurry mass, and the formula is 75 wt% polyacrylamide, 15 wt% chitosan, 6 wt% fatty acid, and 4 wt% carboxymethyl cellulose.

[0029] Filtration: The slurry is pumped into a filter press for dewatering, and the moisture content of the filter cake is controlled at 19.3 wt%.

[0030] Pre-firing: The material blocks after pressure filtration are subjected to preliminary low-temperature firing. The sintering holding temperature is 1200℃, the sintering heating rate is 4℃ / min, and the temperature is held for 90min after reaching the target temperature.

[0031] Coarse grinding: The burned material blocks are initially crushed using a crusher to a fineness of 4.3 mm. Then, an air jet mill is used to further grind the particles, resulting in a final powder D98 powder fineness of 62.51 μm. After grinding, static electricity on the powder surface is eliminated and the powder is collected and bagged.

[0032] Molding: The pre-formed spherical seed crystals are fed into a roll forming machine. While the machine is rotating, the prepared slurry is sprayed in while the powder obtained from the previous crushing and grinding step is added, allowing the powder to fully adhere to the spherical seed crystals and grow. The final spherical seed crystals have an average diameter of 25.61 mm. The moisture content is controlled at 14.62 wt% during the process. The slurry formulation consists of 0.7 wt% polyacrylamide and 99.3 wt% water. The polyacrylamide used is PVA2099 with a molecular weight of 88,000-101,200.

[0033] Drying and sintering: The spherical blanks were dried at 90℃, resulting in a moisture content of 0.82wt%. They were then fired in a kiln to obtain ceramic spheres. The heating rate was controlled at 4℃ / min, the holding temperature was 1400℃, and the holding time was 100min. The final product was alumina grinding balls with an average diameter of 21.50mm and a specific gravity of 3.81g / cm³. 3 Its Vickers hardness is 1483.2.

[0034] Example 2

[0035] A method for preparing impact-resistant ceramic grinding balls using γ-Al2O3 includes the following steps:

[0036] Pre-grinding: The components were mixed in a specific ratio, including 89 wt% γ-Al₂O₃, 3 wt% silica, 2 wt% talc, 2 wt% calcium carbonate, 2 wt% zinc borate, and 2 wt% lanthanum oxide. The mixture was then added to a ball mill and wet-milled with water. The D98 fineness of the slurry after wet milling was measured to be 5.13 μm.

[0037] Flocculation: Add flocculant to the ground slurry and continue ball milling for 15 minutes. The amount of flocculant added is 0.04 wt% of the slurry mass, and the formula is 83 wt% polyacrylamide, 9 wt% chitosan, 6 wt% fatty acids, and 2 wt% carboxymethyl cellulose. Filtration: Pump the slurry into a filter press for dewatering, and control the moisture content of the filter cake to 16.2 wt%.

[0038] Pre-firing: The material blocks after pressure filtration are subjected to preliminary low-temperature firing. The sintering holding temperature is 1150℃, the sintering heating rate is 5℃ / min, and the temperature is held for 90min after reaching the target temperature.

[0039] Coarse grinding: The burned material is initially crushed using a crusher to a fineness of 3.7 mm. Then, an air jet mill is used to further grind the particles, resulting in a final powder D98 powder fineness of 54.89 μm. After grinding, static electricity on the powder surface is eliminated and the powder is collected and bagged.

[0040] Molding: The pre-formed spherical seed crystals are fed into a roll forming machine. While the machine is rotating, the prepared slurry is sprayed in while the powder obtained from the previous crushing and grinding step is added, allowing the powder to fully adhere to the spherical seed crystals and grow. The final spherical seed crystals have an average diameter of 12.08 mm. The moisture content is controlled at 13.04 wt% during the process. The slurry formulation consists of 0.9 wt% polyacrylamide and 99.1 wt% water. The polyacrylamide used is PVA2899, with a molecular weight of 123200-132000.

[0041] Drying and sintering: The spherical blanks were dried at 90℃, resulting in a moisture content of 0.33wt%. They were then fired in a kiln to obtain ceramic spheres. The heating rate was controlled at 6℃ / min, the holding temperature was 1360℃, and the holding time was 90min. The final product was alumina grinding balls with an average diameter of 10.02mm and a specific gravity of 3.84g / cm³. 3 Its Vickers hardness is 1412.8.

[0042] Example 3

[0043] A method for preparing impact-resistant ceramic grinding balls using γ-Al2O3 includes the following steps:

[0044] Pre-grinding: The components were mixed in a specific ratio, including 90 wt% γ-Al₂O₃, 1.5 wt% silica, 2 wt% talc, 1.5 wt% calcium carbonate, 3 wt% zinc borate, and 2 wt% lanthanum oxide. The mixture was then added to a ball mill and wet-milled with water. The D98 fineness of the slurry after wet milling was measured to be 8.54 μm.

[0045] Flocculation: Add flocculant to the ground slurry and continue ball milling for 10 minutes. The amount of flocculant added is 0.01 wt% of the slurry mass, and the formula is 79 wt% polyacrylamide, 7 wt% chitosan, 10 wt% fatty acid, and 4 wt% carboxymethyl cellulose.

[0046] Filtration: The slurry is pumped into a filter press for dewatering, and the moisture content of the filter cake is controlled at 27.5 wt%.

[0047] Pre-firing: The material blocks after pressure filtration are subjected to preliminary low-temperature firing. The sintering holding temperature is 1180℃, the sintering heating rate is 6℃ / min, and the temperature is held for 120min after reaching the target temperature.

[0048] Coarse grinding: The burned material is initially crushed using a crusher to a fineness of 4.2 mm. Then, an air jet mill is used to further grind the particles, resulting in a final powder D98 powder fineness of 72.64 μm. After grinding, static electricity on the powder surface is eliminated and the powder is collected and bagged.

[0049] Molding: The pre-formed spherical seed crystals are fed into a roll forming machine. While the machine is rotating, the prepared slurry is sprayed in while the powder obtained from the previous crushing and grinding step is added, allowing the powder to fully adhere to the spherical seed crystals and grow. The final spherical seed crystals have an average diameter of 60.57 mm. The moisture content is controlled at 14.82 wt% during the process. The slurry formulation consists of 0.5 wt% polyacrylamide and 99.5 wt% water. The polyacrylamide used is PVA2488, with a molecular weight of 101200-110000.

[0050] Drying and sintering: The spherical blanks were dried at 100℃, resulting in a moisture content of 0.49 wt%. They were then fired in a kiln to obtain ceramic spheres. The heating rate was controlled at 4℃ / min, the holding temperature was 1430℃, and the holding time was 60 min. The final product was alumina grinding balls with an average diameter of 10.02 mm and a specific gravity of 3.80 g / cm³. 3 Its Vickers hardness is 1464.2.

[0051] In conjunction with Examples 1 to 3 above, the impact-resistant ceramic grinding balls prepared by the method of the present invention exhibit the following characteristics during grinding under high energy density conditions: as the grinding time increases, the pits gradually become more numerous and deeper, while the non-pits gradually become larger, and large-area wear occurs as the pits connect with each other. Overall, the balls possess good impact resistance and performance stability.

Claims

1. A method for preparing ceramic grinding balls using gamma alumina, characterized in that, Includes the following steps: Step 1, Pre-grinding: Weigh out the specified weights of each component material according to the following formula: 88-95 wt% γ-Al2O3, 0.5-3 wt% SiO2, 0.5-2 wt% talc, 0.5-2 wt% CaCO3, 0.5-3 wt% B2O6Zn3 and 0.5-2 wt% La2O3. Mix them thoroughly to obtain a mixture, and then add the mixture to a ball mill and wet grind with water. Step 2, Flocculation: Add flocculant to the slurry obtained from wet milling in Step 1, and continue wet milling and stirring in a ball mill for 10-15 minutes; the added flocculant accounts for 0.01-0.05 wt% of the total weight of the wet milled slurry, and the flocculant is composed of 75-85 wt% polyacrylamide, 5-15 wt% chitosan, 5-10 wt% fatty acids and 3-5 wt% carboxymethyl cellulose; Step 3, Filtration: Pump the slurry obtained from ball milling in Step 2 into a filter press for dewatering. Control the moisture content of the filter cake obtained from dewatering to 15-30 wt%. Step 4, Pre-firing: The filter cake is pre-firing at a low temperature with a heating rate of 3-6℃ / min until the filter cake reaches 1100-1250℃. Then, the fired filter cake is kept at this temperature range for 60-120 min. Step 5, crushing and coarse grinding: crush the filter cake after low-temperature firing to a particle size of 3-5 mm, and then use an air jet mill to further grind the particles until the fineness of the powder D98 is 40-80 μm; Step 6, Shaping: The pre-made spherical seed crystals are fed into a roll forming machine. While the roll forming machine is rotating, slurry is sprayed in while the powder obtained from the previous crushing and grinding step is added. The powder and the spherical seed crystals are fully bonded and grown to obtain a grown spherical seed crystal with a diameter of 0.36–230 mm. The amount of water sprayed is such that the moisture content of the grown spherical seed crystal is 13–15 wt%. Step 7, Drying and Sintering: Dry the spherical blanks obtained in Step 6 at 80-120℃ until the moisture content of the spherical blanks reaches 0-1wt%; then put the spherical blanks into a kiln for drying, and heat them to 1350-1450℃ at a rate of 4-6℃ / min, and then hold them for 60-100min to obtain ceramic grinding balls with a diameter of 0.3-200mm.

2. The method for preparing ceramic grinding balls using gamma alumina according to claim 1, characterized in that: In step 1, when water is added for wet grinding, the output fineness of the ball mill is 5-10 μm.

3. The method for preparing ceramic grinding balls using gamma alumina according to claim 1, characterized in that: The grain size of the filter cake obtained by the initial low-temperature firing in step 4 is 0.05-2 μm.

4. The method for preparing ceramic grinding balls using gamma alumina according to claim 1, characterized in that: The slurry sprayed in step 6 consists of 0.5-1 wt% polyacrylol and 99-99.5 wt% water.

5. The method for preparing ceramic grinding balls using gamma alumina according to claim 4, characterized in that: The molecular weight of the added polyacrylol is 80,000 to 150,000 da.

6. A ceramic grinding ball using gamma alumina prepared by the method described in claim 1, characterized in that, It is composed of the following components: 88–95 wt% γ-Al₂O₃, 0.5–3 wt% SiO₂, 0.5–2 wt% talc, 0.5–2 wt% CaCO₃, 0.5–3 wt% B₂O₆Zn₃, and 0.5–2 wt% La₂O. 3。