A method for total thermal debinding of zirconia ceramic injection-molded preforms
By using a mixture of nano-carbon powder and submicron alumina powder as embedding powder in zirconia ceramic injection molding, the environmental and efficiency issues of solvent degreasing in zirconia ceramic injection molding are solved, and efficient binder removal and improved green body integrity are achieved.
Patent Information
- Application Number
- CN202311335275.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-10-16
- Publication Date
- 2025-10-31
- Estimated Expiration
- 2043-10-16
AI Technical Summary
In existing zirconia ceramic injection molding processes, solvent debinding involves long solvent removal times, swelling, cracking, and environmental issues. Traditional hot debinding is slow, has a low yield, and is prone to deformation and cracking, especially large-sized preforms which are prone to breakage after debinding.
A C/Al2O3 mixed powder is formed by mixing nano-carbon powder and submicron alumina powder, which is used as a embedding powder for total thermal degreasing. By controlling the heating rate and atmosphere during the thermal degreasing process, uneven distribution and flow of the binder are avoided. The binder is adsorbed by capillary action. Combined with appropriate heating rate and holding time, uniform evaporation and decomposition of the binder are achieved.
It achieves efficient binder removal, avoids defects such as bubbling and cracking of the green body, improves the integrity and yield of large-size green bodies, and reduces environmental pollution and costs.
Smart Images
Figure CN117362029B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of ceramic injection molding, and specifically relates to a method for total thermal debinding of zirconia ceramic injection molded preforms. Background Technology
[0002] Ceramic injection molding is a precision manufacturing process for ceramic parts. Compared with other ceramic preparation technologies, it can rapidly produce complex, irregularly shaped parts with small volume, complex shapes, and high dimensional accuracy. Zirconia ceramics have advantages such as high hardness, high toughness, high flexural strength, low coefficient of friction, strong corrosion resistance, no static electricity, high temperature resistance, and excellent thermal insulation properties, making them widely used in the automotive, medical device, and optical communication fields.
[0003] The preparation process of injection-molded zirconia ceramics mainly includes four stages: feedstock preparation, injection molding, debinding, and sintering. The feedstock consists of zirconia ceramic powder and an organic binder. The binder is a complex mixture, including a soluble binder and a framework binder. The soluble binder is usually a wax or other low-molecular-weight polymer, which functions to improve the rheological properties of the raw materials and surfactants. The framework binder is usually a polyethylene or polypropylene resin, which plays a supporting role during the debinding process. Before sintering, the organic matter inside the injection-molded preform must be removed using appropriate processes without damaging the preform's structure and shape. Therefore, the debinding process is a key step in the preparation of injection-molded zirconia ceramics. Currently, the most commonly used debinding process for injection-molded zirconia ceramic parts (especially those with a minimum size greater than 2mm) is a two-step debinding method combining solvent debinding and thermal debinding. However, solvent debinding has many disadvantages: ① it increases the time required for solvent removal; ② it easily causes swelling, leading to preform cracking; ③ the organic solvents are toxic and environmentally unfriendly, requiring recycling and increasing costs. Currently, in an era that calls for ecological and environmental protection, the total heat degreasing process that does not use solvent degreasing is of great significance.
[0004] Traditional thermal debinding processes have advantages such as mature theoretical development, simple process, low cost, and no need for special equipment. However, they also have disadvantages such as slow debinding speed, long debinding time, low yield (products are prone to deformation, blistering, cracking, and collapse), and long production cycles. Therefore, simply heating the injection-molded preform to remove the binder often results in defects such as blistering and cracking, leading to debinding failure. This is especially true for larger and thicker preforms (over 2mm), where breakage after debinding is a common phenomenon. Summary of the Invention
[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for hot debinding of zirconia ceramic injection-molded preforms by embedding powder.
[0006] The present invention adopts the following technical solution:
[0007] Step (1): Use a ball mill to mix nano-carbon powder and submicron alumina powder evenly to obtain C / Al2O3 mixed powder; the mass ratio of nano-carbon powder to submicron alumina powder is 1:(0.42~2.33); the median diameter of submicron alumina powder is larger than that of nano-carbon powder;
[0008] Step (2): Mix zirconia powder and binder, and injection mold to obtain zirconia blank. Then embed the zirconia blank in the C / Al2O3 mixed powder obtained in step (1) and perform thermal degreasing in air. The mass ratio of zirconia powder to binder is (85.5~87.5):(12.5~14.5).
[0009] Step (3): After hot degreasing is completed, the green body is removed from the powder.
[0010] Preferably, the median diameter of the nano-carbon powder is 20–50 nm, and the median diameter of the submicron alumina powder is 300–500 nm.
[0011] Preferably, in step (1), the ball milling time is 8 to 12 hours, the ball mill speed is 100 to 200 rpm / min, and the ball-to-material ratio (the mass ratio of material to grinding media in the ball mill) is 2:1 to 1:1.
[0012] Preferably, the adhesive in step (2) comprises paraffin wax and polyethylene.
[0013] Preferably, the powder thickness in step (2) is 2-5 mm.
[0014] Preferably, the heating conditions for heat degreasing in step (2) are as follows: heating to 130°C at a heating rate of 5°C / min, then heating to 200°C at a heating rate of 0.5°C / min, then heating to 230°C at a heating rate of 0.1°C / min, and holding at 230°C for 60–120 min; then heating to 550°C at a heating rate of 1°C / min, and finally holding at 550°C for 60–180 min. More preferably, heating to 130°C at a heating rate of 5°C / min, then heating to 200°C at a heating rate of 0.5°C / min, then heating to 230°C at a heating rate of 0.1°C / min, and holding at 230°C for 60 min; then heating to 550°C at a heating rate of 1°C / min, and finally holding at 550°C for 120 min.
[0015] Compared with the prior art, the present invention has the following advantages:
[0016] (1) It does not use the traditional solvent degreasing process, saving organic solvent consumption, reducing costs and reducing environmental pollution.
[0017] (2) The embedded powder full-heat degreasing process can precisely control the removal rate of the binder during the hot degreasing process, reducing defects such as bubbling and cracking. Specifically, it involves precisely configuring composite C / Al2O3 powder with appropriate proportions and particle size distribution. C is nano-sized, and Al2O3 powder is submicron-sized, which can form a good particle size distribution. Strong capillary adsorption will form between the carbon nanoparticles, which essentially changes the distribution state of the organic binder melt on the surface of the green body during the hot degreasing process, including the content of liquid organic binder and the concentration of gaseous products, thereby adsorbing the organic binder molten at low temperature from the green body.
[0018] This invention employs a compounding process using submicron alumina particles. The interleaved distribution of larger alumina powder particles and smaller nano-carbon powder particles provides greater interparticle spacing, facilitating the continued evaporation and decomposition of the binder melt adsorbed in the capillaries between the carbon particles. Therefore, by compounding two powders of different particle sizes, the strong capillary force and adsorption of the binder melt by the smaller powder particles can be simultaneously utilized, along with the advantages of the larger particle size particles, which promote binder evaporation and decomposition. This avoids the problems of uneven gas phase distribution and difficulty in releasing gas phase decomposition products, leading to cracking of the green body, which often result from small interparticle spacing in a single particle size compound.
[0019] (3) The use of powder embedding process is beneficial to improve the integrity of the sample. For larger blanks, powder embedding can make the temperature and atmosphere environment of the blank more stable and uniform. On the other hand, it can also support the blank and prevent the zirconium oxide particles in the blank from moving and rearranging over a large distance during the softening and melting flow of the binder, thereby causing deformation defects.
[0020] (4) In order to cooperate with the powder embedding process and give full play to the melting and adsorption process, the hot degreasing process adopts the method of slowing down the heating rate of the low temperature section below 230°C. This allows the binder to be fully adsorbed into the powder embedding before the binder evaporates or decomposes, preventing the binder from flowing and agglomerating after melting, and avoiding the formation of bubbles and pores at the high temperature degreasing temperature in the later stage. Attached Figure Description
[0021] Figure 1 The image shows the surface morphology of the injection-molded strip after degreasing in Example 1.
[0022] Figure 2 The surface morphology of the degreased injection molding strip in Comparative Example 1 is shown.
[0023] Figure 3 The surface morphology of the degreased injection molding strip in Comparative Example 2 is shown.
[0024] Figure 4 To compare the surface morphology of the degreased injection molding strip in Example 3.
[0025] Figure 5 To compare the surface morphology of the degreased injection molding strip in Example 4. Detailed Implementation
[0026] The present invention will be further described below with reference to specific embodiments, but the methods and technical parameters involved in the solution should not be construed as limitations on the present invention.
[0027] This invention provides a method for thermal debinding of zirconia ceramic injection-molded preforms, comprising: preparation of C / Al2O3 mixed powder and thermal debinding.
[0028] The thermal degreasing process in this embodiment of the invention is as follows:
[0029] Heat to 130℃ at a heating rate of 5℃ / min, then to 200℃ at a heating rate of 0.5℃ / min, then to 230℃ at a heating rate of 0.1℃ / min, and hold at 230℃ for 60–120 min; then heat to 550℃ at a heating rate of 1℃ / min, and finally hold at 550℃ for 60–180 min.
[0030] Test method for degreasing rate: After the extrusion injection molding process, the injection preform is obtained and then degreased for a certain period of time to remove the binder.
[0031] The formula for calculating the defatting rate is as follows:
[0032] P=(M1-M2) / M (1)
[0033] Where M1 represents the mass of the injection-molded preform before degreasing, in g; M2 represents the mass of the injection-molded preform after degreasing, in g; and M represents the total mass of the binder contained in the preform, in g.
[0034] Example 1
[0035] 14g of nano-carbon powder (D50 = 20nm) and 6g of submicron alumina powder (D50 = 300nm) were weighed into a ball mill jar, and 40g of alumina grinding balls were added. The mixture was ball-milled at 100rpm / min for 8 hours using a planetary ball mill to obtain a uniformly mixed C / Al2O3 powder. A rectangular preform with a zirconium oxide content of 87.5% was prepared by injection molding. The preform dimensions were 78.67mm in length, 9.77mm in width, and 3.81mm in height. The preform was weighed.
[0036] The injection-molded preform was then embedded in a C / Al2O3 powder bed, with a powder thickness of 2 mm on the upper surface of the preform. The temperature was raised to 550℃ according to the aforementioned thermal degreasing process parameters. During the heating process, the preform was held at 230℃ for 60 min and at 550℃ for 120 min, respectively. After the 550℃ holding period, the preform was removed from the powder bed, its surface defects were observed, and its mass was weighed. The degreasing rate of the preform was calculated according to formula (1). The surface condition and degreasing rate of the preform are shown in Table 1. A surface diagram of the preform is shown in [reference needed]. Figure 1 .
[0037] Example 2
[0038] 10g of nano-carbon powder (D50 = 20nm) and 10g of submicron alumina powder (D50 = 300nm) were weighed into a ball mill jar, and 40g of alumina grinding balls were added. The mixture was ball-milled at 100rpm / min for 8 hours using a planetary ball mill to obtain a uniformly mixed C / Al2O3 powder. A rectangular preform with a zirconium oxide content of 87.5% was prepared by injection molding. The preform dimensions were: length 78.67mm, width 9.77mm, and height 3.81mm. The preform was weighed.
[0039] The injection-molded preform was then embedded in a C / Al2O3 powder bed, with a powder thickness of 2 mm on the upper surface. The temperature was raised to 550℃ according to the aforementioned thermal degreasing process parameters. During the heating process, the preform was held at 230℃ for 60 min and at 550℃ for 120 min. After the 550℃ holding period, the preform was removed from the powder bed, its surface defects were observed, and its mass was weighed. The degreasing rate of the preform was calculated according to formula (1). The surface condition and degreasing rate of the preform are shown in Table 1.
[0040] Example 3
[0041] 6g of nano-carbon powder (D50 = 20nm) and 14g of submicron alumina powder (D50 = 300nm) were weighed into a ball mill jar, and 40g of alumina grinding balls were added. The mixture was ball-milled at 100rpm / min for 8 hours using a planetary ball mill to obtain a uniformly mixed C / Al2O3 powder. A rectangular preform with a zirconium oxide content of 87.5% was prepared by injection molding. The preform dimensions were 78.67mm in length, 9.77mm in width, and 3.81mm in height. The preform was weighed.
[0042] The injection-molded preform was then embedded in a C / Al2O3 powder bed, with a powder thickness of 2 mm on the upper surface. The temperature was raised to 550℃ according to the aforementioned thermal degreasing process parameters. During the heating process, the preform was held at 230℃ for 60 min and at 550℃ for 120 min. After the 550℃ holding period, the preform was removed from the powder bed, its surface defects were observed, and its mass was weighed. The degreasing rate of the preform was calculated according to formula (1). The surface condition and degreasing rate of the preform are shown in Table 1.
[0043] Example 4
[0044] 14g of nano-carbon powder (D50 = 50nm) and 6g of submicron alumina powder (D50 = 500nm) were weighed into a ball mill jar, and 20g of alumina grinding balls were added. The mixture was ball-milled at 200rpm / min for 12h using a planetary ball mill to obtain a uniformly mixed C / Al2O3 powder. A rectangular preform with a zirconium oxide content of 87.5% was prepared by injection molding. The preform dimensions were 78.67mm in length, 9.77mm in width, and 3.81mm in height. The preform was weighed.
[0045] The injection-molded preform was then embedded in a C / Al2O3 powder bed, with a powder thickness of 5 mm on the upper surface of the preform. The temperature was raised to 550℃ according to the aforementioned thermal degreasing process parameters. During the heating process, the preform was held at 230℃ for 120 min and at 550℃ for 60 min. After the 550℃ holding period, the preform was removed from the powder bed, its surface defects were observed, and its mass was weighed. The degreasing rate of the preform was calculated according to formula (1). The surface condition and degreasing rate of the preform are shown in Table 1.
[0046] Example 5
[0047] 14g of nano-carbon powder (D50 = 50nm) and 6g of submicron alumina powder (D50 = 500nm) were weighed into a ball mill jar, and 20g of alumina grinding balls were added. The mixture was ball-milled at 200rpm / min for 12h using a planetary ball mill to obtain a uniformly mixed C / Al2O3 powder. A rectangular preform with a zirconium oxide content of 87.5% was prepared by injection molding. The preform dimensions were 78.67mm in length, 9.77mm in width, and 3.81mm in height. The preform was weighed.
[0048] The injection-molded preform was then embedded in a C / Al2O3 powder bed, with a powder thickness of 5 mm on the upper surface of the preform. The temperature was raised to 550℃ according to the aforementioned thermal degreasing process parameters. During the heating process, the preform was held at 230℃ for 60 min and at 550℃ for 180 min. After the 550℃ holding period, the preform was removed from the powder bed, its surface defects were observed, and its mass was weighed. The degreasing rate of the preform was calculated according to formula (1). The surface condition and degreasing rate of the preform are shown in Table 1.
[0049] Example 6
[0050] 14g of nano-carbon powder (D50 = 20nm) and 6g of submicron alumina powder (D50 = 300nm) were weighed into a ball mill jar, and 40g of alumina grinding balls were added. The mixture was ball-milled at 100rpm / min for 8 hours using a planetary ball mill to obtain a uniformly mixed C / Al2O3 powder. A rectangular preform with a zirconium oxide content of 85.5% was prepared by injection molding. The preform dimensions were 78.67mm in length, 9.77mm in width, and 3.81mm in height. The preform was weighed.
[0051] The injection-molded preform was then embedded in a C / Al2O3 powder bed, with a powder thickness of 2 mm on the upper surface. The temperature was raised to 550℃ according to the aforementioned thermal degreasing process parameters. During the heating process, the preform was held at 230℃ for 60 min and at 550℃ for 120 min. After the 550℃ holding period, the preform was removed from the powder bed, its surface defects were observed, and its mass was weighed. The degreasing rate of the preform was calculated according to formula (1). The surface condition and degreasing rate of the preform are shown in Table 1.
[0052] Comparative Example 1 (without embedded C / Al2O3 powder)
[0053] A rectangular preform with a zirconium oxide content of 87.5% was prepared by injection molding. The preform dimensions were 78.67 mm in length, 9.77 mm in width, and 3.81 mm in height. Its mass was measured.
[0054] Then, the injection-molded preform was heated to 550℃ according to the aforementioned thermal degreasing process parameters. During the heating process, it was held at 230℃ for 60 min and at 550℃ for 120 min. After the holding time at 550℃, the preform was removed from the powder-embedded container, its surface defect status was observed, and its mass was weighed. The degreasing rate of the preform was calculated according to formula (1). The surface status and degreasing rate of the preform are shown in Table 1. The surface image of the preform is shown in Table 1. Figure 2 .
[0055] Comparative Example 2 (with embedded C powder)
[0056] 20g of nano-carbon powder (D50 = 20nm) was weighed into a ball mill jar, and 40g of alumina grinding balls were added. The mixture was ball-milled for 8 hours at 100rpm / min using a planetary ball mill to obtain dispersed carbon powder. A rectangular preform with a zirconium oxide content of 87.5% was prepared by injection molding. The preform dimensions were: length 78.67mm, width 9.77mm, and height 3.81mm. The preform was weighed.
[0057] The injection-molded preform was then embedded in a C-powder bed, with a powder thickness of 2 mm on the upper surface. The preform was heated to 550°C according to the aforementioned thermal degreasing process parameters. During the heating process, it was held at 230°C for 60 min and at 550°C for 120 min. After the 550°C holding period, the preform was removed from the powder bed, its surface defects were observed, and its mass was weighed. The degreasing rate of the preform was calculated according to formula (1). The surface condition and degreasing rate of the preform are shown in Table 1. A surface diagram of the preform is shown in [reference needed]. Figure 3 .
[0058] Comparative Example 3 (Al2O3 powder embedded)
[0059] 20g of submicron alumina powder (D50 = 300nm) was weighed into a ball mill jar, and 40g of alumina grinding balls were added. The mixture was ball-milled at 100rpm / min for 8 hours using a planetary ball mill to obtain a uniformly mixed Al2O3 powder. A rectangular preform with a zirconium oxide content of 87.5% was prepared by injection molding. The preform dimensions were: length 78.67mm, width 9.77mm, and height 3.81mm. The preform mass was then measured.
[0060] The injection-molded preform was then embedded in a bed of Al2O3 powder, with a powder thickness of 2 mm on the upper surface of the preform. The temperature was raised to 550℃ according to the aforementioned thermal degreasing process parameters. During the heating process, the preform was held at 230℃ for 60 min and at 550℃ for 120 min, respectively. After the 550℃ holding period, the preform was removed from the powder bed, its surface defects were observed, and its mass was weighed. The degreasing rate of the preform was calculated according to formula (1). The surface condition and degreasing rate of the preform are shown in Table 1. A surface diagram of the preform is shown in [Figure 1]. Figure 4 .
[0061] Comparative Example 4 (Rapid Heating)
[0062] 14g of nano-carbon powder (D50 = 20nm) and 6g of submicron alumina powder (D50 = 300nm) were weighed into a ball mill jar, and 40g of alumina grinding balls were added. The mixture was ball-milled at 100rpm / min for 8 hours using a planetary ball mill to obtain a uniformly mixed C / Al2O3 powder. A rectangular preform with a zirconium oxide content of 87.5% was prepared by injection molding. The preform dimensions were 78.67mm in length, 9.77mm in width, and 3.81mm in height. The preform was weighed.
[0063] The injection-molded preform is then embedded in a C / Al2O3 powder bed, with a powder thickness of 2 mm on the upper surface of the preform, and thermal debinding is performed according to the following process:
[0064] Heat to 130°C at a heating rate of 5°C / min, then to 200°C at a heating rate of 1°C / min, and finally to 230°C at a heating rate of 0.2°C / min.
[0065] The billet was removed from the powder-burying chamber, its surface defects were observed, and its mass was weighed. The degreasing rate of the billet was calculated according to formula (1). The surface condition and degreasing rate of the billet are shown in Table 1. The surface diagram of the billet is shown in [reference needed]. Figure 5 .
[0066] Table 1. Surface condition and degreasing rate of the preforms in the examples and comparative examples.
[0067] Surface condition Degreasing rate (%) Example 1 O 99.4 Example 2 O 99.5 Example 3 O 99.7 Example 4 O 99.4 Example 5 O 99.9 Example 6 O 99.2 Comparative Example 1 *** 99.8 Comparative Example 2 * 98.7 Comparative Example 3 ** 99.2 Comparative Example 4 *** 62.3
[0068] ***: Numerous and obvious cracks.
[0069] **: Few cracks, but noticeable.
[0070] *: Cracks are few and not obvious.
[0071] O: No visible cracks.
[0072] From Table 1 and Appendix Figure 1-5 It can be seen that by embedding C / Al2O3 powder and using an appropriate degreasing process, injection-molded zirconia preforms without visible cracks can be obtained, with a degreasing rate of over 99% at 550℃. If only Al2O3 powder or C powder is embedded, the surface of the preform after degreasing will have more defects; when the heating rate is fast below 230℃, the degreasing temperature only reaches 230℃, and severe defects such as cracks and blistering appear on the surface of the preform.
Claims
1. A method for total thermal debinding of zirconia ceramic injection-molded preforms, characterized in that, The method includes the following steps: Step (1): Use a ball mill to mix nano-carbon powder and submicron alumina powder evenly to obtain C / Al2O3 mixed powder; the mass ratio of nano-carbon powder to submicron alumina powder is 1:(0.42~2.33); the median diameter of the submicron alumina powder is larger than the median diameter of the nano-carbon powder; the median diameter of the nano-carbon powder is 20~50 nm, and the median diameter of the submicron alumina powder is 300~500 nm; Step (2): Mix zirconia powder and binder, and injection mold to obtain zirconia preform; then embed the zirconia preform into the C / Al2O3 mixed powder obtained in step (1), and perform thermal degreasing in air; the mass ratio of zirconia powder to binder is (85.5~87.5):(12.5~14.5); the heating conditions for thermal degreasing are: heating to 130℃ at a heating rate of 5℃ / min, then heating to 200℃ at a heating rate of 0.5℃ / min, then heating to 230℃ at a heating rate of 0.1℃ / min, and holding at 230℃ for 60~120min; then heating to 550℃ at a heating rate of 1℃ / min, and finally holding at 550℃ for 60~180min.
2. The method according to claim 1, characterized in that, In step (1), the ball milling time is 8 to 12 hours and the ball mill speed is 100 to 200 rpm / min.
3. The method according to claim 1, characterized in that, In step (1), the ball-to-material ratio is (1-2):
1.
4. The method according to claim 1, characterized in that, The adhesive mentioned in step (2) includes paraffin wax and polyethylene.
5. The method according to claim 1, characterized in that, In step (2), the powder thickness is 2-5 mm.
6. The method according to claim 1, characterized in that, The heating conditions for thermal defatting in step (2) are as follows: Heat to 130℃ at a heating rate of 5℃ / min, then to 200℃ at a heating rate of 0.5℃ / min, then to 230℃ at a heating rate of 0.1℃ / min, and hold at 230℃ for 60 min; then heat to 550℃ at a heating rate of 1℃ / min, and finally hold at 550℃ for 120 min.