Binder for powder injection molding, feeding material and injection molding method

Abstract

The present invention relates to a binder for powder injection molding, a feed material and an injection molding method, and belongs to the field of powder injection molding, wherein the binder comprises 24-46% of water, 20-30% of a skeleton agent, 30-40% of polydopamine, 2-3% of a dispersant, and 2-3% of a lubricant in percentage by weight. The feed material comprises a uniformly mixed powder and a binder for powder injection molding. The powder injection molding process using the binder and the feed material can reduce the use of organic matter, reduce environmental pollution and safety risks, because water is used as a binder. At the same time, due to the good fluidity and permeability of water, the filling and uniformity of the metal slurry can be improved, thereby improving the quality and precision of the molding. In addition, the cost of water itself is low. Since the evaporation temperature of water is low, the time for dehydration, degreasing and sintering can be reduced, saving costs.

Description

Technical Field

[0001] The present invention relates to the field of powder injection molding, in particular to a binder for powder injection molding, a feeding material and an injection molding method. Background Art

[0002] Metal powder injection molding technology is to evenly mix metal powder with an organic binder, granulate it, inject it into the mold cavity under heated plasticization state, and solidify it into shape. Then, the binder in the molded blank is removed by chemical or thermal decomposition method, and finally the final product is obtained by sintering and densification.

[0003] During the feed preparation and injection process, the choice of binder has a significant impact on the injection process, degreasing process, and product appearance and size. Currently, plastic-based binders are the predominant binder in powder injection molding processes. However, in powder injection molding processes, the various binder components of plastic-based binders are exposed to high temperatures and oxidation during mixing or injection, inevitably leading to some deterioration and decomposition. Although the deterioration problem can be alleviated by adding antioxidants, polyoxymethylene still easily decomposes during mixing and injection, emitting a pungent formaldehyde odor. This problem is particularly pronounced when the feed requires mixing and injection at high temperatures, greatly damaging workers' health. Furthermore, the current plastic-based binders have low fluidity, which can easily cause damage to equipment such as molds and screws.

[0004] Therefore, it is necessary to develop a new binder system in order to reduce or eliminate the use of organic substances such as polyoxymethylene, thereby reducing environmental pollution and safety risks. Summary of the Invention

[0005] The first purpose of the present invention is to provide a binder for powder injection molding, which is free from existing plastic-based binders and eliminates the use of polyformaldehyde. At the same time, it can reduce the process difficulty and energy consumption of the injection and degreasing links, which is conducive to reducing environmental pollution and safety risks.

[0006] The technical solution for achieving the first object of the present invention is: the binder for powder injection molding in the present invention includes 24-46% water, 20-30% skeleton agent, 30-40% polydopamine, 2-3% dispersant, and 2-3% lubricant in percentage by weight.

[0007] The water content in the binder is directly proportional to the polydopamine content. Polydopamine can bind to water through hydrogen bonds. The more polydopamine there is, the more water molecules it can bind. Furthermore, due to the presence of a large amount of catechol and primary and secondary amines in its structure, polydopamine possesses exceptionally strong binding forces, allowing it to firmly bind the various components in the binder to the metal powder.

[0008] Furthermore, the polydopamine is prepared by polymerizing dopamine in a Tris-HCl buffer at room temperature for 24 hours.

[0009] Furthermore, the pH of the Tris-HCl buffer is 8.5, and the concentration is 50-100 mg / ml. Under these conditions, dopamine undergoes a cyclization reaction to form an indole structure, thereby forming polydopamine.

[0010] The second object of the present invention is to provide a feed material for powder injection molding, which has good powder uniformity and fluidity, and can use lower injection temperature, mold temperature and injection pressure during injection, thereby ensuring product molding quality and precision.

[0011] The technical solution for achieving the second object of the present invention is as follows: the feedstock for powder injection molding of the present invention comprises a uniformly mixed powder and the aforementioned binder for powder injection molding; the binder accounts for 30% to 70% of the feedstock by volume, with the remainder being powder. Within this range, the feedstock has a moderate viscosity and is suitable for injection. If the binder ratio is below this range, the metal powder content is excessive, resulting in a weak bond between the metal powder and the binder. If the binder ratio exceeds this range, the density of the injected green body is low, which can lead to collapse and deformation during degreasing, excessive dimensional shrinkage after sintering, and poor dimensional stability.

[0012] The present invention utilizes the strong interaction between polydopamine and components such as the skeleton agent, powder, and lubricant to uniformly mix the various components in the feed. At the same time, a large amount of polydopamine and the skeleton agent are cross-linked to form a three-dimensional network structure, which can make the water molecules more firmly bonded to the entire binder system and also provide a certain strength for the subsequent injection molding.

[0013] Furthermore, the powder is 316L stainless steel powder or 17-4PH stainless steel powder.

[0014] A third object of the present invention is to provide a powder injection molding process that utilizes the aforementioned powder injection molding feed material to achieve lower injection temperature, mold temperature, and injection pressure during injection, thereby ensuring product quality and precision while reducing mold and screw wear and saving energy. Furthermore, due to the lower evaporation temperature of water during the degreasing process, the degreasing time and difficulty can be shortened, eliminating the need for complex catalytic degreasing processes such as nitric acid and oxalic acid, and reducing water usage costs.

[0015] The technical solution for achieving the third object of the present invention is: the powder injection molding process of the present invention comprises the following steps:

[0016] S1. Feed material preparation: preparing the above-mentioned feed material for powder injection molding;

[0017] S2. Molding: placing the powder injection molding feed prepared in step S1 into a powder injection molding machine, and preparing an injection blank by injection molding; wherein during injection, the injection pressure is 60-140 MPa, the injection speed is 50-200 mm / s, and the injection temperature is 60-130° C.;

[0018] S3, drying: placing the injection blank into an oven for dehydration to evaporate the water and obtain a dried blank;

[0019] S4, degreasing: degreasing the dried blank to form a degreased blank;

[0020] S5. Sintering: placing the degreased blank in a continuous sintering furnace and sintering it to obtain a sintered blank.

[0021] Furthermore, in the above step S3, the temperature of the oven used for drying the moisture is 70-100°C, and the drying time is 1-4 hours. At this temperature and time, water can be decomposed at an appropriate rate. Below this range, the decomposition speed is too slow and takes too long. Above this range, the decomposition speed is too fast, resulting in defects such as bulging in the product.

[0022] Furthermore, in the above step S4, the degreased blank is placed in a continuous sintering furnace and sintered in a H2 atmosphere to obtain a sintered blank; the sintering temperature T is controlled at 1170-1390°C, and the holding time is 2-2.5 hours.

[0023] The present invention has positive effects: (1) The binder in the present invention eliminates the use of organic substances such as polyformaldehyde, thereby reducing environmental pollution and safety risks.

[0024] (2) After the binder of the present invention is used in the feed preparation, the water content in the binder is directly proportional to the polydopamine content. Polydopamine can bind to water in the form of hydrogen bonds. The more polydopamine there is, the more water it can bind. In addition, due to the presence of a large amount of catechol and primary and secondary amines in the polydopamine structure, polydopamine has a super strong binding force that can firmly bind the various components in the binder and the metal powder together. In addition, the structural stability and uniformity of the injection blank can be further improved by using ingredients such as skeleton agents, dispersants, and lubricants, providing favorable conditions for product injection molding.

[0025] (3) The binder in the present invention utilizes the characteristics of water, namely, the good fluidity and permeability of water, thereby improving the filling and uniformity of the feed, and can use lower injection temperature, mold temperature and injection pressure during injection, and can ensure the quality and precision of product molding. At the same time, in the subsequent degreasing process, due to the low evaporation temperature of water, the degreasing time and difficulty can be shortened, and there is no need to use complex processes such as nitric acid and oxalic acid for catalytic degreasing, and the cost of water use is low. The above factors all prove that using water as a component of the binder can save production energy and time, and improve the economic benefits of the enterprise. DETAILED DESCRIPTION

[0026] (Example 1)

[0027] The binder for powder injection molding in the present invention comprises water, a skeleton agent, polydopamine, a dispersant and a lubricant.

[0028] The specific proportions of the binder are as follows (by weight percentage):

[0029]

[0030] The higher the proportion of polydopamine, the more water it can bind, the better the fluidity of the feed, the lower the pressure and temperature required during the injection process, and the better the appearance and dimensional stability of the product.

[0031] The polydopamine was prepared by polymerizing dopamine in a Tris-HCl buffer (pH=8.5, 80 mg / ml) at room temperature for 24 hours.

[0032] The feed material in the present invention includes uniformly mixed 316L stainless steel powder and the above-mentioned binder; the binder accounts for 65% by volume, and the 316L stainless steel powder accounts for 35% by volume.

[0033] The powder injection molding process of the present invention comprises the following steps:

[0034] S1, preparing the above feed;

[0035] S2, placing the feed prepared in step S1 into a powder injection molding machine, injecting it into the mold cavity at an appropriate pressure and injection speed, and cooling it to form the mold;

[0036] S3, drying and degreasing: drying the injection blank to remove moisture and then thermally degreasing to form a degreased blank;

[0037] S4, sintering: placing the degreased blank in a continuous sintering furnace and sintering to obtain a sintered blank.

[0038] In step S2, during injection, the feed material prepared in step S1 is placed in a powder injection molding machine, injected into a mold cavity under an injection pressure of 80 MPa and an injection temperature of 80° C., and cooled to form;

[0039] In step S3, the preform obtained by injection molding is dried to remove moisture and then thermally degreased to form a degreased preform. The temperature of the oven is 70-100° C. and the drying time is 1-4 hours.

[0040] In step S4, the degreased blank is placed in a continuous sintering furnace and sintered in a H2 atmosphere to obtain a sintered blank; the sintering temperature T is controlled at 1380°C and the holding time is 2 hours.

[0041] The appearance of the sintered blank prepared in this embodiment is smooth as a whole without flow lines or cracks.

[0042] The test data of the sintered blank prepared in this embodiment are shown in the following table:

[0043]

[0044] (Example 2)

[0045] The binder for powder injection molding in the present invention comprises water, a skeleton agent, polydopamine, a dispersant and a lubricant.

[0046] The specific proportions of the binder are as follows (by weight percentage):

[0047]

[0048] The polydopamine was prepared by polymerizing dopamine in Tris-HCl buffer (pH=8.5, 60 mg / ml) at room temperature for 24 hours.

[0049] The feed material in the present invention comprises uniformly mixed 316L stainless steel powder and a binder; the binder accounts for 60% by volume and the powder accounts for 40% by volume.

[0050] The powder injection molding process of the present invention comprises the following steps:

[0051] S1, preparing the above feed;

[0052] S2, placing the feed prepared in step S1 into a powder injection molding machine, injecting it into the mold cavity at an appropriate pressure and injection speed, and cooling it to form the mold;

[0053] S3, drying and degreasing: drying the injection blank to remove moisture and then thermally degreasing to form a degreased blank;

[0054] S4, sintering: placing the degreased blank in a continuous sintering furnace and sintering to obtain a sintered blank.

[0055] In step S2, during injection, the feed material prepared in step S1 is placed in a powder injection molding machine, injected into a mold cavity under an injection pressure of 100 MPa and an injection temperature of 90° C., and cooled to form;

[0056] In step S3, the preform obtained by injection molding is dried to remove moisture and then thermally degreased to form a degreased preform. The temperature of the oven is 70-100° C. and the drying time is 1-4 hours.

[0057] In step S4, the degreased blank is placed in a continuous sintering furnace and sintered in a H2 atmosphere to obtain a sintered blank; the sintering temperature T is controlled at 1380°C and the holding time is 2.5 hours.

[0058] The appearance of the sintered blank prepared in this embodiment is smooth as a whole without flow lines or cracks.

[0059] The test data of the sintered blank prepared in this embodiment are shown in the following table:

[0060]

[0061] (Example 3)

[0062] The binder for powder injection molding in the present invention comprises water, a skeleton agent, polydopamine, a dispersant and a lubricant.

[0063] The specific proportions of the binder are as follows (by weight percentage):

[0064]

[0065] The polydopamine was prepared by polymerizing dopamine in a Tris-HCl buffer (pH=8.5, 80 mg / ml) at room temperature for 24 hours.

[0066] The feed material in the present invention comprises uniformly mixed 316L stainless steel powder and a binder; the binder accounts for 50% by volume, and the powder accounts for 50% by volume.

[0067] The powder injection molding process of the present invention comprises the following steps:

[0068] S1, preparing the above feed;

[0069] S2, placing the feed prepared in step S1 into a powder injection molding machine, injecting it into the mold cavity at an appropriate pressure and injection speed, and cooling it to form the mold;

[0070] S3, drying and degreasing: drying the injection blank to remove moisture and then thermally degreasing to form a degreased blank;

[0071] S4, sintering: placing the degreased blank in a continuous sintering furnace and sintering to obtain a sintered blank.

[0072] In step S2, during injection, the feed material prepared in step S1 is placed in a powder injection molding machine, injected into a mold cavity under an injection pressure of 70 MPa and an injection temperature of 100° C., and cooled to form;

[0073] In step S3, the preform obtained by injection molding is dried to remove moisture and then thermally degreased to form a degreased preform. The temperature of the oven is 70-100° C. and the drying time is 1-4 hours.

[0074] In step S4, the degreased blank is placed in a continuous sintering furnace and sintered in a H2 atmosphere to obtain a sintered blank; the sintering temperature T is controlled at 1380°C and the holding time is 2 hours.

[0075] The appearance of the sintered blank prepared in this embodiment is smooth as a whole without flow lines or cracks.

[0076] The test data of the sintered blank prepared in this embodiment are shown in the following table:

[0077]

[0078] (Example 4)

[0079] The binder for powder injection molding in the present invention comprises water, a skeleton agent, polydopamine, a dispersant and a lubricant.

[0080] The specific proportions of the binder are as follows (by weight percentage):

[0081]

[0082] The polydopamine was prepared by polymerizing dopamine in Tris-HCl buffer (pH=8.5, 50 mg / ml) at room temperature for 24 hours.

[0083] The feed material of the present invention comprises uniformly mixed 17-4PH stainless steel powder and a binder; the binder accounts for 62% by volume, and the powder accounts for 38% by volume.

[0084] The powder injection molding process of the present invention comprises the following steps:

[0085] S1, preparing the above feed;

[0086] S2, placing the feed prepared in step S1 into a powder injection molding machine, injecting it into the mold cavity at an appropriate pressure and injection speed, and cooling it to form the mold;

[0087] S3, drying and degreasing: drying the injection blank to remove moisture and then thermally degreasing to form a degreased blank;

[0088] S4, sintering: placing the degreased blank in a continuous sintering furnace and sintering to obtain a sintered blank.

[0089] In step S2, during injection, the feed material prepared in step S1 is placed in a powder injection molding machine, injected into a mold cavity under an injection pressure of 130 MPa and an injection temperature of 70° C., and cooled to form;

[0090] In step S3, the preform obtained by injection molding is dried to remove moisture and then thermally degreased to form a degreased preform. The temperature of the oven is 70-100° C. and the drying time is 1-4 hours.

[0091] In step S4, the degreased blank is placed in a continuous sintering furnace and sintered in a H2 atmosphere to obtain a sintered blank; the sintering temperature T is controlled at 1280°C and the holding time is 2 hours.

[0092] The appearance of the sintered blank prepared in this embodiment is smooth as a whole without flow lines or cracks.

[0093] The test data of the sintered blank prepared in this embodiment are shown in the following table:

[0094]

[0095] (Example 5)

[0096] The binder for powder injection molding in the present invention comprises water, a skeleton agent, polydopamine, a dispersant and a lubricant.

[0097] The specific proportions of the binder are as follows (by weight percentage):

[0098]

[0099] The polydopamine was prepared by polymerizing dopamine in Tris-HCl buffer (pH=8.5, 90 mg / ml) at room temperature for 24 hours.

[0100] The feed material in the present invention comprises uniformly mixed 17-4PH stainless steel powder and a binder; the binder accounts for 53% by volume, and the powder accounts for 47% by volume.

[0101] The powder injection molding process of the present invention comprises the following steps:

[0102] S1, preparing the above feed;

[0103] S2, placing the feed prepared in step S1 into a powder injection molding machine, injecting it into the mold cavity at an appropriate pressure and injection speed, and cooling it to form the mold;

[0104] S3, drying and degreasing: drying the injection blank to remove moisture and then thermally degreasing to form a degreased blank;

[0105] S4, sintering: placing the degreased blank in a continuous sintering furnace and sintering to obtain a sintered blank.

[0106] In step S2, during injection, the feed material prepared in step S1 is placed in a powder injection molding machine, injected into a mold cavity under an injection pressure of 70 MPa and an injection temperature of 100° C., and cooled to form;

[0107] In step S3, the preform obtained by injection molding is dried to remove moisture and then thermally degreased to form a degreased preform. The temperature of the oven is 70-100° C. and the drying time is 1-4 hours.

[0108] In step S4, the degreased blank is placed in a continuous sintering furnace and sintered in a H2 atmosphere to obtain a sintered blank; the sintering temperature T is controlled at 1290°C and the holding time is 2.5 hours.

[0109] The appearance of the sintered blank prepared in this embodiment is smooth as a whole without flow lines or cracks.

[0110] The test data of the sintered blank prepared in this embodiment are shown in the following table:

[0111]

[0112] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A binder for powder injection molding, characterized in that: According to weight percentage, the composition comprises 24-46% of water, 20-30% of a skeleton agent, 30-40% of polydopamine, 2-3% of a dispersant, and 2-3% of a lubricant.

2. The binder for powder injection molding according to claim 1, characterized in that: The polydopamine is prepared by polymerizing dopamine in a Tris-HCl buffer at room temperature for 24 hours.

3. The binder for powder injection molding according to claim 2, characterized in that: The pH of the Tris-HCl buffer is 8.5, 50-100 mg / ml.

4. A feed material for powder injection molding, characterized in that: The invention comprises uniformly mixed powder and the binder for powder injection molding according to claim 1, 2 or 3; the binder accounts for 30% to 70% of the volume of the feed, and the rest is powder.

5. A feed material for powder injection molding according to claim 4, characterized in that: The powder is 316L stainless steel powder or 17-4PH stainless steel powder.

6. A powder injection molding process, characterized in that The following steps are involved: S1. Feed material preparation: preparing the feed material for powder injection molding according to claim 4; S2. Molding: placing the powder injection molding feed prepared in step S1 into a powder injection molding machine, and preparing an injection blank by injection molding; wherein during injection, the injection pressure is 60-140 MPa, the injection speed is 50-200 mm / s, and the injection temperature is 60-130° C.; S3, drying: placing the injection blank into an oven for dehydration to evaporate the water and obtain a dried blank; S4, degreasing: degreasing the dried blank to form a degreased blank; S5. Sintering: placing the degreased blank in a continuous sintering furnace and sintering it to obtain a sintered blank.

7. The powder injection molding process according to claim 6, characterized in that: In step S3, the temperature of the drying oven for drying the moisture is 70-100° C., and the drying time is 1-4 hours.

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