Powder metallurgy preparation method for slender structural parts

Abstract

The invention discloses a powder metallurgy preparation method for a structural elongated part, comprising the following steps: S1, injection molding: injection molding a mixture containing metal powder and a binder into a blank; S2, degreasing: degreasing the blank, controlling the degreasing time, removing the binder in the blank, and making the residual amount of the binder in the blank 0.7-1.1%; S3, sintering: performing a programmed temperature sintering treatment on the degreased blank, controlling the heat removal time of the sintering front section process, so that the residual 0.7-1.1% of the binder in step S2 is completely removed, and the structural elongated part is sintered. The present invention improves the strength of the bonding line by improving the powder metallurgy process without changing the product structure, and effectively reduces the fracture defect rate of the product.

Description

Technical Field

[0001] The invention belongs to the technical field of powder metallurgy and relates to a powder metallurgy preparation method for a slender structural part. Background Art

[0002] Powder metallurgy is a process technology that produces metal powder or uses metal powder (or a mixture of metal powder and non-metal powder) as raw material, and then forms and sinters it to produce metal materials, composite materials and various types of products. Due to the advantages of powder metallurgy technology, it has become the key to solving new material problems and plays a vital role in the development of new materials.

[0003] For some small and long powder metallurgy products, their structural strength is relatively weak. In addition, the fluidity of powder metallurgy materials themselves in the mold is relatively poor, so two or more glue inlets are required to form the product. However, after two glue inlets are set, there will inevitably be a bonding line area between the two strands of material in the middle of the product. The strength of this bonding line area is relatively weak. If the normal production process is used, the product will break at the bonding line after degreasing and sintering, and the fracture rate is very high. The defective rate of a single fracture is as high as 60%-80%. Therefore, how to solve the problem of slender structural parts being easily broken due to weak strength at the bonding line in the powder metallurgy process is an urgent problem to be solved. Summary of the invention

[0004] In order to overcome the defects of the above-mentioned prior art, the present invention proposes a powder metallurgy preparation method for structural slender parts. Without changing the product structure, the strength of the bonding line is improved by improving the process, so that the product fracture defect rate is reduced from the original 60%-80% to 0.3%-0.9%, which greatly reduces the product fracture defect rate.

[0005] This is achieved specifically through the following technical solutions:

[0006] A powder metallurgy preparation method for a slender structural part comprises the following steps:

[0007] S1. Injection molding: Injection molding a mixture containing metal powder and a binder into a blank;

[0008] S2. Degreasing: Degreasing the blank, controlling the degreasing time, removing the binder in the blank, and making the residual amount of the binder in the blank 0.7-1.1%;

[0009] S3, sintering: the degreased blank is subjected to programmed temperature sintering treatment, and the heat removal time of the pre-sintering process is controlled to completely remove the 0.7-1.1% binder remaining in step S2, and a slender structural part is obtained by sintering.

[0010] Furthermore, in step S2, the degreasing process includes pre-rinsing, multi-stage degreasing and post-rinsing.

[0011] Preferably, in step S2, the time for the pre-rinsing is 75-85 min, the multi-stage degreasing includes one-stage degreasing, two-stage degreasing and three-stage degreasing, the time for the first stage degreasing is 30-40 min, the time for the second stage degreasing is 90-100 min, and the time for the third stage degreasing is 25-35 min, the temperature for the post-rinsing is 136-150°C, and the time for the post-rinsing is 85-95 min.

[0012] Preferably, in step S2, the speed of the fan during degreasing is 400-500 rpm, and the fan provides a protective gas, such as nitrogen, in order to evenly distribute the gasified acid gas throughout the furnace body.

[0013] Furthermore, in step S2, oxalic acid is used to degrease the blank, and the amount of oxalic acid is adjusted to 60-80% of the amount of oxalic acid required for complete degreasing of the blank.

[0014] Preferably, in step S3, the flow rate of the protective gas in the furnace body is controlled so as to obtain a required pulse pressure of 20 kPa.

[0015] Preferably, in step S3, the partial pressure flow rate of the protective gas is controlled to be 25 L / min.

[0016] Furthermore, in the step S1, the mixture is injected into a blank through two injection ports, and during the injection process, the geometric center of the injection port of the blank is degassing.

[0017] Furthermore, in step S3, the total time of the programmed temperature rise is 980-1090 min, and the temperature is finally raised to 1385° C. The first stage is a thermal stripping process in which the temperature is raised to and maintained at 600° C., and the first stage accounts for 30.1-37.8% of the total programmed temperature rise time.

[0018] Furthermore, the control parameters of the programmed temperature are:

[0019] The heating time from the initial temperature to 150°C is 25-35 minutes, and the time to maintain the temperature at 150°C is 5-15 minutes;

[0020] The heating time from 150℃ to 300℃ is 55-65min, and the time of keeping the temperature at 300℃ is 35-45min;

[0021] The heating time from 300℃ to 600℃ is 95-105min, and the time of maintaining the temperature at 600℃ is 95-105min;

[0022] The heating time from 600℃ to 800℃ is 115-125min, and the time of keeping the temperature at 800℃ is 85-95min;

[0023] The heating time from 800℃ to 1050℃ is 85-95min, and the time of keeping the temperature at 1050℃ is 160-170min;

[0024] The heating time from 1050°C to 1385°C is 115-125min, and the time of maintaining the temperature at 1385°C is 160-170min.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] During the injection molding stage, exhaust treatment is performed at the geometric center of the blank glue inlet to increase the strength of the product's bonding line; the degreasing parameters are adjusted to reduce the amount of oxalic acid, degreasing time and fan speed during degreasing, and the chemical reaction rate during degreasing is reduced to make the residual amount of binder in the blank 0.7-1.1%. After the blank is degreased, it can be ensured that the bonding line still maintains a certain strength; the sintering parameters are adjusted, the front stage of sintering (thermal degreasing stage) is adjusted, and the thermal degreasing time is appropriately increased to remove the remaining binder in the degreasing process, thereby improving the strength of the product's bonding line and reducing the product's fracture defect rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 A schematic diagram of a slender structure prepared in Example 1 of the present invention;

[0029] Figure 2 It is a conventional injection mold;

[0030] Figure 3 The injection mold used in Example 1 of the present invention;

[0031] Reference numerals:

[0032] 1-Joining line; 2-Glue inlet; 3-Exhaust insert. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] The present invention provides a powder metallurgy preparation method for a slender structure, comprising the following steps:

[0035] S1. Injection molding: Injection molding a mixture containing metal powder and a binder into a blank;

[0036] S2. Degreasing: Degrease the blank, control the degreasing time, remove the binder in the blank, and make the residual amount of binder in the blank be 0.7-1.1%; reduce the degreasing time so that a small amount of binder remains inside the product after the degreasing process is completed. The purpose is to ensure that after the product is degreased, the bonding line still retains a certain strength and will not break when entering the next process.

[0037] S3, sintering: the degreased blank is subjected to programmed temperature sintering treatment, and the thermal degreasing time of the sintering front process is controlled to completely remove the 0.7-1.1% binder remaining in step S2, and sinter to obtain a slender structural part. By increasing the thermal degreasing time of sintering, the binder that was not completely removed in the degreasing process is degreased by thermal degreasing, which can reduce the thermal expansion and contraction caused by cooling after heating and causing product breakage.

[0038] Furthermore, in step S2, the degreasing process includes pre-rinsing, multi-stage degreasing and post-rinsing.

[0039] Preferably, in step S2, the time for the pre-rinsing is 75-85 minutes, the multi-stage degreasing includes one-stage degreasing, two-stage degreasing and three-stage degreasing, the time for the first stage degreasing is 30-40 minutes, the time for the second stage degreasing is 90-100 minutes, the time for the third stage degreasing is 25-35 minutes, and the temperature for the post-rinsing is 136-150°C, and the time for the post-rinsing is 85-95 minutes.

[0040] Preferably, in step S2, the fan speed during degreasing is 400-500 rpm, oxalic acid is used to degrease the stock, and the amount of oxalic acid fed is adjusted to 60-80% of the amount of oxalic acid required for complete degreasing of the stock. Reducing the amount of acid fed and the fan speed can allow the product to proceed at a lower chemical reaction rate during the degreasing process, ensuring that the morphology of the product in the furnace does not change much.

[0041] Preferably, in step S3, the flow rate of the protective gas in the furnace is controlled so that the required pulse pressure is 20 kPa, and the partial pressure flow rate of the protective gas is controlled to be 25 L / min. The pulse pressure is appropriately increased, and the partial pressure flow rate is increased to reduce the gas disturbance in the furnace at high temperature and ensure the stability of the product.

[0042] Furthermore, in step S1, the mixture is injected into a blank through two injection ports, and during the injection process, the geometric center of the injection port of the blank is degassing.

[0043] Furthermore, in step S3, the total time of the programmed temperature increase is 980-1090 min, and the temperature is finally increased to 1385° C. The first stage is a thermal desorption process in which the temperature is increased to and maintained at 600° C., and the first stage accounts for 30.1-37.8% of the total programmed temperature increase time.

[0044] Furthermore, the control parameters of the programmed temperature are:

[0045] The heating time from the initial temperature to 150°C is 25-35 minutes, and the time to maintain the temperature at 150°C is 5-15 minutes;

[0046] The heating time from 150℃ to 300℃ is 55-65min, and the time of keeping the temperature at 300℃ is 35-45min;

[0047] The heating time from 300℃ to 600℃ is 95-105min, and the time of maintaining the temperature at 600℃ is 95-105min;

[0048] The heating time from 600℃ to 800℃ is 115-125min, and the time of keeping the temperature at 800℃ is 85-95min;

[0049] The heating time from 800℃ to 1050℃ is 85-95min, and the time of keeping the temperature at 1050℃ is 160-170min;

[0050] The heating time from 1050°C to 1385°C is 115-125min, and the time of maintaining the temperature at 1385°C is 160-170min.

[0051] Example 1

[0052] A powder metallurgy preparation method for a slender structural part comprises the following steps:

[0053] S1. Injection molding: A mixture containing metal powder and binder is Figure 1 The mold shown is used for injection molding of blanks. Figure 1In the mold shown, a mixture containing metal powder and a binder is injected into the mold through a glue inlet 1, and exhaust treatment is performed at the geometric center of the two glue inlets. Optionally, an exhaust insert can be provided at the geometric center of the two glue inlets;

[0054] S2. Degreasing: Degreasing the blank, controlling the degreasing time, removing the binder in the blank, and making the residual amount of the binder in the blank 1.1%;

[0055] During the degreasing process, oxalic acid is used to degrease the blank. The amount of oxalic acid fed is adjusted to 70% of the amount required for complete degreasing of the blank, and the fan speed is 30%.

[0056] The degreasing treatment includes pre-rinsing, multi-stage degreasing and post-rinsing. The pre-rinsing time is 80 minutes, the multi-stage degreasing includes one-stage degreasing, two-stage degreasing and three-stage degreasing, the post-rinsing includes one-stage post-rinsing and two-stage post-rinsing, the one-stage degreasing time is 40 minutes, the two-stage degreasing time is 100 minutes, the three-stage degreasing time is 30 minutes, the post-rinsing time is 60 minutes, the two-stage post-rinsing time is 30 minutes, and the post-rinsing temperature is 140°C.

[0057] S3, sintering: the degreased blank is subjected to programmed temperature sintering treatment, the heat removal time of the pre-sintering process is prolonged, the 27% binder remaining in step S2 is completely removed, and a slender structural part is obtained by sintering.

[0058] The flow rate of the protective gas in the furnace body is controlled so that the required pulse pressure is 20 kPa, and the partial pressure flow rate of the protective gas is controlled to be 25 L / min.

[0059] The total time of the programmed temperature rise is 1090 min, and the final temperature rises to 1385 °C. The front stage is a thermal stripping process in which the temperature rises to and remains at 600 °C. The time of the front stage accounts for 31.2% of the total programmed temperature rise time.

[0060] The control parameters of the programmed temperature rise are: the heating time from the initial temperature to 150°C is 30 min, and the time of maintaining the temperature at 150°C is 10 min;

[0061] The heating time from 150℃ to 300℃ is 60min, and the temperature is kept at 300℃ for 40min; the heating time from 300℃ to 600℃ is 100min, and the temperature is kept at 600℃ for 100min;

[0062] The heating time from 600℃ to 800℃ is 120min, and the time of maintaining the temperature at 800℃ is 90min;

[0063] The heating time from 800℃ to 1050℃ is 90min, and the time of maintaining the temperature at 1050℃ is 165min;

[0064] The heating time from 1050°C to 1385°C is 120 min, and the time of maintaining the temperature at 1385°C is 165 min.

[0065] Finally, the yield rate of Example 1 was measured to be 99.6%.

[0066] Example 2

[0067] A powder metallurgy preparation method for a slender structural part comprises the following steps:

[0068] S1. Injection molding: Injection molding a mixture containing metal powder and a binder into a blank;

[0069] S2. Degreasing: Degreasing the blank, controlling the degreasing time, removing the binder in the blank, and making the residual amount of the binder in the blank 0.7%;

[0070] During the degreasing process, oxalic acid is used to degrease the blanks, and the amount of oxalic acid fed is adjusted to 80% of the amount required for complete degreasing of the blanks, and the fan speed is 30%.

[0071] The degreasing treatment includes pre-rinsing, multi-stage degreasing and post-rinsing. The pre-rinsing time is 75 minutes, the multi-stage degreasing includes one-stage degreasing, two-stage degreasing and three-stage degreasing, the post-rinsing includes one-stage post-rinsing and two-stage post-rinsing, the one-stage degreasing time is 30 minutes, the two-stage degreasing time is 90 minutes, the three-stage degreasing time is 25 minutes, and the time is 60 minutes, the two-stage post-rinsing time is 30 minutes, and the post-rinsing temperature is 150°C.

[0072] S3, sintering: the degreased blank is subjected to programmed temperature sintering treatment, the heat removal time of the pre-sintering process is prolonged, the 0.7% binder remaining in step S2 is completely removed, and a slender structural part is obtained by sintering.

[0073] The flow rate of the protective gas in the furnace body is controlled so that the required pulse pressure is 20 kPa, and the partial pressure flow rate of the protective gas is controlled to be 25 L / min.

[0074] The total time of the programmed temperature rise is 1030 min, and the final temperature rises to 1385 °C. The front stage is a thermal stripping process in which the temperature rises to and remains at 800 °C. The time of the front stage accounts for 30.1% of the total programmed temperature rise time.

[0075] The control parameters of the programmed temperature rise are: the heating time from the initial temperature to 150°C is 25 min, and the time of maintaining the temperature at 150°C is 5 min;

[0076] The heating time from 150℃ to 300℃ is 55min, and the time to keep the temperature at 300℃ is 35min; the heating time from 300℃ to 600℃ is 95min, and the time to keep the temperature at 600℃ is 95min;

[0077] The heating time from 600℃ to 800℃ is 115min, and the time of maintaining the temperature at 800℃ is 85min;

[0078] The heating time from 800℃ to 1050℃ is 85min, and the time of maintaining the temperature at 1050℃ is 160min;

[0079] The heating time from 1050°C to 1385°C is 115 minutes, and the time of maintaining the temperature at 1385°C is 160 minutes.

[0080] Finally, the yield rate of Example 2 was measured to be 99.7%.

[0081] Example 3

[0082] A powder metallurgy preparation method for a slender structural part comprises the following steps:

[0083] S1. Injection molding: Injection molding a mixture containing metal powder and a binder into a blank;

[0084] S2. Degreasing: Degreasing the blank, controlling the degreasing time, removing the binder in the blank, and making the residual amount of the binder in the blank 1.1%;

[0085] During the degreasing process, oxalic acid is used to degrease the blanks, and the amount of oxalic acid fed is adjusted to 60% of the amount required for complete degreasing of the blanks, and the fan speed is 30%.

[0086] The degreasing treatment includes pre-rinsing, multi-stage degreasing and post-rinsing. The pre-rinsing time is 85 minutes, the multi-stage degreasing includes one-stage degreasing, two-stage degreasing and three-stage degreasing, the post-rinsing includes one-stage post-rinsing and two-stage post-rinsing, the one-stage degreasing time is 40 minutes, the two-stage degreasing time is 100 minutes, the three-stage degreasing time is 35 minutes, the post-rinsing time is 60 minutes, the two-stage post-rinsing time is 30 minutes, and the post-rinsing temperature is 136°C.

[0087] S3, sintering: the degreased blank is subjected to programmed temperature sintering treatment, the heat removal time of the front stage of sintering is prolonged, the 1.1% binder remaining in step S2 is completely removed, and a slender structural part is obtained by sintering.

[0088] The flow rate of the protective gas in the furnace body is controlled so that the required pulse pressure is 20 kPa, and the partial pressure flow rate of the protective gas is controlled to be 25 L / min.

[0089] The total time of the programmed temperature rise is 980 minutes, and the final temperature rises to 1385°C. The front stage is a thermal stripping process in which the temperature rises to and remains at 800°C. The time of the front stage accounts for 37.8% of the total programmed temperature rise time.

[0090] The control parameters of the programmed temperature rise are: the heating time from the initial temperature to 150°C is 35 min, and the time of maintaining the temperature at 150°C is 15 min;

[0091] The heating time from 150℃ to 300℃ is 65min, and the time to keep the temperature at 300℃ is 45min; the heating time from 300℃ to 600℃ is 105min, and the time to keep the temperature at 600℃ is 105min;

[0092] The heating time from 600℃ to 800℃ is 125min, and the time of maintaining the temperature at 800℃ is 95min;

[0093] The heating time from 800℃ to 1050℃ is 95min, and the time of maintaining the temperature at 1050℃ is 170min;

[0094] The heating time from 1050°C to 1385°C is 125 min, and the time of maintaining the temperature at 1385°C is 170 min.

[0095] Finally, the yield rate of Example 3 was measured to be 99.5%.

[0096] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A powder metallurgy preparation method for a slender structure, characterized in that: The following steps are involved: S1. Injection molding: Injection molding a mixture containing metal powder and a binder into a blank; S2. Degreasing: Degreasing the blank, controlling the degreasing time, removing the binder in the blank, and making the residual amount of the binder in the blank 0.7-1.1%; S3, sintering: the degreased blank is subjected to programmed temperature sintering treatment, the heat removal time of the front stage of sintering is controlled, so that the residual 0.7-1.1% of the binder in step S2 is completely removed, and a slender structure is obtained by sintering; In the step S1, the mixture is injected into a blank through two injection ports, and the geometric center of the blank injection port is vented during the injection process; In the step S2, the speed of the fan during degreasing is 400-500 rpm, oxalic acid is used to degrease the blank, and the amount of oxalic acid fed is adjusted to 60-80% of the amount of oxalic acid required for complete degreasing of the blank; The front stage process is a thermal stripping process in which the temperature is raised to and maintained at 600° C., and the time of the front stage process accounts for 30.1-37.8% of the total program heating time.

2. The powder metallurgy preparation method of a slender structure according to claim 1, characterized in that: In step S2, the degreasing process includes pre-rinsing, multi-stage degreasing and post-rinsing.

3. The powder metallurgy preparation method of a slender structure according to claim 2, characterized in that: In the step S2, the time of the pre-rinsing is 75-85 minutes, the multi-stage degreasing includes one-stage degreasing, two-stage degreasing and three-stage degreasing, the time of the first-stage degreasing is 30-40 minutes, the time of the second-stage degreasing is 90-100 minutes, and the time of the third-stage degreasing is 25-35 minutes, the temperature of the post-rinsing is 136-150°C, and the time of the post-rinsing is 85-95 minutes.

4. The powder metallurgy preparation method of a slender structure according to claim 1, characterized in that: In step S3, the flow rate of the protective gas in the furnace body is controlled so that the required pulse pressure is 20 kPa.

5. The powder metallurgy preparation method of a slender structure according to claim 1, characterized in that: In step S3, the partial pressure flow rate of the protective gas is controlled to be 25 L / min.

6. The powder metallurgy preparation method of a slender structure according to claim 1, characterized in that: In step S3, the total time of the programmed temperature increase is 980-1090 min, and the temperature is finally increased to 1385° C.

7. The powder metallurgy preparation method of a slender structure according to claim 1, characterized in that: The control parameters of the programmed temperature rise are: The heating time from the initial temperature to 150°C is 25-35 minutes, and the time to maintain the temperature at 150°C is 5-15 minutes; The heating time from 150℃ to 300℃ is 55-65min, and the time of keeping the temperature at 300℃ is 35-45min; The heating time from 300℃ to 600℃ is 95-105min, and the time of maintaining the temperature at 600℃ is 95-105min; The heating time from 600℃ to 800℃ is 115-125min, and the time of keeping the temperature at 800℃ is 85-95min; The heating time from 800℃ to 1050℃ is 85-95min, and the time of keeping the temperature at 1050℃ is 160-170min; The heating time from 1050°C to 1385°C is 115-125min, and the time of maintaining the temperature at 1385°C is 160-170min.

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