A manufacturing method of a fastener

Abstract

The present invention provides a manufacturing method for fasteners, comprising the following steps: S1, providing a bar stock: subjecting a blank stock to pre-treatment, blanking, and warm heading in sequence to obtain the bar stock; S2, quenching and tempering treatment: annealing and primary tempering treatment are performed on the bar stock in step S1 under a protective atmosphere; S3, thread rolling: after the bar stock in step S2 is finely processed to the required dimensions, it is fed into a thread rolling machine to perform primary thread rolling and secondary thread rolling in sequence to obtain fasteners; S4, heat treatment: quenching and secondary tempering treatment are performed on the fasteners in step S3; S5, surface treatment: the fasteners in step S4 are placed in a hot-dip galvanizing device to obtain fasteners with an alloy layer thickness of 35 μm to 40 μm. The manufacturing method of the fasteners in the embodiments of the present invention improves the shear strength of the fasteners and extends the service life of the fasteners.

Description

Technical Field

[0001] The present invention relates to the technical field of fastener manufacturing, and particularly relates to a manufacturing method of a fastener. Background Art

[0002] Fasteners are a type of basic mechanical parts used for fastening connections and are extremely widely applied. Fasteners are a product with a very wide range of applications. The production process of fasteners is: casting - upset forging - thread rolling - quenching and tempering treatment - surface treatment.

[0003] In terms of the existing technology, stainless steel is mostly used as the blank material. When blanking, finely processing the blank material, and thread rolling the formed bar stock, due to the high hardness of stainless steel, it is easy to generate processing stress inside the fastener. As the processing progresses, it is easy to cause defects such as microcracks inside the fastener due to stress concentration. Moreover, when blanking, finely processing, and thread rolling, the applied force is relatively large, making it easy for processing tools and thread rolling dies to wear, seriously affecting the service life of the processing equipment. Summary of the Invention

[0004] In view of this, the present invention provides a manufacturing method of a fastener to solve the problem that the fasteners in the existing technology are prone to defects in the processing and manufacturing process.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The manufacturing method of a fastener according to an embodiment of the present invention includes the following steps:

[0007] S1, providing bar stock: successively performing pretreatment, blanking, and warm upset forging on the blank material to obtain bar stock;

[0008] S2, quenching and tempering treatment: annealing and primary tempering treatment are performed on the bar stock in step S1 under a protective atmosphere;

[0009] S3, thread rolling: after finely processing the bar stock in step S2 to the required size, it is sent into a thread rolling machine to perform primary thread rolling and secondary thread rolling in sequence to obtain fasteners;

[0010] S4, heat treatment: quenching and secondary tempering treatment are performed on the fasteners in step S3;

[0011] S5, surface treatment: the fasteners in step S4 are placed in a hot-dip galvanizing device to obtain fasteners with an alloy layer thickness of 35μm - 40μm.

[0012] Preferably, the pretreatment method in step S1 is: heating the blank material to 530 - 550°C at a heating rate of 10°C / min, holding for 30 min, and then cooling to room temperature.

[0013] Preferably, in the step S1, the working temperature of the warm forging machine for warm forging is 450-600 °C, and the stamping speed is 4-5 mm / s.

[0014] Preferably, the step S2 includes:

[0015] S21, in a protective atmosphere, heating the bar stock to 850-910 °C at a heating rate of 15 °C / min, holding for 30 min, and then cooling to room temperature for annealing treatment;

[0016] S22, in a protective atmosphere, heating the annealed bar stock to 530-550 °C at a heating rate of 15 °C / min, holding for 120 min, and then cooling to room temperature with the furnace for a first tempering treatment.

[0017] Preferably, the protective atmosphere is a mixed gas of acetone, methanol and nitrogen, and the molar ratio of acetone, methanol and nitrogen is 3:3:4.

[0018] Preferably, in the step S3, the rolling pressure of the rolling machine for first rolling is 8-10 KN, the rolling circumferential speed is 5 m / min, the rolling pressure of the rolling machine for second rolling is 25-30 KN, and the rolling circumferential speed is 20-25 m / min.

[0019] Preferably, the step S4 includes:

[0020] S41, heating the fastener to 900-930 °C at a heating rate of 25 °C / min, holding for 30 min, and then heating the fastener to 1100-1150 °C at a heating rate of 25 °C / min and holding for 3 h;

[0021] S42, quenching the fastener in step S41 into a water bath and cooling to 350-400 °C;

[0022] S43, quenching the fastener in step S42 into an oil bath and cooling to room temperature;

[0023] S44, heating the fastener in step S43 to 550-600 °C at a heating rate of 25 °C / min, holding for 5 h, and then cooling to room temperature with the furnace for a second tempering treatment.

[0024] Preferably, the step S5 includes:

[0025] S51, after pre-treating the fastener in step S4, placing it in the hot-dip basket of the hot-dip galvanizing equipment, starting the first driving part on the hot-dip galvanizing equipment to swing the hot-dip basket so that the fastener on it falls into the limit slot of the hot-dip basket;

[0026] S52. Use a manipulator to grasp the hook part of the hot-dip basket so that the fastener is completely immersed in the molten liquid of the electrothermal ceramic zinc pot. The hook part is limited on a fixed ring above the electrothermal ceramic zinc pot. The fixed ring drives the electrothermal ceramic zinc pot to rotate and move up and down through a second driving part. While the fixed ring rotates, a third driving part above the electrothermal ceramic zinc pot drives the hot-dip basket to rotate by itself through the hook part, and the rotation direction of the hot-dip basket is opposite to the rotation direction of the fixed ring.

[0027] Preferably, the pretreatment steps in step S51 include:

[0028] S511. Pickle the fastener in step S4 with an acetic acid solution with a concentration of 6 mol / L for 10 - 12 min;

[0029] S512. Wash the fastener in step S511 with a zinc chloride solution with a concentration of 2.5 mol / L for 15 - 20 min;

[0030] S513. Spray the fastener in step S512 with a fluxing solution, wherein the fluxing solution contains 40 - 60 wt% zinc chloride and 40 - 60 wt% ammonium chloride;

[0031] S514. Place the fastener in step S513 in a drying oven at 200 - 300 °C for 20 - 25 min.

[0032] Preferably, the temperature of the molten liquid in the electrothermal ceramic zinc pot is 540 °C - 560 °C, and the action time is 15 - 25 s.

[0033] At least one of the above technical solutions of the present invention has the following beneficial effects:

[0034] 1. According to the manufacturing method of the fastener of the embodiment of the present invention, before cutting the blank, finishing and rolling the thread, the blank is pretreated to facilitate cutting the blank and finishing, improving its processing performance; by performing quenching and tempering treatment on the bar, the plasticity of the bar is improved to facilitate rolling the thread of the bar, so that the mechanical stress generated on the fastener due to processing and rolling can be reduced, the mechanical performance of the fastener is improved, and the rolling pressure can be reduced, avoiding affecting the mechanical strength of the core of the fastener due to excessive rolling pressure, improving the shear strength of the fastener, and extending the service life of the fastener.

[0035] 2. The manufacturing method of the fastener according to the embodiment of the present invention uses the hot-dip galvanizing method to perform surface treatment on the fastener, and improves the existing hot-dip galvanizing equipment, so that an alloy coating with appropriate thickness and meeting the assembly accuracy requirements of the fastener can be obtained within a short galvanizing time. Moreover, due to the large adhesion between the alloy coating and the substrate and the high hardness of the alloy coating, the corrosion resistance of the fastener can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a process flow chart of the manufacturing method of the fastener according to the embodiment of the present invention;

[0037] Figure 2 is a partial structural schematic diagram of the hot-dip galvanizing equipment according to the embodiment of the present invention.

[0038] Reference numerals:

[0039] 100. Hot plating basket; 110. Hook part; 200. Electrothermal ceramic zinc pot; 210. Fixed ring; 300. Second driving part; 400. Third driving part. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the drawings of the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention fall within the scope of protection of the present invention.

[0041] Unless otherwise defined, the technical terms or scientific terms used in the present invention should have the ordinary meaning understood by those of ordinary skill in the art to which the present invention belongs. The "first", "second", and similar terms used in the present invention do not denote any order, quantity, or importance, but are only used to distinguish different components. Similarly, terms such as "a" or "one" do not denote a quantity limitation, but mean that there is at least one. "Connection" or "connected" and similar terms are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Upper", "lower", "left", "right", etc. are only used to represent relative positional relationships, and when the absolute position of the object being described changes, the relative positional relationship also changes accordingly.

[0042] The manufacturing method of the fastener according to the embodiment of the present invention will be specifically described below.

[0043] The manufacturing method of the fastener according to the embodiment of the present invention, as Figure 1As shown in the figure, it includes the following steps: S1, providing bar stock: the blank stock is pre-treated, cut, and warm upset to obtain bar stock; S2, quenching and tempering treatment: in a protective atmosphere, the bar stock in step S1 is annealed and subjected to primary tempering treatment; S3, thread rolling: after the bar stock in step S2 is finely processed to the required size, it is sent into a thread rolling machine for primary thread rolling and secondary thread rolling in sequence to obtain fasteners; S4, heat treatment: the fasteners in step S3 are quenched and subjected to secondary tempering treatment; S5, surface treatment: the fasteners in step S4 are placed in a hot-dip galvanizing device to obtain fasteners with an alloy layer thickness of 35 μm to 40 μm. That is to say, according to the manufacturing method of fasteners in the embodiments of the present invention, before cutting, finishing, and thread rolling the blank stock, the blank stock is pre-treated to facilitate cutting and finishing of the blank stock and improve its machining performance; by quenching and tempering the bar stock, the plasticity of the bar stock is improved to facilitate thread rolling of the bar stock, thereby reducing the mechanical stress generated on the fasteners due to processing and thread rolling, improving the mechanical properties of the fasteners, and reducing the thread rolling pressure to avoid affecting the mechanical strength of the core of the fasteners due to excessive thread rolling pressure, improving the shear strength of the fasteners, and extending the service life of the fasteners.

[0044] According to the manufacturing method of fasteners in the embodiments of the present invention, by pre-treating the blank stock and quenching and tempering the formed bar stock to improve the machining performance of the material and its plasticity, stress concentration generated on the base material of the fasteners during mechanical processing such as cutting, finishing, and thread rolling can be avoided, and the mechanical properties of the fasteners can be improved.

[0045] Preferably, the pre-treatment method in step S1 is: heating the blank stock to 530 - 550 °C at a heating rate of 10 °C / min, holding for 30 min, and then cooling to room temperature. That is to say, taking the blank stock made of stainless steel as an example, after the stainless steel blank stock is cast and formed, quenching treatment is required to improve its strength. In the embodiments of the present invention, tempering treatment is performed on the blank stock before cutting, which can eliminate the residual stress caused by the quenching process of the blank stock. By slowly heating the blank stock, holding, and then cooling to room temperature, the plasticity and toughness of the blank stock can be improved, and the machining performance of the blank stock can be improved. Specifically, the temperature of the blank stock can be set to 530 °C, 540 °C, 550 °C, etc., and this temperature can be appropriately adjusted according to the material and composition of the blank stock, and no specific limitation is made here.

[0046] Preferably, in step S1, the working temperature of the warm forging machine used for warm forging is 450 - 600 °C, and the stamping speed is 4 - 5 mm / s. That is to say, the blank after blanking is formed by warm forging. Compared with cold forging, warm forging can avoid stress hardening of the blank during the deformation process and maintain the plasticity, toughness and ductility of the blank. Specifically, the blank can be heated to 450 °C, 500 °C, 550 °C, 600 °C, and the stamping speed of the warm forging machine is set to 4 mm / s.

[0047] Preferably, step S2 includes: S21, in a protective atmosphere, the bar stock is heated to 850 - 910 °C at a heating rate of 15 °C / min, annealed by cooling to room temperature after holding for 30 min; S22, in a protective atmosphere, the bar stock after annealing treatment is heated to 530 - 550 °C at a heating rate of 15 °C / min, and is cooled to room temperature in the furnace after holding for 120 min for a first tempering treatment. That is to say, in a protective atmosphere, before rolling the threads on the formed bar stock, the bar stock is first heated to the austenitizing temperature for annealing treatment, and then heated again for a first tempering treatment, which can further improve the plasticity and toughness of the bar stock, and avoid excessive rolling pressure due to too high hardness and strength of the bar stock during thread rolling, resulting in mechanical stress in the core of the fastener and affecting the anti-shear performance of the fastener.

[0048] Specifically, the protective atmosphere is a mixed gas of acetone, methanol and nitrogen, and the molar ratio of acetone, methanol and nitrogen molecules is 3:3:4. Carrying out quenching and tempering treatment on the bar stock under the action of the protective atmosphere can avoid harmful gas elements such as S in the air from mixing into the bar stock and improve the mechanical properties and corrosion resistance of the bar stock. More specifically, in the quenching and tempering treatment, the heating temperature of the annealing treatment can be, for example, 850 °C, 880 °C, 910 °C, and the heating temperature of the tempering treatment can be, for example, 530 °C, 540 °C, 550 °C.

[0049] Preferably, in step S3, the rolling pressure of the thread rolling machine for the first thread rolling is 8 - 10 KN, and the circumferential rolling speed is 5 m / min. The rolling pressure of the thread rolling machine for the second thread rolling is 25 - 30 KN, and the circumferential rolling speed is 20 - 25 m / min. That is to say, the method of two - stage thread rolling is used to form threads on the side wall of the bar stock. Under the action of the first thread rolling, thread - shaped pits can be formed on the side wall of the bar stock. Then, under the rolling pressure of the second thread rolling, the strain of the bar stock extends along the pits towards the inside of the bar stock, which can improve the processing accuracy of thread rolling. Compared with the prior art, it can reduce the transverse shear stress generated on the core of the bar stock due to excessive rolling pressure, avoid the generation of micro - cracks, and improve the mechanical properties of the fastener.

[0050] Preferably, step S4 includes: S41, heating the fastener to 900 - 930°C at a heating rate of 25°C / min and holding for 30 min, then heating the fastener to 1100 - 1150°C at a heating rate of 25°C / min and holding for 3 h; S42, quenching the fastener in step S41 into a water bath and cooling it to 350 - 400°C; S43, quenching the fastener in step S42 into an oil bath and cooling it to room temperature; S44, heating the fastener in step S43 to 550 - 600°C at a heating rate of 25°C / min, holding for 5 h, and then cooling it to room temperature in the furnace for secondary tempering treatment. That is to say, the fastener is heat-treated by quenching and secondary tempering to improve the strength and mechanical properties of the fastener. Specifically, the heat treatment process can be, for example: heating the furnace temperature to 930°C at a heating rate of 25°C / min and holding for 30 min, then heating the furnace temperature to 1100°C at a heating rate of 25°C / min and holding for 3 h; S42, quenching the fastener in step S41 into a water bath and cooling it to 400°C; S43, quenching the fastener in step S42 into an oil bath and cooling it to room temperature; S44, placing the fastener in step S43 into a tempering furnace, heating the furnace temperature to 600°C at a heating rate of 25°C / min, holding for 5 h, and then cooling it to room temperature in the furnace for secondary tempering treatment to obtain a high-strength and high-hardness fastener.

[0051] Preferably, step S5 includes: S51, after pre-treating the fastener in step S4, placing it in the hot-dip basket 100 of the hot-dip galvanizing equipment, and starting the first driving part on the hot-dip galvanizing equipment to swing the hot-dip basket 100 so that the fasteners on it fall into the limiting grooves of the hot-dip basket 100; S52, using a manipulator to grasp the hook part 110 of the hot-dip basket 100 to completely immerse the fastener in the molten liquid of the electrothermal ceramic zinc pot 200, and the hook part 110 is limitedly arranged on the fixing ring 210 above the electrothermal ceramic zinc pot 200. The fixing ring 210 drives the electrothermal ceramic zinc pot 200 to rotate and move up and down through the second driving part 300. While the fixing ring 210 rotates, the third driving part 400 above the electrothermal ceramic zinc pot 200 drives the hot-dip basket 100 to rotate self-rotation through the hook part 110, and the self-rotation direction of the hot-dip basket 100 is opposite to the rotation direction of the fixing ring 210.

[0052] That is to say, first, a plurality of limiting grooves are arranged at the bottom of the hot-dip basket 100, and then by swinging the hot-dip basket 100 through the first driving part, the fasteners can be correspondingly arranged in the limiting grooves one by one. The limiting grooves can prevent the adhesion between the fasteners, thereby avoiding the formation of hot-dip defects at the adhesion points; at the same time, during the self-rotation of the hot-dip basket 100 and the rotation driven by the fixing ring 210, the limiting grooves play a role in restricting the movement of the fasteners due to inertia, that is, making the fasteners remain relatively stationary relative to the hot-dip basket 100. During hot-dip galvanizing, it is beneficial for the molten zinc liquid to form a smooth and uniform alloy layer on the surface of the fasteners.

[0053] In the preparation method of the fastener according to the embodiment of the present invention, on the one hand, the hot-dip galvanizing equipment drives the fixing ring 210 and the hot-dip basket 100 provided on the fixing ring 210 to rotate relative to the molten zinc liquid in the electrothermal ceramic zinc pot 200 in sequence through its second driving part 300, so that one side of the fastener contacts the relatively rotating molten zinc liquid, so that one side of the fastener is evenly coated with zinc liquid; on the other hand, the third driving part 400 drives the hot-dip basket 100 to rotate self-rotation through the hook part 110, so that the other side of the fastener contacts the relatively self-rotating molten zinc liquid, so that the other side of the fastener is evenly coated with zinc liquid. That is to say, through the self-rotation of the hot-dip basket, the fixing ring 210 drives it to rotate in the opposite direction to the self-rotation direction and move up and down, so that the molten zinc liquid is evenly coated on the surface of the fastener to obtain a smooth and flat coating surface; and under the action of a shorter hot-dip time, an appropriate coating thickness can be obtained to ensure the assembly accuracy of the fastener.

[0054] Preferably, in the preparation method of the fastener according to the embodiment of the present invention, the hot-dip galvanizing equipment further includes a rotating vane 120 provided on the outer peripheral wall of the hot-dip basket 100. As the hot-dip basket 100 rotates and moves up and down, the rotating vane 120 disturbs the thermal field in the electrothermal ceramic zinc pot 200, so as to play a role in balancing the thermal field in the electrothermal ceramic zinc pot 200. At the same time, the angle of the rotating vane 120 is adjusted so that the heat flow rotates and flows downward and outward at the same time. Through the disturbance of the rotating vane 120, the internal heat gradient of the electrothermal ceramic zinc pot 200 is eliminated, so that the fastener is heated evenly, which is beneficial to the formation of a smooth and uniform alloy layer on the surface of the fastener by the molten zinc liquid.

[0055] Further, an aeration device 500 is provided at the bottom of the electrothermal ceramic zinc pot 200. The shape of the aeration device 500 is the same as that of the bottom of the electrothermal ceramic zinc pot 200, and its size is smaller than that of the bottom of the electrothermal ceramic zinc pot 200. At the same time, an inward-introducing angle structure 510 is provided on the outer periphery of the aeration device 500, so as to form an annular gap between the aeration device 500 and the outer peripheral wall of the bottom of the electrothermal ceramic zinc pot 200. The heat flow that fits the inner peripheral wall of the electrothermal ceramic zinc pot 200 and flows downward enters the aeration device 500 through the angle structure 510. At the center of the top of the aeration device 500, a long strip-shaped air outlet 520 is opened. The long strip-shaped air outlet 520 extends upward a certain distance from the top of the aeration device 500. The width of the long strip-shaped air outlet 520 is smaller than the height of the angle structure 510, and the long strip-shaped air outlet 520 communicates with the internal channel of the aeration device 500. The long strip-shaped air outlet 520 is aligned with the gap between the two hot-dip baskets 100. Thus, after the heat flow enters the aeration device 500, it is sprayed upward through the long strip-shaped air outlet 520 with a smaller diameter and is transmitted to the gap between the two hot-dip baskets 100. This position is also the area with the lowest temperature in the conventional electrothermal ceramic zinc pot 200. Through the aeration device 500, the temperature gradient field in the pot is eliminated, making the heating temperature more uniform. At the same time, through the action of the rotary vane 120 and the aeration device 500, a circulating flow from the inside to the outside and from the bottom to the top is formed in the electrothermal ceramic zinc pot 200, making the temperature field more uniform. The molten zinc liquid is evenly plated on the surface of the fastener to obtain a smooth and flat plating surface, accelerating the hot-dip efficiency, obtaining a suitable coating thickness in a short time, and thus ensuring the assembly accuracy of the fastener.

[0056] Preferably, the pretreatment steps in step S51 include: S511, pickling the fastener in step S4 with an acetic acid solution with a concentration of 6 mol / L for 10 - 12 min; S512, washing the fastener in step S511 with a zinc chloride solution with a concentration of 2.5 mol / L for 15 - 20 min; S513, spraying the fastener in step S512 with a flux solution, where the flux solution contains 40 - 60 wt% zinc chloride and 40 - 60 wt% ammonium chloride; S514, placing the fastener in step S513 in a drying oven at 200 - 300 °C for 20 - 25 min. That is to say, the fastener is pickled and washed in sequence to remove impurities on the surface of the fastener, improve the adhesion between the alloy layer and the substrate after hot-dip plating, and by spraying the flux solution on the surface of the fastener, improve the wetting force on the surface of the fastener to accelerate the formation of the alloy layer between the molten zinc liquid and the iron substrate, further improving the adhesion between the alloy layer and the iron substrate.

[0057] Preferably, the temperature of the molten liquid in the electrothermal ceramic zinc pot is 540 °C to 560 °C, and the galvanizing time is 15 - 25 s. Specifically, for example, the temperature of the molten liquid can be 550 °C, and the action time is 20 s.

[0058] The manufacturing method of the fastener according to the embodiment of the present invention will be further described below in conjunction with specific embodiments.

[0059] Embodiment 1

[0060] S1. Provide a bar stock: Heat the blank stock to 550°C at a heating rate of 10°C / min, hold for 30 min and then cool to room temperature for pretreatment; then cut the pretreated blank stock; adjust the working temperature of the warm forging machine to 600°C, and the stamping speed is 4 mm / s.

[0061] S2. Quenching and tempering treatment: Under the protective atmosphere of acetone, methanol and nitrogen, heat the bar stock to 910°C at a heating rate of 15°C / min, hold for 30 min and then cool to room temperature for annealing treatment; under the protective atmosphere, heat the bar stock after annealing treatment to 550°C at a heating rate of 15°C / min, hold for 120 min and then cool in the furnace to room temperature for the first tempering treatment.

[0062] S3. Thread rolling: After the bar stock in step S2 is finish-machined to the required size, send it into a thread rolling machine for the first thread rolling. The thread rolling pressure of the thread rolling machine for the first thread rolling is 8 KN, and the circumferential rolling speed is 5 m / min. Subsequently, perform the second thread rolling. The thread rolling pressure of the thread rolling machine for the second thread rolling is 25 KN, and the circumferential rolling speed is 25 m / min.

[0063] S4. Heat treatment: S41. Raise the temperature of the fastener to 930°C at a heating rate of 25°C / min and hold for 30 min, then raise the temperature of the fastener to 1100°C at a heating rate of 25°C / min and hold for 3 h; S42. Quench the fastener in step S41 into a water bath and cool to 400°C; S43. Quench the fastener in step S42 into an oil bath and cool to room temperature; S44. Raise the temperature of the fastener in step S43 to 600°C at a heating rate of 25°C / min, hold for 5 h and then cool in the furnace to room temperature for the second tempering treatment to obtain a high-strength and high-hardness fastener.

[0064] S5. Surface treatment: After the fastener in step S4 is pretreated, place it in the hot galvanizing basket 100 of the hot galvanizing equipment, and start the first driving part on the hot galvanizing equipment to swing the hot galvanizing basket 100 so that the fasteners on it fall into the limiting grooves of the hot galvanizing basket 100; S52, as Figure 2As shown in the figure, a manipulator is used to grasp the hook portion 110 of the hot-dip basket 100 so that the fastener is completely immersed in the molten liquid at 550°C in the electrothermal ceramic zinc pot 200. The hook portion 110 is limited on the fixed ring 210 above the electrothermal ceramic zinc pot 200. The fixed ring 210 drives the electrothermal ceramic zinc pot 200 to rotate and move up and down through the second driving portion 300. While the fixed ring 210 rotates, the third driving portion 400 above the electrothermal ceramic zinc pot 200 drives the hot-dip basket 100 to rotate self by means of the hook portion 110. The self-rotation direction of the hot-dip basket 100 is opposite to the rotation direction of the fixed ring 210. After hot-dipping for 25 s, the hot-dip basket 100 is taken out from the molten liquid in the electrothermal ceramic zinc pot 200, and a fastener with an alloy layer thickness of 40.2 μm is obtained.

[0065] Example 2

[0066] The difference from Example 1 is that in step S5, the hot-dip time is 20 s, and a fastener with an alloy layer thickness of 38.7 μm is obtained.

[0067] Example 3

[0068] The difference from Example 1 is that in step S5, the heat time is 15 s, and a fastener with an alloy layer thickness of 35.5 μm is obtained.

[0069] Comparative Example 1

[0070] The difference from Example 1 is that in steps S1’, S2’, and S3’ are different from S1, S2, and S3 in Example 1 respectively. Specifically,

[0071] In step S1’, the blank is cut, the working temperature of the warm heading machine is adjusted to 600°C, and the bar is formed by stamping at a speed of 4 mm / s;

[0072] In step S2’, the formed bar in step S1 is placed in the air and cooled to room temperature;

[0073] In step S3’, the rolling pressure of the rolling machine for rolling threads is 35 KN, and the rolling circumferential speed is 25 m / min.

[0074] Comparative Example 2

[0075] The difference from Example 1 is that step S5’’ is different from S5. Specifically,

[0076] Step S5’’ specifically includes: placing the fasteners in step S4 into the hot-dip basket 100 of the hot-dip galvanizing equipment after pretreatment; S52, using a manipulator to grasp the hook part 110 of the hot-dip basket 100 to completely immerse the fasteners in the molten liquid at 550°C in the electrothermal ceramic zinc pot 200, and the hook part 110 is limited on the fixed ring 210 above the electrothermal ceramic zinc pot 200. The fixed ring 210 drives the electrothermal ceramic zinc pot 200 to rotate and move up and down through the second driving part 300. After hot-dipping for 25 s, the hot-dip basket 100 is taken out from the molten liquid in the electrothermal ceramic zinc pot 200 to obtain fasteners with an alloy layer thickness of 40.2 μm.

[0077] Performance test

[0078] (1) Mechanical strength test

[0079] According to the manufacturing methods of the above-mentioned Examples 1 to 3 and Comparative Examples 1 to 2, the fasteners of Manufacturing Examples 1 to 3 and Comparative Manufacturing Examples 1 to 2 are respectively obtained. The above-mentioned fasteners are subjected to a tensile strength test according to GJB715.23A-2008; the above-mentioned fasteners are subjected to a shear failure load test according to GJB715.26A-2015, and the test results are shown in Table 1 below.

[0080] Table 1 Mechanical strength performance test results of fasteners manufactured under each example and comparative example

[0081]

[0082] As can be seen from the above table: the tensile strength and shear failure load of the fasteners obtained in Manufacturing Examples 1 to 3 are equivalent to those of Comparative Manufacturing Example 2, and the tensile strength and shear failure load of the fasteners obtained in Comparative Manufacturing Example 1 are poor. That is to say, by pretreating the blank before blanking and finish machining of the blank, the residual stress inside the blank can be eliminated, which is convenient for machining and can enhance the mechanical strength of the bar stock; by further quenching and tempering treatment of the bar stock, and then forming threads on the side wall of the bar stock by the method of rolling threads twice, the transverse shear stress generated on the core of the bar stock due to excessive rolling pressure can be reduced, microcracks can be avoided, and the mechanical properties of the fasteners can be improved.

[0083] (2) Corrosion resistance test

[0084] According to the manufacturing methods of the above-mentioned Embodiments 1 to 3 and Comparative Examples 1 to 2, the fasteners of Manufacturing Examples 1 to 3 and Comparative Manufacturing Examples 1 to 2 were obtained respectively. The above-mentioned fasteners were subjected to a neutral salt spray test in accordance with ASTM B117-2019. Specifically, the test conditions for this neutral salt spray test were as follows: Salt solution: a sodium chloride solution with a mass fraction of 5% and a pH of 6.5 to 7.2. The above-mentioned fasteners were suspended in a salt spray test chamber at an angle of 20° with respect to the vertical direction and acted for 48 h and 96 h respectively; then, referring to Table 2 of ISO 4628-1:2016, the corrosion degree was observed and the corrosion degree was rated. The results are shown in Table 2 below.

[0085] Table 2 Test results of the corrosion resistance of the fasteners manufactured under each example and comparative example

[0086]

[0087] As can be seen from the above table: The corrosion resistance of the fasteners obtained in Manufacturing Examples 1 to 3 is equivalent to that of Comparative Manufacturing Example 1, and the corrosion resistance of the fasteners obtained in Comparative Manufacturing Example 2 is poor. That is to say, using the hot-dip galvanizing method of the embodiment of the present invention to perform surface treatment on the fasteners can increase the adhesion between the alloy coating and the substrate and improve the corrosion resistance of the fasteners.

[0088] As described above, before the blank is cut, finish-machined, and thread-rolled in the present invention, the blank is pretreated to facilitate the cutting and finish-machining of the blank and improve its machining performance; by performing quenching and tempering treatment on the bar, the plasticity of the bar is improved to facilitate thread-rolling of the bar, thereby reducing the mechanical stress generated on the fasteners due to processing and thread-rolling, improving the mechanical properties of the fasteners, and reducing the thread-rolling pressure to avoid affecting the mechanical strength of the core of the fasteners due to excessive thread-rolling pressure, improving the shear strength of the fasteners, and extending the service life of the fasteners. At the same time, the present invention uses the hot-dip galvanizing method to perform surface treatment on the fasteners and improves the existing hot-dip galvanizing equipment, so that an alloy coating with an appropriate thickness and meeting the assembly accuracy requirements of the fasteners can be obtained within a short galvanizing time. Moreover, due to the large adhesion between the alloy coating and the substrate and the high hardness of the alloy coating, the corrosion resistance of the fasteners can be improved.

[0089] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle described in the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A manufacturing method of a fastener, characterized in that, it includes the following steps: S1. Provide a bar stock: The blank stock is pre-treated, cut, and warm upset forged in sequence to obtain the bar stock; S2. Tempering treatment: Under a protective atmosphere, anneal and perform a first tempering treatment on the bar stock in step S1; S3. Thread rolling: After the bar stock in step S2 is finely processed to the required size, it is sent into a thread rolling machine to perform first thread rolling and second thread rolling in sequence to obtain the fastener; S4. Heat treatment: Quench and perform a second tempering treatment on the fastener in step S3; S5. Surface treatment: Place the fastener in step S4 in a hot-dip galvanizing device to obtain a fastener with an alloy layer thickness of 35 μm to 40 μm; The hot-dip galvanizing device includes a rotating vane provided on the outer peripheral wall of the hot-dip basket, the angle of the rotating vane is adjustable, and an aeration device is provided at the bottom of the electrothermal ceramic zinc pot; The step S5 includes: S51. After the fastener in step S4 is pre-treated, place it in the hot-dip basket of the hot-dip galvanizing device, and start the first driving part on the hot-dip galvanizing device to swing the hot-dip basket so that the fasteners on it fall into the limiting grooves of the hot-dip basket; S52. Use a manipulator to grab the hook part of the hot-dip basket to completely immerse the fastener in the molten liquid of the electrothermal ceramic zinc pot, and the hook part is limitedly arranged on a fixed ring above the electrothermal ceramic zinc pot. The fixed ring drives the electrothermal ceramic zinc pot to rotate and move up and down through a second driving part. While the fixed ring rotates, a third driving part above the electrothermal ceramic zinc pot drives the hot-dip basket to rotate self by means of the hook part, and the self-rotation direction of the hot-dip basket is opposite to the rotation direction of the fixed ring.

2. The manufacturing method of the fastener according to claim 1, characterized in that, the pre-treatment method in step S1 is: Heat the blank stock to 530 - 550 °C at a heating rate of 10 °C / min, keep it warm for 30 min, and then cool it to room temperature.

3. The manufacturing method of the fastener according to claim 1, characterized in that, in step S1, the working temperature of the warm upset forging machine used for warm upset forging is 450 - 600 °C, and the stamping speed is 4 - 5 mm / s.

4. The manufacturing method of the fastener according to claim 1, characterized in that, step S2 includes: S21. Under a protective atmosphere, heat the bar stock to 850 - 910 °C at a heating rate of 15 °C / min, keep it warm for 30 min, and then cool it to room temperature for annealing treatment; S22. Under a protective atmosphere, heat the bar stock after the annealing treatment to 530 - 550 °C at a heating rate of 15 °C / min, keep it warm for 120 min, and then cool it to room temperature with the furnace for the first tempering treatment.

5. The manufacturing method of the fastener according to claim 4, characterized in that, the protective atmosphere is a mixed gas of acetone, methanol, and nitrogen, and the molar ratio of acetone, methanol, and nitrogen is 3:3:

4.

6. The manufacturing method of the fastener according to claim 1, characterized in that, In step S3, the rolling pressure of the rolling machine for one-time thread rolling is 8 - 10 KN, and the circumferential rolling speed is 5 m / min. The rolling pressure of the rolling machine for secondary thread rolling is 25 - 30 KN, and the circumferential rolling speed is 20 - 25 m / min.

7. The manufacturing method of the fastener according to claim 1, characterized in that, step S4 includes: S41, heating the fastener to 900 - 930 °C at a heating rate of 25 °C / min, holding for 30 min, and then heating the fastener to 1100 - 1150 °C at a heating rate of 25 °C / min and insulating for 3 h; S42, quenching the fastener in step S41 into a water bath and cooling it to 350 - 400 °C; S43, quenching the fastener in step S42 into an oil bath and cooling it to room temperature; S44, heating the fastener in step S43 to 550 - 600 °C at a heating rate of 25 °C / min, holding for 5 h, and then cooling it to room temperature with the furnace for secondary tempering treatment.

8. The manufacturing method of the fastener according to claim 1, characterized in that, the pretreatment steps in step S51 include: S511, pickling the fastener in step S4 with an acetic acid solution having a concentration of 6 mol / L for 10 - 12 min; S512, washing the fastener in step S511 with a zinc chloride solution having a concentration of 2.5 mol / L for 15 - 20 min; S513, spraying the fastener in step S512 with a flux solution, wherein the flux solution contains 40 - 60 wt% zinc chloride and 40 - 60 wt% ammonium chloride; S514, placing the fastener in step S513 in a drying oven at 200 - 300 °C for 20 - 25 min.

9. The manufacturing method of the fastener according to claim 1, characterized in that, the molten liquid temperature of the electrothermal ceramic zinc pot is 540 °C - 560 °C, and the acting time is 15 - 25 s.

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