Method for manufacturing a hexagon bolt

Abstract

The application discloses a manufacturing method of hexagonal bolts, and relates to the technical field of bolt manufacturing, wherein the hexagonal bolts are formed by forging, the method comprises the following steps: after blanking, only the end needing forging is heated, and the 'upsetting and forming' of the heating section is performed by die forging, so that the hexagonal bolts are quickly formed and the temperature is reduced, the hot forming is performed by forging, the surface is polished by a lathe, and no allowance for reprocessing is reserved, when heat treatment is performed in a multi-purpose furnace, the nitrogen protection atmosphere control and carbon potential setting method are adopted to avoid the workpiece surface decarburization in the special heat treatment process, and the surface hardness of the workpiece and the strength value of the hexagonal bolt are ensured, and the hexagonal bolt produced by the above method can keep high precision and ensure the surface hardness of the workpiece and the strength value of the hexagonal bolt.

Description

Technical Field

[0001] This invention relates to the field of bolt manufacturing technology, and more particularly to a method for manufacturing a hexagonal bolt. Background Technology

[0002] There are generally two forming methods in manufacturing hexagonal bolts. One is to process a heat-treated round bar; the other is to forge an untreated round bar by heating it and then heat-treating it.

[0003] The disadvantage of using method one is that the hardened layer is removed during the processing, which reduces the strength of the threaded section of large-sized hexagonal bolts; the disadvantage of using method two is that very little machining allowance is left, and oxidation and decarburization during heat treatment cause uneven surface hardness, or even low surface hardness. Summary of the Invention

[0004] To address the technical problems existing in the background art, this invention proposes a manufacturing method for hexagonal bolts. The method involves forging and hot forming, followed by lathe finishing. During heat treatment in a multi-purpose furnace, a nitrogen protective atmosphere is used to control and stabilize the carbon potential, thus preventing decarburization of the workpiece surface during the special heat treatment process. Afterward, sandblasting and thread rolling are performed. Hexagonal bolts produced in this manner maintain high precision while ensuring the surface hardness of the workpiece and the strength value of the hexagonal bolt.

[0005] The present invention provides a method for manufacturing a hexagonal bolt, comprising the following steps:

[0006] Step 1: Control the chemical composition of the raw materials within the range allowed by the corresponding standards, and then melt and shape them to form a billet;

[0007] Step 2: The billet smelted and formed in Step 1 is cut and forged. The hexagonal bolts adopt a two-stage die forging process. One end of the billet, i.e. the end that needs to be forged, is not forged as a whole. It is upsetting once and hot die forming once, and then cooled. The forging method in this manufacturing process is to heat only the end that needs to be forged after cutting and perform 'upsetting and forming' of the heated section at both ends of the die forging. The forming is fast and the temperature is low.

[0008] Step 3: The bolt blank obtained in Step 2 is machined and pre-inspected. After passing the UT and PT flaw detection, the next step is carried out. The machining is a process used to remove iron oxide scale, also known as the peeling process.

[0009] Step 4: Heat treat the bolt blank obtained in Step 3. When the furnace temperature of the multi-purpose furnace is ≥600℃ during the heat treatment process, nitrogen is introduced and then nitrogen protection is maintained throughout the process. The multi-purpose furnace is sealed during the heat treatment process so that the workpiece is kept under nitrogen protection from the time it leaves the furnace until it enters the quenching oil.

[0010] Step 5: Clean and degrease the bolts manufactured in Step 4;

[0011] Step 6: Temper the bolts;

[0012] Step 7: After tempering, air cool the bolts manufactured in Step 6;

[0013] Step 8: Perform a 100% visual inspection of the bolts manufactured in Step 7 to check for cracks and other surface defects;

[0014] Step 9: Sandblast the bolts manufactured in Step 8;

[0015] Step 10: Perform thread rolling on the bolts manufactured in Step 9;

[0016] Step 11: Perform physical and chemical tests and non-destructive testing on the bolts manufactured in Step 10;

[0017] Step 12: Perform surface treatment on the bolts manufactured in Step 11, and complete the final dimensional inspection, surface inspection and coating inspection. After passing the inspection, package and put them into storage.

[0018] Preferably, in step 2, the forging temperature is 1145℃~1220℃, the holding time is 5~10s, and the heating time should be determined according to the diameter of the blank raw material, with the premise of reaching the target heating temperature.

[0019] Preferably, the cooling method in step 2 is air cooling.

[0020] Preferably, the carbon potential is maintained at 0.38% to 0.48% during the heat treatment process in step 4.

[0021] Preferably, the nitrogen pressure in step 4 is 0.4 to 0.6 MPa.

[0022] Preferably, the tempering process in step 6 needs to be carried out within 4 hours after the quenching process in step 4 is completed.

[0023] The proposed method for manufacturing hexagonal bolts in this invention has the following beneficial technical effects:

[0024] 1. Forging method: This application adopts a manufacturing forging method in which only the end to be forged is heated after blanking, and the two ends are die forged by 'upsetting and forming' in the heating section. Therefore, the hexagonal bolt is formed quickly and the temperature is reduced.

[0025] 2. The workpiece is hot-formed by forging and machined on a lathe to leave no allowance for further processing. During the heat treatment in the multi-purpose furnace, a nitrogen protective atmosphere and a constant carbon potential are used to prevent decarburization of the workpiece surface during the special heat treatment process, ensuring that it does not decarburize or oxidize. After that, sandblasting and thread rolling are performed. The hexagonal bolts produced in the above manner maintain high precision while ensuring the surface hardness of the workpiece and the strength value of the hexagonal bolt.

[0026] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0027] Figure 1 This is a side view of the hexagonal bolts before they enter the multi-purpose furnace for heat treatment, according to the present invention.

[0028] Figure 2 This is a front view schematic diagram of the hexagonal bolts in their state before entering the multi-purpose furnace for heat treatment according to the present invention. Detailed Implementation

[0029] Embodiments of the present invention are described in detail below. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar symbols denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0030] The chemical composition of a hexagonal bolt is within the following range:

[0031] C:0.38%~0.48%; Si:0.15%~0.35%; Mn0.75%~1.0%; P≤0.035%; S≤0.04%;

[0032] Cr: 0.80%–1.10%; Mo: 0.15%–0.25%; the remainder is Fe.

[0033] A method for manufacturing a hexagonal bolt includes the following steps:

[0034] Step 1: Control the chemical composition of the raw materials within the range allowed by the corresponding standards, and then melt and shape them to form a billet;

[0035] Step 2: The billet smelted and formed in Step 1 is cut and forged. The hexagonal bolts adopt a two-stage die forging process. One end of the billet, i.e. the end that needs to be forged, is not forged as a whole. It is upsetting once and hot die forming once. The forging temperature is 1145℃~1220℃, and the holding time is 5~10s. The heating time should be determined according to the diameter of the billet raw material to achieve the target heating temperature. Then, it is cooled by air cooling. The forging method in this manufacturing process is to heat only the end that needs to be forged after cutting and perform 'upsetting and forming' of the heated section at both ends of the die forging. The forming is fast and the temperature is low.

[0036] Step 3: The bolt blank obtained in Step 2 is machined and pre-inspected. After passing the UT and PT flaw detection, the next step is carried out. The machining is a process used to remove iron oxide scale, also known as the peeling process.

[0037] Step 4: Heat treat the bolt blank obtained in Step 3. During the heat treatment process, when the furnace temperature of the multi-purpose furnace is ≥600℃, nitrogen gas is introduced and then nitrogen protection is maintained throughout the process. During the heat treatment process, the carbon potential is maintained at 0.38% to 0.48% and the nitrogen pressure is maintained at 0.4 to 0.6 MPa. The multi-purpose furnace is sealed during the heat treatment process so that the workpiece is under nitrogen protection from the time it leaves the furnace until it enters the quenching oil.

[0038] Step 5: Clean and degrease the bolts manufactured in Step 4;

[0039] Step 6: Temper the bolts. The tempering process must be carried out within 4 hours after the quenching step in Step 4.

[0040] Step 7: After tempering, air cool the bolts manufactured in Step 6;

[0041] Step 8: Perform a 100% visual inspection of the bolts manufactured in Step 7 to check for cracks and other surface defects;

[0042] Step 9: Sandblast the bolts manufactured in Step 8;

[0043] Step 10: Perform thread rolling on the bolts manufactured in Step 9;

[0044] Step 11: Perform physical and chemical tests and non-destructive testing on the bolts manufactured in Step 10;

[0045] Step 12: Perform surface treatment on the bolts manufactured in Step 11, and complete the final dimensional inspection, surface inspection and coating inspection. After passing the inspection, package and put them into storage.

[0046] In terms of forging, this application adopts a manufacturing forging method in which only the end to be forged is heated after blanking, and the two ends are die-forged by 'upsetting and forming' in the heated section. Therefore, the hexagonal bolt is formed quickly and the temperature is reduced.

[0047] It is produced by forging and hot forming, and the surface is machined to a smooth finish. Figures 1-2 In this state, no allowance is left for further processing. When using in-furnace heat treatment, nitrogen protective atmosphere control and carbon potential determination are adopted to avoid decarburization of the workpiece surface during special heat treatment processes, ensuring no decarburization and no oxidation. Afterwards, sandblasting and thread rolling are performed. Hexagonal bolts produced in the above manner maintain high precision while ensuring the surface hardness of the workpiece and the strength value of the hexagonal bolt.

[0048] Example:

[0049] A method for manufacturing a B7 hex bolt includes the following steps:

[0050] (1) Cut 3 / 4-inch B7 round bars and heat them in an induction heating furnace. The control parameters are heating temperature 1180℃ and holding time 8s. After the furnace is removed, the two-stage die forging process of 'upsetting + forming' is performed to form a forging blank.

[0051] (2) Use a lathe to remove the oxide scale from the surface of the forging blank, and finish machine it to the required dimensions according to standard ASME B 18.2.1;

[0052] (3) After the hexagonal bolts of the machined surface pass the UT and PT flaw detection tests, they are heat-treated;

[0053] (4) During heat treatment, maintain the carbon potential at 0.38% to 0.48%; when the furnace temperature of the multi-purpose furnace is ≥600℃ during heat treatment, nitrogen is introduced, and then nitrogen protection is maintained throughout the process; before quenching in the multi-purpose furnace during heat treatment, the furnace door is sealed to ensure that the workpiece is under nitrogen protection from the time it leaves the furnace until it enters the quenching oil; and then it is cleaned and tempered within 4 hours. Nitrogen protection is also maintained during the tempering process; the specific heat treatment process is as follows: quenching at 860±10℃, holding for 1.5h, turning on the stirrer for oil cooling, tempering at 630±10℃, holding for 3h, and air cooling;

[0054] (5) After heat treatment, the bolts are visually inspected for cracks and other surface defects, and sandblasting and thread rolling are performed.

[0055] (6) The hexagonal bolts are subjected to physical and chemical testing, non-destructive testing, and surface treatment. The final dimensions, surface and coating are inspected and then packaged and stored.

[0056] (7) The production efficiency and yield of 3 / 4B7 hex bolts manufactured by this method are high.

[0057] Furthermore, any content not described in detail in this specification is existing technology known to those skilled in the art.

[0058] It should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0059] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0060] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0061] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0062] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for manufacturing a hexagonal bolt, characterized in that, Includes the following steps: Step 1: Control the chemical composition of the raw materials within the range allowed by the corresponding standards, and then melt and shape them to form a billet; Step 2: The billet smelted and formed in Step 1 is cut and forged. The hexagonal bolt adopts a two-stage die forging process. One end of the billet, that is, the end that needs to be forged, is upsetting once and hot die forming once, and then cooled. Step 3: The bolt blank obtained in Step 2 is machined and pre-inspected, and then passed by UT and PT flaw detection before proceeding to the next step; Step 4: Heat treat the bolt blank obtained in Step 3. When the furnace temperature of the multi-purpose furnace is ≥600℃ during the heat treatment process, nitrogen is introduced and then nitrogen protection is maintained throughout the process. The multi-purpose furnace is sealed during the heat treatment process so that the workpiece is kept under nitrogen protection from the time it leaves the furnace until it enters the quenching oil. Step 5: Clean and degrease the bolts manufactured in Step 4; Step 6: Temper the bolts; Step 7: After tempering, air cool the bolts manufactured in Step 6; Step 8: Perform a 100% visual inspection of the bolts manufactured in Step 7 to check for cracks and other surface defects; Step 9: Sandblast the bolts manufactured in Step 8; Step 10: Perform thread rolling on the bolts manufactured in Step 9; Step 11: Perform physical and chemical tests and non-destructive testing on the bolts manufactured in Step 10; Step 12: Perform surface treatment on the bolts manufactured in Step 11, and complete the final dimensional inspection, surface inspection and coating inspection. After passing the inspection, package and put them into storage.

2. The method for manufacturing a hexagonal bolt according to claim 1, characterized in that, In step 2, the forging temperature is 1145℃~1220℃, and the holding time is 5~10s.

3. The method for manufacturing a hexagonal bolt according to claim 1, characterized in that, In step 2, the cooling method is air cooling.

4. The method for manufacturing a hexagonal bolt according to claim 1, characterized in that, During the heat treatment in step 4, the carbon potential is maintained at 0.38% to 0.48%.

5. The method for manufacturing a hexagonal bolt according to claim 1, characterized in that, In step 4, the nitrogen pressure is 0.4–0.6 MPa.

6. The method for manufacturing a hexagonal bolt according to claim 1, characterized in that, The tempering process in step 6 must be carried out within 4 hours after the quenching process in step 4 is completed.

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