Manufacturing process of oil pipe and oil pipe joint and oil pipe system

Abstract

The invention belongs to the technical field of automobiles, and particularly relates to a manufacturing process of an oil pipe and an oil pipe connector and an oil pipe system.The manufacturing process comprises the following steps that a round rod is sequentially subjected to drilling, chambering, hot extrusion, heat treatment, cold rolling and heat treatment, and a round pipe is obtained; the round pipe is sequentially subjected to heat treatment, ball head cold heading, ball head forming, ball head heat treatment and pipe bending, and the oil pipe is obtained; the method comprises the following steps: heating to prepare a blank, forging and forming, performing post-treatment, performing solid solution, and finally performing hot upsetting and acid pickling in sequence to obtain the oil pipe joint. Compared with the prior art, the method solves the problems that in the prior art, when an austenitic stainless steel material is adopted to meet higher working pressure, cold machining in the manufacturing process of the austenitic stainless steel material can cause the material to form austenitic twin crystals, so that the material has magnetism and the hardness is larger than HV300; and the problem that the application in an engine is affected is solved. According to the scheme, austenite twin crystals formed in the cold machining process are eliminated, and the pressure bearing performance of an oil pipe finished product is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of automobiles, and in particular relates to a manufacturing process of an oil pipe and an oil pipe joint, and an oil pipe system. Background Art

[0002] Fuel pipe joints are key components connecting pipelines in oil systems such as fuel, lubrication, and cooling systems. They ensure the sealed transmission of fluids (including fuel, engine oil, and coolant) under high pressure, high temperature, and vibration. For example, a vehicle's brake system typically includes an active oil pump, a piston pump mounted near the tire, and oil pipes connecting the piston pump and the active oil pump. The connector between the oil pipe and the oil pump is a type of oil pipe joint.

[0003] As national regulations on vehicle emissions gradually increase, major automakers are meeting these requirements by reducing displacement and increasing engine operating pressure. This increase in engine operating pressure also increases the operating pressure of existing fuel lines from 350 bar to 500 bar. This significantly reduces the reliability and fatigue resistance of fuel lines and fuel line joints, posing a threat to users.

[0004] For example, CN108555200A discloses a cold forging process for oil pipe joints and its cold forging die, which include the following steps: S0, material preparation; S1, forging guide surface; S2, forging positioning hole; S3, first oil hole forming; S4, second oil hole forming; S5, connector forming; S6, oil hole forming. This solution uses the cold forging process to directly forge the sealing surface, and its coaxiality can meet the requirements, thereby improving the sealing effect; however, for engine oil pipes, austenitic stainless steel materials need to be configured to meet higher working pressures, and austenitic stainless steel materials will produce austenite twins in the material structure after cold working, which will further have magnetic properties and other properties that affect the use of the oil pipe and oil pipe joint in the engine system. In addition, the same problem also exists in the processes disclosed in CN112475811A (a processing technology for oil pipe joints) and CN108637609A (a forming process for engine hydraulic brake oil pipes).

[0005] Therefore, for oil pipes and oil pipe joints with a working pressure increased to 500 bar, the manufacturing and molding processes need to be improved. Summary of the Invention

[0006] The present invention aims to address the aforementioned issues by providing a manufacturing process for fuel pipes and fuel pipe joints, as well as a fuel pipe system. This approach addresses the problem in the prior art of using austenitic stainless steel to meet higher operating pressures. The cold working process employed in the manufacture of fuel pipes and fuel pipe joints can lead to the formation of austenite twins in the material, which in turn makes the material magnetic and has a hardness greater than HV300. This makes further downstream processing difficult and hinders its use in engines. This solution eliminates the austenite twins formed during the cold working process, thereby improving the pressure-bearing performance of the finished fuel pipe.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] The first aspect of the present invention discloses a process for manufacturing an oil pipe, comprising the following steps:

[0009] S1: Round tube manufacturing: round bars are drilled, expanded, hot extruded, heat treated, cold rolled and heat treated in sequence to obtain round tubes;

[0010] S2: Oil pipe forming: The round pipe is sequentially subjected to heat treatment, cold heading, ball head forming, ball head heat treatment and pipe bending to obtain the oil pipe;

[0011] S3: Finished product inspection: The tubing undergoes dimensional inspection, ball head visual inspection, and appearance inspection in sequence, and finally the tubing is obtained as a finished product;

[0012] S4: heating the blank, then forging it into shape, performing solid solution after post-treatment, and finally performing hot upsetting and pickling in sequence to obtain the oil pipe joint.

[0013] Preferably,

[0014] The round rod is made of austenitic stainless steel;

[0015] The finished oil pipe is a stainless steel seamless pipe, which is used to withstand a working pressure of at least 500 bar.

[0016] Preferably, in step S1,

[0017] In the hole enlarging process, heating is first performed by induction heating, and then the hole is enlarged;

[0018] In the hot extrusion, heating is first performed by induction heating, and then hot extrusion is performed.

[0019] Preferably, in step S1,

[0020] The heat treatment step is followed by straightening and pickling.

[0021] Preferably, in step S1,

[0022] Cleaning is performed after said drilling;

[0023] Degreasing is performed after the cold rolling;

[0024] Preferably, in step S2,

[0025] In the cold-forged ball head, the ball head is formed by cold-forging at the end of the round tube, and the ball head is provided with a margin for subsequent processing;

[0026] The ball head forming is to perform fine processing on the ball head after cold heading;

[0027] The ball head heat treatment is to perform a heat treatment at 900-1000°C on the cold plastic area of ​​the ball head after cold heading, so as to eliminate the austenite twins formed in the material structure during the cold heading process and reduce the hardness from greater than HV300 to no more than HV200;

[0028] After the ball head is heat treated, the ball head is polished.

[0029] Preferably, in step S4,

[0030] The temperature of the heating process is not less than 1200°C.

[0031] The forging includes pre-forging and finish forging;

[0032] The post-processing includes trimming, air cooling and shot blasting.

[0033] Preferably, in step S4,

[0034] The solution temperature is 1000-1100° C. and the time is 100-120 minutes. The intermediate product after the solution treatment meets the following requirements: 120-180 HBW5 / 750 (Brinell hardness); metallographic analysis shows no intergranular corrosion cracks; and the grain size grade is ≥4.

[0035] The main purpose of solution heat treatment is to dissolve the strengthening phase in the alloy at high temperature to form a uniform supersaturated solid solution, thereby improving the material's plasticity, toughness, and corrosion resistance, and creating conditions for subsequent aging treatment. The principle is to heat the alloy to a high-temperature single-phase region to fully dissolve the carbides or second phases, then rapidly cool it to inhibit the reformation of precipitated phases and obtain a supersaturated solid solution structure.

[0036] Solution treatment can eliminate the work hardening phenomenon, making stainless steel easier to deform and cut in subsequent processing, reducing processing difficulty and cost.

[0037] Solution treatment can obtain uniform austenitic structure, reduce the internal stress of the material, make stainless steel less likely to crack when subjected to stress, improve toughness and ductility, and make it more suitable for processing needs in complex environments.

[0038] After solution treatment eliminates internal stress, the material is not easily deformed during subsequent processing or use, ensuring dimensional accuracy and structural stability.

[0039] Preferably, the one-piece molding process further comprises the following steps:

[0040] S5: Product inspection of oil pipe joints;

[0041] S6: Cleaning and packaging.

[0042] Preferably,

[0043] In step S5, the product inspection includes penetrant testing and mechanical testing;

[0044] In step S6, during the cleaning and packaging, ultrasonic cleaning is used before packaging.

[0045] A second aspect of the present invention discloses an oil pipe system, comprising oil pipes and oil pipe joints connected to each other, wherein the oil pipes and oil pipe joints are both obtained by any of the above-mentioned manufacturing processes.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] The present invention is mainly intended to eliminate austenite twins in both oil pipes and oil pipe joints, reduce the hardness of the oil pipe ball joint, reduce the difficulty of downstream processing, and enhance fatigue resistance:

[0048] 1. During the manufacturing process of round tubes (billets), hot extrusion is used, which results in fewer micro-cracks on the inner surface compared to the traditional hot piercing process.

[0049] 2. After cold working, especially cold heading of the ball head, heat treatment is added to eliminate the ball head forming stress, eliminate the austenite twins in the material structure, reduce the ball head hardness, and improve the pressure bearing performance of the product;

[0050] 3. Ball head inspection in conjunction with visual inspection can effectively, quickly and non-destructively identify product dimensions, allowing for full batch inspection;

[0051] 4. For the manufacture of oil pipe joints, a solid solution step is mainly used to eliminate austenite twins formed during the manufacture of the oil pipe joints. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 A schematic diagram of the manufacturing process of the oil pipe;

[0053] Figure 2 This is a photo of the oil pipe joint after shot blasting in the manufacturing process;

[0054] Figure 3 The temperature curve of solid solution in the manufacturing process of the oil pipe joint;

[0055] Figure 4 This is a structural diagram of the hot upsetting area (the part outlined in red) in the manufacturing process of the oil pipe joint;

[0056] Figure 5 This is a physical picture of the penetrant testing in the manufacturing process of the oil pipe joint;

[0057] Figure 6 This is a physical picture of the packaging during the manufacturing process of the oil pipe joint. DETAILED DESCRIPTION

[0058] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0059] In the following description, unless otherwise specified, the methods adopted are conventional means in the art, and all matters not covered are common knowledge.

[0060] Example 1

[0061] like Figure 1-6 As shown, a manufacturing process of an oil pipe and an oil pipe joint includes the following steps:

[0062] S1: Round tube manufacturing: round bars are drilled, expanded, hot extruded, heat treated, cold rolled and heat treated in sequence to obtain round tubes;

[0063] S2: Oil pipe forming: The round pipe is sequentially subjected to heat treatment, cold heading, ball head forming, ball head heat treatment and pipe bending to obtain the oil pipe;

[0064] S3: Finished product inspection: The oil pipe undergoes dimensional inspection, ball head visual inspection and appearance inspection in sequence to obtain the finished oil pipe.

[0065] And, a process for integrally forming an oil pipe joint includes the following steps: Figure 5-6 As shown:

[0066] S4: heating the blank, then forging it into shape, performing solid solution after post-treatment, and finally performing hot upsetting and pickling in sequence to obtain the oil pipe joint.

[0067] More specifically, in this embodiment:

[0068] The finished oil pipe is a stainless steel seamless steel pipe, which is used to withstand a working pressure of at least 500 bar. It is made by processing austenitic stainless steel round bars through the oil pipe manufacturing process, such as Figure 1 As shown, the specific steps include:

[0069] S1: Round tube manufacturing: The round bar is drilled and then cleaned to remove the debris generated by the drilling; the drilled round bar is heated by induction heating and the hole formed by the drilling is expanded; the expanded round bar is heated again by induction heating and hot extruded to obtain a tube blank with the target shape and size; the tube blank is heat treated and straightened and pickled, cold rolled and degreased, and then heat treated again and straightened and pickled to form the tube blank into a round tube with the target shape and size. After passing the inspection, it is packaged or transferred to the downstream process.

[0070] S2: Oil pipe forming: Take the round pipe that has passed the inspection (from step S1) and heat treat the round pipe; then form a ball head at one end of the round pipe by cold heading, and further machine the ball head to form it, and clean and remove debris; heat treat the formed ball head and polish it to complete the forming process of the ball head part; then bend the round pipe with the ball head and clean it again to complete the forming of the oil pipe.

[0071] S3: Finished product inspection: The oil pipe obtained in step S2 is subjected to finished product inspection, including dimensional inspection, ball head visual inspection and appearance inspection in sequence. After all the inspections pass, the finished oil pipe is obtained.

[0072] in,

[0073] The hot extrusion process of round tubes and stainless steel seamless steel tube billets can reduce micro cracks on the inner surface of the tube billets.

[0074] Cold heading ball head, the end of the pipe is cold headed and formed, and the ball head retains the subsequent processing allowance.

[0075] Ball head forming, the ball head after cold heading is fine-machined to the required size.

[0076] Heat treatment of the ball head: After cold working, austenitic stainless steel will produce austenite twins in the cold plastic area of ​​the material, which are magnetic and have a hardness greater than HV300. Heat treatment of the cold plastic area (temperature 900-100℃) can eliminate the austenite twins in the material structure and reduce its hardness to HV200.

[0077] Inspection: The ball head size is 100% visually inspected to ensure that parts that do not meet the size are intercepted.

[0078] Furthermore, the manufacturing process steps of the integrally formed oil pipe joint are as follows:

[0079] S4: 1200℃ heating to make blanks, then pre-forging and finish forging to form the blanks, trimming, air cooling and shot blasting (to remove the black skin on the surface) Figure 2As shown) through the tunnel furnace to eliminate the austenite twins generated in the oil pipe joint, the solution temperature curve is as follows Figure 3 As shown, the end is finally hot-forged to strengthen the hardness of the hot-forged area, as shown in Figure 4 As shown, and then pickled to obtain an oil pipe joint.

[0080] Among them, solid solution specifically includes:

[0081] The products are evenly placed in the brazing furnace mesh belt to ensure uniform heating, and the temperature of each zone is set at 1000-1100℃, and the time is controlled at 100-120min. The product obtained by solid solution is subjected to metallographic analysis as needed to ensure that it meets the performance requirements, namely: 120-180HBW5 / 750; intergranular corrosion cracks are not allowed; and the grain size grade is ≥4.

[0082] Among them, pickling specifically includes:

[0083] 1. Pickling: 15-20% HNO3 + 5-8% HF, industrial water, 25 minutes, no heating;

[0084] 2. Pickling: 15-20% HNO3 + 5-8% HF, industrial water, 25 minutes, without heating;

[0085] 3. Wash with industrial water for 3-5 minutes to remove acid;

[0086] 4. Passivation: 35-40% HNO3 + 8-10% HF, 30 min, without heating;

[0087] 5. Wash with industrial water for 3-5 minutes to remove acid;

[0088] 6. Wash with industrial water for 3-5 minutes to remove acid;

[0089] 7. Wash with deionized water for 3-5 minutes to remove acid;

[0090] 8. Wash with hot water, deionized water, heated to 80-90℃, 3-5min, to accelerate the drying and dehydration;

[0091] 9. Dry and let it dry naturally.

[0092] The oil pipe joint obtained by the above process steps was subjected to a salt spray test according to DIN EN ISO 9227:2017 (test conditions: 5% NaCl solution, temperature: 35±2°C, humidity: ~100% RH, sedimentation: 1~2 ml / (h·80 cm 2), pH: 6.5-7.2, time 480h), the test results show that the oil pipe joint has only slight red rust on the surface, and the red rust area accounts for no more than 1.3% of the total area, meeting the technical requirements (the proportion of the rust area on the sample surface to the total area of ​​the sample ≤ 3%)

[0093] Further product inspection is performed on the oil pipe joint obtained by the above process steps, including penetrant testing (fluorescent penetrant, such as Figure 5 The test items and performance indicators of the mechanical properties test are shown in Table 1.

[0094] Table 1 Mechanical properties test items and performance indicators

[0095]

[0096] After testing, the oil pipe joint produced by the above process steps can pass the test requirements.

[0097] The oil pipe joints that have passed the test can be packaged after ultrasonic cleaning. Figure 6 shown.

[0098] The oil pipe and oil pipe joint manufactured and tested in this embodiment are further interconnected to form part of the oil pipe system. Because both the oil pipe and the oil pipe joint undergo heat treatment during the manufacturing process to eliminate austenite twins, this eliminates austenite twins and reduces the difficulty of subsequent processing. Furthermore, eliminating austenite twins reduces stress concentration, improves microstructure uniformity, and enhances the product's pressure-bearing capacity. Therefore, the oil pipe and oil pipe joint combination can function normally under a working pressure of 500 bar. Furthermore, eliminating austenite twins refines grain size and significantly improves mechanical properties, achieving a synergistic improvement in strength, toughness, and corrosion resistance. If the oil pipe and the oil pipe joint are not subjected to the austenite twin elimination step, the presence of austenite twins in the oil pipe and the oil pipe joint can increase tool wear by more than 30%, easily induce crack sources, and increase surface roughness. Furthermore, the anisotropic deformation caused by the austenite twins further causes uneven shrinkage of the material during cutting, resulting in dimensional deformation after processing. It can be seen that for oil pipes and oil pipe joints, when they are used in high-pressure environments (500 bar), it is necessary to eliminate the austenite twins generated during material manufacturing to improve their performance.

[0099] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A manufacturing process for an oil pipe and an oil pipe joint, characterized in that: The steps include: S1: Round tube manufacturing: round bars are drilled, expanded, hot extruded, heat treated, cold rolled and heat treated in sequence to obtain round tubes; S2: Oil pipe forming: The round pipe is sequentially subjected to heat treatment, cold heading, ball head forming, ball head heat treatment and pipe bending to obtain the oil pipe; S3: Finished product inspection: The tubing undergoes dimensional inspection, ball head visual inspection, and appearance inspection in sequence to obtain the finished tubing; S4: heating the blank, then forging it into shape, performing solid solution after post-treatment, and finally performing hot upsetting and pickling in sequence to obtain the oil pipe joint.

2. The manufacturing process of a fuel pipe and a fuel pipe joint according to claim 1, characterized in that: The round rod is made of austenitic stainless steel; The finished oil pipe is a stainless steel seamless pipe, which is used to withstand a working pressure of at least 500 bar.

3. The manufacturing process of a fuel pipe and a fuel pipe joint according to claim 1, characterized in that: In step S1, In the hole enlarging process, heating is first performed by induction heating, and then the hole is enlarged; In the hot extrusion, heating is first performed by induction heating, and then hot extrusion is performed.

4. The manufacturing process of a fuel pipe and a fuel pipe joint according to claim 1, characterized in that: In step S1, The heat treatment step is followed by straightening and pickling.

5. The manufacturing process of a fuel pipe and a fuel pipe joint according to claim 1, characterized in that: In step S1, Cleaning is performed after said drilling; Degreasing is performed after the cold rolling.

6. The manufacturing process of a fuel pipe and a fuel pipe joint according to claim 1, characterized in that: In step S2, In the cold-forged ball head, the ball head is formed by cold-forging at the end of the round tube, and the ball head is provided with a margin for subsequent processing; The ball head forming is to perform fine processing on the ball head after cold heading; The ball head heat treatment is to perform a heat treatment at 900-1000°C on the cold plastic area of ​​the ball head after cold heading, so as to eliminate the austenite twins formed in the material structure during the cold heading process and reduce the hardness from greater than HV300 to no more than HV200; After the ball head is heat treated, the ball head is polished.

7. The manufacturing process of a fuel pipe and a fuel pipe joint according to claim 1, characterized in that: In step S4, The temperature of the heating process is not less than 1200°C. The forging includes pre-forging and finish forging; The post-processing includes trimming, air cooling and shot blasting.

8. The manufacturing process of a fuel pipe and a fuel pipe joint according to claim 1, characterized in that: The one-piece molding process further includes the following steps: S5: Product inspection of oil pipe joints; S6: Cleaning and packaging.

9. The manufacturing process of the oil pipe and the oil pipe joint according to claim 8, characterized in that: In step S5, the product inspection includes penetrant testing and mechanical testing; In step S6, during the cleaning and packaging, ultrasonic cleaning is used before packaging.

10. An oil pipe system, characterized in that: The invention comprises an oil pipe and an oil pipe joint connected to each other, wherein the oil pipe and the oil pipe joint are obtained by the manufacturing process according to any one of claims 1-9.

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