Method for testing delayed fracture resistance of bolt

Abstract

According to the bolt delayed fracture resistance test method, a torque sensor is arranged on a transmission arm of a transmission motor, a screwing sleeve is arranged at the tail end of the transmission arm of the transmission motor, a positioning tool is arranged on the side, provided with the transmission arm, of the transmission motor, a positioning sleeve is arranged on the positioning tool, and the end, provided with a nut, of a test bolt is embedded into the screwing sleeve. The stud end of the test bolt sequentially penetrates through the inclined washer and the positioning baffle and is inserted into the positioning sleeve to be connected with the test nut; and a pressure sensor is arranged between the positioning sleeve and the positioning baffle. The device has the advantages that the inclined pad with a certain angle is placed below the nut of the test bolt, the installation torque required by a customer is applied, the installation mode is close to the actual installation mode, and the stress distribution condition of the test bolt is equal to the stress condition of the test bolt under the actual working condition; if the test bolt is fractured, the delayed fracture resistance of the test bolt is insufficient, and the test is accurate.

Description

Technical Field

[0001] The invention relates to the field of testing technology, and in particular to a testing method for delayed fracture resistance of a bolt. Background Art

[0002] There is a chance of hydrogen penetration in steel fasteners during the smelting, thread extrusion, heat treatment, pickling, electroplating, etc., which leads to the risk of hydrogen embrittlement in high-strength fasteners. Hydrogen embrittlement generally occurs between 24 and 48 hours after installation. At the same time, high-strength fasteners are prone to stress corrosion cracking under the action of stress gradient during service after installation. Stress corrosion cracking is delayed fracture, usually occurring 24 to 48 hours after the installation of bolts, screws, and studs. In recent years, threaded high-strength connections have been widely used, involving national key projects in aviation, aerospace, and petrochemicals. Delayed fracture and hydrogen embrittlement of fasteners will affect the progress and quality of the project. Therefore, there is an urgent need for a detection method that can comprehensively evaluate the hydrogen embrittlement and delayed fracture performance of the actual bolts. Summary of the invention

[0003] The purpose of the present invention is to solve the shortcomings existing in the prior art and to propose a bolt delayed fracture resistance test method for quickly evaluating the delayed fracture resistance and hydrogen embrittlement performance of the bolt through a fixture.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions: A test method for delayed fracture resistance of bolts, comprising a transmission motor, a positioning tool, a positioning sleeve, a pressure sensor, a positioning baffle, an inclined washer, a screwing sleeve, a torque sensor, a test bolt and a test nut, wherein a transmission arm of the transmission motor is provided with a torque sensor, a screwing sleeve is provided at the end of the transmission arm of the transmission motor, the positioning tool is arranged on the transmission arm side of the transmission motor, an installation space is provided between the positioning tool and the screwing sleeve, a positioning sleeve is provided on the positioning tool, a nut end of the test bolt is embedded in the screwing sleeve, a stud end of the test bolt passes through the inclined washer and the positioning baffle in sequence and is inserted into the positioning sleeve and is threadedly connected with the test nut; a pressure sensor is provided between the positioning sleeve and the positioning baffle; S1: Assemble according to the above structure; S2: Set the torque value and select the torque control mode, click the transmission motor to gradually apply the tightening torque; S3: After the tightening torque meets the requirement, the transmission motor automatically reverses and withdraws, the test bolt and the screw sleeve are separated, and the tightening axial force and torque coefficient of the test bolt are obtained; S4: After the tightening axial force obtained from the test of the first test bolt, repeat steps S1 to S3 for the second test bolt, change the test parameters of the transmission motor from the torque control mode to the tightening axial force control mode, and set the tightening axial force to 1.1 times the tightening axial force obtained from the test in S3; S5: Click the transmission motor to tighten the nut and gradually apply the tightening axial force. When the tightening axial force meets the requirement of 1.1 times the tightening axial force obtained in the test of S3, click the transmission motor to stop. The transmission motor does not reverse and exit for 72 hours. S6: The transmission motor is reversed and withdrawn after 72 hours, and the test bolt and the screw sleeve are separated; S7: After the test bolts are tested, use a 30x magnifying glass to check whether there are cracks on the threads and the R angle of the nuts. If there are no cracks, the batch is considered qualified. If obvious cracks are visible, the batch is considered unqualified.

[0005] Furthermore, the nut contact surface of the inclined washer 8 is an inclined surface with an angle of 4 degrees.

[0006] Furthermore, an inner hole is provided on the positioning sleeve, the inner cavity radius at the rear end of the inner hole is larger than the inner hole radius, the stud end of the test bolt is inserted into the inner hole, a nut with a radius larger than the inner hole radius is threadedly connected to the stud end of the test bolt in the inner cavity, and a flat washer is provided between the left side of the inner hole wall and the nut.

[0007] Furthermore, an outer edge is arranged outside the positioning sleeve, and a spoke-type pressure sensor is arranged between the outer edge and both sides of the positioning baffle in the horizontal direction.

[0008] Furthermore, the threads of the test bolts were coated with MoS2.

[0009] Furthermore, in S7, when suspected cracks are difficult to identify by visual inspection, thermal acid etching is further used for confirmation.

[0010] Further, S4: after the tightening axial force obtained from the test of the first test bolt, the second test bolt is assembled according to the above structure; the test parameters of the transmission motor are changed from the torque control mode to the tightening axial force control mode, and the tightening axial force is set to 1.1 times the tightening axial force obtained in the test in S3.

[0011] The beneficial effects of the present invention are as follows: the present invention places an inclined washer with a certain angle under the nut of the test bolt, applies the installation torque required by the customer, the installation method is close to the actual installation method, the stress distribution of the test bolt is equal to the stress of the test bolt under the actual working conditions, if the test bolt breaks, it means that the delayed fracture resistance of the test bolt is insufficient, and the test is accurate; Hydrogen embrittlement and delayed fracture generally occur between 24 and 48 hours after installation. This patent is placed under simulated installation conditions for 72 hours to meet the requirements of the delayed fracture resistance test of the bolts. After the test, use a 30x magnifying glass to check the condition of the thread root to clearly know the fatigue strength of the thread. If there are defects on the thread surface, the defects on the thread surface will tear open to form crack sources. After the test, conduct an appearance inspection of the test screw thread. If a crack source is found at the bottom of the thread, it means that the thread strength of the test screw does not meet the requirements.

[0012] After the test, use a 30x magnifying glass to check the R angle of the nut to clearly know the strength capacity of the nut. If the nut strength is insufficient, this test method can be used to test whether the nut will crack when the test bolt is subjected to a certain bending stress under the working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of the structure of the present invention.

[0014] Figure 2 It is a schematic diagram of the test bolt connection structure.

[0015] 1 is a test bolt; 2 is a test nut; 3 is a transmission motor; 4 is a positioning tool; 5 is a positioning sleeve; 6 is a pressure sensor; 7 is a positioning baffle; 8 is an inclined washer; 9 is a screw sleeve; 10 is a torque sensor; 11 is an inner hole; 12 is a flat washer; 13 is an outer edge. DETAILED DESCRIPTION

[0016] The following will be combined with the attached embodiment of the present invention Figure 1 , the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0017] Example 1 Reference Figure 1 , a test method for delayed fracture resistance of a bolt, comprising a transmission motor 3, a positioning tool 4, a positioning sleeve 5, a pressure sensor 6, a positioning baffle 7, an inclined washer 8, a screwing sleeve 9, a torque sensor 10, a test bolt 1 and a test nut 2, a transmission arm of the transmission motor 3 is provided with a torque sensor 10, a screwing sleeve 9 is provided at the end of the transmission arm of the transmission motor 3, the positioning tool 4 is arranged on the transmission arm side of the transmission motor 3, an installation space is provided between the positioning tool 4 and the screwing sleeve 9, a positioning sleeve 5 is provided on the positioning tool 4, a nut end of the test bolt 1 is embedded in the screwing sleeve 9, the stud end of the test bolt 1 passes through the inclined washer 8 and the positioning baffle 7 in sequence and is inserted into the positioning sleeve 5 and is threadedly connected with the test nut 2; a pressure sensor is provided between the positioning sleeve 5 and the positioning baffle 7; S1: Assemble according to the above structure; S2: Set the torque value and select the torque control mode, click the transmission motor to gradually apply the tightening torque; S3: After the tightening torque meets the requirement, the transmission motor automatically reverses and withdraws, the test bolt and the screw sleeve are separated, and the tightening axial force and torque coefficient of the test bolt are obtained; S4: After the tightening axial force obtained from the test of the first test bolt, repeat steps S1 to S3 for the second test bolt, change the test parameters of the transmission motor from the torque control mode to the tightening axial force control mode, and set the tightening axial force to 1.1 times the tightening axial force obtained from the test in S3; S5: Click the transmission motor to tighten the nut and gradually apply the tightening axial force. When the tightening axial force meets the requirement of 1.1 times the tightening axial force obtained in the test of S3, click the transmission motor to stop. The transmission motor does not reverse and exit for 72 hours.

[0018] S6: The transmission motor is reversed and withdrawn after 72 hours, and the test bolt and the screw sleeve are separated; S7: After the test bolts are tested, use a 30x magnifying glass to check whether there are cracks on the threads and the R angle of the nuts. If there are no cracks, the batch is considered qualified. If obvious cracks are visible, the batch is considered unqualified.

[0019] A test method for the delayed fracture resistance of bolts. The contact surface of the nut with the bevel washer is a 4-degree bevel.

[0020] A testing method for delayed fracture resistance of a bolt, wherein an inner hole 11 is provided on a positioning sleeve, the inner cavity radius at the rear end of the inner hole is larger than the inner hole radius, the stud end of the test bolt is inserted into the inner hole, a nut with a radius larger than the inner hole radius is threadedly connected to the stud end of the test bolt in the inner cavity, and a flat washer 12 is provided between the left side of the inner hole wall and the nut.

[0021] A testing method for delayed fracture resistance of bolts. An outer edge 13 is arranged outside a positioning sleeve, and a spoke-type pressure sensor is arranged between the outer edge and both sides of a positioning baffle in a horizontal direction.

[0022] A test method for the delayed fracture resistance of bolts, the threads of the test bolts are coated with MoS2.

[0023] A test method for delayed fracture resistance of bolts. In S7, when suspected cracks are difficult to identify by visual inspection, hot acid etching is further used to confirm.

[0024] A test method for delayed fracture resistance of a bolt, S4: after the tightening axial force obtained from the test of the first test bolt, the second test bolt is assembled according to the above structure; the test parameters of the transmission motor are changed from the torque control mode to the tightening axial force control mode, and the tightening axial force is set to 1.1 times the tightening axial force obtained in the test in S3.

[0025] A test method for delayed fracture resistance of bolts, wherein the tolerance of tightening torque in S2 is controlled within ±10% of the tightening torque; Tightening torque setting: Set the tightening torque according to different specifications or the tightening torque required by the customer for actual installation. The tightening torque is as follows: Serial number Test bolt size Performance level Tightening torque value 1 M20 10.9 520N.M 2 M22 10.9 720N.M 3 M24 10.9 920N.M 4 M27 10.9 1320N.M 5 M30 10.9 1820N.M 6 M30 12.9 2500N.M A test method for delayed fracture resistance of bolts. The contact surface of the nut of the bevel washer is a 4-degree bevel. The bevel washer has an inner chamfer and an outer chamfer. When installed, the outer chamfer of the washer faces the head. The hardness of the washer should be above 50HRC.

[0026] A test method for delayed fracture resistance of bolts. The flat washer has inner chamfer and outer chamfer. When installed, the outer chamfer of the washer faces the nut. The hardness of the flat washer should meet the requirement of 35 to 45 HRC.

[0027] A test method for delayed fracture resistance of bolts, working principle: a knob installation torque is generated by a transmission motor to tighten the test bolt, thereby simulating the installation of the test bolt to generate torque and preload, and then testing the torque coefficient and preload of the test bolt, and after the bolt bears the preload, testing whether the test bolt can reach the predetermined load and meet the performance requirements.

[0028] The above are only preferred specific implementation modes of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for testing delayed fracture resistance of a bolt, comprising a transmission motor (3), a positioning tool (4), a positioning sleeve (5), a pressure sensor (6), a positioning baffle (7), an inclined washer (8), a screw sleeve (9), a torque sensor (10), a test bolt (1) and a test nut (2), characterized in that: A torque sensor (10) is provided on the transmission arm of the transmission motor (3); a screw sleeve (9) is provided at the end of the transmission arm of the transmission motor (3); a positioning tool (4) is arranged on the transmission arm side of the transmission motor (3); an installation space is provided between the positioning tool (4) and the screw sleeve (9); a positioning sleeve (5) is provided on the positioning tool (4); a nut end of the test bolt (1) is embedded in the screw sleeve (9); a stud end of the test bolt (1) passes through an inclined washer (8) and a positioning baffle (7) in sequence and is inserted into the positioning sleeve (5) to be threadedly connected with the test nut (2); a pressure sensor (6) is provided between the positioning sleeve (5) and the positioning baffle (7); S1: Assemble according to the above structure; S2: Set the torque value and select the torque control mode. Click the transmission motor (3) to gradually apply the tightening torque. S3: After the tightening torque meets the requirement, the transmission motor (3) automatically withdraws in the reverse direction, the test bolt (1) and the screw sleeve (9) are separated, and the tightening axial force and torque coefficient of the test bolt (1) are obtained; S4: After the tightening axial force obtained by the test of the first test bolt (1), repeat the steps S1 to S3 for the second test bolt (1), change the test parameters of the transmission motor (3) from the torque control mode to the tightening axial force control mode, and set the tightening axial force to 1.1 times the tightening axial force obtained by the test in S3; S5: Click the transmission motor (3) and tighten the nut to gradually apply the tightening axial force. When the tightening axial force meets the requirement of 1.1 times the tightening axial force obtained in the test of S3, click the transmission motor to stop. The transmission motor does not reverse and exit for 72 hours. S6: After 72 hours, the transmission motor is withdrawn in the reverse direction, and the test bolt (1) and the screw sleeve (9) are separated; S7: After the test bolts (1) are tested, use a 30x magnifying glass to check whether there are cracks on the threads and the R angle of the nuts. If there are no cracks, the batch is considered qualified. If obvious cracks are visible, the batch is considered unqualified.

2. A bolt delayed fracture resistance test method according to claim 1, characterized in that: The nut contact surface of the bevel washer (8) is a 4-degree bevel.

3. A bolt delayed fracture resistance test method according to claim 1, characterized in that: An inner hole (11) is provided on the positioning sleeve, the inner cavity radius at the rear end of the inner hole (11) is larger than the inner hole radius, the stud end of the test bolt is inserted into the inner hole, a nut with a radius larger than the inner hole radius is threadedly connected to the stud end of the test bolt in the inner cavity, and a flat washer (12) is provided between the left side of the inner hole wall and the nut.

4. A bolt delayed fracture resistance test method according to claim 1, characterized in that: An outer edge (13) is provided outside the positioning sleeve, and a spoke-type pressure sensor is provided between the outer edge and two sides of the positioning baffle in the horizontal direction.

5. A bolt delayed fracture resistance test method according to claim 1, characterized in that: The threads of the test bolts were coated with MoS2.

6. A bolt delayed fracture resistance test method according to claim 1, characterized in that: In S7, when suspected cracks are difficult to identify by visual inspection, thermal acid etching is further used to confirm.

7. A test method for delayed fracture resistance of bolts according to claim 1, characterized in that: S4: after the tightening axial force obtained from the test of the first test bolt, the second test bolt is assembled according to the above structure; the test parameters of the transmission motor are changed from a torque control mode to a tightening axial force control mode, and the tightening axial force is set at 1.1 times the tightening axial force obtained in the test in S3.

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