After more than 60 years of development, thread-locking adhesives have been widely used in various industries. However, the anti-loosening property of thread-locking glue has not received widespread attention and attention in the industry. At present, there are no standards and methods for corresponding evaluation in the industry, and related research is also rare. However, in the fastener industry, GB/T 10431-2008 "Fastener lateral vibration test method [1] method" standard for testing and verification of fasteners has been widely recognized by upstream and downstream enterprises in the industry. . The method was proposed by German engineer Gerhard H. Junker based on the fact that when the lateral force acting on the fastener causes a relative movement between the thread pair and the bearing surface, the fastener will self-loose and the transverse vibration pair The self-looseness of the fastener is far beyond the influence of axial vibration. At present, this kind of test method has been widely used in the domestic automobile, railway and other industries [2~4]. A lot of research at home and abroad shows that the looseness of the fastener is mainly caused by the lateral vibration load, so it can be compared by the lateral vibration test. Evaluation of the anti-loose [5, 6] performance of the anti-loose method. Thread-locking anaerobic adhesive is a chemical anti-loose evaluation method for fasteners. Therefore, in theory, its anti-loosening performance can be evaluated by referring to GB/T 10431-2008 standard. Huitian Company has developed a new generation of thread-locking anaerobic adhesives 7243 and 7263 for the shortcomings of traditional thread-locking adhesives, such as sensitivity to materials, low temperature resistance and poor oil tolerance. The specific performance is that the curing effect on the inert material is greatly improved, and the material is not sensitive; the temperature resistance is improved from 150 ° C to 180 ° C; the superior oil tolerance and the slight oil surface surface curing performance are not affected. Among them, the new generation of thread-locking anaerobic adhesive 7243 is medium-strength type, and 7263 is high-strength type. This study will refer to the GB/T 10431-2008 standard to test the difference in lateral vibration performance of the two types of rubber before and after the test, to examine the anti-loosening properties of these two kinds of thread-locking anaerobic adhesive, for the future lock anaerobic thread The standardization of the rubber anti-loose performance test method provides some reference basis.
1 Experimental part
1.1 Introduction to the loosening mechanism and anti-loose measures of threaded fasteners
The biggest disadvantage of threaded fasteners is that they are prone to looseness during use. The mechanism of loosening failure of threaded fasteners is generally divided into tension relaxation and looseness of rotation. Tension relaxation is caused by the looseness of the fastener or the "collapse" of the connecting piece. It can be solved by improving the rigidity of the material, adding the gasket, etc. The looseness caused by the tension relaxation cannot be solved by using the anaerobic adhesive. Since the friction angle is larger than the angle of the thread, there is also a condition that the thread is self-locking, and the threaded fastener does not loosen under normal conditions. However, when subjected to variable loads (such as severe vibration and shock loads) under working conditions, the threaded fasteners produce microscopic slippage on the threads and bearing surfaces. This relative microscopic motion makes the coefficient of friction relatively high. The static value becomes a lower dynamic value, at which time the axial force acting on the thread forms an internal release torque in the circumferential direction that causes the nut to loosen, causing the nut to begin to loosen, multiple cycles until tightening The piece is loose, and this looseness is called loosening of the rotation. The use of thread-locking anaerobic adhesive is an effective measure to prevent the loosening of the threaded fastener. The mechanism is that the thread-locking anaerobic adhesive fills the gap of the threaded joint. When the glue is solidified, the mating surface is glued into a whole. Eliminates the root cause of fretting wear.
1.2 Experimental instruments
(1) Lateral vibration testing machine, electromagnetic testing machine developed by Zhejiang National Inspection and Testing Technology Co., Ltd. (as shown in Figure 1, the test clamping device part fully meets the requirements of GB/T 10431-2008 standard, that is, utilization The fastener clamped by the certain tightening force on the testing machine generates alternating lateral displacement between the two metal plates, causing the connection to loosen, resulting in a reduction or even complete loss of the clamping force. Continuously recording the instantaneous value of the clamping force, According to the comparison of the recorded data, the looseness of the fastener can be judged. The lateral vibration load is generated by the speed and torque of the main motor transmitted to the rotating spindle through the timing belt system and the electromagnetic clutch. The rotating spindle is in the clutch moving plate. Under the action of the S, the N-pole permanent magnet rotates, so that the S, N-pole magnetic lines produce a cyclical change of absorption and repulsive. Because of this periodic magnetic force, it is converted into a fixed by the permanent magnet translation mechanism. Frequency (12.5 Hz) and axial reciprocating resonant motion of a specified amplitude, while using the adjustment of the magnet gap to obtain lateral vibrational forces and amplitudes of different magnitudes ).
Figure 1 Transverse vibration testing machine
Fig.1 Transverse vibration testing machine
(2) Experimental fixture, self-made (in accordance with the "Experimental device for nut experiment" specified in GB/T 10431 standard).
(3) Test bolts, 10.9 grade M10 plated zinc bolts (accuracy of 6g) specified in GB/T5782-2016 "Hexagon head bolts".
(4) Test nut, 10 grade M10 chrome-plated zinc nut (accuracy 6H) specified in GB/T6170-2000 "Type 1 Hex Nut".
1.3 Test methods and data processing
Test method: According to GB/T10431-2008 "Fastener lateral vibration test method" standard (10 samples are tested in each condition group, the vibration frequency is 12.5Hz, the amplitude is 1mm, the vibration frequency is 3000 times, Under the condition that the number of vibrations is the same, the higher the clamping force retention rate after the fastener vibrates, the better the anti-loose performance is).
2 Results and discussion
2.1 Non-adhesive anti-loosening performance
The smaller the initial preload, the looser the uncoated fastener. In the industrial field, the pre-tightening force of the fastener installation is generally between 30% and 70% of the bolt-assured load. The 10.9 grade M10 color-plated zinc bolts have a guaranteed load of 48.1kN. Three initial clamping forces were selected during the study to test: 1 about 40% bolt-assured load (about 19.24kN); 2 about 50% bolt-assured load (about 24.05kN); 3 about 70% bolt guaranteed load (about 33.67kN). Under the three initial clamping forces, the transverse vibration test effects of the blank fasteners are shown in Figures 2(a), 2(b) and 2(c), respectively. When the initial clamping force is 40% bolt guarantee load and 50% bolt guarantee load, the anti-loose effect is relatively poor, the clamping force is quickly attenuated after the fastener is vibrated, and the initial pre-tightening force is increased to 70% bolt-assured load. The probability of fastener loosening is greatly reduced, and most of the sample pre-tightening force is maintained above 80%, which means that the initial pre-tightening force can be improved, and the fastening ability of the fastener can be improved to some extent. Even so, there is always a large probability of loosening, and the reliability of the anti-loose is not ideal. In addition, the higher initial preload force helps to improve the anti-slipping property, but the friction coefficient of the installation tool and the bolt is very high, and the slightest inattention may cause overload, which may cause new potential hidden dangers. This is because it is impossible to ensure uniform uniformity of friction coefficient in the manufacture of threaded fasteners, and there is a certain fluctuation between individuals. If the fluctuation range is too large, the actual preload force may exceed the fastener guaranteed load. Requirements, there is a risk of overload.
2.2 Glue-like anti-loosening properties
Tested for the anti-loosening properties of rubberized fasteners under different initial preloads (approximately 40% bolt guaranteed load, approximately 50% bolt guaranteed load and approximately 70% bolt guaranteed load), wherein threaded locking anaerobic adhesive 7243 was applied. As shown in Figures 3(a), 3(b) and 3(c); the threaded locking anaerobic adhesive 7263 is shown in Figures 4(a), 4(b) and 4(c). It can be seen from Fig. 3 and Fig. 4 that under different preload conditions, the pre-tightening force of the fasteners assembled by curing 7243 or 7263 lock glue is maintained at 95% or more of the initial preload force during the lateral vibration. Compared with the non-adhesive sample, the rubberized fastener not only improves the anti-loosening property, but also improves the anti-loose reliability, and has a very good anti-loosening effect even at a low pre-tightening force. This means that the use of locking glue as a loosening measure can properly reduce the pre-tightening force requirements, thereby reducing the friction coefficient of the installation tool and the fastener, and is a very simple and economical anti-loose measure. This is precisely because there is a large gap in the thread engagement area when the glue is not locked, and the thread of the meshing area is unevenly distributed by the [7] force. When the lateral impact vibration is received, the rotation looseness is prone to occur; and after the thread locking glue is used, the gap of the thread auxiliary region is completely filled and solidified by the solidified material of the locking glue, so that the bolt and the nut are connected after being tightened. As a whole, the pre-tightening force is more evenly distributed in the threaded meshing area, so it is difficult to loosen in the lateral vibration.
2.3 Effect of Torque Strength on Locking Resistance
The torque strength of the two types of thread locking glues 7243 and 7263 under different conditions was tested, as shown in Table 1. It can be seen from Table 1: Although the torque strength (destructive torque and pull-out torque) of 7263 under various conditions is significantly higher than 7243, both of them performed very well in the above-mentioned anti-loose performance test, and no obvious was found. Difference, this shows that there is no correlation between the strength of the locking rubber torque and its anti-loose performance. At present, many people often think that the higher the torque strength of the thread-locking anaerobic rubber, the better the anti-loose performance, but from the experimental results, there is no direct correspondence between the two, so it is not appropriate to simply lock the anaerobic rubber torque with the thread. The strength is used to evaluate the effectiveness of the anti-loose ability. The reason for the analysis may be that after the use of the thread locking glue, the locking glue will have two effects after solidification in the gap of the meshing zone, one is the bonding effect (expressed as the torque strength); the second is the filling effect (the screwing is made) More uniform force). Both of these effects may have a positive effect on the anti-loosening property, but the filling effect is dominant. Therefore, regardless of the high or low torque strength of the thread-locking anaerobic adhesive, as long as it is solidified in the meshing zone, an excellent filling effect is produced, and further Shows excellent anti-loosening effect.
Figure 2: Results of lateral vibration test of blank set fasteners with initial clamping force
Fig.2 Transverse vibration test results of blank group fasteners with different initial clamping force
Fig. 3 Transverse vibration test results of 7243 locking rubber fasteners with different initial clamping forces
Fig.3 Transverse vibration test results of fasteners coated with 7243 thread locking anaerobic adhesive for different initial clamping force
Figure 4 Transverse vibration test results of 7265 lock rubber fasteners with different initial clamping forces
Fig.4 Transverse vibration test results of fasteners coated with 7263 thread locking anaerobic adhesives fordifferent initial clamping force
3 Conclusion
(1) Uncoated rubber fasteners are relatively easy to loosen. Although the initial pre-tightening force can be improved to some extent, there is always a large probability of loosening, and the reliability of anti-looseness is not ideal.
(2) Compared with uncoated fasteners, the locking adhesives 7243 and 7263 not only significantly improve the fastener's looseness, but also increase the reliability of the lock, even at lower preload conditions. It also has a very good anti-loose effect.
(3) There is no correlation between the torque strength of the thread-locking anaerobic rubber and its anti-loose performance. It is not advisable to use the torque strength of the thread-locking anaerobic rubber to evaluate its anti-loosening ability.
references
[1] GB/T 10431-2008, Test method for lateral vibration of fasteners [S]. Beijing: China Standard Press, 2008.
[ 2 ] Junker GH . Criteria for selfloosening of fasteners under vibration [J]. Aircraft Engineering & Aerospace Technology, 1969, 44(10): 14-16.
[3] Li Weirong. Research on anti-loose technology and test method of threaded fasteners [D]. Hefei: Hefei University of Technology, 2005.
[4] Zhang Ting, Jiang Zhaoxi, Feng Mei. Comparison of anti-vibration and anti-loose properties of fasteners [J] . Metal Products, 2012, 38(1): 78-80.
[5] Ai Shaohua, Zhao Jingzuo, Han Shengli. Study on the use of pre-coated anaerobic adhesive on fasteners [J]. Bonding, 2013, 34(12): 50-53.
[6] Ai Shaohua, Zhao Jingzuo, Han Shengli. Effects of thread-locking anaerobic adhesive on the friction coefficient and torque coefficient of fasteners [J]. Bonding, 2016, 37(1): 45-47.
[7] Xiao Weiqun. Failure mode, mechanism analysis and design principles of high-strength threaded fasteners [J]. Automotive Technology and Materials, 2006, 21(7): 26-28.
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