Fatigue Failure Analysis and Protective Measures of Compressor Cylinder Head Bolts

1 The force analysis of the bolt subjected to the axial variable load has been tightened tightly at the time of assembly, and each bolt is pre-stressed. After the cylinder is inflated, the working load assumed by each bolt is the corpse. Due to the influence of the bolt and the deformation of the coupled member 12, the total tensile force of the bolt after the cylinder intake is not, and the stiffness of the bolt is related to the stiffness of the coupling.

At this time, the axial tensile force of the bolt is increased, and the corresponding deformation amount of the bolt is 8+8, and the total elongation of the bolt is 81+8, and the connected member is correspondingly stretched according to the overall deformation coordination condition of the joint. In the middle, at this time, the force of the bolt is changed from 0 to 0, and the force of the joint is changed into a residual preload. The total tension of the bolt is 0 = +.

From the ancient can be introduced, so that the relative stiffness, then, = due to the repeated intake and exhaust of the cylinder, the working load of each bolt is changed between, the total pulling force in the bolt caused by Change between.

2 The main influencing factors of bolt fatigue failure Engineering is divided into high cycle fatigue and low cycle fatigue. During the period of use, the stress cycle exceeding 105 times is called high cycle fatigue, and the cycle number is 102105 times, which is called low cycle fatigue. For a container that uses a bolt-coupled pressure, the stress cycle does not exceed 105 times, so it is a range of low cycle fatigue.

Force modulus, section shrinkage when the core material breaks; CT, the material's endurance limit, the mechanical properties of the 2,9 equivalent alternating material, the field + can be larger by the angled bolt, the life will be reduced. The main factors affecting the equivalent alternating stress amplitude are the alternating stress amplitude, and the true average stress. Here, we discuss the effect of average stress on low cycle fatigue.

Stress, =+, can, the true average stress has no effect on fatigue life.

In the actual cycle, the first load changes along 0 to 8 lines, and in the subsequent cycles, the actual stress changes along line 80.

Therefore, the first and subsequent cycles, =, the average stress is. From the first cycle to the subsequent cycle, the average stress decreases, from the calculated value, = 712 to the true value, = Liaochang Ting 1. Therefore, Liao. 5 Ting 12 Ting. ! The effect of average stress on fatigue life will be reduced.

The load varies along the zero line of 0 people, and the zero line along the unloading, and the subsequent cycle will move along the parallel edge 80. If the yield limits of the tensile and compressive are equal, then the true value of the average stress is clearly seen to be automatically adjusted to zero amiO. That is, when CT12CTs, the average stress has no effect on the fatigue life.

The bolt stress does not exceed 2 so the influence of the average stress should be considered and corrected on the design fatigue curve. The effect of stress amplitude on the fatigue life of bolts is now discussed.

The corresponding maximum tensile stress on the dangerous section of the bolt = 5, the minimum tensile stress = Qp2, defined by the formula, the cyclic stress amplitude is determined by the formula, the stress amplitude, and the work load plant and bolt stiffness and the stiffness of the joint.

From the above analysis, it is known that the main factors affecting the fatigue life of bolts are the average stress and the stress amplitude. Of course, temperature and its mechanical properties also have an effect on its longevity and will not be discussed here. Therefore, for the bolt connection subjected to the variable load, not only the static strength calculation according to the maximum stress but also the cyclic stress amplitude of the thread portion is checked.

3 Measures to Improve the Fatigue Strength of Bolts As discussed above, the smaller the allowable stress amplitude, the longer the bolt life. And the main measures to improve the strength of fatigue 97 are 1 to reduce the working load, the smaller the smaller the fixed working load, the smaller.

If the remaining preload and working load are maintained, the bolt stiffness is reduced or the stiffness of the joint is increased to reduce the stress amplitude of the bolt. If these two measures are taken at the same time, the effect is better.

For example, the purpose of changing the bolt connection of the cylinder end cover from 5 6 to 5 is to increase the bolt length and reduce the bolt rigidity, thereby improving the fatigue strength of the bolt.

In order to ensure a tight joint, the soft gasket with a shape seal ratio of 4 is properly sealed, which increases the rigidity of the joint, thereby increasing the bolt strength, and the magic seal effect is better.

When the stress and strain relationship of the 6ic heart is used as a common nut, the load distribution between the threads is uneven and the load distribution is uneven. The load-bearing nut can be used, and will not be discussed in detail here.

4 Reducing stress concentration and additional stress Due to some negligence in design, manufacture and installation, the bolt is sometimes subjected to additional bending stress, which has a great influence on the bolt strength and should be avoided as much as possible. In addition, in the manufacturing process, the method of using cold head bolts and rolling threads, or heat treatment methods such as cyanidation shot blasting can effectively improve the bolt connection of the compressor cylinder head of the bolt 4 The cylinder repeatedly generates intake and exhaust, and each bolt is fatigue-damaged by the axial variable load. As mentioned above, the stress amplitude and average stress are the main factors affecting the fatigue strength of the bolt under variable load. The bolts should be stopped at the appropriate position on the 50th page. A shallow groove can also be opened to apply pressure in the appropriate direction to cause plastic deformation of the amount of contraction 8 at the orifice of the die seat. The deformation will be in the same direction as the circumference. The processed bearing bush can meet the requirements of the sample with the tiled thinned area and the inner hole surface.

By adopting the above technical measures, the inner surface processing process of the bearing bush and the shaving and thinning processing process can be combined into one process, and the quality of the product is also obviously improved. The processing method has been widely applied to the bearing manufacturers in China.

4 Conclusion, the seal of the shape seal (9) in the process of cracking to damage under the action of the soft gasket sealing force, the internal damage is gradually accumulated, and the damage is accumulated to a certain extent. Therefore, each stress greater than the fatigue allowable stress causes a loss of secondary life per cycle. In the actual work of the compressor, from design to operation, it should be noted that any stress greater than the allowable stress is included in the fatigue damage; the actual stress increases when the stress is concentrated; the influence of the absolute size surface roughness and the safety factor.

Editor-in-Chief Wu Zongze. Mechanical parts 0. Beijing Central Radio and Television University published Dong Qinghua. Mechanical Parts. Beijing China Agricultural Machinery Press, 1981.

Editor-in-Chief Chen Guoli. Pressure vessel and chemical equipment elbow. Guangzhou South China University of Technology. Mechanical design and manufacturing in the field of research. Has published 7 papers.

The amount of shading is the design element of the bearing bush, which is to improve the reliability of the bearing work and to improve the amount of the shingle of the bush at the split surface.

The method of processing the thickness of the wadding by using the structure of the elastic deformation of the mold base or the plastic deformation and other similar effects to reduce the thickness of the shank of the seat hole to meet the processing requirements of the wall thickness of the bearing bush, Helping to improve quality and reduce costs, the method has been widely used in bearing production plants.

1 Yuan Hui, Chen Boxian and so on. Reliability analysis and improvement of interference fit of thin-walled bushings.

2 Chen Boxian. The design of the thin-walled bearing bush is calculated and improved. Internal Combustion Engine Engineering, the first author of the introduction of Chen Boling, female, born in 1954, Taishan, Guangdong, undergraduate, lecturer. Artificial intelligence and mechanical design techniques in the field of research. 9 papers have been published.

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