Kunming University of Science and Technology, Japan 600 hydraulic universal testing machine hydraulic clamping piston rod damage analysis and improvement Guo Leikui Department of Electronic Information and Mechanical Engineering, Kunming University, Kunming, Yunnan, 65,8 due to the bending of the rod caused by eccentric compression The normal stress is superimposed on the normal stress generated by compression and the stress concentration. For the cause of the damage, the piston rod push-pull plate is improved, and the effect is remarkable.
It is necessary and meaningful to analyze the damage of the piston rod, find out the cause of its premature failure, improve the structural design or take effective measures to prolong its service life to play the necessary capacity of the equipment for teaching and research services.
Failure Analysis of 1600 Hydraulic Clamping Piston Rod 1.1 Clamping Mechanism and Piston Rod Pushing Plate Jane 131.2 Clamping Mechanism Motion Analysis Under the action of clamping afterburning cylinder, the clamping piston rod push-pull plate is within the stroke range of 45mm vertical distance Reciprocating up and down. After the push-pull plate moves to the gap between the jaw plate 31 and the jaw plate, the entire clamping mechanism is moved. When moving down, the jaws clamp the test piece; when moving up, the jaws release the test piece. There is a time difference between the movement of the clamping piston rod push-pull plate and the movement of the jaw jaw jaws, and the push-pull plate transmits the force momentum to the stationary jaws and the jaws. There is an impact between the push-pull plate and the jaw plate, and the piston rod is also subjected to this effect.
1.3 The clamping piston rod is moved downward by the axial pulling or pressure clamping mechanism, and the piston rod is subjected to the axial pressure; the mechanism moves upwards, and the piston rod is subjected to the axial pulling force. The push-pull force applied by the manufacturer's piston rod is 1.4. When the clamping piston rod is subjected to the tensile and compressive force, the normal stress of the piston rod cross-section changes with time and stress, and is affected by the alternating stress. The fatigue limit of the component under the symmetrical cycle is the lowest, which is approximated by the symmetric cyclic alternating stress. The fatigue limit of 1.5 clamping piston rod shape under the tension-symmetric cyclic alternating stress causes severe stress concentration on the piston rod. The diameter of the polished rod is 20, the diameter of the threaded rod is 10, and the cross-section transition is Right angle step, the screw is tapped and threaded. A stress concentration is formed at the transition section of the polished rod and the threaded rod.
In the engineering, under the action of symmetric cyclic alternating stress, considering the stress concentration of the member, the influence of the size and surface quality factors, the fatigue limit of the member subjected to the alternating stress of tension and compression is. 6 The relative deviation of the left and right sides of the jaw plate is caused by the eccentric compression of the clamping piston rod, which causes additional bending and normal stress. In the engineering, the welding part or some test pieces are difficult to make the clamping part coaxial; If the clamp test piece is not operated properly, the gap between the jaw clamp plate and the push-pull plate is too large, causing the opposite sides of the jaw to be opposite, causing the piston rod to be eccentrically pressed. The additional bending normal stress is 1 for the bending section of the threaded rod cross section. the amount.
1.7 Actual calculation In summary, the maximum stress that can be withstood when the clamping piston rod is working is because the clamping cylinder pressure range is 0 = 6,83, and the clamped specimen diameter range is 0=1426 corresponding to the measured eccentricity The corresponding normal stress range is under the action of symmetric cyclic alternating stress. The fatigue strength condition of the member is 40Cr, A=80OMPa, threaded, threaded rod finishing, which can be qualitatively analyzed and quantitatively calculated. It is believed that under the action of alternating stress, the clamping piston rod firstly generates cracks on the transition section of the polished rod and the threaded rod due to the impact stress concentration. After a certain number of stress cycles, the crack expands continuously, and finally under an accidental impact or vibration. The piston rod is along the weakened section and suddenly breaks due to insufficient strength.
The above analysis was confirmed by the fact that the piston rod was broken. The rods are destroyed in the transition zone between the polished rod and the threaded rod. The fractures are in the white bright area and the coarse sugar area, and there is no obvious plastic deformation, which is brittle fracture.
2Improvement 2.1 Change the built-in clamping cylinder for the external type mainly for the new equipment that is being produced or to be shipped. Refer to Jia 100 type external manual clamping mechanism, and manually apply the force to the hydraulic lever to achieve the hydraulic clamp. tight.
2.2 reduce or eliminate the impact stress concentration eccentric compression for the equipment in use, increase the diameter of the threaded rod portion, so that 20221. adhesion layer 1 stomach thick oil-resistant butadiene glue on the bottom of the push-pull plate 3 reduce the plate and The gap between the jaws of the jaws forces the left and right jaws to be at the same time, preventing the rod from being eccentrically pressed, avoiding the additional bending normal stress, ensuring that the stress during the working of the rod is lower than that of the 32-inch rubber layer and also slowing down the impact. .
2.3 Changing the connection mode between the piston rod and the push-pull plate adopts the hot-rolling integral forming process, rolling the clamping piston rod and the push-pull plate into a member, designing the reinforcing rib on the front and rear sides of the piston rod, and increasing the thickness of the push-pull plate. Coordinate the movement to eliminate the large drop in fatigue limit caused by stress concentration and the possible bending normal stress caused by the eccentric compression of the rod.
3 Conclusions The improvement measures of Section 2.2 were adopted. The service life of the piston rod was increased from the average of 650 per pole before the change to an average of 2,1001 per pole. The service life extension rate was 223. The actual utilization rate of the equipment was improved, and the actual utilization rate was improved. The role and benefits of the equipment. The improvement effect is significant.
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Yantai Tianbing Construction Machinery Co., Ltd