2 load capacity analysis of the main hydraulic cylinder
2. 1 cylinder failure characteristics
The main hydraulic cylinders of several tension leveling machines of the bloomer of the steelmaking plant frequently have cracks in the fastening bolts of the cylinders. The fracture phenomenon is as follows: bolt breakage occurs during stable production or during delivery to the spindle When breaking, usually 8 full breaks, it is not clear which one is broken; the cylinder is a combined cylinder provided by DAN IEL I.
Based on this, the overall analysis of the working load characteristics of the cylinder is carried out to find the main source of the bolt fracture.
2. 2 analysis of cylinder load characteristics
1) Main pressure lower cylinder For the tension leveler, its function is mainly used to control the vertical blanking force of the upper and lower pinch rolls of the straightening machine to the casting blank, so as to realize the clamping force, the pulling force and the dynamic lightness of the casting blank. Press down.
2) This special structure has the following features: (1) A coaxial connection between the piston rod of the cylinder and the pressing frame of the upper pinch roller ensures that the piston rod of the cylinder is not subjected to excessive bending moment in the width direction; (2) The vertical four guide rods directly bear the lateral action of the blanking resistance in the direction of the casting flow, ensuring that the piston rod only bears the vertical belly force; (3) an arc-shaped bearing bush is used between the piston rod connecting shafts of the cylinder It can well eliminate the bending force transmission effect in the direction of the casting flow, and avoid the excessive bending moment of the cylinder piston rod in the casting flow direction.
3) Analysis of the load on the cylinder body: It can be seen that the structural characteristics of the main hydraulic cylinder are as follows: (1) The entire cylinder is connected and fixed by the bottom connecting disc and the upper frame of the tension leveler; (2) the cylindrical protrusion, the bottom flange and The bottom connecting discs are only pre-tightened by eight fastening bolts; (3) The load force level of the fastening bolts is only the sum of the tightening force and the hydraulic pressure of the hydraulic cylinder.
According to the above structural analysis results, the finite element modeling of the cylinder body can be performed by the finite element analysis software ANSYS.
2. 3 finite element modeling
1) Based on the symmetrical characteristics of the cylinder load, in order to improve the calculation efficiency, this model is established as a 1 / 3 3D solid 1:1 model of the cylinder entity.
2) In order to ensure good bearing consistency between the cylinder contact model and the real object, a plurality of nonlinear contact pairs are established in the model to simulate the contact force transmission characteristics of the actual cylinder, mainly as follows: (1) The outer wall surface of the rod of the piston rod Establishing a contact pair with the inner wall surface of the bottom flange; (2) establishing a contact pair between the piston outer wall surface of the piston rod and the inner wall surface of the cylinder middle cylinder; (3) two fastenings contained in the 1 / 4 model The outer wall surface of the screw of the bolt and the end surface of the nut are all in contact.
At the same time, in order to simulate the preload force of the actual fastening bolt, a predetermined preload force is applied in the boundary condition of the mold model. At the same time, the model adopts the three-dimensional solid element Solid45, all contact sections adopt the Contact174 and target170 units, and all the split surfaces are loaded with symmetrical boundary conditions.
2. 4 finite element analysis
According to the pre-tightening characteristics of the bolt, the corresponding boundary condition load is set, and the maximum practical working load of 16 MPa is applied in the hydraulic cylinder. The three-dimensional stress distribution cloud diagram of each joint structure can be obtained as follows: 1) The tightening bolt force: the maximum stress The level is 551 MPa, distributed at the joint of the screw and the nut; 2) the bottom connecting disc: the maximum stress level of the connecting disc is 278 MPa, distributed in the area of ​​the screw hole; 3) the bottom flange: the maximum stress level is 56. 9 MPa, distribution The connection area between the screw hole area and the outer surface; 4) The middle cylinder of the cylinder: the maximum stress level is 484 MPa, which is mainly distributed in the screw hole contact area.
3 oil tank structure transformation proposal
Based on the analysis results, it is known that the fastening bolt is most likely to break. Once the oil pressure reaches 16 MPa, the stress level reaches or exceeds the strength limit of the bolt itself, and fracture is inevitable. After any one of them breaks, the remaining 7 must carry the load level of the previous 8 pieces, so in the actual case, once broken, 8 pieces must be broken at the same time. According to the results of this analysis, the following suggestions for improvement are proposed for the design: 1) increase the height of the cylindrical pedestal, increase the height of the supporting pedestal, and increase the peripheral diameter of the bottom flange. The purpose is to increase the tightness. The bolt diameter of the bolt increases the diameter of the bolt hole, thereby reducing the overall working stress level of the bolt and the stress level of the bolt hole area, reducing the possibility of fracture; 2) processing the bottom flange and the bottom disc into one piece (integral casting) At the same time, increase the diameter of the outer diameter of the cylindrical boss, the purpose is to reduce the number of screw connectors, improve the stability of the screw bearing (may be limited by the difficulty of the processing process); 3) when the cylinder is assembled, check 8 tight Whether the pre-tightening force of the fixing bolts is consistent, try to prevent the possibility of large difference in pre-tightening force; the supplier has carried out the corresponding structural transformation of the cylinder under the suggestion of this improvement and re-use it on the site. The effect was found: none of the cylinders failed after the transformation. It can be seen that this analysis provides direct theoretical support for the stable production of the bloomer. At the same time, this analysis provides a scientific check method for the analysis and calculation of the capacity of the main hydraulic cylinder of the casting machine. .
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