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Analysis on the reason of steel rod breaking in rod mill

Analysis on the reason of rod breaking of rod mill


Under normal circumstances, the grinding rods are arranged in parallel. If the arrangement order is disturbed, it will cause the direct impact between the grinding rod and the grinding rod, worsen the stress condition of the grinding rod, and lead to the fracture of the grinding rod. Many factors lead to the disorder of the arrangement of the grinding rod.


Key words: rod mill, rod arrangement, disorder and fracture


1, foreword


During the operation of rod mill, two kinds of damage often occur to the rod mill. One is the wear caused by the nail rolling, carving and ploughing of the edges and corners of the rock block, and the other is the impact fracture caused by the impact with the rock block. Among them, wear is absolute and inevitable. No matter what kind of rod mill and rod are adopted, no matter what kind of rock is ground and what kind of operation conditions are adopted, it is difficult to avoid occasionally. Fracture is different. Although many projects have broken the rod when using the rod mill, some of them are still very serious, but some of them are very few, some of them are not even happened at all. For example, in one project, mbz21003600 rod mill is used to grind quartzite and quartz sandstone with grain size of 5-40mm and compressive strength of 160-330mpa. Although its feeding amount is far more than the nameplate value, it rarely breaks the rod. In another project, when the same rod mill is used to grind gravel with grain size of 5-20mm, limestone and dolomite accounting for about 60%, sandstone and quartz sandstone accounting for about 37%, its feeding amount is only (30-35 )It is also rare to break the rod. In the first project, mbz15003000 rod mill is used to grind granite and granodiorite with a compressive strength of 200MPa. Although the feed particle size is 5-20mm and the feed volume is 1110 kg / h, there is no broken rod at all. These show that the broken bar is the same as the worn part, it is not absolute and inevitable. On the contrary, it can be avoided as long as the causes are clear and corresponding measures are taken. At least, the number of broken bars can be greatly reduced.


2 causes of grinding rod fracture


The cause of grinding rod fracture is complex. In addition to the excess mechanical energy of grinding rod itself, so that there is more energy left after the transformation into rock crushing work and some corresponding and inevitable useless work, the parallel arrangement order of grinding rod is disturbed, which is also a very important reason.


The grinding bar, which has a certain diameter of round steel bar and chip slender bar, has a length ratio of 30-80. Only when these slender bars are stacked together, their longitudinal axis remains parallel, and their cross-section is arranged in the shape of "plum blossom", can they become the closest arrangement and occupy the smallest space, that is to say, in a certain size of space, they contain the most grinding bars and have the highest grinding efficiency. At the same time, only this kind of arrangement can ensure that the grinding rod falls on the rock block in the crack of the lower layer rod when it is dropped and dropped, and not directly collide with the lower layer rod. The impact force that the grinding rod receives when it collides with the rock block can become the dispersive force distributed in the length direction and be the impact pressure. Only in this way can we make full use of the strength of the grinding rod and give full play to its bearing capacity. Under normal circumstances, the grinding rod can automatically form this regular arrangement under the restriction of gravity and the boundary condition of grinding cylinder, even when the grinding cylinder rotates. This is because the cross-section of the grinding rod is round. No matter how closely they are arranged, there are always strip-shaped groove gaps between the rod and the rod. Due to the effect of gravity and the rotation of the grinding cylinder, the upper grinding rod will automatically roll into the groove gap of the lower grinding rod to make itself in a low-energy position. Once the upper grinding rod falls into the gap between the lower grinding rods, it will be in a stable state even if it is constrained by it. Without certain force, it is impossible to change its parallel arrangement state beyond the "groove ridge". However, if a gap between the grinding rods is partially blocked, one end of its corresponding upper grinding rod will be raised to become skewed; if a gap is completely or largely blocked, its corresponding upper grinding rod will completely lose the constraint of this gap and become more free. At this time, as long as the rod is subject to a small external force, it will change its original "posture" and become reclining. After a grinding rod tilts, its spatial position relationship with other grinding rods around it changes from parallel to skew, and the line contact relationship between grinding rods correspondingly changes to point contact. In this way, when the other grinding rods fall back, they will not hit the rock block, but hit the crooked grinding rod below, forming a direct impact between the grinding rod and the grinding rod; moreover, the impact force is no longer the impact pressure distributed along the longitudinal direction of the rod, but the concentrated force acting on the contact point; as a result, even if the stress in the grinding rod is changed from the original stress dominated by pressure to the bending stress, the impact force will be Even if the stress in the grinding rod gets worse, under the action of this stress, the grinding rod without obvious defects may have defects due to excessive local stress, while the grinding rod with obvious defects will have stress concentration at its defects, which will promote the development and expansion of these defects and finally lead to the fracture of the grinding rod. It has been proved that as long as one grinding rod is skewed, it may cause the above results, and even cause the flocculent disorder of other grinding rod arrangement, resulting in the so-called "disordered rod" and serious rod breaking phenomenon.


  


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