In the late 1980s, with the development of foreign graded crushing technology, mineral sizers crusher rose and became a new crushing equipment. The crushing teeth are arranged in spiral on the tooth roller, and the material is broken by rotating parallel tooth rollers towards or opposite each other. Because the equipment is only larger than the product size of the material crushing, and less than the product size of the material directly sieve, so it is also called screening crusher.mineral sizers crusher makes full use of the characteristics that the shear and tensile strength of the material is far less than the compressive strength, and uses the shear and tensile strength to break the material.
Therefore,mineral sizers crusher has the characteristics of low energy consumption, small over-crushing rate, simple structure, convenient maintenance and so on. It is one of the essential crushing equipment in many large coal mines and open-pit mines in China.
1. Existing problems of beam crushing device
The 2PGC-1370mineral sizers crusher is selected for a domestic mining plant. The installed power is 2×250kW, the diameter of crushing roll is 1370mm, the production capacity is 2000t/h, the maximum feeding particle size is 1500mm, the discharging particle size is 300mm, and the crushing material is limestone. After commissioning and running, the crushing roller has great crushing force, the material is occluding smoothly, and the output is up to the standard. However, after 3 months of use, the fixed bolts of the broken beam broke frequently and were replaced once every 1 to 2 months on average. Later, the strength of the broken bolt was changed from 10.9 to 12.9, and the bolt broke again after being used for about two months.
1.1 Structure of beam crushing device
mineral sizers crusher consists of motor, hydraulic coupler, reducer, toothed coupling, crushing roll, box and crushing beam, and its structure is shown in Figure 1. The upper area between the teeth of the two crushing rollers is the first level crushing area. Through the crushing roller teeth occlusion, the primary is realized, which is mainly responsible for crushing large materials. The two triangular areas between the lower crushing roll and the crushing beam are the secondary crushing zones. The secondary crushing of materials can be realized through the occlusion of the crushing roll teeth and the crushing beam teeth. Through two crushing, the crushing ratio can reach about 6:1, the discharge particle size is uniform.
The broken beam is a key component to realize secondary crushing, improve crushing ratio and control particle size. The broken beam device is formed by the broken beam body, the broken beam teeth and the particle size regulating device, and its structure is shown in Figure 2. The broken beam is fixed on the box with bolts, and the teeth of the broken beam are connected with the broken beam through a flat bond and fixed with bolts. With the wear of the crushing teeth, the discharge particle size
In this case, the particle size can be adjusted by the particle size adjustment device (see Figure 3). Adjustment method: By twisting the long bolt, lift the broken beam to the appropriate height, then relax the long bolt, add the gasket, adjust the broken beam, and then fix it with the fixing bolt. Namely, by reducing the distance between the crushing roller and the crushing beam crushing chamber to compensate the crushing tooth wear amount, so as to meet the set particle size requirements again.
1.2 Check the strength of bolts
In view of the fixed bolt fracture, it is considered that the broken beam is caused by too much force. The bolt adopts M36 high-strength bolt. In order to prevent the broken beam from loosening, a large pre-tightening force Fo=350000N is selected. The force diagram of the broken beam is shown in Figure 4.
Stress analysis was made on the tooth tip of crushing roller.
Where: T is crushing roll torque, N·m; T is the reverse torque of the broken beam on the roller teeth, N·m; N is the motor power; N = 250 kw. n is the speed of crushing roll, n=24r/min; k is the overload factor at the moment of impact, which is 1.5; F is the tangential force of the broken beam on the roller teeth, N; D is the diameter of crushing roll, which is 1.37m.
Then the shear stress of bolt is analyzed.
Where, F. Is the horizontal shear force on the bolt, N; F' is the reaction of F, N; a is the tooth inclination Angle of the broken beam, a=30°; r is the horizontal shear stress on the bolt; d1 is the M36 bolt path, d1=0.03166m; [r] is the allowable shear stress of bolt, which is 210MPa; [o-1 is the allowable value of alternating stress of bolt, which is 350MPa.
The calculation results show that the horizontal shear stress of the fixed bolt is greater than the allowable stress, which leads to the bolt fracture. In the vertical direction, due to the vertical additional force F on the bolt. Contrary to the direction of bolt pretightening force Fo, the total tensile stress will be less than the pretightening force, so it is not considered.
2 Improvement measures screw
After the bolt is broken, if it is not treated in time, the broken beam will be displaced, and the teeth of the crushing roll and the teeth of the crushing beam will interfere with each other, resulting in excessive wear and even fracture of the teeth of the crushing roll. Therefore, when encountering refractory or dense materials, the mine needs to be extra cautious. Once the load current is slightly larger, the feed speed should be reduced immediately or the machine should be shut down. The bolts should be checked every day, and the problems should be replaced in time.
A number of approaches were tried to solve this problem, but the simple, practical wedge-fixing method was chosen, as shown in Figure 5.
Using the original box space, add support frame and wedge iron at both ends of the box. The mating surface of the wedge iron and the support frame is 1:12 inclined, and the small inclination is adopted. After the wedge is tight, it is more reliable and not easy to loose. The support frame is solidly welded to the box, and the wedge iron is used to evenly wedge the broken beam and the support frame. After the bolts are firmly fixed, the wedge iron is spot welded to the support frame. When the particle size needs to be adjusted, it is only necessary to grind the spot welding of the wedge, raise the broken beam, and then tighten the wedge and screw on the fixing bolt after re-leveling. The wedge structure makes full use of wedge iron to bear the horizontal breaking force, and the fixed bolt is only subjected to the vertical force, without the horizontal shear force, which greatly improves the reliability of bolt connection.
3 Use Effect
After the modification, the broken beam was tracked for 2 to 3 months to check the broken beam and 4 fixing bolts, and no signs of loosening were found. It has been used normally for 2 years without any bolt breakage. The mine does not have to routinely check bolts every day, which reduces the labor intensity of workers. When the equipment encounters difficult or dense materials, it can pass smoothly without stopping the machine. The equipment utilization rate has been greatly improved, and the hourly output has been increased by about 30% compared with before. The comprehensive crushing capacity and cost performance are even higher than that of imported crushing equipment.
4 Conclusion
When mineral sizers crusher is crushing limestone, the beam crushing device is easily damaged under the action of huge impact force. By adding a set of wedge mechanism to bear the horizontal crushing force, the fixed bolt is avoided by shear action, which successfully solves the problem of frequent bolt breakage and greatly improves the utilization rate of the equipment. The wedge mechanism can also provide some reference for the fixing of complex mechanical parts in other industries.