This paper introduces that in order to improve production efficiency, the production unit lengthens the protractor of BOOMER281, replacing the original BMH2337 protractor with BMH2343 protractor. Whether the strength of the propuller beam after lengthening meets the safety requirements is mainly whether the strength of the crutching shaft can meet the requirements. In view of whether the shaft can meet the safety requirements, the strength of the shaft is checked after the truck stops and works, and the conclusion is drawn that it is feasible to use the lengthened propulsion beam and lengthened drill rod. After the propulsion beam is lengthened, the load on the crutch bearing becomes larger, and the crutch shaft is the most important part of the propulsion system. In the production process, the shaft is easy to crack or even break, which requires the shaft to do a good job in peacetime inspection, once the crack is found to be handled in time. In this paper, the crack repair of the crank shaft is also introduced. Due to the large load of the crank shaft and the complex force during work, these require the repair process of the crank shaft to be improved, so that the repaired crank shaft can meet the requirements of use. It is also very important to check the quality of shaft repair after overhaul. This paper also introduces the quality requirements of overhaul. The propulsive beam component is an important part of the truck, and the maintenance of propulsive beam component is also introduced in this paper.

Boomer series trucks produced by AtlasCopco, Sweden, have the characteristics of excellent performance, high efficiency, low energy consumption, mechatronics and so on, and are the main equipment used for mining underground roadways at home and abroad. Boomer281 series driving trolley mainly undertakes the driving work of underground driving roadway. The operating efficiency of the equipment is 170 m/month · Platform), the specification of the driving roadway is 5 meters × 3.8 meters, the average consumption of spare parts before the improvement in 2017 was 8.48 yuan/meter ³ (no water electricity).

After the improvement of the technology, 4.3 meters of drill rod was used to replace the original 3.66 meters of drill rod for the experiment. The experimental results show that the specific consumption of dynamite is reduced after the improvement of mining process. However, in the actual operation process, it is necessary to drill the drill rod with 3.66 meters, change the drill rod with 4.3 meters on the basis of the original hole, and then continue to drill the hole, resulting in a significant increase in the labor intensity of the operator. A lengthened propulsion beam (BMH2343) was ordered in the second half of 2017. The maintenance department decided to test the BMH2337 propelling beam on a roadheader first, replacing the original BMH2343 extended propelling beam on the roadheader. After the propulsion beam is lengthened, the big arm and the turning mechanism can meet the strength requirements. Mainly, whether the strength of the turning shaft of the turning arm can meet the requirements of use needs to be tested and checked for a period of time.

1BOOMER281 Strength check of turning shaft of driving trolley

BOOMER281 The shape of the propeller compensation arm of the driving car is “ ┳” The specific structure is shown in Figure 1. The turning shaft of the crank arm and the rotating device at the front end of the telescopic arm are gap fit; The turning shaft is inserted in the hollow shaft hole at the front end of the turning cylinder, the hollow shaft hole is equipped with a copper sleeve, and the turning shaft is connected with the turning cylinder through the copper sleeve. Inside the arm is the propulsion compensation cylinder, which is fixed with the propulsion beam (roughly shaped like “ U” The rock drill, rubber hose roller, stable drill frame, etc. are fixed on the propulsion beam through the tray, and the propulsion cylinder is fixed inside the propulsion beam. The propulsor beam and its auxiliary equipment are the main parts of the drilling of the truck, including the propulsor cylinder, the compensation cylinder, the rock drill and the steady drill frame. The weight of all the components of the propulsion beam needs to be supported by the crank shaft.

▲ Figure 1 Driving truck arm

1.1 Force analysis of crank shaft

The force analysis of the crank shaft can be divided into two cases: one is the maximum load of the crank shaft under the prohibition of the equipment, and the second is the maximum load of the crank shaft during the work of the equipment. When the car is at rest, only when the shaft of the arm is placed horizontally, the load strength of the shaft is the greatest. In other positions, the crank shaft is subject to either a combination of bending and stretching or a combination of bending and compression. Only in the horizontal position is the pivot subject only to bending deformation. At this time, the force on the turning shaft is the greatest, so the turning shaft is the most dangerous when it is in the horizontal position. In addition, when the car is working, the crank shaft not only receives the bending force of the static load, but also suffers the dynamic load brought by the high-speed impact and rotation of the rock drill.

1.2 Force analysis of the crank shaft when the vehicle is stationary

When the equipment is at rest, the crank shaft is only subjected to static load, and the effect is equivalent to the uniform load on the cantilever beam. Because the crank arm and the rotary cylinder are connected by the side cylinder, the propulsion beam can rotate up and down around the center line of the crank shaft of the crank arm, so it will not suffer torsional deformation and will not produce torsional stress during static and operation.

Total gravity supported by the crutches: G total = G rock drill +G extended propulsion beam +G propulsion cylinder +G tubing +G pallet +G tubing support +G drilling tool +G other

Check the relevant information of the equipment, G total = m total g≈ 1.3 & times; 10000 Ｎ

The length of the shaft L = 530mm = 0.53m, uniform load concentration q = G total/L = 24.53kN/m

Maximum shearＱｍａｘ＝ｑ＊ｘｍａｘ＝ｑ＊Ｌ＝２４.５３×０.５３＝１３ｋＮ

Bending moment M（ｘ）＝ｑｘ＊ｘ／２＝ｑｘ²／２（０≤ｘ≤Ｌ）

The maximum bending moment produced by static force M staticｍａｘ＝ｑ（ｘｍａｘ）²／２＝３.４４５ＫＮ·ｍ

During the operation of the trolley, the bending moment generated by the rotation is the same as that generated by the static force. It is known from the equipment data that the torque of the COP1238ME rock drill during the rotation is: 500N· m, which is equivalent to the couple m = 500N acting on the crank shaft; m. In order to more intuitively explain the relationship between shear moment and force couple m, see Figure 2.

▲ Figure 2 Force analysis diagram of the arm

So Mmax = M static max+m = 3445+500 = 3945 (N· m)

From the knowledge of material mechanics: the bending section coefficient of hollow circular section Wz = π D³ (1-α 4) / 32 where α = d/D

Wz = 3.14× 87³× [1- (58/87) 4] / 32 = 5.19× 10-5 (m³)

The maximum normal stress is calculated as follows: σ max = M max/Wz

σ max = 3.945× 10 ³ N· m/(5.19× 10-5m³) ≈ 76.01 MPa 

It can be clearly seen from the bending moment diagram that the bend shaft of the crank arm is subject to the largest bending moment at the root, that is to say, this is the most dangerous place for the crank arm, which is consistent with the fault phenomenon found in the overhaul.

1.3 Force analysis of the crank shaft when the vehicle is working

BOOMER281 boring car in the process of drilling, mainly through the impact of COP1238ME rock drill, rotation, and the propulsion cylinder in the propulsion beam to complete the drilling task. In the process of operation, the rock drill in Meishan Iron Mine uses the second gear, the impact frequency is 50HZ, the impact reaction mainly acts on the crank shaft, resulting in the crank arm and the crank shaft being subjected to alternating load.

Impact force F = P impact pressure · S impact area＝２００×１０５Ｐａ×π／４×（ｄ１²－ｄ２²）＝２００×１０５Ｐａ×３.１４×（４４２－３８２）／４×１０－６ｍ²＝７.７２×１０³Ｎ

Impact reaction force acting on the arm of the crankＦ、＝Ｆ＝７.７２×１０³Ｎ

According to the force analysis, the impact reaction force acts on the center line of the drill rod, translates this force to the geometric center line of the propulsion compensation, in addition to an overturning moment (because the crank shaft can rotate freely, so the overturning moment is not considered), the impact reaction force gives the crank shaft a bending stress on the longitudinal section of the crank shaft.

σ’ｍａｘ＝Ｍｍａｘ／Ｗ＝Ｆ’·ｒArm radius／［πＤ³（１－α４）／３２］amongα＝ｄ／Ｄ＝７.７２×１０³×０.０６１Ｎ·ｍ／５.１９×１０－５ｍ³＝９.０７Ｍｐａ

1.4 Strength check

It is known from the mechanical strength theory of materials：σ²＝σｍａｘ²＋σ’ｍａｘ²

σ＝７６.５５Ｍｐａ

According to the information of the equipment, the material used for the crank arm is alloy structural steel (40Cr tempering treatment), and the yield limit of this material is σ s ranges from 550 to 800Mpa. Because the working conditions of the crank arm are relatively harsh, the blank parts in the processing process are achieved by casting, and the safety factor ns = 4 is known by the knowledge of material mechanics.

Allowable stress of shaft material [σ] = σ s/ns = 550/4 = 137.5Mpa.

σ = 76.55Mpa < [σ] = 137.5Mpa

Therefore, the strength of the crank arm of the modified driving truck can meet the requirements, meet the needs of production, and is safe in the operation process.

2 Pivot repair

The crank shaft is an important part of supporting the crank arm and propelling beam. When the truck is working, the force of the crank shaft is complicated, and the force of the crank bearing is very large, and the crank shaft is prone to fatigue cracking. If not treated in time, the pivot shaft will break in serious cases. Since the crank shaft is the only part of the connection between the propulsion beam and the turnover cylinder, the service life of the crank shaft is directly related to the performance of the whole car.

Regular inspection of the shaft is particularly important, when the shaft is found to have small cracks, it must be welded and repaired in time, and the material of the shaft must be determined before welding and repair. BOOMER281 driving car shaft materials often have 45 # steel, 375SiMn2MoV, 38CrMoAl, 30CrMnSiNi2A, 30CrMnSiA and other several, for different materials, should choose the appropriate welding process to weld the fracture site. Before welding, it is necessary to open a groove at the crack, and the Angle of the groove is generally 60° The groove should be polished with a grinder. At 3cm around the welding position, it is necessary to do a good job of rust removal to remove the oxide layer and nitriding layer. The depth of grinding is generally guaranteed to be above 0.5mm to ensure welding quality and welding strength. The whole shaft should be preheated to about 250℃ before welding, and full arc welding should be ensured during welding. After welding, it is necessary to temper in time, and the tempering temperature is controlled at 450℃ ~ 480℃. After tempering, heat preservation should be done for 2 to 3 hours. After welding, the welding joint should be inspected with ultrasonic wave to check whether there is a large slag inclusion or porosity and other defects at the weld. After the inspection, the hardness of the welding surface should be tested, and the hardness of the welding surface should be similar to the normal surface.

3 Advance beam component inspection and maintenance

3.1 Propulsion beam inspection and maintenance

The push beam is an important part of the drilling platform, the surface of the push beam is installed with stainless steel plate, stainless steel plate and the rock drill skateboard connection there is a non-metallic gasket made of wear-resistant material, this wear-resistant gasket can effectively prevent the rock drill skateboard in the front and back movement, reduce the push beam stainless steel plate and slide caused by friction wear. The gasket can adjust the gap between the slide of the rock drill and the propulsion beam to ensure the smooth movement of the rock drill on the propulsion beam. Therefore, once the non-metallic adjustment gasket is found to be seriously worn, it should be replaced in time to prevent the rock drill from contacting directly with the surface of the propulsion beam, thus wearing the stainless steel plate and slide on the surface of the propulsion beam. Due to the poor underground environment, more dust, ground inequality unfavorable factors, resulting in the joint of the drill and the propulsion beam easy to loosen, the adjustment gasket easy to wear. Once loose is found in the usual inspection, it should be tightened in time, and the adjustment gasket should be replaced in time once worn.

3.2 Maintenance of Hydraulic tubing of rock drill

Rock drill is an important part of the boring truck, the rock drill has two working modes of rotation and impact, rotation and impact of both work must be powered by high pressure oil. There are a lot of high pressure oil pipes installed on the rock drill, these high pressure oil pipes must be fixed on the equipment, if not fixed, the high pressure oil pipes shaking is easy to damage or clamp. Therefore, it is usually necessary to check whether the oil pipe is fixed firmly, and once the pipe hoop is loose, the screw of the pipe hoop must be tightened immediately.

Once the hydraulic oil pipe is damaged or the joint leaks oil, it will also make the rock drill can not work normally, and the oil pipe must be replaced and the oil pipe joint must be tightened.

3.3 Adjustment of the Gripper

The gripper is the key part of the rock drill moving on the propulsion beam, the gripper is divided into two halves, the upper and lower two halves are connected by a screw, and the screw can be positioned on the propulsion beam after tightening. If the clamp is not tight, it will cause the rock drill to shake when working, thus affecting the rock drill can not drill normally.

The hole through the bolt on the gripper is generally made of long holes so that the axial adjustment of the rock drill can be made. When adjusting the gripper, loosen the connecting screw of the gripper, adjust the position of the gripper, so that the slide above the upper part of the gripper is positioned on the top of the beam, which is 7 ~ 10mm higher than the beam, and then move the lower part of the gripper, so that the gap between the lower part of the gripper and the beam is 1 ~ 2mm, and tighten the upper and lower connecting screw of the gripper. Move along the slide, if the slide moves smoothly, the gripper adjustment is appropriate, if the slide does not move smoothly, it means that the gripper is too tight and needs to be re-adjusted.

A replaceable slider is installed on the gripper, and the slider is fixed on the gripper with 3 keys. It is necessary to check the slider regularly. If the thickness of the slider is less than 2mm, the slider must be replaced to prevent the gripper from contacting the beam directly.

3.4 Inspection and replacement of guide rail

The rock drill is installed on the sliding guide rail and slides back and forth on the guide rail. If the gap between the guide rail and the beam is large, or the guide rail has been seriously worn or deformed, it will cause the rock drill to be blocked when advancing or returning on the sliding rail, at this time, the sliding rail must be replaced.

4 Conclusion

By checking the strength of the drive shaft of BOOMER281 driving trolley, it is theoretically verified that the drive shaft can meet the strength requirements of the extension of the propulsion beam, and the average consumption of spare parts of the improved driving trolley is reduced to 6.12 yuan/cubic meter (without water electricity). However, in the actual use process, some operators may not add butter in place during use, resulting in local wear of the shaft of the arm, reducing the strength of the shaft; At present, there are many domestic crank shafts, and whether domestic crank shafts can meet the material requirements of imported spare parts and the heat treatment process (grasp the temperature at each stage, control the annealing process after processing, etc.) and achieve the effect are in the test. If the appropriate welding process is selected, the function of the crank shaft can be restored and the service life of the equipment can be extended. Localization of spare parts and repair of spare parts effectively reduce the cost of spare parts consumption. Usually, it is necessary to strengthen the planned maintenance and daily inspection of the equipment, every time to carefully check the use of the shaft and lubrication, and timely and effective rectification of the safety hazards, to ensure the safe, smooth and effective operation of the equipment.