1. Basic Structure of Front Wheel Bearing of Truck

Truck wheel bearing is used is rolling bearing, roller bearing structure as shown in figure 1, truck wheel assembly installed inside and outside the two sets of bearings, the bearings with grease lubrication, according to the using performance and design principle of bearing with the taper roller bearing, its basic structure is made up of bearing outer ring, inner ring, rolling body, keep frame of four parts.The outer ring and the inner ring are respectively assembled together with the journal and the bearing seat. The outer ring is usually fixed and the inner ring rotates with the journal.Raceway operation of the inner and outer rings of the rolling body;The cage separates the rolling element evenly to avoid direct contact between adjacent rolling elements and increase wear.

2. Cause analysis of damage of truck front wheel bearing

2.1 Reasons for operation

2.1.1 overload

The loading quality of the whole truck is designed to be 260t. Due to the heavy production task and the limited skills of the operators, truck overload frequently occurs, which increases the load bearing of the front wheel and the pressure of the front wheel bearing of the truck, so the front wheel bearing is easy to cause damage.

2.1.2 Lack of operational skills

Truck when running at high speed, the operator use braking frequency increases or the brake is used more urgent, so the truck and load because of the impact loads will be most focused on the front axle, front axle under the impact of the main effects on the front wheel bearings, such a big impact role will inevitably intensify bearing damage, so as to greatly reduce the service life of bearing.

2.1.3 Continuous operation

In open pit mining area, heavy truck operators use 4 shifts and 3 reverse operation forms, so continuous operation phenomenon often appears.When the first shift of operation is over, the truck will be handed over to the next shift operator without failure, which will lead to incomplete heat dissipation of the truck and long-term high temperature. The temperature of the front wheel bearing will also rise, so that the lubrication performance of the grease will be reduced, thus aggravating the wear of the front wheel bearing.

2.2 Quality problems of accessories

2.2.1 Unreasonable selection of bearings

1) Influence of bearing structure design.The structural design of bearings is determined according to the use performance target values, such as load capacity, life, accuracy: reliability, vibration, wear, friction torque, etc.Sometimes due to the limited level of the designer, the bearing manufacturing process is poor, the clearance is unreasonable, and even deviates from the target value, which is easy to cause the early failure of the bearing.

2) Influence of bearing material quality.In terms of the quality of bearing material itself, there are cracks, spots and burrs on the bearing surface, and these defects are the main reasons for bearing damage [41].

2.2.2 The selection of grease is unreasonable

Heavy truck production operation tasks, because of the working environment temperature difference is bigger, the viscosity changes of the grease, the grease has no resistance to high temperature and high pressure, long time can reduce the viscosity of the grease and become diluted, it will lead to huge loss of grease, reduce the grease inside the bearing, seriously affect the efficiency of bearing lubrication, will eventually increase the bearing wear, result in bearing damage.

2.3 Maintenance skill factors

2.3.1 Use of liquid nitrogen Before installing the bearing, liquid nitrogen should be used to soak the bearing sleeve, in order to make the bearing sleeve shrink and easy to install.Short immersion time can not be correctly installed;Long soaking time will reduce the toughness of bearing sleeve;If the toughness decreases, the service life of the bearing sleeve will be reduced, which seriously affects the use of bearings.

2.3.2 Improper Clearance Measurement After the bearing is fixed, the clearance between the bearing and the pressure plate should be measured. But sometimes in the process of measurement, the personnel ignore the accuracy of the vernier caliper. The vernier caliper does not return to zero, which increases the measured clearance, affects the service life of the bearing, and the bearing will be damaged.

2.3.3 Adding and subtraction adjustment pad Wrong amount of adjustment pad will seriously affect the use of bearings. Sometimes maintenance personnel do not add adjustment pad according to the specified measured value, but add it according to their own experience, which eventually leads to more or less adjustment pad, affecting the use of bearings.

2.3.4 Pressure plate bolts are not in place. When the bearing is in good condition and the pressure plate is in good condition, the fixing bolts of the pressure plate should be tightened. Sometimes the maintenance personnel do not tighten the fixing bolts according to the standard torque, so that there is a certain gap between the pressure plate and the bearing;Truck running for a long time will make the pressure plate loose, resulting in bearing damage.

2.3.5 Unsuitable installation of internal grinding sleeve Internal grinding sleeve is a sleeve installed to prevent the friction between the kingpin and the forward elevation Angle. If the installation of internal grinding sleeve is inappropriate, the kingpin is easy to swing, which will wear the inner grinding sleeve and increase the movement of the bearing, thus affecting the life of the bearing.

2.3.6 The installed kingpin has wear. The kingpin has fixed forward elevation Angle. When using the kingpin, its surface must be smooth and without wear.However, sometimes due to the neglect of maintenance personnel, there are many burrs on the kingpin, and serious scratches are also used. Such use will cause the kingpin to be worn and affect the use of bearings.

2.3.7 Front suspension refueling does not meet the standard

The front suspension acts as both a spring and a shock absorber.The action of the spring is achieved by compressing nitrogen, and the action of the shock absorber is achieved by controlling the flow of oil between the suspension inner and outer oil chambers.If the filling ratio of the front suspension is not appropriate, it will reduce the load-bearing mass of the front suspension, but will increase the load-bearing mass of the front wheel bearing, which will seriously affect the service life of the bearing for a long time.

3. Preventive measures and maintenance suggestions for damage of front wheel bearings

3.1. Improve the responsibility of operators

3.1.1 Truck drivers should carefully study the standard operating procedures of this post

1) Carefully check the truck before the shift, and report the defective truck to the maintenance personnel in time to eliminate the hidden danger of the truck.

2) The truck driver should drive correctly. During the driving process of the truck, the driver should apply the power brake correctly and eliminate the frequent use of the working brake.

3) In the process of driving, once the truck breaks down, the driver should stop the truck at a safe place quickly, hit the mask, turn off the engine, and report to the maintenance personnel in time.

4) During loading and unloading, the driver should avoid steering the truck to the killing wheel.

Truck drivers should abide by the professional requirements of the operators, improve their own civilized driving quality and pay attention to the professional ethics of the operators.Once the truck is found abnormal, abnormal sound, abnormal ambiguity and other situations in the process of operation, the driver should stop in time to a safe place, so that the maintenance personnel can check, and at the same time, it can also contain the expansion of the fault.

3.2, do a good job of truck failure prevention

The prevention of truck accidents not only includes the major mechanical failures, such as the cracking of the structural parts of the truck and the damage of front wheel bearings, but also includes some normal zero failures.Fault prevention can effectively reduce the probability of truck failure and prevent the deterioration of truck performance.The spot inspection of mechanical and electrical equipment in Shenhua Haerwusu open-pit coal mine every morning is a very effective preventive means. During the spot inspection, not only clear tracking inspection records have been made for each part of the truck, but also repeated inspection can be made for some parts prone to failure to ensure the stable and good operation of the truck.What's more, the inspection personnel can also make full communication with the shift driver, can fully understand the running state of the truck.

3.3. Choose a good maintenance method

During maintenance, maintenance personnel and maintenance methods should be determined according to the damage degree of the truck, and economic benefits should also be considered to ensure that the production efficiency of the truck can be improved.

3.4. Improve the working environment

Change the bumpy road of open-pit mining area, choose the road with small slope and flat;Truck operation is prohibited in rain and snow weather. Truck continuous operation and high-temperature operation are prohibited.

3.5. Regular maintenance

According to the standard provisions, the front wheel bearing in 10,000 h plan maintenance, maintenance to completely replace the bearing, bearing sleeve, grease, pressure bearing, etc., to ensure the reasonable operation of the truck.

3.6 Choose qualified accessories

3.6.1 Choose qualified bearings

In the selection of bearing materials, it is necessary to use regular products. The products must be used for high strength, high temperature and pressure resistance, and high speed rotation speed.Under normal circumstances:

(1) at high temperature is not easy to aging, decomposition, low temperature is not easy to hardening, brittle crack;

(2) with the density of the material, so as to resist the corrosion performance of the strong medium, in the acid and alkaline environment for a long time;

(3) to have aging resistance, to be durable;

④ with small friction coefficient and good wear resistance, etc.

3.6.2 Matters to be noted in the selection of grease

1) The viscosity of grease should be appropriate to avoid viscosity changes due to temperature changes

2) Because the truck works under the environmental conditions of wind, sun, rain, dust and so on for a long time, it should have good rust and corrosion prevention.

3) Because the truck works outdoors for a long time, the temperature difference between winter and summer, day and night is large, the selected grease should be adapted to a 30oC ~ 40.C use.

3.7. Improve the skills of maintenance personnel

3.7.1 Use liquid nitrogen correctly to check whether the new bearing sleeve is damaged, burr and other phenomena. If so, repair as required.Put the bearing sleeve in the basin, slowly pour the liquid nitrogen into the basin, soak the bearing sleeve for 10 ~ 15min, when it is completely cooled, install it into the corresponding hole according to the correct method.

3.7.2 Add an adjustment pad according to the standard measurement clearance. When measuring, first reset the vernier caliper to zero, press the small bearing with the fixed bolt on the pressure plate, and measure the clearance of the bearing;Adjustment pads are added according to the measured clearance to ensure proper use of bearings.

In general, the torque of the fixed bolt of the press plate is 650(N·m). When the torque is in school, we shall calibrate it in sequence, such as 100(N·m), 200(N·m), 30(N·m), 400(N·m), 500(N·m) and 650(N·m), until the bolt is fastened in place, and then lock the bolt in a diagonal locking way with the locking wire.

3.7.4 Choose the right kingpin The kingpin selected shall be smooth, rust free, burr free and scratch free.

3.7.5 Carefully install the inner grinding bearing sleeve When installing the inner grinding bearing sleeve, the upper and lower surfaces should be kept parallel to ensure proper installation. During installation, ensure that the inner grinding bearing sleeve will not move, which will also prevent the swing of the kingpin.

3.7.6 The front suspension refueling shall be refueled according to the following standards: 36.7L;Inflation: 1755mm.