Rod mill failure analysis and solutions

Rod mill mining site introduction. Henan Deya Machinery Equipment Co., Ltd. provides four rod mills for a group company in Shanxi to produce filled aggregate rod mill sand for the group’s underground mine, which now has two systems, old and new. The old system was put into operation in 1998, and the new system was put into operation in 2009 as the company’s mine output increased year by year. The production capacity of the old system is 1.8 million t/a, and the production capacity of the new system is 2.5 million t/a. The rod mill is the main grinding equipment, and there are now four MBY2700×3600 overflow rod mills produced by Henan Deya Machinery Co., Ltd.

1. Application Status

Rod mill working principle, the synchronous motor drives the pinion, which meshes with the large gear ring fixed on the cylinder to drive the cylinder for rotary motion. The failure of the pinion and bearing of rod mill is the main factor causing the downtime of rod mill and the consumption of spare parts. The consumption statistics of the pinion and bearing in the past 5 years are listed in the table below.

Pinion and bearing consumption statistics
Rod mill

As the above table shows, reducing pinion and bearing failures in rod mills plays an important role in ensuring continuous system operation and reducing cost pressure. Pinions and bearings are outsourced parts, and problems in processing and manufacturing (forging, heat treatment and cutting), transportation and storage can reduce their service life, so we will not repeat them here.

Deya machinery’s technical team combines years of work experience to analyze the main causes of pinion and bearing failures during installation, adjustment and daily maintenance, and to propose solutions.

2 Cause Analysis

2.1 Installation error

During installation, there are errors in the flatness and parallelism of the cylinder, motor and pinion base, resulting in the foundation sinking. When the rod mill is in operation, the vibration of the transmission system makes the pinion and bearing subject to impact load, which accelerates wear and tear and even causes the pinion base to crack.

2.2 Untimely pre-tightening of ground bolts

During the operation of rod mill, the ground bolts of synchronous motor and pinion bearing housing will be loosened by the inertia force of the cylinder, resulting in the displacement of transmission parts, causing the synchronous motor shaft to be different from the hollow shaft of the cylinder, thus generating vibration.

2.3 Pinion gear surface change is not timely

The pinion is the active gear, when running, the upper tooth surface is easy to wear, the tooth profile becomes thin, the tooth side clearance increases, easy to produce impact vibration, intensify the wear of the tooth surface. After a period of operation, the 3640 cylindrical roller bearing installed on the pinion shaft wears, the axial and radial clearance between the bearing and the pinion shaft increases, and the radial runout of the pinion shaft occurs, which causes the top clearance of the gear to change constantly, generating impact vibration and noise, and increasing tooth surface wear.

2.4 Untimely cleaning of impurities in gear sub

The mortar leaks and scales up after mixing with the lubricating oil, producing impurities. Although the anti-sand ring is installed outside the big gear ring to prevent mortar from entering the tooth surface, its sealing performance is poor. The lining plate inside the cylinder is fixed by bolts, after running for a period of time, the lining plate bolts near the big gear ring gradually loosen, if not tightened in time, the mortar is thrown out through the lining plate bolt holes and enters the meshing surface of the big and small gears. If it is not tightened in time, the mortar will be thrown out through the liner bolt hole and enter the meshing surface of the large and small gears, destroying the lubricating oil film on the tooth surface, causing the gears to dry wear, resulting in direct contact of the tooth surface, affecting the normal meshing of the gears and damaging the gears.
rod mill

3. Solutions

3.1 Monitor foundation sinkage

After the rod mill is put into operation, the sinking amount of the foundation should be measured regularly because of the flatness and parallelism errors during the installation stage.
(1) When the foundation sinks in a small amount, shims should be added to the base to eliminate the effect of foundation sinking by adjusting the thickness of the shims.
(2) When the amount of foundation sinking exceeds the standard, the foundation should be re-poured.

3.2 Pre-tighten the foundation bolts

Check the ground bolts of motor and rod mill pinion base in time, if they are loose, they should be tightened in time, and in serious cases, stop the mill and re-correct the rod mill transmission system.

3.3 Regularly check the working condition of gears and bearings

Once it is found that the large and small gears have strange sound, the rotation is not smooth and the bearing temperature is abnormal, it must be carefully checked to find the reason.
(1) When the top of the pinion gear teeth and large gear ring tooth root clearance is large, the center distance of the gear pair should be readjusted; when the tooth surface of the pinion gear along the direction of rotation is seriously worn, the surface should be changed so that the other side is the main force surface; when the gear has broken teeth, it should be replaced immediately.
(2) When the axial clearance of the bearing is large, the pinion shaft should be repaired. When the radial clearance of the pinion is too large, the copper piece should be added; when the axial clearance and radial clearance cannot be adjusted, or when the rollers show pitting and inflexible rotation, they should be replaced immediately.

3.4 Check the liner fastening and clean up the impurities in time

When there is impurity in the gear sub, it should clean them first, and then check the liner fastening condition.
(1) If the fixing bolt is loose, it should be tightened in time.
(2) If the fixing bolt is slipped or worn seriously, it should be replaced immediately.
(3) Replace the rubber gasket in time, clean the mortar and oil on the root of the teeth regularly, and clean the meshing surface of the large and small gears.

3.5 Make sure the gear is well lubricated

At present, the old system rod mill adopts the intermittent lubrication method of refueling with a refueling spoon through the refueling hole on the gear cover at regular intervals every shift; the new system adopts automatic jet lubrication device for the large and small gears in the transmission department, and the rod mill is lubricated by jet lubrication for 15s every 4h of operation, which reduces the labor intensity of workers and improves the lubrication conditions and the service life of large and small gears.

3.6 Intensify equipment management

Strengthen the professional training of equipment and improve the operation skills of workers; further standardize, quantify and refine the management rules and regulations, maintenance regulations, overhaul technical standards and point inspection standards. Through the implementation of the systems, regulations and standards, the basic management of equipment is gradually consolidated to achieve standardized, standardized, procedural and informationized management of equipment.

4. Conclusion

Aiming at the parts and causes of rod mill failure, we formulate and implement solution measures from both technical and management aspects to reduce the failure rate of rod mill pinion and bearing from the source, relieve cost pressure, realize continuous, stable and balanced production of rod mill sand system, enhance the supply capacity of filling aggregate and better meet the downhole production needs.

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