01 Introduction

The 2,000,000 t cement production line system of a company consists of two sets of ф4.2m×13m mills, and the supporting main reducers are JS150 products developed by a well-known gearbox company in China in the 1980s. Its main technical parameters are: input power 3550kW；; The input speed is 744r/min, the speed ratio is 47.2952: 1, the matching motor is YR900-8, the rated power is 3550kW, the rated voltage is 6000V, and the rated current is 412.9A A.

The two sets of mill systems have been running smoothly since they were put into production in 2010. On September 20th, 2015, during the routine equipment inspection, the inspectors found that the running noise of the main reducer of Unit 2 was slightly higher than that of Unit 1 and before. In view of the existing problems, the factory immediately set up a professional technical team, and through a series of investigation and treatment, the accident was safely and effectively eliminated in the bud in a short time.

01 troubleshooting and maintenance plan

1.1 Preliminary judgment

Firstly, the contact and wear of each tooth surface are observed by stopping the machine and uncovering the cover, and the contact of each tooth surface is good; Understand the lubrication condition in the early stage in detail, and the oil quantity, pressure and oil quality of the oil pump are all normal; Check the display and curves of vibration, temperature and current of the central control instrument, and there is no abnormality.

Then, when the professional VM22 vibrometer was changed to detect each bearing position on the reducer, it was found that the acceleration of the high-speed bearing position near the coupling end was abnormal, reaching about 50 m/s, and it was judged that there would be a high equipment safety risk if the reducer continued to operate.

The peak season of cement production in the company is the current period when the hidden danger occurs. At the same time, the company has no experience in equipment maintenance for this large reducer with double power split structure, and if the treatment is delayed or the operation with hidden danger is carried out, it will very likely lead to a major equipment accident. Finally, it was decided to set up a special technical maintenance team to organize the maintenance force of our company to complete this work.

1.2 analysis of hidden host structure

Verification of original technical data: This series of speed reducers adopts the structural form of central drive, double power split, torque shaft load sharing and symmetrical arrangement of two-stage speed reduction. After carburizing and hardening, the main tooth surfaces are ground, tooth profile and tooth direction trimmed, and the gear accuracy is above Grade 6 of GB100095. The shell structure is a large welded structural steel box body, and the inner part of which carries a disc thrust bearing with multi-degree-of-freedom thin-wall sliding bearing and high-speed toothed shaft. The whole monitoring system adopts PTl00 end platinum thermal resistance, which displays and monitors the temperature of all bearings through multi-channel temperature inspection instrument, and adopts centralized thin oil lubrication system to lubricate all bearings and gears.

Through the analysis of the performance, structure and principle of the main engine, it is necessary to successfully complete the maintenance task. First, all work should be carried out strictly according to various maintenance standards; Second, find out the fundamental causes of hidden dangers and thoroughly handle the problems; Third, consider some difficulties that may be encountered in dismantling the torsion shaft in advance; Fourthly, all equipment, especially the position of double shunt gears, cannot be displaced, because the original tooth surfaces are matched and the bearing shells have been strictly assembled in the manufacturer; Fifth, emphasize all safety rules in the whole overhaul process.

1.3 preparation of bearing accessories and determination of lifting scheme of parts

By uncovering the end cover of the bearing at the coupling end of the high-speed shaft, it can be verified that the bearing is a 23248CAME 4SN bearing. Since the machine has been running for 5 years and the high-speed bearing is supported by two bearings inside and outside, it must be replaced in pairs, that is, it must be an internationally renowned bearing brand, and all technical parameters of the bearing must be comprehensively tested after purchase.

As the equipment is located at a height of 5m, the steel beam ceiling structure is adopted, and the steel beam profile is made of thin channel steel, which cannot be used as a hanging beam. However, if the ceiling is lifted off and then restored after dismantling, its integrity will be destroyed, which will delay time and consume cost, and there will be a certain hoisting height from the top of the reducer to the canopy. Therefore, the project team hired a professional crane mechanic to accurately verify and calculate the position of the crane, the size of the counterweight, the length of the arm, the size of the steel rope and the weight of the suspended parts, and worked out a plan in advance: a 25t plus 2t steel ball counterweight and a 50t car were used for joint hoisting, which could solve the hoisting of all the dismantled parts without removing the ceiling, effectively shortening the whole overhaul for at least 1 ~ 2 days.

02. Specific implementation

2.1 Preparation of construction personnel and instruments

Personnel preparation: 1 constructor, 1 safety officer, 4 fitters, 3 riggers and 1 welder.

Preparation of tools and instruments: 1 for 25t and 50t truck cranes, several steel ropes, and fitter tools including various wrenches, hammers, polishers, gourds, oil tops, lifting lugs, oxygen, acetylene, etc.

Site preparation: before shutdown, switch off the main motor after power failure, hang a safety card, and arrange and clean the places where all accessories are placed after disassembly.

2.2 disassembly construction

First, untie all bolts of the upper shell of the reducer, remove the bolts of the front and rear end covers, position the 25t and 50t cranes and jointly lift the upper shell out, then remove all temperature control and vibration connections and protect them from damage, and then remove all lubricating oil pipes. Then dismantle the torsion bar, input stage big teeth and high-speed shaft assembly, pay attention to the meshing position of the high-speed teeth and the left and right input stage big teeth, mark them with paint, and use tools to pull out the fixed pins at both ends of one torsion bar one by one and number them. After all of them are removed, remove the motor junction box to facilitate one-time removal of the torsion bar, then remove the top cover of the input stage gear bearing bush, remove the input stage gear by crane, and mark the upward position with paint to facilitate subsequent in-situ reassembly. After the big teeth of one input stage are removed, the high-speed teeth and bearings can be easily pulled out as a whole, and the forklift truck can be used to reverse to the professional installation shed, and the coupling and bearings can be removed.

After the high-speed shaft bearing was disassembled in the shed, it was found that the clearance of the no-load end bearing was slightly larger, which proved that the no-load end bearing was not the problem. However, when the bearing at the loaded end of the coupling is removed, it is found that the whole circle of the bearing near the outer track is worn and pitting corrosion is serious, thus finding the root cause of acceleration change during detection.

2.3 Assembly of high-speed shaft components and problems encountered

After all the original bearings are removed and cleaned according to the working procedure, the new bearings are installed. After installation, the maximum clearance of each new bearing is 0.30mm in free state, and each bearing raceway can rotate freely by hand, and all the working procedures meet the maintenance standards. However, all the high-speed bearing components are assembled and reset to the reducer. After the top covers of each outer ring are reset and fastened, it is found that when each ball cage is manually rotated, the balls on the coupling track are tight, and the other three rows are loose. It is judged that the clearance has changed to some extent after the bearing is installed, which is the reason for pitting failure of only one track outside the four rows of raceways.

The reasons for the above faults are, firstly, the errors produced by the original equipment hole processing tools; Second, it may be caused by the slight deformation of the stress changes of its components. If thoroughly treated, the entire reducer base must be sent to a professional machine tool for re-alignment, which is difficult and costly; If it is not treated, the hidden trouble of pitting corrosion or bearing burning will continue to appear. Finally, the lead wire method of bearing outer ring, which is common in mechanical maintenance, is worked out, that is, lead wires are placed on the joint surface of bearing and bearing seat respectively, and the upper cover of bearing seat is installed to evenly compress the bolts of bearing seat. After fastening, all bolts are loosened, and the lead wires are taken out, and their thickness is measured by micrometer respectively. The average algebraic difference is the clearance or interference value between bearing seat and bearing. According to the numerical value, it is determined whether the bearing seat joint surface is coated with copper or the outer ring of the bearing is coated with copper, which can preliminarily eliminate pitting corrosion and wear caused by tight bearing balls. In this treatment, it is calculated that 0.30mm thin copper skin is added to both sides of the bearing seat. The test run and load production tracking in the following months show that the bearing temperature and amplitude at the early hidden danger are kept in good condition, thus confirming the correctness of this simple scheme.

2.4 Precautions for Parts Reinstallation

First of all, before installation, all parts of the lower box should be thoroughly cleaned, and the surface should be dried with compressed air to ensure the cleanliness of installation. In particular, the bearings should never fall into iron filings, lime sand and other foreign matters. At the same time, carefully check the same group marks and orientation marks on the end faces of bearings and gear assemblies, and install them only after they are confirmed to be correct, so as to avoid rework and parts damage.

Secondly, for the input shaft assembly, first install the half coupling on the input shaft, and pay attention to the O-shaped rubber sealing ring and the bearing retainer ring on the input shaft before installation. Lift the cleaned input shaft assembly horizontally, slowly put the bearings at both ends in the bearing seat holes (inject a small amount of grease into the rolling bearings), put the left and right marks on the gear end face, and put the torsion bar and each upper cover back and tighten evenly. After the whole reducer is basically installed in place, re-use the laser centering instrument or dial indicator to accurately align the radial and axial deflection of the coupling between the motor and reducer, which should not be greater than 0.1mm, and it is recommended that it should be controlled within 0.05 mm.

In addition, the elastic pin coupling is adopted for the motor and reducer, so the processing error of the rubber ring must be paid close attention to. During this overhaul, all the aged aprons in previous operation were replaced, but after alignment and bolt fastening, the temperature of motor bearing bush suddenly appeared to jump when commissioning. Finally, after investigation, the main reason was due to the processing error of the aprons, that is, the length of the new aprons increased by 2mm compared with the original aprons, so the main motor shaft was forcibly pulled during fastening, resulting in axial displacement of the whole motor, resulting in friction and heating of the shaft diameter on the bearing bush.

03 Conclusions

Sudden hidden trouble of equipment, experience value of maintenance and limited space of equipment bring some difficulties to the emergency repair. However, after our low-cost, safe, meticulous and solid work, the whole emergency repair work took only 4 days. Follow-up observation after emergency repair shows that its continuous and stable operation as of October, 2016 proves that it is a very successful example of low-cost and safe emergency repair.

As a cement production enterprise, the long-term, continuous and stable operation of equipment is our constant goal. However, being good at discovering hidden dangers in the production process and timely, safely and effectively handling hidden dangers through our own efforts are our capabilities in the management of modern new dry-process equipment.

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