Abstract: As the key component of the shield machine, the main bearing plays a vital role in the use of the shield machine. In order to solve the problem of repairing the defects of the main bearing, based on a case of remanufacturing the main bearing of a shield machine, the causes of defects such as cratering and corrosion of the main bearing were analyzed, and the basic principle and remanufacturing process of the main bearing were introduced. The feasibility of the remanufacturing scheme is proved by comparing the measurement data of the main bearing before and after remanufacturing and its practical application.
With the continuous acceleration of the development and utilization of underground space in my country, shield construction has been widely used in the development and utilization of urban underground space as a main method for infrastructure construction such as tunnels, subways, urban pipelines, river crossings and sea crossings. In recent years, the construction of rail transit in major cities across the country has developed vigorously. With the continuous increase of intercity railways and cross-river and sea-crossing projects, the demand for domestic shield machines has continued to increase. At present, the number of domestic shield machines has reached more than 1,500 sets. As the core component of the shield machine, the main bearing mainly adopts foreign products such as SKF and RotheErde. Once the main bearing fails or the shield machine reaches the designed service life (generally 8-10km), it will be scrapped. Expensive. This paper provides a more economical and effective solution for the user to improve the service life and reliability of the main bearing through the research on the disassembly and repair of the main bearing of a Herrenknecht shield machine.
1. Main bearing
1.1 Historical usage
The shield machine has been out of the factory since 2008. It has completed several bidding sections in Guangzhou, Shenzhen, Changsha and other regions, and has accumulated a total of 11km. It has been working in hard rock and uneven soft and hard strata in South China. During this period, the main bearing has not been subjected to any Inspection and repair.
1.2 Main drive structure
The main bearing brand studied in this paper is SKF (SKF) internal tooth three-row cylindrical roller bearing, model SKFRKSSAS87610, bearing outer diameter is 2620mm, inner diameter is 1890mm, and height is 409.4mm.
The main function of the main bearing is to drive the cutter head of the shield machine to rotate, and at the same time bear the axial force, radial load and overturning moment ; the parts 1 and 5 are fixed on the front shield of the shield machine by bolts, which play a fixed role. ; The shield machine adopts motor or hydraulic pump as the power source of the cutter head, and through the reducer, the output gear engages the inner gear of the part 6, and the cutter head is connected with the part 6 through the bolt, thereby driving the cutter head to rotate. The main, auxiliary thrust and radial rollers are evenly distributed in the bearing. During use, rollers 2 and 4 can carry axial force and overturning moment , while roller 3 can carry radial force. The main bearing structure is shown in Figure 1.
2. Main bearing state before remanufacturing
Under normal circumstances, the main bearing of the shield machine needs to be disassembled and tested when the running mileage exceeds 5km. According to statistics, the main bearing has been excavated for 11km and has a running time of about 8,500h. It has not been disassembled, inspected or maintained during use. The main testing items of this main bearing include appearance inspection, size mapping, raceway surface hardness testing, microscopic observation, raceway flaw detection, tooth surface flaw detection, rolling element testing, cage testing, etc. The main problems are as follows: main, auxiliary, There are pressure pits, corrosion and wear on the surface of the radial raceway; there are pressure pits and wear on the main, auxiliary and radial rolling elements, and the variation of the whole batch grouping exceeds the standard; the installation reference surface is corroded and uneven; the axial clearance of the main bearing , Radial clearance, outer ring radial runout is too large. The measurement data are shown in Table 1 and Table 2.
3. Analysis of main bearing remanufacturing technology
3.1 Analysis of main bearing defects
The main bearing mainly relies on the main drive seal of the shield machine to be isolated from the outside world. With the aging and wear of the seal in long-term use , a small amount of impurities and moisture will inevitably enter the inside of the bearing, causing the raceway surface and roller to form crushing If the main bearing is insufficiently lubricated , the above defects will be exacerbated; if the quality of the gear oil cannot be replaced in time, the metal particles and water contained in the oil will cause the bearing surface to form craters and rust ; The unreasonable use of electric welding machines and other equipment on the shield machine will cause the current to pass through the main bearing and cause electrical corrosion defects.
Corrosion and cratering will cause stress concentration around the defect, which will lead to the accelerated expansion of the area of the defect, and eventually lead to the early fatigue of the surface metal and the peeling of the hardened layer. The deformation of the main bearing ring after long-term stress will cause changes in the axial and radial clearances (the main bearing itself has small axial and radial clearances), which is easy to cause local jamming and accelerate the raceway surface and rolling elements. The wear speed and the deformation of the ferrule also affect the reduction of the meshing area between the inner ring gear and the pinion, resulting in uneven force when the gear meshes.
Due to the long rolling elements of the main bearing and the different linear speeds at both ends, if the variation of the rolling elements in the whole batch exceeds the standard, it is easy to cause inconsistent wear of the rolling elements, which will cause the shield machine to be loaded on each rolling element when it is advancing. The force is not uniform, increasing the risk of roller crushing. In addition, the corrosion and unevenness of the installation reference surface will cause the deformation of the bearing in the bolted state to affect the axial clearance when it is installed again. The axial and radial clearances of the main bearing are too large. If the overturning moment of the soft and hard uneven formation is large, the contact area between the rolling element and the raceway surface will be reduced, and the wear of the rolling element and the raceway surface will also be accelerated.
3.2 The basic principle of main bearing remanufacturing
Bearing remanufacturing refers to the repair and replacement of worn or damaged surfaces and components that play a key role in bearing performance and life before the bearing service life reaches a turning point . The main and auxiliary thrust raceway surfaces and radial raceway surfaces will form defects such as rust and pressure pits after long-term use. The defect layer on the surface is removed by grinding, so that the outer surface can reach the new standard again; the raceway surface has A certain depth of carburized layer, a small amount of wear will not affect its strength. The main and auxiliary thrust rollers are repaired to remove surface rust, crater and other defects, and those with major defects are remade according to the size of the repaired mold. After the main and auxiliary thrust raceway surfaces and the main and auxiliary thrust rollers are treated, the overall height of the bearing will be reduced, but it will not affect the assembly and use. After the radial raceway is ground, the installation clearance of the original radial roller will increase, so the radial roller needs to be remade according to the grinding amount of the radial raceway.
4. Remanufacturing technical measures and effects
4.1 Remanufacturing technical indicators
The remanufactured bearing will restore the surface finish of the raceway, remove the pitting and rust defects on the raceway surface, restore the smoothness and accuracy of the bearing ring, and restore the surface finish of the rolling element and the accuracy of the grouping difference. Reach 70% of the service life of the new bearing (excluding factors such as harsh ground, excessive torque of the reducer, excessive propulsion of the oil cylinder, and operating specifications).
Remanufacturing technical requirements: axial runout is less than or equal to 0.05mm; axial clearance is 0.07-0.13mm; radial clearance is 0.13-0.18mm.
4.2 Remanufacturing Process Control
(1) Grind the main and auxiliary thrust raceway surfaces of the outer ring to remove surface corrosion, crater and other defects, and control the single-sided grinding amount within 0.15-0.5 mm; hardness needs to be carried out for every 0.1 mm of grinding. The hardness of each place shall not be lower than HRC56.5, and the depth of the deepest local defect shall be measured in time; the surface roughness of the raceway is less than or equal to 0.5 μm, and the surface crack inspection (100% surface fluorescent magnetic particle inspection) shall be carried out after the raceway is ground. There shall be no surface cracks. The hardness of the raceway surface is HRC565～620; the radial raceway surface of the outer ring is rounded to remove surface defects, and the surface roughness is less than or equal to 0.5μm.
(2) Grind the main and auxiliary thrust raceway surfaces of the inner ring to remove surface corrosion, crater and other defects. The grinding amount is determined according to the depth of the defect, and the single-sided grinding amount is controlled within 0.2-0.5 mm. Grinding 0.1mm requires a hardness test, and the hardness of each location shall not be lower than HRC56.5, and the depth of the local deepest defect shall be measured in time. The surface roughness is less than or equal to 0.5μm, and the surface crack inspection (100% surface magnetic particle inspection) shall be carried out after the raceway grinding, and there shall be no surface cracks. The hardness of the raceway surface is HRC565～62; the radial raceway surface of the inner ring is rounded to remove surface defects.
(3) Grinding the outer diameter of the main thrust rolling element (the maximum grinding amount of the outer diameter is less than 0.3 mm), remove defects such as rust, the variation of the rolling element batch diameter is less than 5 μm, and the surface roughness of the rolling element rolling surface is less than 0.25 μm. 100% of the body should be checked for cracks, no cracks are allowed.
(4) Grinding the outer diameter of the auxiliary thrust rolling element (the maximum grinding amount of the outer diameter is less than 0.2 mm) to remove defects such as rust. 100% of the body should be checked for cracks, no cracks are allowed.
(5) Replace the radial rolling elements (according to the grinding amount of the radial raceway and the radial clearance), the material is ZGCr15SiMn-GJB6484, the hardness is HRC58~62, and the newly manufactured rolling elements should be tested for cracks. The diameter variation is less than 5μm, and the surface roughness of the rolling surface of the rolling element is less than 0.25 μm, and the rolling element should be 100% magnetic particle inspection, and cracks are not allowed.
(6) Assembling, fitting and matching clearance.
(7) Reshape the cage and remove the rust on the surface and in the pocket.
4.3 State after remanufacturing
It can be seen from Table 3 that the technical indicators of the main bearing have been greatly improved after remanufacturing, reaching the expected remanufacturing target, and passed the review and acceptance of the expert meeting. At present, the main bearing has been assembled with the shield machine, and the tunnel has been successfully excavated for about 1km in South China. Through the oil detection during the construction process , the online monitoring system  to detect vibration, noise, etc., as well as the tunneling parameters. Analysis, the use of the main bearing indicators are normal and reliable, as shown in Table 3.
In this paper, through the remanufacturing technology and case analysis of the main bearing of the shield machine, the general remanufacturing technology of the main bearing of the 2600mm shield machine is summarized. cost and shorten the procurement cycle. Under the current theme of vigorously advocating the construction of a conservation-oriented and environment-friendly society and the development of a circular economy, the remanufacturing of shield machines and their components is an inevitable choice for the green transformation and upgrading of the shield machine industry; among them, the main bearing is the shield machine The core components, which depend on imports for a long time, are generally scrapped after failure or when the shield machine reaches its service life, resulting in a large waste of resources. Therefore, it is urgent to carry out the remanufacturing work of the main bearing of the shield machine and accumulate relevant experience, and provide Preparation for the subsequent localization of the main bearing of the shield machine.
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