Archive for year: 2019

The reclaimer is a continuous and efficient bulk loading and unloading machine. It is widely used in raw materials fields of power plants, ports, steel plants, chemical plants, cement plants and other basic industries. It is suitable for strip or circular storage yards. Piles of bulk raw materials such as coal, iron ore, and limestone are taken continuously.

The slewing bearings of the reclaimer are most commonly used in the following three types: tapered roller slewing bearing, trolley type support, and rotary large bearing type support.

2. Slewing bearing type and structure type

2.1. Trolley type slewing bearing

The trolley type slewing bearing completes the turning motion by rolling the wheel along the circumference.
This type of support requires high assembly and machining accuracy. If it is slightly improper, the wheel rolling circle will not be perpendicular to the radius of gyration, and abnormal noise will occur.

When the slewing device is being repaired, it is necessary to use lifting equipment, large jacks, and necessary fixing and welding. The equipment needs to be disassembled locally, and many safety problems need to be dealt with.

Because of the relatively high height of the trolley itself, this type of support can easily increase the height of the center of gravity of the whole machine, which in turn affects the stability of the whole machine.

2.2. Rotary large bearing slewing bearing

There are many kinds of structural forms in this type of support. Among them, three rows of roller bearings are the most capable ones in various types. They have three races, and the upper and lower and the radial races are separated so that each row The load of the roller can be accurately determined, can withstand large axial forces, tipping moment and large radial force, and is especially suitable for heavy machinery such as reclaimer.
When the slewing device is being repaired, a large amount of work is required to replace the large bearing. It is necessary to use lifting equipment, large jacks, and necessary fixing and welding. The equipment needs to be disassembled locally, and many safety problems need to be dealt with. The maintenance cycle also takes about half a month. In terms of cost, if the large bearing is used as the slewing bearing, if the margin of choice is large, the bearing needs to be replaced in about ten years. The shortest in the country has five or six years to replace the large bearing equipment. The price of large bearings is relatively high, and the price of bearings of about 3 meters is more than 200,000 yuan.
The stacker and reclaimer is a large-scale mechanical equipment for open air operations. When using large rotating bearings, measures must be taken to prevent dust and water. It is very difficult to guarantee the above two. After the dust enters the water, it will increase the wear and corrosion of the bearing and reduce the service life of the bearing. In addition, large bearings should be placed horizontally during transportation and storage, and must be stored in a dry environment. The storage period should exceed a certain period of time, and other storage measures or anti-rust measures should be taken. Although the large bearing is simple to install, small in size and space saving, its cost is still relatively high.

2.3. Conical roller slewing bearing

After the support of the slewing roller, the cost is not much different from other support forms, but it has significant structural features:

2.3.1. No lubrication required: In actual operation, the roller and the bearing are almost unstressed due to the upper and lower pressure of the roller, and the load on the shaft and the bearing is only the additional load when the cage is fixed. Each roller bearing uses oil-impregnated bearings, so no lubrication is required.

2.3.2. Convenient maintenance: When using the conical roller support method, the maintenance is relatively simple and easy. It does not require large lifting equipment and jacks to complete, and the maintenance time is short, the maintenance cost is low, and it can be completed in one day.

2.3.3. The height of the center of gravity of the whole machine is low: because the diameter of the conical roller is relatively small, the overall height of the supporting device will be small, whether under normal working conditions or under high wind conditions, the supporting method is The stability of the machine will be better.

2.3.4. Low cost of spare parts: The conical roller type slewing bearing does not need to be replaced as a whole during maintenance. It only needs to be used with several rollers, and the spare parts cost is low.

2.3.5. Long service life: There are two reasons for the long service life of the tapered roller: First, the shaft and bearing of the tapered roller do not bear the supporting force of the slewing bearing, so that the bearing and the shaft have a long service life; the second is the diameter of the tapered roller. It is much larger than the diameter of the roller in the large bearing of the slewing bearing. Because of the large radius of curvature and the large number of tapered rollers, the contact stress of the tapered roller is small, so the large bearing has a relatively long service life.

2.3.6. Applicable to harsh environments: The stacker and reclaimer are large-scale mechanical equipment for open-air operation. The conical roller does not have to worry about dust and rain in specific use. Dust and rain do not have too much influence on the conical roller. The reason is that the diameter of the conical roller is much larger than the diameter of the roller of the large bearing, and the effect of a small amount of corrosion and dust on the conical roller and raceway is very small. The rollers and raceways should be properly greased during normal operation.

3. Summary

In the selection of the three slewing modes, in addition to the user’s designation, comprehensive aspects such as maintenance, installation, load capacity, space size, cost, machine stability, etc., the tapered roller slewing is preferred.

Abstract The paper introduces several key processes of large-scale pivoting support and measures taken for the production with the result that the products can meet the requirements marked in the drawings.

Descriptors super huge bearing, processing , quench-hardening, deformation.

Large slewing bearing, also known as slewing bearing or extra large bearing, is a large bearing capable of withstanding comprehensive loads. It can withstand large radial loads, axial loads and tipping moments. Slewing bearings are widely used in hoisting and transporting machinery. , port machinery, ship machinery and other large-scale rotary devices.

Due to the large volume of the large slewing bearing, the small cross-sectional area of the part, the high machining precision, the long process, and the easy deformation, the difficulty of machining increases. We have adopted corresponding technical measures for the support rings and outer rings of the slewing bearings, and according to the design. It is required to be processed, assembled by commissioning and more than one year of use inspection, which fully meets the original design requirements, and some aspects are even higher than the original design requirements.

1. Selection of rough forging

The large-sized workpiece of the slewing bearing has a support ring, an outer ring and a fixing ring. Since the support ring and the fixed ring are thin-walled annular parts, if the blank of one piece needs to be large when forging, and the heat treatment is prevented, the amount of quenching and tempering needs to be increased. Since the dimensions of the inner and outer rings of the retaining ring and the supporting ring are relatively similar, after repeated analysis, it is relatively easy to forge a large forging, and the fixing ring and the supporting ring are forged into one body, so that one set of slewing bearings has two blank forgings, one for outer The ring, the other is a forging of the retaining ring and the support ring.

2. Rough machining

The key to roughing is whether to separate the retaining ring from the support ring. The roughing process is a process before quenching and tempering. If the retaining ring is separated from the support ring, the amount of the retaining ring should be increased, and the deformation during the heat treatment is easy to increase; if it is not separated, during the semi-finishing process, due to the high hardness of the quenching and tempering, the machining and the large ring cut open. It is more difficult. From the perspective of the overall manufacturing process, it is not separated, and then separated after being tempered.

First, the amount of deformation during the quenching and tempering process is reduced.

Second, it is beneficial to better heat treatment, thus ensuring the quality of the heat treatment process. Through this analysis, we decided not to separate the retaining ring from the support ring before heat treatment, thus making the overall The roughing allowance is correspondingly reduced.

3. Since the fixing ring and the supporting ring require the hardened layer to be 3 to 5 mm, the hardness after surface quenching reaches HRC 55 to 60. The diameter of the part is large, but the cross-sectional area is small. After the car is finished, the surface is quenched. If the deformation is too poor, it can only be scrapped and the loss is too great. If quenching first, the thickness of the hardened layer should be 3~5 mm. If the amount of space is smaller than the shape variable, it will cause waste.

If the amount is larger than the shape variable, it is difficult to process. The amount of deformation is 1. 5 mm, such a 2 mm retention, the amount of the hardened layer is 2 mm, and the thickness of the hardened layer is 5 to 7 mm. Sufficient, after the quenching and tempering process, after the hardness test is passed, we test the support ring and the fixed ring and the outer ring, and find that the deformation amount is up to 1 mm, the minimum is 0.70 mm, and the amount is not exceeded. If it is reworked, it can also be supported by multiple points. The quenching surface can be 1.5 mm. If there are more support points, the retention can be reduced to 1 mm.

4. Finishing

In the turning process, since the hardness is basically HRC 59-60, we use the special alloy tool we developed and use the low-speed small feed for turning. When the amount is 0. 02 mm, it is ground with a bowl-shaped grinding wheel. When required for size, it is ground with a polishing belt to achieve the dimensional and roughness requirements of the drawings, laying the foundation for the manufacture of high quality slewing bearings.

First, introduction

During the loading and unloading operation of the door machine, it is inevitable that accidental centrifugal force and stress concentration will occur during the simultaneous operation of turning and lifting, resulting in damage of the large rotating bearing (the bearing type used in the 40-ton door machine described in this paper is 132.50.1500.03K5). Since the bulk cargo terminal in the Huanghua Port area is in the form of a water surface support beam, the carrying capacity is 8 tons/m2, and the replacement of the slewing bearing requires the upper and lower halves of the door machine to be separated before the bearing can be taken out. The upper part of the door machine weighs about 350 tons.

If a large crane is used, it will exceed the load capacity of the wharf. If the use of offshore floating cranes requires at least 1,000 tons of floating cranes, the rental cost will exceed one million yuan. The most economical solution is at the door. The heavy-duty jacks are placed at the four brackets under the slewing bearing, and the replacement of the slewing bearing can be realized by lifting the height to the height at which the bearing can be pulled out.

However, in this way, the upper part of the door machine is in suspension state, and it needs to be fastened to ensure safety, and it is very important to prevent wind and solid. The jacking process requires four jacks to be lifted at the same time to avoid offset dumping. To meet the above requirements, a strict construction management plan and a scientific replacement repair process must be established.

Second, safety preparation before construction

The risk of this maintenance operation is mainly: the upper part of the door lift and the falling process are suspended and unconnected, so the weather influence factor is large, it is necessary to check the local accurate weather forecast, and choose sunny and windless weather to ensure the sudden rise during the jacking process. In the case of strong wind or other bad weather, the safety of the operation must be properly prepared and emergency prepared. The windproof emergency plan must be prepared before the maintenance work can be carried out. The power transmission must be confirmed before the power transmission can be implemented to avoid power consumption. In the event of a safety accident, the jacking process must be carried out at a wind level below 5.

The maintenance process should clarify the responsibilities of each management personnel. It is necessary to organize the relevant technical management personnel and maintenance units of all departments of the company to participate in the maintenance equipment meeting, and make detailed arrangements for the machinery, tools and related procedures required during the maintenance operation. The division of labor makes detailed arrangements.

Third, the slewing bearing replacement repair process

1. Welding work and other preliminary work

(1) Under the plane. The maintenance area is remotely isolated before the operation. The ground is made of 24# channel steel splicing door-shaped frame, the middle beam is used to weld the hoist to disassemble the bearing. The bottom of the machine is welded and the bottom and the diagonal are slotted steel and angle steel fixed support, to ensure the replacement of the bearing frame level, so as to avoid When the bearing is tilted, the cutting and angle of the base are too large to be easily grooved.

(2) On board. The jacking support needs to cut the large lifting lugs, smooth and smooth, and the lower part is welded and supported by the base with the same thickness and long ribs. Three single lugs are welded to the disassembled bearing frame. Two lifting lugs are welded on the tail weight of the door machine, and the second rear support lifting lugs are used for diagonally pulling the 10-ton chain hoist.

(3) Inside the center slip ring. After the high-voltage power failure, remove the center slip ring and each control circuit, seal the joint with thick waterproof tape, and mark it with the mark paper. The center slip ring is wrapped with asbestos cloth to prevent electric welding and gas cutting Mars damage the line. Internal front, rear, left and right 4 points welded monolithic lifting lugs for adjusting the radial position of the new bearing. The slewing anchor is removed and sealed with iron plates. Remove 24 concentrated lubricating oil pipes and fold them up. Cut the upper and lower ladders along the bearing to support the rear upper and lower center slip rings (can be replaced by moving ladders). Check whether the other positions of the center slip ring are completely removed or the bearing is pulled out, and it is removed and fixed in time.

(4) Positioning. Move the door machine to an anchor position that does not affect the loading and unloading position, connect the windproof cable and anchor, and drop the windproof iron wedge. Adjust the amplitude to a position of up to 43 meters, with the boom facing the shore (positioning position during installation, while the wind direction of the pier is parallel to the boom, reducing the wind on the door machine). Disassemble the oil-saving plate of the large rotating bearing and clean the oil pan and bearing grease.

2. Lifting insurance and testing

(1) Use of the top lift insurance bolt. Remove 80 sets of inner and outer fixing bolts. Because the pre-tightening force is too large, the gas-cut longitudinal cutting nut can be used and removed twice. For the first time, remove the inner and outer two-thirds of the fixing bolts. Wait until the maintenance site has no wind. Prepare to remove the remaining one-third of the bolts before lifting. When removing the outer bolt holes, wear 1/3 safety bolts (M42×680). The front jack test.

(2) Because the jack plays an important role in the jacking process, a total of six 320-ton jacks are required, of which two are reserved. Place the bottom of the jack flat on the top lifting point of the jacking support and align it with the top lifting seat. After all the fixing bolts and the upper and lower connections are removed, use 4 jacks to test pressure at the same time to ensure that each jack is strenuous and lift at the same speed, otherwise replace the spare jack.

3. Lifting process

Since the wind will cause certain risks during the jacking process, it must be ensured that the jacking is completed once in the shortest time of downloading when the wind is small enough.
The lifting process is unified by the construction manager and the password is commanded and kept in sync. One measuring person is set inside and outside, and each measurement is carried out at a height of 50 mm to ensure that the error is within 5 mm. The height of the top plane is kept uniform by adjusting the jack separately. At the same time, the position of the jack cylinder and the crescent plate are used for pressure relief protection, and the length of the safety bolt is adjusted after jacking. After the upper plane is adjusted, the next jacking is performed. Tighten the upper nut during the jacking process, leaving a 50 mm clearance between the lower nut and the large ring gear, and at a height of 40 mm per jacking, loosen the lower nut until the jacking reaches the required height of 282 mm.

After the support and the block are supported on the inner side of the jacking support to the upper rib position of the door machine, the gap of 3 mm is reserved, and the jack is relieved according to the unified password of the commander. After the four points are stabilized, the block is added at the bottom of the jack. Keep the minimum stroke of the jack. Continue to rise and repeat the first jacking process after the jack is struggling. During the jacking process, the upper part of the door machine should be kept stable, and the four-point personnel should be uniformly lifted or released to ensure that the measurement error does not exceed 5 mm after each jacking.

Insurance process: After lifting up again to 282 mm in one reverse gear, stop the jacking, and finally measure the height of the four-point position, and adjust the same with the anti-pressure pressure crescent pad to ensure that the jacking pad reaches 3 mm gap. Simultaneously. The jack pressure is released, and the rigid support is used instead of the oil pressure to make the door machine rigid support. Then measure the height of the upper and lower support bases with a tape measure, and cut the same length of 24# channel steel welded on the side of the jack for longitudinal extension insurance. The front side of the door machine is slanted with ∠100 × 100×8 angle steel for two-way diagonal pulling, as a rigid anti-friction insurance to prevent the door machine from rotating to produce shearing force; the rear side of the door machine is inclined by two 10 ton chain hoists. As a flexible insurance to prevent rotation, to absorb part of the vibration force. There is enough space at the frame to allow for the removal of large bearings.

4. Disassembly and assembly of large bearings

(1) Disassembly process

After the door lifts are secured, use two 5 ton chain hoists to suspend the lifting lugs on both sides of the bearing frame, and the other end of the bearing bolt holes on the cap bolts to see the gap between the two sides to adjust and stretch. Before the stretching, use a screw jack to carry out the lifting and then pull out. During the stretching process, adjust the bolt hole suspension bolt position to fit the gap between the two sides and the pinion gap for pulling out. After pulling the half-position, suspend the special rope buckle for lifting, and pull the large bearing to the frame to lift the position, then command the door driver to hang the bearing.

(2) Installation of new bearing process

Before installation, pay attention to clean the new bearing first, fill up the grease, and block the oil passage cavity with the oil filler hole. Lifting 200mm from the ground before lifting to adjust the horizontal position to keep the large bearing in a horizontal position, so as not to be placed on the bracket and then slipped. To avoid shearing the base, apply a small amount of lubricant to the base. After stretching in place, adjust the position of the large bearing with the four lifting lugs inside the cylinder. After the bolt holes are aligned, prepare the mounting surface for machining.

5. Bearing mounting surface processing cleaning

Clean the upper and lower flange faces before installing new bearings. The measurement process is to select the highest point on the diameter of the diagonal wire ropes for each of the diagonal personnel, and use the feeler gauge to measure the amount of depression at other points on the same line. If you do not touch the wire, you can put it into the gap. The maximum size of the feeler is the amount of depression. At least two points of vertical line are measured.

New bearings can be installed after measurement. If the upper flange surface is first processed after the new bearing is in place, the relative flatness of the upper joint surface and the upper flange surface of the bearing should be adjusted, and then the output gear of the rotary motor should be adjusted. The pinion tooth surface is combined with the large ring gear tooth surface. 3 can be. If the two pinions interfere, one of the pinions can be removed, the high voltage is sent to the door, and the first gear is rotated to see if there is radial movement or turbulence. A small knife holder can be installed after smoothing. The flatness of the tool holder and the flatness of the bearing need to be extremely accurate, and the precision of the upper flange surface can be ensured within the accuracy of 0.2 mm. In the processing, it is important to ensure the bearing joint surface, the upper plane of the tool holder and the upper flange surface are parallel. The bearing surface is the reference, and the other two planes are guaranteed to be parallel to the reference surface. The flatness and finish should be within 0.2 mm after turning.

6. Remove the insurance decentralization process

After machining, the bearing frame is cut, as well as windproof insurance. After cutting the channel in the reverse position, it must be polished with an angle grinder to place the reverse support. The door machine decentralization process is the reverse operation of the jacking process. The operation process must be listened to by the same commander, and each measurement is adjusted within 50 mm each time to ensure that the 4-point error is within 5 mm. After one reverse gear The door machine can be lowered. Perforate the bolts in place before fully placing them in position and adjust the bearing position so that the bolts are not subject to shear forces.

7. Tightening bolt process

After the bearing is completely placed in place, the studs can be put up and down by hand to ensure that at least 3 buckles are exposed above and below, and a strong flat pad is placed under the nut. Spring pads are strictly prohibited. After the bearing is adjusted and positioned, use a torque wrench to separate the low, medium and high 3 preloads, and tighten them symmetrically in the direction of 180°. The sequence of steps is in accordance with the instruction manual. Finally, the pre-tightening force of the mounting bolt is 70% of the bolt yield strength, that is, the pre-tightening force of the 10.9 bolt is 665 kN.

8. Test run test

Install the bearing and the center slip ring for electrical and centralized lubrication, and after connecting the oil pan, pinion and other accessories, test the large bearing for refueling test. Use the 1st speed rotary test to check the meshing of the tooth surface, whether there is any abnormal sound when listening to the rotation, and measure whether the radial runout clearance of the pitch circle is less than 0.7 mm, and whether the clearance between the bearing and the flange surface is less than 0.2 mm. Then carry out the 2nd and 4th gear tests to confirm that there is no abnormality in the left and right and the maximum and minimum amplitude rotation. After the test run is stable and noiseless, it can be restored to normal use.

First, the status quo of the bearing “running circle” problem

The so-called bearing “running circle” is that the outer ring of the bearing and the bearing seat or the inner ring and the shaft have a relative movement. The planetary gear of the gearbox has a running ring that will cause irreparable damage to the gearbox.

Since the beginning of 2015, the running wind turbines have gradually exposed the problem of gearbox bearings “running circles”. According to incomplete statistics, in recent years, more than 100,000 units installed in China have suffered from “bearing running circle” failures, accounting for more than 10%. Not only are the double-fed motor units with more bearing applications, but also the main drive system bearings. Similar failures occurred in fewer direct-drive units, and the total number exceeded 1,000. According to a team of power equipment research institutes who recently measured the results of a group of operating units, the vibration spectrum showed a fairly high percentage of the unit’s running problems (according to what they say is almost 100%). Some units of foreign manufacturers also have bearing running problems. From the overall situation of the found bearing “running circle”, the high-speed end of the gearbox has a higher proportion, and the proportion of the planetary gear bearing “running circle” is lower. However, in the products of several manufacturers, the proportion of “running circles” of planetary gear bearings is relatively high, and batch failures occur.

The loss caused by the bearing running circle will greatly increase the operation and maintenance cost of the wind turbine, and may also affect the insurance company’s premium rate in the future.

At present, most of the domestic manufacturers, developers, and insurance companies that have bearing running circles do not understand this situation. The faults are handled by the gearbox factory itself, and the customer’s transmission is not truthfully told. In this case, this high-risk, high-cost failure has become a huge potential risk in the wind power operation and insurance industry.

Most of the handling of the “running circle” failure of the high-speed end bearing of the gearbox is solved by inserting or using a polymer binder after the fault is discovered. These two methods have relatively mature experience in ground equipment, but for the high-speed end bearing of the wind turbine gearbox, whether it can guarantee long-term use after repair, there is no mature experience.

For the planetary gear bearing “running circle”, there is no mature technology that finds the “running circle” fault in advance in China, and the difference in the spectrum of the bearing “running circle” due to the difference between the unit form and the operating environment, so most planetary gears Bearing “running” failure is confirmed after the transmission is damaged.

For the main bearing running ring of the direct drive unit, if no obvious damage is found in the bearing, the method of adjusting the bearing clearance is adopted; if the bearing is damaged, the main bearing is replaced.

Second, the analysis of the problem of bearing “running circle”

It is fundamentally due to improper bearing selection, improper structural design and load design, improper process control during manufacturing, improper adjustment of bearing clearance, improper bearing lubrication, improper storage or transportation of equipment, etc., resulting in bearing roller and bearing raceway. Severe sliding semi-dry friction occurs, eventually leading to the bearing “running circle”.

1. Spindle bearing

(1) The main shaft bearings of MW-class wind turbines with double-row spherical roller bearings are subjected to axial and radial loads at the same time, and the probability of failure is high. This is because the double row spherical roller bearing has a large clearance, and the bearing on the upwind side bears a small load. Most of the radial load and the axial force are received by the downwind bearing, causing excessive roller slippage. Poor lubrication causes the material to change from pitting to sticking, the seat ring and the roller and the cage are deformed unevenly, which changes the coordination between the race and the bearing seat, and causes common faults such as “running circle” and jamming.

(2) When designing the new transmission system, the spindle bearing has rarely used the self-aligning bearing. It is recommended to use the tapered roller bearing. The radial and axial bearing capacity is strong. The roller can be evenly loaded by pre-tightening, and the roller is not easy. Produces sliding friction. However, due to the high installation and technical requirements of the assembly process, improper adjustment of the bearing clearance can still cause semi-dry rolling friction, and then run-loop failure.

(3) The bearing assembly adopts the hot charging method. Since there is not enough heating device, the local heating method is used, and the heating is uneven, resulting in bearing deformation.

(4) During the transportation process, the unit’s damping measures are improper, or a part of the bearing is bearing for a long time, causing local deformation of the raceway.

(5) There are two main lubrication methods for the main shaft bearings of wind turbines currently in operation: grease lubrication and pressure lubricant lubrication, in which the lubricating oil with a higher proportion of lubrication is generally 10-20 rpm, which is low. The rotational speed of the spindle bearing and the planet carrier support bearing is often difficult to form. If the thickness of the oil film is insufficient to separate the two metal surfaces, the lubrication does not achieve the predetermined effect, the bearing will wear out early, the material peeling damage will occur, and the semi-dry sliding friction will occur, which in turn will cause the bearing to run. The pressure lubrication method is very beneficial to improve the working condition of the bearing. In addition to forming the oil film to protect the rolling roller in time, it can also take away heat and abrasive grains to prolong the service life. It is recommended that the spindle bearings be lubricated with pressure oil if conditions permit.

2. Transmission bearing

The ratio of the running ring of the high-speed shaft-side bearing in the gearbox is higher than that of the planetary gear bearing, and the reason for the difference is different.

3. High speed shaft side bearing

(1) The matching tolerance of the bearing and the bearing housing is unreasonable, resulting in insufficient interference. Since the external environment in which the wind turbines operate varies greatly, it is very likely that the standard tolerance zone will not be able to adapt to the operating conditions.

(2) The process control during assembly is not strict, which results in the matching of the limit deviation between the bearing and the bearing seat and the deviation under the limit. At the assembly site, it has actually been found that the assembler selects a bearing with a small amount of interference for fitting.

4. Planetary wheel bearing

(1) The maximum power of the wind turbine gearbox in actual use may reach more than 3 times of the nominal power. Especially in the case of growing blades, the moment of inertia of the wind turbine is greatly increased, and the impact load on the drive train during the start and stop of the unit is increased. It also greatly increased the domestic unit to increase the blade on the basis of the prototype, and did not redesign the gearbox accordingly, resulting in the case of the gearbox planetary shaft system and the intermediate shaft system with relatively poor rigidity. The load increases the occurrence of bearing stress concentration, which in turn causes the bearing to run.

(2) The planetary gear train structure design is weak. The national standard GB / T19073 wind turbine gearbox specifies that the thickness of the planetary gear hub should not be less than 3 times the modulus, in order to ensure that the gear race has sufficient rigidity to resist the deformation caused by the gear force. The deformation of the planetary gear is one of the important reasons for the bearing running circle. The gearbox failure of the planetary gear bearing in the domestic gearbox factory occurs precisely because the design does not meet the thickness requirements of the gear hub proposed by the standard.

For the planetary shaft system, the floating planetary gear shifting mechanism is adopted abroad to achieve the purpose of uniform loading. However, such structures are more complicated in gearbox assembly and adjustment.

Aiming at the situation that the planetary gear structure size is difficult to meet the rigidity requirement due to the space limitation of the wind turbine, the solution of integrating the planetary gear with the bearing outer ring and the integrated flexible pin scheme similar to Timken (see Figure 1) are proposed abroad. Several gearboxes have been trial-produced by the domestic Hangzhou Gear and the South High Gear with integrated structure and integrated flexible pin structure. Since the planetary gears are machined, heat treated and tested in the gearbox and bearing factories according to the machining process, the cost of the gearbox is greatly increased. Domestic wind power machine enterprises are difficult to accept under the current market price. Foreign machine companies have adopted gearboxes of this type in batches.

Suggestions based on current realities:

1. From the current situation reflected in all aspects, it is imperative for the wind turbines that have been put into operation to find the harbinger of the bearing running circle in time before the destructive accident. This can eliminate the accident in the bud. However, due to the different structure of the wind turbine, the operating environment is different, the bearing positions are different, and the vibration characteristics of various types of bearing running rings have not been mastered technically. What can be done at present is to collect the vibration monitoring records of wind turbines that have already had accidents, organize professional teams to analyze them, find out the regularity items as soon as possible, and then verify and promote them in the running wind farm. There are already a number of manufacturing companies, development and operation companies and research institutions expressed their willingness to participate and provide verification conditions.

2. The analysis in front of this report is based only on previous theories, experiences and available cases. The current large number of accidents have not yet been fully grasped. In order to conduct an accident analysis, each gearbox manufacturer should no longer use the pretext of keeping the so-called “trade secrets” as an excuse to refuse public accidents. The result of this can only cause deeper damage to China’s wind power industry. Only by thoroughly grasping the real situation of the accident in the industry and thoroughly analyzing the possible causes can we find the root cause of the defect and take effective measures to solve it. At the same time, provide basic data for mastering accident monitoring and early warning technology. It is recommended that all enterprises involved in similar accidents should truthfully provide accidents to the whole machine enterprises, development and operation enterprises and research institutions.

3. Bearings should be equipped with sufficient tooling to prevent invisible damage during assembly. The assembly with interference fit is preferably to uniformly heat the bearing by a closed heating device. The heating temperature should not be too high, and it is in a positive clearance state during the heating process, and does not squash the roller and deform. When conditions permit, it is recommended to assemble the bearing by means of a freezer shaft. The lubrication of the bearings should be highly valued. In addition to ensuring adequate lubrication, adequate measures must be taken to ensure the cleanliness of the fluid.

4. In the selection of bearings and their cooperation, the host and components and the bearing supply unit should work closely together, timely exchange and feedback, and reasonable selection of bearings and cooperation. The shaft and hole of the bearing of the device should be selected according to the tolerance of the diameter of the bearing ring, and the tolerance range should be properly tightened to ensure the interference of the fit.

5. Strengthen the training and training of professional and technical workers to ensure that the assembly and clearance adjustment of the bearings meet the technical requirements.

6. During the assembly process, the shafting should be centered repeatedly to mitigate the effects of additional loads.

7. Strengthen the processing of gearbox, the technical procedures of the assembly site, the process hygiene management, ensure the processing of the gearbox, and the assembly process is carried out under strict process conditions.

8. Prepare technical guidelines related to the transportation and storage of wind turbines and main shafts to prevent deformation of the lower end raceways and rollers of the main shaft bearings due to the large gravity of the main shaft during transportation and non-operational stages.

9. Enhance the rigidity of the wind turbine frame to prevent abnormal eccentric load of each bearing caused by deformation.

10. Strengthen the daily maintenance of wind turbines, strictly abide by the safe operating regulations, and have sufficient countermeasures for the impacts of different processes such as starting, braking, stopping, and deactivating the unit.

11. The wind turbine should be equipped with relevant detection devices to perform instantaneous monitoring of the vibration and temperature of the transmission system, analyze the measurement data, accurately find the cause, and issue an early warning to avoid downtime due to failure.

12. Strengthen the design research of wind turbines. Based on the reliability analysis, the system analyzes the impact of the abnormal transient load on the key parts of the transmission system for the severe working conditions of the unit, and compiles the load spectrum that is more in line with the actual working conditions. Fully guarantee the safety margin of the system and components. Improve the layout and structure of the drive system to reduce the effects of transient anomalous shock loads.

13. Reasonably select the structural form of the unit transmission system on the basis of accumulated experience, and adopt the mature and proven transmission form as much as possible. The new transmission form and structural arrangement should not be easily adopted without demonstration.

14. The original bearing life calculation theory has been difficult to meet the requirements of modern wind turbine gearbox bearing calculations. The relevant information manufacturer of the new bearing life calculation method proposed by the international famous bearing company is generally less public. At present, the calculation of bearing life is generally estimated based on the life calculation method proposed by each bearing manufacturer. Bearing life calculation methods are numerous, the influencing factors are complex, the load data is scarce, and the complex load processing methods are imperfect. The processing of transient loads, braking loads, ultimate loads, etc., which are often encountered during the use of the unit, is estimated empirically. In addition, the linear cumulative damage theory used in the process of variable load processing does not truly reflect the actual damage, which will lead to an increase in the gap between design calculation and practical application. To this end, it is recommended to strengthen the research on the theory of domestic bearing life in combination with the actual needs of wind turbines.

15. It is recommended to strengthen the research on bearing design, materials, technology and inspection technology in the special field of wind power high load capacity, high reliability and long life as soon as possible. The bearing industry and wind turbine manufacturing enterprises, wind power transmission equipment manufacturing enterprises jointly carry out research work, accumulate experience for the design and manufacture of wind power bearings, and strive to make breakthroughs as soon as possible.