Analysis of the causes and preventive measures of bearing cracks in grinding processing

Mechanical grinding is a method of manufacturing a common metal cutting, the bearing processing industry also been widely used, the bearing parts of heat hardening, or reticular cracking may occur more rules during grinding arrangement of small cracks, known as grinding cracks, it not only affects the appearance of bearing parts, more importantly, also directly affect the quality of the bearing parts. This paper analyzes the causes of bearing parts produced grinding cracks in the grinding process, then take preventive measures, so as to effectively prevent the generation of grinding cracks.
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First, the reasons bearing grinding cracks
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Generating bearing grinding cracks caused by the grinding heat, the surface temperature of the bearing up to 800-1000 ° C or more grinding. Tissue quenched steel is of martensite and residual austenite certain number of them are in a expanded state (without tempering). With increasing expansion and contraction of martensite steel carbon content increases, the steel grinding cracks generated surface of the bearing is particularly important. Effect of grinding heat of retained austenite in hardened steel that is subject to decomposition during grinding, gradually transformed into martensite, martensite this renewed focus on the surface of the part, causing local expansion of the bearing surface, increased parts of the surface stress, stress concentration resulting in grinding, will continue to accelerate the grinding surface of the grinding cracks produced; in addition, the nascent large Chuai martensite, grinding easily accelerate the production of grinding cracks.
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On the other hand, grinding when the grinding machine parts, parts of both pressure and tensile force is, contributing to the generation of grinding cracks. If the cooling is insufficient at the grinding, since the heat generated during grinding, the grinding surface of the sheet sufficient to re-austenitization, quenching and then quenched again into martensite, so that the surface layer of additional stress in the organization, coupled with the amount of heat generated by the grinding surface of the bearing temperature rises fast, fast cooling, which is superimposed the stress and thermal stress may lead to the grinding surface of the grinding cracks generation.
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Second, it characterized in bearing grinding crack
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Usually the grinding cracks significantly different quenching cracks, cracks occur only in the grinding surface of the grinding, shallow, and substantially uniform depth. Lighter grinding cracks perpendicular or nearly parallel to a line perpendicular to the grinding direction and are regularly arranged strips crack, which is a kind of cracks, crack more severe form of tortoiseshell (closed network like), a depth of approximately 0.03 ~ 0.15ram, with obvious cracks after acid etching, which is the second crack.
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Third, grinding cracks Prevention
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From the above analysis of the root cause to know that the generation of the grinding cracks are in a quenched martensite expanded state, the presence of stress. To reduce or eliminate such stress, the stress to be tempered i.e. quenching, tempering is performed, waste of time must be more than 4h. With increasing tempering time, the possibility of grinding cracks decreases. In addition, bearing in rapidly heated to about 100 degrees C and rapid cooling will crack. To prevent cold cracks, the part should be tempered at about 150 to 200 degrees Celsius, if heated to 300 degrees Celsius to continue bearing surface shrinkage cracks again, to prevent the generation of cracks, the bearings should be tempered at about 300 degrees Celsius. It is noteworthy that, bearing around 300 degrees Celsius tempering the hardness will drop, something should not be used. Is produced through a tempering still grinding cracks, which can be tempered or secondary artificial aging treatment, this method is very effective.

Slewing ring

It produces grinding cracks due to heat caused by grinding, so reducing the grinding heat is the key to solve the grinding cracks. Wet milling method is generally employed, but in any case the injection coolant, the coolant no method to arrive at the grinding surface grinding, grinding heat and therefore can not reduce the grinding point. Coolant only part of the grinding point of the grinding wheel and grinding after cooling being passed instantaneously, while the quenching effect of the cooling liquid to make the grinding point. Thus increasing the amount of coolant is one of the main measures to minimize the grinding zone of the grinding heat. If dry milling process, grinding feed less, grinding cracks can be reduced. However, this method is not very significant, and dusty, affecting the work of a bad environment, should not be taken.
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Selection softer durometer, coarser sand to the grinding wheel, grinding heat can be reduced. However, coarser particles can affect parts of the surface roughness, high surface roughness for the part, can not use this method, and therefore subject to certain restrictions. The crude fraction, grinding, selection of both coarse particles coarser soft grinding wheel, the grinding facilitate strength, improve efficiency, and then be fine-grained grinding wheel, grinding feed amount is small. Two points were roughing and finishing, this is the ideal method.
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Self-sharpening properties of a good choice of abrasive wheel, the grinding wheel surface timely removal of waste material, reducing the grinding feed, increasing the number of grinding table speed is reduced, which is an effective way to grinding cracks is reduced.
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The rotational speed of the grinding wheel and part of one of the factors is the main, large wheel rotation runout, ran large parts are grinding cracks incentives. Increase in time accuracy of the grinding wheel and the rotary part so as to eliminate the grinding cracks caused by various factors as much as possible.
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Fourth, the method of preventing the surface of the bearing steel grinding cracks
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In grinding, the grinding cracks generated surface bearing steel, the main method for preventing:
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① reduce grinding heat to solve the grinding cracks.
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② points coarse, fine grinding, both coarse particles selected coarse grinding soft grinding wheel.
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③ Selection good performance since the sharp abrasive wheel, the grinding wheel surface timely removal of waste material, reducing the grinding feed, increasing the number of grinding table speed is reduced.
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④ increase in time accuracy of the grinding wheel and the rotating parts so as to eliminate cracks caused by grinding possible.
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These are the bearings on the causes and preventive measures of cracks in the grinding process analysis reports, I hope you can help look after. Luoyang permanent crown diameter slewing bearings are mainly production of 50-9800mm / wheel bearings and various high-precision rotary bearing, a large thrust ball bearings, bearings and other non-standard shaped products, precision covering P0, P6, P5, P4 four grades, the product type comprises a single row four-point contact ball structure, cross-cylindrical roller structure, a triple-row cylindrical roller structure, a double structure volleyball, the ball joint structure of columns, thin-walled flange structure, large thrust ball structure. Welcome to the needs of friends to call detailed consultation.

What are the requirements for the packaging of bearings?

For bearing products, packaging is very important, not only to prevent rust, but also to protect the bearing from bumps during transportation and damage to the bearing. Bearing packaging is divided into inner packaging and outer packaging. So, what are the requirements for the packaging of bearings?

First, the inner packaging of the bearing

After the bearing is manufactured and passed the inspection, it will be cleaned and anti-rust treated, and then put into the inner packaging to achieve the purpose of waterproof, moisture-proof, dust-proof, shock-proof, maintain the quality and accuracy of the bearing, and facilitate the use and sale. .

1. The inner packaging of the bearing is divided into three categories according to the anti-rust period

① Short anti-rust period packaging

The anti-rust period is 3-6 months, which is suitable for bearings that are shipped to the same subscriber in large quantities and put into use in a short period of time. The two parties have agreed to use simple packaging based on the principle of ease of use.

② General anti-rust period packaging

The anti-rust period is one year, suitable for general-purpose bearings.

③ Long anti-rust period packaging

The anti-rust period is two years, suitable for special and precision bearings.

2, bearing inner packaging material requirements

There are polyethylene plastic tube (box), kraft paper, plain and wrinkled polyethylene composite paper, paper box, polyethylene or polyethylene plastic film, nylon fastening tape or plastic woven fastening tape, waterproof high-strength plastic tape, burlap bag, etc. . All of the above materials need to ensure that the corrosion resistance test of the material is qualified.

3, the requirements of bearing inner packaging method

①Miniature bearing

Every 10~15 sets of bearings are packed into a plastic tube, and every 5~10 plastic tubes are packed into a carton (or bag or roll pack).

②Medium and small bearings

Multiple sets of bearings are wrapped with polyethylene film, kraft paper or polyethylene composite paper for external use; multiple sets of bearings are packed into a plastic tube (box); single set of bearings is packed in polyethylene film bags, folded or sealed before repacking Into a paper box.

③Large bearing

Pack it in a single set of polyethylene film or polyethylene composite paper, and then put it into a carton; use a polyethylene film bag, pack the single set of folded bag openings, and then put it into a carton; put the single set into a special plastic box; Three-layer wrap-around packaging: polyethylene film tape or composite paper tape for the inner layer, fastening tape for the middle layer, and waterproof permeable plastic tape for the outer layer.

④Extra large bearing

Single set of three-layer wrapping packaging (same as above).

Single-by-four-layer wrapping package: After the above-mentioned three-layer wrapping package, the outer layer is wrapped with a layer of linen tape.

For separable tapered roller bearings with outer diameter ≥150mm, the inner and outer components should be lined with polyethylene film before packaging, or the inner and outer components should be packaged separately. For interchangeable cylindrical roller bearings with an outer diameter of ≥150mm, because the complete package is easy to be damaged, the inner and outer components can generally be packaged separately.

Secone. Standards for bearing outer packaging requirements

1. General materials and requirements for outer packaging of bearings

① Double corrugated boxes, the total weight (gross weight) of each box does not exceed 25kg, and the outside of the box is bound with plastic strapping.

② Nail board box (wooden box), the total weight of each box does not exceed 30kg, and the outside of the box is bound with blue steel tape.

③ Calcium plastic corrugated box, the total weight of each box does not exceed 25kg, and the box is bound with plastic strapping.

When packing bearing products with inner packaging into the box, plastic bags or plastic films should be lined in the box first; if there are gaps in the box, it should be filled with corrugated paper blocks, paper scraps and other dry materials.

2, pay special attention

It is especially important to emphasize that due to the heavy weight of large bearings, packing straps should be added to the packaging box to ensure the convenience of bearing handling and other processes. For the packaging of large bearings, each manufacturer has its own characteristics, such as the material requirements for the outer packaging, anti-counterfeiting marks, and so on.

Compared to other products, the packaging and transportation of bearings are very important. Whether it is a bearing manufacturer or a motor manufacturer, we are inseparable from the transportation link without exception. We must fully communicate with the transportation party and take necessary precautions.

How to maintain the crane slewing ring?

The slewing bearing is an important “joint” of the crane, so its maintenance is very important. So how to maintain the crane slewing ring?

When carrying out maintenance work, the first thing to pay attention to is the danger of being dragged into the rotating pinion, as well as the danger of crushing and shearing. When performing the following tasks, make sure that when starting the engine to perform the necessary slewing and luffing actions, any maintenance personnel are not in the danger zone between the main boom, the upper car and the reel, or between the exit and the reel. Dangerous areas, except for crane operators (in the driver’s cab).

1. Check the bolts of the slewing ring

1. Before each crane work or at least once a week, visually inspect the bolts on the slewing ring;

2. After the slewing ring has been working for 100 working hours, check whether the bolts are loose or not. Check again at the 300th working hour; check every 500 working hours thereafter; shorten the inspection interval for severe working conditions. If the bolts are found to be loose during the inspection, please stop the construction work and contact the local after-sales service department immediately. The factory or professional technicians will inspect and decide whether to disassemble and inspect immediately.

3. The slewing ring is filled with lithium grease before installation.

4. When replacing bolts, wipe the bolts clean, apply thread fastening glue and tighten them; use a crane in accordance with the requirements of the operation manual and lifting performance table, or check the fastening bolts regularly as required to avoid fatigue damage of the bolts. danger.

2. Routine inspection of slewing ring

1. Regularly check the flexibility of rotation; if noise or impact is found, stop the machine for inspection and troubleshoot immediately, and dismantle and inspect if necessary;

2. Regularly check whether the rotary gear ring is cracked or damaged, and whether the meshing tooth surface has biting, gnawing, peeling, etc.;

3. Regularly check the integrity of the seal. If the seal band is found to be damaged, it should be replaced in time, and if it is found to be off, it should be reset in time.

Three, lubricate the tooth surface of the slewing ring

The slewing ring gear has been coated with anti-rust oil before leaving the factory. The effective period of this anti-rust is generally 3 to 6 months. After the effective period, the anti-rust oil should be coated in time. In addition, during use, prevent the slewing bearing from being directly exposed to sunlight. It is forbidden to rinse the slewing bearing directly with water to prevent water from entering the raceway, and prevent hard foreign objects from approaching or entering the tooth meshing area.

Fourth, the raceway of the sliding slewing ring

The raceway must be filled with grease regularly according to the working environment. After working for 50 working hours, the raceway should be filled with lubricating grease, and then again every 300 working hours. The slewing bearing must be filled with grease before and after being placed for a long time.

If using a steam jet cleaner or a fixed water sprayer to clean the crane, care must be taken to ensure that water does not seep into the slewing ring connection, and then the slewing ring connection must be lubricated. In special working environments, such as tropical, high humidity, dust, large temperature changes, and continuous work, the lubrication cycle should be shortened.

Grease filling should be carried out when the slewing ring rotates slowly. When the lubricating grease overflows from the seal, the filling is completed. The overflowing grease will form a thin film to act as a seal.

Why the slewing bearing is not installed smoothly or even cannot rotate?

Sometimes the technical indicators were normal when the rotation performance was tested in the factory, but the newly installed slewing bearing and slewing ring showed inflexible rotation. In addition, why the slewing bearing is not installed smoothly or even cannot rotate?

Reasons for the unsmooth installation of the slewing bearing

1, mounting hole. The threaded hole of the mounting hole is not standardized, the thread is not completely, and the thread is defective, which causes the bolt to be unable to be screwed in.

2. The center diameter and chord length of the mounting hole are out of tolerance too much, such as 3-5mm, causing the bolt to fail to perforate.

3, the positioning hole and the step size are out of tolerance and cannot be matched.

4. The bearing after heavy load has a dead center or ellipse in rotation, causing it to fail to operate normally.

5. The bearing is not in the installation direction of the installation design drawing, resulting in the opposite direction of the taper pin, which has potential safety hazards.

6. Interference of installation parts, such as tooth tip interference, there will be teeth gnawing phenomenon, and individual parts conflict with each other.

7. The negative clearance design is unreasonable, resulting in oblique force, unbalanced load and clearance after installation.

8. The equipment structure design is unreasonable, causing the debugging to not be carried out normally.

The slewing bearing may be difficult to rotate or unable to rotate

1. Idling of newly purchased products is not flexible

Please check the production date of the slewing bearing. If it takes a long time (such as more than half a year) and the climate is cold, it is possible that the salt mist and other temperament in the raceway will double the rotation resistance, which will make the slewing ring not work properly (cold areas, more prominent in winter) ) Elimination method: If it can run without other abnormalities, it can be used normally.

2, the operation after installation is not flexible

It may be that the surface of the main machine device and the surface of the slewing ring are not properly matched, resulting in that the axial clearance of the slewing ring behind the device cannot compensate for the deformation of the slewing ring. The slewing ring is in a state of negative clearance, and the rolling elements are difficult to run in the raceway (sometimes with abnormalities). Noise) or poor meshing of the large and small gears; or foreign matter stuck in the large and small gears. Elimination method: re-process the plane of the main machine device to make the device plane meet the requirements; re-adjust the gear meshing backlash according to the requirements, especially pay attention to the gear jump position; check to ensure that there is no foreign matter in the meshing position of the large and small gears; exchange a slewing bearing with a larger gap .

3, the operation is not flexible during use

The sealing strip is damaged, causing foreign matter to enter the raceway (such as poor working conditions, dust immersed in the raceway, etc.), and the isolation block is deformed and difficult to operate; there are hard objects or other conditions at the meshing of the large and small gears, such as broken teeth.

The above is an analysis of the annoying reasons why the slewing bearing is not installed smoothly or even cannot rotate. I hope everyone will be helpful after reading it. When testing the rotation performance of the new bearing, it can rotate lightly, but at this time, it does not represent a reasonable index. The contact point, contact angle, and relative position of the connecting point of the channel are in line, and whether the two circles are close to the perfect circle. The two circles are completely or close to positive balance. In layman’s terms, just like the two rails of a train, they should be close to theoretical parallel, high and low parallel, so that the train will be stable, high-speed, orderly and safe. Therefore, to test the rotation performance, the loading experiment is a very important basis and effective means.

What is the impact of the amount of grease injected on the bearing?

We all know that grease has good adhesion, wear resistance, temperature resistance, rust resistance and lubricity, can improve high temperature oxidation resistance, delay aging, can dissolve carbon deposits, and prevent metal wear debris and oil stains. Poly, to improve the wear resistance, pressure resistance and corrosion resistance of machinery, it will be commonly used in bearing products. For sealed bearings, appropriate grease has been filled during production; for open bearings, a sealing device is also installed in the host to prevent grease leakage. Today, the editor will talk to you about the impact of the amount of bearing grease on the bearing?

The amount of grease injected into the bearing will have a certain impact on its operation. If the amount of grease is too small, it is easy to cause lack of grease or dry friction, which will affect the life span. Too much grease will cause the bearing temperature to rise. A large amount of grease leakage not only pollutes the environment, but also causes waste. It can be seen that the amount of grease injected into the bearing should be as small as possible on the premise of ensuring sufficient lubrication of the bearing.

After understanding the movement process of grease in the bearing, it will naturally come to a conclusion: the grease in the bearing should not be too much. Too much grease is not only a waste, but also harmful. The higher the speed of the bearing, the greater the harm.

The more grease is filled, the greater the friction torque. With the same filling amount, the friction torque of the sealed bearing is greater than that of the open bearing. After the grease filling amount is equivalent to 60% of the internal space volume of the bearing, the friction torque no longer increases significantly. This is because most of the grease in the open bearing has been squeezed out, and the grease in the sealed bearing has also leaked out.

With the increase of the grease filling, the temperature rise of the bearing increases linearly. The temperature rise of the sealed bearing is higher than that of the open bearing at the same filling amount.

Slewing ring

It is generally believed that the grease filling amount of sealed rolling bearings should not exceed about 50% of the internal space. Tests have shown that 20% to 30% of ball bearings is appropriate.

Correct lubrication and regular maintenance can avoid bearing damage caused by lubrication problems. To ensure reasonable lubrication:

• Follow the instructions set by the device manufacturer for each device;

• When adding grease, it should be filled between the rolling parts of the bearing and the housing (or retainer) to ensure that sufficient grease enters and the surface of the key raceway is fully lubricated;

• Pay attention to when the bearing should be greased (Re-lubrication);

• Monitor the indicating instruments of the equipment, so as to find signs of problems as early as possible, such as temperature fluctuations and/or abnormal high temperatures;

• Pay attention to equipment noise or abnormal vibration;

• Observe lubricating oil leakage;

• Regularly sample the lubricating oil and check for contamination.

When injecting grease in addition, the site should be clean and clean, and the tools used should be cleaned with gasoline. After the grease is filled, other parts should be assembled as soon as possible to prevent the grease entering the bearing from entraining dust and sundries, especially sand and iron filings.

What is the slewing ring gear module?

Slewing bearing is one of the important parts of many modern machinery and equipment. It is called “joint of machine”. Many people are familiar with various parameters of slewing bearing, including clearance, inner and outer diameter, friction coefficient, etc. Many of my friends don’t know the module of supporting gear, so let’s follow the editor today to understand it.

 

  1. what is the slewing ring gear module

 

The length of the arc (gear)/straight line (rack) occupied by a single gear tooth in the indexing circle (gear)/or line (rack), its length is π * m, and m is the modulus.

 

What does the module of the slewing ring represent: The module of the slewing ring represents the product of the tooth pitch and the number of teeth of the slewing ring gear, which is the circumference of the index circle. The gear modulus of the slewing ring determines the size of the tooth. The gear modulus is a basic parameter for the calculation of the gear size. The symbol is “m”. Gear cutters can be standardized, so that the standard modulus of gears can be standardized for mass production. Facilitate the replacement of later accessories. In the same way, “modulus” refers to the ratio of the pitch t between the tooth profiles of two adjacent gear teeth on the same side and the circumference ratio π (m=t/π), in millimeters.

 

If the number of teeth of the slewing ring gear is constant, the larger the gear modulus, the larger the radial dimension of the gear. The teeth of a gear with a large modulus are thick, and for two gears with the same number of teeth, the outer circle of the gear with a large modulus is larger. Therefore, the modulus of the gear in a watch is very small, and the modulus of the flywheel and transmission gear on the mechanical punching machine is large. The modulus of the two meshing gears must be the same. Modulus is the basic parameter of gear design, and it is used in many calculations of gear design.

 

 

  1. Reasonable selection of gear modulus

 

When designing a gear, one of the important parameters is this modulus. The gnawing of the gear will produce gnawing pulsation. The main reason is that it has a great relationship with the elastic deformation of the gear teeth. It is a basic part of the gear design. Parameter-gear modulus, if it is a relatively large modulus (that is, a gear with a relatively large size), it will also have a relatively large load-bearing capacity. The modulus parameter is inversely proportional to the degree of bending of the gear teeth. The increase of the modulus means that the rigidity of the gear teeth is improved, so that the elastic deformation of the gear teeth will not be great when the gnawing transmission is carried out, which greatly reduces the impact force formed by the gear teeth, thereby achieving The purpose is always greatly reduced. Therefore, from this point of view, the modulus should be increased appropriately, but the error generated when machining gears is also related to the modulus. If the modulus is increased, the tooth profile and pitch will also be increased. At this time, the error of gnawing noise will also increase accordingly, so the choice of modulus should be determined according to the specific situation.

 

In the case of keeping the modulus unchanged, the diameter of the gear is proportional to the number of teeth, so the change of the number of teeth will also change the bending amount and elastic stiffness of the gear teeth: the strength of the noise generated by the sound source is not only related to the energy of the vibration source It is related to the size of the radiation area. If the radiation area is increased, the radiation power will also increase. Increasing the diameter of the gear will increase the noise radiation area, which will greatly affect the gear. Effective noise control. Therefore, in the relevant design, within the permissible range of ensuring the strength of the gear, the number of teeth and the small modulus should be used as much as possible, and the reasonable selection of materials and heat treatment methods can be combined to promote the improvement of the strength of the gear teeth, thereby Reduce the gear tooth diameter to achieve the purpose of reducing gear noise.

 

The above is the relevant introduction about the slewing ring gear module. In the slewing ring selection process, the first two sets of data listed in the national standard parameters of the slewing ring module should be selected first, which is more important for the adaptation of the bearing and the replacement of accessories. Convenient, but non-standard gears with customized bearing module requirements for bearings used in special machines are not within the above constraints.

What is the material used to make the slewing bearing

The common structural forms of slewing bearings are single-row, double-row four-point contact ball slewing bearings, double-row angular contact thrust ball slewing bearings, crossed cylindrical roller and crossed tapered roller slewing bearings, three-row cylindrical roller slewing bearings, balls Different structural forms such as column hybrid slewing bearing. Although the structure is different, the materials used are similar, and the material of the slewing bearing directly determines the performance and service life of the bearing. Today, the editor will take everyone to understand what materials are used for the slewing bearings.

1. Material for ferrule and rolling element

Because the bearing should have the characteristics of long life, high precision, low heat generation, high speed, high rigidity, low noise, high wear resistance, etc., it is required that the bearing steel should have the characteristics of high hardness, uniform hardness, high elasticity, and high limit. .

Under normal circumstances, the slewing bearing rolling element adopts integrally hardened carbon chromium bearing steel. The grade is made of GCr15 or GCr15SiMn steel; the slewing bearing ring is made of surface hardened steel. When the user has no special requirements, it is generally made of 50Mn steel, but sometimes in order to meet the needs of the host in some special applications, it can also be provided by the user. For specific use conditions, select other grades of surface hardened steel, such as 42CrMo, 5CrMnMo, etc.

(1) 42CrMo is a high-carbon steel with good quenching and tempering performance and quenching performance. It is an ideal material for slewing bearings.

(2) 50Mn has good hardenability and is also a high-quality choice for slewing bearings.

(3) 40Cr is also good in terms of mechanical properties, and it is still in the stage of exploration and practice.

(4) GCr15 small slewing bearing can be selected, but it is generally not recommended to use it because of the trouble of milling and drilling in the process due to the full quenching.

Slewing bearing

2. Material for cage

The cage for slewing bearings has a structure such as an integral type, a segmented type, and a spacer type. Among them, the integral and segmented cages are made of No. 20 steel or ZL102 cast aluminum alloy. The isolation block is made of polyamide 1010 resin, ZL102 cast aluminum alloy, etc.

3. Sealing ring materials

The slewing bearing seal ring is made of oil-resistant rubber or nitrile rubber.

The code of the ferrule material and the supply status of the blank is in accordance with the regulations in the table. In the table, “T” indicates that the ferrule blank is supplied in the quenched and tempered state, and “Z” indicates that the ferrule blank is supplied in the normalized state.

The slewing bearing seal ring is made of oil-resistant rubber or NBR nitrile rubber. Compared with nitrile rubber, hydrogenated nitrile rubber has better oil resistance, but if you are not too demanding on oil resistance, use nitrile rubber, because hydrogenated nitrile rubber is relatively expensive. Nitrile rubber also has a certain degree of acid and alkali resistance. However, silica gel should be selected if the requirements for oil resistance and acid and alkali are higher, but its price is higher.

In summary, we know that the materials used in slewing bearings are related to their main body and parts. The main body is made of metal, while other parts, such as seals, are made of rubber. If you need this kind of bearing, you must pay attention to the integrity of these materials and high-quality effects when purchasing to ensure the function of the operation. Luoyang Hengguan Bearing provides high-quality, high-performance slewing bearing products for market customers. Everyone is welcome to call for detailed consultation.

Analysis on the Causes and Preventive Measures of Vibration of Slewing Bearings in Operation

Slewing bearing can also be called turntable bearing and rotating bearing. It is one of the important parts of modern construction machinery slewing devices, such as excavators, cranes, pile drivers, graders, road rollers, dynamic compactors, roadheaders, tower cranes, etc. Slewing bearings are always used. Due to the large load during operation and the harsh working environment, the operation is not smooth (jitter) and excessive noise (abnormal noise) failure occurs. So, what is the cause of jitter when the slewing ring is running? How to prevent it? Next, follow the editor to understand it.

Reasons for the vibration of the slewing bearing during work

1. The internal machining accuracy of the slewing ring

The machining accuracy of the steel balls inside the slewing ring and the machining accuracy of the internal raceway are not high, or there are quality defects and the lack of lubricating oil in the raceway. The roller collides with the spacer, which directly affects the smoothness of the slewing ring operation and the level of noise, so check When the slewing bearing is defective, sometimes the frequency of failure is reduced by replacing the steel ball.

2. The gear processing is not precise enough

The gear accuracy grade of the slewing ring should be between 7 and 11, which determines the stability of the slewing ring transmission, the uniformity of load distribution and the transmission accuracy. The higher the gear accuracy, the denser the contact spots on the meshing tooth surface, so that the noise value is reduced and the smooth operation is improved.

3. Welding defects of upper and lower supports

If the welding quality is not up to standard, the weld defects need to be repaired and repaired. During repair welding, not only new welding stress will be generated, but also the flatness of the machined mounting surface will be greatly affected. At the same time, the current generated by welding will also cause a certain amount of internal rolling elements and raceways when passing through the slewing ring. damage. In addition, if the assembly errors generated in the manufacturing and assembly, the pin and bolt pre-tightening in the on-site installation do not meet the specified requirements, abnormal noise or jitter will also occur.

4. Quality problems of gears and starting motors

Because the gear has been loaded for a long time, small pieces of metal or strip-shaped metal iron filings will fall off near the pitch line of the tooth surface, resulting in pitting or tooth gnawing. The pitting corrosion of the tooth surface continues to expand with the increase of working time, so that the meshed tooth profile is damaged, the noise and impact during rotation increase, and the metal particles that impact repeatedly accelerate the wear of the tooth surface, forming a vicious circle. In addition, the manufacturing and assembly of the starter motor in the slewing mechanism has its own defects, which produces shock jitter, and the meshing process between the drive wheel and the support is unstable, which also increases the jitter frequency and the decibel of abnormal noise.

Preventive measures against shaking of slewing ring

1. Installation and operation

High-strength bolts should be used for the installation of the slewing bearing. The bolts and nuts should meet the requirements of GB3098.1 and GB3098.2. Spring washers are prohibited. Before the installation bolts are tightened, the meshing adjustment of the large and small gears (backlash) must be carried out to ensure that the meshing of the slewing ring and the pinion meets the requirements. The mounting bolts should be tightened at 180°. The mounting plane must be clean and flat, free of burrs, iron filings and other debris. The plane must meet the following requirements: The slewing bearing often has broken teeth during operation, so it is also in operation. Consider the influence of wind on the slewing support. If the boom cannot rotate freely with the wind after the specified wind power is exceeded or the operation is stopped, the gear or slewing bearing meshing with the support may be damaged, and serious safety accidents may occur. Therefore, detailed inspections should be done during installation and operation.

2, tightening bolts

The connecting bolts of the slewing bearing and the upper and lower supports are subjected to axial pulsating load in addition to the pre-tightening force, which will cause the bolts to elongate or the connecting surface to deform, which makes the bolts loose. After the bolt connection is loosened and the pre-tightening force fails to meet the requirements, the axial clearance increases, the rolling elements are rotated by a large overturning moment, and the raceway edge is subjected to huge contact stress, causing damage to the raceway edge. Therefore, the tightening of the slewing bearing bolts must be checked regularly to make it reach the specified pre-tightening force, which is generally 400-500N.m.

3, internal lubrication of the slewing ring

In daily use, each part should be lubricated according to the lubricant, lubrication method, and lubrication cycle in accordance with the instructions in the operation manual in time and on time. Corresponding ball slewing bearings are generally filled once every 100 hours of operation, and roller slewing bearings are filled once every 50 hours. The lubrication cycle should be shortened for the special working environment with a lot of dust, high humidity and high temperature difference. Each lubrication must fill the raceway until the lubricating oil seeps out. While filling, the slewing ring needs to be slowly rotated to make the grease evenly filled. By adding lubricating oil for maintenance, the friction between the gear pairs can be reduced, and the wear rate of the gear ring can be slowed down. The oil film formed can also act as a shock absorbing ring, eliminating part of the vibration energy generated during operation. In addition, the lubricating oil film can also lubricate and clean the friction surfaces well, prevent rust, and eliminate the influence of iron filings on the friction surface. Thereby reducing the friction noise of operation and increasing the service life of the support.

The above is the analysis and explanation of the reasons and preventive measures for the shaking of the slewing ring during operation. I hope it will be helpful after reading it. Luoyang Hengguan Bearing is a slewing ring/slewing bearing comprehensive entity enterprise integrating design, research and development, production, sales and service. Mainly engaged in a variety of high-precision slewing bearings, large thrust ball bearings, non-standard special-shaped bearings and other products, and also provide customers with customized exclusive bearing products. Everyone is welcome to call for detailed consultation.

What does the tolerance of the slewing ring mean?

There are many technical indicators that reflect the accuracy of slewing bearings and slewing bearings, such as axial clearance and radial clearance, end jump and radial jump, parallel difference and inside and outside difference, roughness, dimensional tolerance, position tolerance, etc. So, do you know what the tolerance of slewing ring refers to?

The dimensional accuracy and rotation accuracy of the slewing bearing are based on ISO and JIS standards. For machinery that requires high precision and high-speed operation, it is recommended to use bearings with accuracy grade 5 or above. Deep groove ball bearings, radial thrust ball bearings or cylindrical roller slewing bearings are suitable for machinery with high operating accuracy.

Slewing ring

The inner diameter and outer diameter of the rolling slewing ring are manufactured according to standard tolerances. The tightness of the slewing ring inner ring and shaft, outer ring and seat hole can only be achieved by controlling the tolerance of the journal and the tolerance of the seat hole. Tolerance includes shape tolerance and position tolerance.

When the dimensional tolerance accuracy is determined, the shape tolerance has an appropriate value, that is, generally about 50% of the dimensional tolerance value is used as the shape tolerance value; about 20% of the dimensional tolerance value in the instrument industry is used as the shape tolerance value; heavy industry Approximately 70% of the dimensional tolerance value is used as the shape tolerance value. This shows that. The higher the dimensional tolerance accuracy, the smaller the proportion of the shape tolerance to the dimensional tolerance. Therefore, when designing the size and shape tolerance requirements, except for special circumstances, when the dimensional accuracy is determined, the 50% dimensional tolerance value is generally used as the shape tolerance value , Which is not only good for manufacturing but also good for ensuring quality.

There is also a certain relationship between shape tolerance and position tolerance. From the perspective of the cause of the error, the shape error is caused by machine tool vibration, tool vibration, spindle runout, etc.; while the position error is caused by the non-parallelism of the machine tool rails, the non-parallel or non-perpendicular tool clamping, and the effect of clamping force. As a result, from the definition of tolerance zone, the position error includes the shape error of the measured surface. For example, the parallelism error contains the flatness error, so the position error is much larger than the shape error. Therefore, under normal circumstances, when there is no further requirement, the position tolerance is given, and the shape tolerance is no longer given. When there are special requirements, the shape and position tolerance requirements can be marked at the same time, but the marked shape tolerance value should be less than the marked position tolerance value, otherwise, the parts cannot be manufactured according to the design requirements during production.

Slewing bearing

The slewing bearing and slewing ring have high precision, which represents the level of precision and processing technology, which means higher value. They are generally used for precision machine tools, precision equipment and high-precision instruments to achieve measurement and control, positioning and pointing. The runout is controlled at 0.02, ~ 0.05, the clearance value is controlled at 0.01-0.06, the roughness is controlled at Ra1.6/0.8, the hardness is uniformly distributed, the parallel difference is controlled at 0.015, and the dimensional tolerance must be in accordance with the requirements of the drawing.

Inspection before operation of mining machinery bearings

After the bearing is installed, in order to ensure the smooth operation of the bearing, the inspection work before the bearing operation should be paid attention to.

For small machines, you can directly rotate the bearing by hand to see if it can run smoothly. In daily inspection operations, common poor operation phenomena mainly include: poor operation due to foreign objects, scars and indentations; poor operation due to improper installation; large installation errors due to too small clearance, etc. The reason is that the torque is too large, resulting in poor operation of the bearing, etc. If no abnormality is found after careful inspection, the bearing can be used for the next step of power operation.

For large machinery, manual rotation is not possible, but inertial operation can be carried out by stopping the power in time after starting without load, and then carefully observing the vibration and noise of the bearing and the actual contact of each rotating part to confirm that there is no After the abnormality, the next power rotation stage can be carried out.

Power rotation, this stage generally starts from the no-load low-speed stage and gradually increases to the rated operating speed. During the trial operation stage, the focus should be on checking: whether there is abnormal sound in the bearing, whether there is lubricant leakage, and whether the bearing has a large temperature rise change, etc. If an abnormality occurs during the trial operation of the bearing, the bearing should be carefully inspected even if the operation is stopped, and the bearing should be disassembled and inspected if necessary.

The temperature rise of the bearing can usually be known by inspecting the bearing housing, but it is also possible to directly inspect the temperature of the outer ring of the bearing with the aid of the oil filling hole, so that the inspection result obtained will be more accurate. The bearing temperature of mining machinery generally rises gradually from the beginning of the bearing operation, and the bearing temperature usually tends to stabilize after rising to a certain temperature. If the bearing is installed improperly, it may cause the bearing temperature to rise sharply and produce abnormal temperature rise. In addition, excessive bearing lubricant, too small internal free gap, severe wear of the ball, high-speed rotation, etc., may also cause a transitional temperature rise of the bearing.