Cylindrical roller bearing types and failure treatment methods

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Cylindrical roller bearing types and failure treatment methods
Cylindrical roller bearing types and failure treatment methods

Introduction to Cylindrical Roller Bearings

Cylindrical rollers and raceways are linear contact bearings. Load capacity, mainly bear radial load. The friction between the rolling element and the rib of the ring is small, which is suitable for high-speed rotation. Cylindrical roller bearing types and failure treatment methods.

According to whether the ring has ribs or not, it can be divided into single row cylindrical roller bearings such as NU, NJ, NUP, N, NF, and double row cylindrical roller bearings such as NNU and NN. The bearing is a structure in which the inner ring and the outer ring can be separated.

Cylindrical roller bearings without ribs on the inner or outer ring, the inner and outer rings can move relative to the axial direction. So they can be used as free end bearings.

Cylindrical roller bearings with double ribs on one side of the inner ring and outer ring and a single rib on the other side of the ring can withstand a certain degree of axial load in one direction. Generally, a steel stamping cage is used, or a copper alloy turning solid cage is used. However, there are also part of the use of polyamide forming cage.

Features of Cylindrical Roller Bearings

  1. The roller and the raceway are in line contact or trimmed line contact, and the radial bearing capacity is large, which is suitable for bearing heavy loads and impact loads.
  2. The friction coefficient is small, suitable for high speed, and the limit speed is close to that of deep groove ball bearings.
  3. N type and NU type can move axially, which can adapt to the change of the relative position of the shaft and the shell caused by thermal expansion or installation error, and can be used as free end support.
  4. The processing requirements for the shaft or seat hole are high, and the relative deflection of the outer ring axis after the bearing is installed should be strictly controlled to avoid contact stress concentration.
  5. The inner ring or outer ring can be separated for easy installation and removal

Cylindrical roller bearing category

Cylindrical roller bearings are separable bearings, which are very convenient to install and disassemble. Bearings can withstand large radial loads and are suitable for use in high-speed operation.

This type of bearing allows the angle error (inclination) between the axis of the inner ring and the axis of the outer ring to be very small, only 2′ to 4′. Therefore, the machining accuracy of the shaft and the bearing seat is relatively high. Otherwise, uneven load or stress concentration will easily occur at the contact part of the raceway. However, the occurrence of stress concentrations can be reduced by modifying the contact busbars of the rollers or raceways.

Cylindrical roller bearings can be divided into different structures such as single-row, double-row and multi-row cylindrical roller bearings according to the number of rows of rolling elements installed.

Different structural bearings are also reflected in the design of the position of the rib. Among them, the commonly used cylindrical roller bearings have the following forms:

Single-row cylindrical roller bearings: Single-row cylindrical roller bearings are separable bearings, which are easy to install and disassemble. Both rings can be tightly fitted, and the contact line between the rollers and the raceway is corrected to reduce stress concentration.

Double row cylindrical roller bearing: Double row cylindrical roller bearing belongs to the floating bearing, and its separability makes the installation and disassembly very convenient. Both ferrules can have a tight fit. Double row cylindrical roller bearings are hardly allowed to have a tilt angle.

single row bearing

N, NU type

The outer ring of the N-type bearing has no ribs, and there are ribs on both sides of the inner ring. Displacement in both axial directions between the shaft and the bearing housing can be allowed. The NU type bearing has ribs on both sides of the outer ring and no ribs on the inner ring. It is also possible to allow displacement of the shaft relative to the bearing housing in both axial directions. Therefore, this type of structure is suitable for use as a loose end bearing.

NJ, NF type

NJ type bearings have ribs on both sides of the outer ring, and ribs on one side of the inner ring. Can withstand a certain amount of unidirectional axial load. NF type has ribs on one side of the outer ring and ribs on both sides of the inner ring. It can also bear a certain amount of unidirectional axial load. Therefore, this type of structure is suitable for use as a unidirectional axial locating bearing.

NUP, NFP type

NUP type bearings have ribs on both sides of the outer ring, a (fixed) single rib on one side of the inner ring, and a separable flat rib on the other side. Can withstand a certain amount of bidirectional axial load.

The bearing outer ring of the NFP type has a (fixed) single rib on one side, and a separable flat rib on the other side, with ribs on both sides of the inner ring. It can also withstand a certain amount of bidirectional axial load. This type of structural bearing can limit the displacement of the shaft relative to the bearing seat in both axial directions. Therefore, it is suitable for use as a fixed end bearing.

NH (NJ+HJ) type

The NH type bearing is the combination of the NJ type bearing and the HJ type inclined retaining ring. Because the inner ring of the NUP type bearing is short, and the flat retaining ring is not fixed, it is inconvenient to use, while the NH type bearing can use the width of the entire inner ring of the NJ type bearing to maintain a tighter fit with the shaft. Moreover, the NH type bearing is more convenient to install and disassemble.

NH type bearings can limit the displacement of the shaft relative to the bearing seat in both axial directions. Therefore, it is suitable for use as a fixed end bearing.

Double row bearing

Double row cylindrical roller bearings have two structures: cylindrical inner hole and conical inner hole (bearing rear code plus K). This type of bearing has the advantages of compact structure, high rigidity, large bearing capacity, and small deformation after being loaded, and is especially suitable for the support of machine tool spindles. The conical inner hole can also play the role of micro-adjustment of the clearance and can simplify the structure of the positioning device and facilitate installation and disassembly. Commonly used double row cylindrical roller bearings have the following forms:

NN, NNU type

The outer ring of the NN type bearing has no ribs, and there are ribs on both sides of the inner ring and a middle rib in the middle. Displacement in two directions in the axial direction between the shaft and the bearing housing can be allowed.

The outer ring of the NNU bearing has ribs on both sides and a middle rib in the middle, and the inner ring has no ribs. Displacement in two directions in the axial direction between the shaft and the bearing housing can be allowed. Therefore, this type of structure is suitable for the moving end bearing. The cages of this type of bearings are mostly car-made solid cages.

NNF type

NNF type bearing is a double row full complement cylindrical roller bearing. The bearing consists of one outer ring with middle rib and two inner rings with double rib. The rollers are guided by the ribs of the inner ring, and the two inner rings are held together by a clamping ring. In addition to bearing large radial and axial loads, this structure can also bear overturning moments. So it is often used as a fixed end bearing.

Contact seals are used on both sides of the NNF bearing. The bearing is filled with grease, and the working temperature of the grease is -50°C to +110°C. But due to the limitation of the sealing material. The working temperature of the bearing is limited to -40°C to +80°C. In the case of good working conditions, the sealed NNF bearing does not need maintenance. If the bearing is in a water vapor or polluted environment for a long time, and it is running at medium and high speed. It can be adjusted through the lubricating oil groove and lubricating oil hole on the outer ring. Bearings are relubricated.

Four row bearing

Four-row cylindrical roller bearings are mainly used in cold and hot rolling mills, billet mills and other rolling mill machinery. The bearing is a separate structure, and the bearing ring and rolling element components can be easily separated. Installation and disassembly are very convenient.

FC type

The FC type bearing consists of two outer rings and an inner ring. Each outer ring has ribs on both sides and a middle rib in the middle, and the inner ring has no ribs.

FCD type

FCD type bearing is actually a combination of two NN type bearings.

FC type and FCD type bearings can allow axial displacement in two directions between the shaft and the bearing housing. Therefore, this type of structure is suitable for the moving end bearing. The cage of this type of bearing is mostly made of car body

Cylindrical roller bearing applications

Large and medium-sized electric motors, rolling stock, machine tool spindles, internal combustion engines, generators, gas turbines, gearboxes, rolling mills, vibrating screens, and hoisting and transporting machinery, etc.

The method of adjusting the radial clearance of cylindrical roller bearing

The commonly used methods for adjusting the radial clearance of full complement cylindrical roller bearings are as follows:

  1. The side clearance of cylindrical and elliptical bearing bushes can be adjusted by manual grinding and scraping or by adding pads and turning the bearing in the middle of the bearing.
  2. For the top clearance of cylindrical and elliptical bearing bushes, manual grinding and scraping can be used. The method of adding pads to the middle face of the bearing when the situation permits.
  3. For the fixed bearing bush with multiple oil wedges, in principle. It is not allowed to repair and adjust the bearing bush clearance. If the clearance is not suitable, the new pad should be replaced.
  4. For multi-oil wedge tiltable bearing pads, scraping pads are not allowed to be repaired, and the pads should be replaced when the clearance is not suitable. For tiles with adjustable thickness. The number of tiles can be adjusted by adding a stainless steel pad under the adjustment block behind the tile, or by reducing the thickness of the adjustment block. Note that for multi-oil wedge tiltable bearing pads. The thickness error between the pads in the same group should be less than 0.01mm.

Reasons for the failure of cylindrical roller bearings:

The main purpose of preload: The main purpose and representative examples of preload can be given some examples to prove to understand:

(1) While accurately determining the position of the shaft in the radial direction and the axial direction, the runout of the shaft is suppressed.

(2) Improve the rigidity of the FAG bearing. Bearings for spindles of machine tools and bearings for pinions of bicycle differential mechanisms.

(3) Prevent vibration in the axial direction and abnormal sound caused by resonance. Bearings for small motors.

For cylindrical roller bearings under combined load, due to the increase in the number of rolling elements under load, the frictional resistance increases. The heat generation increases, the lubrication and cooling conditions become worse, and the force acting on the cage also increases. So, It must be adjusted by multiplying the limit speed of the bearing by a reduction factor f2 according to the type of FAG bearing and the size of the load angle.

If the limit speed and rotation speed of the selected cylindrical roller bearing cannot meet the application requirements.

Some improvement techniques can be used to improve to meet the requirements. Such as increasing the bearing tolerance level; appropriately increasing the clearance; using special materials and improving the structure of the cage; changing the lubrication method, such as using oil and gas, oil mist and jet lubrication; improving cooling conditions, etc.

In the process of using FAG bearings, the phenomenon of temperature rise is easy to occur. When the temperature of the cylindrical roller bearing rises, first judge whether it is misoperation, if it does rise, do the following

Treatment methods for the failure of cylindrical roller bearings:

(1) Check whether the cooling water pressure, water flow and piping system are normal. If the water pressure is low, it may be that the filter is blocked. If it cannot be handled in time, it can be stopped for processing. When it is confirmed that it can work, it can be put into use.

(2) Check the oil pressure of the governor. If the oil pressure is low, the cooling water hydraulic valve may be closed.

(3) Check whether there is abnormal sound in the FAG bearing, and check whether the swing of the cylindrical roller bearing is abnormal.

(4) Take oil samples to observe whether the color of the oil has changed. And conduct tests to see if it has deteriorated. If it is confirmed that it is deteriorated, it should be stopped and replaced with new oil.

(5) Check whether the oil level of the oil standard is normal. Check whether the oil drain valve of the oil tank is closed tightly. If it has been closed tightly, it should be replenished with oil. If the sealant gasket sees oil, it should be stopped.

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