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General knowledge of cylindrical roller bearings

General knowledge of cylindrical roller bearings

2021-07-08

Cylindrical roller bearing belongs to the separation type bearing, it is very convenient to install and disassemble.Cylindrical roller bearings can bear large radial loads and are suitable for use at high speed.

The allowable Angle error (inclination) between the inner ring axis and the outer ring axis of such bearings is very small, only 2 '~ 4'.Therefore, the machining accuracy of the shaft and the bearing seat is relatively high otherwise, it is easy to appear uneven load or stress concentration in the raceway contact parts.The stress concentration can be reduced by modifying the roller or raceway contact bus.

Cylindrical roller bearings can be divided into single row, double row and multi-row cylindrical roller bearings and other different structures according to the different number of rows of rollers installed.Different structures of bearings are also shown in the design of the position of the flange.Among them, the commonly used cylindrical roller bearings have the following forms:

Single row cylindrical roller bearings

N, NU type

The outer ring of the N type bearing has no flanges, and the two sides of the inner ring have flanges.The displacement of the shaft relative to the bearing pedestal in both axial directions can be allowed.

The NU type bearing has flaps on both sides of the outer ring and no flaps on the inner ring.Displacements in both axial directions between the shafts relative to the bearing pedestals may also be allowed.

Therefore, this kind of structure is suitable for the use of swimming end bearings.

NJ, NF type

The outer ring of NJ bearing is provided with flaps on both sides, and the inner ring is provided with flaps on one side.Can withstand a certain amount of unidirectional axial load.

The outer ring of the NF type has a baffle on one side and the inner ring has a baffle on both sides.It can also bear a certain amount of unidirectional axial load.

Therefore, this kind of structure is suitable for use as a unidirectional axial positioning bearing.

NUP, NFP

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

One side of the outer ring of the NFP bearing has a (fixed) single baffle edge, and the other side is a separable flat baffle edge, and the inner ring has baffle edge on both sides.It can also bear a certain amount of bidirectional axial load.

This kind of bearing structure can limit the displacement of the shaft relative to the bearing seat in two axial directions.Therefore, it is suitable for use as a fixed end bearing.

Nh (Nj + Hj)

NH type bearing is a combination of NJ type bearing and HJ type oblique retaining ring structure.Because the inner ring of NUP bearing is short, coupled with the flat stop ring is not fixed, it is inconvenient to use, while NH bearing can use the width of the entire inner ring of NJ bearing to maintain a closer match with the shaft.And NH type bearings in the installation and disassembly is more convenient.

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

Double row cylindrical roller bearings

Double row cylindrical roller bearings have cylindrical inner hole and conical inner hole (bearing rear code plus K) two kinds of structure.This kind of bearing has the advantages of compact structure, large rigidity, large bearing capacity, small deformation after being loaded, etc., and is especially suitable for supporting machine tool spindle.The conical inner hole can also play the role of minor adjustment of clearance, and can simplify the positioning device structure, convenient installation and disassembly.

The commonly used double-row cylindrical roller bearings have the following forms:

NN, NNU type

The outer ring of NN type bearing has no baffle, and the inner ring has baffle on both sides and a middle baffle on the middle.The axial displacement of the shaft relative to the bearing seat can be allowed in two directions.

The outer ring of NNU bearing has flaps on both sides and a middle flaps in the middle, while the inner ring has no flaps.The axial displacement of the shaft relative to the bearing seat can be allowed in two directions.

, this kind of structure is suitable for swimming end bearings.The cages of this type of bearing are mostly made of vehicle solid cages.

NNF type

NNF type bearing is a double row full cylinder roller bearing, bearing consists of one outer ring with the middle guard and two inner rings with double guard.The roller is guided by the guard edge of the inner ring, and the two inner rings are fixed together with a fastening ring.In addition to the large radial and axial loads, the structure can also withstand overturning moment, so it is commonly used as a fixed end bearing.

NNF type bearing adopts contact seal on both sides.The bearing is filled with grease, the working temperature of the grease is -50℃ to +110℃, but due to the limitation of the sealing material, the working temperature of the bearing is limited to -40℃ to +80℃.Under good working conditions, NNF bearings with seals need not be maintained. If the bearing is in water vapor or polluted environment for a long time and is in medium or high-speed operation, the bearing can be supplemented with lubrication oil groove and lubricating oil hole on the outer ring.

Four rows of cylindrical roller bearings

Four row cylindrical roller bearings are mainly used in rolling machines such as cold and hot rolling mills and blank cutting mills. The bearings are of separated structure, and the bearing rings and rolling components can be conveniently separated. Therefore, the cleaning, inspection, installation, disassembly and assembly of the bearings are very convenient.

FC type

FC type bearings consist of two outer rings and an inner ring, each outer ring has a guard on both sides of the middle guard, the inner ring has no guard.

FCD type

FCD type bearing is actually made up of two NN type bearings.

FC type and FCD type bearings can allow two directions of axial displacement between the shaft and the bearing pedestal.Therefore, this kind of structure is suitable for swimming end bearings.The cages of this type of bearing are mostly made of vehicle solid cages.

cage

Single row cylindrical roller bearing cages are mostly steel plate stamping cages and brass car solid cages. Bearings with glass fiber reinforced nylon 66 cages can also be designed and provided according to the use occasions and customer requirements. Bearings with glass fiber reinforced nylon 66 cages can be continuously operated at +120℃.

For single row cylindrical roller bearing cages working under continuous high temperature or harsh conditions, it is recommended to adopt steel sheet stamping cages and brass car solid cages.

Double (four) row cylindrical roller bearing cages are all made of brass car solid cages.

Axial load carrying capacity

The cylindrical roller bearing with the inner and outer rings with the flanges designed by the special structure can bear not only the radial load but also a certain axial load.Its axial load bearing capacity mainly depends on the form of the contact surface between the roller end face and the flange, lubrication conditions, working temperature and bearing heat dissipation, etc.

A sufficiently accurate allowable axial load can be calculated according to the following assumed conditions

Type in the

Fmax- Maximum allowable axial load, kN

C0- Basic static load rating, kN

FR - Actual radial bearing load, kN

N - speed, r/min

D (D) - bearing inner (outer) diameter, ㎜

K1 - coefficient, 1.5 for oil lubrication and 0.5 for grease lubrication

K2 - coefficient is 1.5 for oil lubrication and 0.15 for grease lubrication

The above formula is based on the condition that the temperature difference between the working temperature of the bearing and the ambient temperature is 60℃ and the viscosity ratio is greater than or equal to 2.

It is necessary to remind that cylindrical roller bearings without special design of roller end face and flange are not suitable for the above formula.

In order to prevent the flange fracture and the fixed or occasional axial load FA on the bearing, the technical department suggests that the value should not be greater than the following:

Dimensions 2 series bearings, FA < 0.0045D1.5 (D is bearing outer diameter ㎜) kN

Other size series bearing, Fa < 0.0023d1.7 (D is bearing outer diameter ㎜) kN

For the axial load FA with short or occasional action, it is recommended not to be greater than the following values:

FA = 0.007D1.7 (D is the outer diameter of the bearing) kN

When a single row cylindrical roller bearing bears a large axial load, the size and axial runout of the shoulder shoulder must meet certain requirements in order to make the flange bear uniform load and achieve a certain rotation accuracy.For the axial runout accuracy of the shoulder retaining, please refer to the related content of "Bearing Application" in the review section.For the diameter of the baffle (hole) shoulder (see Figure 1), the technical department recommends that the height of the baffle side of the inner ring be half of the baffle height to avoid the baffle bearing cyclic stress. For the baffle side of the inner ring, the diameter of the shaft shoulder can be calculated by the following formula:

DA = 0.5 (D1 +F)

Type in the

Da - Shaft shoulder diameter, ㎜

D1 - Diameter of inner ring edge, ㎜

F - inner ring raceway diameter, ㎜

When the Angle error between the inner ring and the outer ring is more than 1 ', the load bearing condition on the flange will be greatly changed.The safety factors in the above reference values may not be applicable.In this case, please consult the technical department.

In order to ensure that cylindrical roller bearings can still work normally under axial load, especially under large axial load, the technical department reminds us of the following points:

1) The radial clearance inside the bearing should be controlled within the required range, and it should be small rather than large.

2) Use lubricants containing extreme pressure additives.

The smaller the load

In order to ensure the bearing to obtain a good running state, single row cylindrical roller bearings, like other ball bearings and roller bearings, must apply a certain amount of small load, especially for high speed, high acceleration, or work under the condition of frequent changes in the direction of load.Because of these working conditions, the inertial force of the roller and the cage and the friction in the lubricant will have a bad effect on the rolling and rotating accuracy of the bearing, and there may be harmful sliding movement on the bearing between the roller and the raceway.

The small load Fmin required by a single row cylindrical roller bearing can be estimated by the following formula:

Type in the

N - Working speed, r/min

Nr - (0.8 ~ 0.9) limit speed, r/min

Average diameter of DM - bearing DM =0.5(D +D),mm

Kr - Small load coefficient.

Size series

KR 10 2, 3, 4 22 23

100 150 200 250

Larger smaller loads may be required when starting at low temperatures or when the lubricant viscosity is high.Normally, the weight of the bearing support itself plus the load borne by the bearing has exceeded the required small load.If the small load has not been reached, additional radial load must be applied to the bearing to meet the requirements of the small load.

Dimensions, tolerances, clearance

The external dimensions of standard cylindrical roller bearings conform to GB/T273.3 "General Scheme for External Dimensions of Rolling Bearings Circular Bearings", GB/T283 "External Dimensions of Rolling Bearings Circular Roller Bearings", GB/T285 "External Dimensions of Rolling Bearings Double Row Circular Roller Bearings", JB/T5389.1 "Rolling Bearings"Rolling mill with four row cylindrical roller bearings, etc.

The tolerance of standard cylindrical roller bearings conforms to the provisions of GB/T307.1 "Rolling Bearing Centripetal Bearing Tolerance" and other standards.

The clearance of standard cylindrical roller bearings conforms to the provisions of GB/T4604 "radial clearance of rolling bearings".

The dimensional tolerance class of standard cylindrical roller bearings is generally P0 class (ordinary class), and the clearance is 0 group (basic group). If the customer has other special (including non-standard) dimensions, tolerance and clearance, the corresponding products can be provided.

Equivalent dynamic load

For cylindrical roller bearings bearing dynamic loads, when used as swimming end bearings, the equivalent dynamic load can be calculated as follows:

P = Fr

If the bearing bears an axial load in one or two directions, its equivalent dynamic load can be calculated as follows:

When Fa/Fr≤ E, P = Fr

Fa/Fr > E P = 0.92Fr + Yfa

Type in the

E - limit value, E = 0.2 for size series 2, 3, and 4, and E = 0.3 for other series

Y - Axial load factor, Y = 0.6 for size series 2, 3 and 4, Y = 0.4 for other series

Cylindrical roller bearings bearing axial load must bear radial load at the same time to achieve the ideal operation effect, but the axial load and radial load ratio should be less than 0.5.

Equivalent static load

For cylindrical roller bearings bearing static load, the equivalent static load can be calculated according to the following methods:

P0 = Fr

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