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Analysis of the check and balance of rolling NSK bearing
Source: China Bearing Network Time: 2013-03-25
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Mass production of components; due to the non-uniformity of the data; the life expectancy of the bearing is highly discrete; the longest and shortest life can be several tens of times; the accounting method must be used for disposal.
2. The total extra life: refers to the 90% reliability, common data and processing quality, the life expectancy under the premise of the practice; indicated by the symbol L10 (r) or L10h (h).
3. Fundamental additional dynamic load (C): a stable load acceptable to the bearing at a base extra life of one million revolutions (106). That is, under the effect of a fundamental extra dynamic load; the bearing can operate at 106 revolutions without pitting failure; Its reliability is 90%. The fundamental extra dynamic load is large; the load bearing bearing fatigue resistance is correspondingly strong.
4. Fundamental additional static load (radial C0r; axial C0a): refers to the imaginary radial load or central axial static load of the maximum load of the bearing and the center of the raceway touch the same contact stress.
In the depiction, three basic parameters of the dynamic bearing are commonly used: the fundamental extra dynamic load Cr (radial) or Ca (axial) that meets the demand for fatigue life; the fundamental extra static strength C0r (radial) that meets the static strength requirement ) or C0a (axial) and the limit speed of the bearing bearing wear N0. Various bearing function index values ​​C, C0, N0, etc. can be found in the relevant manual.
2 The number of life check calculation formula The life of the dynamic bearing decreases with the increase of the load; the relationship between the lifespan and the load is shown in Figure 17-6; the curve equation is PεL10=constant P-equivalent dynamic load; N, L10 - the fundamental extra life; often in 106r (when the life is one million revolutions; L10 = 1), ε-life index; ball bearing ε = 3; roller bearing ε = 10 / 3.
The fundamental extra dynamic load C obtained by the manual is based on L10=1 and the reliability is 90%. Therefore, the fundamental extra life L10 of the rotational speed unit is Cε× when the equivalent dynamic load of the bearing is P. 1=Pε×L10
L10=(C/P)ε106r(17.6)
If the bearing operation speed is nr/min; the fundamental extra life h in hours can be obtained (17. 7)
L10≥Lh'.Lh' should be taken as the expected service life of the NSK bearing. Generally refer to the expected service life of the machine overhaul period.
If the bearing is equivalent to the dynamic load P and the expected service life Lh', the corresponding additional dynamic load C' can be obtained by the following formula; it must meet the following requirement N with the C value of the selected bearing type. .8)
3 equivalent dynamic loads are in practical conditions; dynamic bearings are often subjected to combined radial and axial loads; in order to calculate the bearing life, the fundamental additional dynamic load is compared with the practical load; the practical work load needs to be converted into Equivalent dynamic load. Under the effect of equivalent dynamic load; the life of the bearing is the same as the life of the bearing under the combined load. The equivalent dynamic load P is calculated as P=XFr+YFa.
Where Fr-radial load; N, Fa-axial load; N, X; Y-radial dynamic load factor and axial dynamic load coefficient; obtained from Table 17-7.
The load calculation of the 4-angle touch bearing is for the "3" and "7" type bearings; due to the characteristics of its own layout; when there is a radial force effect, the derivative S will occur; in the accounting, it should be considered.
1. Device mode must be paired device: formal (or "face-to-face") - the distance between the two fulcrums is short, see Figure 17-7a. Reverse loading (or become "back to back") - long distance between two points; used for cantilever transmission Bearing of the piece; see Figure 17-7b.
2. The effect point of the bearing effect force on the shaft is the point on the axis of the moving body and the touch point of the raceway; see Figure 17-8. O in the figure; the distance from the outer end face is a; this value can be Check the manual.
3. The axial force is analyzed. The axial load subjected to the angular contact bearing should be considered together with the additional axial force induced by the radial force and the other axial force acting on the shaft; the balance of the force is calculated according to the detailed situation. .
FR and FA respectively act as radial and axial loads on the shaft; the radial reaction forces of the two bearings are Fr1 and Fr2; the corresponding additional axial forces are Fs1 and Fs2. The effects are on the axial axes. The force is shown in Figure 17-10.
According to the balance of the shaft, the axial forces of the bearings I and II are analyzed according to the following two conditions:
- Assume FS1+FA>Fs2 (Fig. 17-11); the axis has a tendency to move to the right; the bearing II is "pressed"; the right end of the shaft will be subjected to an equilibrium reaction force Fs2' through the bearing II; The axial force of bearing II is Fa2=Fs2+Fs2'=Fs1+FA
Because bearing I is only subjected to additional axial force; therefore Fa1=FS1
- Assume FS1+FAs2 (Fig. 17-12); the axis has a tendency to move to the left; the bearing I" is pressed"; at this moment, the left end of the shaft will be subjected to a balanced reaction force Fs1' through the bearing I; The axial force on the bearing is Fa1=Fs1+FS1'=Fs2-FA
Fa2=Fs2
The method of calculating the axial force of the angular contact bearing can be summarized as follows: 1) It is determined that the full axial force on the shaft (including the external load and the additional axial force of the bearing) is directed by the direction; the "pressed" end bearing is judged, 2) "pressure The axial force of the tight end bearing is the algebraic sum of all axial forces except for its own additional axial force. 3) The axial force of the other end bearing is its own additional axial force.
5 static load and limit speed calculation formula 1. Static load accounting static load refers to the effect of the NSK bearing ring on the bearing when the relative rotational speed is zero. In order to restrain the dynamic elastic bearing from excessive static stress and permanent deformation under static load effect; static load accounting is required. Static load selection of bearings; its fundamental formula is C0 ≥ C0 ' = S0P0
Where C0 - fundamental extra static load; N, C0 '- accounting for additional static load; N, P0 - equivalent static load; N, S0 - safety factor.
Stop bearing, slow rocking or very low speed bearings; safety factor can be selected in Table 17-9.
If the bearing speed is low; when the operation accuracy and conflict torque demand are not high; allow a large touch stress; S0 <1. Thrust spherical roller bearing; whether it can rotate or not; S0 ≥ 4.
2. When the rotational speed of the limit-rotation dynamic spring bearing is too high, high temperature will occur between the conflicting surfaces; the smoothing agent function will be affected; the oil film will be damaged; then the moving body will be tempered or the component will be glued.
The limit rotation speed N0 of the dynamic spring bearing refers to the bearing value under the premise of the certain operation; the speed value of the bearing can reach the highest heat balance temperature. The working speed of the bearing should be lower than the limit speed.
The limit speed values ​​given in the dynamic bearing function table are determined on the premise of smooth grease and oil smoothness; and only for class 0 public service, smooth cooling normal, cooperation with rigid bearing housing and shaft, bearing load P≤ 0. 1C (C is the fundamental extra dynamic load of the bearing; the radial bearing is only subjected to radial load; the thrust bearing is only subjected to axial load).
When the dynamic bearing load P>0. 1C; the touch stress will increase, the bearing will accept the combined load; the loaded moving body will be added; this will increase the conflict between the bearing touch and the appearance; the smooth condition will deteriorate. At the moment; The speed value should be corrected; the practice allowable speed value can be calculated as follows: N=f1f2N0
In the formula N-practice allowable speed; r/min, N0-bearing limit speed; r/min, f1-load factor, f2-load spread coefficient.
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