Allowable load
●Basic dynamic load rating (C)
Basic dynamic load rating is to make a group of the same linear system walk under the same conditions, 90% of which will not cause material damage due to rolling fatigue, and when walking in a constant direction 50×103m The same size load.
Basic dynamic load rating is to make a group of the same linear system walk under the same conditions, 90% of which will not cause material damage due to rolling fatigue, and when walking in a constant direction 50×103m The same size load.
●Basic static load rating (Co) The
basic static load rating refers to the static load required for the sum of the permanent deformation of the rolling element and the permanent deformation of the rolling surface at the contact portion that is subjected to the maximum stress is 0.0001 times the diameter of the rolling element .
basic static load rating refers to the static load required for the sum of the permanent deformation of the rolling element and the permanent deformation of the rolling surface at the contact portion that is subjected to the maximum stress is 0.0001 times the diameter of the rolling element .
● The allowable static moment (MP, MY, MR)
moment load is subjected to the static moment load limit determined by the basic static rated load Co and the same permanent deformation.
moment load is subjected to the static moment load limit determined by the basic static rated load Co and the same permanent deformation.
●Static safety factor (fS)
The basic static rated load Co that is borne at rest or at low speeds is used by dividing the static safety factor fs shown in Table-1 according to the conditions of use.
The basic static rated load Co that is borne at rest or at low speeds is used by dividing the static safety factor fs shown in Table-1 according to the conditions of use.
Table-1 Static safety factor (lower limit of fS)
|
Conditions of Use
|
lower limit of fS
|
| Under normal operating conditions | 1～2 |
| When smooth mobile performance is required | 2～4 |
| When there is vibration or impact | 3～5 |
fS: Static safety factor Co: Basic static rated load (N)
MP, MY, MR: Allowable static moment (N・m)
MP, MY, MR: Allowable static moment (N・m)
life
When a linear system is subjected to a load and performs a linear reciprocating motion, due to repeated stresses often acting on the rolling elements or rolling surfaces, scaly damage called material fatigue spalling occurs. The total walking distance before this initial flaking occurs is called the life of the linear system.
● Rated life (L)
Rated life refers to the total distance traveled when 90% of the same linear system is run under the same conditions, respectively, without peeling.
Rated life refers to the total distance traveled when 90% of the same linear system is run under the same conditions, respectively, without peeling.
The rated life can be calculated according to the following formula based on the basic dynamic rated load and the load applied to the linear system.
L: rated life (km)
C: basic dynamic rated load (N)
P: applied load (N)
C: basic dynamic rated load (N)
P: applied load (N)
●When the linear system is actually used, the load calculation should be performed first. It is not easy to find the load in linear reciprocating motion by calculation, because there is vibration or shock during the movement, and the distribution of vibration or shock relative to the linear system must also be fully considered. In addition, the operating temperature will also have a great impact on life. Adding these conditions together, the above calculation formula becomes the following formula.
L: Rated life (km)
fH: Hardness coefficient (see Figure-1)
C: Basic dynamic rated load (N)
fT: Temperature coefficient (see Figure-2)
P: Applied load (N)
fC: Contact coefficient (see table －3）
fW: load factor (see Table-4)
fH: Hardness coefficient (see Figure-1)
C: Basic dynamic rated load (N)
fT: Temperature coefficient (see Figure-2)
P: Applied load (N)
fC: Contact coefficient (see table －3）
fW: load factor (see Table-4)
The life time can be calculated by finding the walking distance per unit time.
When the stroke length and number of strokes are constant, it can be obtained according to the following formula.
Lh: life time (hr)
ℓs: stroke length (m)
L: rated life (km)
n1: number of round trips per minute (cpm)
ℓs: stroke length (m)
L: rated life (km)
n1: number of round trips per minute (cpm)
Friction resistance and necessary thrust
Friction resistance (necessary thrust) can be calculated according to the following formula based on the load and the inherent sealing resistance of the system.
F: Friction resistance (N)
μ: Dynamic friction coefficient
W: Load
f: Sealing resistance (2N～5N)
μ: Dynamic friction coefficient
W: Load
f: Sealing resistance (2N～5N)
Table-2 Coefficient of Dynamic Friction
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species
|
Coefficient of dynamic friction (μ)
|
| Miniature linear guide | 0.004～0.006 |
| Medium load linear guide | 0.002～0.003 |
| Linear slide | 0.001～0.003 |
| Linear slide | 0.001～0.003 |
| Linear Bearings | 0.002～0.003 |
| Linear ball bushing | 0.0006～0.0012 |
●Hardness factor (fH)
When using a linear system, even the shaft where the balls are in contact must have sufficient hardness. If the proper hardness is not achieved, the allowable load will be reduced, thereby shortening the service life.
Please correct the rated life with the hardness coefficient.
●Contact coefficient (fC)
When actually using a linear system, usually more than two linear systems are used on one axis. In this case, the load applied to each linear system varies depending on the processing accuracy, and will not become a balanced load. As a result, the allowable load of each linear system varies depending on the number of linear systems on each axis.
Please correct the rated life using the contact coefficient of Table-2.
●Load factor (fW)
When calculating the load acting on a linear system, in addition to the weight of the object, the inertial force or moment load generated by the speed of movement and their time-varying relationship must be correctly obtained. However, in the reciprocating motion, in addition to repeating the start and stop frequently, it is also necessary to consider factors such as vibration and shock, and it is difficult to calculate correctly.
Therefore, the load factor shown in Table-3 can be used to simplify the life calculation.
Linear Bearings
The rated life can be calculated according to the following formula based on the basic dynamic rated load and the load imposed on the linear bearing.
L: rated life (km) fH: hardness coefficient (see Figure-1)
C: Basic dynamic rated load (N) fT: Temperature coefficient (see Figure-2)
P: acting load (N) fC: contact coefficient (see Table-3)
fw: load factor (see Table-4)
Life time can be calculated by finding the walking distance per unit time. When the stroke length and number of strokes are constant, it can be obtained according to the following formula.
LLh: life time (hr) ℓs: stroke length (m)
L: Rated life (km) n1: Number of round trips per minute (cpm)
● Temperature coefficient (fT)
If the temperature of the linear system exceeds 100°C, the hardness of the linear system and the shaft will decrease, and the allowable load will be reduced to lower than the load at normal temperature, and the life will be shortened accordingly.
Please use the temperature coefficient to correct the rated life.
Table-3. Contact coefficient
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Number of linear bearings assembled on 1 shaft
|
Contact coefficient fc
|
| 1 | 1.00 |
| 2 | 0.81 |
| 3 | 0.72 |
| 4 | 0.66 |
| 5 | 0.61 |
Table-4. Load factor
|
Conditions of Use
|
fw
|
| When there is no external impact and vibration, and the speed is slower than 15m/min |
1.0～1.5 |
| There is no particularly obvious impact and vibration, the speed is below 60m/min at medium speed |
1.5～2.0 |
| External shock and vibration, speed above 60m/min at high speed |
2.0～3.5 |
Linear ball bushing
The rated life can be calculated according to the following formula based on the basic dynamic rated load and the load applied to the linear bearing.
L: rated life (km) fH: hardness coefficient (see Figure-1)
C: Basic dynamic rated load (N) fT: Temperature coefficient (see Figure-2)
P: acting load (N) fC: contact coefficient (see Table-3)
fw: load factor (see Table-4)
Life time
・ When rotating and reciprocating
L: rated life (km) fH: hardness coefficient (see Figure-1)
・ When reciprocating
LLh: life time (hr) S: stroke length (mm)
n: speed per minute (rpm) n1: number of strokes per minute (cpm)
dm: pitch diameter of the ball (mm) ≈ 1.15dr