315 2Allowable Load t#BTJD %ZOBNJD -PBE 3BUJOH $ Basic dynamic load rating is a constant load applied in a constant direction that enables each linear system of the same series to travel 50×103m under the same conditions, without 90% of the material suffering damage from rolling contact fatigue. t#BTJD 4UBUJD -PBE 3BUJOH $P Basic static load rating is the static load exerted on contacting parts under maximum stress, at which the sum of the permanent deformation in the rolling element and rolling contact surface equals 0.0001 times the diameter of the rolling element. t"MMPXBCMF 4UBUJD .PNFOU .P, MY, MR) Allowable static moment is a critical static moment load that acts upon a system at the loading moment. It is set in accordance with the permanent deformation as in basic static load rating Co. t4UBUJD 4BGFUZ 'BDUPS GS) Static safety factors are given in Table-1. When a linear system is still or moving at low speed, basic static load rating Co must be divided by fs in accordance with the conditions of use. Allowable Load (N) ≤ Co/fS Allowable Moment (N·m) ≤ (MP, MY, MR)/fS fS: Static Safety Factor Co: Basic Static Load (N) MP, MY, MR : Static Allowable Moment (N·m) 2Life Span When a load is applied to a linear system, the system moves back and forth in a linear direction. In the process, repeated stress acts upon rolling elements and rolling contact surfaces, causing damage referred to as flaking from material fatigue. The life span of a linear system is measured in terms of the total travel distance covered by the system up until initial flaking occurs. tRated Life Span (L) Rated life span is the total travel distance that each linear system of the same series can endure under the same conditions, without the occurrence of flaking in 90% of the system. Rated life span can be obtained as follows from the basic dynamic load rating and various loads exerted on the linear system. For Ball Bearings For Roller Bearings L: Rated Life Span (km) C: Basic Dynamic Load Rating (N) P: Acting Load (N) C 3 L= ·50 P ( ) C 10/3 L= ·50 P ( ) When actually using a linear system, the first thing you must do is to calculate the load. It is necessary to consider load also in terms of vibration and impact that occur during operation, as well as its distribution across the entire linear system as it moves back and forth in a linear direction. Calculations are not simple. Operating temperature also significantly influences useful life. When these parameters are taken into consideration, the above formula is transformed as follows: For Ball Bearings For Roller Bearings fH·fT·fC C 3 L= · ·50 fW P ( ) ( ) fH·fT·fC C 10/3 L= · ·50 fW P L: Rated Life Span (km) fH: Hardness Coefficient (See Fig.1) C: Basic Dynamic Load Rating (N) fT: Temperature Coefficient (See Fig.2) P: Acting Load (N) fC: Contact Coefficient (See Table 3) fW: Load Coefficient (See Table 4) The Life span can be computed as a number of hours by obtaining the travel distance for a unit of time. It can be obtained by using the following formula, in which stroke length and stroke cycles are assumed to be constant. L·103 Lh= 2·ℓs·n1·60 Lh: Life Span Hours (hr) ℓs: Stroke Length (m) L: Rated Life Span (km) n1: Reciprocating Times per Minute (cpm) Using the following formula, the friction resistance (required thrust) can be obtained from the load and the seal resistance specified by the system. F= μ·W+f F: Friction Resistance (N) μ: Dynamic Friction Coefficient W: Weight Loaded f: Seal Resistance (2N~5N) Table-1. Static Safety Factor(Lower Limit of fs) Condition of Use Lower Limit of fs Under Normal Operating Conditions 1~2 When Smooth Travel is Required 2~4 When Subjected to Vibrations, Impacts 3~5 Table-2. Dynamic Friction Coefficient Type Dynamic Friction Coefficient (μ) Miniature Slide Guides 0.004~0.006 Medium Load Slide Guides 0.002~0.003 Slide Ways 0.001~0.003 Slide Tables 0.001~0.003 Linear Bushings 0.002~0.003 Linear Ball Bushings 0.0006~0.0012 2Friction Resistance and Required Thrust Linear Guide Calculation of Life Span of Linear Systems 1
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