316 TECHNICAL INFORMATION t)BSEOFTT $PFGýDJFOU GH) In a linear system, the shaft must be hard enough to withstand contact with the ball bearings. Unless sufficient hardness is provided, the allowable load can decrease, resulting in a short useful life. Compensate the rated life span with the hardness coefficient. t$POUBDU $PFGýDJFOU GC) In general, two or more linear systems are used with each shaft. Depending on the machining precision, the load exerted on each of the respective systems can vary. In this case, the load applied on each linear system changes depending on the machining precision, therefore it cannot be uniformly applied. As a result, allowable load per linear system changes depending on the number of linear systems on one axis. Compensate the rated life span with the contact coefficient in Table-3. t-PBE $PFGýDJFOU GW) When calculating the load that acts on a linear system, it is necessary to work with precise figures for material weight, the force of inertia resulting from operating speed, load moment, various changes that occur over time, and so on. However, it is difficult to have accurate calculation for oscillating movement as beside the normal repetition of start and stop, other factors such as vibration and impact also need to be considered. Therefore, the life span calculation needs to be simplified using the load coefficient in Table-4. QLinear Bushings Rated life span can be obtained as follows from the basic dynamic load rating and the load to the linear bushing. fH·fT·fC C 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: Working Load (N) fC: Contact Coefficient (See Table3) fw: Load Coefficient (See Table4) 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 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) t5FNQFSBUVSF $PFGýDJFOU GT) When temperature in a linear system exceeds 100˚C, the hardness of the system and the shaft become degraded. This decreases the allowable load to a greater extent than when the system is used at ambient temperature, and can shorten the life span. Compensate the rated life span with the temperature coefficient. 100 150 200 250 0.5 0.6 0.7 0.8 0.9 1.0 Fig.-2 Temperature Coefficient Condition of Use fw Low speed with no external vibration or impact (Max. 15m/min) 1.0~1.5 Middle range speed with no exerted vibration or impact of considerable force(Max. 60m/min) 1.5~2.0 High speed with no external vibration or impact (Over 60m/min) 2.0~3.5 Table-3. Contact Coefficient Table-4. Load Coefficients QLinear Ball Bushings Rated life span can be obtained as follows from the basic dynamic load rating and the load to the linear ball bushing. L: Rated Life Span (km) fH: Hardness Coefficient (See Fig.1) C: Basic Dynamic Load Rating (N) fT: Temperature Coefficient (See Fig.2) P: Working Load (N) fC: Contact Coefficient (See Table 3) fw: Load Coefficient (See Table 4) Life Span Hours ·For revolution and reciprocating motion ·For reciprocating motion ·Revolution and reciprocal motion allowable values DN≥dm·n+10·S·n1 Lh:Life Span Hours(hr) S: Stroke Length(mm) n: Revolutions per Minute(rpm) n1:Strokes Per Minute(cpm) dm:Pitch Diameter of Ball(mm)≈1.15dr fH·fT·fC C 3 L= · ·50 fw P ( ) 106·L Lh= 60 (dm·n)2+(10·S·n1)2/dm 106·L Lh= 600·S·n1/(π·dm) Fig-1. Hardness Coefficient 60 50 40 30 20 10 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Track Surface Hardness HRC Temperature of Linear System ˚C Number of Bearings per Shaft Contact Coefficient fc 1 1.00 2 0.81 3 0.72 4 0.66 5 0.61 fH Hardness Coefficient fT Temperature Coefficient
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