Page 462 - MiSUMi 2025

Economy series Technical Data - Calculation of Life Span of Linear Bushings
Linear Bushings

QCharacteristics of Linear Bushings
QExternal View QStructure
Outer Cylinder Retainer · Unlimited stroke linear motion mechanism utilizing rolling steel balls
Side Ring · When used with linear shafts, linear motion is achieved by
recirculation of the steel balls inside raceway groves formed
by outer cylinder and retainer.
· Can obtain linear motion with lower friction compared to slide
Steel Balls bearings, and used for many applications such as transfer
equipment and semiconductor manufacturing systems
QAllowable Load
•Basic Static Load Rating (Co) •Allowable Static Moment (Mo)
Basic Static Load Rating is static load exerted on contacting Static Allowable Limit Load when a moment load is applied.
parts under maximum stress, at which the sum of the permanent Determined by permanent deformation same as Basic Static Load
deformation in the rolling element and rolling contact surface Rating.
equals 0.0001 times of the diameter of the rolling element.
•Basic Dynamic Load Rating (C)
Basic Dynamic Load Rating is the static load applied in a constant
direction that enables each linear system of the same series to
travel 50km under the same condition, without 90% of the material
suffering damage from rolling contact fatigue.
QLife
4 When the linear systems are in motion with loads, rolling surfaces and races are subject to repeated stress and will show stress induced flaking that seems scaly. 4
The total run distance of a linear system until this flaking will first appear is the Life of linear system.
Linear Guides / Linear Shafts / Linear Bushing / Ball Splines / Oil Free Bushings • Hardness Factor (fH) fw P ) 3 L : Rated Life (km) fW: Load Factor (Refer to Table-4) Oil Free Bushings Linear Bushing / Ball Splines / Linear Guides / Linear Shafts /
Rated life can be obtained from the Basic Dynamic Load Rating and the actual load applied on the linear bushings, as shown below.
(
fH·fT·fC C
C : Basic Dynamic Load Rating (N)
fH: Hardness Factor (Refer to Fig-1)

L= · ·50

fT: Temperature Factor (Refer to Fig-2) P : Applied Load (N)
fC: Contact Factor (Refer to Table-3)
• Temperature Factor (fT)
For linear systems, ample hardness of the shafts that ball contact
is needed. If the ample hardness of the shafts are not obtained,
hardness will be reduced and allowable loads and life will be
the allowable loads are reduced and the life will be shortened. If linear systems are exposed to temperature higher than 100°C,
reduced.
Linear Guides Fig-1. Hardness Factor Fig-2. Temperature Factor Guides Linear
1.0
1.0
0.9 0.9
P.04-011 0.8 0.8 P.04-011
Cross Roller Guides Hardness Factor fH 0.7 Temperature Factor fT 0.7 Guides Cross Roller
0.6
0.6
0.5
P.04-039 0.4 0.5 100 150 200 250 P.04-039
0.3
Linear Shafts / Bushings 0.2 60 50 40 30 20 10 Linear System Section Temperature °C Bushings Linear Shafts /
0.1
P.04-043 • Contact Factor (fC) Raceway Hardness HRC • Load Factor (fW) P.04-043
More than 2 linear systems are used for 1 shaft, in general. In
Ball Splines this case, the load on each linear system will vary depending on it requires inertia force attributed to motion velocity or moment loads. Ball Splines
To calculate load applied to the linear system, in addition to object weight,
machining accuracies and will not be equally distributed loads. As
Further, it is necessary to accurately determine the temporal change
of each. However, for reciprocating motion applications, it is difficult to
the result, allowable load per linear system will vary depending on
P.04-107 the number of linear systems used on one shaft. obtain accurate calculations due to the effects of vibrations and shocks. P.04-107
Therefore, use the Table below in order to simplify the Life Calculations.
Table-3 Contact Factor Table-4 Load Factor
Oil Free Bushings Number of bushings on one shaft Contact Factor fc No external shocks or vibrations 1.0~1.5 Bushings Oil Free
Condition
fW
1.00
1
Low Speed 15m / min. or Less
3 2 0.81 No excessive external shocks or vibrations 1.5~2.0
0.72
Medium Speed 60m / min. or Less
P.04-126 4 5 0.66 External shocks and vibrations present 2.0~3.5 P.04-126
Shaft Supports / Collars Life in hours can be obtained by calculating travel distance per hour. When stroke length and stroke cycles are fixed, see the equation below. Collars Shaft Supports /
0.61
High speed over 60m / min.
Lh : Life Hours (hr)
L·10
3
L : Rated Life (km)
2·Ls·n1·60
n1 : Reciprocating Cycles per Minute (cpm)
P.04-144 Lh= Ls: Stroke Length (m) P.04-144
04-077 04-078