Rated Load and Nominal Life
Rated Loads in All Directions
The basic load rating in the specification table indicates the rated load in the radial direction as shown in Fig.2 . The rated loads in the reverse radial and lateral directions are obtained from Table1 below.
| Basic dynamic load rating | Basic static load rating | |
|---|---|---|
| Radial direction | C (indicated in the specification table) | C0 (indicated in the specification table) |
| Reverse radial direction | CL=C | C0L=C0 |
| Lateral directions | CT=1.47C | C0T=1.73C0 |
Static Safety Factor fS
Model ER may receive an unexpected external force while it is stationary or operative due to the generation of an inertia caused by vibrations and impact or start and stop. It is necessary to con- sider a static safety factor against such a working load.
| fS | Static safety factor (see Table2 ) |
|---|---|
| fC | Contact factor (see Table3 ) |
| C0 | Basic static load rating (N) |
| PC | Calculated load (N) |
Static Safety Factor (Guideline)
Treat the values in Table 2 as estimates for the lower limit of the static safety factor based on operating conditions.
| Load conditions1 | Lower limit of fS |
|---|---|
| Without vibration or impact | 1 to 1.3 |
| With vibration or impact | 2 to 7 |
- 1 In general, factors that cause vibration and impacts include acceleration and deceleration, sudden starts and stops, transmission of vibration and impacts from external devices and machines, and changes in processing force over time.
Calculating the Nominal Life
The nominal life of the THK precision linear pack is defined as 50 km. The nominal life (L10) is cal- culated from the basic dynamic load rating (C) and the load acting on the precision linear pack (PC) using the following formula.
| L10 | Nominal life (km) |
|---|---|
| C | Basic dynamic load rating (N) |
| PC | Calculated load (N) |
When comparing the nominal life (L10), you must take into account whether the basic dynamic load rating was defined based on 50 km or 100 km. Convert the basic dynamic load rating based on ISO 14728-1 as necessary.
ISO-regulated basic dynamic load rating conversion formulas:
| C50 | Basic dynamic load rating based on a nominal life of 50 km |
|---|---|
| C100 | Basic dynamic load rating based on a nominal life of 100 km |
Calculating the Modified Nominal Life
During use, a precision linear pack may be subjected to vibrations and shocks as well as fluctuating loads, which are difficult to detect. In addition, having precision linear packs arranged in close contact will have a decisive impact on the service life. Taking these factors into account, the modified nominal life (L10m ) can be calculated according to the following formula (2).
Modified factor α
| α | Modified factor |
|---|---|
| fC | Contact factor (see Table3) |
| fW | Load factor (see Table4 ) |
Modified nominal life L10m
| L10m | Modified nominal life (km) |
|---|---|
| C | Basic dynamic load rating (N) |
| PC | Calculated load (N) |
Calculating the Service Life Time
When the nominal life (L10) has been obtained, if the stroke length and the number of reciprocations per minute are constant, the service life time is obtained using the following formula.
| Lh | Service life time (h) |
|---|---|
| ℓS | Stroke length (mm) |
| n1 | Number of reciprocations per minute(min-1) |
fc:Contact Factor
When multiple inner blocks are used in close contact with each other, their linear motion is affected by a moment load and mounting accuracy, making it difficult to achieve uniform load distribution. In such applications, multiply the basic load rating (C) and (C0) by the corre- sponding contact factor in Table3 .
| Number of inner blocks in close contact with each other |
Contact factor fC |
|---|---|
| 2 | 0.81 |
| 3 | 0.72 |
| Normal use 1 | 1 |
fW : Load Factor
In general, reciprocating machines tend to involve vibrations or impact during operation. It is extremely difficult to accurately determine vibrations generated during high-speed operation and impact during frequent start and stop. Therefore, when the actual load applied on model ER cannot be obtained, or when speed and vibrations have a significant influence, divide the basic dynamic load rating (C) by the corresponding load factor in Table4 of empirically obtained data.
| Vibrations/(br) impact | Speed (V) | fW |
|---|---|---|
| Faint | Very low V≦0.25m/s |
1 to 1.2 |
| Weak | Slow 0.25<V≦1m/s |
1.2 to 1.5 |
