The load rating of a linear guide (also called linear motion bearing or rail system) determines its capacity to handle forces and moments without premature failure. Key ratings include:

1. Static Load Rating (C₀)

Definition: Maximum load the guide can withstand without permanent deformation when stationary or at very low speeds.

Purpose: Ensures structural integrity during setup, shutdown, or impact.

Safety Margin: Applied loads should be ≤ 30–50% of C₀ for reliability.

2. Dynamic Load Rating (C)

Definition: Constant load under which the guide achieves 50 km of travel with 90% reliability (L₁₀ life).

Life Calculation:

L₁₀ = (C / P)³ × 50 km  

L₁₀: Basic rating life (km).

P: Equivalent dynamic load (N).

Note: Actual life depends on lubrication, alignment, and load direction.

3. Moment Load Ratings

Linear guides resist rotational forces (moments):

Mₓ (Roll): Rotation around the rail axis.

Mᵧ (Pitch): Rotation perpendicular to the rail.

M_z (Yaw): Rotation parallel to the rail.

Manufacturers specify moment capacities (e.g., M_A, M_B, M_C).

4. Equivalent Load (P)

Combine radial, axial, and moment loads into a single equivalent load:

P = P_radial + 0.5 × P_axial + (C / M_rating) × |M|  

Coefficients vary by manufacturer—consult technical docs.

5. Factors Affecting Load Capacity

Mounting Orientation: Horizontal vs. vertical impacts load distribution.

Precision Alignment: Misalignment reduces capacity by 20–50%.

Vibration/Shock: Dynamic loads exceed static values—use safety factors.

Temperature/Lubrication: High temps or poor lubrication reduce capacity.

Example Calculation:

Assume:

Dynamic load rating (C) = 10 kN

Radial load (F_Y) = 1.5 kN

Pitch moment (M_Y) = 30 Nm

Moment rating for M_Y = 50 Nm

Equivalent Load:

P = 1.5 kN + (10 / 50) × 30 = 1.5 + 6.0 = 7.5 kN  

Life Calculation:

L₁₀ = (10 / 7.5)³ × 50 km ≈ 118 km  

Key Recommendations:

Safety Factor: Use 1.5–3× for static loads; 1.2–2× for dynamic loads.

Moment Loads: Often limit capacity more than radial/axial forces—verify moment ratings.

Manufacturer Data: Always refer to brand-specific catalogs (e.g., Hiwin, THK, Bosch Rexroth).

Testing: For critical applications, conduct real-world load testing.

For specific applications, share details (load direction, speed, environment) to refine guidance!