Selecting a Support Unit (Bearing Housing):
Fixed End (Drive End): An angular contact ball bearing pair (typically back-to-back DB or face-to-face DF) capable of supporting both axial and radial loads must be used and preloaded. Maximum axial load must be supported.
Supported End (Non-Drive End):
Fixed-Fixed: Fixed bearing housings are used on both ends. This provides the highest rigidity and stability, but requires high installation requirements (precisely controlling thermal expansion compensation).
Fixed-Supported: The drive end is fixed, while deep groove ball bearings or cylindrical roller bearings are used on the support end (supporting only radial loads but allowing axial float). This is the most common configuration and allows for thermal expansion.
Fixed-Free: The drive end is fixed, while the support end is unconstrained (simple and inexpensive). This configuration offers poor rigidity and is only suitable for short strokes, low precision, and low loads.
Key: The selected bearing must meet the screw’s speed and life requirements (bearing life calculation).
Selecting a Lubrication Method:
Grease lubrication: The most common configuration and requires minimal maintenance (regular refilling). Suitable for most low- to medium-speed, general-use applications. A grease with the appropriate viscosity and consistency must be selected.
Oil lubrication: Provides good heat dissipation and is suitable for high-speed, heavy-load, and long-life applications. However, it requires an oil system, which is complex to maintain and may leak.
Solid lubrication (such as graphite): Suitable for extreme environments (ultra-high/low temperatures, vacuum, high contamination, and maintenance-free).
Sealing: Nuts typically come with built-in wipers. For harsh environments, consider additional protective covers or telescopic sleeves.
Consider thermal expansion (critical for long strokes):
The operating temperature rise of the screw will cause elongation. For long-stroke applications, the following should be considered:
Accurately calculate the temperature rise (frictional power loss) and thermal expansion ΔL = α * L * ΔT.
Allow compensation in the support method (e.g., using a fixed-support structure).
Perform thermal compensation in the control system (requires a temperature sensor).
Select a material with a low thermal expansion coefficient (such as a ceramic ball screw).