Ayberk Erturk
OAV Air Bearings
Princeton, New Jersey, 08540, USA
3 min read
Introduction
In the world of precision machining, maintaining high accuracy and repeatability is paramount, especially in industries like aerospace, medical devices, and semiconductor manufacturing. A key component ensuring this precision is the air bearing. These near-frictionless devices provide exceptional stiffness and load-carrying capacity. However, their performance can be significantly impacted by temperature fluctuations. This blog post explores how these thermal variations affect air bearing performance and discusses innovative solutions to mitigate these effects.
The Fundamentals of Air Bearings
Air bearings operate on a thin film of pressurized air, creating a nearly frictionless interface between the bearing and its mating surface. The integrity and uniformity of this air film are crucial for optimal performance. Temperature fluctuations can disrupt this delicate balance, affecting both the pressure and stability of the air film and the material properties of the bearing components.
The Challenge of Temperature Fluctuations
When temperatures fluctuate, the components of air bearings undergo thermal expansion and contraction. This leads to variations in the air gap, which in turn affects the bearing's load capacity and stiffness. The governing equation for thermal expansion is: ΔL = α L ΔT where: - ΔL is the change in length, - α is the coefficient of thermal expansion, - L is the original length, - ΔT is the temperature change.
Advanced Materials: INVAR
To combat the adverse effects of temperature fluctuations, advanced materials like INVAR are utilized in air bearings. INVAR is an iron-nickel alloy with an exceptionally low coefficient of thermal expansion (α ≈ 1.2 × 10⁻⁶ /°C) . This makes it ideal for precision applications where dimensional stability is critical.
Benefits of INVAR:
- Dimensional Stability: Minimal expansion or contraction with temperature changes, ensuring a consistent air gap and stable bearing performance.
- High Strength and Durability: Maintains structural integrity under varying thermal conditions.
- Thermal Conductivity: Efficient heat dissipation reduces localized thermal stresses.
Experimental Analysis
To evaluate the impact of temperature fluctuations on air bearing performance, a series of tests were conducted using OAV Air Bearings' OAVTB60i20W temperature-controlled air bearings. These tests measured performance metrics such as load capacity, stiffness, and air gap uniformity under controlled temperature variations.
Key Findings:
- Changes in Diameters: The graphite air bushing's inside diameter increased by approximately 9.208 microns, while the INVAR shaft's diameter increased by about 1.8 microns when heated from 25°C to 100°C.
- Clearance: The initial clearance of 18 microns at room temperature increased to approximately 25.408 microns at 100°C.
- Stiffness: The stiffness of the air bearing decreased from 23 N/μm to 17.84 N/μm without air cooling. With effective air cooling, the stiffness decreased to 18.26 N/μm.
Graphs:
1. Changes in Diameters: Graph illustrating the expansion of graphite bushing and INVAR shaft from room temperature to 100°C.
2. Clearance Change: Graph showing the increase in clearance between the graphite bushing and the INVAR shaft with and without air cooling.
3. Stiffness Changes: Graph depicting the stiffness variations of the graphite bushing and INVAR shaft with temperature changes and the effect of air cooling.
Conclusion
Temperature fluctuations pose significant challenges to the performance of air bearings in precision machining. The use of advanced materials like INVAR offers a robust solution by providing exceptional dimensional stability and durability. Experimental results demonstrate that air cooling effectively reduces the thermal expansion of graphite bushings, thereby maintaining tighter tolerances and higher stiffness.
OAV Air Bearings' high-temperature thrust air bearings exemplify this innovation, designed to operate under extreme environmental conditions without sacrificing precision or quality. As the industry continues to advance, the importance of material selection in designing high-performance air bearings becomes increasingly evident, paving the way for further innovations in precision engineering.