Yes, some rotary screw compressors are oil-free.
Rotary screw compressors are not uniformly oil-free; they fall into two primary classifications based on their design and operation regarding lubrication.
As stated, rotary screw compressors are divided into two main categories: Oil-injected and oil-free. This distinction is crucial for determining the quality of the compressed air produced and the compressor's suitable applications.
Understanding the Two Categories
1. Oil-Injected Rotary Screw Compressors
In oil-injected compressors, oil is injected into the compression chamber. This oil serves multiple purposes:
- Lubrication: It lubricates the rotors, reducing wear and tear.
- Cooling: It helps dissipate the heat generated during the compression process.
- Sealing: It creates a seal between the rotors and the housing, improving efficiency.
While oil-injected compressors are highly efficient and widely used, the compressed air exiting the unit contains oil vapor and aerosols. This air often requires filtration to remove the oil before being used in many applications.
2. Oil-Free Rotary Screw Compressors
Oil-free rotary screw compressors are designed so that no oil comes into contact with the air being compressed. They achieve this through:
- Precise Manufacturing: The rotors are machined to extremely tight tolerances and do not touch each other or the housing.
- Timing Gears: Separate timing gears, located in a sealed gearbox lubricated with oil, ensure the precise synchronization of the rotors without direct contact.
- Alternative Sealing: Labyrinth seals or other methods are used to prevent oil from the gearbox or bearings from entering the compression chamber.
This design ensures that the air discharged from the compressor is free of added oil contamination.
Why Choose Oil-Free?
The choice between oil-injected and oil-free depends heavily on the required air quality for a specific application.
- Purity: Oil-free compressors are essential when the compressed air must be completely free from oil contamination.
- Product Integrity: Industries where compressed air comes into direct contact with the final product, or where any trace of oil could cause damage or spoilage, require oil-free air.
Here's a simple comparison:
| Feature | Oil-Injected Rotary Screw | Oil-Free Rotary Screw |
|---|---|---|
| Air Purity | Contains oil residue | No added oil in compressed air |
| Lubrication | Oil in compression chamber | Oil in separate gearbox/bearings |
| Rotor Contact | Often touch/close contact | Rotors do not touch |
| Complexity | Simpler design | More complex design |
| Cost | Generally lower initial | Generally higher initial |
Applications
Industries that commonly require oil-free compressed air from rotary screw compressors include:
- Food & Beverage: Processing, packaging, and transportation where air contacts consumables.
- Pharmaceutical: Manufacturing medications and sterile environments.
- Electronics: Cleanroom operations and component manufacturing.
- Textiles: Preventing oil stains on fabrics.
- Medical: Breathing air in hospitals (often requires further purification), powering medical devices.
- Chemical: Processes where oil could contaminate reactions or products.
In summary, while the technology exists for rotary screw compressors to operate without oil contaminating the air, it's important to distinguish them from their oil-injected counterparts, as both types are available and serve different needs.
