Oil Free Air Compressors

Oil free air compressors are ideal for industries that require clean, contaminant-free air, including hospitals, pharmaceutical manufacturing, electronics, food and beverage processing, automotive, and textiles. These systems are known for their compact design, reliability, and low vibration, but they face efficiency challenges due to the absence of oil as a sealing agent.

In oil free rotary screw compressors, the lack of oil means there’s nothing to fill the air gaps between the two rotors and housing. Gaps are like a door that won’t completely close and leaks cold air, and in compressors, leaks limit maximum discharge pressure and reduce efficiency and generate hot air. To minimize losses, OEMs carefully machine and grind rotors and housings so that gaps are small; but even with CNC machining precision, the ideal—zero clearance—is impractical because of the possibility of metal-to-metal contact and the resulting galling and scuffing that can lead to seizure.

For small compressors, the industry standard static air gap clearance is 0.002 in. This is difficult and time consuming to achieve; common practice is to custom match male and female rotors for optimum fit. This extensive and exacting added machining slows production and drives up manufacturing costs, so the resulting compressor is a compromise between small gaps/high efficiency and potential surface collisions and contact wear.

Worse is if the gap is a bit too small. The galling and seizure of rotors need to be scrapped in many cases. The cost of “when is close enough” can, however, be improved with modern coating technology. This is where modern oil free air compressor rotor coatings come into play.

Conformable Surface That Seals . . . A True Dynamic Gasket

Traditional surface treatments – such as hard anodizing, chrome plating, and PTFE coatings – lack this adaptability and offer only short-term resistance to wear.

To address these challenges, Orion developed a proprietary coating technology: DB L-908, a conformable coating that is tenaciously bonded, yet gives it a structure that is slick, but deformable so that it conforms and minimizes air-gaps between high speed mating surfaces (see Figures 1 and 2 below).

Engineered specifically for air compressor rotor coatings, the DB L-908 coating is designed as a conformable, bonded seal that behaves like a dynamic gasket, adapting to slight variations between rotor surfaces and housing geometry.

DB L-908 is applied  in thicknesses from 0.002 to 0.008 inches with a tight tolerance of ±0.001 inches. It is applied thick enough on rotors so that there is a slight, purposeful, initial interference fit between rotors. During assembly, an initial, single revolution of the rotors causes the opposing mating surfaces to permanently compress the coating to form a zero-leak seal between them. The robotic application means customers can expect to receive a consistent, precise and repeatable coating application on every single rotor - from batch to batch, year after year.

Once compressed, the film stays compressed as it has zero-compression recovery. Particles of PTFE give the contact area low friction and reduce inter-surface friction as the rotors warm up in the initial use or run-in. The air gap remains at zero and widens slightly as the rotors get warmer in operation.

The net effect is a minimum 5% increase in efficiency of oil free rotary screw compressors, along with a reduction in noise and a reduced output temperature of the air.

By using rotary screw air compressor coatings like DB L-908, manufacturers now have access to durable, high-performance coatings for air compressor rotors that enhance both reliability and efficiency in demanding, oil-free environments.

As a leader in high-performance functional coatings and their precise, repeatable application, Orion remains committed to pushing the boundaries of what's possible in industrial coatings.

Contact us today to speak with a technical consultant about your oil free air compressor coating project.