Oil-Free Scroll Technology 101
Advanced by Air Squared for Over Thirty Years
Oil-Free Scroll Technology
Not familiar with oil-free scroll technology? This is the best place to start for a basic understanding of the technology behind Air Squared.
What is scroll technology? It’s the common technology behind scroll-type compressors, vacuum pumps, and expanders. They are generally defined as positive displacement devices having orbital motion and interleaving scrolls used to compress, pump, or expand fluids. Sound complicated? It actually isn’t. In fact, scroll-type devices are often referred to informally as “the elegant solution,” due to their simplistic design and quiet, smooth operation
Range Technical Overview
Design Experience Range
Product Line Coverage
Oil-Free Scroll Technology
The scroll concept is actually quite old. The initial patents date back to the early 1900s. Unfortunately, the technology to fabricate scrolls accurately did not exist, and the concept was forgotten.
In 1972 the scroll concept was re-invented by a physicist named Niels Young. Mr. Young brought the idea to Arthur D. Little, Inc. of Cambridge, MA. Arthur D. Little saw its potential and began the development of a feasibility model in January 1973.
With pressure to significantly improve refrigeration compressor efficiency, the potential and advantages of a scroll compressor were recognized by the refrigeration industry in the mid-1970s. A scroll compressor offered improved efficiency, with the added benefit of greater reliability, smoother operation, and lower noise. Arthur D. Little began the development of a scroll-type compressor for refrigeration for the Trane Co. in late 1973.
Today, scroll compressors are used extensively for refrigeration by many well-known companies, including Trane, Hitachi, and Copeland.
Léon Creux awarded first scroll patent
Scroll concept re-invented by physicist Niels Young
Niels Young, John McCullough, and Robert Shaffer begin scroll compressor research at Arthur D. Little
Sanden begins manufacturing the first scroll compressor
Emerson-Copeland, the largest scroll producer in the world today, begins manufacturing their first scroll design
Robert Shaffer founds Air Squared, Inc. in Cincinnati, OH, with the goal of developing and licensing compressor technology in various market areas
Robert Shaffer and Mike Mansdorfer found Air Squared Manufacturing, Inc. in Broomfield, CO with the goal of mass-producing unique oil-free scroll compressor and vacuum pump designs for OEMs.
A compact scroll compressor developed by Air Squared operates perfectly on the surface of Mars, helping convert carbon dioxide into oxygen as part of the Mars Oxygen In-Situ Resource Utilization Experiment onboard the Perseverance rover.
Oil-Free Scroll Technology
How it Works
Basic Principles of Operation
The two primary components, a “fixed scroll” and an “orbiting scroll,” are and the namesake of scroll-type designs. One scroll is index 180º with respect to the other, allowing the two scrolls to mesh together. The orbiting scroll is coupled to a crankshaft and orbits eccentrically, following a fixed path with respect to the fixed scroll.
During operation, a series of crescent-shaped pockets are created between the two scrolls. In the case of a scroll compressor, the working fluid moves from the periphery (inlet) towards the center (discharge) through increasingly smaller pockets, generating compression.
Similar principles apply for a scroll vacuum pump and a scroll expander.
Design and Construction
Involute geometry is complex, the design itself is not
Informally referred to as “the elegant solution,” standard oil-free scroll designs are simplistic and have few primary moving parts.
The “scroll pack” assembly is the heart of the design and consists of all primary and wearing components.
- The primary components are the fixed scroll, orbiting scroll, and three idler shafts that secure the position of the orbiting scroll relative to the fixed scroll.
- The wearing components are two tip seals, installed in the fixed scroll involute and orbiting scroll involute, and bearings around each idler shaft (“idler bearings”) and in orbiting scroll (“drive bearing”).
The “drive” assembly consists of a housing, motor, and crankshaft that drives the scroll pack. Most designs will also include a mounted fan for air cooling during operation.
Scroll Involute Sizing
The scroll involute geometry directly influences all performance parameters of the design. The primary design parameters of any scroll device are volume ratio and suction volume. The required pressure ratio and flow rate define the necessary volume ratio and suction volume.
The Volume of gas entering the inlet of the involutes every revolution
A higher flow rate requires a larger suction volume (at a fixed speed).
A larger suction volume requires an increase of involute height, pitch, or both.
An increase of involute height increases a design’s axial length, while an increase of involute pitch increases a design’s diameter.
The ratio of inlet (suction) volume to the discharge volume
A higher pressure ratio requires a larger volume ratio.
A larger volume ratio requires an increase of involute wraps.
An increase of involute wraps increases a design’s diameter.