Scroll vs Screw Compressors: What is the difference?
We’ll compare scroll vs screw compressors along with their pros, cons, and suitable industries and applications for each to help you make an informed decision.
The oil-injected screw compressor for the machine industry
If you work in the machine industry, there are several options available for compressed air delivery. These include fixed speed and VSD oil-injected screw compressor equipment and piston compressors. In fact, there is a wide range of air compressor options to choose from. That said, oil injected rotary screw compressors in most cases are the most efficient solution for machine manufacturing.
This is a result of their ability to run for long periods and save on energy costs. The latter is specifically due to variable speed drive (VSD) technology. With that, there are many applications that can benefit from an oil injected screw compressor. These include the following.
- Pneumatic tools for assembly lines
- Actuation of robotic arms and automated systems
- Precision cutting, drilling, and metalworking
- Milling and grinding (removing debris)
- Clamping
- Paint spraying and surface finishing
- Mist lubrication
- Material handling, conveying, and packaging
When considering compressed air equipment for any sector of the machine industry, it's important to choose the right one. This is why we've compiled information about how an oil injected compressor works. The information below will better explain why it's optimal for the mentioned application.
How a rotary screw compressor works
By comparison to the piston compressor, a rotary screw machine is more complex. This is why piston compressors are generally cheaper to purchase. However, their simple design also means they typically need long cool down periods in between uses and they tend to be less efficient. Therefore, they're better suited for less demanding applications than the machine industry requires.
You can find a simple diagram of how a piston compressor works below. For further information, you can consult related articles on the topic.
With a rotary screw compressor, there are a male and a female rotor that rotate in opposite directions. When this occurs, air is drawn in and compressed. This is because of the small space between the rotors and their housing, which decreases throughout the process. To create the desired working pressure, this compression is adjusted with the ratio of the length and pitch of the screw.
Of course, this is the most basic explanation of how a rotary screw compressor works. To better visualize what we've explained, please find a diagram below.
In addition to what's explained above, there are two main working principles of a rotary screw compressor. These are fixed speed and VSD. The difference is fairly straightforward. Fixed speed machines always run at 100% motor speed (regardless of demand) and VSD compressors slow down when demand drops. Atlas Copco recently also introduced the dual speed compressor. It operates at two speeds, one for maximum capacity and a minimum speed during unload. It can also be upgraded to VSD functionality.
Since a VSD compressor only runs at full motor speed when demand is high, they consume much less electricity. One reason for choosing a fixed speed machine over a VSD compressor is its lower investment costs. However, since energy costs make up a majority of operating a compressor, the efficiency benefits of VSD compressors are such that a quick ROI is the standard.
An oil injected screw compressor vs oil free
On top of the types of compressors (piston, rotary screw, etc.), there are different ways of cooling them. The most common way is with oil lubrication. When oil is injected in the compression chamber, it cools and lubricates the element. This is essential to reduce the high levels of friction and heat that occur when the rotors come into contact.
However, one drawback of using an oil injected machine is that small particles of oil can end up in the compressed air. This is not good for applications that directly impact humans, like food and beverage and medical. In such instances, oil free equipment is required. That said, oil free rotary screw machines require alternative forms of cooling.
With these compressors, timing gears are used, and the rotors don't come in contact with each other. They also require more stages than oil injected machines to achieve high pressure levels. As a result, oil free compressors tend to cost more. When working in an industry such as machine production and assembly, oil free air isn't necessary.
Of course, it's always best to consult the relevant ISO 8573-1 air quality class for your application. This will help you determine the right air treatment equipment to use, including filters and dryers.
Choosing the right equipment
While this article provides a brief overview of the types of compressors and the ways they're cooled, it's only the beginning. For example, Atlas Copco GA VSDS machines are up to 60% more efficient than fixed-speed machines. If you'd like more information on the various types of compressors offered, feel free to reach out. Our team is happy to help.
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