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A plasma cutter is a machine that uses ionized gas or plasma to cut steel, stainless steel, aluminum, brass, copper, and other conductive metals. A typical portable plasma cutter has an air compressor. An air compressor allows your plasma cutter to make precise cuts. Your machine may come with its own internal air compressor. This built-in compressor has advantages and disadvantages. That means that buying a plasma cutter without an air compressor makes sense in some cases.
Understanding a Plasma Cutter
A plasma cutter is a machine that produces an arc of ionized gas. Gas becomes ionized at extremely high temperatures. A plasma arc’s temperature is at least 28000 degrees Celsius (50000 degrees Fahrenheit). At this temperature, the outer electrons of the gas molecules are knocked out of their orbitals. What you get is a stream of plasma. This stream of hot ionized gas can cut ferrous and non-ferrous materials.
Basically, what a plasma cutter does is force gas through a small nozzle in the torch. This gas can be ordinary air or varying mixtures of oxygen, nitrogen, and argon. Then the machine uses electricity to heat up this flow of gas , which now becomes a plasma jet. So in a nutshell, a plasma cutter uses gas and electricity to cut materials (1).
Where does an air compressor matter in this process?
An air compressor forces compressed air through the nozzle. This helps create a jet of plasma. Without the pressure from the compressor, you’ll end up with a weak stream of air coming out of the nozzle, and that’s not going to cut anything. In other words, it’s impossible to do plasma cutting without compressed air. The high speed of the plasma jet also helps blow away slag and dross that may otherwise hang under the edges of the cut.
Many plasma cutters have built-in compressors, but some don’t. when you buy a machine that doesn’t come with a compressor, you may have to invest in a separate air compressor. That shouldn’t be a problem, since you can easily connect an air compressor to the plasma cutter and then get down to business. So if for some reason you acquire a plasma cutter that has no internal air compressor, just drive to a local hardware shop and buy a compressor.
Advantages of a Built-in Air Compressor
Built-in air compressors have key advantages. The most obvious is convenience. If your plasma cutter already comes with an air compressor, you don’t have to shop around for a separate one. Also, an air compressor built for the machine is logically compatible with the machine. That comes with its own benefits. For instance, it allows for more precise cutting, which in turn means cleaner cuts. Nevertheless, you can replicate the same benefits using an external air compressor by adjusting the pressure to produce cuts that are just as precise and clean.
More importantly, with a built-in air compressor, you don’t have to power two machines. Thus, you save on your electric bill.
Disadvantages of a Built-in Air Compressor
The main drawback of buying plasma cutters with fixed air-compressors is the price. They’re much more expensive than those without air compressors. In many cases, you can save money by buying a plasma cutter and a standard air compressor.
Air compressors need fixed air pressure. If there’s any leak in the system, the plasma cutter may not work or may work ineffectively. Plasma cutters with integrated compressors are more prone to having air valve leaks. These leaks reduce the efficiency of the machine.
Speaking of efficiency, it’s important that we talk about the general problem among plasma cutters with internal air compressors. They are notorious for having performance issues. Manufacturers have to shave off the cutting capacity of their machines when they add compressors in the systems. For instance, the Hobart 12ci comes with its air compressor. Priced at almost $750 and rated at 12A, the machine is claimed to have a severance cut of 1/4”, but it’s best used for 1/8” sheets. For the same amount of money, you can find another plasma cutter without an air compressor that can cut 1/2” steel.
Can’t manufacturers design plasma cutting machines with compressors and good performance? Sure. The Hypertherm Powermax 30 Air has a severance capacity of 5/8” at 5 ipm, but the cheapest unit on Ebay costs $1794!
Now, if you’re concerned with performance, note that plasma cutters with integrated compressors have lower duty cycles. A typical system of this type has around 30 percent duty cycle, which indicates it can only run for 3 minutes for every 10 minutes without overheating.
Since there are pros and cons to owning a plasma cutter with its own compressor, it’s wise to weigh your options. Nonetheless, there are times wherein having a machine with an internal compressor makes sense. If you do plasma cutting outdoors or in the field, you most probably don’t prefer lugging an additional machine along and having to hook it up to your power source with the plasma cutter. And if you’re not cutting anything thicker than 1/4”, you should be fine.