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It’s hard to imagine a world without plasma cutters. Industrial construction, automotive, ship building, and metal fabrication industries rely on plasma cutting to work with aluminum, brass, copper, and steel. You can’t possibly think of automotive manufacturing or repair without plasma cutting. Huge beams and metal sheets used in construction are cut using, you guessed it, plasma cutters.
Plasma cutters can look like giant machines used chiefly in large metal fabrication industries for precise cuts. They also come as compact devices with handheld torches seen primarily in workshops (1,2).
Understanding Plasma – The Fourth State of Matter
Before we delve into plasma cutting, we have to first ask what plasma is. A lot of people have vague conceptions of what plasma is. Plasma is simply ionized gas. Ordinary gas is composed of molecules. For example, oxygen gas is composed of an oxygen gas molecule, which is just two oxygen atoms that share their outermost electrons. To form plasma, a gas molecule should be heated to a point where the molecules separate and the individual atoms lose their outermost electrons. Remember that electrons are negatively charged particles. So when an atom loses its electrons, it becomes positively charged. Thus, plasma is like a collection of negative charged and positively charged particles.
Because plasma is essentially a soup of ions, it’s able to conduct electricity. This electrical conductivity of plasma is a useful property in plasma cutting. What your plasma cutter does is use this conductivity to form an arc between the plasma torch and the metal piece or sheet you want to cut. This makes plasma cutting faster and more efficient than oxyfuel cutting.
What a Plasma Cutter Does
A plasma cutting system works with compressed gas fed through a hose and into a small channel in the torch. Inside the plasma torch is a negatively charged electrode. When this electrode touches the workpiece, it creates an electrical circuit and a spark is generated. This spark heats the stream of gas being ejected from the torch to 40,000 degrees Fahrenheit, high enough to turn gas into plasma. This stream of plasma moves at anywhere around 20,000 feet per second. This jet of plasma rapidly melts and cuts through a metal plate or sheet.
Because hot molten metal tends to react with oxygen in the air, the area being cut needs to be protected from oxidation. This is why plasma cutting torches have two channels. One channel streams compressed gas, and the other channel feeds shielding gas, which surrounds the cutting area to provide shielding from ambient air.
Types of Plasma Cutters
Plasma cutters come in different brands, models, and sizes. The most common ones are those you see in workshops. Nonetheless, the much less talked about industrial giants are automated machines with robotic arms.
Handheld Plasma Systems
Handheld plasma cutters are the ones you see in most workshops or fab shops. Handheld units are used not only by handymen but also by hobbyists and professionals. They are compact and portable, factors that allow them to be used in a number of situations. A typical manual plasma cutter has an electrode and a nozzle inside the plasma torch. The torch has a trigger, which you press to allow the current, plasma gas, and shielding gas to flow. As the flowing compressed air builds up, it forces the electrode and the nozzle apart. An electrical spark then turns the jet of compressed air into plasma.
You need a plasma arc between the torch and the workpiece before you can start cutting. Although there are different ways to strike an arc, a common way is to touch the tip of the torch to the workpiece. The arc creates a current flow between the electrode and the metal workpiece. The current and airflow remain flowing until you stop pressing the trigger. Some plasma cutters use a high frequency circuit to start the arc.
High Definition Precision Plasma Cutting
The main difference between a conventional and a precision plasma cutting system is that the former uses shop air or ordinary air, while the latter uses different types of gases. Precision plasma units may use nitrogen, oxygen, or a mixture of hydrogen, argon, and nitrogen. Whereas a conventional plasma cutter has an amperage of 12-20 kilo amps per square inch, a precision plasma cutter operates at about 40-50 kilo amps per square inch. Better gas mixture and higher amperage allow for high definition cuts, which are necessary for industrial metal cutting.
The anatomy of a precision plasma torch differs from that of a conventional plasma torch. In the former, a swirl ring separates the nozzle from the electrode, so these parts don’t touch the way they do in a conventional plasma torch. The swirl ring has small vent holes that create a swirling jet of plasma. The design of high definition plasma cutting systems allows for the best cuts possible for any metal cutting system. They also have more complex torches designed for better control of the arc.
Plasma Cutter Reviews
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Conclusion
Although plasma cutters come in different designs, sizes, and prices, they all work the same way. They utilize ionized gas to cut conductive metals that can’t be cut in any other way. From its nascence at Union Carbide’s welding lab, the plasma cutter has evolved in many ways. Today’s plasma cutters can be guided by computers to produce accurate cuts with no dross and minimal material wastage. Technological advancements have made these machines so affordable and convenient that a handyman can use one to cut steel plates in his garage.
