LINCOLN Electric has looked at the factors to be considered when choosing plasma cutting technology.
Plasma cutting uses a high velocity jet of ionised gas which conducts electricity from the torch to the work piece. This process heats the workpiece to melt the material, while the gas stream blows the molten metal away to complete the severance. The most common gas type used is compressed air, which is widely available.
It can be used on any type of conductive metal such as mild steel, aluminium and stainless steel. Unlike oxyfuel cutting which works by oxidising the metal, it is not limited to ferrous metals and steel. Plasma is also faster on thinner materials, although oxyfuel shines best in heavier plate applications.
The cost of plasma cutting machines is in decline, and units are getting smaller, more portable and packed with better technology. At the same time, plasma cutting is said to be easy to use, and provide high quality cuts and faster travel speeds.
Lincoln recommends the use of plasma for occasional repair and maintenance work, higher cutting volumes, and as an alternative to mechanical saws.
When purchasing a plasma cutting machine, buyers should look at eleven factors.
The amperage and cutting ability of the machine should be chosen based on the thickness of the metal to be cut. Lower amperages will be suitable for thinner material. While smaller machines might be able to cut through any given thickness, the quality of the cut will be affected.
Amperage will also affect cutting speed. If cutting speed is a critical factor, the machine should be chosen with amperage that can handle twice the normal cutting thickness. The duty cycle is also an important factor if long or automated cuts are required. Duty cycle is the time of continuous cutting permitted before the machine overheats. The higher the duty cycle, the longer non-interrupted cuts can be.
Many plasma cutters use high frequency starting to conduct electricity through the air to create an arc. However, high frequency can affect computers or office equipment in the area. Alternatives to high frequency starting include lift arc or dual winding.
Like most cutting technologies, plasma cutting torches have consumables, which are items which wear away with use and require replacements. The lower the number of consumable parts, the less replacement needed and the more cost savings. Also, the life of consumables will contribute to costs or savings.
Buyers should test the machines by making test cuts on a number of units. Cut the same thickness of material at the same rate of speed to determine the one with the best quality. Cuts should be compared by examining the plate for dross on the bottom side and the angle of the gap left by the cut. Plasma cutters with a tight focused arc concentrate more cutting power on the work piece.
Plasma cutters should also provide a quick, positive transfer from pilot to cutting at a large transfer height. To test this characteristic, use the machine to cut expanded metal or gratings.
Working visibility is also important when choosing machines. Visibility is determined by the geometry of the torch. A smaller, compact torch or an extended nozzle will allow a better view of where the cutting is happening.
If the machine will need to be moved around for a variety of cutting applications, portability is key factor. In such cases, the unit needs to be portable, lightweight and have a means of transportation such as an undercarriage or shoulder strap. Machines with small footprints might also be desirable depending on the floor space available.
Units should offer storage for the work cable, torch and consumables, so these components do not risk getting damaged or lost during transport.
If the machine is going to be used or moved around, ruggedness is another important aspect to look for. Ruggedness determines durability and protection for parts. Controls should be protected, as should fittings, torch connections and other integral parts. Filters should be installed on the air intake to remove oil from compressed air. Oil can cause arcing and reduce cutting performance.
The units should also be comfortable, ergonomic and easy to use. Having a user-friendly control panel will allow for a shallower learning curve.
Additionally, the machines should have safety features. For example, nozzle-in-place safety sensors ensure the cutter will not start an arc unless the nozzle is in place. This prevents accidental exposure to high voltages. Pre-flow sequence is another safety feature, which provides an advanced warning before the arc starts.
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