Plasma Torch Consumables
With time and use of the plasma cutting system, the consumables of the plasma torch undergo wear resulting in diminished accuracy and quality of the finished parts. Signs such as the build-up of dross at the bottom, distortion of the edges and increased edge bevel are indications that the consumables require changing. Typically, when any of these problems occur, the operator simply replaces the entire set of consumables i.e. the nozzle, the shield cap and the electrode instead of checking each individual component separately and determining what requires replacement. This results in an overall increase in the operation and production cost and also the excessive usage of consumables.
The cost of cnc consumables can be minimised by recognising the wear in the consumables and changing them only if definitely required. Some of the signs of consumable wear requiring replacement are:
Inner Retaining Cap
The inner retaining cap helps to circulate the coolant outside the nozzle and distribute the gas to the shield cap via the holes present in the insulator ring. The inner retaining ring is not affected by the plasma arc and can last up to 30 electrode replacements or more and should be replaced only if the orifice is out of round, burnt, bent or if the holes in the insulator ring or copper body are blocked.
Outer Retaining Cap
The outer cap is made of brass and holds all the consumables tightly to the plasma torch head and must be replaced only if it is dented, any one of the ends are burnt, there is a build-up of slag or you find it difficult to thread the cap on to the head of the torch.
The shield cap helps to constrict the shielding gas and provides additional cooling and an enhanced cut edge. The shield cap is not usually affected by the plasma arc; however, since it is close to the workpiece, it can be damaged due to pierces too close to the plate and torch crashes. The shield cap is vital for edge quality and if it becomes out of round, bent or burnt, it must be replaced. Any slag build-up on the shield cap can be removed with the help of an abrasive hand pad. You must inspect the O-rings to ensure that there are no cracks, tears and nicks and ensure that they are lubricated well using the lubrication recommended by the manufacturer.
The torch has a copper nozzle which constricts the plasma arc through the orifice and when the nozzle is new, the orifice is perfectly round and has a sharply defined edge, which is extremely important for good cut quality. When the orifice of the nozzle becomes out of round either on the inner or outer bore, you must replace the nozzle. If you notice any black marks on the nozzle, these are swirl marks usually caused by the starting of the arc but does not require the replacement of the nozzle.
The swirl ring in the plasma torch is usually made of a tough material such as ceramic or Vespel and is not affected by the plasma arc. The swirl ring acts as an insulator between the nozzle and the electrode and also helps to swirl the plasma in order to produce precise cuts. The holes in the nozzle must be dirt and debris-free, and if you notice any chipping or cracking in the nozzle, you must replace it.
There are several factors that affect the life of the plasma torch consumables and since the plasma cutter is used in different conditions and every application is different, it is difficult to really determine the number of pierces each component will produce. A better way to determine if the consumable needs replacement is by visual inspection of the component and also when the quality of the cut diminishes. An important point to remember is that every part of the plasma torch plays a very important role in the life of the plasma system and in producing the highest cut quality. So, apart from just the nozzle, electrode and shield cap, it is also very important to check the swirl ring and the outer and inner retaining caps of the torch.