Identifying damaged consumables
Over time and with constant use, the components and consumables of a plasma cutting system naturally wear out. This results in reduced quality and precision of the produced parts. Important signs that indicate a consumable requires change is when you notice an increase in the bevel edge, edge distortions and build-up of dross at the bottom. When such problems crops up, many times the operator replaces all the consumables such as the shield cap, electrode and nozzle instead of individual components. This results in superfluous usage of consumables and increases the overall operation cost. The production cost of each finished part also increases significantly.
The torch consumables’ life are affected by many variables and it is a better option to learn to identify what is wrong with any consumable by inspecting it visually when the cut quality drops. Not only must the nozzle, shield cap and electrode be inspected, it is important to examine the swirl ring and the inner as well as the outer retaining caps also for any defects. We go into the depths of how you can identify damaged consumables at the earliest in this two part series. We kick off part one of this series with an eye on some of the key consumables.
The Outer Retaining Cap
The outer retaining cap is a brass cap that keeps all the components together onto the head of the torch. The outer cap should be replaced only if there is any damage such as burns or dents on either of the openings, slag build up, or if you face any difficulty in threading the cap onto the torch head.
The Inner Retaining Cap
The inner retaining cap has a body made of copper with an insulator ring that is placed on it. This helps in installing the inner retaining cap into the shield cap. The function of the inner retaining cap is to ensure that the coolant is circulated outside the nozzle and to ensure that the gas is distributed through the tiny holes that are present in the insulator ring to the shield cap. This component is not exposed to the plasma arc and can withstand use up to at least thirty electrode replacements.
You must replace the inner retaining cap only if the aperture is bent, burnt, out of shape, or the minute holes in the insulator ring or copper body are blocked.
The Shield Cap
The shield cap funnels the shielding gas and is used for additional nozzle cooling and improved cut edge. Though the shield cap is not exposed to the plasma arc, because it is very close to the workpiece, it is prone to damage from torch pierces and crashes that are made near the plate.
The orifice in the shield cap is critical to the edge cut quality and when the shield cap becomes bent, burnt or out of shape, it must be replaced. If there is any slag or splatter build-up on the shield cap, it can be removed by using an abrasive hand pad. Care must be taken not to use sandpaper to remove the slag.
The O-rings must be inspected regularly for any cracks, tears, nicks and the O-rings must be lubricated properly.
The nozzle that is usually made of copper directs the plasma arc through a small aperture of varying diameter. This orifice is in a perfectly rounded shape and has a sharp, defined edge when the nozzle is new. This is the most critical part of the plasma torch which results in precise and top cut quality.
When the aperture begins to go out of shape in the inner or outer bore, the nozzle must be replaced. Sometimes, you may find some light swirl marks on the inside surface of the nozzle. This is caused by the arc starting and does not warrant a nozzle replacement.
The Swirl Ring
This is usually manufactured with a material that is resistant to high temperature such as ceramic or Vespel. Hence, the swirl ring is not eroded by the plasma arc. The swirl ring insulates the nozzle and the electrode and also serves as a means to cause the swirling of the plasma gas, which is required to make precise and accurate cuts.
You must take care that the tiny holes in the swirl ring remain clean and free from any dirt or debris. If there is any cracking or chipping in the swirl ring, it must be replaced.
This is usually manufactured using copper or silver or a mix of both metals. It contains an emitter rod insert that is made of tungsten or hafnium. This emitter rod stops the electrode from burning when exposed to the high current arc.
The emitter rod is consumed for the entire duration that the plasma torch is switched on. Ultimately, it will reach a point where the plasma arc will jump to the electrode directly. This can cause a blowout and can also damage the shield cap, nozzle and eventually the head of the torch too.
Consumables play a very important role in the life and performance of a plasma cutting system. Every component plays a very vital role in producing the highest quality, precision cuts. Therefore, constant inspection, monitoring and replacement of consumables is very critical to the maintenance of your plasma cutter.