Plasma cutting has become a technique of choice for many metal fabricators, even for cutting metals of extreme thickness because of the precision and speed of the cutting process. Today, high-density cutting systems have the ability to produce high-tolerance, accurate cuts effectively and quickly. However, the entire process hinges on one important factor i.e. piercing through.
At the Torch Nozzle
It is possible to reduce blowback by using a more pointed torch-tip angle. You can avoid the spatter from hitting the surface of the torch by using a more slender and longer front end on the plasma torch.
You can have plasma torches fitted with shield cups that are water cooled. So, when the spatter touches the cool torch, instead of attaching itself to the torch, it quickly solidifies. This slag can be flaked off easily. Keep the torch as cool as possible, as the slag tends to stick to the shield cup if the torch is hot.
Today, many integrated plasma cutting systems have an extra nozzle near the plasma torch which blows oxygen while piercing. This causes the molten material to be blown away from the torch.
A piercing strategy that is not effective can lead to a stalled or stagnated pierce which results in the collection of a molten pool of metal beneath the pierce hole. This molten metal is heated and reheated by the plasma energy but the heat does not affect the non-melted metal underneath.
This can be overcome by using the process of a stationary pierce from a power source with enough energy. You may use a long travel pierce; however, sometimes even this may not be helpful.
In such cases, the plasma cutting system can execute a double pierce. The metal thickness is pierced partway by the plasma arc, the arc stops, leaving behind a hole. The spatter is then scraped off from the surface of the plate and the plasma torch is repositioned in such a way that the plasma arc pierces around 0.25 inches from the pierce hole’s side wall. This allows the gases and the molten metal to be blown down and up the side wall of the pierce hole, till the plasma arc penetrates the bottom of the plate.
Piercing is a very crucial element of plasma cutting and an operator must evaluate all factors before deciding the most efficient and cost-effective piercing strategy.