The shield in the plasma torch has 2 main functions i.e. during piercing and if there is any accidental contact with the workpiece, the shield protects the nozzle from double arcing. The second function is that the shield directs the gas flow so that it controls the plasma arc resulting in a squarer cut and also helps to cool the nozzle.
Why Does the Shield Fail?
The shield is quite robust and has quite a long life. However, the main reason for the failure of the shield is if the piercing is done very close to the workpiece. So, it is extremely important to read the instruction manual and follow the settings for pierce height and pierce delay times as recommended.
Also, ensure that you check the THC or torch height control to ensure that the IHS or initial height sensing is working properly. Another reason for shield failure is the overuse of the electrode until it completely fails. Using the electrode till it fails can cause the torch and the consumables to be damaged irreparably.
The two important aspects of the shield are the orifices – the main and the bleed orifices. The main orifice in the shield must be centred perfectly to the nozzle’s main orifice, while the bleed orifice controls the squareness of the cut edge.
When you inspect the shield, ensure that the main orifice is perfectly round and has sharp edges and the bleed orifices should not be clogged and be free of any debris or metal. If the shield has any metal accumulated, it can still be used. You must first remove the accumulated metal as much as possible. Next, examine the main orifice and check it from inside and outside. Then check the bleed orifices. If the bleed orifices are not clogged with debris and the shield orifice is still round in shape, you can continue using the shield.
Tips to Minimise Amount of Metal on the Shield
Here are some tips that can help to reduce the amount of metal that sticks to the shield. First, inspect the shield and then polish it with a rough cleaning pad before putting it back onto the plasma torch. When new, the shield will not accumulate much of the metal as compared to one that has been used for long and contains spatter on it.
You can spray a MIG welding anti-spatter spray that is water-based and not oil or silicone-based sprays on the shield front. It is ideal to use the spray on the shield once it is reinstalled on the plasma torch so that the spray is not rubbed off while you assemble the torch.
By using these tips and tricks, you can ensure that the life of the shield of the plasma torch is prolonged and it can be used for a long time and not replaced frequently.