When using a plasma cutting machine, the plasma torch and the consumables can become very hot as the temperature of the plasma arc can go up to 20,000°F. Hence, water cooling systems are used to cool down the plasma cutter and its parts. The water cooling system consists of coolant and water, cooling hoses, a pump and a heat exchanger.
If the plasma cutting system becomes overheated often, over time the torch and the consumables will wear out quickly and eventually the torch and the leads will burn out. If you do not attend to the problem, you may have to replace the pump and the motor too.
The Torch Cooling System
Typically the PAC cooling system comprises the following elements: plasma torch, coolant, pump, motor, cooling lines, filter, flow switch, reservoir and heat exchanger. In this two-part article, we will look at the functions of these various components.
Plasma Cutting Torch
The plasma torch operates at very high temperatures and gets overheated. It requires water cooling to keep the torch as well as the parts from overheating and burning out. The plasma arc is generated by the copper electrode which is very close to the heat and hence requires most cooling.
Common Torch Problems
The torch can get blocked by debris and particles over time. The melted copper from the electrode can block the tiny holes and cut off the water flow. If the water tube is damaged, bent or not fitted into the torch correctly, the flow of the cooling water is reduced. If the O-ring sealing surface or the O-rings are damaged, this can cause the cooling fluid to leak. The coolant may leak out of the tubes and fittings which can result in low tank levels and hence reduced cooling.
Usually, the coolant used to cool the plasma torch is a mixture of propylene or ethylene glycol and de-ionized water that is used to depress the freezing point. Some torches also use only plain de-ionized water. De-ionized water is used as it does not contain conductive ions that cause problems in the cutting system.
Common Coolant Problems
The coolant can become contaminated with regular usage of the torch by bits of wire, hose, dirt, rust, copper from the failed consumables, etc. The presence of these contaminants reduces the cooling efficiency of the coolant and also reduces the rate of flow. If this happens, you may need to flush the system and also replace the filter and the coolant.
Also, if the conductivity of the torch coolant is very high, electricity may get conducted through the cooling water in the plasma torch. This may result in hard starting of the arc when the plasma torch is starting an arc between the copper nozzle and the electrode.
It is recommended that you use OEM coolants and check the coolant’s conductivity periodically.
Usually, in a plasma cutting system, the pump and the motor are directly connected. Typically, plasma systems use rotary vane or carbon vane pumps as they are quite robust and simple.
Common Pump Problems
The carbon vanes in the pump wear out over time with normal use due to heat and friction. You can reduce this wear and tear by making necessary adjustments to the pump.
The bearings may wear out over time, which may cause excessive heat and noise and ultimately lead to failure of the pump. The material contained in the pump vanes can wear out and finally the pump will not be able to build up any pressure. These worn parts can be replaced by reconditioning the pump at the factory or the pump itself may require replacement.
The small screen filter present in most filter pumps may get clogged with debris and cause a restriction in the flow.
The problem of overheating of the plasma torch and hence the downtime and expenditure caused by it can be avoided if you understand the plasma cutting machine and its parts properly thereby being able to troubleshoot whenever problems occur. Problems can also be avoided through periodical preventive maintenance. In the second part of this article, we will look at other components that comprise the cooling system in a plasma cutting system.