by Phil Parker
Longer consumable life can result in significant cost savings
Today’s plasma consumables are capable of lasting longer than ever before. Unfortunately, many businesses are not enjoying the cost savings longer consumable life can bring. Here’s a look at six reasons why.
Premature or improper consumable change outs. Changing out consumables prematurely is a common cause of excessive consumable use. Sometimes users automatically pull consumables after a set number of pierces or hours. Other times they remove consumables, primarily swirl rings and the new generation of silver/hafnium electrodes, too soon. Generally, replace standard all-copper electrodes when the hafnium pit depth reaches 0.040 to 0.050 of an inch or 0.080 to 0.1 of an inch for silver/hafnium electrodes. On average, nozzle/electrode change out ratio is 1-to-1 for copper electrodes and 2-to-1 for silver. A swirl ring can last 10 to 15 nozzle/electrode change outs with proper O-ring lubrication. Insufficient lubrication can lead to damage during insertion or extraction. Too much can lead to blocked swirl passages, cut quality problems and/or improper cooling. Change shields if visibly worn or when cut quality deteriorates. Retaining caps can last for 50+ nozzle/electrode change outs.
Pierce height.Proper pierce height is critical. If too low, spatter blown back during the piercing process may penetrate the shield orifice and cause double arcing. If too high, excess pilot arcing will occur. The proper height is 1.5 to 2 times the correct torch-to-work distance during cutting.
Ramp down errors. Some plasma systems equipped with oxygen cutting capability extend consumable life by ramping gas pressures and current levels at the beginning and end of a cut. For proper ramp down at the end of a cut, the cut must end on the plate. If the arc terminates abruptly too much hafnium can eject, translating into a loss of up to 15 arc starts. When cutting holes, reduce errors by programming the CNC to eliminate the lead-out.
Gas leaks or a contaminated gas supply.
Gas supply issues are probably the most common cause of excessive consumable wear. Occasionally run a system gas leak test. If a problem is found check for restrictions in leads, leaks in leads or connections, and gas impurities stemming from leaks or the gas supply system itself.
Improper coolant flow. High-end mechanized plasma systems generally have liquid-cooled torches and consumables. Proper coolant flow is essential to proper consumable wear. Flow restrictions reduce consumable cooling, leading to excessive heat buildup and rapid erosion. For this reason, check the coolant system filter to make sure it isn’t clogged, perform a test to ensure flows are consistent with OEM specifications, and check for leaks.
Poor work cable connection. A good electrical connection is essential for proper system operation and consumable life. During the pilot arc phase of arc initiation, the arc is established between the electrode and nozzle. Normally, arc transfer occurs within 100 milliseconds. A poor connection can delay that a half second or more, risking increased consumable wear, and misfiring. In most systems, the connection is through the slats to the table ground. Too much slag on the slats will inhibit current flow. Connect the work cable from the power supply to the table ground, and attach a jumper cable from the table ground to the work piece. If not possible, then regularly remove excess slag from your slats.
Plasma cutting is an essential first operation when fabricating, but cost savings require that systems be properly operated and maintained. By doing what’s necessary to optimize consumable life, the operator is on his way to realizing those potential savings. SMT
Phil Parker is product manager, mechanized plasma, Hypertherm, Hanover, NH.