Acceptable vs. non-acceptable consumable wear - the electrode
Following a recent post on consumables (Controlling the cost of consumables) we had a request to post pictures so you could see what acceptable versus non-acceptable consumables look like. We'll start today with the electrode and continue on in the coming weeks with the other critical consumables.
The electrode provides power to the plasma arc and conducts high voltage energy during the starting sequence, so it handles a lot of heat and has to be precisely manufactured to ensure it has an excellent thermal and electrical connection.
As mentioned in our Controlling the cost of consumables post, you'll want to regularly measure your electrode for wear by looking at the hafnium emitter found in the very center. The photo below shows a brand new electrode on the left and a partially used electrode on the right. You can see the hafnium is a nice shiny, silver color on the new electrode and a blackened pit on the used electrode.
The partially used electrode has 34 15 minute cycles on it. Meaning it cut continuously for 15 minutes, stopped, re-pierced, then cut again for another 15 minutes. By the time those 34 cut cycles were finished, this electrode had the equivalent of 8.5 hours of arc-on time and had cut 6,800 linear feet of 1/2 inch thick steel. That's a lot of cutting!
Does anyone want to guess how much "wear" it has? It has 0.023 of an inch of wear because the hafnium pit depth is 0.023 of an inch deeper than the new electrode. This electrode is only half consumed since our standard all-copper electrodes can wear to a pit depth of 0.040 to 0.045 of an inch. If you go much deeper than that, you'll experience catastrophic failure which isn't pretty as you can see below.
Not only is catastrophic failure ugly, it is expensive! Instead of simply replacing an electrode, this entire consumable set (and maybe even the torch) will have to be scrapped. After a while, you can pretty much tell how worn an electrode is just by looking at it. But, if you want a more precise way to measure wear, Hypertherm does sell a dial indicator to accurately measure wear. The photo below shows the indicator with the partially used electrode on it.
As a reminder, the 0.040 recommended pit depth is for our standard all-copper electrodes. If you are using a silver electrode you can actually go to 0.080 of an inch, which is twice the pit depth of a standard electrode.