Check whether your shielding actually protects titanium, tantalum, niobium, or nickel alloys. The calculator works out the cup's gas flow regime, the oxygen and moisture reaching the weld, how far behind the arc the metal stays hot enough to contaminate, and the weld color you should expect.
A #8 cup is 12.7 mm (1/2 in) ID; #12 is 19 mm. 1 CFH = 0.472 L/min.
Net heat input includes arc efficiency (e.g. GTAW: 0.65 × V × I / v). Need it? Use the heat input calculator.
Re < 2000: laminar, coherent gas column. Above 2300: turbulent, pulls in air.
Titanium, tantalum, and niobium soak up oxygen, nitrogen, and hydrogen whenever they're hot, and that pickup embrittles the weld long before it looks burnt. Protection fails in two ways: air gets into the gas shield, or hot metal leaves the shield too soon.
Doubling the flow to 30 L/min pushes Re to about 3700 and makes shielding worse, not better.
A laminar gas column leaves the cup as a coherent slug that pushes air aside. Once the Reynolds number passes about 2300, the column's edge breaks into eddies that pull surrounding air inward, the same way a fast jet entrains its surroundings. A gas lens straightens the flow with fine screens, so the column stays coherent at higher flows and longer standoffs.
Helium has about one tenth the density of argon, so at the same flow its Reynolds number is roughly ten times lower and it never goes turbulent. But it is also far lighter than air: in a down-hand weld it floats away from the joint, and a draft pushes it aside much more easily. That's why helium-rich mixes need 2-3 times the argon flow. The tool weights this with a Richardson number (buoyancy against jet momentum).
| Color | Typical meaning for titanium |
|---|---|
| Bright silver | Well protected |
| Light straw | Thin oxide; usually acceptable |
| Dark straw / gold | Remove and re-inspect per spec |
| Blue / violet | Contaminated; reject on most specs |
| Gray | Heavily contaminated, embrittled |
| White / flaky | Thick oxide and alpha case, brittle |
Color comes from an oxide film whose thickness rises with temperature and with oxygen in the gas. Acceptance limits vary: check AWS D17.1, AWS G2.4, or your customer specification. Bright color doesn't prove the absence of contamination, so hardness or bend tests are still used to qualify procedures.
The entrainment model is a semi-empirical index built from jet-mixing physics and calibrated to typical shop experience. It isn't a CFD solution. It ignores arc-driven plasma jets, joint geometry, torch angle, hose permeation, and leaks in fittings. Root-side (back-purge) protection is not modeled; reactive-metal welds need it as much as the face. For production, measure oxygen at the weld with an analyzer and confirm the result on test coupons.
Jeffrium designs custom trailing shields and gas-delivery systems, optimizes chamber purge and oxygen monitoring, and builds oxidation models around your parts and specifications, so reactive-metal welds come out bright and pass inspection the first time.