NCCER Welding flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Acetylene Working Pressure Limit

Acetylene in hoses, torches, and piping must never exceed 15 psig. Above that pressure free acetylene can decompose violently even without oxygen, so cylinders are manifolded rather than over-pressurized.

Oxygen Cylinder Valve Position

Oxygen cylinder valves are opened fully when in use so the valve seats against the stem packing and seals around the stem. Acetylene valves are opened no more than one and a half turns.

Flashback Arrestor Placement

Flashback arrestors are installed at the regulator outlet and at the torch inlet. They stop a flame traveling backward through the hose after a backfire and protect the cylinders from ignition.

Cylinder Storage Separation

Oxygen and fuel-gas cylinders stored in the same area must be separated by at least 20 ft, or by a noncombustible barrier at least 5 ft high with a half-hour fire rating.

SMAW Filter Shade, 1/8 inch

For shielded metal arc welding with electrodes from 1/32 to 5/32 in, the OSHA minimum protective shade is 7 and the typical shade is 10; larger electrodes require darker lenses.

Work Lead Clamp Location

The work lead or ground clamp attaches directly to the workpiece or to the table holding it. Never ground through building steel, chains, slings, or gas cylinders, which can overheat or arc.

Neutral Flame

A neutral oxyfuel flame burns one part oxygen to one part acetylene and shows a single sharply defined inner cone. It is used for cutting steel and heating most carbon steels.

Oxyacetylene Flame Temperature

A neutral oxyacetylene flame reaches about 5,580 degrees Fahrenheit, or 3,080 degrees Celsius. This is the hottest common fuel-gas flame; oxypropane and oxyhydrogen flames are cooler and preheat more slowly.

Carburizing Flame

A carburizing or reducing flame has excess acetylene and shows three zones: the inner cone, a feathery intermediate zone, and an outer envelope. A long feather indicates excess acetylene; it suits brazing.

Cutting Preheat Temperature

Steel is preheated to about 1,400 to 1,600 degrees Fahrenheit, a dull cherry red, before the cutting oxygen is opened. The oxygen jet then oxidizes the iron and blows slag through the kerf.

One-Seventh Withdrawal Rule

Do not draw more than about one-seventh of an acetylene cylinder's contents in one hour. Faster withdrawal pulls acetone out with the gas, changing the flame and damaging the cylinder.

Backfire Versus Flashback

A backfire is a momentary burn-back at the torch tip, marked by a pop or whistle, that usually goes out or relights. A flashback travels back through the hose toward the regulator.

V-Groove Bevel Angle

Each plate is beveled 30 to 37.5 degrees, producing an included groove angle of 60 to 75 degrees. A typical root face is 1/16 in and root opening is 1/16 to 1/8 in.

Joint Cleaning Zone

Before welding, the joint and at least 1 in (25 mm) on each side must be free of mill scale, rust, oil, paint, and moisture, because these contaminants cause porosity and incomplete fusion.

Undercut Causes

Undercut is a groove melted into the base metal at the weld toe that is left unfilled. Causes are excessive current, a long arc, wrong electrode angle, or too fast travel.

Fillet Weld Gauge

A fillet weld gauge measures leg length and throat of a fillet weld for comparison with the drawing. Leg length is measured directly; theoretical throat is 0.707 times the leg.

Backstep Welding

Backstep welding deposits short beads in the direction opposite to overall weld progress so each new bead overlaps a hot one. It reduces distortion and is common on thin plate.

Porosity Causes

Porosity is gas trapped in the solidified weld as rounded voids. Common causes are moisture, oil, paint, and rust in the joint, a long arc, wet electrodes, or lost shielding gas.

E7018 Classification

E means arc-welding electrode, 70 means 70,000 psi minimum tensile strength, 1 means all positions, and 8 means a low-hydrogen iron-powder coating usable on AC or DCEP.

E6010 Polarity

E6010 is a cellulosic-sodium electrode with a deep digging arc used for root passes in pipe. It runs only on direct current electrode positive (DCEP, reverse polarity), never AC.

Arc Blow Remedies

Arc blow is arc deflection caused by magnetic forces and is common with DC near the work connection. Remedies include moving the work clamp, shortening the arc, reducing current, and switching to AC.

Low-Hydrogen Holding Oven

E7018 and other low-hydrogen electrodes are kept in a holding oven at 250 to 300 degrees Fahrenheit and are limited to about four hours of air exposure before redrying is required.

DCEP Versus DCEN

With direct current electrode positive, heat concentrates at the workpiece for deep penetration. Electrode negative shifts heat to the electrode, giving shallower penetration and a higher deposition rate.

Weave Bead Width Limit

A weave bead should not exceed about 2.5 to 3 times the electrode diameter. Wider weaving loses penetration at the bead edges, traps slag, and increases heat input and distortion.

Duty Cycle Meaning

Duty cycle is the percentage of any 10-minute period a machine can weld at its rated output. A 60 percent duty cycle at 200 amps allows 6 minutes welding and 4 minutes cooling.

GMAW Voltage Controls

In gas metal arc welding with a constant-voltage supply, voltage sets arc length while wire-feed speed sets current. Too little voltage stubs the wire; too much causes spatter and lack of fusion.

Spray Transfer Requirement

Spray transfer needs an argon-rich shielding gas of at least 80 percent argon and current above the transition value. It gives high deposition with little spatter but is limited to flat and horizontal.

GTAW Aluminum Polarity

Aluminum is welded with alternating current so the electrode-positive half cycle breaks up the refractory aluminum oxide, while the electrode-negative half limits tungsten heat and provides penetration.

E71T-11 Electrode

E71T-11 is a self-shielded flux-cored electrode with 70,000 psi minimum tensile strength that runs in all positions without external shielding gas, so it tolerates wind outdoors.

Tungsten Grind Direction

Grind the tungsten electrode longitudinally, parallel to its axis, with a taper two to two and a half times the electrode diameter. Radial grinding grooves make the arc wander and split.

GMAW Contact Tip Distance

Contact-tip-to-work distance for gas metal arc welding is normally 3/8 to 1/2 in. Increasing it reduces welding current and raises the chance of lack of fusion and an unstable arc.

GTAW DCEN Heat Split

With direct current electrode negative, roughly two-thirds of the arc heat enters the workpiece, giving deep penetration and letting a small-diameter tungsten electrode carry high current.