Your Answer : (Not Answered)

Correct Answer : B

The distance is the leg length.

A fillet weld is roughly triangular in section. Its leg length is the distance from the root of the joint to the toe of the weld along each plate; it is how fillet welds are usually specified (for example, a 6 mm fillet).

Throat thickness is the shortest distance from the root to the face of the weld, which for an equal-leg fillet is about 0.7 times the leg. Reinforcement is the excess metal above the plate surface in a butt weld, and root gap is the space between the parts before welding.

Your Answer : (Not Answered)

Correct Answer : C

Low hydrogen electrodes are baked to make welding free from moisture pick up.

Their basic (lime-fluoride) coatings absorb moisture from the air. In the arc, that water breaks down and releases hydrogen into the weld, which can cause hydrogen cracking, the very problem these electrodes are meant to prevent. Baking (typically at a few hundred degrees) drives off the moisture, and the electrodes are then kept in a holding oven until use.

Baking does not set the weld's strength, prevent arc blow (a magnetic effect) or reduce the current needed.

Your Answer : (Not Answered)

Correct Answer : A

Metal active gas (MAG) welding uses carbon dioxide.

The word 'active' means the shielding gas takes part in the arc chemistry. Carbon dioxide, alone or mixed with argon, is the usual active gas: it is cheap and gives deep penetration on steel. Using CO₂ is also why MAG is often called CO₂ welding.

Argon and helium are inert gases, which define metal inert gas (MIG) welding, not MAG. Nitrogen is not used as a shielding gas for steel, since it causes porosity and brittleness.

Your Answer : (Not Answered)

Correct Answer : D

Helium or argon is used to act as a shielding medium.

In metal inert gas (MIG) welding, the inert gas flows from the nozzle around the arc and the molten pool, keeping out oxygen and nitrogen from the air, which would otherwise cause oxidation and porosity. Being inert, argon and helium do not react with the weld metal.

MIG welding uses no flux; the gas does the job flux does in stick welding. Any cooling is incidental, and the electrode wire is consumed rather than protected for its own sake.

Your Answer : (Not Answered)

Correct Answer : C

Preheating is essential when welding cast iron.

Cast iron is brittle and has a high carbon content. If the weld area heats and cools quickly, the uneven contraction cracks it, and the rapid cooling forms hard, brittle white iron and martensite near the weld. Preheating the casting (often to a few hundred degrees) and cooling it slowly reduces these thermal stresses.

Some tool steels such as high speed steel are also preheated, but cast iron is the standard case where preheating is essential. Stainless steel and German silver (a copper-nickel-zinc alloy) are normally joined without it.

Your Answer : (Not Answered)

Correct Answer : D

Copper is used because it is a good conductor of heat.

The bit of a soldering iron must take heat from the heater (or flame) and pass it quickly to the joint, so that the solder melts and flows. Copper is one of the best thermal conductors among common metals, and solder wets it easily, which is why the bit is made of copper.

Weight and thermal expansion are not reasons for choosing it, and a bad conductor of heat would be useless for a soldering bit.

Your Answer : (Not Answered)

Correct Answer : C

The principal materials of solder are tin and lead.

Traditional soft solder is a tin-lead alloy, typically 60/40 or 63/37 tin to lead, which melts at about 183 °C to 190 °C, low enough to join electrical connections and sheet metal without melting the parts. Lead-free solders now replace the lead with small amounts of copper, silver or bismuth, but tin remains the main metal.

Copper is the metal usually being soldered, not the solder, and zinc-lead and tin-copper pairs are not the classic soldering alloy.

Your Answer : (Not Answered)

Correct Answer : A

The arc length should be about equal to the diameter of the electrode (d).

A normal arc is roughly as long as the core wire of the electrode is thick; with a 3.15 mm electrode, for example, the arc should be about 3 mm. At that length the arc is stable, the metal transfers cleanly and the shielding from the coating is effective.

An arc of 1.5d, 2d or 3d is a long arc: the voltage rises, the arc wanders, spatter increases, penetration falls and air reaches the molten metal, giving porosity. So the longer options are wrong.

Your Answer : (Not Answered)

Correct Answer : B

The keyed answer is welding with light coated electrodes.

With straight polarity the electrode is negative and the work is positive, so more of the arc heat goes into the work and the electrode melts more slowly. In the trade-school convention this paper follows, bare and lightly coated electrodes are run on straight polarity, while heavy coatings are paired with reverse polarity.

Heavy and super heavy coated electrodes, and sheet metal work where deep penetration would burn through, are the cases the convention assigns to the other arrangement. Polarity in practice depends on the electrode class and the maker's data sheet, so this item is a textbook rule rather than a universal one.

Your Answer : (Not Answered)

Correct Answer : A

The three elements are current, voltage and speed of travel.

These are the three variables in the heat input of an arc weld, the energy delivered per unit length of weld:

\[ \text{heat input} = \frac{V \times I}{\text{travel speed}} \]

Too much heat input burns through or distorts the work; too little gives poor fusion. Controlling current, voltage and travel speed controls the weld.

Arc length is not a separate element: the arc voltage rises and falls with the arc length, so the two describe the same variable. Every option that lists arc length alongside voltage, or in place of one of the three, is therefore wrong.

Your Answer : (Not Answered)

Correct Answer : C

Spot welding is used on a lap joint.

In spot welding two copper electrodes squeeze the overlapping sheets and pass a heavy current through them; the weld nugget forms where the sheets touch, between the electrodes. The sheets must overlap so that the current passes through both, which is a lap joint, as in car body panels.

In butt, T and corner joints the parts do not overlap face to face, so there is nowhere for the electrodes to clamp both sheets together.

Your Answer : (Not Answered)

Correct Answer : A

Projection welding is a multi-spot welding process.

Small projections are pressed into one of the parts beforehand. When the electrodes clamp the parts and the current flows, it concentrates at the projections, so several spot welds form at once, in a single operation.

Cross-wire welding of mesh is one use of the same principle, with the wires themselves acting as projections, but it is an application, not a description of the process. Continuous spot welding describes seam welding, and making cantilevers is not what the process is for.

Your Answer : (Not Answered)

Correct Answer : C

The one that is not a type of resistance welding is pressure welding.

Pressure welding is the broad family of processes that join metal by applying pressure, with or without heat. Resistance welding is one member of that family, not the other way round, so pressure welding is not a resistance welding process.

Spot welding, butt welding and percussion welding are all genuine resistance processes: in each, the heat comes from passing a heavy current through the parts at the joint, with pressure applied to complete the weld.

Your Answer : (Not Answered)

Correct Answer : D

The voltage does not depend on the length of weld.

In resistance welding the voltage only has to drive the welding current through the resistance at the joint. That resistance is set by the composition of the metal (its resistivity), the area of contact the current passes through, and the thickness of the parts being joined.

The overall length of a weld is made up by making more spots or running the seam further; each spot or section is welded under the same conditions, so the length does not change the voltage required. Composition, area and thickness all do, which is why they are wrong answers here.

Your Answer : (Not Answered)

Correct Answer : A

Railway rails are widely joined by thermit welding.

Thermit welding needs no electricity: a mixture of aluminium powder and iron oxide is ignited in a crucible above the joint, and the reaction produces molten steel that runs into a mould round the rail ends. The equipment is portable, which suits welding rails on site to make long welded track without joints.

Ultrasonic welding is for thin sheets and foils, explosive welding for cladding plates, and percussion welding for small parts such as wires; none is used to join rails in the field.

Your Answer : (Not Answered)

Correct Answer : C

Electroslag welding is performed in the vertical position.

Electroslag welding joins thick plates in a single pass. The plates stand on edge with a gap between them, and water-cooled copper shoes close the gap on each side. A pool of molten slag, kept hot by the current passing through it, melts the electrode wire and the plate edges, and the weld builds upwards as the shoes move up the joint.

The molten slag and metal would run away in flat, horizontal or overhead positions, so the process only works vertically.

Your Answer : (Not Answered)

Correct Answer : D

Heat comes from a chemical reaction in thermit welding.

Thermit welding uses a mixture of aluminium powder and iron oxide. Once ignited, the aluminium reduces the iron oxide in a strongly exothermic reaction, producing molten iron at well above 2,500 °C, which runs into a mould around the joint. It is widely used for joining railway rails.

The other processes get their heat physically, not chemically: resistance welding from the electrical resistance of the joint to a heavy current, friction welding from rubbing the parts together under pressure, and tungsten arc welding from an electric arc.

Your Answer : (Not Answered)

Correct Answer : D

The effect is contamination in the weld.

In TIG welding the tungsten electrode should never melt or touch the pool. If the tip melts or dips in, particles of tungsten are left in the weld metal as tungsten inclusions. These are foreign, very hard particles that show up on radiographs and weaken the joint, so the contaminated area is normally ground out.

A melting electrode destabilises rather than stabilises the arc. Cracks and lack of fusion have other causes, such as cooling stresses and too little heat.

Your Answer : (Not Answered)

Correct Answer : B

Incomplete fusion is caused by very low current.

With too little current the arc does not supply enough heat to melt the edges of the parent metal properly. The weld metal then lies on the surface or against the side walls without fusing into them, leaving unfused regions that weaken the joint.

Very high current tends to cause undercut, burn-through and spatter rather than lack of fusion. A wide bead is not in itself a cause. Since low current is a recognised cause, 'None of the above' is wrong.

Your Answer : (Not Answered)

Correct Answer : B

A guided bend test determines ductility.

A strip cut across the weld is bent round a former of set radius, usually through 180°, with the weld at the bend. The outer surface is stretched heavily; if the weld and the heat-affected zone can bend without cracking or opening up, they have adequate ductility and soundness. Face, root and side bend tests check different surfaces.

Tensile strength and percentage of elongation are measured in a tensile test, and impact value in a Charpy or Izod notched-bar test.