Kay & Associates Brazing Quiz

For this month’s column we would like to challenge our readers to have some fun with a brazing quiz. If you would like to try our Brazing Quiz, please e-mail your responses to Quiz@vacaero.com listing the numbers 1 through 20 and your correct “letter” response next to each number. The responders who answer all questions correctly will be announced in the June issue of VAC AERO’s Vacuum Heat Treating Process & Technology Newsletter.

• Reprinted with permission from the Welding Journal, April issue, American Welding Society, Miami, Fla.
• Please make sure the words “Brazing Quiz” are placed in the “Subject” line.
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• Information provided in this Quiz is intended for training and educational purposes only, and is subject to the same conditions specified in our PRIVACY POLICY.

1. Which one of the following temperatures is the actual, correct, exact temperature that officially separates brazing from soldering?

a. 800°F
b. 840°F
c. 450°C

2. Which one of the following is most important for optimal brazing results?

a. gravity
b. capillary attraction
c. RMS surface roughness

3. BAg-1 can be safely used in a vacuum furnace if:

a. vacuum level is limited to about 10e-1 max.
b. a strong back-fill pressure of argon is used
c. should never be used in a vacuum furnace

4. When Ni-brazing, in order to prevent the formation of “continuous” non-ductile centerline eutectics in the joint, the optimal joint clearance range should be:

a. 0.000” to 0.003” (0.000 to 0.075 mm)
b. 0.004” to 0.007” (0.10 to 0.15 mm)
c. tight clearance is not actually required, since a good diffusion cycle will eliminate any continuous centerline eutectics that may have formed.

5. The first practical nickel-based brazing filler metal (BFM) was developed shortly after WWII by evaluating which one of the following materials as a potential applicant for high-temp brazing?

a. A thermal spray powder
b. Oak-Ridge lab metallurgists evaluated “boronizing” a special Inconel alloy.
c. It was discovered by accident when a nickel-based super-alloy began to sag due to eutectic-melting when in direct contact with a graphite plate during heat-treating.

6. When did the practice of brazing first begin?

a. First used by the Vikings to produce specialized multi-pointed weapons.
b. Process was developed by British ship-builders during Napoleonic wars.
c. Brazing was known and used by the ancient Egyptians.

7. The in-service re-melt temperature of some nickel-based BFM’s can be several hundred degrees higher than the original brazing temperature because of which specific metallic element that is part of the chemistry of the BFM?

a. Silicon
b. Chromium
c. Boron

8. When properly made, which is stronger, a welded joint or a brazed joint?

a. A welded joint should always be stronger than a brazed joint.
b. The strengths should be equal, because a properly made weldment or brazement should always fail in the base-metal, outside the joint.
c. Since brazing does not melt the base-metal, a brazed joint should always be stronger than a weldment made on the same base metal.

9. Brazing fluxes help to prevent oxidation of the base-metals on which it is coated. Which flux can handle higher temperatures, and for a longer time, and also be potentially more effective on refractory metals?

a. White flux (which meets AMS 3410 requirements)
b. Black flux (which meets AMS 3411 requirements)

10. When brazing pure-copper to pure-copper using the BCuP family of BFMs, is a brazing flux usually required?

a. Yes.
b. No

11. Brazing aluminum base-metals together using the BAlSi class of BFMs can be easily done in a standard high-temp vacuum furnace used by many companies for nickel-brazing aerospace components, as long as the level of vacuum is maintained at 10e-5 or harder (i.e., at 10e-6, -7, etc.).

a. True
b. False

12. Because many people feel that a braze-fillet contributes significantly to the overall strength of a brazed joint, it is therefore wise to specify a minimum fillet size on engineering drawings and in process specs/procedures, so that brazing personnel and engineers will know how big a braze fillet they should produce.

a. True
b. False

13. In a similar vein, it is usually a good recommendation to build up a large braze-fillet in the corner of two parts being brazed together at right angles (in which there is a 90-degree corner at that joint edge), since the large fillet is an excellent way to help spread the stress that would otherwise try to concentrate in that sharp corner.

a. True
b False

14. When vacuum brazing, which is more important?

a. Level of vacuum in the furnace
b. The leak-up rate of the vacuum chamber

15. When brazing with a torch, the adjustment of the torch flame is important. For most applications, it is recommended to adjust the flame so that it is:

a. Slightly oxidizing
b. Neutral
c. Slightly carburizing

16. When vacuum brazing a 304-type base metal it is recommended that only 304L be used rather than standard 304 material, because the 304L has far less carbon in it. This is important because:

a. With less carbon, there is much less chance of carburizing the brazed joint.
b. Carbon wants to react with the chromium in the stainless steel at elevated temps to form chrome-carbides that migrate to grain boundaries, thereby reducing the amount of chromium-oxide on the surface of the stainless to keep it corrosion resistant.
c. BFMs react adversely with carbon-containing materials, thereby preventing adequate “wetting” of the joint faying surfaces, thus causing excessive voids in the joint, and sometimes “leakers”.

17. When furnace brazing, it is often found necessary to have one or more built-in “holds” at various temperatures on the way up to brazing-temp in order to allow for thermal-equilibrium to occur in the furnace chamber. These “holds” are necessary because:

a. The heating rates used are too rapid, thus causing thinner parts to heat up faster than heavier parts in the load.
b. The intermediate holds are timed so that the total brazing cycle meets minimum cycle times for the base metals being joined.
c. At each intermediate “hold” point, metallurgical reactions are allowed to occur that cannot efficiently be completed at other temperatures.

18. When vacuum brazing, one of the terms used to describe the level of vacuum is the word “Torr”. Where does this word come from?

a. In honor of Jonathan Torrberson, a man who claimed to invent the first practical vacuum furnace back in 1819.
b. an abbreviation for “torrid”, a term describing the extreme temperatures used in a vacuum furnace when brazing.
c. Named after Evangelista Torricelli, and Italian scientist in the early 1600’s.

19. When induction-brazing a round steel bar assembly that is placed inside a circular induction coil, the “coupling distance” of the induction coil is very important. Coupling distance is:

a. the distance between the electrical junctions in the power-head of the inductor where it is connected inside the power-unit, always inversely proportional to the coil diameter.
b. the distance between the ID of the induction coil and the OD of the part being heated inside the coil.
c. the distance between the outside edge of the induction coil to the nearest piece of conductive metal in the immediate vicinity of the induction brazing unit.

20. When brazing a tube into a fitting in which the tube and fitting are made from two different kinds of metals with different coefficients of thermal expansion, it would usually be best (from a brazed-joint integrity perspective) to select those base metals so that the higher-expanding metal is:

a. the outer member (the fitting)
b. the inner member (the tube)

NEXT MONTH: Answers to these questions will be published in June’s Vacuum Heat Treating Process & Technology Newsletter. We will also be announcing the winners who answered all questions correctly.