Brazing Etc 7

Question 1

How do brazing and soldering differ from fusion welding?

Answer 1

No melting of base metal occurs in brazing and soldering

Question 2

How do brazing and soldering differ from solid state welding processes?

Answer 2

Filler isn’t added in solid state welding

Question 3

What’s the technical difference between brazing and soldering?

Answer 3

In brazing the filler metal melts above 450C but in soldering it melts at 450 or below.

Question 4

Under what circumstances would brazing/soldering be preferred over welding?

Answer 4

1) if vase metals have poor weldability
2) if the parts can’t tolerate the high temps in welding
3) production rates need to be faster and less expensive than welding
4) joint areas are inaccessible for welding
5) the high strength of a welded joint isn’t necessary

Question 5

What are the two joint types commonly used in brazing?

Answer 5

Butt and lap joints

Question 6

Certain changes in joint configuration are usually made to improve the strength of brazed joints, what are some of these?

Answer 6

1) in butt joints the butting surface areas are increased in various ways such as scarfing or stepping the edges. In brazed or soldered lap joints, the overlap area is made as large as possible.

Question 7

The molten filler metal in brazing is distributed throughout the joint by capillary action. What is this?

Answer 7

The physical tendency for liquids to be drawn into a small diameter tube or other narrow openings in spite of the force of gravity. It’s caused by the adhesive attraction between the liquid molecules and the solid surfaces that define the narrow openings.

Question 8

What are desirable characteristics of brazing flux?

Answer 8

1) low melting point
2) low viscosity when melted
3) promotes wetting if metal surfaces
4) protects the joint until solidification

Question 9

Disadvantages and limitations of brazing:

Answer 9

1) strength of the brazed joint is less than welded
2) high service temperatures may weaken a brazed joint
3) part sizes are limited
4) colour of filler metal is often different than that of the base metals

Question 10

What are the functions served by the bit of a soldering iron in hand soldering?

Answer 10

1) provide heat to the parts
2) melt the solder
3) convey solder to the joint
4) withdraw excess solder from joint

Question 11

What’s wave soldering?

Answer 11

Involves the flow of molten solder onto the underside of a printed circuit board to provide soldered connections between the component leads that project through holes in the boards and the cooper circuit lands on the board

Question 12

Advantages of soldering:

Answer 12

1) lower heat energy required than brazing or welding
2) various heating methods available
3) good electrical/thermal conductivity
4) capable of making air/liquid tight joints
5) ease of repair and rework

Question 13

Disadvantages of soldering:

Answer 13

1) low mechanical strength unless reinforced

2) elevated service temperatures can weaken the joint

Question 14

What is meant by curing? (Adhesives)

Answer 14

A chemical reaction where the adhesive transforms from a liquid to a solid and in the process forms the surface attachment between two adherends.

Question 15

What’s are curing methods?

Answer 15

1) chemical reactions between two components of the adhesive
2) heating
3) UV
4) pressure

Question 16

Name the basic categories of commercial adhesives?

Answer 16

1) natural (starch, collagen)
2) inorganic (sodium silicate)
3) synthetic (thermoplastic/sets like epoxies and acrylics)

Question 17

What are some methods used to apply adhesives in industrial production operations?

Answer 17

1) manual brushing
2) manual rollers
3) silk screening
4) flow guns
5) spraying
5) automatic dispensers
7) roll coating

Question 18

Advantages of adhesive bending over joining methods

Answer 18

1) applicable to lots of materials
2) fragile parts can be joined
3) bonding occurs over whole SA
4) certain adhesives are flexible when cured so can tolerate service strains
5) low curing temperatures
6) some adhesives work as sealants as well as bondants.
7) simplified joint design

Question 19

Limitations of adhesive bonding?

Answer 19

1) not so strong as others
2) must be compatible with adherend materials
3) service temperatures are limited
4) surfaces to be bonded must be clean
5) curing times can limit production rates
6) bond inspection is hard

Question 20

How does mechanical assembly differ from welding brazing etc.?

Answer 20

Used mechanical fastening for joining parts whereas other methods use heat/pressure sometimes with a filler to permanently join. Many mechanical fasteners allow for disassembly.

Question 21

Why do things sometimes need dissembling?

Answer 21

Repair, replace, maintenance, make adjustments

Question 22

Technical difference between a screw and a bolt?

Answer 22

Both are externally threaded fasteners. Screw is generally assembled into a blind thread hole whereas a bolt is assembled using a nut

Question 23

What is torque turn tightening?

Answer 23

Tightening of threaded fastener to a certain low torque level and then advancing the fastener by a specified amount of turn

Question 24

Define proof strength as the term applies in threaded fasteners

Answer 24

Maximum tensile stress that an externally threaded fastener can sustain without permanent deformation

Question 25

Three ways a threaded fastener can fail during tightening

Answer 25

Ya 1)stripping of bolt or screw threads

2) stripping of internal fastener threads
3) excessive tensile load on bolt/screw CSA

Question 26

What’s a rivet

Answer 26

An unthreaded headed pin used to join two parts by inserting the pin through holes in the parts and deforming the unheaded portion over the opposite side

Question 27

Difference between a shrink fit and expansion fit in assembly

Answer 27

In shrink fit the outer part is heated whereas in expansion fit the inner part is cooled and upon warming it expands to cause an interference fit with its mating part

Question 28

Advantages of snap fitting

Answer 28

1) method is fast
2) no tooling required
3) parts can be designed with self aligning features for ease of mating

Question 29

Identify some general principles for design for assembly:

Answer 29

1) use fewest number of parts
2) reduce number of threaded fasteners
3) standardise fasteners
4) design parts to be symmetrical
5) avoid parts that tangle

Question 30

Identify some general principles and guidelines to automated assembly:

Answer 30

1) use modularity
2) reduce need for multiple components to be handles at once
3) limit the required directions of access
4) only use high quality components
5) use snap fitting