Brazing Etc 7 Flashcards
How do brazing and soldering differ from fusion welding?
No melting of base metal occurs in brazing and soldering
How do brazing and soldering differ from solid state welding processes?
Filler isn’t added in solid state welding
What’s the technical difference between brazing and soldering?
In brazing the filler metal melts above 450C but in soldering it melts at 450 or below.
Under what circumstances would brazing/soldering be preferred over welding?
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
What are the two joint types commonly used in brazing?
Butt and lap joints
Certain changes in joint configuration are usually made to improve the strength of brazed joints, what are some of these?
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.
The molten filler metal in brazing is distributed throughout the joint by capillary action. What is this?
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.
What are desirable characteristics of brazing flux?
1) low melting point
2) low viscosity when melted
3) promotes wetting if metal surfaces
4) protects the joint until solidification
Disadvantages and limitations of brazing:
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
What are the functions served by the bit of a soldering iron in hand soldering?
1) provide heat to the parts
2) melt the solder
3) convey solder to the joint
4) withdraw excess solder from joint
What’s wave soldering?
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
Advantages of soldering:
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
Disadvantages of soldering:
1) low mechanical strength unless reinforced
2) elevated service temperatures can weaken the joint
What is meant by curing? (Adhesives)
A chemical reaction where the adhesive transforms from a liquid to a solid and in the process forms the surface attachment between two adherends.
What’s are curing methods?
1) chemical reactions between two components of the adhesive
2) heating
3) UV
4) pressure
Name the basic categories of commercial adhesives?
1) natural (starch, collagen)
2) inorganic (sodium silicate)
3) synthetic (thermoplastic/sets like epoxies and acrylics)
What are some methods used to apply adhesives in industrial production operations?
1) manual brushing
2) manual rollers
3) silk screening
4) flow guns
5) spraying
5) automatic dispensers
7) roll coating
Advantages of adhesive bending over joining methods
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
Limitations of adhesive bonding?
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
How does mechanical assembly differ from welding brazing etc.?
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.
Why do things sometimes need dissembling?
Repair, replace, maintenance, make adjustments
Technical difference between a screw and a bolt?
Both are externally threaded fasteners. Screw is generally assembled into a blind thread hole whereas a bolt is assembled using a nut
What is torque turn tightening?
Tightening of threaded fastener to a certain low torque level and then advancing the fastener by a specified amount of turn
Define proof strength as the term applies in threaded fasteners
Maximum tensile stress that an externally threaded fastener can sustain without permanent deformation
Three ways a threaded fastener can fail during tightening
Ya 1)stripping of bolt or screw threads
2) stripping of internal fastener threads
3) excessive tensile load on bolt/screw CSA
What’s a rivet
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
Difference between a shrink fit and expansion fit in assembly
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
Advantages of snap fitting
1) method is fast
2) no tooling required
3) parts can be designed with self aligning features for ease of mating
Identify some general principles for design for assembly:
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
Identify some general principles and guidelines to automated assembly:
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
