Brazing Technology | How To Brazing | Brazing Joints | Brazing Filler and Flux

What is Brazing

Brazing Technology is a joining process in which a filler metal is melted and dispersed by capillary action between the faying surfaces of the metal parts being joined. No melting of the base metals occurs in brazing; only the filler metals are melted. In brazing, the filler metal (also called as brazing metal), has a melting point is above 840° F (450° C) but below the melting point of the base metal to be joined. Tensile strength of the joint is about 40000 psi.

Advantages of Brazing:

Brazing has numerous advantages compared to welding:

  1. Any metals can be joined including dissimilar metals
  2. Certain brazing methods can be performed quickly and consistently, thus permitting high cycle rates and automated production
  3. Some methods allow multiple joints to be brazed simultaneously
  4. Brazing can be applied to join thin walled parts (But welding doesn’t)
  5. Less heat and power are required than in fusion welding
  6. Brazed joint’s never penetrate the base metal (were the welded joint penetrate the base metal)

Limitations of Brazing:

Brazing also has some disadvantages:

  1. Brazing’s joint strength is normally less than that of a welded joint
  2. Even though the strength of a good brazed joint is better than that of the filler metal, it is likely to be less than that of the base metals
  3. High operational temperatures may weaken the brazed joint
  4. The color of the metal in the brazed joint may not match the color of the base metal parts. It is an aesthetic disadvantage.

Brazing Joints:

Brazing Filler metal:

  • Copper brazing filler metal
  • Silver brazing filler metal
  • Coated brass brazing filler metal
  • Nickel brazing
  • Aluminum brazing
  • Mild steel brazing
  • Aluminium – silicon brazing
  • Copper – phosphorus brazing
  • Magnesium brazing

To qualify as a brazing metal, the following characteristics are needed:

  1. Melting temperature must be compatible with base metal
  2. Low surface tension in liquid phase for good weldability
  3. High fluidity for penetration into the interface
  4. Capability of being brazed into a joint of adequate strength for the application
  5. Avoidance of chemical and physical interactions with base metal

Filler metals practiced to the brazing operation in a variety of ways. The brazed metal comes as wire, rod, sheets, strips, powders, pastes and preformed parts made of braze metal. They designed to fit a particular joining configuration and cladding on one surface to be brazed.

Brazing Flux:

Brazing fluxes (aluminum brazing flux, silver brazing flux) serve as a similar purpose as in welding. They dissolve or combine or slow down the formation of oxides and other unwanted by products in the brazing process. Use of a flux doesn’t substitute for the cleaning steps described previously.

Brazing Fluxes are available in three phases. They are:

  1. Paste
  2. Powder
  3. Liquid

Characteristics of a good flux include:
  1. Flux has low melting temperature
  2. It has low viscosity so that it can be displaced by the filler metal
  3. Fluxes facilitates wetting
  4. It protects the joint until solidification of the filler metal starts. The flux should also be easy to remove after brazing operations.
  5. Chemically cleans the metal surfaces
  6. It shields the process from oxidation and atmospheric contamination

Underwater Welding | Underwater Welding Dangers | Hyperbaric Welding

Underwater welding process

Underwater welding offers a mode of assembly or repairs the structures underwater. It is a type of technology for repairing marine structures. Unconventional methods such as clamp and grout repairs (which may set up inappropriately high loading on offshore structures), and the use of bolted flanges for the tie-ins, are not necessarily always satisfactory.

There are many applications for underwater welding skills such as:

  1. Repairing ships,
  2. Working on oil platforms and
  3. Maintaining underwater pipelines.

People with skills and experience in this field can find employment all over the world.

Why underwater welding needed?

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Principles of underwater welding

Underwater welding is a type of welding which takes place underwater. Among the number of different welding techniques, ‘arc welding’ is most common.

Power supply:

DC 300 to 400 Amps (AC welding is not used due to electrical safety and difficulty in maintaining the arc underwater)

Polarity:

Negative polarity (If positive polarity which causes deterioration due to electrolysis takes place)

Underwater welding Requirements:

  • Arc welding torch
  • Collet or Grip
  • Oxygen valve
  • Flash arrester

Water proofing surface electrodes:

  • Epoxy 152
  • Lee lac
  • Ployurethane

Underwater welding can be divided into two main types that have been in use for many years:

Underwater wet welding:

Manual Metal Arc Welding (MMA) is the most common process. Flux Cored Arc Welding (FCAW) has been widely used. FCAW, which has the advantages of being relatively insensitive to depth and which tends itself to robotic operation has the potential for use in deep water repairs.

Advantages:
  • Very fast welding in underwater
  • Cheapest welding
  • Tensile strength is high
  • No habitat required
  • No need of construction
Disadvantages:
  • Due to Rapid quenching reduces impact strength and ductility
  • Poor visibility in water
  • Possible of Hydrogen embrittlement

Hyperbaric welding or Dry welding:

In which a chamber is sealed around the structure to be welded and is filled with a inert gas (commonly Helium containing 0.5 bar of oxygen) at the generally accepted pressure.

Cofferdam welding:

This method is carried out in the dry air; where a rigid steel structure to house the welding is sealed against the side of the structures to be welded and is open to the atmosphere.

Large Habitat:

Small Habitat:

Dry Habitat welding:

Welding takes place at ambient water pressure in a large chamber were the water is displaced.

Dry chamber welding:

Welding at ambient water pressure in simple open bottom dry chambers that accommodates the head and shoulder of welder.

Dry spot welding:

Welding at ambient water pressure in a small transparent, gas filled enclosure with the welder in the water and arm inside the chamber.

Advantage:
  • Good quality welds
  • Possible testing methods such as NDT inspection, driver monitoring
  • Safety to welder due to risks in welding
Disadvantage:
  • Large, complex construction equipments required to weld
  • Higher costs of welding equipment
  • Unreachable place cant welded

Underwater Welding Dangers or Risks:

For the humans involved, the risks are of three main types:

  1. There is a probable risk to the welder / diver due to electric shock. Precautions include, completing enough electrical insulation of the welding equipment, shutting off the electricity supply immediately the arc is extinguished and limiting the open circuit voltage of Manual metal arc welding sets.
  2. Hydrogen and oxygen are formed by the arc in wet welding and cutting process. Precautions must be taken to avoid the built up of pockets of gas which are potentially explosive.
  3. The other main area of risks is the life / health of the welder / diver from nitrogen gas introduced into the bloodstream during exposure to air at increased pressure. Precautions include the provision of an emergency air or gas supply, stand by divers and decompression chambers to avoid decompression sickness following saturation diving or too rapid return to the surface from a deep dive. For the structures being welded by wet underwater welding, inspection following welding may be more difficult than for welds deposited in air. Guaranteeing the integrity of these type underwater welds may be more difficult and there is a danger, which defects may stay behind undetected.
Future Developments:
  • Alternative welding methods such as Friction welding, Stud Welding and Explosive welding can be used
  • Development of THOR -1 (“TIG Hyperbaric Orbital Robot) for the automatic welding in underwater