permits the parts to be brazed or soldered in an oven or by other means without need of human attention to feed in the filler metal at the right time and place. See Figure 3–18.
Figure 3–18Method of preplacing brazing filler metal
What is stop-off used for?
Stop-off is used to outline the area not to be brazed. It prevents the flux from entering that area.
What are the most common solders?
Tin-lead alloys are the most common solders. It is customary to indicate the tin percentage first, then the lead content and the same with other two-metal alloys. A 40/60 tin-lead solder is 40% tin and 60% lead.
Tin-lead solders 35%/65%, 40%/60% and 50%/50% are popular because of their low liquidus temperatures. Tin-lead solders 60%/40% and the 63%/37% eutectic are used when low-processing temperatures are needed. Tin-silver, tin-copper-silver, and tin-antimony alloys are used where lead must be eliminated for health reasons as in stainless steel fabrication for kitchens, food processing equipment, and copper potable water systems. Never use lead-containing solder on potable water systems.
What are some other less common solders?
•Bismuth-containing solders provide alloys with very low melting temperatures for sprinkler heads and heat detectors for alarms.
•Indium alloys with liquidus temperatures as low as 230°F (138°C) are used for glass-to-glass and glass-to-metal seals in electronics.
Troubleshooting Brazing & Soldering Processes
Problem: No flow or no wetting.
Causes:
•Wrong braze filler
•Temperature too low
•Time at temperature too short
•Parts not properly cleaned
•Parts fit poorly
•Heat source in wrong location
Problem: Excess flow or wetting causes hole plugging or brazing wrong joints.
Causes:
•Temperature too high
•Time at temperature too long
•Too much filler material
•No stop-off used
Problem: Erosion—Braze filler material eats away parent metal.
Causes:
•Temperature too high
•Time at temperature too long
•Excessive braze filler metal
•Cold worked parts
Safety
What special chemical hazards do brazing and soldering present and what precautions must be taken?
Base metals and filler metals may contain toxic materials such as: antimony, arsenic, barium, beryllium, cadmium, chromium, cobalt, mercury, nickel, selenium, silver, vanadium, or zinc. These will be vaporized during brazing or soldering and cause skin, eye, breathing, or serious nervous system problems. Some of these toxic materials are cumulative such as lead and may be absorbed through the skin. The following precautions are essential:
•Keep your head out of the brazing or soldering plume.
•Perform brazing or soldering in a well ventilated area.
•On failure of normal ventilating equipment, use respiratory equipment.
Many brazing and soldering fluxes and heating bath salts contain fluorides. Others contain acids and aluminum salts. The following precautions apply:
•Avoid direct contact with skin.
•Do not eat or keep food near these materials.
•Do not smoke around these materials.
•Insure MSDSs are affixed to containers of these materials and major equipment using them so they are visible to you and others.
What is an excellent source of information about these hazards in addition to the MSDSs?
See the AWS booklet Z49.1, Safety in Welding, Cutting and Allied Processes.
What eye protection is needed for brazing and soldering?
•For soldering, wear safety glasses or face shields to protect the eyes from external injuries caused by sparks, flying metal, or solder splashes.
•For brazing, using a number 5 tinted lenses will protect against internal (retinal) eye damage caused by viewing the radiation coming off hot metal. Some brazing requires darker lens shades of up to number 8.
What other safety precautions must be taken while soldering or welding?
•Skin protection from sparks and hot metal prevented by gloves and nonflammable clothing.
•Fires from the welding process can be prevented by moving flammables away from the weld zone and having water or fire extinguishers close at hand.
•Use adequate ventilation when using cleaning solvents to prepare the joints; chlorinated hydrocarbons are toxic and may create phosgene gas when heated.
•Always wear chemical-type eye goggles or face shields, rubber gloves, and long sleeves while using cleaning solutions, pickling solutions, or acids. Note that chemical-type goggles do not have ventilation holes above the eyes where splashes could enter.
Experience is the name everyonegives to their mistakes.
Oscar Wilde
Introduction
There is a lot of material common to the electrically-based welding processes —SMAW, GMAW, FCAW, and GTAW, so it makes sense to cover them all at once. The joints and positions are also common to OAW. These items are:
•Joint types
•Joint edge preparation
•Parts of a
