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====== Session 7 - Joining Techniques ======

===== Soft Soldering =====

==== Safety ====

  - Always wear safety glasses.   Wear dark safety glasses when hard soldering large joints.
  - Use a spark lighter to light torch.
  - Open gas valve first to light then open air or oxygen.
  - Close gas first to shut off flame then shut off air or oxygen.
  - Red hose is always gas and green hose air or oxygen.
  - Watch where flame is pointed.  Keep all flammable materials, cutting oils, solvents etc. off soldering bench and away from open flames.
  - Handle hot parts with pliers.
  - Let part cool slowly.  If you plunge it into water you may get burned by the steam.
  - Make sure gas is turned off at torch and at cylinder or inline valve when you are finished.
  - Fire extinguisher is next to door and fire blanket next to soldering bench.

  - Soft Solder Characteristics
    * Relatively low temperature.  350 - 450 degrees F.
    * Tin/lead or tin/silver alloy 
    * Routine soldering of brass and copper 50% lead/50% tin alloy common. 60/40 also used.  Stay Brite solder for lead free joints.
    * Low strength, shear strength ~5000 psi.
  - Joint preparation
    - Clean surfaces with emery paper or steel wool
    - Wipe with acetone or alcohol
    - Coat both surfaces with Nokorode paste flux
    - Joint clearance for soft soldering .002" - .004" per side for diameters of 1/4" to 1"
  - Heating methods for soft soldering
    * Propane or Mapp gas torch
    * City gas/air
    * City gas/oxygen (hotter)
    * Hot plate
  - Soldering of joint
    - Heat indirectly, do not burn off flux.
    - Concentrate heat on heavier part and where you want the solder to flow. Keep flame moving to prevent hot spots.
    - Test temperature of part by touching solder to joint.  Let part melt solder, not flame.
    - Solder will flow into joint by capillary action.
    - Add just enough solder to fill joint and produce a fillet or buildup of solder at the part juncture.
    - Let joint cool in air, do not quench in water.
    - Clean with hot soap and water to remove flux.
    - Test joint with low pressure (10-20 psi) and SNOOP or helium leak detector.

===== Hard or Silver Soldering =====

==== Torch safety ====

  - Open oxygen cylinder slowly, first.  Open valve completely.
  - Next open acetylene cylinder 1/4 to 1/3 turn only.
  - Set regulators for proper pressure according to tip size.
    * Oxygen ~ 15 psi max. 
    * Acetylene ~ 5 psi max.
  - Wear dark safety glasses
  - Use spark/torch lighter to light torch not a match.
  - Open acetylene needle valve on torch ~ 1/4 to 1/2 turn.
  - Point tip away from you and cylinders.
  - Ignite gas.
  - Open oxygen needle valve on torch and adjust flame for "neutral" flame for soldering.
  - To shut off torch: close acetylene valve first, then oxygen.

  - Silver solder characteristics
    * High melting point 1100 - 1300 degrees F.
    * Common alloy 60% silver, 30% copper, 10% tin.
    * Strong joints, ~30-50,000 psi tensile strength, depending upon the alloy and joint design.
    * Copper, brass, stainless steel, steel, nickel, tungsten, and other materials can be silver soldered.
  - Joint preparation
    - Clean surfaces with emery paper.
    - Wipe with acetone or alcohol.
    - Coat both surfaces with white paste flux.
    - Joint clearances .001" - .003" per side for diameters of 1/4" to 1".
  - Heating methods for silver soldering
    * City gas and oxygen for small parts.
    * Oxygen and acetylene gas (hotter, ~6000 degrees F)
    * Furnace

  * Soldering of joint
    - Heat until white crystalline flux turns to a glassy/clear.  This is approaching the proper temperature. Part will be dull red in color.  Do not overheat and turn part black.  If this happens let part cool, sand off all oxidation, clean and flux.
    - Keep flame moving to prevent burning off all flux.
    - Test temperature of part by touching solder to joint.  Let part melt solder, not flame.
    - Solder will flow into joint by capillary action.
    - Add just enough solder to fill joint and produce a fillet or buildup of solder at the part juncture.
    - Let joint cool in air, do not quench in water.
    - Clean with hot soap and water to remove flux.
    - Test joint with low pressure (10-20 psi) and SNOOP or helium leak detector.

===== Welding =====

  * Characteristics of TIG (tungsten inert gas welding)
    * Parts fused together by heating above the melting temperature of the base metal.
    * TIG (tungsten inert gas) or heliarc welding used mostly for non ferrous metals such as stainless steel, aluminum, OFHC copper, and titanium.
    * Welded joints stronger than soldering.
    * Heating of welded joints is more localized than silver soldering so less cleanup is required.  Base metal is also closer to it’s original state than with silver soldering.
    * Parts clean (no flux residue or solder)
    * Proper joint design important.

  * Characteristics of spot welding
    * Also called resistance welding.
    * Good for joining sheet metal and wires.
    * Joint is heated by brief passage of large electrical current through a spot contact between the two pieces to be joined.
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