TM 9-243 SOLDERING – CONTINUED The  interchangeable  copper  tips  are  coated  with  iron, .008 inch thick to reduce scaling and wear caused by tin- copper alloying The tip is pre-tinned by dipping into pure tin.    These  tips  should  never  be  filed.    To  clean  the  tip and remove oxidation wipe it with cleaning pad. The  heat  shunt  is  provided  for  use  when  working  with delicate    precision    components    such    as    transistors, diodes, miniature capacitors, and chokes. The excessive heat of the soldering  iron  will  damage the  component  if  the  heat shunt, which dissipates heat, is not used. BASIC SOLDERING TECHNIQUES TEMPERATURE When  soldering  with  rosin core   solder,   temperatures in   excess   of   600°F.   must be avoided or the rosin will tend to carbonize and hinder  rather  than  aid  the soldering operation. Efficient soldering is promoted by using a soldering iron with adequate   heat   storage   capacity.      Such   a   device   will maintain    proper    operating    temperature    in    use.        No attempt to solder must be made by heating an undersize or   otherwise   inadequate   soldering   iron   to   excessive temperature. HEATING The surfaces of the parts to be joined must be heated to a  temperature  above  the  flow  temperature  of  the  solder (400-600°F.  for  60/40 flux cored solder). NOTE When   working   on   vertical   terminals,   tin   only   one surface of the iron to restrict solder flow to that side. COOLING Liquids  are  not  to  be  used  to  cool  a  soldered  joint.    By using  proper  solder  and  soldering  techniques  a  joint  will not become so hot that it needs rapid cooling to prevent the   wire   insulation   from   charring.      In   special   cases involving    assemblies    with    polystyrene    or    other    low melting  point  insulation,  the  Insulation  may  be  placed  in a  cooling  bath.    However,  in  no  case  should  the  cooling medium contact the soldered joint. COPPER BIT SOLDERING IRONS The heat transmitting ability of copper-bit soldering irons is seriously impaired by the formation of oxides on the bit surface.  The formation of such oxides can be effectively retarded by maintaining a liberal     coating     of solder on the surface   of   the   bit. Plated    tips    resist corrosion   and   last longer because the   plating,   unlike copper, is not affected chemically by solder.    These  tips should  not  be  filed or  ground  on  the  bench  grinder.    If  cleaning  is  required, the   point   of   the   iron   should   be   dipped   in   flux   and retinned. FLUX RESIDUE REMOVAL After the joint has cooled, the residues from active fluxes can     be     completely     removed     or     neutralized     using Methylene Chloride or Tecsolve 928. SOLDERING SAFETY PRACTICES OBSERVE THE FOLLOWING RULES WHEN SOLDERING: 1.    Safety glasses or appropriate    eye    protection must be worn. 2.    The  soldering  iron  should  be  placed  in  the  holder when not being used. 3.    Never  try  to  remove  solder from  the  iron  by  flicking  the iron.    This  can  put  solder  in the  eyes  and  on  clothes;  it can    also    put    a    short    in equipment. Use the cleaning pad provided. 4.    Be  careful  to  pick  the  iron  up  by  the  handle.    Never point  with  the  iron  or  use  it  as  a  tool  to  straighten terminals. 5.     Unplug  the  iron  if  it  is  not  to  be  used  for  a  period  of time. 6.    When returning the soldering iron to stock, be sure that all excess solder is removed.  It is good practice to loosen the tip of the iron when not in use; this prevents the tip from corroding tight on the handle. 53-9/(53-10 blank)  Change 3