Soldering is the process of joining metal by using an alloy with a lower melting point than the metals being joined. When metal is heated to a high temperature, the metals’ crystals move apart, which opens up microscopic spaces. The alloy, called solder, melts and flows into the spaces of the expanded metal, creating a strong joint. We are using hard, or silver, solder which is not to be confused with soft or lead/tin solders.
When choosing a solder, a general rule is
to use the solder that has about the same strength and color as the metals
being joined. Hard silver solder is the closest match to sterling silver.
Properties
of common metals and solders:
Name
|
Ag
(silver)
|
Cu
(copper)
|
Ni
(nickel)
|
Zn
(zinc)
|
Sn
(tin)
|
Melt
Pt ยบ F
|
Copper
|
99
|
1981
|
||||
Bronze
|
90
|
10
|
~1750
|
|||
Brass
|
70
|
30
|
1750
|
|||
Nickel silver
|
60
|
20
|
20
|
2030
|
||
Fine silver
|
99.9
|
1761
|
||||
Sterling silver
|
92.5
|
7.5
|
1640
|
|||
Hard solder
|
76
|
21
|
3
|
1425
|
||
Medium solder
|
70
|
20
|
10
|
1390
|
||
Easy solder
|
60
|
25
|
15
|
1325
|
Process and Tips
Good
Fit: Solder does not fill large gaps. If
pieces do not fit tightly the solder won’t make a strong joint or may only flow
to one side of joint.
Cleaning: Joint and solder must be CLEAN and
free of dirt, oil, tape, pickle, pencil, etc.
Flux: Use a brush to coat the joint
evenly. During soldering, flux protects the metal surface from oxidation and
breaks the surface tension of solder so that it can flow.
Solder: Use the right kind and amount of
solder: use only enough solder to fill the seam. Excess solder takes time to
remove. Solder must be placed so that it touches both pieces to be joined.
Solder flows towards heat so consider the direction of flow, and plan solder
placement for minimum clean-up.
Heat: Pieces being soldered must reach the
soldering temperature together. Consider the size of pieces, and heat sinks
such as binding wire, steel mesh, soldering boards, etc. Heat the whole piece
and avoid heating solder directly. Heat must be applied equally to all pieces
being joined. If not, solder will flow to the hottest piece only. Position the
torch to draw the solder through the joint. Using a soft flame, slowly and
evenly heat the joint and surrounding metal before flowing the solder. Let the
heat of the metal flow the solder, don’t directly flow the solder with the
flame.
Heating tips:
•
Volume of pieces must be considered. If a small thin piece is being soldered to
a heavy large piece, all of the heat should be directed onto the large piece.
•
When soldering an enclosed object, such as a bead, provide a vent for gasses
inside. They will expand rapidly and can cause the piece to explode.
•
Zinc in the solder will burn off as a vapor, changing the alloy’s proportions.
Each time solder becomes fluid its melting point is raised. Overheating can
cause a pitted seam.
Pickle: Pickle dissolves surface oxidation and flux residue from a metal’s surface and also absorbs copper ions, making it a green/blue color. Pickle the piece to clean the surface after soldering. Do not quench the piece immediately after soldering.
Safety: Use ventilation for flux/zinc vapors. If you use a tool
that gets hot like tongs or a soldering pick, quench it so the next person
doesn’t burn themselves.
Solder Cleanup: After completing all soldering on a piece, use files and
sandpaper to remove any solder that has flowed out of the joint. If you clean
up solder then raise the piece to soldering temperatures again, the previous
solder may flow, leaving gaps. Cover previous seams with yellow ochre to
prevent this. For the first soldering, use a solder with as high a melting
point as possible, which will enable you to do secondary soldering or repairs
with a lower-melting solder.
Firescale: After completing all finishing,
there may be cloudy purple stains on the surface. This is called ‘firescale’
and is a result of the copper content of sterling silver. It appears after
sterling silver has been heated to soldering temperatures, and can be removed
by two methods. The first is to physically remove the firescale using
sandpaper, leaving the sterling silver surface. The second method is to gently
heat the piece with a torch until a gray oxide appears (watch carefully and do
not overheat). While the piece is still hot, it is quenched in hot pickle (be
careful of splashes!!) and allowed to sit for a few minutes. After pickling,
the piece is cleaned with dish detergent and a scrub pad. This process is
repeated several times until the surface is a bright, matte white, which is
actually a thin plating of fine silver.
Troubleshooting
Problem
|
Reason
|
Solution
|
Incomplete/unsoldered
joint
|
• Not enough
heat
• Not enough
flux
• Metal is dirty
• Prolonged
heating
|
• Clean joint
• Use more flux
|
Solder will not
fill a joint
|
• Joint too wide
|
• Clean joint
and fit tightly
|
Solder balls up
|
• Heat may be
flowing
away from joint
• Metal or
solder is dirty
• Joint has
oxidized
|
• Avoid direct
flame on solder
• Clean and flux
|
Solder jumps to
one side of joint
|
• One side is
hotter than
the other
|
• Heat the
heavier piece first, use care with flame placement
|
The aim of this project is to practice soldering for when we make a silver ring. The final piece would then be a 'Solder bowl'-somewhere to keep the cut solder pieces.
Step 1
Firstly, we will solder the band by pulling the two ends of the strip of copper to meet, it is important that the ends are parallel to each other, as the solder wont run through if there is a gap.
Step 2
After it has been cleaned and pickled, it goes on to a tool, which is basically a large ring mandrel to shape it into a perfect circle.
Step 3
On to the bowl part, it needs to be cut perfectly for it to sit on the ring base evenly. It is then annealed and pickled to soften the metal, ready to be domed. I will keep the ring base near, so that I can measure the bowl needs to be domed.
Step 4
Once it is domed enough, it is ready to be soldered to the ring base.
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