Hard-soldering with Silver Solder
Hard-soldering is chiefly of two kinds, brazing and silver-soldering,
the former being employed for iron and steel, the solder used being
known as “spelter,” a brass alloy which can be obtained in various
degrees of fineness. For copper, brass, and nickel silver, alloys
containing silver are the best solders. In both forms of hard-soldering,
the flux is borax.
The methods of silver-soldering vary with the size of the work. A
jeweller may hold the work in his hand, on the end of a piece of binding
wire or on a square of charcoal, the heat being applied by a mouth
blowlamp from a horizontal gas jet, as already described. Larger work
demands a flame of greater intensity, and sufficient air can be supplied
only by a footblower or similar device, or, as an alternative, from the
flame of a suitable blowlamp.
=Silver Solder.=--This can be purchased at prices up to 3s. 6d. or so
per ounce in sheet form, about 1/32 in. thick. Where the solder is
melted down by the amateur, a good way to obtain the sheet form is to
turn the globule of molten metal on to the bench and to place a flat
iron on it; but the result will not be equal to a rolled ingot.
An old shop method of making silver-solder is to melt up old silver
(using current silver coinage is an expensive method of obtaining the
silver, and is said to be illegal) with some _brass_ pins, not the iron
ones so common now.
According to W. H. Jubb, two solders compulsory for silver articles that
have to be sent to assay for hallmarking are: (1) 12 parts standard
silver and 1 part brass; (2) 6 parts standard silver and 1 part brass.
No. 1 has a low melting point, and is termed “quick,” and No. 2, which
requires a higher temperature, is called “stark” (in some parts of the
country, “fine”), but the use of this term here is misleading. No. 2
should be used at the first heating and No. 1 at the second. These
should make ideal solders for beginner’s use, as the chances of burning
the work, even thin brass, are almost nil.
(3) 2 parts brass, 1 part standard silver; (4) 5 parts brass, 2 parts
standard silver. Whereas Nos. 1 and 2 are “silver solders,” Nos. 3 and 4
are termed “German silver solders,” as they are not so white and are
used on German or nickel silver (an alloy of copper and nickel). Both
Nos. 3 and 4 are good, have a comparatively low melting point, are much
less expensive than Nos. 1 and 2, and, if plenty of wet borax is used,
will “strike up” well. No. 3 is recommended.
“Standard silver” is about 95 per cent. pure silver. Old “sterling
silver” is 92·5 per cent. pure silver.
In making any of the above solders the brass and silver should be melted
together, and care should be taken to see that the metal is clean
beforehand. Where large quantities of solder are made, the metals are
scoured with emery cloth before they are put into the crucible.
=Requisites for Silver-soldering.=--For light jobs in silver-soldering
the special tools and materials required are as follow: Suitable gas jet
or other flame, mouth blowpipe, scraper, jar containing a sulphuric acid
“pickle,” piece of slate, camel-hair brush, pieces of lump borax, two
grades of silver solder, charcoal block, iron binding wire.
The pickle is made by pouring 1 part of common sulphuric acid into 20
parts of water, and its function is to remove all dirt and borax from
the metal. Silver-soldered articles should not be thrown into the pickle
until they are nearly cold, as otherwise the joints may crack, but in
the preparatory annealing (that is, softening) of plain metal, wire,
rod or tubing, the article may be put into the pickle when hot--but take
care of the splashes! Plunging hot copper or brass into cold water does
not have the effect of hardening it. Before placing a job in the pickle,
remove any iron binding, as this is immediately attacked by the acid.
Often it is advisable to heat the metal and put it “through the pickle”
before working on it, especially in the case of tubing that has been
lying by for some time and has become dirty.
For heavier work, a foot-bellows and gas blowpipe, or else a blowlamp,
are essential. An “Ætna” paraffin blowlamp with horizontal burner will
be found quite satisfactory, although, of course, if a gas supply is
available in the workshop the user will find that a foot-bellows and
blowpipe are more convenient. A blowlamp or blowpipe requires a suitable
tray or “forge” of sheet-iron in which coke and odd pieces of brick or
tile may be laid and used to pack round the object whilst the flame is
being played on the part to be soldered.
[Illustration: Figs. 56 and 57.--Clip for Holding and Applying Silver
Solder]
[Illustration: Fig. 58.--Pricker and Spatula for Consolidating Joints
and Applying Solder]
Among the smaller additional tools that will be required will be a clip
to hold the solder (Figs. 56 and 57) and a brass pricker (Fig. 58).
=Preparing the Borax Flux.=--Make up the flux on the slate by rubbing on
it a piece of the lump borax moistened with water. This paste may be
applied with the camel-hair brush to the parts to be jointed. The flux
prevents the oxidisation of the surfaces, which would resist the
amalgamation of the metals and the solder.
=The Method of Silver-soldering.=--In hard-soldering with silver solder,
first file or scrape the parts bright, and cover them and the solder
with the borax paste. Heat gently at first so as to harden the borax;
then continue to heat by blowpipe until a red heat is reached, at which
the solder will run. The secret is to blow continuously until the solder
runs, and not to stop half-way.
For soldering a silver watch case, an ordinary easy-running silver
solder, which melts at a lower heat than silver, will do. But to make
sure, shred the solder into very thin strips, and apply plenty of borax
to them as well as to the joint to be united. Use the blowpipe gently at
first so as to bake the borax, then heat the case all over almost to the
melting point of the solder, and direct the flame to the part to be
soldered until the solder runs and glistens. Cease blowing instantly,
and plunge the case into a solution of sulphuric acid 1 part and water
10 parts, to whiten it; then wash in hot water and dry in sawdust. Be
careful to remove all steel springs before soldering the case.
=Soldering Small Work with Paillons.=--These are small squares, say, 1/8
in., of sheet silver solder, made by using the snips as in Fig. 61, and
prepared by well covering with the borax paste. Each paillon is placed
in position with the tip of the brush, this job requiring a little
practice. The solder should be clean, and if not, should be made so by
passing through the fire and pickling. The work with the paillons in
position should be slowly heated by blowing the gas jet on a part of the
job farthest away from the solder; the borax will dry, and should the
solder have moved, replace it with a suitable tool or the point of the
wet camel-hair brush. The heat must not be applied too suddenly at
first, otherwise the borax will boil up and push off the pieces of
solder. The heat may be increased when the bubbling has ceased. Do not
hold the work too far away, or it will get dirty in the smoke of the
flame, or yet too near, else the gas will not be used to advantage. As
the work begins to get hot, slowly work the flame towards the joint
until the solder melts and runs into the joint. Give it now a little
extra heat to get the solder thoroughly down into the crevices, and then
let the work cool down. When nearly cold twist off the iron binding wire
and put the job into the pickle. Leave the work in the pickle about ten
minutes, when all the borax will be dissolved.
[Illustration: Fig. 59.--Section through Pipes prepared for
Silver-soldering]
[Illustration: Fig. 60.--Pipes prepared for Silver-soldering]
[Illustration: Fig. 61.--Cutting Up Silver Solder into Paillons]
=Larger Work.=--An example of silver-soldering larger work is the
joining together of two pipes, one smaller than the other. The best
course to adopt is to file or scrape the end of the smaller and the
inside of the larger (reaming and filing them if necessary) until a good
fitting joint is obtained, as in Figs. 59 and 60. A strip of solder is
then cut off, and, after the joint is well coated with borax paste, this
solder may be wound round the smaller pipe. If the joint is soldered in
a vertical position, the larger pipe should be the lower. The heat
should be conserved by laying the work in the coke and building the
same round, or, if the work is too large or the joint in an awkward part
of the pipe, a shield of tin plate or iron should be placed behind the
joint so that the flame is thrown back on to the work. Should the pipe
be attached in close proximity to the joint to a heavy piece of metal,
then warm this metal up first, otherwise all the heat will travel to
this part, and the work will take much longer to get to the proper
temperature. In all cases where one part of the joint is of heavier
substance than the other, that part should receive the greater amount of
attention from the flame.
=Quenching Silver-soldered Work.=--Many craftsmen object to the cooling
of the work by plunging it into water or pickle whilst it is hot; but no
damage or cracking of the joint occurs, it is thought, if the work is
not plunged when it is red hot or anywhere near red hot. Plunging into a
pickle certainly cracks the burnt-in borax, which can be readily removed
and the joint examined to better advantage. Many a silver-soldered
joint has been passed as quite sound when it has only been the borax
that has been stopping the interstices, and only after it has been
placed under service for some time does the faulty joint make itself
apparent.
Silver-soldering cannot be done on work that has been previously
soft-soldered unless the soft-soldered part is first cut away; but, of
course, soft-soldering can be readily accomplished after
silver-soldering or brazing so long as the work is clean and all burnt
borax is first removed.
=Removing Soldering Marks.=--Solder will run away from a part of a joint
instead of running into it when the edges of the joint have been
imperfectly cleaned preparatory to the application of flux and solder;
also, if some dirt has got into the flux, or on the paillons of solder
employed. Another cause is unequal heating of the joint, or allowing it
to expand too much whilst being heated. The resulting fire marks may be
removed by warming the articles on a pan over gas, and plunging them
whilst warm into the sulphuric acid pickle. Or the marks may be removed
in a hot and strong solution of potassium cyanide, and the polish
renewed by a light polishing with a revolving swansdown mop and rouge
composition.