The process of joining metal parts through the use of
heat and a filler metal is commonly called “soldering” by manufacturing
jewelers and silversmiths. Actually, this term is incorrect by today’s
definitions. The joining of metals in the temperature range of 1100° R (593° C.) to 1600° E (871° C.) is
properly called brazing. (The term “soldering”
is used to describe metal-joining operations at temperatures below 800° E (427° C.).)
However, the term “soldering” is so firmly
established in the industry that we will use it in the discussion that follows,
rather than the more technically exact term “brazing:” No harm will be done,
as long as it is understood that when we talk about soldering we are talking
about metal joining operations in the 1100° E to 1600° F
range (593° to 871° C.).
Soldering is the joining of metals through the use of heat and a filler metal -a solder whose melting point is about 1100° E (593° C.) but below the melting point of the metals being joined. In soldering, heat is applied broadly to the area of the joint. The solder is then brought into contact with the heated parts. It melts instantly and is drawn by capillary action through the entire joint, creating a strong, permanent bond between the two metals.
A soldered joint in a sense “makes itself” Capillary action does the work, drawing the molten solder completely through the joint. But even a properly designed soldered joint can turn out imperfectly unless the correct soldering procedures are followed. These procedures can be boiled down to six basic steps. They’re generally simple to perform (some take only a few seconds), but every one of them is essential to the completion of a strong, clean soldered joint.
As we’ve noted, soldering operates on the principle of capillary action. And capillarity works best where there are close clearances between the metals being joined. How close? The strongest joints are made at clearances of .0015”-about half the thickness of this page.
However, soldering is a “forgiving” process, and clearances ranging from .001” to .005” will still produce high-strength joints. In actual shop practice, an easy slip fit between two tubular parts, or simply resting one flat part on top of the other is all the clearance you’ll usually need. The average mill finish of the metals imparts enough surface roughness to create capillary paths for the flow of the molten solder.
Capillary action works properly only when the surfaces of the metals are clean. If the parts you’re soldering are factory-fresh they’ll require no cleaning. But if the metal surfaces bear contaminants-oil, grease, scale or dirt-those contaminants have to be removed, or they’ll form a barrier between the metal surfaces and the soldering alloy. You should remove the oil and grease first, using a degreasing solvent. Scale and dirt can then be removed chemically, with an acid pickle treatment, or mechanically.
Flux is a chemical compound applied to the joint surfaces before soldering. A coating of flux shields the metal surfaces from the air and prevents the formation of oxides, which would interfere with the bonding action of the soldering alloy. Flux is usually applied with a brush to the metal surfaces. It should be applied generously, as insurance against oxidation, and the joint should be soldered as soon as possible after the flux is applied.
There are many kinds of flux available, but for the kind of soldering done by manufacturing jewelers and silversmiths, a single, general purpose flux, such as Handy & Harman’s Handy Flux, will cover just about all applications. In addition to its protective function, Handy Flux also serves as a useful temperature indicator. As the metal parts are heated the flux coating
changes in appearance, until it indicates that the joint is hot enough for soldering. The chart above shows how Handy Flux acts as a guide to soldering temperature.
Once the parts are cleaned and fluxed, they are ready for soldering. Now you have to hold them in correct alignment during the heating and cooling cycles, so that capillary action can do its job.
The easiest way to hold parts together, if their shape and joint conformations permit, is by gravity -simply resting one part on the other. You can even add additional weight to give gravity a helping hand. Or you can use any clamping or supporting device-spring clamp, vise or pliers-that holds the parts together long enough to complete the soldering operation.
If you have a number of identical assemblies to solder, it may pay to make a supporting jig. The jig should be designed for minimum contact with the parts, so heat is
not conducted away from the joint area. Materials used for the jig should be poor heat conductors (like stainless steel or ceramics) that won’t draw heat away from the joint, rather than good conductors like aluminum or copper.
The actual soldering operation involves heating the assembly to soldering temperature (hot enough to melt the solder but below the melting point of the metals) and flowing the solder through the joint.
The most common method of heating is the hand-held torch fueled by oxygen and acetylene (or natural gas or propane). You light the torch and apply heat to the joint area, working broadly and keeping the torch in constant motion. In heating pieces of unequal mass, favor the heavier piece to avoid overheating the lighter member. In joining two different kinds of metal, favor the metal that is the more rapid heat conductor.
If you’ve used Handy Flux to flux the parts, the point at which the flux is completely clear indicates that the joint area has reached (or is near) soldering temperature. At this point you simply touch the solder rod (or wire) to the joint line. The heated assembly will melt off a portion of the solder, which will instantly be drawn by capillary action through the entire joint area, forming a strong, permanent bond.
Cleaning the soldered joint is usually a two-step operation-first ‘ removing flux residues and, second, pickling to remove any oxide scale formed during soldering.
Most brazing fluxes are water soluble, so you can remove the residues by quenching the assembly in hot water as soon as the solder has solidified. Tapping the flux, or light brushing while the assembly is immersed in water, will speed the process. After you’ve removed the flux, you can use a pickling treatment to get rid of any oxides that may have formed during the heating cycle on areas unprotected by flux. Use the pickle recommended by the manufacturer of the soldering materials you’re using.
Once you’ve removed potentially corrosive flux residues and oxides, further finishing operations should not be required.
Handy & Harman manufactures a complete range of karat gold solders, silver solders and fluxing materials. These products are standardized, and fabricated under rigorous quality control procedures. There is no variation in composition, properties or working characteristics from lot to lot.
Handy & Harman’s karat gold solders are supplied in the following karat designations: 6, 8, 10, 12, 14, 16,18 and 19. Both yellow and white colors are available in the various karat groups, as well as three application levels-Easy Medium and Hard. Their gold content ranges from approximately 25% to 80%, and their fine silver content from 2.5% to 58%.
All gold solders are supplied as strip, round wire, chips and powder. The strip ranges in thickness from .003” to .020” (or heavier where required), and from 1/4” to 3” in width. Wire diameters are from .007” to .093” (or heavier).
Properties and applications of Handy & Harman karat
gold solders are described in Chart J.
Handy & Harman manufactures four standardized solders for sterling silver. These solders cover virtually all silversmithing and jewelry joining operations. They contain high percentages of silver, and are color matches for sterling. A range of flow points facilitates sequential, or step soldering of several adjacent joints on the same piece.
The silver solders, like the gold solders, are furnished
as strip, round wire, chips and powder. Properties and applications of Handy
& Harman silver solders are described in Chart K.
In addition to solders formulated specifically for sterling silver, Handy & Harman manufactures a wide variety of silver soldering alloys for joining any ferrous or nonferrous metal which might be used as a base for plating, since these alloys accept plating readily. Their flow points range from 1145° E (619°C.) to 1805° R, (985°C.) and their silver contents range from 5% to 80%. Full information on these alloys is available on request from Handy & Harman.
Handy & Harman’s Handy Flux has for many years been the all-purpose flux most widely used by manufacturing jewelers and silversmiths. Fully molten at 1100° E (593° C.), it provides excellent protection of parts up to temperatures of 1600° E (871° C.). Handy Flux is available in paste form, in jars of 1/2, 1 and 5 lbs., as well as in 25 and 50 lb. pails.
Handy Flux is also made in liquid form. Handy Liquid Flux, available in 1 pint, 1 quart and 1 gallon containers, is used where only a limited fluxing action is desired, for example in the soldering of extremely light joints or small findings.
All Handy & Harman soldering materials are made in standard sizes, dimensions and formulations. However, these specifications may be varied or exceeded to meet special customer requirements. Full information on standard and special products is available on request from Handy & Harman.
in soldering (brazing) there is always the possibility of dangerous fumes arising from zinc and cadmium bearing filler metals and from fluorides from fluxes. The following well-tested precautions should be followed to guard against any hazard from these fumes.
1. Ventilate confined areas. Use ventilating fans and exhaust hoods to carry all fumes away from work and air supplied respirators as required.
2. Clean metals thoroughly. A surface contaminant of unknown composition on metals may add to fume hazard and may cause a too-rapid breakdown of flux, leading to overheating and fuming.
3. Use sufficient flux. Flux protects the metals being joined during the heating cycle. Full flux coverage reduces the chance of fumes.
4. Heat metals broadly. Heat the metals broadly and uniformly. Intense localized heating uses up flux, increases danger of fuming. Apply heat only to metals being joined, not to filler metal. (Direct flame on filler metals causes overheating and fuming.)
5. Know your metals. Be especially careful not to overheat assembly when using filler metals that contain cadmium. Consult the Material Safety Data Sheet for maximum recommended brazing temperature of a specific filler metal. The filler metal carries a warning label. Be sure to look for it and follow instructions carefully.
(Also consult American National Standard 249.1, “Safety in Welding and Cutting’; published by the American Welding Society (AWS), 550 N.W. LeJeune Rd., Miami, FL 33126.)