Friday, May 13, 2011

Fourth Entry: How to Solder (An Introduction to Silver Brazing)

Welcome to the fourth entry in this series of articles. In the previous article I discussed rolling metal into sheet form CLICK HERE to visit that article. In this article, I will go over basic soldering techniques as well as some basic soldering guidelines, tips and pointers. There are many different ways to solder, different types of solders and metals that can be joined using this technique. In this article I will be specifically dealing with torch soldering (or “silver brazing”) precious and semi-precious metals with silver (or gold) solders; although this article may be practical for other forms of soldering as well.  

Necessary Materials and Tools:

-Metal to solder together
-Small Paint Brushes/ Tweezers/ Soldering Picks
-Binding Wire/ Third Hand
-Quench/ Pickle Rinse
-Scissors/ Snips
-Soldering/ Annealing Area
-File/ Sandpaper

As mentioned in the introduction, this article is technically about “silver brazing” and not normal soldering. The main difference being that brazing occurs when the material being used to join two (or more) pieces has a melting point above 450°C. Although, both techniques are different by definition, one could use this technique with solders that melt below 450°C as well. 

Before beginning, make sure you have an adequate, clean work space constructed out of appropriate heat resistant materials and plenty of ventilation. Different surfaces and materials are better suited for specific soldering needs, some commonly used surfaces include: fire bricks, charcoal blocks, steal wire mesh, pumice stones and many others. With time and practice every individual finds the materials and tools that best suit his or her needs and unfortunately soldering does not become a precision art without years of patience and practice.
Just as there are a variety of surfaces to solder on there are a variety of different solders. A solder or brazing material is typically an alloy of similar composition to the piece/s being joined and has a melting temperature just below the temperature of the piece/s to be joined. Modern silver solders are typically alloys of silver, copper and zinc; gold solders are typically alloys of gold, silver and copper. The type of solder one uses will depend on the materials to be joined and many times it can be useful to use solders with different melting points on pieces with many soldered elements/seams (more about this later).

The most common “silver solder” is usually found in sheet form and is then cut into tiny square chips or “pallions”. This is the most common form of silver solder most likely because it can be easily produced using basic metal-smithing tools. Solder can also be purchased as wire or paste and each type of solder does the same basic job. However different types of solder may be better suited for specific tasks. For example: Paste solder is often used in filigree work as it can be more easily distributed and cover a wide area without leaving much residual mess. And solder in wire form is best suited for “feed soldering”, where a work piece is fluxed and heated and the solder wire is introduced or “fed” into the desired seams and gaps.   
Once we have an adequate place and all the appropriate tools, materials and equipment together we can prepare our pieces to be soldered together. First determine what pieces are going to be joined and how you want them put together. Make sure that the pieces to be joined are clean and as close to finished as possible with the areas that are to be soldered freshly filed and sanded.

Once your pieces are clean and ready to be joined, it is time to figure out how to position them appropriately. If we are joining two flat pieces end to end they could be placed on a flat brick. If two pieces need to be at 90 degrees from one another you could position one flat and support the other with a third hand. For even more complex assemblages sometimes it is necessary to use binding wire to “tie” pieces together before soldering; preferably a thin gauge stainless steel wire. 

Once the pieces are properly laid out and the seams to be soldered fit snugly together we can begin to apply our flux and solder. I typically start my projects with hard solder (higher melting point, lower zinc content) and depending on the amount of soldered elements to be added to the piece, may later switch to a “softer” / “easier” solder (lower melting point, higher zinc content) to ensure I do not over heat my previously soldered seams; as they are very sensitive to overheating. TIP: Another way to ensure your seams are protected, if you don’t have multiple solders available to you, is to paint a layer of clay or “white-out” over your previously soldered seams. This material will work as an insulating heat sink, pulling excess heat away from your seam/s. Keep in mind that clay is probably the healthier option as “white-out” smells really bad when lit on fire… NOTE: Always make sure to solder in a well-ventilated area.

After cutting out a few chips of solder from my sheet, I dip a fine tipped brush into my well of flux and pick up a few chips with the damp end of the brush. I then carefully place the chips (one or two at a time) along the seam/s or piece/s I want to join together. One could also use a pair of tweezers or a “soldering pick” to move the chips into position. One can also add some extra flux to the seam although excessive flux can occasionally complicate the soldering process. NOTE: A small brush can help wick away excess flux or add additional flux; also note there are many different types of fluxes, not all of them are liquid.
It is important to use enough solder to fill the desired gap or seam but, if too much solder is used one waists material and time in having to perform unnecessary and excess clean-up work after soldering. It can often be difficult to decide how much solder is enough but with time and practice one begins to better understand the way the materials work. There are also some instances where excess solder may be useful and/or easily removable. This is not to say we should waste materials but I personally rather perform a little extra clean up or enjoy a little extra solder to having to fill-in solder seams and pits. NOTE: If one were using paste solder, the flux is incorporated into the paste so one needs only apply the paste to the desired work area. 

Once the chips are properly placed and there is enough solder present to fill the seam, we can begin to heat our piece/s up to soldering temperature. Similar to melting material for casting or annealing material for cold working/ manipulation, we want to slowly and evenly heat the work area and the piece/s. Introduce the flame slowly, if the flux is heated too rapidly it may vaporize, boil and sputter sending the carefully placed solder chips across the room forcing you to start over. Generally speaking we want to use a medium size flame with a bushy tip and not very aggressive. The size of your torch and the type of flame you use will depend greatly on the size of the piece you are working on or the type of soldering to be done. These are just a few general guidelines that have helped me over the years.
Most importantly, make sure you are evenly distributing your heat around the piece/s and work area, this is not like using glue, you don’t want to focus the heat on the area of the seam but you want the areas around the seam to become hot enough to pull the solder into the seam/ gap. Solder will ‘flow” toward the hottest areas due to a form of “capillary action” but will not flow properly unless the entire piece is evenly heated.
I enjoy thinking of it like an ice cube melting on a road, filling all the cracks beneath it with water. If the heat (from the sun) were focused on the ice cube instead of across the entire road, the ice cube would vaporize and no water would ever fill the cracks on the road beneath it. If you see your solder balling up into molten blobs that don’t spread across the surface of the metal this is exactly what is happening (assuming your surfaces have been properly cleaned). This is really the most important concept in soldering; it is all about heat control and distribution. Very rarely do we use a very hot, very aggressive (whistling) flame when soldering.
In order to evenly distribute the heat, pay close attention to the color changes that occur to your materials when annealing as these color changes are great indicators of the temperatures of your materials. Also pay close attention to your flux as it too functions as a great temperature indicator. After your flux stops sputtering you should see it turn a frosty/ crystalline white and shortly after you should see it go liquid over your hot metal. Once this temperature is reached your solder should be rapidly approaching its melting point as well. Keep moving your heat around the work area from one side to the other or in circular motions making sure the heat is even on all the elements to be soldered upon, only then can you begin to centralize the heat a bit and focus the heat on the area where your solder chips have been placed.

In the blink of an eye you should see the solder go from solid chips to molten blob/ puddles. At this point it is very important to either move the heat along the seam if there are more chips that have not flowed yet or remove the heat if your solder has all melted/ flowed. Turn off your torch and place it in a safe location. Allow the freshly soldered piece to cool in the air for a few moments and once the piece has cooled, place it in a warm pickle bath to remove any excess flux and fire scale. NOTE/TIP: If the solder is not flowing where it needs to go a soldering pick can sometimes be used to move/ guide the molten solder along a desired path. Although it is very important to do this very quickly as the solder can become overheated if molten for too long, which results in a pitted seam as the zinc vaporizes from the solder alloy. Care should also be taken to not solder the pick to the piece as this is just frustrating and embarrassing.

Allow the piece to soak in the pickle bath for a few moments so that it becomes nice and clean. Remove the piece from the bath and rinse off any excess pickle solution in a sink with running water or in a pickle rinse/ quench. Now you can inspect your newly soldered piece for any gaps or pits in the seam. 

This one looks like it will work just fine for my needs but if you happen to have missed a spot, set up and try it again. There are an infinite variety of soldering methods and techniques but these are the most basic and commonly used techniques I have encountered so far. Perhaps in the future I will make another entry with some additional “advanced” soldering techniques we shall see.
For now I leave you with the "Fifth Entry: How to Fabricate Tubing (Creating a Fine Silver Tube)". As always I hope you found this article to be helpful and informative and I hope you come back for more. Until next time,
Peace and Love.  

Daniel Icaza 5/13/11

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