Alloys and Their Correct Cooling Methods
There are four typical methods of cooling, and the type of alloy being annealed will dictate the method (see table):1. Water quench from red heat. This method can be used for alloys that are age hardened and will result in maximum ductility, however may result in some distortion to the work piece.
2. Natural air cool. This method may be used for alloys that do not age harden or require a slow cooling rate if susceptible to quench cracking.
3. Air cool to “black heat” and then water quench. Black heat is a description used for when the work piece no longer glows red (840°F- 930°F). This method is usually employed for alloys that, if quenched above this temperature, will result in cracking due to the generation of internal stresses. Once the metal has cooled to the above temperature,
water quenching will then result in optimum properties for further cold working operations to take place.
4. Cool by any of the above methods. These alloys will be unaffected by the cooling method, however, the best advice is to avoid quenching from red heat to minimize distortion effects.
Please note that the above recommendations are for optimum results. It is possible to anneal most alloys by heat-treating to a variety of temperatures, times and cool by several different methods and still achieve acceptable results.
White Alloys and the White Gold Index
Hoover & Strong customers will no doubt want to know where our white alloys sit on the MJSA white gold index. This index works by measuring the yellowness of a color, and so the lower the number, the less yellow it is. The assumption is then that if it’s less yellow, it’s “whiter. The value assigned is known as a “YI” value, so here are the MJSA specified levels:• Grade 1: “Good white” alloys. These are described as alloys that will not require rhodium plating. They must measure less than 19 on the YI index.
• Grade 2: “Reasonable white” alloys. These are described as alloys where rhodium plating is an option. They must measure between 19 and 24.5 on the YI index.
• Grade 3: “Poor white” alloys. These are described as having “incomplete bleaching” and require rhodium plating. They must measure between 24.5 and 32 on the YI index.
A non-white alloy is described as one that measures above 32 on the YI index.This is how H&S alloys measure on the YI Index:
As you can see from the above table, the majority of our white alloys make the “premium” or Grade 1 standard and do not require rhodium plating.Of the three that are Grade 2 white alloys, 14KW is very close to being a Grade 1 with a value of 19, which is the borderline value between the premium and next grade. The other two are well above the limit of Grade 3.
TruPd™ has the same value as 950 platinum-ruthenium. It is extremely difficult to tell the difference between these two alloys with the naked eye.
Argentium® Sterling Silver
What’s the worst thing about working with sterling silver? Firescale! This copper oxide is hard to remove at the best of times. You need to pickle, maybe abrade as well to remove deep-seated oxide and the residual copper-rich pink areas from your jewelry. So Hoover & Strong has made this much easier. We now have Argentium sterling silver, a sterling alloy for jewelers and silversmiths who no longer want to deal with firescale.
Argentium sterling silver is also heat hardenable, tarnish resistant and has excellent mechanical properties, making all forms of fabrication easy. For a final operation to make your jewelry stronger, heat treat it to achieve hardness values approximately twice that of annealed standard sterling silver. Unlike traditional sterling silver, Argentium sterling silver casts and solders without fire scale. It can also be laser and resistance welded.
Argentium is available in sheet, round wire and selected sizing and shape wire profiles.
Annealing: If using a furnace, the annealing temperature range is 1050 to 1150°F (565 to 620°C) with a dwell time ranging form 30 to 60 minutes at temperature, depending on size of the furnace load. If torch annealing, a dull red is the color to look for, but this alloy displays a lighter color when heated, so take care. If the metal looks yellow or light orange, it is too hot.
Increasing the hardness of Argentium: This alloy may be age hardened by annealing at 1150°F for 1 hour followed by a water quench, then aged at 580°F for 1-2 hours. Hardness values of up to 125HV can be achieved – twice that of annealed standard sterling silver. This heat treatment operation will also help improve the tarnish resistance of Argentium.
Polishing: To avoid contamination from other alloys in the workshop environment, it is ideal to have separate polishing wheels for use on Argentium sterling silver only. If this is not possible, thoroughly rake wheels before use.
Soldering: Because Argentium sterling silver displays a lighter color when heated, a little more care must be taken during heating operations. Low temperature solders are therefore recommended, we recommend solders with flow points below 1400°F. Use our Argentium hard, medium and easy solders for best results because it is important to avoid
overheating this metal. Use standard soldering fluxes.
• Density: 10.3 g/cm3 (5.42 troy ounces/in3)
• Melting range: 1410°F – 1610°F (766 – 877°C) • Hardness values: Annealed: 60 HV
• Hard rolled: 110 HV
• Age Hardened: 125 HV
Casting Argentium sterling silver:
Use the following information to successfully cast Argentium silver.
• Melt range: 1410°F – 1610°F (766 – 877°C)
• Casting range: 1740 – 1780°F (950 – 980°C)
• Flask temperatures: 950 – 1000°F (510 – 538°C). Do not exceed 1250°F.
• Density: 10.3 g/cm3 (5.42 troy ounces/in3)
• Quench time: 15 minutes minimum to prevent cracking.
• Recycling: We recommend using at least 50% fresh metal with each cast.
• Hardening: If flasks are quenched after 15 minutes, the castings will have the same hardness as standard sterling silver. The hardness of castings can be increased by leaving them in the flask until cold, or by heat treating the whole tree/individual castings in an oven set at 580°F (300°C) for 45 minutes then air cool.
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