Learn the secrets to quality metal fabrication from Stuller’s in-house team of experts.
Annealing is a process, which eliminates the stresses created during mechanical working or deformation of an alloy, so that the material can be restored to maximum softness. In the metals industry, this involves heating a metal to an elevated temperature for a controlled length of time, followed by natural or forced cooling back to room temperature.
Annealing is very important commercially, because it restores ductility to a metal that has been severely cold worked. Therefore, by interposing annealing operations after severe deformation, it is possible to deform metal to a great extent.
General Annealing and Softening Guidelines
It is important to realize time, temperature, and cooling rate are important variables in controlling the outcome of an annealing process. In general, annealing should be completed in a time that is measured in minutes, not hours. Metals can be softened to a certain point and no further, regardless of how long they are exposed to elevated temperatures.
Generally, anytime you heat a typical jewelry alloy to a red color (above 1050°F) the alloy will begin to get softer. Exceptions would be 950Pd and 950Pt alloys —they will not soften until much higher temperatures are reached (above 1700°F).
Karat golds are a little more complicated since compositions vary considerably. In general, yellow, green, and red alloys can be softened by heating to 1250°F (677°C) for 10 minutes followed by water quench. Time will be determined by the alloy and the size and shape of the piece. Green and yellow gold can be cold worked up to 60% before annealing is required. When referring to red gold, it can be cold worked up to 50% before annealing is required.
To soften sterling silver, heat to 1100°F (593°C) followed by water quench. Silver can be cold worked up to 70% before annealing is required.
To soften platinum, heat material to bright orange color, 1800°F (982°C). Let the piece air cool or quench after reaching bright orange color. Platinum can be cold worked up to 70% before annealing is required.
Note: Annealing gold, silver, and platinum for too long can cause grain growth, which may make finishing difficult.
|METAL||ANNEALING TEMPERATURE||ANNEALING TIME||TORCH SOFTENING|
|Platinum||1800°F (982°C)||Most 950 Pd and 950 Pt alloys can be annealed by holding for 15 minutes @ 1800°F followed by water quenching.||950Pd and 950Pt can be adequately softened by torch heating to a bright orange color, no special cooling required.|
|Yellow Gold||1250°F (676°C)||Hold for 10 minutes @ 1250°F followed by water quenching.||Most yellow gold alloys can be adequately softened by torch heating to a low red color followed by water quenching.|
|White Gold||1350°F (732°C)||Hold for 10 minutes @ 1350°F followed by water quenching.||Most white gold alloys can be adequately softened by torch heating to a dull orange followed by water quenching.|
|Sterling Silver||1100°F (593°C)||Hold for 10 minutes @ 1100°F followed by water quenching.||Most sterling silver alloys can be adequately softened by torch heating to a low red color followed by water quenching.|
Hardening Gold, Silver, and Platinum
When talking about jewelry alloys, temper refers to the hardness and strength that is created in sheet, wire, and other types of products by controlled amounts of cold work during rolling or wire drawing. Simply put, cold work is deformation.
|METAL||HEAT HARDENING||COLD WORK|
|Gold||Most yellow gold alloys cannot be hardened by heating — a select few can. Green and red alloys cannot be heat hardened with very good success — an exception is 18KR. Process for heat harden select alloys, anneal for 30 minutes at 1250°F (676°C) followed by rapid water quenching. To harden, heat to 650°F (343°C) for 30 minutes, quench or air cool.||Karat golds will work-harden when rolled, drawn, or forged. The more you reduce the thickness, the harder the metal gets.|
|Silver||Many silver alloys can be heat hardened. Process to heat harden, anneal for 30 minutes at 1200°F (760°C) for assembled pieces and 1370°F (743°C) for non-assembled pieces followed by rapid water quenching. To harden, heat to 650°F (343°C) for 30 minutes, quench or air cool. For Continuum sterling silver, use a higher temperature of 800°F (427°C) for 30 minutes to harden.||Fine and sterling silver will work-harden when rolled, drawn, or forged.|
|Platinum||Most of the platinum alloys cannot be appreciably heat hardened.||Platinum alloys will work-harden when rolled, drawn, or forged.|
Rolling Procedure Steps for Sheet Metal
Anneal ingot or sheet, pickle, rinse in water and dry.
Apply snug pressure on rollers, commence to roll. After each sweep through the mill, rotate the material from end to end before passing through the mill again.
When the metal becomes hard, repeat steps 1 and 2 until the desired thickness is reached. Common practice for silver is to roll sheets from 3mm to 1mm before annealing.
Common Rolling Problems, Causes, and Corrections
Problem #1: Buckling
- Direction is changed during rolling without first annealing.
- Not enough reduction per pass when rolling.
- Rollers have a worn area.
- Rollers are no longer parallel.
- Too much reduction.
- Remove metal, anneal, proceed.
- Adjust rolls to apply greater force.
- Replace or have rolls conditioned.
- Adjust the rollers.
Problem #2: Cracks Along Edges
- The ingot rolled is not of uniform shape.
- Metal rolled too much without annealing.
- Saw out sections that contain cracks or holes. Anneal, forge out material around the cavities so they align with the edge.
- Anneal, proceed to roll.
Problem #3: Cracking & Flaking Surfaces
- The metal ingot mold is too cold when metal poured.
- Too much old metal is in the pour.
- Metal is annealed too often.
- Metal is contaminated with foreign matter.
- Remelt, cast ingot, and roll again.
- If problem persists, refine the metal before attempting to proceed.
Problem #4: Sheet Pulls to One Side
- Rollers are not even.
- Thickness of ingot is not uniform.
- Correct by applying equal pressure to both sides of mill.
Problem #5: Rod Is Wavy When Rolled
- There is not enough tension on the free end of the rod.
- There is not enough reduction per pass when rolling.
- Correct by placing one end of the rod in the mill and hold the other end tightly with one hand while rolling.
- Adjust rolls to apply greater force.