The Annealing Process


An Easy Beginners Guide on how to anneal different metals

To define the annealing process in simple terms means to remove any stresses and return material to a soft and workable state.

This is especially so in metals that become work-hardened, like copper and brass, although brass can become very brittle and fracture easily if this happens.

In steels, this annealing process is generally used to make the metal more pliable and less likely to fracture, easier to drill and shape.

This annealing process can also be used on glass. In other words, if you have a material that turns liquid upon heating (disregarding the temperature for now) then it can be annealed.


How To Anneal Copper

Copper should be clean and bright, otherwise oxides will form and become embedded in the surface on heat-up, and should be warmed up generally rather than at a specific point with what’s known in the UK as a blow-lamp – sometimes known as a blowtorch elsewhere (a kitchen stove will do this at a push for small sections or thin sheets of copper) although copper tends to spread heat quickly through the metal anyway.

Once a background heat is produced, when the metal shows different colors radiating away from the heat source, then you are looking for a dark red (plum color) reaching the part you want annealing – it’s like the colors of the rainbow moving from blue through to bright red and leading up to white at the hottest, although you are not likely to get anywhere near that with a blowtorch.

Once this occurs quickly immerse the copper you are annealing into a water bath, and that’s it. Job done.

The easy test is to tap it with a screwdriver or something similar. If you hear a ringing sound, the copper is still hard and needs to be annealed again. If the sound is dull then you have annealed the copper properly.

Don’t delay the quenching too much otherwise you will not achieve the annealed copper you were aiming for.

Before you begin to work the copper you must remove any surface oxides that have formed with a wire brush, wire wool or emery cloth as these become embedded, spoiling the appearance, and are difficult to remove later.


How To Anneal Brass

Annealing brass is very similar to copper, although the temperature should be a little cooler as it usually contains zinc which melts at a lower temperature.

What you are looking for as you apply the flame of your blow-lamp onto the part to be annealed is the tell-tale colours again.

When the brass starts to show a blackened colour, then is the time to quench it quickly before cleaning it up.


How To Anneal Aluminium (Aluminum)

Now here you need to be very careful as the difference in temperature between softening and melting is marginal.

If you try to anneal aluminium without cleaning the surface you will get to the stage when heating where the surface looks solid because of the surface oxides, but the inside will be turned into a liquid, meaning the piece you are heating will collapse once the surface tension is destroyed and you will have a blob of aluminium remaining.

Clean up the metal first before coating it with household soap, directly from the bar, covering the area of the aluminium you need to anneal (any brand will do providing it is a solid household soap and there is no built-in conditioner for dry skin included).

With your blow-lamp set at low heat, run it around the surface, warming the work generally and make a point of not keeping your flame in one place for too long.

Keep warming it up until you see the soap turning black and then shut the heat off rapidly and dunk it in water.

Clean it up and the jobs done…

You can see here that rather than watching for colors like on the steel, brass and copper process, the signal is the start of the burning of the soap, meaning it has reached the right temperature.


How To Anneal Steel

Annealing steel is generally needed when you are dealing with heat hardened steels.

Steel generally needs to be heated to cherry red and allowed to cool down naturally, the slower the better.

What the heating does is to allow the molecules within the steel to align properly and the slow cooling keeps them aligned, that way making the steel more easily worked.

Looking at a blacksmith and his forge you will see that while the metal is hot it can be shaped easily with a good clout because the molecules are in line. When the work has cooled after being beaten, the molecules are out of line and the metal is harder and more likely to fracture. Obviously the more impacts it receives the harder (and more brittle) it becomes.

This is what is known as ‘work hardening’!


How To Anneal Stainless Steel

To anneal stainless steel, basically softening it, requires a lot more heat (1900°F / 1000+°C) than annealing steel in that an orangey-red color needs to be achieved with your blow-lamp, but it also needs to be kept orange for at least ten minutes – preferably longer to do it properly.

It all depends on the size of the piece of stainless steel you want to anneal. Larger flat pieces will definitely warp as they need to be cooled very quickly to stop the chromium and the carbon bonding – it’s the chromium that makes it stainless – so be prepared to have to flatten the sheet out. For small sections this is not so much of a problem.

If you have the option, being left in a kiln for around an hour at those temperatures for thicker sections, then quenching quickly does the best job.

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