Bonsai is a fun hobby for many people. Copper wire is used often in this hobby and can be much easier to work with after proper copper annealing.
Work Hardening the Copper Wire
Copper is a metal that features a cubic crystal structure. The specific variation, or the face centered cubic, provides the extreme ductility that allows the copper wire to be bent into sharp curves. Aluminum, gold and silver all have this same crystal structure.
Bending the copper wire will work harden it. This process presents defects referred to as dislocations to the structure. The dislocations hamper further deformation while making the copper strong and hard. Thus, the copper wire cannot be bent again easily. This is the reason that copper works so well for bonsai because it will bend with ease initially, but then it will hold the shape.
Annealing the Copper Wire
Copper annealing will do away with the dislocations to allow the copper to go back to perfect crystals. Then, the copper wire can be used again because it will be soft and easy to bend.
Typically, copper annealing is done at more than half of the melting point of the absolute temperature scale. The melting point of copper is about 1981°F, so copper annealing is done at temperatures higher than 761°F. However, it will take quite a while at the lower end of the range. Therefore, it is usually don at about 1292°F to 1472°F.
It is possible for copper wire to be work hardened and annealed a number of times for use by bonsai enthusiasts. Especially, since this type of hobby does not require meticulously controlled properties. However, the properties are going to degrade over time with repeated cycles for a number of different reasons, such as oxidation.
After annealing at a realistic cooling rate, copper will keep the soft crystal structure. Water cooling is recommended in order to prevent the excessive surface oxidation. Unlike steel, which will change dramatically with rapid cooling, copper can be cooled fast enough to turn it into a brittle material. Generally, this will involve cooling rates that are greater than 18000032°F per second. This can only be done by spraying a thin film onto a very cold surface, which requires very expensive equipment.
Bonsai wire does not require strong measures to be taken in order to prevent oxidation, unlike with electronics or jewelry. Therefore, it can be heated to a dull red glow and work fine.
At Franklin Brazing, we have continuous furnaces that provide exceptional heating and cooling cycle performance. When it comes to copper annealing, rest assured that you will receive the best possible service to meet your application needs.