Annealing furnaces & ovens Carbolite Gero
Carbolite Gero offers a wide range of annealing furnace and annealing oven solutions, from standard to fully custom designed units. Below you will find suitable products sorted by atmosphere as well as a general introduction.
INTRODUCTION TO ANNEALING WITH FURNACES AND OVENS
Annealing is a heat treatment process that alters the physical properties of a metal in order to increase its ductility and make it easier to work with.
Metals are heated above their recrystallisation temperature and are kept at a steady temperature for a required length of time, before being allowed to cool. This method changes the internal microstructure of the metal as the atoms diffuse through the solid material, reducing the number of dislocations (linear defects within the metal's crystalline structure), increasing the size of the grains within the structure, and reducing stresses, resulting in a more workable material.
There are three stages to the process: recovery, recrystallization, and grain growth.
STAGE 1: RECOVERY
The recovery stage involves heating the metal to soften it and remove dislocations and internal stresses. The process of heating provides the energy required to break bonds and increases the rate at which atoms diffuse through the solid material.
STAGE 2: RECRYSTALLIZATION
During the recrystallization stage new “strain-free” grains will nucleate (form) and replace those deformed by dislocations and internal stresses. If the process is allowed to progress to the “grain growth” stage, the grains will continue to increase in size.
STAGE 3: GRAIN GROWTH
If the annealing process continues beyond the recrystallization stage, the grain growth stage occurs. A piece of metal with large grains has higher ductility and machinability, but lower yield strength than a piece of the same material with smaller grains. The size of the resulting grains depends on both the temperature and processing time. Once the annealed metal has been worked, it is possible to increase its strength by subjecting it to other processes such as hardening and tempering.
REMOVING DISLOCATIONS VIA ANNEALING PROCESSES
When stress is applied to a metal, plastic deformation can occur, which generates defects in the crystalline structure, known as “dislocations”. The higher the number of dislocations within the material structure, and the more they move against each other, the harder the material becomes. Thus the aim of annealing is to prevent this by reducing the number of dislocations.
INDUSTRIES THAT USE ANNEALING FURNACES
Annealing is used throughout various metalworking industries, such as steel production, sheet metal manufacturing, and jewellery making. The overall process is the same, but the scale at which it is carried out depends on the industry.
Manufacturing facilities will utilise large units to anneal batches of material, whilst jewellers may use a smaller annealing oven, or even gas-powered blowtorches to anneal bespoke pieces of jewellery.
Although blowtorches may be convenient for some, a digitally controlled furnace or oven will always offer greater precision, temperature uniformity, and repeatability.
ANNEALING TEMPERATURES REQUIRED FOR DIFFERENT METALS
Different metals have different annealing temperatures. The table below shows examples of metals commonly used within manufacturing and jewellery making, alongside both their anneal and melting ranges.
| Metal | Annealing temperature* | Melting temperature* |
| Aluminium | 300 – 410°C | 660°C |
| Brass | 500 – 550°C | >930°C |
| Copper | 371 – 649°C | 1084°C |
| Gold (24k) | 200°C | 1064°C |
| Platinum | 700°C | 1768°C |
| Stainless steel | >1000°C | 1400 – 1510°C |
| Sterling silver | 649°C | 894°C |