Annealing with Induction Heating

Learn how Ambrell can help you improve your annealing process! Induction heating concentrates the energy in your part only, so you don't need a torch or a costly batch furnace process. Anneal your assemblies in a repeatable, precise process.

Applications Database

Access these helpful Application Notes after a brief registration:
Annealing SS bread cutting blades
Anealing Tungsten rods
Annealing Steel Tubes
Annealing Steel Regulator Bases for fuel injection system
Achieving Uniform Hardness on Saw Blades
Annealing Thread Ring Gauge Blocks
Annealing Brazing Wire
Band Annealing on Titanium Fasteners
Annealing the End of Metal Stamp Sets

Overview

Annealing is a heat treatment in which a material is exposed to an elevated temperature for an extended time and then slowly cooled. Annealing heat treatments are largely characterized by induced microstructural changes which are ultimately responsible for altering the material's mechanical properties. The goal of this process is to reduce the hardness of the metal and improve its ductility.

Annealing specifically refers to the process of bringing a material to its softest possible point. A tempering process softens the metal but not to the full extent possible.

The degree of temper depends on the material, the maximum temperature reached and the length of the cool down time. Process or Stress Relief Annealing is used to negate the effects of cold work; that is, to soften and increase the ductility of a previously strain-hardened metal. Internal stresses may develop as a result of plastic deformation processes such as machining or grinding, non-uniform cooling in a welding or casting process, or a phase transformation. Distortion and warping may occur if the internal stresses are not removed. Annealing will eliminate these stresses when the part is heated to the recommended temperature, held there long enough, and slowly cooled to room temperature.

Using Induction

Induction heating provides:

• reliable
• repeatable
• non-contact
• energy-efficient
• flameless

heat in a minimal amount of time. Very small areas are heated within precise production tolerances without disturbing individual metallurgical characteristics. Parts are annealed with induction under a controlled atmosphere without flux or any additional cleaning steps.

Induction can be used for either surface or through heating; case annealing is possible depending on time, temperature and the material's characteristics.

Closed loop control, through the use of an optical pyrometer or other temperature sensing device, can provide constant heat with a tolerance as low as 3°C at 700°C. Induction heating also ideal for in-line production processes because of its ability to produce repeatable, rapid and accurate heating cycles.

Typical systems for induction annealing range from 1 to 250kW.

Setup

Annealing processes consists of three stages. First, the metal part is placed inside an induction coil and heated until the part reaches the desired temperature. The temperature can be checked with an optical pyrometer, temperature sensing paint or other temperature-sensing device. The second stage is holding or soaking at the correct temperature, which can be accomplished with a closed loop temperature control system. The annealed part is then cooled to room temperature.

Materials Needed

Metal to be annealed:
Temperature Sensing Device: The temperature of the metal is checked with an optical pyrometer, temperature sensing paint or other sensing mechanism.
Closed Loop Temperature Control System: The control system monitors and constantly adjusts the output of the power supply so as to maintain the correct surface temperature on the part. This allows the core of the part to reach a uniform temperature.
Heat source: Fast, precise heating works best.

Common Problems

The proper tempering temperature is determined by the type of material and the amount of temper required; you may need to experiment a bit to find the optimum level. Once the correct parameters have been established, the process can be repeated with accuracy.
During booth heating and cooling, temperature gradients exist between the inside and outside sections of the part. If the rate of temperature change is too great, these gradients and internal stresses may lead to warping or even cracking.

Solutions

Time is of the utmost importance. The actual annealing time must be long enough to allow any necessary transformation to take place.
Surface oxidation or scaling may be prevented or minimized by annealing at a relatively low temperature or in a non-oxidizing atmosphere.