Annealing Basics - Part 2 of 3
Contributed by Mike Glasman.
Temperature Measurement, Equipment, and...When You Know It's Time to Throw the BS Flag
Part of the journey towards being "Best in Class" as a club is providing technical information you so can make informed decisions on what you need to do to succeed. Last month we covered what happens and changes when brass cases are fired and re-sized, and we covered needed concepts to help you understand why brass has limited life with respect to performance and longevity.
In this installment annealing basics will be discussed.
To review - annealing rifle brass at 750 degrees for a second or two in the area of the neck where the bullet is seated slightly lowers the strength of the brass and improves ductility. This provides more consistent neck tension from case-to-case, improves accuracy, and improves case life with respect to neck splitting. Annealing should not be performed below the shoulder of the case because this weakens the case where it needs to be strongest.
Before starting with how to anneal, let's dispel some myths heard in the pits and on forums...
- "I anneal till the color changes from shiny till it turns slightly red in a darkened room." You exceeded 900 degrees F and have ruined that brass because it's now way past being able to maintain neck tension. Grain growth has occurred in the material and it's not possible to recover from that condition.
- "I put heat on the brass till the color changes from shiny to " NOPE. The color change is due to oxidation or a reaction that occurs with contaminants on the surface of the hot brass and room air. This is not a reliable indication of annealing temperature.
- I use an infrared gun to measure " Well, unless you have a very sophisticated infrared measurement instrument that can isolate a small target such as a brass case, this is not a reliable way to measure temperature. Not to mention, you need to know the emissivity of hot, oxidized brass for accurate infrared temperature measurement, and you will need to do a lot of work to qualify your measurement methods. And you can't use it with propane-fired machines
The common theme here is none of the above methods provide an accurate, reliable, repeatable means of measuring temperature. The key to successful annealing is accurate, consistent heating.
Now that you know what not to do for temperature measurement, let's discuss acceptable methods. As indicated last month, it's vital that you achieve the proper annealing temperature, otherwise, annealing transformation will not occur, or you will over-anneal and irretrievably ruin the brass.
The best way to measure temperature for our purposes is with a product called Tempilaq. This is a paint containing a substance that melts at a given temperature and is available at Brownells, or on Amazon, etc. For us, we need to anneal at 750 degrees F and Tempilaq Part Number 24423 is what should be used. ( See http://www.tempil.com/temperature-indicators/temperature-indicating-liquids/tempilaq- indicating-liquids/ ) This is an affordable, accurate, simple, reliable, and time-tested method of temperature indication for this kind of application. The author has relied on these products in his professional life in attainment and verification of pre-and post-weld heat treatment for nuclear welding and related heat treatment, and these products have always performed in a certifiable manner.
Part 3 of this series will discuss annealing machines. As always, if you have questions, contact Mike Glasman at email@example.com
See 'ya on the range! Mike Glasman