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CHEAP CASE NECK INDUCTION ANNEALER
EXPERIMENT
By Wayne McLerran
Posted 12/7/18

Please note that the experiment was not successful but the details
should be interesting and you should learn something from the article.

If you’re already annealing your brass case necks or considering doing
so you’ve no doubt researched the subject to some extent on the
Internet.  There have been numerous threads on reloading forums
discussing annealing brass cases to soften the work-hardened necks,
extending the life of the cases and arguably increasing the accuracy of
the ammo.  Induction technology seems to be the latest trend when
designing case annealers.  But induction annealers are very expensive,
typically around $1,000 or more.  Therefore I thought I’d take a shot,
pun intended, at configuring a cheap solution with $100.00 being the
maximum expenditure.

Run a search on eBay or Amazon.com for “induction heaters” and you’
ll find many, many units in the $30 to $40 range with some as low as
$12.  They’re typically used with a round ceramic crucible that fits
inside a 2” diameter coil made from 5mm outside diameter (OD)
copper tubing.  Made by companies in China and Hong Kong, the
heaters are used to melt precious metals and other materials and,
depending on the unit, run off of 12V to 48V DC.  They could be
connected to a car battery for 12V or two batteries in series for 24V,
etc.  But a much better solution is to purchase a switching power
supply, also available cheaply from similar sources.  Although I have a
very nice propane-powered Vertex Bench Source brand annealer, I
was curious enough to purchase one of the Chinese 12V to 48V units
and a switching power supply to see if it could be modified to work for
annealing case necks.

If you research the suppliers of ready to use albeit expensive case-
neck induction annealers you’ll find they’re rated at around 1000W
(watts) in order to anneal a typical case neck in 3 seconds or so.  
Therefore, since power measured in watts is equal to voltage (V) x
current measured in amps (A), an equivalent unit powered by 48V
would require a power supply capable of supplying approximately
21A.  But since $100.00 was my self-imposed limit a 24V 20A setup
was selected.  The combination of induction heaters and power
supplys are available on eBay for around $60, and lower power
combinations are available for less.  Will they work annealing case
necks?  There was only one way to find out.

A 1000W ZVS induction heater and a 24V 20A switching power supply
were ordered off eBay from Chinese and Hong Kong suppliers.  The
total cost was $59.26.  The heater came with a fan attached to aid in
cooling the electronics.  In less than two weeks the units arrived.  A
2” diameter coil came with induction heater electronics.  There were
no instructions but after inspecting the unit closely it was obvious how
to install the induction coil and how to connect the required power.
Although the induction heater could handle up to 48V DC, the
recommendation was to use it with a 24V power supply.  By the way,
while researching the subject of cheap Chinese or Hong Kong
induction heaters I ran across several warnings not to apply power
without the induction coil installed or the heater electronics will be
damaged.

Induction heaters work on the principal of creating “eddy currents”,
which are localized electric currents induced in a conductor by a
varying or changing magnetic field.  When current flows through a
coil, a magnetic field is created around and inside the coil.  When a
conductive material is inserted into the coil the quickly changing
magnetic field produces eddy currents in the material.  The materials
resistance to eddy currents generates the heat.

The 2” diameter coil supplied with the induction heater was designed
to heat precious metals in a ceramic crucible.  Although it quickly
heated iron rods of various diameters red hot, it would not heat a
solid brass rod or .45-70 case neck when inserted in the coil.  Ferrous
metals such as iron and steel are much easier to induction heat than
non-ferrous metals such as aluminum, copper and brass.  Non-ferrous
metals, especially those with low resistance to electrical currents,
require a higher concentration of magnetic fields and eddy currents.  
One method to increase the frequency and concentration of magnetic
fields and eddy currents is to reduce the coil diameter.  After
experimenting with different size coils made from 12-gauge copper
wire, the unit would very quickly heat case necks with a 1” inside
diameter (ID) coil.  Since a 1” coil would be hard to form using the
5mm outside diameter (OD) copper tubing supplied with the unit, one
was made from 4mm OD copper tubing ordered on Amazon.com from
a Chinese supplier.  The 1 meter length of tubing was $7.81.  The coil
was formed by slowly wrapping it around a 1” diameter wooden
dowel, allowing for sufficient length on each end to attach to the
heater electronics and vinyl tubing for cooling.

By the way, I quickly realized why the supplied 2” diameter coil was
made of copper tubing rather than solid copper wire.  Even with the
unit running without an item inserted in the coil, the coil eventually
gets warm due to the eddy currents created in the coil by the coil
itself.  And when used to heat metal, the radiant heating from the
metal will definitely heat the coil.  Therefore the coil is made from
copper tubing to allow pumping cool water through it for extended
use, which is especially important when the diameter of the coil is
reduced.

To cool the coil a small cheap 115V (AC) submersible water pump was
purchased from Amazon.com, one made for fish aquariums and bird
baths.  The price was $8.65 and a length of 0.170 ID, 1/4” OD clear
vinyl tubing was purchased from a local hobby shop for $1.95.  After
connecting the tubing to the induction coil and pump, the pump was
submersed in a bowl of cool water.  It worked great and supplied
plenty of cooling as long as the water was not allowed to get
excessive hot.

Finally, due to the induction heater design, a switch must be used to
connect the output of the power supply to the induction heater.  The
switch does provide the capability of turning the heater on and off as
needed rather than unplugging or turning off the power supply.  But
more important, it’s required to “shock” the heater circuitry into
running correctly.  If the heater was connected directly to the power
supply, as the supply was turned on the relatively slow increase in
power supply voltage would destroy the MOSFETs (transistors in the
heater).  Suffice it to say that the coil circuitry must be “kick
started” to oscillate or ring properly to create the quickly changing
magnetic field, which is accomplished
by the switch.  Therefore the
power supply must be on and running prior to engaging the switch to
the heater.  Adding a switch was less than $5.

Once everything was setup and connected (the induction coil
connected as noted earlier, the water pump running and water
flowing through the coil), the power supply and then the induction
heater was turned on.  A .45-70 case neck was inserted into the coil.  
Only 4 seconds was required to anneal it which was obvious by the
neck color change.  So, for less than $83 I had a functional and cheap
case neck induction annealer.  But there was a problem!

After annealing several case necks I became aware of an unusual
burning
smell.  It turns out the bottom of the circuit board was
blistered and burned close to the input to the coil and some of the
large capacitors were getting extremely hot.  The smaller diameter
coil more than doubled the current requirement of the heater
circuitry.  As illustrated in the photos below, without an item inserted
in the coils (unloaded) the original 2” diameter coil setup current
draw was 3A with 24V.  With the 1” diameter coil the unloaded
current draw was 9A.  Inserting a metal rod or case neck into the coil
essentially doubled the unloaded current draw of both setups.  After
attempting some modifications to the circuitry to fix the problem it
was obvious the circuit board design and some of the components
were not adequate to handle the increase current.  So the experiment
was not a success.  No doubt a beefier circuit board could be designed
to work, which I may tackle at a later date.
Although the original goal of the experiment was not realized I
learned a good bit during the process.  By the way, after repairing
the burned section of the circuit board and with the original larger
coil installed, the setup works fine and the heater can be used as
designed.  Without the multimeter and amp gauge components, the
setup will be kept handy in my workshop for quickly heating up
smaller metal parts for hardening and other applications.

Wishing you great shooting.
Wayne