INDUCTION ANNEALING -suggestions

[camac]

Like quite a few guys on this group I am toying with converting to induction annealing. From the outside it appears control of temperature and time, plus fairly even heat distribution seem to be in its favour. My issue comes from sourcing a decent product.
Obviously the mini ductor is being used by some and I am toying with this approach but this tool is a little expensive for the average loader and it appears as though you would have to add external control gear to control temperature and time (please correct me if I am wrong).
Obviously there are other options. Does anyone have any suggestions?? (remembering coil voltage has to be safe! I imagine replacing the element with a coil on the portable cooktops might be dangerous voltage??)

 

[Gearheadpyro]

Sourcing an induction heater has been the single largest challenge in my quest to automate this annealing process. I have finally found a less expensive option (about 1/3-1/2 the price) that works even better than the Mini-Ductor. I've put together a new video that shows it working (at long last)...

New Model Induction Heater

The mini-ductor is a good tool for heating steel, iron, or other ferrous metals (as it was designed). It can be made to work on brass cases, but is not terribly efficient. Add to this the cost of the tool and it gets a little iffy.

You will need to add a timer to the unit; either one on the main power cord, or (what I did) hook up a timer to control a relay, and run the switches wires through the relay.

The most effective way to control temperature is to control the time. IR temperature sensors will not read on brass so controlling the temp this way is ineffective. Put some tempilaq on the cases to measure temperature.

Induction heaters work on fairly low coil voltage, but the mini-ductor runs almost 30 amps of current through the work coil. The heater I'm using now runs almost 75 amps. It's a lot of current, and the coil does get hot as a result. What causes them to heat though is not the current, it's the frequency that the coil runs at (usually between 50khz and 250 mhz, depending on size and load).

PM me if you have any other questions.

 

[camac]

Thanks greatly Gearheadpyro. I watched your other stuff with great interest too. I may PM you but will try and keep the general discussion on here as I am sure it greatly interests some of the members.
Temperature and time control are the things that really interest me after years of annealling - no doubt often the "wrong way". We are told it takes some time for the crystals to align at 650 F, and at somewhere between 8-900 is too hot. Glowing red is too hot, but below that may be too cool or too short to get that consistent neck tension we crave. trying to control the temp around 750F for a few seconds is pretty tricky with a gas torch but we must get it close as the benefits are obviously there. My hope is with induction you could set the "power" level correctly to not let it get to 800 even after a long time (such as the induction cook tops with 10 power levels). Then you could control the time exposure to ensure correct time above 750. I notice you seem to favour time in controlling temp with a higher power setting. In your experience is this a pipe dream? ie if I set the power too low, will it take too long to heat up the brass, hence transferring too much heat to base of shell??
Thanks CAM
There is another post video that comes up near yours on youtube where someone has converted one of the hotplates I mentioned (around $60.00).

 

[Gearheadpyro]

I've seen the converted hot plate video, and looked at doing that, but it presents several unique challenges. One of the largest is it takes a certain frequency to heat brass (and a LOT of power). The cook tops are not designed for that and would (likely) overload in short order.

I do favor time in controlling the amount of heat with this process for several reasons.

1. It is extremely difficult to control power output of an induction work coil. You can set power ranges, but the load (the case) the coil shape, the coil size, what other metals are around the coil, etc..., all affect the actual power output. Thus you could not set a heater to never go over X temperature without controlling the heat cycle. This leads to my next point.

2. Most of the induction cooktops I have seen have an infared temperature sensor in the body. They read the temperature off of the pan, then adjust the duty cycle of the coil based on that reading. Brass will not read a temperature with these sensors. The IR emissivity is simply too low.

3. When you anneal with propane it takes time for the case to heat from the outside in, thus you need to hold the case at a temperature for a given time. Because cases are fairly thin though, an induction heater will heat all the way through the metal at the same time. This greatly improves consistency from piece to piece, so long as you are consistent with the times (thus my computer controlling it). You can watch the even heat on new cases. The grains visually change as it approaches the correct temperature, on the inside and out. When a case is overheated it will first turn pink at all sharp corners (case neck and shoulders), then the inside of the case turns red first.

700F - 750F is the temp I aim for with the induction heater. It seems to be soft enough for the benefits, but not oversoft. I only need to get the case to that temperature, I don't need to hold it there like with propane.

The biggest thing to watch out for with an induction heater is overheating the case. Because it heats so quickly it is very easy to overheat. When I set my heater up for a case I'll start off at a time of only 1 second, then I'll watch my tempilaq as I bump the heat cycles up (letting the case fully cool in between runs).

 

[camac]

thanks again GHP - I am still trying to gather the concept together and am probably a little electronically challenged. I would have thought in this case - once you have the same case size, same coil, same amount of metal around coil etc then apart from heat build up the load should have been fairly consistent - Am I missing something here??.
Point taken about IR control - will challenge my electronics guy here with that one.
Also noted about load on small induction stove top.
Can I talk you into making a few machines to save me the hassle????

 

[Gearheadpyro]

I'm working on an automatic machine that I would like to be able to bring to market. Currently I am just waiting on the funds to purchase a number of different custom machined aluminum components. (If anyone has a machine shop and will do a few small jobs please PM me).

I'd love to know what your "electronics guy" comes up with for temp control. Please keep me informed.

You are correct about the load being fairly consistent under those circumstances, but if you switch calibers then all bets are off. Even if you switch from some thick LC brass to some thin Winchester brass you would overpower the workpiece. This is why I favor controlling with time. I set the time up for a lot of cases, then run it. When a variable changes, the time changes.

 

[camac]

Thanks again GHP.
OK I will try and relay some of the information gathered - once again I am not the expert so could get a little bit of it wrong.
But some of these may be worth discussing.

1) Brass emissivity is not only very low but varies with temp (ie goes from shiny reflective surface to dull, blued/greyed/purple etc which actually improves emissivity as it gets hotter) - it might (possibly?) give a reasonable reading at the temps we are talking about but certainly would be hard to calibrate (due to varying emissivity - expected to range from .3-.5) so you could only use as a relative guide not as a temp reading. BUT As emissivity of brass is low it is unlikely to "shut" stove top down (or reduce heat cycle) due to too much heat. He indeed could use other temperature indicators to control cycle but most of them are contact probes and it is unlikely to work (due to the extremely quick heating) and get an accurate measurement to control cycle quickly enough. Finally we discussed bypassing IR sensor with a variable resistor (as mentioned earlier) that could effectively be set at a certain resistance, thus setting the inductor at a constant power level - He needs to take a look at stove top (or other). to work this out more accurately.

2) With power set at a constant, indeed time is your next control point.

3) How about using exhaust matte black paint and IR temps on your "calibration cases"? (is increased load significant?? but then the same for th tempilaq)
4) Alternatively, leave the carbon on outside of neck - it has a much better emissivity.... ?

If you need a few Aluminium parts made in exchange for a prototype model?? or similar deal then PM me with some diagrams I will let you know if I can do them on the lathes/mills etc we have here. (I make heat sinks etc but do not have production line or CNC machinery).

Cheers,
CAM

 

[Gearheadpyro]

Yes, the color does change, but not consistently. Some cases will be darker or shinier than others when the tempilaq reads the same temp. Both are annealed, but look different. The differences in color are especially apparent with different brands of brass.

You are also correct that because the IR sensor will not read, it will read low and thus not shut the power off.

A contact probe would not work. As it is metal, it would be subject to the same heat as the case (and possibly more so because the ones I have a steel probes).

Plugging in a resistor would work (although you would actually need 2 or three). The only issue I see here is the way the stove top uses that signal. This would effectively reduce the amount of power given to the case, but not control the time. We want the case to heat as quickly as possible, but not for very long.

I'm pretty sure that the matte plack paint and IR sensor would work ok to figure out what the time you need is. I doubt it would have an effect on the load unless it is a metallic paint. Tempilaq seems to have no change on the time needed.

Leaving the carbon on the case does improve the readability of the case, but it is very unreliable. I experimented with this early on in my work on my automatic annealer. Different amounts of carbon put out different temp signals. I think this is due to how much of the IR beam hits the carbon. It also produces a bad side effect of "burning" the carbon into the case. I'm a little bit of a stickler for shiny cases, so I didn't like this.

I will send you a PM with the drawings soon. I have a busy day with a Friends of NRA banquet tomorrow. All of my drawings now are in the free CAD program from emachineshop.com. I was going to use them until I saw the prices ( ). I do not have autocad. The parts for prototype sounds like we might be able to make something happen. I'm looking to go ahead and put 10 of these machines together, so once it starts running I'll need some beta-testers.