Induction coil design
Posted 31 March 2012 - 06:53 PM
I was recently asked to start a tread on induction coil design.
I'll open with a link to this three part article on the subject.
Note the "flow" of the current and how stacking the coil can increase heating in areas. This may come in handy when heating unequal parts evenly...say a bolt head and shaft...the head has more mass and takes more time to heat.
Some units may not sense a load unless there is inefficiency in the coil...my larger unit is such..its minimum setting is near 5kw so small items actually require an inefficient coil for it to work at all.
Note also that some simple heating coils need odd contortions to get the power to the area required without cancelation and getting even heating. Some of the smaller induction units work at such a high frequency that they may not heat stock well....in industry efficiency is the name of the game,but in our work it often comes down to ....will it work at all. A 15kw unit at 30,000 or more hertz can do wonderful work, but it is far from an industrial machine and has limitations that can be worked around...but only to a limit. For deep heating a lower Hz rate is far better and may be worth the expense..especially if found on the used market.
I would avoid the motor generator units as they have parts issues.
Posted 31 March 2012 - 09:23 PM
Learning about the design of these coils is one of my goals in the upcoming year.
As I mentioned in the other thread, I have on of Grant's machines that I hoped would allow me to forge during the cold, dark Alaskan winters when the temperature dropped in the negative numbers. Unfortunately, since I have yet to get my head wrapped around coil design, I've used the machine very infrequently (even after paying an electrician a bazillion dollars to wire it up . . .the cable to the machine is literally 1.25" diameter!!).
"It is not the critic who counts; not the man who points out how the strong man stumbles, or where the doer of deeds could have done them better. The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood, who strives valiantly; who errs and comes short again and again; because there is not effort without error and shortcomings; but who does actually strive to do the deed; who knows the great enthusiasm, the great devotion, who spends himself in a worthy cause, who at the best knows in the end the triumph of high achievement and who at the worst, if he fails, at least he fails while daring greatly." -- Theodore Roosevelt
Posted 02 April 2012 - 11:46 AM
Take care, Craig
Posted 02 April 2012 - 08:02 PM
Thanks for developing the topic Ric. I'm glad the Sarver unit is still available, and I'll keep a watch out for your updates here.
Take care, Craig
I have asked Stanley Zinn (author of the above link) if he was interested in writing a booklet specific to the small shop regarding these high freq lower power induction units. I am not sure he will take on the topic (I do not "know him" per se, but his article is very good and he does consultation work..so..a booklet seems like a big article to me), but if he does not then I will find another more versed than I to do the work.
I envision it something like Dr. James Batson's Hydraulic press booklet.....general info and practical "how-to" about what can...safely...be done with these units. It will not be about building the induction unit, but rather using it well.
What is induction
How these small units work vs the larger big brothers in industry
General coil design and theory
tube diam and wall thicknesses
odd shaped coils and how to bend them
what really happens in the field and what other applications it can be used for
Melting, heat treating and control...for when you do not just want to make things hot, but hot with a temp in mind.
that sort of thing.
Such information could only increase the demand for the units...taking some of the mystery out of them. Perhaps Larry Langdon who has taken over the business would be on board with such a thing as well...I have not asked him.
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