November 8, 201312 yr Ok im new to this and not the most knowledgeable on electronics but a friend who is is helping me, I have seen a design online for a 3 to 10kw unit but it gives lots of options and maths. I heat a lot of 1/2" ( 12mm ) round and square for regular items I make so was looking at making it just for that. skin effect! have read that low frequencies for deep heating and higher for heating the surface, as im only doing 1/2" thick what do you thing the best frequency to aim for is? how much power! will 3kw be enough or should I look at more? here in the UK we have 240 volt single phase mains. was thinking of an addition in the form of a timer for heat time, do you think this is a good idea? reheat time will probably be a lot shorter than first heat and will it also be quicker if reheating something I have drawn out thinner.
November 13, 201312 yr not an expert ... but go for the biggest kw ... skin effect... yep the high freq heats about 1/16" skin ... but that quickly wicks into the core .... medium freq costs much more money ... not worth it for just 1/2" barstock ... but if you have the bucks timer... depends on your work... if your doing production type work then maybe ... but i never use the timer on mine reheat is somewhat quicker... heats fast to non-mag then it slows down going higher ... also ... heating depends on the closeness of the coils to the work piece......... if you have huge coils and a small bitty bar, coupling is poorer and heating is slow ... if your gonna make one... make it so that you can change out coils very quickly to suite the work you are doing ... and go for the highest kw unit ... you can turn it down good luck G
November 13, 201312 yr Author the unit i am looking at was aimed at 70khz but turned out to be 66khz, as most of my work is the 1/2" i would make coils that are best for that size but I would have bigger for other stuff. in the shop at the moment we have 14 coke forges so im not short of something for bigger jobs ;) one reason for 3kw is this is what we get from a normal wall socket here in the uk, in the shop we have bigger including a lot of 415v 3 phase at 32a per phase but if it plugs into the normal domestic sockets it can be used anywhere. looking for sources of the components now, have all the major ones sorted.
November 13, 201312 yr The commercial one I saw in use had a foot switch as the heats were short enough that standing there holding the piece and stepping on the switch was not a problem.
November 13, 201312 yr Author was going to use a footswitch but as so much of the things I suddenly need to make another batch of are the same 2 items and each will need x seconds to heat being able to switch it to a fixed time may be useful, sort of press footswitch and release for x seconds but also be able to press and hold for other stuff. the design im building has virtually no controls on it and uses a phase locked loop. yes I will make it easy to change coils
November 14, 201312 yr Ok im new to this and not the most knowledgeable on electronics but a friend who is is helping me, I have seen a design online for a 3 to 10kw unit but it gives lots of options and maths. I heat a lot of 1/2" ( 12mm ) round and square for regular items I make so was looking at making it just for that. skin effect! have read that low frequencies for deep heating and higher for heating the surface, as im only doing 1/2" thick what do you thing the best frequency to aim for is? how much power! will 3kw be enough or should I look at more? here in the UK we have 240 volt single phase mains. was thinking of an addition in the form of a timer for heat time, do you think this is a good idea? reheat time will probably be a lot shorter than first heat and will it also be quicker if reheating something I have drawn out thinner. I'm getting my numbers from Elements of Indution Heating Design, Control, and Applications by Zinn & Semantin. For a 1/2" round bar, you'll want about 30kHz minimum. Power calculations get complex, but you should be able to heat 6" of your 1/2" round to forging temperature in a little more than four minutes with 3kW. If you've got a good close coil. Maybe less if you wrap it in thermal insulation. That's probably not what you wanted to hear, but physics is physics. Your rule of thumb here is 400 watt-hours per kilogram, assuming minimal losses to the atmosphere. A 15kW machine will work quite well, and the commercial ones adjust their frequency automatically.
November 14, 201312 yr Author thank you for the reply. I will only need to heat up about 2" of either 1/2" section, was hoping for a faster result but will make a machine anyway and see what I can do. it is still faster than lighting the coke forge to do just a few and cleaner.
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