gm78
Newbie level 1
Hello,
Hope this is not in the wrong area....
First a small introduction about myself, I'm a french 40 years old, recently laid of, I used to work in the banking industry in computer science (not one of those how got those fat bonuses, so I'm theoretically one of the good guys....)
I'm reconverting in engineering (a longtime passion of mine) and one of the projects I'm working on requires a nitriding process, since I already have some prior experience in vacuum technology and since I want to keep this process on the environmentally and staff friendly side (ie no ammonia gas or cyanide salts...) I'm going for the go for the ion nitriding hot wall process.
Basically this process consist of heating up a workpiece in a near vacuum (2 to 10 Torr, you can gets this low with only a primary pump like a double stage vane pump, no turbo molecular or diffusion pump needed) in a trace hydrogen and nitrogen atmosphere and establishing a potential between the workpiece (the cathode) and the enclosure (the anode) of 500 to 1000 V DC, this ionizes the nitrogen and propels those ions towards the workpiece where nitrogen diffusion occurs (it's actually a bit more complex, depends on the alloys etc etc...) the big advantage of this process is that it is done at a "low" temperature (anything from 350°C to 650°C depending on the alloy and that this temperature is bellow the phase change temperature of the alloy thus no phase change thus very little distortion, thus little post machining required (which is all for the best since the nitride layer can go up to 78 HRC)
Anyways, sorry for the long explanation, I just feel it's only fair to let people understand what the "big picture" is.
So here's what I REALY, (again "e-diot" ie electronicaly inept here...) need help with:
I need to build a square wave generator (low = 0V high = 500V to 1000V) that enables me to vary the frequency (from 1KHz to about 25KHz) and the duty cycle (from 2.5% to 85%) the current requirement is relatively low, you need about 3 A/m² of workpiece, in my case the workpiece will be .5m² max so 1.5 A should be enough.
Almost forgot to mention.... It would be appreciable if one could stand on the ground and touch the enclosure without becoming an element of entertainement for surounding staff.... ie anode set to 0V = GND and Cathode (deep inside the vacuum enclosure) set to - high voltage.
I have rather limited knowledge in electronics, I did a little work in university on binary circuits and such but nothing quite so specific.
I suppose that the solution would break down into 4 parts:
1 - The pulse generator :
555 timer based ?
or maybe better with a digital circuit ? Like for instance a clock running at max frequency feeding a counters that outputs high while count (mod max freq) is below Time Up, and then low while (mod max freq) is above Time Up ?
2 - a driver circuit to tie the pulse generator into a power circuit
3 - a power circuit that takes the pulse signal gets feed high voltage and outputs the resulting wave (IGBT i guess i think a APT 11GF120KR is able to handle 1200V and could probably deal with 25kHz)
4- a variable voltage supply to feed the power circuit.
Now I can probably remember enough of my classes to build the pulse generator (I already simulated a 555 circuit for the less than 50% duty cycle and one for the more than 50% duty cycle) but the rest is driving me nuts....
So is this the proper way to start ?
Do any of you have any suggestions ?
Regards,
Hope this is not in the wrong area....
First a small introduction about myself, I'm a french 40 years old, recently laid of, I used to work in the banking industry in computer science (not one of those how got those fat bonuses, so I'm theoretically one of the good guys....)
I'm reconverting in engineering (a longtime passion of mine) and one of the projects I'm working on requires a nitriding process, since I already have some prior experience in vacuum technology and since I want to keep this process on the environmentally and staff friendly side (ie no ammonia gas or cyanide salts...) I'm going for the go for the ion nitriding hot wall process.
Basically this process consist of heating up a workpiece in a near vacuum (2 to 10 Torr, you can gets this low with only a primary pump like a double stage vane pump, no turbo molecular or diffusion pump needed) in a trace hydrogen and nitrogen atmosphere and establishing a potential between the workpiece (the cathode) and the enclosure (the anode) of 500 to 1000 V DC, this ionizes the nitrogen and propels those ions towards the workpiece where nitrogen diffusion occurs (it's actually a bit more complex, depends on the alloys etc etc...) the big advantage of this process is that it is done at a "low" temperature (anything from 350°C to 650°C depending on the alloy and that this temperature is bellow the phase change temperature of the alloy thus no phase change thus very little distortion, thus little post machining required (which is all for the best since the nitride layer can go up to 78 HRC)
Anyways, sorry for the long explanation, I just feel it's only fair to let people understand what the "big picture" is.
So here's what I REALY, (again "e-diot" ie electronicaly inept here...) need help with:
I need to build a square wave generator (low = 0V high = 500V to 1000V) that enables me to vary the frequency (from 1KHz to about 25KHz) and the duty cycle (from 2.5% to 85%) the current requirement is relatively low, you need about 3 A/m² of workpiece, in my case the workpiece will be .5m² max so 1.5 A should be enough.
Almost forgot to mention.... It would be appreciable if one could stand on the ground and touch the enclosure without becoming an element of entertainement for surounding staff.... ie anode set to 0V = GND and Cathode (deep inside the vacuum enclosure) set to - high voltage.
I have rather limited knowledge in electronics, I did a little work in university on binary circuits and such but nothing quite so specific.
I suppose that the solution would break down into 4 parts:
1 - The pulse generator :
555 timer based ?
or maybe better with a digital circuit ? Like for instance a clock running at max frequency feeding a counters that outputs high while count (mod max freq) is below Time Up, and then low while (mod max freq) is above Time Up ?
2 - a driver circuit to tie the pulse generator into a power circuit
3 - a power circuit that takes the pulse signal gets feed high voltage and outputs the resulting wave (IGBT i guess i think a APT 11GF120KR is able to handle 1200V and could probably deal with 25kHz)
4- a variable voltage supply to feed the power circuit.
Now I can probably remember enough of my classes to build the pulse generator (I already simulated a 555 circuit for the less than 50% duty cycle and one for the more than 50% duty cycle) but the rest is driving me nuts....
So is this the proper way to start ?
Do any of you have any suggestions ?
Regards,
