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timgunn

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Everything posted by timgunn

  1. Just a thought on the parts list. You've not mentioned any parts for a choke. It could just be that you have the bits already so didn't need to order them, but if you've not allowed for chokes, I'd recommend you do. Getting both welding and HT temperatures from the same forge is much easier with good air control.
  2. http://amalcarb.co.uk/downloadfiles/amal/amal_gas_injectors.pdf Available from http://burlen.co.uk/?___store=default I think it'll almost certainly be a phone call job, as they are not really standard enough to sell online: jet sizing is fairly critical. Amal jet sizing is a little esoteric but they should be able to work things out. I did some playing with jet sizes on high-pressure Propane, ending up with a 0.6mm Mig tip, with about a 0.74mm diameter orifice, in a 1" LV Amal injector. It seems about right. It should be ok to scale this, so about 0.55mm for a 3/4" and about 0.
  3. I don't know if I can explain this well. When I've tried face to face, folk either get it straight away or their eyes glaze over. It is important to understand the difference between heat and temperature. We can adjust the temperature at which gas burns by adjusting the air-to-fuel ratio. Maximum temperature is achieved when all of the fuel gas burns with all of the oxygen in the air, leaving no unburnt gas and no unburnt oxygen. This is a neutral flame. If we add more air, it can't contribute to the burn, because all the gas has already been used up. All that happens is that the e
  4. As Podmajersky says, AC motors on VFDs can be run above their rated speed and this is very likely to be what you have seen. With a DC motor, the only thing that the controller can vary is the Voltage. Speed follows Voltage and once the maximum voltage is reached, that's it. AC drives control both frequency and Voltage. Below rated frequency and Voltage, both increase together, giving a constant torque characteristic. Once the rated Voltage is reached, the drive stops increasing the Voltage, but can continue to increase the Frequency. The motor speed will continue to increase with the f
  5. I didn't try a star-wheel dresser, though I have one and use it on bench grinders. When I've used them, I've always had the impression they worked by pulling out the high grains and they seem to give a more agressive wheel than a diamond does to me. It might just be my imagination though. I was after fine, so didn't even think about using it on the wet wheel. With hindsight, it may work better for truing up the wheel. I found it quite hard to true it up freehand, as it's so slow; I'd hit the high spot and then it took a second and a half to come round again. Any slight pressure on the dres
  6. Dan, check out the motor and drive carefully (pics would be interesting). I think you'll find it's much slower. I have a 4" x 24" natural stone wheel on the original motor and drive. It turns at 42 RPM, which gives a 3 MPH surface speed. For dressing, one of the diamond jobbies that looks like a 2" long piece of 1/2" box section with a diamond-coated face and a handle, worked pretty well, if very very slowly, on mine. I tried a single-point diamond, but the slow speed made it awkward to avoid cutting threads. Watch out for the big nut, visible in the pic in post #2, backing off and let
  7. If wire will do, and you have a thermocouple supplier anywhere nearby (there are probably more about than you'd expect), they may be worth a phone call for scrap. Type R and S thermocouples are Platinum on one leg and and Platinum/Rhodium alloy on the other. It still won't be cheap though.
  8. One of the reasons for going wider than seems necessary, is to reduce the radiative heating effect of the elements on the workpiece. The elements radiate heat and this radiated heat effectively reduces with distance from the hot elements. If you read the manuals for the big-name ovens, I'm pretty sure they'll mention this. I don't think it is likely to be much of an issue at Austenitizing temperatures, but it can seriously louse up tempering. What happens is that the elements radiate heat in all directions along line-of-sight. Most of the radiated heat will hit the walls, ceiling,e
  9. Read up on the subject as much as you can. Look at what others have done and try to picture how some of the "improvements" that people add would affect the way that you work. Be sceptical. The Mypin controller looks like it can do what you need it to do BUT.... In the hands of a half-way decent control engineer, I am sure it will be no problem. Because you needed to ask the question, it seems fair to assume that you are not a control engineer. There are guys on this forum, and doubtless many others, who either are control engineers or have enough experience and knowledge to pas
  10. Do you know what the "spring steel" actually is? I know that EM45 is a spring steel available in the UK. It's a Silicon-Manganese steel and needs higher-than-normal-Carbon-steel temperatures for Austenitizing: well above non-magnetic. Could you have something like this? It will harden, it just needs a higher temperature, so all is not lost if that's what you have.
  11. Scott, There's some risk attached to everything we do and common sense goes a long way towards keeping us safe. My day job involves designing, modifying and maintaining machinery. I have no control over the end users of the machines, so I tend to assume they will find some new and interesting way of killing or maiming themselves if given the chance. Common sense doesn't enter into it. That thought process tends to get ingrained. When I've built ovens for other people, it's seemed pretty safe to assume they have no real interest in the technical details of how the oven works (if th
  12. Relays or new SSRs? I've tried both SSRs and contactors for the output stage and find SSRs preferable for the speed of operation; I find that a 2-second cycle time is definitely better than 4 seconds. I can't see any improvement going to 1 second, but I'm not sure whether that's because there's no improvement or because my testing setup is not good enough to detect any improvement there might be. I've found Fotek branded SSRs, bought from the far East via ebay, to be pretty good. All of the five HT ovens I've built so far have gone to people I like. I fit RCDs (GFCIs?) and
  13. Try disconnecting the DC input to the SSRs and switching on. If the elements still power up, you definitely have bad SSRs.
  14. Side channel blowers, also known as regenerative blowers are nice. They look different to most centrifugal blowers, having the inlet and outlet close together on the outside of the casing. It's worth googling them to understand how they work; if I try to explain, people will go all glassy-eyed and nod off. Small ones are usually built with the motor integral and the motor is pretty much a standard 2-pole industrial motor except for the drive-end casing which forms part of the blower casing. This means the motor runs at around 3500 RPM and the whole thing is nice and quiet. The perf
  15. The pyrometer itself, or at least the readout, is the cheap and easy part. I use a TM902C bought off ebay; a search will find these at 5 or 6 bucks, delivered from China. They take a type K thermocouple input and have a miniature (flat-pin) socket. Too cheap not to have IMO. Slight downside for those that think in Fahrenheit is that they only read in Centigrade. Those I've had all read to 1365 degC (2489 degF), despite being marked 750 degC or 1300 degC. You will need to spend considerably more on the thermocouple. I use Mineral-Insulated thermocouples of 6mm (1/4") diameter and 600mm
  16. I think you've missed the all-important 2 Alan. It's CO2 (Carbon Dioxide) that's heavier than air and will extiguish a candle. Its Relative Molecular Mass is 40. The RMM of air is about 29. CO (Carbon Monoxide) is a little lighter than air and is a flammable gas. Its RMM is 16. The differences between the RMMs of CO2, Air and CO are not all that great. As a result, little or no separation will normally occur over the sort of timescales that we are usually concerned with. This is partly due to the fact that, in our application, both CO and CO2 are produced along with lots of heat an
  17. What's the Hones Buzzer burner originally from, Sam? It looks like Hones make several that could be useful, but the blurb seems to suggest they need secondary air in most applications (I'm not sure about the high-pressure version), so may run way too rich for a forge. I've been playing with Amal atmospheric injectors lately, which are designed for low pressure but work very well on high-pressure Propane when fitted with much smaller jets. I could be telling Granny how to suck eggs, but if yours doesn't play right off the bat, you may need a smaller gas jet.
  18. 3' long flames are not a problem where there is the space to accommodate them. Maybe a brick kiln or large pottery kiln. In general, we have small workpieces which set the minimum size of our forges, but any extra volume means extra surface area, which means heat loss, which means gas consumption, which means running cost. I'm not familiar with pottery kiln burners, but a lot of industrial Venturi burners only draw in part of their combustion air as primary air, the rest comes in as secondary air. The primary air part-burns the gas in the central cone, leaving the part-burned gas to mix wi
  19. The sightly unhelpful answer is that it depends on exactly what you are intending to use it for. As a display,it will show the temperature of an attached thermocouple (so long as you use a thermocouple it recognizes) in your choice of units. The type K thermocouple is the most common general-purpose thermocouple and it will recognize that. As far as using it for control goes, it has a DC pulse output to drive a Solid State Relay, which is the sort of output that is often used for electric HT ovens/furnaces/kilns. If you would want to switch a gas solenoid valve instead, for a tem
  20. The 1/12 is just feet to inches. You want feet/min, but the drive wheel diameter starts off in inches.
  21. You're welcome, Scott, but the thanks may be premature. Please let us know when you get it working properly. Also whether or not you'd recommend the controller?
  22. I'm assuming you are using a type K thermocouple and the D1S-VR controller with the SSR output to run an electric kiln/oven/furnace. I also assume you may want to treat Stainless steels at some point, so will want to be able to go above 1000 degC (1832 degF), and that you do not need alarms. I have not used the Sestos controller myself, so this isn't necessarily reliable. However, based on my experience of other controllers and the manual, such as it is, I think you will probably want all factory default settings except for the following: Ctl This is the output cycle time. Default
  23. For general workshop lighting, I like fluorescents with "daylight" tubes (6000 K or thereabouts). They are a little harsh for some people, so you may prefer "cool white". I always try to use High Frequency fittings (with electronic ballasts) to minimize the stroboscopic effect when rotating machinery or power tools are likely to be used in the room. Local lighting for rotating machinery really needs to be completely flicker-free. It tended to be Tungsten-Halogen in my day, but I'd imagine LEDs running on DC should get the job done. With low ceilings and therefore low lights, I tend to
  24. Dave, there are a few things to consider that may not be too obvious at first. Your motor rating plate shows a current of 11.8 Amps. However it is a 3-phase motor, so that is 11.8 Amps per Phase. I think (and I may be wrong) that the maths give 1.73 times the phase current needed for perfect conversion from single-phase. That would give 20.4 Amps of single-phase supply needed, plus a bit extra because the conversion will not be perfect. I'm guessing a bit, but I suspect it'll need around a 25A supply. 3kW/4HP is about the top end of the power range for VFDs running from a 220V sing
  25. As I understand it, motors tend to be designed for mass manufacture. Most of the bits of an 1800 RPM 145tc motor end up the same as those on the 3600 RPM 145tc motor built on the same production line. Only the stator windings will be different, and these don't rotate. All the moving parts of the 1800 RPM motor will therefore have been designed for 3600 RPM. Electrically, the motor will have been designed for 60 Hz (possibly both 60 Hz and 50 Hz, if aimed at a world market) and optimized for that frequency. Moving away from the design frequency will gradually increase internal losses un
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