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Everything posted by timgunn

  1. The best hydraulic system I have ever seen for a limited-power forging press is the Anyang design, which uses a swash-plate pump with variable displacement. At low pressure, the pump is at full stroke and the ram moves fast. As the resistance increases, the pump stroke decreases, the ram speed decreases and the pressure developed increases. This means that the system is able to use the full power of the motor throughout the cycle. I think the 25-tonne Anyang press uses a motor that is either 4 HP (3 kW) or 4 kW. It is pretty impressive and I get the feeling it probably out-performs most 10 HP presses and many 15 HP forging presses (though I have to confess to pathetically little actual forging experience myself). All of the fixed-displacement-pump systems that I have seen move at a fixed speed and only use a fraction of the available motor power until the resistance is very close to maximum. 2HP is pitifully little power for a forging press. I would be looking for ways to increase the available power, rather than trying to build something that will work poorly, at best, on the power that you already have available. If a bigger electrical supply is out of the question, could you use a gas- or diesel-engined power pack for instance? Work is Force times Distance. Power is work per unit time. I struggle a little with US units, so we'll convert to units I understand. I think a US ton is 2000 Lb (as opposed to the 2240 Lb of the British ton or the 1000 kg of the Metric Tonne) 16 US tons is therefore 32000 Lb 32000 Lb is 14,545 kg and each kg of mass exerts a downward force of 9.8 Newtons at the surface of the Earth. 32000 lb (force) is therefore (14545 x 9.8) = 142545 Newtons 2 HP is 1500 Watts (as close as makes no difference). Power(Watts) is Work done(Joules) per unit time(seconds), so 2 HP(1500 Watts) is 1500 Joules/second. Distance is Work/force, so the distance over which 2 HP can exert 16 tons of force in one second is 1500/142545N = 0.0105 metres. That gives a speed of 10.5 mm/sec for a 16-ton ram driven by a PERFECTLY EFFICIENT system: about 0.4 inches/second. Perfectly efficient is unattainable. It's over 30 years since I played with Hydraulics as part of my job, but I don't ever recall them being particularly efficient. Even allowing for 30 years of development, I don't think there would be much chance of exceeding 1/4" per second with a real-world 2HP, 16-ton system. Hydraulics are usually used because they offer a convenient way to achieve a numerically large mechanical advantage. Levers are usually very efficient compared to Hydraulics, but trying to combine the two seems like adding a lot of complication. If you want to be able to keep the stroke short with different thicknesses of workpiece, you could use adjustable limit switches to limit the return stroke or, if you are using a very basic power pack with just a relief valve, threaded adjustable stops on the return stroke.
  2. First question is whether the motor is wired correctly? Over here, most small 3-phase motors are wound to be run at 230V in Delta or 400V in star (wye). Connecting a motor over here to 230V in Wye gives a similar problem to yours, easily sorted by reconnecting in Delta. I am in the UK and strongly advise you to avail yourself of local knowledge. I'm not sure whether the high Voltage being double the low Voltage on your nameplate means there are 2 sets of windings, to be wired in parallel for 230V or series for 460V. Check your wiring diagram. Are the PBxx settings correct for your motor?
  3. That looks old. I would not try running it on a VFD unless a Sine-Wave filter was used in the circuit. What follows is "as I understand things": somewhat oversimplified and perhaps not technically accurate, but close enough for me to get my head around. YMMV and it is worth researching things further if you are intending to go that way. Old motors often used a brittle Shellac-based impregnation material for the windings. I think some of the early synthetic impregnation materials were also rather brittle. Later polymeric resins are much "tougher". My rather limited experience is that post-1980-ish motors are no problem with VFDs. Pre-1960-ish motors are a problem and between 1960 and 1980, things are unclear. On a true sine wave supply (mains), the voltage rise is quite slow. As the current rises, the magnetic fields around each of the coils rise and interact with the other coils in the winding. I think they cause the windings to move towards each other, compressing the insulation, with each peak (positive and negative), causing the characteristic transformer hum tone. VFDs use PWM to switch a DC Voltage on and off very fast (most modern VFDs switch at 4 kHz and up), giving an almost instantaneous Voltage (and current) rise time. The force exerted is dependent on the rate-of-change-of-Current, so the mechanical forces on the insulation are very much higher than when run from "real" mains power. On a motor with brittle insulation, the forces are higher than the insulation can withstand and tiny cracks form. The upshot is that old motors tend to fail very quickly when run from VFDs. There are some other factors that come into play as well, but I can get my head around the one I've described and it has been sufficient to keep me from going down that particular rabbit-hole. A Sine-Wave filter can be fitted between the VFD and the motor to smooth out the high-frequency stuff and leave a sinusoidal waveform very similar to "true" mains (though still with the Variable Frequency that we want for speed control). These will often let you run an old motor on a VFD. Sinusoidal filters typically seem to cost "about" as much as the VFD with which they are used, so they are not cheap. If an old motor has been rewound, it will have been done with the materials used at the time, so a 1935 motor rewound in 1995 can be treated as a 1995 motor (unless it was specifically rewound with 1935 materials as a museum piece, for example).
  4. It's not entirely clear what you mean here. Do you mean the size of the hole through your "refractory" and into which you stick the torch, or the size of the gas jet in the torch? I once made a 2-brick forge and tapered the hole for the torch to go in. By moving the torch in and out of the tapered hole (wider at the outside), it was possible to vary the amount of air that was drawn in and thereby vary the temperature. (tip: in most cases, more air = hotter) The problem with using a torch, which is designed to work in open air and draw secondary air, is that it usually can't get enough secondary air to burn with the gas when used in a forge. If you open out the gas jet, you will almost certainly make things worse: even more gas and no more air producing an even richer burn and lower temperature.
  5. Drop the Hz on the VFD to two-thirds of the frequency intended by the supplier (hopefully, that's the mains frequency where you are) to get the same speed as you'll get with the 6-pole motor and see how it goes.
  6. On a Venturi burner, knowing the pressure is useful, rather than essential, mainly to allow the operator to start the forge, set it to where it was last time it did the same job, and get on with something else while it gets to temperature. I always used to fit a gauge at the mixer (and still do when I want other folk to see what is happening with the burner), but now use plugged welding regulators on my forges. These have graduations marked on the body so that the skirt of the adjusting knob shows the pressure they are set to. They have the advantage of being built "industrial", with a nice big adjusting knob intended for use by someone wearing heavy welding gloves. It sounds like a pretty crude way of knowing the pressure, but there are not many gauges that provide significantly more accuracy/repeatability at reasonable cost. I like to keep all of my controls at the gas cylinder end: it's the direction I head if things start going wrong and I don't want to introduce the need to make an extra decision while the midden is hitting the windmill. I'm also not keen on adding weight to the end of the burner. There are various different gauges available. As said, very few will offer good accuracy at anything like reasonable cost. I tend to use glycerine-filled gauges with 1/4" bottom connections. These have stainless steel cases with sufficient structural integrity to contain the glycerine and the 1/4" connection is a lot harder to break than a 1/8" one. I have seen 1/8" back-entry gauges, salvaged from the regulators of old compressors, fitted on burners and try to keep my distance. If I *really* want to know what the pressure is doing, I use a 4-20 mA pressure transmitter and a datalogger, but I'm probably a little more anal than most smiths. It is worth pointing out that gas flow through a jet does not vary linearly with pressure, but as the square root of the pressure. If you want to double the gas flow, you need 4 times the pressure. Doubling the pressure will give 1.41 times the gas flow and halving it will give 0.707 times the gas flow. If you want to spend money to find out what is happening with your forge, you will almost certainly get more bang for your buck by investing it in a decent thermocouple and pyrometer.
  7. Ouch. What did it cost? I’ve been fortunate enough to salvage a few type S over the years. Even without having to consider the cost, their fragility is quite limiting.
  8. Wherever you buy your thermocouples should be able to supply them. Otherwise search for "thermowell". I'm the wrong side of the pond to recommend suppliers. Although they are used a lot in industry, they are not often the best solution in "our" applications. Thermowells tend to slow thermocouple response and tend to be very spendy in anything more exotic than 316 SS. Mineral Insulated thermocouple asssemblies are often a better option. I strongly recommend spending a few minutes scrutinising and understanding the process you are dealing with and the temperature you need to measure, before sitting down with a cup of coffee, notebook, pen and calling the technical sales folks at Omega to ask their advice. It is worth mentioning that bespoke thermocouples are pretty normal in industry, so the premium for non-standard is usually surprisingly small. It does mean dealing with a specialist temperature control business, rather than a box-shifter, but this gives you access to their technical knowledge and experience.
  9. 230V single phase at 50A is 11500 VA: There will be a power factor to consider, so probably not enough to run a 15 HP (11,250 W) motor via a VFD, but more than adequate for any motor/VFD you might fit to a 2" wide belt grinder.
  10. Dudley is actually in the "Black Country", west of Birmingham (England) and about 80 miles as the crow flies from Sheffield. This thread reminds me of the saying that to an American, 200 years is a long time and to an Englishman, 200 miles is a long way.
  11. I'm not sure whether it applies to your controller, but I've come across some that are initially set for 1 decimal place, limiting the maximum to 999.9 degrees. Changing to zero decimal places gives access to the full temperature range. Worth a try?
  12. It'll almost certainly be Auber Instruments. Auber tend to be highly rated in America. They don't have a presence in Europe so I have not used them myself. I use Omega or Automation Direct for the ramp/soak controllers on my HT ovens. Both seem to be US companies with a presence in the UK. Both have knowledgeable and patient technical support staff. I gather Auber also have knowledgeable and patient support staff. The best advice I can give to anyone on controllers, VFDs and other electronic gizmos is as follows: Shop around. Read the specs carefully and list the "possibles". Find the manuals online and download them. Read them. Properly. This is likely to mean printing hard copy and making notes. If you are more together than me, it'll probably involve multi-coloured highlighters. If you don't understand at least most of what is in the manual, cross it off your possibles list. If you cannot download the manual from a readily accessible website without signing up to being spammed, cross it off your possibles list. Read any reviews you can find on your possibles list. Narrow down your buying choices so that you can make an informed decision. There are some geeky folk on the forums (I count myself among them) who have some general experience of PID controllers, VFDs and the sort of stuff "we" might find useful. If you run into a problem and need to ask for help online, there's a pretty good chance one of these geeky types can help, but only if they can access the manual. A link to the manual gives you a good chance of assistance. No link to a manual means you are on your own. Manuals are expensive things: paying a specialist writer-of-manuals to write a manual (in their own language) does not come cheap. Keep this in mind.
  13. My recommendation would be to build a completely separate control box: Preferably a metal enclosure (to help with cooling the SSR) fitted with cable and plug to plug it into a mains socket, power to the PID controller taken from inside the box and the PID controller output switching an SSR, which switches the power to a power socket on the front of the box. I fit a miniature thermocouple socket to the front of the box so that the thermocouple just plugs in. The one in the photo is larger and much fancier than necessary, having been assembled for a 28"-long HT oven I built. Once built, it can be used to control pretty much anything: Austenitizing HT oven, tempering oven, salt pot, electric crucible furnace.
  14. Looks pretty reasonable so far. It looks like you are using the terminals on the PID controller to carry the full element power with 2 wires in each? If so, I would suggest a minor wiring change to keep the big currents off the PID terminals: incoming power directly to the SSR and a second small wire in the SSR terminal to take power down to the PID controller. It's probably easiest to use a big terminal block to join the power wires on the other leg, with a small wire from that terminal to the other PID power terminal. The PID controller terminals are unlikely to be rated for high current and they can get pretty warm once serious Amps start flowing. It's not unknown for them to get hot enough to melt the plastic and lunch the PID controller. The DC to the input side of the SSR only needs little wires and they don't get hot (switching the SSR usually takes about 30 mA max at 3-32V). I usually try to use obviously-different wire for mains and low-Voltage control circuits in any enclosure. My experience is that stuff usually goes wrong when I'm tired and anything that might help me to avoid confusion and a mains jolt seems like a good idea. Caveat: American wiring is something of a mystery to me. I've built about 8 HT ovens so far, but they have been on European 230V mains supplies with one 230VAC hot leg and a Neutral at Earth (Ground) Potential.
  15. I don't know how much you've played with the burners yet, but it's worth choosing a fixed value for the gas pressure, letting the forge get to temperature, then making adjustments to the choke to see how that affects the temperature. Adjusting the choke should adjust the air:fuel ratio and with it the flame temperature. Adjusting the pressure should adjust the amount of flame you have. You'll adjust both in normal use, but it's worth spending half an hour or so early on just getting a feel for what does what. Maximum flame temperature is reached at an air:fuel ratio that is close to stoichiometric. It's hotter than we usually want/need (well above the melting point of Iron) and "we" tend to run more fuel-rich and cooler. Running fuel-rich means that there is a reducing atmosphere in the forge that tends to grab any Oxygen before it can react with the workpiece to form scale. The partially-burned gases finish burning when they reach Oxygen in the air outside the forge and this is what gives the Dragons Breath. It looks like you have a fair amount of adjustment available both ways. Opening the chokes should get the forge hotter, closing the chokes should make it cooler. A hotter flame should also get it to any given temperature faster.
  16. "The reason for the 5 HP is because running a 3 phase motor on a VFD you only get 2/3 the rated HP just like running a static phase converter." That's news to me. What is your source for this information? I'm pretty sure it's wrong generally, though there may be specific circumstances under which it is the case. The only one I can think of offhand is when the supply Voltage is less than the motor rated Voltage, but I'm sure there are others. I've been using VFDs for over 30 years and I've never been told by a motor- or drive-supplier that I need to derate a motor by 1/3rd in order to run it from a VFD.
  17. “Venturi” is the term used to describe the shape of the classical Naturally-Aspirated mixer. It tends to get used (incorrectly) for any Naturally Aspirated burner: one which does not use an air blower to provide the air. Get the back-pressure down by reducing the restriction on the openings and see if it improves. If you still can’t get it hot enough, have Dragons Breath and the gas jets are changeable, fitting the next size down jets will probably get the temperature significantly higher.
  18. Looks like it's a high-speed drill press from a quick google: possibly 1500-10000 RPM, though the one in the link below looks to be 3-phase and is in Europe. If the pulleys and motor pole count are the same, it'll be around 1800-12000 RPM on 60 Hz mains. A bargain if that's what you need, but not really a general-purpose tool. http://unimachines.at/tischbohrmaschine-super-valmer-model-6-1970-14105.html
  19. Note that it makes it more rigid, rather than hard: When you press a thumb into blanket, it doesn't take much force to press it down by, say, 1/8" and it springs back. With rigidizer, it'll take noticeably more force and it won't spring back. The rigidizer seems to get fairly rigid as soon as it is fully dry, then get more rigid once it has been fired to high temperature. If your plan is to rigidize, then coat with a castable refractory, I'd not worry too much about it. The general consensus seems to be that the refractory bonds better to wetted blanket and the usual practice is to spritz the blanket with water before applying the refractory. If you wait until the refractory has crisped up at the surface, spritz it and apply the refractory, you should be fine. If you rigidize and apply the refractory while it's still wet, you should also be fine, but your drying time is likely to be much longer: moisture can escape from the exposed blanket face much more easily than it can escape through the layer of refractory. Drying time is VERY location-dependent. Some places, you'll need to slow initial drying down by covering the forge with plastic to give the (castable) refractory time to set properly. Other places, you'll struggle to get it dry at all. I'm in the wetter bit of England, just North of Manchester, and fall into the latter category. Dry is IMPORTANT: if the low-permeability layer is not dry, it'll flash off steam inside and blow it apart. It may not be impressive or even immediately apparent, but it'll leave cracks where the steam forced its way out. I'm pretty sure this has caused the early demise of many forges built by impatient would-be smiths. Using a fireclay-based refractory cement/mortar as a coating, the steam flash-off causes paper-thin bubbles to rise, harden and break up. If I really need to make a forge with refractory cement, it gets dried over 8+ hours in the oven (the actual time taken depending on how long I can be sure the wife will be out).
  20. 1/4 DIN is definitely better for my middle-aged eyes, but 1/16 DIN is cheaper. My first homebuilt HT oven used a relay-output controller and contactor. It was noisy and when I did some testing with a borrowed high-end controller, several thermocouples and a datalogger, it was clear that shorter cycle times gave better stability. It was also clear that radiative (over)heating was a potential issue, particularly at tempering temperatures, and that ramp/soak capability would be worth having. The controllers I have been using for my more recent homebuilt ovens have been either Omega CN7823 or Automation Direct SL4848VR. They seem to be the same controller with different badges and I buy whichever is cheapest at the time. They have ramp/soak capability. The graphs were from a series of different-diameter thermocouples, intended to (loosely) approximate the heating effect at different thicknesses on the bevels. The thermocouples were out of my box-of-bits and I knew nothing about them except that they were Mineral Insulated typeK and of different diameters. Exp had an exposed junction. I do not know whether the others had grounded or ungrounded junctions, though ungrounded seems most likely. The setpoint in both cases was 250 degC, 482 degF. The control thermocouple was a 6mm Mineral Insulated typeN with an insulated (ungrounded) junction and Nicrobel sheath. The 30-min (-ish) slow ramp-to-temperature gave a peak radiative overshoot of 19 degC, 34 degF. Without the ramp, the peak radiative overshoot was 119 degC, 214 degF. Further testing showed that slower ramping helped and there were small errors due to thermocouple tolerances which may account for as much as 10 degC, 18 degF. There was also a saw-tooth variation about the setpoint once it was reached, with the pitch and amplitude directly proportional to the output cycle time. There were clear improvements from reducing the cycle time down to 5 seconds. I "think" there was an improvement between 5 seconds and 2 seconds and that I could tell which was which from the charts. Unfortunately I lost the data to a hard-drive failure and these 2 charts were all that I had backed up. I use a 2-second output cycle and fit an LED indicator to the control panel that is lit when the element is powered. By watching it for 2 seconds, you get a surprisingly good idea of how much of the output cycle is powered, even from 20-30 ft away.
  21. The kiln is almost certain to be able to achieve Austenitizing temperature for Carbon steels at its design Voltage. There's a good chance it'll be able to handle most of the less-exotic stainless steels too. I don't know which of the controllers from Banggood you are looking at. They list several and I don't think they are all suitable for a HT setup. Some, particularly the Rex C100, seem to have factory-configured input ranges which cannot be changed by the end user. A 400 degC maximum on a typeK thermocouple seems to be the most common input and this is not much use to us. There is an XMT612 controller listed and this "may" be the same controller as a tet612 that I used a few years ago. The tet612 had fully-user-configurable input ranges and worked pretty well for me. As Dan says, the controller needs to have some means of modulating the heat input to the oven. This is usually done with a Solid State Relay switched to provide time-proportioning control. I have found a 2-second output cycle time gives about the best results. The controller needs to have a DC pulse output to trigger the SSR. On US 220V supplies, I understand 2 SSRs are normally used, one for each "hot". Most controllers with pulse DC outputs can trigger 2 SSRs in parallel. Whatever controller you get, make sure you have downloaded, read and (mostly) understood the manual BEFORE you buy. The download needs to be from a site accessible without opening some sort of account or logging in with anything that could be interpreted as a "feel free to spam me" permission. I would expect the potential supplier to be able to provide a link to the manual As you say, this is not really in your comfort zone and you may need to ask for help. If you ask for help with a link to the manual, someone with a general understanding of PID controllers can probably help. If they cannot access the manual, you are on your own. One thing worth mentioning is that it is wise to use a 48mm x 48mm (1/16 DIN) controller and to leave a bit of extra length on the wiring: maybe 2". 1/16th DIN is the most common size for controllers and a later upgrade to a ramp/soak controller is easy later on. Any 1/16 DIN controller will fit the mounting hole, but some are longer than others and the terminal layout may be different, Having the wires long enough to reach can save a lot of cussing if you ever change the controller.
  22. Some conversion factors might prove helpful. 64 kg/m3 is 4 lb/cu ft 97 kg/m3 is 6 lb/cu ft 128 kg/m3 is 8 lb/cu ft 160 kg/m3 is 10 lb/cu ft The 128 kg/m3, 8 lb/cu ft, density is usually recommended. 160 might be marginally better, but it's not usually easy to come by. 2 layers of 25mm, 1", are usually best in a round forge, as single layer of 50mm, 2", is more difficult to wrap smoothly. In general, the material recommended for forges is high-temperature Ceramic Fibre Blanket. Usually rated to around 2600 degF or 1400 degC. Insulfrax products are made by Unifrax and I think the Insulfrax range is a series of Low BioPersistence products made from Alkaline Earth Silicate fibres. The LBP fibres are soluble (I assume pretty slowly) in body fluids. The presumption seems to be that they are likely to be safer than insoluble Ceramic fibres over the long term. A ceramic fibre inhaled today will still be in the lung in 50 years. An LBP fibre inhaled today will not. Different products have different temperature ratings, but the Low BioPersistence fibres generally tend to have significantly lower temperature ratings than the Ceramic fibre products. In the UK and much of Europe, it is becoming increasingly difficult to obtain non-LBP blanket. The lower temperature rating of the LBP products means that the material used to provide a hot-face coating should ideally also provide insulative properties. This will help to limit the temperature at the interface of the hard refractory and fibre to less than the rated temperature of the fibre product. If using a 1400 degC-rated Ceramic fibre blanket, insulation is less of a consideration for the coating layer. The big names in refractories are Insulfrax and Morgan Thermal Ceramics. Insulfrax are best known for fibre products. Morgan Thermal Ceramics cover the full range of castables, Insulating Fire Bricks and fibre products. In my (admittedly fairly limited) experience, the Ceramic fibre blankets from other manufacturers seem to perform just as well as the big-name products of similar density and temperature rating. The best materials to use for the hot-face layer tend to be castables. A lot of folk use refractory mortar because it is cheap and readily available, but it does not last nearly as long as a well-chosen castable. For burners, I would strongly suggest an Amal atmospheric injector from Burlen Fuel systems. You'll need gas fittings to connect to the injector, but the burner tube can be a straight section of pipe, threaded at one end to screw into the injector: I'd source a long stainless steel nipple from ebay or similar. This does away with any concerns over galv pipework, saves a lot of time and effort on your part and produces a burner that is extremely adjustable. Buy the burner factory-jetted for Butane, not for Propane, as it will give a higher maximum flame temperature on Propane than will the Propane-jetted injector. I'd only use a single burner, mainly to avoid the hassle of trying to balance two burners to the same mixture/temperature, and size it for your chamber. A 3/4" burner is good for about 350 cu in and a 1" burner is good for about 600 cu in, both to welding temperature. A rear pass-through port is a good idea if there's any chance you'll want to do long stuff. You can block it off if you are only doing short stuff. I pack in an offcut of blanket personally, but I've seen others use IFB cut to fit. With an Amal injector-based burner, the temperature control available with the screwed choke means that you are very unlikely to need a muffle tube for HT, though you MUST do your HT outdoors. Closing down the choke to get HT temperatures causes massive amounts of Carbon Monoxide and death is a very real possibility if you run the forge in an enclosed space.
  23. A VFD takes mains power in, rectifies it to DC internally, then synthesizes something that looks to a 3-phase motor sufficiently like a 3-phase sinusoidal waveform for the motor to behave as if it is powered by one. The clever bit is that the VFD can vary the apparent Voltage and Frequency and make the motor run at variable speed. VFDs are available for single-phase 230V input or for 400V 3-phase input. If you get a 230V single-phase one, it can run on UK domestic mains. The biggest you'll be able to run from a 13A socket will be a 3 HP/2.2 kW. It's not really worth getting any other size IMHO. They can run motors smaller than their maximum rating, but not bigger. If you use a 230V VFD, the output will be 3-phase 230V. The vast majority of 3-phase motors up to 3 HP/2.2 kW are wound for 400V connected in Star (Wye) or 230V connected in Delta and can run fine on a single-phase-input VFD. You'll need to check when ordering though. Over 3 HP/2.2 kW, motors tend to be wound for about 700V in star and 400V in Delta to enable star-delta starting (an old-school way of reducing motor starting current. It has largely been supplanted by VFDs). These cannot run on 230V 3-phase. Here in Europe (for the present), we have 50 Hz mains: 50 cycles/sec, 3000 cycles/min. Other parts of the world have 60 Hz mains: 60 cycles/sec, 3600 cycles/min. It's the reason you'll see the different motor speeds quoted on opposite sides of the pond. A 2-pole motor will run at an RPM equal to or just below the frequency of its power supply (3000 or 3600 RPM). A 4-pole motor will run at, or just below, an RPM equal to half the power supply frequency (1500 or 1800 RPM). 6-pole: one third (1000 or 1200 RPM), 8-pole; one quarter (750 or 900 RPM), and so on. We tend to use either 2-pole or 4-pole motors and in Europe, motors generally conform to IEC standards. Across the pond, they tend to use motors to NEMA standards. NEMA motors are pricy over here and offer no inherent benefit. They tend to be used where expensive machine modifications would be necessary to change to an IEC motor. For a serious belt grinder, you'll probably want a 90-frame motor in a long casing (90L). This will most likely be 1.5 kW/2 HP if it's a 4-pole or 2.2 kW/3 HP if it's a 2-pole. The shaft size of 90-frame motors is 24mm. Because half the world uses 60 Hz mains and the other half uses 50 Hz, meaning that maximum mains speed is 3600 RPM, motors are designed to run to 3600 RPM. It is not cost-effective for motor manufacturers to design a completely different motor for each speed, so the only difference between the 2-pole, 4-pole and 6-pole motors in a particular frame size is the winding. The winding is attached to the inside of the outer casing and is static. This means that all the moving parts are good to 3600 RPM. We can run a 4-pole motor to 120 Hz to get 3600 RPM using a VFD, or we can run a 2-pole to 60 Hz to get the same 3600 RPM. At the bottom end of the speed range, most drive/motor combinations are able to run smoothly down to about 10 Hz. Below this, running from the simpler V/Hz drives, things tend to feel "coggy". The V/Hz drives use a fixed (usually linear) relationship between Voltage and Frequency to determine what will be supplied to the motor and this linear relationship tends to break down once it gets that far from the design frequency. There are also drives which have "Sensorless Vector" capability. These measure the time difference between peak current and peak Voltage internally, calculate to determine the phase angle between them, then fine-tune the Voltage in real time to maintain the design angle (the motor Power Factor defines this angle, being its Cosine). These can keep the motor running smoothly well below 10 Hz and usually down to 1 or 2 Hz. A 2-pole motor on a V/Hz drive has about a 6:1 speed range (600-3600 RPM, 10-60 Hz). A 4-pole motor on a V/Hz drive has about a 12:1 speed range (300-3600 RPM, 10-120 Hz). Either motor has a much greater speed range when run from a SV drive with smooth running down to 1 Hz achievable if needed. VFDs switch large currents very fast and produce some heat, which must be dissipated. Most VFDs have ventilation fans and allow airflow over the power components to cool them. They are intended for use in clean conditions (usually sealed electrical enclosures). If there is airborne steel dust (which is both conductive and magnetic) it will flow across the power electronics, where the magnetic fields caused by the switching will capture it and attract the metallic dust right onto the power components. The short-circuit that results is usually quite spectacular and is invariably expensive, killing the VFD completely. If they are going to be in the same room as a grinder, we need to use VFDs that are protected against such dust to IP66 or NEMA4 standards. We can either mount an unsealed drive in a sealed enclosure ourselves, with sealed control switches and speed control knob, or we can buy a drive that is designed to be sealed to IP66 from the factory and which has the sealed control knobs, etc on the front. The latter is by far the better option for the non-electrician. To buy and enclose an unsealed (IP20) drive properly, with sealed controls, to IP66 is about as expensive as buying an IP66 drive to begin with. In the US, the KBAC series of sealed drives from KB Electronics are the go-to. In Europe, the Invertec IP66 drives tend to be the ones people use for grinders. The current ones are SV drives so you get the low speed capability. I'd recommend a 90L-frame motor and an Invertek ODE-3-220105-1F4Y VFD. The drive is expensive, but it's a cry once thing. I'd try for a 2 HP, 4-pole motor for personal preference, but would be pretty happy with a 3HP, 2-pole. If you are anywhere near Lancashire, I can sort you a foot-mount 90L 2-pole 3 HP from a compressor, gratis.
  24. timgunn

    Spring rate

    Given that a failing hammer can also take parts of the operator off, I'd feel happier with: yes, mild would have worked in that application just fine as long as the fatigue limit didn't get exceeded.
  25. What with? With 2 cuts and probably some tidying up with a grinder, it should be less than a days work to make a better post anvil than many smiths are ever likely to own. That seems like an excellent use of your time to me.
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