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Posts 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 0.37mm for a 1/2", but Owen may have better information.

  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 extra air absorbs some of the heat energy and reduces the temperature of the flame. Because there is unburned oxygen remaining, this gives an oxidizing flame.


    If we go the other way and increase the amount of gas, it can't contribute to the burn, because all the oxygen has already been used up. All that happens is the extra gas absorbs some of the heat energy and reduces the temperature of the flame. Because there is unburnt gas remaining, this gives a reducing flame. Once the hot unburnt gas leaves the forge, it mixes with air, gets the oxygen it needs and continues to burn as the dragons breath.


    What I think you need to do is adjust your burner to give a flame of the correct temperature. I think you'll be choked down quite hard on the air port. You should then be able to increase your gas pressure to make the flame bigger (but not hotter). The area by the burner will always be hotter than the last few inches of the forge, but increasing the size of the flame should reduce the differential. At some point, you'll get an even enough temperature to be usable.


    Running with the flame much hotter than the temperature you want will just cause uneven heating.


    If at all possible, get hold of a thermocouple and readout and measure the flame temperature whilst adjusting the air.


    Sputtering is often a result of too low a gas pressure. When the flame travels through the mixture faster than the mixture is moving in the opposite direction, it will run down the burner tube until it runs out of mixture to burn. The flame will then go out. The gas continues to be fed, draws air, mixes with it and, shortly after, reaches the forge, where it ignites and the process repeats. Often, increasing gas pressure wil cure the sputtering because it increases the mixture speed until it is faster than the flame speed.

  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 frequency, but the torque will reduce as the speed increases, giving a constant power characteristic.

  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 dresser just kept it in contact with the stone and resulted in a smoothly-surfaced but eccentric stone.

  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 letting the stone move; you;ll never get it back in exactly the same place and you'll have to true the wheel with the dresser again. It gets tedious remarkably quickly.


    Nice score though.

  7. 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,etc, where it will be absorbed by the inside of the oven, heating the structure of the oven. This has a lot of thermal mass and relatively little surface area exposed to the radiated heat.


    Some of the radiated heat will reach the blade directly. The blade has lots of surface area and not much thermal mass, causing the temperature to rise rapidly. If we are talking about a blade being tempered, it may well have a black surface from the hardening process and it will certainly have a cross-section that gets thinner as it approaches the cutting edge. This means that the effect of radiative heating will be to raise the temperature of the edge more than that of the spine, unless steps are taken to mitigate the radiative heating effect. Placing a single blade in a rack which supports it so that both sides are exposed to the elements is pretty much guaranteed to maximize the unwanted effect.


    There are several things that can be done.


    First is to put a barrier between the elements and the workpiece to put the blade in shadow.


    The second is to position the thermocouple so that it is the fastest-heating thing in the oven. The thermocouple itself will need to be specified for the fastest possible response and the PID tuning will need to be done on the second firing; the first will establish a nice black oxide layer on the thermocouple, which is then a permanent feature. The black layer will mean the thermocouple responds differently to the first heat (when it was shiny) and probably heats faster when subjected to radiative heating.


    The third is to minimize the duration of radiative heating by bringing the oven up to temperature before loading the workpiece, open it, insert the workpiece and close it as quickly as possible to avoid the temperature dropping far.


    The fourth is to program a slow ramp up to temperature. This obviously needs a ramp/soak controller, but will eliminate the problem. It does require the user to actually use the ramp/soak facility though, and the ramp needs to be fairly long; perhaps an hour from room temperature to tempering temperature.


    I suspect most people use method 3, probably without even being aware of the issue, and rely on the oven manufacturer to have dealt with method 2, so far as is reasonably practicable.


    The oven manufacturer will usually also have dealt with at least part of method 4, by providing for ramp/soak control. The user decides whether or not to avail himself/herself of this facility.


    Method 1 is easy, as long as the oven is wide enough. I know at least one good knifemaker who gets impressive results tempering his knives in a tray of dry sand. I did some testing with stainless-steel sheet "screens" and that seemed to work, as did ceramic tiles.

  8. 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 pass for one in a poor light (I count myself among the latter). If they know what you are struggling with, they can probably help.


    To help, they will need access to the manual.


    I would not buy a controller unless I had already downloaded the manual from a publicly accessible website and added the location to bookmarks/favorites. If help is needed, it's just a case of asking for help with a link to the manual. I'd also want to check the manual is usable; there's a world of difference between a manual written by someone who writes technical manuals in a language they, and you, are fluent in, and a babelfish translation to English of something written in Chinese or similar.


    As a first step, I'd ask the ebay vendor if they can provide a link to the manual before you make any buying decision. If so, post the link here.


    Personally, I'd always use a ramp/soak controller. I built my first HT oven with a basic PID controller, which was free. I have bought ramp/soak controllers for each of the 4 HT ovens I've built since, despite having access to free basic controllers. Obviously YMMV.


    I would not reduce the width to 3"; The area is more important than the internal volume in determining heating rate and maximum temperature.


    With a 5" x 3" x 18" chamber, you'd have 318 sqIn of area on the inside. Going to 5" wide would give 400 sqin total. The smaller volume only saves 20% of the area, but I'm sure it would lose considerably more than 20% of its "usefulness" in doing so.


    Enjoy it. It's a fun thing to do and very rewarding.

  9. 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.

  10. 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 they did, they'd have built their own), so I try to build something that is as close to foolproof as I can make it. Also, once it has left my hands, I have no control at all over who gets to use it.


    The first HT oven I built was for an electrician. I could reasonably assume he'd understand the risks, so the control circuitry was broadly similar to the majority of the wiring diagrams on the web. The second was for a young knifemaker who was still at school, so I added a couple of extra safety features to bring it up to a standard I'd be happy to let my own kids loose on. The extras only added about $15 to the cost and perhaps 15 minutes to the build time, so I've stuck with that design on the others.


    In the wiring diagram in your original post, there is mains power to the SSRs at all times, unless the main power is switched off by the operator. The toggle and door switches only interrupt the switching signal to the SSRs, so if one of the SSRs fails in the way that yours seems to have failed ("closed" in relay terms), the elements will be live. I add an electromechanical contactor (basically a big relay) in the AC feed to the SSRs and pull in the contactor with the door and toggle switches.


    I gather there are some significant differences between Europe and North America in the way mains power is distributed and these may affect the danger posed by contact with conductors; here in Europe, our domestic supply is 230V on the hot leg and the Neutral is at Ground potential. Touch live and you get the full 230V to ground. It's not nice.


    I'm not entirely sure what you'll get if you do the same on a 220V circuit in the USA. I hava the impression you usually have a centre-tap to ground on the transformer, so would only effectively see half the voltage to ground if you touch live.


    Things are also different when building for ones own use; the user will have had the technical knowledge to build the oven, so will be able to make informed choices about its use based on that knowledge. The combination of the control circuit and competent operator normally provides adequate safety for most real-world situations.


    Apologies if my earlier post came across as doom-mongering. It wasn't my intention.








  11. 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 use an "extra" electromechanical contactor in the mains supply to the SSR, simply because I'm not happy with the idea of an SSR as the only thing between a friend and electrocution.

  12. 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 performance curve is interesting and gives high pressure at low flow. Because of the way they work, the maximum pressure is much higher than a normal centrifugal blower of similar size and RPM can manage.


    Flow control on a fixed-speed side-channel blower is best done by bleeding off surplus flow, rather than by throttling the output. Throttling the output causes the pressure to rise and actually increases the power consumption. If throttling is unavoidable, it can be done on the suction side. I think throttling is probably good for a smelt, as the pressure rises if the tuyere becomes partially obstructed, so the reduction in airflow seems to be less than it would be if a "normal" centrifugal fan was used.


    Owen Bush has a nice little Elmo Reitschle unit which I've seen used on a couple of smelts. It seems to work very well. I think it's one of these:




    On 60 Hz mains, peak pressure at around 150 mbar is about 2.2 PSI and peak flow at 100 M3/hr is about 60 CFM.


    Anyone looking for a blower in the UK might be interested in this supplier:




    Although the maximum flow seems quite low compared to simple centrifugal types, the pressure/flow curve means that the side-channel units tend to have higher flows when used with typical tuyeres, which have smaller areas than the discharge ports of the blowers they are often used with. Larger units are obviously available as well, if more pressure/flow is needed.


    Some of the manufacturers that spring to mind are Nash/Elmo/Reitschle, Rotron, Gast, Becker. I have a UniJet 75, which I think is made by Cattani and marketed as a dental dry suction pump. It was listed on ebay as a vacuum pump. Among the other applications I've seen for small side-channel blowers are air knives for drying and spa blowers.


    New prices are generally high enough to rule them out for our applications. Secondhand prices are quite reasonable, at least in the UK, but they don't seem to come up all that often.

  13. Since we are talking about Forge Temp. I have a question.. Where can I find a good/not to much money Pyrometer ?? I got my forge going but I have no idea what the temp is.. I'm pretty sure I am going to have to redo it because the only way it works well is with the air at full blast and the propane cut way back.. Plus I don't like the pin valve I got because it's not working that well.. Thanks


    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 (24") length with a plastic handle and curly cable, ending in a miniature plug to suit the TM902C and my other (much more expensive but no more accurate) instruments.


    I also have a couple of longer 6mm MI type K transition joint thermocouples. These also work well and are off-the-shelf items, just needing the plug fitting. The sheaths on those I have are type 310 stainless steel, rated for 1100 degC (1202 degF), but they seem to work fine up to the 1365 degC maximum for the sort of timescales they see when used for checking/adjusting my forge.


    There are cheaper unsheathed thermocouples intended for fixed installations. They need a sheath if they are going to be in a forge for long and ceramic sheaths are available for this.These are good if you can put them in the right location to measure the temperature that you are interested in. Most of the forges I have had any dealings with have had temperature variations throughout the internal space. A long handheld probe will let you measure and understand the variations, helping to find a useful location for the fixed thermocouple if that is the way you intend to go. The ceramic sheaths are pretty good insulators and therefore slow the response to temperature changes. This means they tend to damp out fluctuations and can make a forge appear much more stable than it really is. It's one of the reasons I like to check the temperature stability and distribution before going that route.


    Most thermocouples are made to order. I try to specify "Grounded junctions" for the handled ones. This reduces the response time significantly when compared with "insulated junctions", but does have minor disadvantages in other areas.


    If you are in an industrial area, there is a good chance there will be a thermocouple supplier fairly near. If not, Omega are about the biggest name in temperature control and it's worth talking to them (www.omega.com) if you need to order with shipping. They have knowledgable technical support and I like their Omegaclad XL sheath material. Either way, I'd strongly recommend talking to the technical guru at whichever supplier you use and listening to their advise.

  14. 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 and even hot CO2 is lighter than cool air, so will tend to rise.


    Neither CO2 nor CO is healthy to have around: CO2 is usually present because the Oxygen in the air has been burned with a Carbon-containing fuel (or respired by a life-form; it is present in a concentration of 3-5% in the air you normally breathe out). The main risk from CO2 is usually considered to be the lack of remaining Oxygen in the air, causing asphyxiation.


    CO kills at much lower concentrations. It binds tightly to the Oxygen-carrying locations in the red blood cells, preventing them doing their normal job of carrying Oxygen to where it is needed. It's worth bearing this in mind; CO attaches to the Oxygen-carrying sites much more readily than it leaves them; going outside for a short breather during a forging session will not actually do much to reduce the blood CO level once it has been raised.

    • Like 1
  15. 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.

  16. 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 with the atmosphere and complete the burn as the outer bushy part of the flame. In a forge, the only route for the air to get in is usually as the primary air. Any secondary mixing can only happen once the part-burned gases leave the forge and can mix with the atmosphere, where they burn as the dragons breath.


    If starting with a commercial Venturi burner, it is often necessary to substantially increase the proportion of primary air for use in a forge. The easiest way to do this is usually to fit a smaller gas jet.


    In addition, many commercial Venturi burners run on low gas pressures, which give low gas velocity through the Venturi throat and less "draw" than high-pressure jets would give. Again, "we" are likely to need smaller jets than would be typical for industrial use.


    I have been playing with "Amal" atmospheric injectors lately and have been getting reasonably good results with the 1" size used with 0.6mm MIG tips as gas jets running on Propane at 0-4 Bar (0-60 PSI). I've been able to maintain stable temperatures all the way from from 750 degC (1382 degF) to 1410 degC (2570 degF). I think there's a bit of scope for further tuning with proper jets, but I needed to get somewhere fairly close as a starting point.


    The Amal Gas Injectors leaflet can be found at http://www.amalcarb.co.uk/downloads.aspx


    I have been using a forge constructed from 20 IFBs to play with, giving a chamber 6" x 6" x 13 1/2". Running on a 19Kg (circa 50 Lb) cylinder, freezing has only become an issue when the cylinder is close to empty and the ambient temperature is close to freezing.


    The time to heat is longer than I'd like; forging temperature takes a minute or two, but welding temperature needs a good half hour. My IFBs are cheap grade 23s and are about twice as dense as the Morgan Thermal Ceramics JM23s I use for my electric HT ovens. I'm pretty sure the thermal mass is the reason for the slow starting. The JM 23s are 3 times the price here and I was only aiming for a quick-and-dirty test bed for the burner.


    I'll be building a round one next, lined with CF blanket, for better insulation and lower thermal mass. If I could get it over here, I'd try bubble Alumina for a flux-resistant lining on the bottom over the blanket, and aiming to keep it reasonably thin in order to minimize the thermal mass.


    With available materials being limited, I will probably have to go with dense castable instead of bubble Alumina.


    Whatever you end up going for, I'm convinced the difference between very good and just so-so is the burner. Get that less than excellent and you'll have a lousy forge, regardless of how well-engineered it may be structurally.

  17. 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 temperature-controlled drum HT forge for example, you would probably do better with a relay output.


    72 x 72mm is a fairly unusual size. 48 x 48mm and 96 x 96 mm are more common, with 48 x 48 usually being significantly cheaper. I tend to stick to the more common sizes because it makes it easy to change them later on as your needs change. A basic controller, like the one in the link, will generally be all you need for HT of carbon steels, but many people feel a ramp/soak controller is worthwhile for stainless steels.


    I was not able to find a manual for that particular controller online within a few minutes of starting to google it. I would not buy it for this reason alone.


    To elaborate, if you run into difficulty, you can call for help on the interweb with a link to the manual, and there's a fair chance that someone who knows a bit about controllers in general can chime in and help, without necessarily having used the particular model you are using. Without the link to the manual, you are on your own.


    Trying to set up your first controller using a manual translated from Chinese using Babelfish or Google Translate can be a tad frustrating.


    For an information-only temperature display, you are probably better with a battery-powered handheld unit, freeing you from mains power. I use the TM902C, bought from ebay, but I think in degC. If you really need degF, you'll have to find something appropriate. Something to be aware of is that type K thermocouples can measure up to 1365 degC (2489 degF). A 3 1/2-digit display showing degF with a maximum count of 1999 will cut off the top of the useful range.


    The TM902C only works with type K thermocouples. I like this, as it means there's no chance of setting the wrong thermocouple type and getting wrong readings.


    Don't think that cheap means inaccurate. My TM902Cs agree with each other, with instruments costing over 20 times the price and with my calibration checker.


    The readout is only part of the story and the likelihood is that you'll need to spend more time and money sourcing the thermocouple itself than you will the display.


    I'd suggest a phone call to Omega to discuss your thermocouple and controller needs. Read up on things first, by all means. Make sure you have worked out (and made notes on) exactly what you are trying to do, then put your credit card out of reach, phone them and ask for their recommendation. See what they come back with and think about it before actually ordering.




    Price-wise, I find Omega expensive on hand-held instruments, but good on thermocouples. They are also good on ramp/soak controllers.


    Even for basic controllers, having a proper manual, written in English by someone who writes manuals for a living, can be worth paying a premium for. The support and advice also has a value, which you'll probably be able to gauge from the initial phone call.

  18. 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 is 4 seconds. I'd suggest 2 seconds.

    D1P Decimal point position. Default is 1, set to 0 (1 limits max display to 999.9)

    d1H Display High range. Set to 1300.


    Once you have the settings in, I recommend you run an autotune at a fairly typical tempering temperature first. Maybe 250 degC. I think the way to do this is:

    Power the elements with the setpoint at zero (how you do this will depend on your setup; it might be close the door, press a button, plug it in, or any one of a number of other ways), raise the setpoint to 250 degC then immediately press the AT button for 2 seconds. It should start flashing the AT display. Let it do its thing; I'd expect it to take several minutes.


    If successful, the autotune should complete and the controller should just keep working and hold the 250 degree setpoint.


    You can then adjust the setpoint as you see fit. Watch for the temperature overshooting the setpoint and see if you are happy with it.


    Other than that it's quick, the reason I suggest tuning at a low temperature is mainly due to overshoot; if you tune at high temperature, I find you tend to get overshoot at low temperature. If you tune at low temperature, you seem to get a slower approach to the setpoint when it is set at high temperature. You take a choice, but slow approach to Austenitizing doesn't seem to do as much harm as overshootin the tempering temperature.


    Of course, if you only use it for Austenitizing and temper with something else, you should tune at high temperature.

  19. 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 use weatherproof outdoor fittings in the workshop and garage. Not for the weatherproofing, but because they offer some mechanical protection to the tube. Little shards of glass and white powder raining down while I try to find the off switch for the grinder in the dark, isn't an experience I particularly wish to repeat.


    I also try to have two independent light sources in the room (a window counts if there is one), on separate circuits (no common fuse, breaker or RCD/GFCI) for the same reason.

  20. 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 single-phase supply. Many manufacturers stop at 2.2kW/3HP and to go any bigger, a 3-phase supply into the drive is needed. A few years ago, I needed a 3kW/4HP single-phase 230V drive and the only one I could easily get in the UK was a Siemens G110.


    I've heard pretty good things about the HuanYang drives sold on ebay, but haven't had a play with one yet. There are plenty listed as 3kW/4HP, but all the photos accompaying the listings show the 2.2kW/3HP version.


    If it's for a grinder, you'll need to ensure grinding dust can't get anywhere near the innards of the drive. There are several options, from mounting the drive in a separate "clean" room, through filtered-ventilated enclosures, sealed enclosures and factory-built sealed drives. Dealing with the heat produced by the drive is the most awkward part of this. I assume from your location that you are not going to have to deal with tropical temperatures, so a drive in a sealed enclosure may do the job very well. The enclosure will probably need to be fairly big though.

  21. 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 until the motor becomes too inefficient to be useful.


    Most motor and VFD manufacturers seem to recommend a speed range of 10 Hz to 100 Hz for a 4-pole motor. My limited personal experience suggests they've got it about right.


    For a motor rated for 1800 RPM at 60 Hz, 10-100 Hz gives a speed range of 300-3000 RPM.


    A 3600 RPM motor could probably be run over the same 10-100 Hz frequency range, giving 600-6000 RPM. Motor life would probably be shortened dramatically, as everything above 3600 RPM would exceed the design speed.


    If using a TEFC motor, you need to be aware that you'll need to derate below about 25 Hz, as the cooling airflow is reduced at low speed and the motor is more prone to overheating. In most cases, you just need to be aware of it; I don't imagine you'll be leaning hard on the platen for long periods at such low speeds, so the derate will probably be taken care of naturally. (If I'm wrong on this, please somebody let me know soon, before I build my grinder)


    I have run 4-pole motors at 120 Hz, 3600 RPM, but they feel as if the torque is down. I've tried running below 10 Hz on a basic V/F drive (Voltage and Frequency are varied together) and the motor felt "coggy". Using a slightly higher-specced "Sensorless Vector" drive kept the same motor feeling smooth at 3 Hz. SV is worth knowing about if you need very low speed, but I don't think it's needed on a grinder.

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