Jump to content


  • Content Count

  • Joined

  • Last visited

  • Days Won


Posts posted by timgunn

  1. 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.

  2. 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. 

    • Like 1
  3. 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.


  4. 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.

  5. 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?

  6. 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.


    • Like 1
  7. 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. 

    • Like 1
  8. 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.

  9. 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.


  10. "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. 

    • Thanks 1
  11. “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.

  12. 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).


    • Haha 1
  13. 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. 

    GraphPIDto250deg.GIFGraphRampto250deg (1).GIF


    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. 


  14. 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.

  15. 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. 


    • Like 1
  16. 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.


    • Like 3
  17. 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.

  18. I've had pretty good results with a few of the cheap Chinese pyrometers. I have access to a thermocouple calibrator and always check the accuracy of the pyrometers across the intended working range before using them in anger.

    Until a couple of years ago, I used to recommend the TM902C, available for around 5 bucks delivered. I'd had maybe 20, ordered in ones and twos over maybe 4 or 5 years. They were boringly accurate from 0 degC to 1370 degC (32 degF to 2500 degF) and came with a glassfiber-insulated bead probe that was good to 400 degC (750 degF) and was flexible enough to be closed in an domestic oven door to check tempering temperatures. 

    A couple of years ago, I ordered ten of them. When they arrived, I checked them on the calibrator and found they were accurate up to 800 degC but then became progressively inaccurate. I can't remember whether they showed 1370 degC at an input of 1290 degC, or showed 1290 degC at an input of 1370 degC: either way I was not happy with them. They were very consistent and all read the same on any given input signal.

    Side-by-side, there were external differences between the good ones and the bad ones, but these would not be obvious on an ebay listing so I stopped using or recommending them.

    I have since used DM6801 digital thermometers and found them boringly accurate. 10-20 bucks delivered from China. The supplied bead-type probe is PVC insulated and only good to a little over the boiling point of water: not much use to most of us.

    Whatever pyrometer you get, the supplied thermocouple will not be any use in a forge and you'll need to go to a thermocouple specialist.

    The "best" probe I have used for "our" purposes is an Omega KHXL-14U-RSC-24 which is a handled type K Mineral Insulated probe 1/4" diameter and 24" long below the handle. The sheath material is Omegas proprietary "Super Omegaclad XL", which is not really necessary for Heat-Treating, but seems to be the best I've found for surviving being used to occasionally check forge temperatures without going to painfully expensive Type S, Platinum-based, thermocouples. The assembly includes a curly cable and miniature plug.


    Using the part number builder on the page does not allow anything longer than 18", but putting the desired part number into the search box, top-right, will get you a price. For sword-length stuff, a 36", 48" or even 60" might even be worthwhile.

    I am cheap and tend to use similar thermocouples from the company we use at work. However, these "only" have a type 310 Stainless steel sheath, which is rated to 1100 deg (2012 degF) and will last pretty much indefinitely for HT, but doesn't last many cycles to 1300 degC-plus when used for checking welding temperatures are being reached.

    • Thanks 1
  19. A Kiln/HT oven will certainly allow you to do things that no forge can realistically manage.

    Power input is typically around 3 kW. I have built HT ovens up to 27" long that will reach 1300 degC (in about an hour and 45 minutes) and will run from a standard UK domestic outlet: 13A at 230V nominal rating, so 3 kW. Bigger ones might use more power, smaller ones might use less. 

    Lower temperatures are reached much faster. When I first tested the 27" oven from cold (maybe 10 degC, 50 degF), 800 degC, 1472 degF was reached in 22 ½ minutes, 1100 degC, 2012 degF took 54 ½ minutes, the temperature at an hour was 1125 degC, 2057 degF and 1177 degC (2150 degF) took 71 minutes.

    As Brian says, once the desired temperature is reached, the PID controller will cycle the power on and off as needed to maintain temperature, so the average power drawn during the "hold" will be less than the heat-up, which will usually be at full power unless you are "ramping". 

    A fairly typical HT cycle for O1 might be to heat the oven to 800 degC and stabilize it (call it 30 minutes at 3 kW, for 1.5 kWhr), triple normalize; Work in, allow the temperature to recover, soak for 10 min, pull out and cool to black. Repeat. Repeat. (Call it an hour at 33% power, so 1 hr at 1 kW for 1 kWhr) Then Austenitize: work in, allow temperature to recover, soak for 20 min (call it 30 min at 33% power, 30 min at 1 kW for 0.5 kWhr). Quench workpiece(s) and switch off oven. 

    Total power consumed 3 kWhr. 

    You might expect to maybe double that for a Stainless HT, but to put things into perspective, unless you only do single blades each time, 6 kWhr is still unlikely to significantly exceed the cost of HT foil. 

    The numbers I've given are probably high-side figures. I don't have hard data, but I'm pretty sure the same homebuilt 27" oven was actually showing a steady-state output cycle of only 18% during the 1100 degC, 2012 degF hold section of a Stainless Heat Treat: when I delivered it, the new owner gave it a test run while we drank tea. I use a 2-second output cycle and always have an LED that is switched with the elements. I was surprised the "on" part of the cycle seemed so short and pulled up the output cycle display on the controller. It read 18%.

    The heating load of a HT oven is entirely resistive: it does not have the starting surge of a motor load or the horrible Power Factor of some modern electronics. So long as you do not exceed the outlet rating, I would not expect any new and interesting problems with mains power supplies, even in the middle of nowhere. The short-cycling 3 kW output would be harsh on a small generator, were you to run it from one, but I'd not anticipate a problem once the generator gets above maybe 10 kW or so.

    • Thanks 1
  20. The first question is probably "what does the motor rating plate tell you about the motor?" and the second is "what do you want it to do and how do you want to tell it to do it?" 

    The motor rating plate should give you a bunch of values that need to go into group 2 of the programming. The values you are likely to have are 02-01, 02-03, 02-04, 02-05, 02-06. If the motor plate gives you any others in an obvious way, put them in. Otherwise leave the settings as the defaults.

    The default command source seems to be the keypad. If you have a speed control potentiometer (twiddly knob) on the front, set parameter 00-05 to "1" to enable speed control from it. 

    It looks like it should run on the start and stop buttons on the keypad and should go to whatever speed the knob is set to. Once running, adjust the knob to adjust the speed. It looks like the default acceleration and deceleration times are 10 seconds, so there will be a lag if you turn the knob fast.

    The drive is environmentally protected to IP20: effectively fingerproof. It is not sealed against dust and metallic grinding dust WILL kill it very quickly unless you take steps to seal the drive. Bear this in mind when you first fire it up: do not get over-enthusiastic, start grinding and cause fireworks. The quickest anyone I know personally has killed a drive this way is around 2 minutes from first switching it on.

    You'll then need to decide how you are going to protect the drive and how you are going to control it in whatever protection you come up with (if it's in a box, you won't be able to get at its front panel). You can also decide on the speed range you want.

    Some of the remaining parameters will set the drive up for the speed range and command source you decide to use. Many of the others are there to interface with control processes in industrial automation and will not be needed for a grinder with a human operator.

    I mount IP20 drives in IP66 enclosures and fit a remote control box on a trailing lead with start and stop buttons, a keyed forward/reverse switch (the key is taken out when running a machine that should not be reversed) and a speed control potentiometer. The box has a 3-phase socket on the front so I can plug in different machines. It's usually as cheap to buy an IP66 drive to begin with, and is much less effort. 

  21. It looks like the burner is choked down to me: The air holes are covered so there is not much air flow for the gas to burn with. Try changing absolutely nothing except the choke sleeve position: move it towards the forge and uncover more holes to get more air in.

    See what happens and let us know.

    If you can, take photos in the dark. The most useful shot is often one across the mouth of the forge to show how much Dragons Breath there is, and what colour it is: In daylight, the DB flame does not show particularly well and digital cameras tend to do strange things to the white balance so that the flame colour in the photo is not the actual colour.

    Taking a tight shot directly into a forge can be completely useless because the camera will adjust the colour and a real dull red will look in a photo just like a real bright orange in another photo.

  22. Are 17-4 and 18-8 foils actually that much more readily available at .001"-.002" thicknesses and in knifemaker-type quantities? 

    321 is not all that far off being an 18-8 stainless: it's effectively 18-10 with up to 0.8% added Titanium, which apparently improves high-temperature stability. I think 321 was developed to counter cracking in aircraft engine exhausts. Neither 304 nor 316 are particularly recommended for high temperatures.

    309 is higher in both Chromium and Nickel for use at higher temperatures.

    They get used because they are known to work reliably in their specific applications. "Someone" did some work to identify suitable materials for the tasks and that is what they came up with. Most folk seem to accept the consensus view and pony up for the proven product.

    Using 321 when heat-treating steels that "need" 309 has been known to fail and I'm pretty sure an evening spent searching the knifemaking forums will provide some insight into the sort of things that can go wrong: I'm pretty certain I've seen posts about the foil welding to the workpiece and to failure of the envelope allowing contact of the workpiece with air.

    If you have easy access to other grades of SS foil and can do some testing, I'd certainly love to see your results.

  • Create New...