BobL

Electrolysis of a water NaCl solution will make Cl and H gas but it cannot make Na gas, so the Na stays dissolved in the water. When solid NaCl is molten it no longer exists as a crystal of NaCl but liquid Na+ and Cl- ions. In this state (ie no water) electrolysis can extract liquid Na, and Cl gas. If the salt is held molten at near boiling temperature (1413ºC) it can release small amounts of Cl gas. The amount is small but can be enough to "irritate eyes" but this is a minor risk compared to other problems with using molten salts. Like you said heat treatment won't be working at these temperatures Despite the above, NaCl is used in fire extinguishers to fight light (magnesium, sodium and potassium) metal fires. The salt is encased in a fire retardant plastic which immediately melts releasing the salt which cools the fire and together with the plastic smothers the fire.

Yep - a small woof. It reminded me of igniting hydrogen in a test tube

Thanks for the info. While I agree your explanation sounds more likely it is worth noting I could not smell any mercaptan after flushing or when I cut the first end of of the tank off.

I realize this is an old thread but thought I would add my experience on opening up a 10 gallon gas cylinder. It took a fair bit of effort but eventually I got the valve off. Tipping it upside down and a handful of rust fell out that had a faint odour of mercaptan (the smelly oil they add so that gas can be smelled) Then I filled it up with water and left it in the sun all day and then tipped the water out. I did this at least 5 times. Then I cut it open at one end with a thin kerf cutting wheel - no problem. The steel was 1/8th"thick and encrusted with a 1/16" layer of rust Then I cut the other end - this was through a weld - I had gone half way when there was a small woof and a flash of flame from the open end. What I suspect happened was even after what I did there was still a small pocket of gas trapped either in the weld or rust.

Cheers Toolish, I really like the look and feel of old school tools and have been bodging a few by welding etc but would prefer to be forging them properly. Here are a few more I did all the metal and woodwork for.

Everyone says g'day so let me say that as well. I've been a hobby wood working tool maker for about 5 years so have had to harden and temper tool steel for some time. I was doing this where I used to work in computer controlled furnaces but also have done some simple heat treatments at home in my shed with a MAPP torch and a few fire bricks. I retired two months ago and did a blacksmithing course - loved it. Then got really excited about the feasibility of tool making using some blacksmithing techniques and have built a forge and eventually found this site with the recommendation from AndrewOC. Here's a couple of samples of what I do. The is a set of woodwork plane makers floats (rasps) these are tools for making wooden planes. This is a set of tools for a luthier friend of mine I also mill all the wood for the handles - The float handles are pear wood and the luthier set are Redgum and Sheoak.

I realise this is an old thread but I wonder if anyone else has been using an optical pyrometer since this thread has been posted and if there is anything to watch out for while using one ? I managed to obtained access to an (>40 years) old PYRO optical pyrometer which uses a disappearing filament method. The pyrohead, meter, photo tripod adapter and a range of focal length lenses all come in this handy in a lab padded suitcase. The only thing missing is the original power supply. Fortunately I used the same pyro at university nearly 40 years ago so I am familiar with how it works and know that it uses a variable ~3V DC power supply (PS). It will even function on 2AA batteries but it can only be accurately calibrated using a variable PC. I don't have a 3V DC power supply so I adapted a 5 - 12 V PS and a large variable resistor. Here's how it all looks when it's setup The range of lenses means it can be used over distances from about 5" to infinity from the item being measured. This is of course necessary as the unit should not be too close to the forge. Here's the scale - plenty of range and sensitivity but I doubt I will be needing any more than the first range (650 to 1400ºC). My experience is that in practice the object needed to be at ~750ºC before it could be measured reliably but that is still a useful starting temp. It even has a couple of calibration points on the scale whereby it has to be drawing so many mA at specific points in the scale. These points can be checked with a mA meter and the PS V tickled up and down til it shows the right current. My forge is awaiting a gas line to my shop so I can't play with it yet. I have a a thermocouple and IR scope type thermometer that I can cross check with. I will report back when I make a few measurements

I knew about using the the yellow teflon tape from lab renos at work and then walking around the side of our house just the other day I noticed whoever did the gas plumbing used the white stuff. Most people will know about this but just in case, the tape works better if (facing the front end of the thread) you wind it clockwise. If you wind it the other way the winding action tends to draw the tape away from the thread.

No worries about the information - I spent years working on this stuff as part of my day job where I designed and even built (some with my own hands) laboratories where we used and distilled our own chemicals like concentrated hydrochloric and nitric acid, so I am happy that it is useful elsewhere. eg I have also helped many woodworkers with their dust extraction systems etc If anyone on this forum wants help setting up their exhaust systems them I am only too pleased to be able to do so. For air flow measurements I use hot wire anemometers which are accurate air flow sensors that measure air speeds from 60 mph down to about 1mph. I also have access to particle measuring instrumentation that can measure dust down to 0.3 microns in size so I can detect for instance combustion dusts from motor vehicle traffic and welding.I have not tried this in my shop ith the forge (awaiting installation of a natural gas line to my shop) but I will do so once I get everything running again. I'm sorry I did not emphasise in my previous post that "any ventilation is better than no ventilation". A big axial fan in a wall and a wide open door or window is a good start, especially if the forge is in line with both. RE; mixing the air in a shop with ceiling fans This won't really help much. I always reckon it's better to devote fan energy into as much exhaustion as possible and preferably at the source of the problem which in our cases are forges. If the bad air is already at ceiling level it makes more sense to exhaust it from there rather than trying to get it back down into the middle of the shop and then move it out from that area. Of course not everyone can put ceiling mounted exhaust fans in their shop so they have to use sideways solutions. The best solutions are overhead or side draft hoods ducted to outside the shop using 6" ducting which can move 1250 cfm - this requires a 1.5 - 2HP blower and generates quite a fast torrent of air which may be too much for some forges if the inlets are too close to the forge. I would think a ~1/2HP impeller using 4" ducting (400 cfm) would be more than enough to exhaust the gasses from a small forge. My welding bay fume hood is a 1/2 HP motor , 6" diam metal ducting , 500 cfm unit that allows me to just park my (mobile) forge underneath it. BTW Your idea of using a push-pull system can be very effective when applied to arranging a steady draft between inlet and exhaustion points. e.g. If a "doorway"-"forge"-"exhaust fan" line cannot be set up, then using a second axial fan to push air into a shop to create an inlet-forge-outlet line will improve things.

Having worked with fans, dust exclusion and air movement for more than 30 years I can tell you it doesn't quite work like that. What happens is that within a short period of time (ie seconds) some of the air that is sucked in is also sucked out and an oscillating fan doesn't do anything to assist this happening. I have done measurements of ventilated laboratories and the very best one can expect is a 50% air exchange in the time calculated for one room air turn over, and that is provided that there are large vents at evenly spaced locations all around the walls at both floor and ceiling level. A 50% turnover means multiplying your 3.6 minute x two or 7.2 minutes. If you don't have the evenly spaced vents in the walls etc in practice it will be X3 or X4. Axial flow fans such as the air king model are not very effective at room ventilation especially if there are any sort of restrictions involved on the intakes. What is important for pollutant removal is where the extraction is located and the best place is as close as possible to the pollutant production e.g. a fume hood above or to y side of a source will be much better than just extracting air from a wall. eg 200 cfm close to a forge may be more effective than 2000 cfm on a wall. The other thing to be very wary off are the CFM claims by most fan manufacturers. Some are theoretical numbers which are almost meaningless. Most ratings are for unconstrained fans, so as soon as any housing, grating or ducting is added their flow reduces very significantly. For example a 4"diam opening simply cannot pass more than ~400 cfm of air at the sorts of pressures (<20" of water pressure) most axial/squirrel/impeller fans generate. A 6" diam duct can only pass ~1250 cfm. If yoanur extraction system uses these duct sizes then these are the real figures that should be use in air turnover calculations. I have done extensive measurements of many different fans and dust extractors to verify all of the above.

Look out for scrap metal as you cannot have too much of it I've also only just started and am finding that prices are as long as a piece of string and depends on the condition of the item, the greed of the seller and where you live, especially for heavy stuff like anvils. Look around on-line will give you a ballpark although sometimes inflated idea of prices BTW a hammar in Australian is a side loading freight container crane.

One of the best things I included when I built my home shop was a small fume hood with overhead canopy and wrap around doors. I measured the fan air speed and it pulls 500 cfm. I use it for welding, metal grinding, and cutting and small spray painting jobs, and now I find I can back my gas forge up to it so the forge exhaust vent is effectively under the fume hood canopy and is thus exhausted outside the shop. If I wish I can also switch on my wood working dust extractor (1260 cfm) which has intakes at the other end of the shop and also vents outside my shop. The two units combined will theoretically vent my shop in just over two minutes. I did not have a forge anywhere near my horizon when I built the fume hood but I'm sure glad I built it.

I attended a one day blacksmithing course a while back and got enthused enough to build a natural gas powered forge over a couple of weeks. We live one a small inner city block about 1 mile in a straight line from city centre so I have a few limitations, like noise and space but I do have a compact metal/wood shop with a fume hood that I can use the forge in. Internal dimensions of the opens space are 8" in diameter x 14" long Doorway uses a 6.5 lb lead counterweight that balances the silica firebricks. The other frame in front of the doorway is an removable air curtin. The frame also can hold a piece of pyrex glass from an old door oven so one can watch what is going on with the doorway up without getting cooked. That frame is on a hinge and can be rotated right out of the way as required. The air supply is a variable speed 1800W vacuum cleaner that runs at about 1/3rd of full power. I got it up to 1200ºC before I melted the thermocouple. It uses 2 cubic metres or 3 lbs of gas an hour. So far it runs off the NG bayonet on our back veranda but this has me excited enough to extend the gas line to the workshop.

The metal work end of my shop has mini corrugated iron (we call it miniorb) and rock wool insulation behind it. The miniorb is surprisingly sound deflection/absorbing - I wish I had done my whole shop with it. Here it is just before all the machinery was installed . Of course the painted floor is a bit of a waste around the forge but I wanted to keep the concrete dust down in other areas of the shop.

Where I live in Perth Australia is more than 1000 miles from any other big city so anvils are rare. The problem is exacerbated locally by one indivdual who has collected over 1000 anvils and just has them all over his back garden going rusty. I had to travel 400 miles to get my anvil and if it was not from someone I knew this collector probably would have picked this one up as well.