heres a dumb suggestion, a deep well at one end, or both ends, motorized push scraper, on timer or sensor triggered, to push crystal buildup into well.
Self scraping silver cells
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I've decided on a 2 stage approach. As this project requires a reconfiguration of the cells to have a self scraping cylindrical cathode, I figure the first thing to do is to get that process working. The silver can be collected in a polypropylene container placed beneath the cathode and emptied periodically. My biggest concern is the electrical contact on the rotating cathode, it will spin slowly but the guy we will probably have build it has concerns about the heat buildup at the contact point as we are running at 200 amps.
The next phase would be to replace the collection container with a funnel shaped concentrator and a worm drive to continuously pump it up. But that's after the rotating scraper re-design.
By making the cells deep enough the container can accumulate over a longer period and allow this to work 24 hours a day but be staffed for only 8.
While awaiting the prototype rotating cell to be made we've installed timers to shut the cells down after a second shift when the cells are last scraped, and start them up 5 hours before the first shift arrives so the first thing they do is harvest the overnight accumulations. So with a timer we were able to only lose about 15% of production capacity while saving 33% of the labor.
The next phase would be to replace the collection container with a funnel shaped concentrator and a worm drive to continuously pump it up. But that's after the rotating scraper re-design.
By making the cells deep enough the container can accumulate over a longer period and allow this to work 24 hours a day but be staffed for only 8.
While awaiting the prototype rotating cell to be made we've installed timers to shut the cells down after a second shift when the cells are last scraped, and start them up 5 hours before the first shift arrives so the first thing they do is harvest the overnight accumulations. So with a timer we were able to only lose about 15% of production capacity while saving 33% of the labor.
A
Anonymous
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4metals said:
Heat should not be too great, as 200 amp * .5v = 100 watts * 3.4ish btu/hr = 340 btu/hr this should be fairly easy to heat sink away.
Jim
qst42know
Well-known member
Will we be able to see some photos of what you've come up with when it's finished?
Please! :mrgreen:
Please! :mrgreen:
I don't know if that will be possible as I'm being paid to develop this for a refiner, it is his property and his to do with as he pleases. An unfortunate side effect of consulting, covered somewhere in the small print.
4metals,
200A requires a conductor (if copper) of about 0.2 sq in cross sectional area - 1000A/sq.in, to prevent heating.
You should definitely look into those electrolytic units used for plating silver from photo fixer. They're like ready made for what I visualize you need. All of your engineering problems have already been worked out for you. Every one I've ever seen uses rotating cathodes in order to constantly renew the cathode film. The silver thiosulfate complex ion is negative and is repelled by the cathode. A rotating cathode solves the problem. I can't remember the RPM but they don't turn very fast - I'm guessing 10-12 RPM, more or less.
These SS cathodes are usually about 6"-8" dia. x 8"-12", or more, long in the larger units, although I have seen a lot of different sized cathodes. Some have 3 or more cathode units in one tank and, if I remember right, all 3 ran off the same gear mechanism. The silver can get 1/4" thick and the cathodes get quite heavy (28# on an 8x12 cathode drum). The silver is brittle and is removed in chunks with a hammer. For these reasons, everything is pretty heavy duty. The cathodes run vertically. They've been using these units for a long time and all the bugs have been designed out of them. They are workhorse machines. With x-rays going digital, I would think there would be a lot of used units available. Most every hospital of any size, has (or, had) one, most probably stored somewhere in a warehouse.
200A requires a conductor (if copper) of about 0.2 sq in cross sectional area - 1000A/sq.in, to prevent heating.
You should definitely look into those electrolytic units used for plating silver from photo fixer. They're like ready made for what I visualize you need. All of your engineering problems have already been worked out for you. Every one I've ever seen uses rotating cathodes in order to constantly renew the cathode film. The silver thiosulfate complex ion is negative and is repelled by the cathode. A rotating cathode solves the problem. I can't remember the RPM but they don't turn very fast - I'm guessing 10-12 RPM, more or less.
These SS cathodes are usually about 6"-8" dia. x 8"-12", or more, long in the larger units, although I have seen a lot of different sized cathodes. Some have 3 or more cathode units in one tank and, if I remember right, all 3 ran off the same gear mechanism. The silver can get 1/4" thick and the cathodes get quite heavy (28# on an 8x12 cathode drum). The silver is brittle and is removed in chunks with a hammer. For these reasons, everything is pretty heavy duty. The cathodes run vertically. They've been using these units for a long time and all the bugs have been designed out of them. They are workhorse machines. With x-rays going digital, I would think there would be a lot of used units available. Most every hospital of any size, has (or, had) one, most probably stored somewhere in a warehouse.
aflacglobal
Well-known member
Link Link !
qst42know
Well-known member
4metals said:
Sorry I asked. I hadn't considered that.
A
Anonymous
Guest
goldsilverpro said:
Hi Chris,
Conductor sizing is by amperage, I just did not think with the actual amount of power being applied and with the amount of heat that would sink into the electrolyte, that 340 or so btu/hr would cause heat at the junction, exspecially if a carbon graphite contact was used. I was also addressing the contact point, 3/0 copper would handle 200 amp or if you were using taps you can size even smaller. The main concern on conductor sizing is voltage drop, which causes 2 problems power wasted as heat and the resultant conductor heating causing problems with the insulation.
But all in all my point was the 340 btu/hr.
Jim
Dick
Thanks, looks like a nice way to connect.
Thanks, looks like a nice way to connect.
Your welcome.
I've been following this thread and think that a rotating cathode is the way to go.
If it is fitted with 2 scrapers the wipe each side into a small v shaped sloped tray that uses a small wash stream to carry the silver over the side if the tank and into a settling tank. Then the fluid can be recirculated back to the trays.
That seems like a lot simpler machine to build than a mechanical scraper to clean the bottom of the tank.
Then the problem becomes, how do you change annodes with the axle running down the top of the tank?
dickb
I've been following this thread and think that a rotating cathode is the way to go.
If it is fitted with 2 scrapers the wipe each side into a small v shaped sloped tray that uses a small wash stream to carry the silver over the side if the tank and into a settling tank. Then the fluid can be recirculated back to the trays.
That seems like a lot simpler machine to build than a mechanical scraper to clean the bottom of the tank.
Then the problem becomes, how do you change annodes with the axle running down the top of the tank?
dickb
Dick
My thoughts were to use a cylindrical cathode so all of the falling crystal will collect in a circular area. Then a funnel will concentrate the fallen silver to the center of the funnel where a worm drive screw angled at 45 to 60 degrees along the side of the funnel (depending on the design limits, depth and diameter) to lift the crystal over the side of the cell.
If I understand your idea correctly you will let fluid flow carry the crystal out a hole below solution level and use a pump to return the solution to the cell. Sort of like bailing a boat in reverse. Whenever I design things I always think of worst case scenarios because they can and will happen sooner or later. A hole beneath the operating level of the solution needs to be closed if the power goes off or if the pump clogs. In my day I've come in to many floods caused by those once in a while snafu's.
I'm not totally sold on my own ideas yet, there have been some excellent suggestions as to the rotating cathode contacts. I'm quite sure one of those electrical contact devices will make it into the final design. As far as the screw goes, I'm banking on the silver crystal sliding up in front of the screw, but realistically some may get burnished on to the cylinder eventually. One fix for that is to remove the lift unit from the cell when the cell goes down for solution change-out and soak it in 50% nitric to clean up the stainless pipe and recover the silver. I can use a slow speed high torque motor which has a slip gear if the resistance is too high so it will stop spinning and not burn out the motor.
Thanks again for the input.
My thoughts were to use a cylindrical cathode so all of the falling crystal will collect in a circular area. Then a funnel will concentrate the fallen silver to the center of the funnel where a worm drive screw angled at 45 to 60 degrees along the side of the funnel (depending on the design limits, depth and diameter) to lift the crystal over the side of the cell.
If I understand your idea correctly you will let fluid flow carry the crystal out a hole below solution level and use a pump to return the solution to the cell. Sort of like bailing a boat in reverse. Whenever I design things I always think of worst case scenarios because they can and will happen sooner or later. A hole beneath the operating level of the solution needs to be closed if the power goes off or if the pump clogs. In my day I've come in to many floods caused by those once in a while snafu's.
I'm not totally sold on my own ideas yet, there have been some excellent suggestions as to the rotating cathode contacts. I'm quite sure one of those electrical contact devices will make it into the final design. As far as the screw goes, I'm banking on the silver crystal sliding up in front of the screw, but realistically some may get burnished on to the cylinder eventually. One fix for that is to remove the lift unit from the cell when the cell goes down for solution change-out and soak it in 50% nitric to clean up the stainless pipe and recover the silver. I can use a slow speed high torque motor which has a slip gear if the resistance is too high so it will stop spinning and not burn out the motor.
Thanks again for the input.
qst42know
Well-known member
How abrasive are silver crystals?
Would a PVC lift tube be sufficient?
Something like this.
http://www.brockmfg.com/uploads/pdf/BR_1946_0108BrockFlex_AugerEM.pdf
I don't know if the screw is available in stainless.
Would a PVC lift tube be sufficient?
Something like this.
http://www.brockmfg.com/uploads/pdf/BR_1946_0108BrockFlex_AugerEM.pdf
I don't know if the screw is available in stainless.
A picture is worth 10,000 words. To simplify imagine a disk brake with brake pads rubbing both sides.
A SS barrel cut in half top to bottom as the tank. 2 bearings mounted in the center with an axle running down the center above the top of the tank. On the axle 3 round disks about 1/2" thick and of a dia that will not touch the outside if the tank. Disks spaced in fron the tank ends and at the center of the shaft. Then 2 - 1/2 disks as annodes spaced half way between the cathodes with both the cathodes and annodes insulated from each other.
The Cathode disks rotate at 1 rpm with about 33% of the lower surface wetted in the tank and rotating clockwise. Annodes and fixed. They enter the fluid at about 3:30 and exit at about 8:30 on a clock face.
At about 3:00 a U shapped trough with 2 spring scrappers wipe both sides the disk and the crystals slide down into the trough. It is made from angle iron (X6) with the v facing up and the wipers on the top edge of the edge closest to the disk.
The ends near the axle are capped and have a fitting to plumb the wash tank fluid into the trough (X6). The flow carries the crystals over the top edge of the cell and into a manifold from all three cathodes which carries the crystals to a settling tank seperate from the cell. After the fluid settles the crystals in this tank, a small pump returns the wash fluid back the the scraper troughs. Repeat.
All of this mechanism would have to lift off the cell for cleaning and replacing annodes.
Does this help paint a picture in your mind of what I am trying to express?
Dickb
A SS barrel cut in half top to bottom as the tank. 2 bearings mounted in the center with an axle running down the center above the top of the tank. On the axle 3 round disks about 1/2" thick and of a dia that will not touch the outside if the tank. Disks spaced in fron the tank ends and at the center of the shaft. Then 2 - 1/2 disks as annodes spaced half way between the cathodes with both the cathodes and annodes insulated from each other.
The Cathode disks rotate at 1 rpm with about 33% of the lower surface wetted in the tank and rotating clockwise. Annodes and fixed. They enter the fluid at about 3:30 and exit at about 8:30 on a clock face.
At about 3:00 a U shapped trough with 2 spring scrappers wipe both sides the disk and the crystals slide down into the trough. It is made from angle iron (X6) with the v facing up and the wipers on the top edge of the edge closest to the disk.
The ends near the axle are capped and have a fitting to plumb the wash tank fluid into the trough (X6). The flow carries the crystals over the top edge of the cell and into a manifold from all three cathodes which carries the crystals to a settling tank seperate from the cell. After the fluid settles the crystals in this tank, a small pump returns the wash fluid back the the scraper troughs. Repeat.
All of this mechanism would have to lift off the cell for cleaning and replacing annodes.
Does this help paint a picture in your mind of what I am trying to express?
Dickb
Dick
That's not unlike the pictures posted early on in this thread. My concern is scraping from the top leaves the crystals that fall down from the cathode lying on the bottom. Of the 5 cells this guy has running it never fails that at any given time one of them is dropping crystal to the bottom between scrapings. Now with continuous scraping this may not be an issue and in some cells it is never an issue now, but it does happen often enough and if it continues to happen, crystals on the bottom will remain unharvested, or at least not harvested easily.
Quest
Those screw augers are very neat. The hollow center will allow excessive amounts of crystal to fall back through and may prevent the crushing I am concerned about. So screws like that could be PVC or polypropylene. Plus a plastic screw and funnel has an advantage over stainless in that if it does inadvertently touch a buss bar it won't be conductive.
That's not unlike the pictures posted early on in this thread. My concern is scraping from the top leaves the crystals that fall down from the cathode lying on the bottom. Of the 5 cells this guy has running it never fails that at any given time one of them is dropping crystal to the bottom between scrapings. Now with continuous scraping this may not be an issue and in some cells it is never an issue now, but it does happen often enough and if it continues to happen, crystals on the bottom will remain unharvested, or at least not harvested easily.
Quest
Those screw augers are very neat. The hollow center will allow excessive amounts of crystal to fall back through and may prevent the crushing I am concerned about. So screws like that could be PVC or polypropylene. Plus a plastic screw and funnel has an advantage over stainless in that if it does inadvertently touch a buss bar it won't be conductive.
qst42know
Well-known member
I used to work on a machining center that used a coiled auger. Even if you forgot to turn it on right away and it got completely buried it caught up very quickly.
To clarify, the top of the scrapers are resting against the disk in the horizontal position and as the disk turns, the crystals are lifted off the surface of the disk and slide down the outside surface of the scraper and into the v-trough. Just as a shovel is pushed along the sidewalk and the dirt goes into the bowl of the shovel. Most of the scrapings should end up in the trough and not in the cell tank. vIv The 2 v's are the troughs and the I is the cathode.
dickb
dickb
Just to update this thread, the Archemedes screw idea looked promising but the crystals chewed up the screw, it worked out that if the screw was tight to the wall of the cylinder evacuating the cell it pumped solution out which had to be returned to the cell. Increasing the clearance between the screw and the cylinder wall (by replacing the auger with one of a slightly smaller OD) allowed drainage but also allowed crystals to wedge under the screw and chew up the equipment. Plus the screws are expensive.
While this development process was going on I had a 4 foot long Thum cell running. The anode basket was about 18" long and was slid from one end to the other after 4 hours so the cell only had to be scraped once a day for an 8 hour shift. This got me thinking and what we ended up with is a cell that is 12 feet long. The anode basket travels over the cells length at the rate of 6 inches an hour. At the end of 24 hours the cathode, which covered the entire bottom of the cell looks like silver astro turf. Before the crystals grow long enough to be a problem the anode basket is further down the tank so the rapid growth area moves as well. Bottom line, full power production with one scraping every 24 hours.
First thing every morning the cell is scraped and the anode basket is restocked with bars and slid back to the starting point for another 24 hours of continuous production.
Not exactly self scraping but the main purpose was to allow continuous (24 hour) operation without 3 shifts of labor.
I still have some analytical work to do, I'm not sure the cell will produce the same purity silver as the copper levels grow because of the configuration there are some low current density areas which may behave erratically as copper concentration grows. After 1 week of continuous operation (and only 5 scrapings) the silver was still looking very nice with no detectable copper (via AA).
What I like is this is a simple approach to the problem and so far.....so good.
While this development process was going on I had a 4 foot long Thum cell running. The anode basket was about 18" long and was slid from one end to the other after 4 hours so the cell only had to be scraped once a day for an 8 hour shift. This got me thinking and what we ended up with is a cell that is 12 feet long. The anode basket travels over the cells length at the rate of 6 inches an hour. At the end of 24 hours the cathode, which covered the entire bottom of the cell looks like silver astro turf. Before the crystals grow long enough to be a problem the anode basket is further down the tank so the rapid growth area moves as well. Bottom line, full power production with one scraping every 24 hours.
First thing every morning the cell is scraped and the anode basket is restocked with bars and slid back to the starting point for another 24 hours of continuous production.
Not exactly self scraping but the main purpose was to allow continuous (24 hour) operation without 3 shifts of labor.
I still have some analytical work to do, I'm not sure the cell will produce the same purity silver as the copper levels grow because of the configuration there are some low current density areas which may behave erratically as copper concentration grows. After 1 week of continuous operation (and only 5 scrapings) the silver was still looking very nice with no detectable copper (via AA).
What I like is this is a simple approach to the problem and so far.....so good.
HAuCl4
Well-known member
In the spirit of simplicity: If you put a PVC tube with 2 valves at the bottom of your collecting funnel, you do not need any archimedes screw or other complex contraptions. Leave top valve open, silver fills the tube between valves (make this tube wide enough and long enough that the required volume of silver fits in easily during the time that there's nobody to attend the cells). Then when people arrive, close top valve, open bottom valve, silver falls out. Close bottom valve, open top valve, and replenish liquid. Very simple. I can draw a diagram later.
Use normal scrapers like those depicted in old books and a collecting funnel steep enough that the cystals slide into the PVC tube. A little extra volume of electrolite is the only downside to this. 8)
You can even have 1 person on call to come and collect the crystals if you put sensors and an alarm on the collecting tube. :shock:
If one times it all well and have the matching anode sizes, I guess one could get away with just 1 shift or less. Come once a day to cast anodes, replace them in the cells and pull, wash and melt the silver crystals. Maybe even have sensors and alarms for "emergencies" or automatic shutdowns to send you an instant message. As simple or as complicated as one wants really.
Never done it, but have seen the ideas above implemented in other or related industrial setups. Even live video surveillance over the internet can be cheaply implemented nowadays.
Use normal scrapers like those depicted in old books and a collecting funnel steep enough that the cystals slide into the PVC tube. A little extra volume of electrolite is the only downside to this. 8)
You can even have 1 person on call to come and collect the crystals if you put sensors and an alarm on the collecting tube. :shock:
If one times it all well and have the matching anode sizes, I guess one could get away with just 1 shift or less. Come once a day to cast anodes, replace them in the cells and pull, wash and melt the silver crystals. Maybe even have sensors and alarms for "emergencies" or automatic shutdowns to send you an instant message. As simple or as complicated as one wants really.
Never done it, but have seen the ideas above implemented in other or related industrial setups. Even live video surveillance over the internet can be cheaply implemented nowadays.
