Apr 2 2012
It's not actually for use on a dredge,.........it's going to be bank mounted, but I'm going to be suctioning up material off of bedrock. It's going to be steel(so I can weld it)and it's going to be heavy(same reason). Thinking right now of building it primrily from 1/8" sheet steel. Weight isn't much of a factor. I'll be moving it around with the excavator or the boomtruck. Either way; 500# or so won't be a problem. I'm thinking(at least at this point)of building it as one complete unit with about 7' of jet tube feeding into a crashbox, feeding into about 8' of sluice. Just working out dimensions in my head right now.
I want the crashbox because it's simpler to build and more foolproof. Also shorter overall and more forgiving on the HP requirements. The churning action of the box also outweighs the smoother feed of the flared designs in this case(I'm expecting mostly cemented gravels).
I envision the whole rig sitting on a gravel dike between the dredge pond and what I'll call the 'tailings' pond. One point to be considered is that due to the suction intake, no rock over about 2" will be allowed up the hose, but a fair amount of the material dredged will probably be sharply angular. I'm also going to run it with tremendous suction, so there's going to be more water running through the sluice than on a typical 6" dredge. It's all mechanized; no diver. Bedrock will be broken up and processed. All this has got me guessing on the sluicebox dimensions. I'm finding examples of factory 6" dredges with sluiceboxes from 20" to 26" wide. With all the extra water and no large rocks to move, I'm considering widening out the box to somewhere around 30". Pretty sure I'm going to flare the sluice and run primarily expanded metal riffles, maybe with some angle iron at the head. Maybe 24" wide at the crashbox and widening out to 30" at the discharge just to be safe. If it wasn't for all the angular rock I'm expecting to tear up I wouldn't be so worried about going too wide.
Apr 2 2012
Sounds good. Go wider, you can always put in 2x4 or 2x6 on the inside side walls to effectively narrow it, if you need to later.
30" should be fine, this is a single box right? Those 24" ones are "triples" with two stages stacked on the second half.
I'd shy away from the angle iron, it causes lots of turbidity, negating some of the settling that happens in the flare. Try larger raised expanded metal for the first 6" to 12" if you are looking for trapping larger gold.
Apr 3 2012
I just hope my fabrication plan works out, or else I'll be welding bead forever. I bought two sheets, 47" x 84" x 3/16. The first will become the flared sluicebox. I'm going to lay it face-down and score two lines with the Makita/cutting blade,........30" wide at the upper and 36" wide at the lower end,.........and attempt to break along the scored lines by hand. That should create a flared sluice with sides 8.5" high at the upper and 5.5" high at the lower end. I'm thinking(hoping)that a 1/16" deep scored line will allow the fold and still leave plenty of strength at the break. I'll probably reinforce with some scrap angle tacked in.
The second sheet for the crashbox gets a little bit more complicated. I'll cut 30" off of one end, leaving the sheet at 47" x 54". I'll rip that one in two and have two sheets 23.5" x 54". Both of those will be scored to break 90 degrees at the 24"/30" point. By flipping them around, I can create the 30" wide floor and one 24" side with one; the 30" back and the opposite 24" side with the other. That's gonna require 78" of weld bead to create the outer portion of the 'box'. The leftover 30" piece will get scored and wrapped to become the inner crashbox itself. All outer corners will get wrapped with angle iron reinforcement.
I have something I may try with the expanded riffles. Since they're flared same as the sluice, I'm considering tipping the sluice sidewalls in 30 degrees from vertical, something like this,........
/_______________\ looking up from the discharge end.
/-----------------------\ with the expanded in.
The expanded will drop right down into the sluice above the carpet, but with the flare of the sluice, driving the expanded upstream will force it tight along the sides and tight to the bottom due to the tipped in sidewalls,.............in theory. There may be a tendancy to pucker up the center of the expanded tho. Should easily pop loose with a smack in the downstream direction. Not sure whether to try to lever it tightly into place from th bottom or maybe pull it forward with a boat winch from the top. I'll try to get some pics during assembly that will make it all easier to explain.
And it's getting heavy already. About 650# yesterday with the sheet and expanded and that's not including any part of the jet. Probably gonna be 800# before it's done.
Apr 3 2012
It doesn't have to be gold bearing, just small gravel and sand from a gravel pit. I think you will find that the increased friction loss will result in moderate to severe loading-up along the sides.
I am a fan of tapered sluices, but the design isn't a cure-all and presents some problems of its own.
What a tapered sluice does do is:
Twists the lateral currents caused by friction against the side walls towards downstream rather than across the sluice.
It lowers the water level a bit and promotes laminar currents in the lower portion of the sluice. This enhances the sluice's ability to recover small/flour gold.
But this same taper can create some problems too:
The slope MUST be increased to clear light fines from the lower portion of the sluice. The increased current is counter-productive to recovery of small gold.
Because of the water level drops as it goes down the sluice, there is an increase in loading up of larger material in the lower portion of the sluice. The water depth must be higher than the material you want flushed from the sluice. Again this is counter-productive in increasing the laminar flow in the lower portion of the sluice.
How do I know? Been there, done that. I have mixed feelings about tapered sluices for general purposes. Where they shine is when you classify tight and practice good water depth discipline. If you attempt to put a tapered sluice on a float system, you must grossly over-size the flotation platform. This is due to the slurry shifting the weight and balance of the sluice and altering the slope.
I still have and use tapered sluices, but NOT on a floating platform. I also classify to 1/4". Actually the screening is 1/4", but there is very little that gets through the screen larger than 3/16" and most is 1/8" and smaller. See Taggart, "Handbook of Mineral Dressing" also quoted in Wills, "Mineral Processing Technology".
Apr 3 2012
Apr 4 2012
Apr 4 2012
Apr 4 2012
Heading down Sacto way tomorrow to pick up my pop. We'll discuss the options on the way back and try to decide whether we really want to waste another week cutting and welding. You can probably expect to hear from us later in the week.
Apr 23 2012
Level manufacturers make levels that have like four level bubbles in them, used by electricians and ironworkers for the most common angles they use when bending conduit and rebar. They can be custom ordered, or bought at regular stores, and prices are very reasonable.
If you want to have a x degree riffle, and an x degree angle to your sluice, just order it, and it will be set in epoxy on a 6" level, and you can strap that on to whatever you're working with at the time. Down and dirty.