dredge classifier mesh size minimum

[spaghettigold]

Hi all

I always see that the minimum wire mesh opening size for classification in dredges is 1/8 of a inch.I,ve read somewhere that the smaller sizes tend to blind in submerged dredge screens with no vibration.
Has enyone ever tried it with smaller sizes like 1mm(0,039 inch or 2mm 0,078inch) and if so is the performance of the mesh so bad to prevent you from further use.
Would be nice to direct the fine blacksand that cloggs up my fines section over very low profile ribbed rubber matting ,as a under -under section,sorta like in a clean-up sluice at the bottom.

Emilio

 

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[Hoser John]

Every component of a dredge mandates the other pieces fabrication. From the jet/header/flare/pj/sn/flared box/expanded jet flair/over-under classification/triple sluice/size of dredge and on and on. I much prefer punch plate as much more control on what goes down to my undercurrent and less water requirements plus much better recovery for me. Your tiny mesh I would never waste time/money on as not economically viable-ifn' it don't pay I don't play- John

 

[winners58]

Double-screen Classification System in Dredging-Dave Mack
.

 

[spaghettigold]

Every component of a dredge mandates the other pieces fabrication. From the jet/header/flare/pj/sn/flared box/expanded jet flair/over-under classification/triple sluice/size of dredge and on and on. I much prefer punch plate as much more control on what goes down to my undercurrent and less water requirements plus much better recovery for me. Your tiny mesh I would never waste time/money on as not economically viable-ifn' it don't pay I don't play- John

everything has its advantages and disadvantages.Like you say john ,i like the punch plate because it requires less water because the rocks slide well over it,while the mesh makes points with more open screen surface and more scrubbing action maybe.
In this case the the viability i,m seeking is less clean ups which are very time consuming.Most of the gold i find is in the 2mm to 4mm range (0.078 to 0.15 inches) The thought is to direct the smaller minus2mm heavies to another under section so that the normal fines section(where most of my values are) does not clogg up with the fine magnetite sand that is abundant here.

 

[spaghettigold]

Double-screen Classification System in Dredging-Dave Mack
.

yep winner ,i,ve watched that many times.But he also uses 1/8 inch screen. Here is his 5 genereration (i believe) Changed quite a bit .Open riffels first and after that everything above 1/8 goes to tailings which i find a bit risky in my set up because it happends that i find flat flakes bigger than 1/8 that jumped the riffels at flare outlet and stopped in my expanded section.Maybe because my riffels are installed 1 inch deeper than the flare outlet and some flat peaces don,t make it down quick enough to the riffles .His riffels are set at outlet height.I,m changing some things now.
Ever some body used smaller mesh or punch plate?

 

[njcommercialdiver]

sounds like your fine section needs more flow if its clogging up.

you can put a magnet bar across the top of box inlet to catch a lot of the magnetics to keep them out of the fines section. Ive seen guys run a 3/4" diameter piece of pvc pipe the width of the sluice filled with round magnets . one guy used suction cups to hold it to the sides, another one notched the top edge of his box and screwed bolts into the end caps of pipe and just let it sit in the notches, when it starts to get full of mags, he just lifts it out, gives it a few taps on side of pontoon and the mags shake off

 

[spaghettigold]

sounds like your fine section needs more flow if its clogging up.

you can put a magnet bar across the top of box inlet to catch a lot of the magnetics to keep them out of the fines section. Ive seen guys run a 3/4" diameter piece of pvc pipe the width of the sluice filled with round magnets . one guy used suction cups to hold it to the sides, another one notched the top edge of his box and screwed bolts into the end caps of pipe and just let it sit in the notches, when it starts to get full of mags, he just lifts it out, gives it a few taps on side of pontoon and the mags shake off

yes,the flow is one of the problems ,especially when i,m working in sites with not much drop.Don,t know ifyou know ,i,m running a gravity dredge.

I now want to raise the mesh a little and remove the riffels that i installed in the fines section to push down the expanded ,to improove the flow there.This will take away water above the mesh,so i,m risking to have the oversize rocks sitting in the sluice.Thats why i added two new inlets to the flare. View attachment 1304905 . We,ll see if it works like in my imagination.

As for the magnets it,s beeing a while ago i,m dreaming of a trommel that has no holes in the first maybe 10 inches,but magnets on the outside all around,inside ,where the spray bar would normally be,a scraping plate with a little sluice underneeth with no mattings .The magnetics fall of the scraper ,inside the canal that goes all the way thru the trommel ( where the spray bar would be)and is discharged in to separat containers for further processing,since i,ve seen gold stuck between blacksand whyle playing with a magnet when i was panning. Your solution would be less complicated ...Maybe i like it complicated?..and automatic!
If i get to do all the other mods i have to do first,if there,s some time and cash left ,atleast your suggestion is the only realistic for this season.

 

[winners58]

what I see is the water flow is more like a highbanker where the water is falling rather than being pushed like a dredge.
maybe a boil box / fluid bed area at the top to slow the heavy's and let the lightest of the light keep going out the box.
if you had more flow you could rig up a sump to take all the fines and run them through a separate box.

 

[spaghettigold]

what I see is the water flow is more like a highbanker where the water is falling rather than being pushed like a dredge.
maybe a boil box / fluid bed area at the top to slow the heavy's and let the lightest of the light keep going out the box.
if you had more flow you could rig up a sump to take all the fines and run them through a separate box.

The flow varies with every site and i don,t know yet where exactly i,m going to dredge .We thought about the sump style last year,to get rid of oversize,but that would require additional drop and more work from the tender to get rid of the tails.Did you ever heard of enybody using smaller screens winner?

 

[winners58]

I like the one you posted using the miners moss as a screen, don't like the large riffles though.
saw one one on a proline once that the classifier jiggled from the water flowing over it.
looked for a photo couldn't find one, maybe someone that has one could post a photo
I'm tiring to rethink my box too, I have a lot of black sands, more than a couple hours it clog's up.

 

[spaghettigold]

I like the one you posted using the miners moss as a screen, don't like the large riffles though.
saw one one on a proline once that the classifier jiggled from the water flowing over it.
looked for a photo couldn't find one, maybe someone that has one could post a photo
I'm tiring to rethink my box too, I have a lot of black sands, more than a couple hours it clog's up.

yes,nice idea with the moss as classifier over the 1/8 screen,sort of fluid bed too. He,s put the 1/8 screen before the big riffels section so the material is stratified when flowing over the first finesscreen,then the big riffels for the casual nuggets .I,ve read about the proline "wave "classifier,but never saw a pic either.
I,m wondering why no manufacturer of dredges has come up with a sort of automatic demagnetizing device ,doesnt have to be complicated,like a magnetic conveyor belt with scraper ,turning around the flare outlet for example.Maybe because this is only a problem in few spots with heavie magnetics and fine gold together.
Why you don,t like the big riffels?