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911Metallurgy
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Gravity Concentration Shaking Table ( 14:31:03 FriJun 24 2016 )

Hello everyone,

I found a very interesting piece on Shaker Tables. Here is a summary of what it's about. The full PDF is in the footer of https://www.911metallurgist.com/blog/gold-shaking-tables

One of the functions of minerals processing, is concentration. Concentration may be simply defined as the upgrading of a mineral. That is, to increase the fraction of the valuable material versus the discard material. This may be achieved with a host of different processes. What these methods have in common is that they take into consideration the physical properties of the material(s) of interest. Of course, unlike processes in pyro-metallurgy and hydro-metallurgy, which take into account the chemical properties of ore material. In this investigation, the primary physical property considered relates closely with gravity; density. Second to that, is the texture (and size) of the material - which also affects the efficiency of the separation mechanism, specifically, on a shaking table.
The experiment investigates the separation of materials of different densities 011 a shaking table. The variables that affect the efficiency of separation are the material feed rate, water flow rate, slope of the deck and the frequency of the vibration of the table. However, in this investigation, the feed rate is kept constant at 22.17 g/minute, the water flow rate at 0.21 litres/second and the slope of the deck at 19. For simplicity, the frequency is the only variable of the experiment.

When the frequency was set at 30 HZ, the grade of the concentrate was not as good as it was expected. Since the recovery was a low 58%, it was expected for the grade to be high since the grade-recovery relationship is typically inversely proportional. Also, considering that the separation process lasted for more than 2 hours, it was expected that ample time was allowed for excellent separation. However, this was not the case. Surprisingly, the experiment at higher frequency (40 Hz) resulted in a higher grade concentrate i.e 30% versus 28%. This is surprising also because the separation profile was more uniform at the lower frequency compared to when the rate of oscillations was higher.

On a large scale, the 40 Hz process should be more preferable. The separation process consumes less water, energy, and takes a relatively shorter amount of time. It would therefore be more economical.
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I hope you like.



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Mineral Processing
 
 
Fleng
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Re: Gravity Concentration Shaking Table ( 17:09:54 MonJun 27 2016 )

Your article talks about the "speed" of the table being 180-270 strokes per minute. This corresponds to about 3-5 hz not 30-40 hz. That- as Jerry Lee Lewis would say is a whole lotta shakin' going on.

Did you lose a digit somewhere?

  
911Metallurgy
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Re: Gravity Concentration Shaking Table ( 22:42:02 MonJun 27 2016 )

Hi Fleng, the article is there and refers to 30-40 Hz several times..



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Fleng
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Re: Gravity Concentration Shaking Table ( 18:28:51 TueJun 28 2016 )

From page 2 of the second article I see that the table calls for "...a slow forward stroke and rapid return". Technically this is two different frequencies. The reason I asked is because in your web page the table calls for "15-20mm stroke lengths at around 280 rpm".

Again from the Operation of Shaking Tables, "The speed of the table usually ranges from 180 to 270 rpm and the strokes are from 1/2" to 1 1/2" long.

These reference 3-4.5 hz operation. Looking at the video it is apparent that this is indeed the actual operating frequency. 30-40 hz would not be easy to see.

It could be that the 2nd paper was looking at the "rapid return" stroke. The slow forward stroke was 3-4.5 hz and the rapid return was 30-40 hz. From page 12 of the first article (scanned page 19), the eccentric cam is rotating at 300 strokes per minute (5hz) with a strong rubber band producing an "end-knock" effect. Actually this is acting as a frequency "damper" slowing the effective frequency but the key work here is eccentric. This suggests that forward stroke and return stroke are indeed intended to differ.

What is important to note is that the shaker table is undergoing a complex motion with at least two different components (forward and return) and some kind of damping determined by the elastic properties of the rubber band (or old car inner tube as it were). We can't boil this down to 30-40 hz or maybe 37. It just isn't that simple.

I do want to thank you for your work on the subject because I wanted to try my hand at building a shaker table and there are some finer points that are not obvious.

  
911Metallurgy
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Re: Gravity Concentration Shaking Table ( 15:38:56 WedJun 29 2016 )

You are welcome. Let us know how you make out.



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911Metallurgy
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Re: Gravity Concentration Shaking Table ( 14:44:36 TueJul 5 2016 )

here is a rarity in the World of shaker table https://www.911metallurgist.com/blog/diagonal-plane-shaking-table-design

[2 edits; Last edit by 911Metallurgy at 14:46:34 Tue Jul 5 2016]



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geowizard
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Re: Gravity Concentration Shaking Table ( 03:38:10 ThuJul 7 2016 )

David,

A frequency of 3 to 4 Hz (cycles per second) is realistic.

I'm having a problem with the reference to 30 to 40 cycles per second. That's a very high frequency to shake a large mass. A gasoline engine idles at 500 to 700 RPM. A frequency of 30 Hz is equal to 1800 RPM.

- Geowizard

  
geowizard
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Re: Gravity Concentration Shaking Table ( 04:23:42 SunJul 17 2016 )


The table I have here at Ophir is a mid range table made by GMS.

It uses a 1.5 HP electric motor that runs at 1725 RPM. The belt drive reduction is 4.57 giving a shake speed of 6.3 cycles per second.

Physics tells us; Force = Mass x Acceleration.

So, the table should have variable seed control to accommodate different sizes (mass) of gold. Higher number of cycles for a given stroke means more acceleration.

- Geowizard

  
geowizard
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Re: Gravity Concentration Shaking Table ( 22:01:23 FriSep 1 2017 )

This thread may have some current relevance;

What is the "rate" of the "stroke"?

What is the "length" of the "stroke"?

What is the spacing of the ridges on the table?

What is HAPPENING to those particles? :smile:

- Geowizard

  
micropedes1
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Re: Gravity Concentration Shaking Table ( 01:58:07 MonSep 4 2017 )

I ran a home made Wilfley bump table before I got my Gemini table. It performed its very best at 136 bumps per MINUTE. Nothing more than a spring and an off center cam. No adjustment. But it worked!

  
geowizard
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Re: Gravity Concentration Shaking Table ( 16:21:58 SunSep 10 2017 )

Glen,

What was the stroke?

Spacing of riffles?

- Geowizard

  

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