Crushing, Screening & Conveying

Crushing, Screening & Conveying 2017-04-04T06:57:13+00:00
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How to Evaluate/Estimate a Crusher Product Size (9 replies)

Bob Mathias
2 years ago
Bob Mathias 2 years ago

When a gyratory crusher's mantle is replaced, how does the operator know that the correct product size is being achieved at start-up? How does one Evaluate or Estimate to best control a Crusher Product Size ?

Tony Verdeschi
2 years ago
Tony Verdeschi 2 years ago

Hi Bob,
Image analysis technologies, such as WipWare's conveyor belt systems, are capable of analyzing material post-crusher on a continuous basis. Operators can use this sizing data not only to ensure the correct particle size is being achieved at start-up, but to detect liner wearing in real-time.
In early 2000 I have operated Nordberg cone crusher where there is ASR system. Automatic set regulating system. Uniform product size and uniform wear on mantle. Long life. What type of system is there today in Gyratory crusher?

Victor Bergman
2 years ago
Victor Bergman 2 years ago

Prior to start up you can size the crusher using balls of the correct size for the desired opening. ( i have seen balls made from sheets of rubber stacked with a bolt through it, toy balls of the right size, a ball of tin foil etc.) You are measuring the closed side setting. (CSS) note that if the concave liners were not replaced at the same time as the mantel you may need to run the crusher as you drop the tin foil ball down on a rope through the lowest nip point. If you do this with the crusher running you need to do it at start up before the mantel starts to spin. If you do not have image analysis on the belt you will need to do a belt cut sample on the stopped belt, removing 2 - 5 meters of material for size analysis and then adjusting the MPS to give the desired crush size.

Helena Russell
2 years ago
Helena Russell 2 years ago

Tin foil balls is a simple and cheap way to check gap. Lower down on rope and measure, do in a couple of spots to check.
In addition, one can take crushed sample and have a screen analysis done at css and upper and lower sizes as one ball test may not give accurate resultas. More number of balls at close interval need to be sent and different sizes including the average may be taken to see tha product characteristics.

Most accurate is to lead the crusher, when molding your lead an eye must be placed in the mold to anchor your wire, w shaped welding rod will suffice,fasten electrical wire etc to your lead, start the crusher, lower the lead into it and move it around one full rotation, then measure the width of the lead, this insures you get the closed side gap.

Tin balls are cheep and easy to drop and measure after crushed. More practical. Any number of times it may be used and measured. Simple and availability of Tin is more at less cost. After measurement reuse it immediately. Lead need to be melted, molded, etc.

Alan Carter
2 years ago
Alan Carter 2 years ago

If there is a surge hopper below the gyratory crusher as in most cases, actul product sizes at the discharge of hopper will be different than the crusher discharge because of degradation of lumps. Practical data will be to take a sample at dischrge of hopper in conveyor . This depends also on feed characteristics whether hard, medium or soft ore. The determination of size by bll method is more theoretical and do not really serve on practical point of view.

CSS is not relevant for gyratory crusher operation, but OSS.
On the contrary to cone crushers, gyratory crushers have a small cone angle, which locates the contact zone between particles and crushing elements at an upper area of the chamber, not at the bottom. This implies that the limited number of comminution events (1 single rock probably will get at most 2 strokes before exiting the gyratory) in a gyratory crusher is happening away from the area where CSS is measured. After the particle is fractured, the limiting factor now becomes the area available for the crushed particles to exit the chamber. And this is defined by the OSS, not the CSS. Therefore the role of the CSS is neglectable.

Tony Verdeschi
2 years ago
Tony Verdeschi 2 years ago

to clarify for the original question, "how does the operator know that the correct product size is being achieved at start-up?"

The ore that is crushed can be checked using a belt sample(s).

If the particle size distribution on the belt is not what is needed the main shaft can be adjusted to open or close the gap.

once the OSS needed to produce the proper mill feed is known it can be set each time a mantel is changed

This should give the proper particle size at start up, and checked as the mantel and concave liners wear.

in a mine a gyratory crusher is usually below a feed pocket, and the distance to the lowest nip point is far beyond an operators reach, the operator can get the OSS in two ways,

* OSS - with the crusher down use a ball to drop through the widest open point. you can test for go / no go by using smaller to larger balls. Note that it may be a challenge to get the ball(s) down the pocket, over the material and through the widest part of the opening, which may be poorly accessibility (on the far side, under a spider arm etc).

* OSS use the desired size ball for the needed gap, lower it into the crusher as above and lower the main shaft until the ball passes at the widest gap.

2) CSS - as noted above, use a Ball or "Slug" made of tin foil to drop through the lowest nip point with the crusher running. by rope. similar to gaping a cone crusher the tin foil slug will be caught in the nip point and crushed. To determine the OSS just measure the slug and add the total throw of the eccentric.

Bill Fraser
2 years ago
Bill Fraser 2 years ago

easiest way is online video survey system on site to measure the crushed production, we always have some deviation during practical operation, so we need build a database to calibrate the data from online survey system; most accurate way is take some sample from discharge conveyor or transport conveyor and do screen test, how and where take sample and screen wen get much reference form many version of mineral processing handbook; most theoretical way is get a datasheet from gyratory crusher vendor about the relation ship between production size distribution and definite CSS and OSS, or you can build such database by your site operation team through ex-operations experience. Then use a tin foil ball method to get the CSS and OSS data.

Paul Morrow
2 years ago
Paul Morrow 2 years ago

If a book was ever written on the topic of comminution- that would be a big subject: from the pit to the grinding circuit. Comminution starts at the pit and progresses from there.
Things to include- how to recognize when a cone crusher is tramping, where to measure CSS and OSS on crushers (a few schools of thought on that one), where to measure the gap on cone crushers, how to recognize that your cone/jaw is wearing, how to unbog a crusher, explain the diference between single and double toggled crushers, what causes a conveyor to track, how to re-track a conveyor, best ways to clear blocked chutes, the pros and cons of adding water to a chute, dust suppression, classification-the difference between poly/rubber and steel screens and the best classifiers, how to detirmine the throw of a screen, the best way to run hydro cyclones, how to run hydrocylones, the best way to run a grinding circuit, the relationship between cyclone pressure, density, feed rate and mill speed, how a centrifcal pump works, how a positive displacement pump works,types of pumps, types of valves, how to trouble shoot pumps.I could go on, I guess it depends on if you are doing a filed operators handbook of mineral processing or one for Metallurgist.

Helena Russell
2 years ago
Helena Russell 2 years ago

If it's an older crusher then the old system is effective, as for safety,I've never seen or heard of any incidents using this method, it's quick, simple, accurate. I think most should concentrate on the areas where accidents and incidents occur if serious about safety, lets start with light vehicles as with any area in this Industry common sense and logic are necessary.

1 year ago
David 1 year ago

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