Re: Double-Roll Crushers: Variables For Preventing Fines
Originally posted by imascominerals
We are using a double roll crusher to break Cornerstone TH-90 perlite ore down in order to obtain a 50-70 US mesh cut (roughly 200-350 microns) of the material.
Unfortunately, our feedstock material only contains roughly 10% of this target particle size so it is necessary to use our double-roll crusher to crush our larger size particles to this specific size.
The material being fed into the crusher is oversized material retained on a 36T (541 micron tensile-bolting cloth) screen with particles in the range of about 300-500 microns.
Our crusher is currently set to about a 500 micron gap, as 400 and 600 micron gaps produce too much fines and not enough larger particle size crushing respectively. Varying the roll speeds has shown that slower speeds facilite more residence time in the crusher such that there are too many fines being produced, while at higher speeds there are fewer fines produced.
We want to obtain more crushed material at around the 230-330 micron range but varying the above seems to change the distribution of only larger particles and fines, but not within this range.
Does anybody have any suggestions or know where I may be able to find more information about this? Thanks.
A wobbler feeder before your crusher is your best for this to scalp the undersize material-there are a lot of manufacturers world wide. ■
Re: Double-Roll Crushers: Variables For Preventing Fines
Thanks, I am looking into this but we actually have already screened the undersized material from the raw feedstock before feeding it into the crusher.
An analysis of the particle distribution of this screened feedstock indicates that there are little to no fines, and the problem we are having is that too many fines are produced after crushing as opposed to the presence of too many fines before crushing. ■
Crushing Perlite
Perlite has a glasslike structure and shatters like a glass when crushed. It does not have a crystaline structure, that can fracture along crystal boundaries and give a cubical product.
You desire a product which is a course powder in a narrow size range (probably expanded to a course grade product).
A double roll crusher of any type will give a crushed product which can be plotted on a curve ( screen opening vs % passing). This curve will always have a tail (fines).
You can reduce the tail by close-circuiting the operation and setting crusher gap opening higher. I presume you are already doing so. ■
Roll Crusher Etc.
Vinayak is right in what he is saying,
maybe you should think in terms of an impactor such as a small spokane crusher/vertical or a Bradford breaker/horizntal due to the crystaline structure; they work very well for rock salt due to its crytal structure.
lzaharis ■
Re: Double-Roll Crushers: Variables For Preventing Fines
Thank you for the useful information.
I did not think about the glasslike structure and particle shattering but it makes more sense now. It is absolutely true also that we are observing "tails" at the end of our particle distribution plots.
We would like to try widening our roll gaps to at least twice the diameter of our largest particles and bulk feeding the roll crusher to see whether we can obtain some favorable results. Also, we are working on adjusting our shieve sizes to achieve a 2-to-1 gear ratio such that our two rolls are rotating at different speeds, since we only have one VFD. What are your opinions on this? ■
Re: Double-Roll Crushers: Variables For Preventing Fines
I read others post notices that the fines breakage generation is better with an impactor that creates a fast breakage rate.
This is counter to laboratory experiments and intuition. Breakage is highly dependent on the sonic or shock wave transmission rate through the rock medium.
Applying a slow breakage rate produces a higher breakage energy efficiency and lower fines due to the control of the shock wave in the rock.
The total surface area liberated is one measure of energy consumed. A large body of experiments demonstrate the events. How do you create dust and noise?
High impact produces a lot of secondary breakage from the reflective shock wave within the rock and reverbs of the impact hammer, crusher anvil, et al. This is well documented in many comminution publications and research activity.
Noise, dust and related events do not break rock but consume energy. Also, the crack propogation through the rock will take differing paths depending on the rate. Slower is better at creating homogeneous breakage patterns. A faster rate of breakage concentrates the areas of breakage and increases the fines and dust.
Thus, I argue a roll crusher will produce less fines than an impact crusher. However, it is also true that the degree of reduction must be controlled to minimize breakage in the fines region. The steps of reduction should be properly evaluated in the laboratory.
Self breakage (gravity drop - depending on rock size), drop hammer, and 3-point slow hydraulic breakage should be able to prove the point and so direct the best procedure. ■
Send A Test Sample
I agree with Nordell, in that......a 45 gallon drum or two of feed material......to an outfit like METSO....to their test lab and you will have the actual test results from a lab unit in the proper type of crusher whether it be by COMPRESSION or by IMPACT or ROCK on ROCK will easily be determined.
Almost sounds like a ROR impact style crusher might be the answer here....we are impacting the rock from the closed ROTOR to a ROCK SHELF......to basically SHAPE the product vs IMPACT like we would with a ROCK ON ROCK style......which in fact yields much less FINES or bottom end of your product sieve analysis.
Cubicity vs elongated is also a favourable product result. ■
Double-Roll Crushers: Variables for Preventing Fines
We are using a double roll crusher to break Cornerstone TH-90 perlite ore down in order to obtain a 50-70 US mesh cut (roughly 200-350 microns) of the material.
Unfortunately, our feedstock material only contains roughly 10% of this target particle size so it is necessary to use our double-roll crusher to crush our larger size particles to this specific size.
The material being fed into the crusher is oversized material retained on a 36T (541 micron tensile-bolting cloth) screen with particles in the range of about 300-500 microns.
Our crusher is currently set to about a 500 micron gap, as 400 and 600 micron gaps produce too much fines and not enough larger particle size crushing respectively. Varying the roll speeds has shown that slower speeds facilite more residence time in the crusher such that there are too many fines being produced, while at higher speeds there are fewer fines produced.
We want to obtain more crushed material at around the 230-330 micron range but varying the above seems to change the distribution of only larger particles and fines, but not within this range.
Does anybody have any suggestions or know where I may be able to find more information about this? Thanks. ■