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21904 (5/00) - 1 - © 2000 Cedarapids, Inc.

VSI Primer

A Terex Company

I - IntroductionThe intent of this primer is to help you betterunderstand VSIs, and the applications they fit inbest. VSIs work well in many applications, oftenoutproducing HSIs, cones, and rolls. The "how" and"why" is in this primer. Knowing the desired productsize, the intended feed size, the rock type with it'sabrasiveness and friability, any constraints of theapplication, like available power, will help you workthrough this primer to successful applications. It isintended as a resource to refer back to.

II - Good ApplicationsVSIs offer the user many advantages over othermethods of crushing, if the model size, crushingchamber and impeller speed are correctly selected.VSIs find suitable applications as secondary, tertiary,quaternary, or recrush machines in a satellite circuit.A brief look at their merits:

• High tonnage

• Low capital investment

• Very portable

• Excellent versatility: The ability to make concreterock or man. sand.

• 'Cubical' particle shape.

• Accepts feed sizes other finishing machinescan't.

More specific to production requirements, VSIsexcel at making certain product sizes. The mostcommon applications are:

• Making chips.

• Chips with manufactured sand.

• Manufactured sand.

• Concrete rock.

• Soft stone elimination (beneficiation).

• Putting a high fracture count on round gravel.

• Shaping.

Chart # 1 shows a rough comparison of how the VSIstacks up in each of these applications. But if thiswere the whole story, everyone would probablyoperate VSIs. Chart # 2 begins to qualify the merit

of the VSI for these different applications by lookingat two more factors: Maximum feed size, andabrasiveness of the material to be crushed. Withfeed sizes much larger than 6" we do not usuallyrecommend the VSI.

In section X we will look deeper at the "how" and"why" of these applications and others:

• Why a VSI has no equal when crushing peagravel to manufactured sand.

• How the crushing chamber design maximizesfractured faces.

• How a producer increased sand production 50%by a chamber configuration change in the samemodel size VSI.

• How the VSI can be adapted to produce a higherpercentage of rock, and less man-sand than acone crusher.

III - Gear Drive vs. Belt DriveVersatility: While there are a number of variablesin configuring the VSI that the user has control over,none offer greater flexibility than impeller speedvariation. Cedarapids' gear drive design offers theultimate in speed change flexibility, it can be teamedwith a diesel engine for instantaneous speed changes,or with electric motors where sheave changes areeasy because they're out in the open and liftingequipment can be used.

Motor commonality: Motors of the 200 to 300 hprange are common in today's crushing plants. Butmotors that mount vertically are not so common.For those producers who wish to use existing motors,the gear drive configuration offers a substantialsavings by not requiring that vertical mount motorsbe purchased.

IV - Balancing a CircuitNormally VSIs are utilized as "finishing" machines,that is, the last crusher to process the rock before itgoes to the sizing and classifying equipment, and tothe stockpile. Closed circuit operation is commonbecause of the final sizing screen, and because VSIsdo not usually control a top size to 100% passing.

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21904 (5/00) - 2 - © 2000 Cedarapids, Inc.

VSI Primer

A Terex Company

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Chart 2 - VSI compared to other crushers by feed size and abrasion

Chart 1 - VSI compared to other crushers by product

Good

Fair

Poor

6" Maximum Feed

0

1

2

3

4

5

VSI Cone Roll HSI Mill

Abra

3" Maximum Feed

0

1

2

3

4

5

VSI Cone Roll HSI Mill

Abra

1-1/2" Maximum Feed

0

1

2

3

4

5

VSI Cone Roll HSI Mill

Abra

3/8" Maximum Feed

0

1

2

3

4

5

VSI Cone Roll HSI Mill

Abra

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VSI Primer

A Terex Company

Since the crushers are notoriously high tonnagecapacity, the need for screening often increases. Forexample a 54II as a finishing crusher often demandsa 6x20 screen to handle the load when making chips.A 2100 VSI, in the same application could requiretwo 6x20 screens. Why? When the user screens atsmaller sizes, the cone crusher is usually set to atighter CSS setting. While the screen has lesscapacity per square foot, the cone crusher also has areduced gross throughput capacity. The grossthroughput capacity of the VSI remains moreconstant. So the demand for screen area goes up asthe screen cloth opening size goes down.

Balancing an entire circuit requires analysis of theprimary and secondary crushers to assure a goodmatch of capacity and the ability of each to preparean acceptable feed size for the next machine.

V - Selecting A Model SizeMatching the correct VSI to the application requiresanalyzing the expected feed size, the expected grossthroughput tonnage, and the desired product size.

• Feed Size: Each model and crushing chamberhas a maximum feed size limit. See chart # 3 forthe range of MAXIMUM feed sizes that eachmodel size can accept with each crushing chamberconfiguration. A feed size range of 3" to 1⁄2"would be considered a 3" maximum feed in thischart.

• Tonnage: Each model size has a maximumtonnage capability which can be affected byvariations in feed size or crushing chamberconfiguration. The nominal maximum tonnagefor each from the spec. sheet can be used as astarting guide, then use charts # 4 or 5 as anadjuster to calculate a more accurate maximumtonnage capability. For example, a tonnagerequirement of 240 tph, plus recirculated load,having a maximum particle size of 2-1⁄

4" will

exceed the capability of the model 1800 VSI fortonnage, but not for feed size. Even so, youshould move up to the 2100 in this example.

• Product Desired: Some models are betteradapted at making certain product sizes. Forexample the model 2600 VSI is well applied

making concrete rock, but since it does notaccept a rotor with anvil ring, it is not as good atmaking manufactured sand as the other twomodels. See chart # 6, and section VI.

VI - Selecting A Crushing ChamberOnce a model size is selected, the correct crushingchamber needs to be determined for either the 2100or 1800 VSI. The open shoe table is the only optionavailable in the 2600. Factors to consider are feedsize, tonnage, desired product size, and abrasivenessof the material to be crushed.

• Feed Size: Chart # 3 shows the feed sizecapability of each crushing chamber, and isfurther broken down into the models that areavailable with each crushing chamber. Forexample under the heading of open shoe tablethe Model 2100 can accept 3" feed size, but the1800 takes 2-1⁄4". Should a rotor be selected, asmaller feed size, like 1-1⁄2" is more suitable. Thefeed sizes are determined for each configurationbased on the capability of the metallurgy, and themaximum impeller speed (see section IX for afurther description of why the metallurgy affectsthe feed size). The impeller speed is critical tothe feed size limits because as the impeller speedincreases, and as the feed size increases theimpact force the rock applies to the parts of theimpeller increases.

• Tonnage: When you consulted chart # 4 or 5 ontonnage capability of each model size, younoticed that the impeller tables have differentcapacities than the rotors. If more than onecrushing chamber is shown to be suitable for theapplication in question, then a very high or verylow tonnage requirement might affect thecrushing chamber choice.

• Product Desired: Desired product has a stronginfluence on the crushing chamber you shouldchoose. Take a look at chart # 6. It shows whichchambers are the most suitable for the productsindicated. One check in the box means that thecrushing chamber configuration is good atmaking that product size. Two checks mean thatconfiguration is usually the best at making that

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21904 (5/00) - 4 - © 2000 Cedarapids, Inc.

VSI Primer

A Terex Company

6" (150 mm)

Model 2600

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3" (75 mm)

2-1/4" (57 mm)2" (50 mm)

1-1/2" (38 mm)

1" (25 mm)3/8" (9.5 mm)

Model 2100

Model 1800

Chart 3 - Qualifying crushingchamber based on feed size

5003 223/4 21/2 21/4 13/4 11/2 11/4

3/41/2

1/41 0

475

450

425

400

375

350

325

300

275

250

225

200TPH

5003 223/4 21/2 21/4 13/4 11/2 11/4

3/41/2

1/41 0

475

450

425

400

375

350

325

300

275

250

225

200TPH

Chart 4 - VSI 2100 capacityHow top feed size affects it

Table Capacity

Rotor Capacity

Capacity will approach upper curve with rounded,free flowing material, feed well centered in feed tube,no surges, etc.Capacity will approach lower curve with angular,non-free flowing material, feed off-center in tube,insufficient horsepower, etc.

product. Note that in some cases more than onecrushing chamber configuration have two checks.If more than one chamber is equally suitable fora production need, the feed size and/or tonnagelimits may define which you should select. If acrushing chamber is being picked to satisfyvarying needs, you can select a crushing chamberthat suits each, or in models 2100 and 1800 youcan order multiple chambers and change them inthe field to customize the machine for each job.Also see section X for more complete descriptionbased on desired product.

• Abrasiveness: Section VIII describes how wecalculate abrasiveness of rocks, and what factorswe consider when determining the appropriatecrushing chamber configuration for any givenmaterial. Chart # 10 shows some different rocktypes and their relative abrasiveness on a commonscale. After adjusting the test data for variablesin the application that affect how long the partslast, we have a more methodical way of estimatingthe likely part life. Chart #7 shows the roughrange of material abrasiveness that each chamberconfiguration can work cost effectively in. Notethat some of the bands do not have clear concise

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21904 (5/00) - 5 - © 2000 Cedarapids, Inc.

VSI Primer

A Terex Company

350221/4 13/4 11/2 11/4

3/41/2

1/41 0

325

300

275

250

225

200

175

150TPH

350221/4 13/4 11/2 11/4

3/41/2

1/41 0

325

300

275

250

225

200

175

150TPH

Chart 5 - VSI 1800 capacityHow top feed size affects itTable Capacity Rotor Capacity

Capacity will approach upper curve with rounded, free flowing material, feedwell centered in feed tube, no surges, etc.Capacity will approach lower curve with angular, non-free flowing material,feed off-center in tube, insufficient horsepower, etc.

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Chart 6 - Selecting crushing chamber based on product desired

= Suitable Choice = Best Choice

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VSI Primer

A Terex Company

ends, meaning that the applicability dependspartly on what other tools would be available todo the job, and that some bands overlap. Thepurpose of this chart is to give an idea of whethera particular crushing chamber might be suitable.After that, more specific data is available insection X, under the category of the productdesired.

VII - Power RequirementsTwo factors determine most of the horsepowerrequirement for a VSI: Impeller speed and grossthroughput tons. Chart # 8 shows an approximaterelationship between impeller speed and horsepowerrequired per ton. This guideline can then be multipliedby the gross throughput tonnage for an approximateoverall horsepower required. Caution should beused, as there is some slight variation betweenimpellers. The reason for this is that differentimpellers require different power running emptydue to WK2 and air flow variances, giving a slightlydifferent starting point for the power curve.

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Chart 7 - Qualifying crushing chamber based on abrasiveness of rock

2

1

0

700800

9001000

11001200

IMPELLER SPEED

HP

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15001600

1700

Chart 8 - Horsepower per ton ofcrusher output

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VSI Primer

A Terex Company

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Chart 9 - VSI horsepower requirements

A guide to estimate the horsepower required per ton when producing different sizematerials with different crushing chamber configurations. It assumes hard stone or gravel.

Notes: Maximum allowable applied horsepower is600 hp for 2100 and 2600 VSI and 500 hp for 1800 VSI

IGNEOUS

0 2 4 6 8 10

SEDIMENTARY

METAMORPHIC

Granite

Rhyolite

Andesite

Basalt

Shale

Limestone

Dolomite

Sandstone

Quartzite

Slate

Hornfels

Serpentine

Chart 10 - Relative abrasion: different rock types

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VSI Primer

A Terex Company

Chart # 9 shows the approximate horsepower requiredper NET ton to produce any given product size. Thischart has recirculated load calculated into it, andpresents the information based on NET tons asopposed to gross throughput tons. Which crushingchamber will ultimately be the lowest cost for aparticular application requires analyzing theefficiency of that crushing chamber via a combinationof wear cost and power cost per ton of net product.You must know the power cost in your area as it isapplied to crushing plants.

VIII - AbrasivenessRelative Abrasiveness of Rock Types: Chart #10shows a variety of rock types all compared to acommon scale of abrasiveness. Put into perspectiveyou can see that a rather "abrasive" limestone may belower in abrasiveness than a medium abrasion basalt.

Cedarapids VSIs are applied in literally all abrasiveranges. The availability of different crushingchambers offers a tool that is right for mostabrasiveness categories. For example, the open shoeand closed shoe tables work very effectively inmaterials with relative abrasiveness from zero to amedium-high rating. On the other hand the rotorwith rockshelf is successfully applied in material atthe very high rating, some with silica contentsexceeding 98%.

Speaking in terms of relative wear cost, if a VSI wereapplied for one specific job, and then crushingchambers were alternated in it, the user couldexperience wear costs varying by as much as 80%.This may or may not be worth changing from theideal configuration just to save wear cost. Let's lookat two examples: Assume an application to makechips with manufactured sand.

Scenario #1. The user finds these wear costs in highabrasion materials:

Open shoe table with anvils: ..................... $.70 cpt

Rotor and anvils ........................................ $.49 cpt(30% savings)

Rotor and rockshelf .................................. $.14 cpt(80% savings)

Scenario #2. The user finds these wear costs in lowabrasion materials:

Open shoe table with anvils: ..................... $.05 cpt

Rotor with anvils ...................................... $.03 cpt(30% savings)

Rotor with rockshelf ................................. $.01 cpt(80% savings)

Scenario #1 makes it obvious why a user wouldchange configurations even though the rotor androckshelf might not be the absolute best for thisproduction requirement. But the choice is not soclear in scenario #2. Other factors could easilyswing the choice. The increased power demandfrom the rotor/rockshelf could easily make more ofa cost difference than the wear cost.

We offer this flexibility so that a machine that is costeffective in low and medium abrasion materials canalso be cost effective in high abrasion materials, bysimply changing out the crushing chamber. So whenconsidering abrasion, give equal thought to powerdemand.

Calculating a Wear Factor: Cedarapids' test labcan take a great deal of the mystery out of thisdetermination. Over the years we have compiledthousands of test reports to rely on for comparativedata of different rocks and minerals. More importantis the interpretation of the test data. Silica contenthas universally been considered the best guideline ofabrasiveness. We have found that other factors enterthe equation, like the moisture content, the impellerspeed, and the tonnage to the machine. We alsoperform a true impact abrasion test called a "BurbankTest". Taken as a block of information to be usedtogether, the chemical analysis and the pertinentdata from the application are used to adjust theAbrasion Index Number (AIN) from the BurbankTest. While this formula is not foolproof, it doesgive as good a guide to expected part life as isavailable today (from small batch lab tests).

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The formula we use is:

WF = AIN x (Khp) ÷ (Kaf)

Where :WF = Wear FactorAIN = Abrasion Index NumberKhp = adjusting factor from the "hardparts"

(chemical)Kaf = adjusting factor from the compilation of

application factors.

The Wear Factor is taken to charts for either quarriedmaterial or gravel, and an expected part life isobtained for the most commonly replaced parts,either impeller shoes or tungsten carbide tips. Theexpected cost for consumption of that part can becalculated by using the price of that part, and theexpected production rate of the machine or plant.Then we use typical consumption ratios between thepart calculated and other wear parts in the machine.

As you can see, the results and the estimate are onlyas accurate as the information we begin with. Sampleintegrity is absolutely critical, and having good dataabout the application increases the accuracy of theadjusting factors.

IX - Application Do's and Don'tsA vertical shaft is one of the more forgiving crushersavailable. It readily accepts higher percents ofmoisture and sticky material, gap graded feed, surgesand intermittent feed. But there are certain limitationsthat the unit is sensitive to by design. Part of thesensitivity is due to the use of tungsten-carbide, orhigh-chrome iron wear parts.

• Oversize Feed: VSIs are sensitive to feed size.Increasing the feed size diameter by 25% doublesthe mass of the particle. Utilizing high chrome-iron wear parts, the VSI has a natural sensitivityto oversize feed, because the increased weight ofthe rock puts an increased impact force on thechrome-iron part, risking breakage. As the wearparts increase in hardness, they also becomemore sensitive to particle mass. The tungstencarbide tip in the Rotor requires a smallermaximum feed size than either the open shoetable, or the closed shoe table. See chart # 3.

Follow the maximum feed size guidelines. Usea vibrating screen to control feed size if there isany chance of oversized feed causing a problemin the VSI.

• Tramp Metal: Sensitivity to tramp metal shouldnow be obvious. The VSI is not designed tocrush iron or steel. Due to the metallurgy, thereisn't a lot of forgiveness in the machine for trampmetal. Utilize a magnet, or metal detector, orboth to protect the VSI from receiving trampmetal.

• Overspeed: Increased impeller speed can havethe same affect as oversize feed. In addition thepotential arises to overspeed the machine to thepoint where the wear parts risk damage due tocentrifugal force. Be sure that the maximumimpeller speed for each configuration used in theVSI is understood and adhered to. Lower impellerspeeds are, of course, acceptable and are a majorpart of why the is one of the most flexiblecrushers on the market.

• Moisture: Usually a moisture content over 9%is not recommended, although VSIs aresuccessfully applied with above 11% moisture.Of particular concern is the cast rotor androckshelf, where a slurry feed will not allowproper buildup to achieve the rock on rock action.

X - Putting It To Work, By ApplicationConcrete Rock, Minimum Sand:

How:

• Best Crushing Chamber: Open shoe table andanvils.

• Best Feed Size: Max. feed size 3" or larger.

• Best Impeller Speed: Slow to medium-slow.

Why?

Slow impeller speed has many advantages. Lessfines generation is most obvious, also reduced wearcost (sometimes as low as 50% compared to max.speed applications), reduced power consumption,and ability to easily take feed size right up to themaximum size for that model VSI. Open shoe tableat slow speed doesn't overcrush. Other merits:

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VSI Primer

A Terex Company

Particle shape improvement a must for concretepumping. Soft stone elimination can control"poppers".

Example 1) Gradation chart A (page 11) shows thefeed and output of a VSI model 2100, equipped witha 5-shoe table and anvils in soft limestone. Theimpeller is at 61% of maximum speed. The slowimpeller speed allowed the user to maximize productyield at 77%. The 5 shoe table assures space for themaximum feed size to pass unobstructed.

Example 2) Gradation chart B (page 11) shows twomodel 2600 output gradations at different impellerspeeds while crushing basalt. Also shown on thechart is the output gradation of a 54" rollercone.Note the difference in the shape of the VSI outputcurves. The slower speed curve is noticeably steeperin the concrete rock sizes, indicated a higherpercentage of production in that size range. Themodel 2600 is an excellent candidate for concreterock production in medium and low abrasionmaterials due to the increased feed size capabilityand it's extremely high tonnage capacity (600 tphplus).

Chips, Minimum Fines:

How?

• Best Crushing Chamber:Closed 6-shoe tablewith anvils.

• Best Feed Size: Maximum feed size 1.5" to 2.5".

• Best Impeller Speed: 75-80% of Maximum.

Why?

More impeller shoes and closer shoe to anvil spacingimproves top sizing, hence yield. Coupled with thelow reduction ratio that the slow speed offers, thismakes the VSI is the best chip maker in the industry.Offers extremely high tonnage and flexibility tocontrol fines production better than virtually anyother type of crusher. Third stage crushing generallybecomes a bottleneck when making chips, but theVSI can balance with the capacity of the primary andsecondary parts of the circuit. Do not skimp onscreening, the product size is small enough to demandquite a bit of screen area. Not uncommon for model2100 to keep two 6x20 horizontal screens busy.

Other merits: elimination of the soft stone, improvedparticle shape, better screening.

Example 1) Gradation chart C (page 12) shows achip making effort in limestone. The VSI droppedfines production compared to both hammermill androll crusher that were in it's place previously,improving the product to waste ratio. Tonnage ofchip product increased two and a half times comparedto either previous machine, from 90 tph to 230 tph.Diesel power allowed the producer to pinpoint theoptimum impeller speed in only a day or two.

Example 2) Gradation chart D (page 12) shows thedramatic effect on minimizing fines production thatthis user achieved by loading up the crushing chamberof a model 2100 with a high output six shoe table.Feed was gravel, which flowed well through the feedtube, allowing the producer to increase tonnagefrom 350 tph to about 500 tph of crusher throughput.Not only did the gross tons increase, but also theratio of desired product (3⁄8" by 1⁄8") to fines improved.

Manufactured Sand:

How?

• Best Crushing Chamber: Rotor with anvils.

• Best Feed Size: Max. feed size .75", or up to1.5".

• Best Impeller Speed: 90-100% of Maximum.

Why?

The maximum tip speed of virtually all impellershoe tables is about 130 mph. The maximum tipspeed of the rotor in the model 2100 is about 160mph, in the model 1800 it's about 180 mph. Theadditional velocity is required to efficiently crushthe recirculated product that is near to the closedcircuit size. The use of a rotor versus open or closedshoe table will substantially lengthened the partreplacement interval, and also improve anvilutilization because the rotor throws the material in abroader pattern (vertically) against the anvil. Othermerits: Use of a VSI compared to a "sand cone"allows forgiveness of gaps and surges in the feed,and a substantial savings in capital investment.

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Gradation Chart A

Gradation Chart B

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Gradation Chart C

Gradation Chart D

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Example 1) Gradation chart E shows the differenceto the product gradation and the production ratewhen the user replaced a shoe table in a CedarapidsVSI with the cast rotor, leaving anvils in place. Notonly did the rotor solve the deficiency in the mid-range sizes (16 mesh and 30 mesh), it increasedproduction by about 50%, from 78 to 117 tph.

Example 2) Gradation chart F shows the differencebetween the product of a 2100 with rotor and anvilsand a model 1800 with rotor and anvils. The feedsize was the same: A pea gravel size with 80%passing the #4 mesh. The additional reduction isstrictly a function of the increased velocity the1800's rotor can achieve, about 180 mph.

In this case the producer turned reject material thatcould not be sold for $.50 per ton into a profitablemanufactured sand that met the specificationrequired. How else would the producer do this job?Most of the feed is smaller than the closed sizesetting possible in compression crushers. Possiblya high speed cone could crush the material if feedconditions were right, but the circuit layout, with awash screen, precludes the use of a high speed conedue to packing. Note that normally we recommendthe moisture content be held as low as possible,usually below 6%, to control wear, and permit betterbuild up in the rotor. In this case the user claimssuccess with about 11% moisture.

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Gradation Chart EManufactured Sand

Gradation Chart F

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Chips With Manufactured Sand:

How?

• Best Crushing Chamber: Closed 6-shoe table,rotor with anvils, (but all are suitable).

• Best Feed Size: Maximum feed can range from1" to 3".

• Best Impeller Speed: 70-100% of maximum,depending on rock friability and balance ofproducts desired.

Why?

Chips with "crusher fines" as they are often called,is certainly a mainstream application in the aggregateindustry. The merits of the VSI compared to othertypes of crushers would fall to tonnage, circuitbalance, the ratio of one product to another, or otherconcerns like capital investment and portability.The crushing chamber can be selected based onabrasiveness of rock, and the feed size to be crushed.

Example 1) Gradation chart G (page 15) shows animpeller table equipped VSI where crusher productwas screened at 1⁄2". A variety of impeller speedswere used to determine the ratios of chips to crusherfines. Assuming a split at #4 mesh, fines productionranged between 35 and 60% of the 1⁄2" minus.

Example 2) Gradation chart I (page 16) shows theeffect of varying the impeller speed with the samecrushing chamber. This example is in limestone, butthe variation is similar with hard rock, though thepercents passing may not be as high.

Example 3) Gradation chart H (page 15) shows threedifferent crushing chambers with the same feed, ahard basalt. Note that the impeller speed is the samefor the open shoe table with anvils and the rotor withanvils (1190 rpm), but has been sped up for the rotorwith rockshelf. It's clear in this chart that the use ofanvils increases chip production.

Look carefully at the shape of the gradation curve forthe rotor with anvils and the gradation curve for therotor with rockshelf. The tendency of the rotor withrockshelf is to be a poor topsizer. Both the curvesshow the same percentage passing the #4 mesh,which isn't always the case, but the difference inshape of the curves is common. The point is that for

a given amount passing the #4, the rockshelf tends togenerate less chips, or intermediate size, and moreminus #200 mesh. The curve tends to flatten outwith a very steep portion at the largest sizes.

Why is this significant? If you were to change yourrecommendation for crushing chamber based on theabrasiveness of the rock, you might also affect themix of product sizes. It could work to the positive,or be a detriment. #200 mesh production can betaboo. But either way, if you understand that thisdifference with the rockshelf exists, you can guideyour customer around "suprises". Also be carefulwhen recommending the rotor with rockshelf toassure sufficient tons to the machine. The rotor withrockshelf configuration relies on particle collisions,hence it crushes better when it is being fed 80-100%of capacity.

Beneficiation:

How?

• Best Crushing Chamber: All.

• Best Feed Size: All.

• Best Impeller Speed: Usually slow or very slow.

Why?

Beneficiation is "...to treat a raw material so as toimprove properties..." In other words, if the user hasa contamination problem in his deposit, whetherquarried stone or gravel, the effort is to differentiallycrush out the contaminant. This works veryeffectively when the good stone and the contaminantvary in friability. If the contaminant is softer, oreven much harder, hard enough to be very brittle,both can be crushed together and then screened tomake the separation. Note that the soft stone has togo somewhere, presumably into the sand product.

As you can see, the impeller speed should be slowenough that it does not over crush the good stone, yetjust fast enough to blow apart the softer stuff. Thisimpeller speed varies widely from application toapplication, so there is no one "right" answer. Someexperimenting at location with the machine willlikely be required. Other merits: May eliminate theneed for a heavy media jig, can usually be achievedwhile accomplishing needed reduction task too.

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VSI Primer

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Gradation Chart G

Gradation Chart H

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Gradation Chart I

Example 1) When crushing a soft marginal limestone,a user compared the sodium sulfate test results of thecrushed product of a cone crusher to that of a VSI.He tried it at many different impeller speeds andwith different impeller tables. The results wereconsistent that the product from the VSI improvedthe soundness test results, anywhere from 8% to44%.

Example 2) A user in gravel reported that his pit waspreviously plagued by soft stone contaminants,including coal. Sometimes the percentage reachedas high as 6%. Crushing with a VSI at the final stagereduced the percentage to less than 1⁄2%, and let thematerial pass specifications for a higher valueproduct.

Fractured Faces

How?

• Best Crushing Chamber: Rotor with anvils,open or closed table with anvils.

• Best Feed Size: 1-1⁄4" or smaller (Product sizedround rock).

• Best Impeller Speed: As required to achievedesired fractured face count.

Why?

The answer to why the VSI works for this applicationis in the design. Putting a fractured face on materialthat is small is difficult (at best) with other crushers,but the VSI has no "closed side setting". Everyparticle that goes into the feed tube gets thrown fromthe impeller to the anvils (or rock bed if used). Soevery particle has a chance to be fractured, unlike amachine with a closed side setting, where the particlessmaller than the setting could just roll through. TheVSI stands apart from all other designs of crushersfor this reason. Even the horizontal shaft impactordoes not have the precise control over the crushingfunction that the VSI offers.

But how to correctly apply it varies with the need.Given the same crushing chamber configuration, a

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VSI Primer

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eziSeveiS ecaF1 ecaF2

"4/3 %0.001 %0.001

"2/1 %9.09 %1.88

"8/3 %5.49 %2.39

"4/1 %7.99 %5.99

hseM01 %0.001 %0.001

Chart J - Fracture count

3⁄8" rock requires a faster impeller speed to fracturethan does a 1" rock. Tougher rock requires increasedspeed over a more friable rock. But usually the needis to limit fines generation, so the gradation demandsthe slowest impeller speed practicable. As you cansee, the best solution is to estimate what speed willcome closest to the gradation desired, then adjustbased on fractured face requirements. A fracturedface requirement of 75% may not require anyadjustment of the impeller speed, but a fracturedface requirement of 95% could require a significantincrease in impeller speed.

A word of caution about crushing chambers: Thevariation in fractured face count between all newparts and all worn parts is more dramatic withimpeller shoes and anvils than it is with rotor andanvils, or rotor and rockshelf. As the parts wear thetrajectory changes, and the angle of the impact facechanges. This can be partly compensated for byincreasing the impeller speed if the unit is dieselpowered. But the rotor solves a good portion of theproblem by itself. And since the feed size is excellentfor the rotor, it's usually a good marriage. Therockshelf has the hardest time achieving highfractured face counts in some materials, but has themost consistent results through the life of the parts.

New Shoes/New Anvils

Chart J shows the results of a producer in hard gravelwhen utilizing a model 1800 VSI to achieve singleand two face fracture counts. Note that this particularjob spec. required fractured face count down to the#10 mesh.