QUARTERLYISSN 1232-9312 3/2017 (106)

PROBLEMY EKSPLOATACJI

Journal of MachineC o n s t r u c t i o n and Maintenance

Bogdan KOSTURKIEWICZ, Andrzej JANEWICZ, Marek HRYNIEWICZAGH University of Science and Technology, Faculty of Mechanical Engineering and Robotics, Cracow, Polandkostur@agh.edu.pl; janewicz@agh.edu.pl; mhryniew@agh.edu.pl

SELECTION METHOD FOR THE ROLL PRESS FEEDER

Key words: briquetting, roll presses, screw feeder, tapering-channels feeder.

Abstract: Two types of feeders used for feeding fine-grained materials into the briquetting roll press are presented in this article. Both components enable, to varying degrees, the change of pressure exerted on the material and the briquette compaction degree. It ensures obtaining the proper mechanical strength of the briquettes in the case of unstable feeding material properties and is used to increase the area of application for a given roll press. Based on own experiences of the authors from the experimental research, a simple method of selecting the roll press feeder has been presented. The method was verified in laboratory conditions.

Metoda doboru zasilacza prasy walcowej

Słowa kluczowe: brykietowanie, prasy walcowe, zasilacz ślimakowy, zasilacz zbieżnokanałowy.

Streszczenie: W artykule zwrócono uwagę na 2 rodzaje zasilaczy, które stosuje się w przypadku brykietowania w prasie wal-cowej materiałów trudnych do scalania. Oba podzespoły umożliwiają zmianę wartości nacisku wywieranego na materiał oraz stopnia zagęszczenia brykietów. Zapewnia to uzyskanie odpowiedniej ich wytrzymałości mechanicznej w przypadku niesta-bilnych właściwości nadawy oraz służy rozszerzeniu obszaru stosowania określonej prasy walcowej. Na podstawie własnych doświadczeń wynikających z badań eksperymentalnych opracowano metodę doboru zasilacza prasy walcowej, którą przedsta-wiono w niniejszym artykule. Została ona zweryfikowana w warunkach laboratoryjnych.

Introduction, purpose of the tests

Using roll presses for briquetting fine-grainedmaterials is more andmore popular. That is dueto the benefits that include continuous work,the possibility of achieving high efficiency,lower power requirements and greater durability of forming element when compared to other briquetting presses. Some materials which arebriquetting in roll presses often require a high degreeofcompactionandahighvalueofexertedpressure. A solution that enables the change ofboth these parameters during the press operation canbeselected.Ithasanimportantmeaninginthecase of unstable feeding properties or the change of briquettedmaterial. For a specific roll press it

canbeachievedbyusingaproperfeeder.Thetypeand construction features of the feeder depend on the properties of the compacting fine-grainedmaterial,especiallyitssusceptibilitytocompaction[1].There are fewpublicationson this subject intheliterature.Itisduetothecompetitionbetweencompanies where research is conducted and roll presses are constructed. Some articles includethe results of the studies on screw feeders [2–4]and the model of material flow in such devices [5–8].Theabovementionedargumentscausedthatthe publication authors took proper action. Theirpurposewas to develop amethodof selection ofthe roll press feederwith given construction andtechnicalcharacteristics.Theresultswereshowninthisarticle.

p. 4�–�1

46 Journal of Machine Construction and Maintenance | PROBLEMY EKSPLOATACJI | 3/2017

1. Gravity and tapering-channel feeder

The most often used method of feeding material into thebriquettingzone isgravityfeeding.It isconductedby using a gravity hopper with proper geometricconstruction features. In this case, thewall inclinationangle and the outlet size are important factors. Theirselection is decided by the following parameters: the densityofthefine-grainedmaterialforbriquetting,thecoefficientofsidepressure,andthecoefficientsofstaticandkineticexternalfriction.Thegravityhoppermaybesubjectedtothevibratingmotion.Itenablestheprimaryfeed venting and enhances the parameters of the flowintotherollpresscompactingzone.

TheDepartment ofManufacturingSystemsAGHUST employees have developed a new type of feederthat combines the features of vibration and gravityfeeders[9].Itiscalleda“tapering-channelfeeder.”This

component is designed to work with a roll press with a horizontal layout of forming rollers. Construction,the kinetic diagram and the operation method of the tapering-channelfeederisshowninFig.1.

The use of the elements of compacting aims to initially pack the grainedmaterial in forming cavitiesandextendthetimeunderpressure.Itisconnectedwiththeincreaseinitsvalue.

Theoretical considerations related to condensing the fine-grained material in the roll press led to theidealizationofthecompactingsystem.Briquettingwasreplaced with rolling the loose material by using the “replacement roller layout” [10, 11].After comparingthetotalvolumeoftheformingcavitiesinthebriquetteworkingrollerwiththevolumeofflatrolledbandinthereplacement layout dependence (1)wasachieved thatshows the relation between roller radiuses in real and replacement layouts:

Fig. 1. Tapering-channel feeder: a) diagram: 1 – working rings of the roll press, 2 – feeding container, 3 – elements of preliminary compacting, 4 – elements separating the flowing feed, φ – initial compacting zone in tapering channels of the feeder, α – zone of densification and briquetting of the roll press, β – zone of briquette back-expansion, b) geometry of the thickening channel: Ro – roller radius in the replacement layout, R – real roller radius, Rφ – radius of the channel inlet slot, rw – thickness of the strip in the replacement layout, Hk – the height of the channel inlet slot, hk – the height of the channel outlet slot, Φ – total zone of compaction [9]

(1)

whereRo–rollerradiusinthereplacementlayout[m],R–realrollerradius[m],k–numberofrollerformingcavities[-],Vb –briquettevolume[m

3],B–rolleractivewidth[m].

Compaction degree s achievable in the roll presswiththefeederisprovidedbythedependence(2):

(2)

wheresw–initialcompactiondegreeinthefeeder[-],sb –thecompactiondegreeachievedinthezone betweenpressrollers[-].

R R kVBob= −2

2π

s s sw b=

Journal of Machine Construction and Maintenance | PROBLEMY EKSPLOATACJI | 3/2017 4747

Thecompactiondegreeachievableinthetapering-channel feeder is provided by the following formula(3):

(3)

where Hk –theheightofthechannelinletslot[m], hk –theheightofthechanneloutletslot[m].

The compaction degree achievable in the zonebetweenthepressrollersis[11]:

(4)

wherehp – the distance between replacement rollers

atthenipanglelevelthatdeterminesthebeginningofmaterialcompacting[m],

e – slot width between rollers in the replacementlayout[m].

After using Formulas (3) and (4) with theDependence (2) and transforming the expression,Formula(5)wasobtained,whichenablesthecalculationof the height of the inlet slot required to achieve thetotal compaction degree s that enables the required mechanical strength of briquette:

(5)

The total compaction degree required is definedin the experimental way by the determination of the material compaction characteristics. In theoreticalconsiderations, the limitingconditions that result fromtheplasticmaterialflowshouldbeincluded.

2. Screw feeder

A screw feeder is a component that is often used to feedmaterialintothecompactingzoneofarollpress.Itisawell-knownconstructionsolution.Basicfunctionsofthis feeder include homogenization and initial material compactionaswellasovercomingtheresistanceofflowcausedbydamming in theoutlet.The screw feeder isusedinthecaseofclassicbriquettingandcompacting,which is based on material compacting in the press withsmooth rollers.Figure2showsbothexamplesofthescrewfeederoperation.Theuseofthescrewfeederprovides beneficial effects of an increase in materialpressure, an increase in the compaction degree, andensuringtheuniformityoftheflow.Itguaranteesstableproduct quality as well as increased press efficiency.

Theaforementionedissueswerethesubjectofresearchthatwas also presented in other publications [12–16].However, informationon the selectionof constructionfeaturesofthefeederwasnotprovided.

The screw feeder has the functions that make two zones: feeding and homogenization and initial compaction. Material feeding and homogenizing isachievedbyusingthecatcherandfirstscrewcoil.Theinitial compaction zone includes the section from the first to the last screw coil. In this zone, the materialis initially vented. It is also affected by the properscrewandcylindersurfaceshape.Thecylindershouldbe constructed so that resistance caused by friction betweenmovedfine-grainedmaterial and itswallwasas big as possible. Such situation takes place whencylinder walls are grooved. In that case, the flowingfine-grainedmaterialfillsthegrooves.Inconsequence,internalfrictionoccursonthesurfacewherefine-grainedmaterial and thecylinderare incontact. Incontrast tothecylinderwalls,thefrictionalresistanceonthescrewsurfaceshouldbeaslowaspossible.Hence,thesurfaceroughness of the proper feeder working element should be taken into consideration. Cylindrical and taperedscrewswithfixedorvariablestrokeareused.Dependingon the width of working rollers, the screw feeder isequippedwithoneorseveralworkingelements.

Fromthepointofviewofthecorrectnessofmaterialcompactionprocess in therollpress, it is important toselecttheproperrotationalspeedofthescrew.Inordertodetermineit,aconditionoffixedmassflowthroughthe screw feeder and roll press was considered. Thecondition is as follows: (6)

where Qm –massflowrateofthescrewfeeder[kg/h],

Wm –massflowrateoftherollpress[kg/h].

SubstitutingforQm[16]:

(7)

wherez –numberofscrews[-],Dz –externalscrewdiameter[m],Dw –internalscrewdiameter[m], Dm= (Dz+Dw)/2[m],nsl –screwrotaryspeed[rpm],β –angleofflowoffine-grainedmaterialinthe

screwfeeder[°],φm –averageinclinationangleofthescrewline

[°],ρw –densityof thematerialflowingoutof the

screwfeeder[kg/m3].

s H rh rwk w

k w=

++

shebp=

Hes h r

hrk

k w

pw=

+( )−

Q Wm m=

Q z D D D nm z w m slm

mw= −( )

+15 2 2 2π

β ϕβ ϕ

ρtan tan

tan tan

48 Journal of Machine Construction and Maintenance | PROBLEMY EKSPLOATACJI | 3/2017

and for Wm[15]:

W V i nm b b w b= 60 ρ (8)

where Vb–briquettevolume[m

3], ib–numberofformingcavities[-], nw–pressrollerrotaryspeed[rpm], ρb–briquettedensity[kg/m

3].

a dependence was obtained (9) that allows for thecalculation of the screw rotary speed as follows:

nV i n

z D D Dslb b w b m

z w m m w

=+( )

−( )60

15 2 2 2

ρ β φ

π β φ ρ

tan tan

tan tan (9)

The quotient of the volume density and thematerialflowingoutofthescrewfeederisthedegreeofcompactionachievedinthezonebetweenrollers.TakingthisintoconsiderationandusingFormula(4),wehaveadependence(10)thatisusedtocalculatethedensityofmaterialflowingoutofthescrewfeeder.

ρρ

wb

p

eh

= (10)

The authors’ own observations of the benefits ofusing the screw feeder in the roll press assembly are presentedinFig.3.Itenablesincreasingthenipangleαsl from several to tens of percent in comparison tothegravityfeedαg.Itcausesanincreaseinthetimeofpressure on the compacted material and the growth of its maximumvaluepmax.Wecanassumethat theangleofreturndeformationγsl = γg under condition that the use ofgravityfeedenablesachievingproperbriquetteswithsatisfactorymechanicalstrength.

Fig. 3. Diagram showing the influence of the feeder (left side: screw feeder, right side: gravity feeder) on the nip angle value and unit pressure in the roll press forming cavity [16]

The analysis has shown that the feeder affects the materialcompactionprocessinrollpressanditsresults.There are different types of this component; however,inpractice,threetypesarecommonlyused.Themethoddescribed below can be used during selection. It isrelatedtosuchacasewherethepressefficiencyanditsworkingrollergeometryareknown.

3. Characteristics of the selection method for the roll press feeder

The selection procedure for the roll press feeder is presentedinFigure4.Thereare5stages.

The first is related to experimental determinationof the material compaction characteristics, itsanalysis, and the selection of the proper feeder. If thematerial compaction degree does not exceed 2.0, it

Fig. 2. The examples of the use of screw feeders in roll press assembly to execute the process of a) briquetting, b) compacting [15]

Journal of Machine Construction and Maintenance | PROBLEMY EKSPLOATACJI | 3/2017 4949

is recommended to use the gravity feeder, under thecondition that the feed has stable properties. In theoppositecase, thepressshouldbeequippedwith,e.g.,atapering-channelfeeder.Achievingthehighermaterialcompactiondegreerequiresusingascrewfeeder.Ifthedegreeof compactiondoesnot exceed2.6, cylindricalscrewsareused.Highervaluescanbeobtainedbytheuseoftaperedscrews.Theseobservationswereshownin selected examples being the results of the authors’ownresearch(Fig.5).

Duringthesecondstageofexperimentalresearch,the angle of internal friction and the angle of kinetic external friction were determined. If the compactiondegreerequiredisnotlowerthan2.0,theeffectiveangleof internal friction is determined instead of the angle of internalfriction.

The third stage is related to the selection of the feeder, thedeterminationof itsgeometricconstructionfeatures,andthekinematicparametersofthelaboratoryversion.

Fig. 4. Selection method for the roll press feeder

�0 Journal of Machine Construction and Maintenance | PROBLEMY EKSPLOATACJI | 3/2017

The fourth stage is the experimental verificationof the susceptibility of the fine-grained material onbriquetting in the roll press with selected feeder equippedwithproperworkingelements.Theexecutionispossibleonlyiftheproperlaboratorybaseisavailable.Confirmationoftheapplicabilityofthegivenfeederinthe roll press laboratory assembly means that the next stagecanbecommenced.

In the fifth stage, the geometric constructionfeaturesofanindustrialfeeder’sworkingelementsareselected.Next, thematerial compactionprocess in therollpress is simulated toverify theappropriatenessofthe chosen solution.A necessary condition to executethat task is the familiarity with the construction of the givenrollpressanditstechnicalcharacteristics.

Conclusion

Thepropertiesofloosematerialhaveanimportantinfluenceon thecompactionprocess in rollpressesandtheresults.Sometimesthepropertieschangefordifferentreasons.Thereisanincreasingneedforbriquettingwithmorethanjustonematerialinthepress.Thechangeofthetype or properties may cause worsening in the quality of briquettes.Toavoidsuchaphenomenon,thepressshouldbeequippedwithaproperfeeder.Theuseofthefeederenables changing the compaction time and unit pressure valueatwhich thematerial is compactedorbriquetted.Itaffectsthemaximumdegreeofbriquettecompaction.

Inthisway,onecanstabilizeitsmechanicalstrength,whichdecidesthequalityoftheproduct.Theselectionof the proper feeder and its construction features and parameters is ensured by the method presented in this

Fig. 5. Examples of the relation between the material compaction curves and the feeding type: Zone I – feeding with the gravity feeder or tapering-channel feeder, Zone II – feeding with cylindrical screws, Zone III – feeding with tapered screws [16]

article.Itwasdesignedonthebasisoftheauthors’ownresearchconductedovermanyyears forcognitiveandutilitarian purposes. The method was verified in thelaboratory-scale using the following materials: calcium fluoride,copperconcentrate,browncoal,bearingchips,dustsofferro-silicon,graphitedusts,ashesfromtheheatandpowergeneratingplant andpost-regenerative ironoxide. Itwassuccessfullyusedduring theselectionofthe feeder for an industrial roll press used for briquetting severaltypesofbrowncoalofdifferentproperties.

Further research is being conducted to improvetherollpressesandtheprocessofpressurecompaction.It mostly applies to continuous compaction of hard-to-briquettematerials. It isanticipated that the resultswillallowforanimprovementoftheselectionmethodofrollpressfeeders.

The problem of selecting the proper screw feeder alsoappliestofine-grainedmaterialcompaction[6]andgrainedmaterialmilling[4].

Acknowledgements

This article has been prepared within the scope of statutoryactivity,ContractNo.11.11.130.957.

References

1. Johanson J.R.: Roll press feed system. PowderHandl.Process,1996,8,2,pp.159–163.

2. DecR.,KomarekR.:Testing performance of rollforce feed systems. 23rd Biennal Conference,Seattle,Washington1993,pp.65–75.

Journal of Machine Construction and Maintenance | PROBLEMY EKSPLOATACJI | 3/2017 �1�1

3. Dai J., Grace J.R.: Biomass granular screwfeeding:Anexperimentalinvestigation.Biomass&Bioenergy2011,35,pp.942–955.

4. SanderU.,SchönertK.:Operationalconditionsofa screw-feeder-equipped high-pressure rollermill.PowderTechnology,1999,105,pp.40–55.

5. Dai J., Grace J.R.: A model for biomass screwfeeding.PowderTechnology,2008,186,pp.40–55.

6. Roberts A.W.: The influence of granular vortexmotiononthevolumetricperformanceofenclosedscrew conveyors. PowderTechnology, 1999, 104,pp.56–67.

7. YuY.,ArnoldP.C.:Theoreticalmodelingoftorquerequirementsforsinglefeeders.PowderTechnology,1997,93,pp.151–162.

8. Reynolds G., Ingale R., Roberts R., Kothari S.,Gururajan B.: Practical application of rollercompaction process modeling. Computers andChemicalEngineering,2010,34,pp.1049–1057.

9. Janewicz A.: Wpływ parametrów zasilacza zbież-nokanałowego na zapotrzebowanie energii procesubrykietowaniawprasiewalcowej.ProblemyEksplo-atacji,2006,3,pp.117–124(inPolish).

10. BembenekM., Hryniewicz M.: Badania i opraco-wanie metody doboru układu zagęszczania prasywalcowej. Kraków: Wydawnictwa AGH 2010 (inPolish).

11. Hryniewicz M.: Metoda doboru pras walcowychoraz założeń do ichmodernizacji lub konstrukcji.Kraków:WydawnictwaAGH1997(inPolish).

12. GuigonP.,SimoniO.:RollPressdesign–influenceof force feed systems on compaction. PowderTechnology,2003,130,pp.41–48.

13. SimoniO.,GuigonP.:InteractionbetweenFeedingand Compaction During Lactose Compaction in aLaboratoryRollPress.KONAPowderandParticleJournal,2000,18,pp.131–138.

14. SimoniO.,GuigonP.:Correlationbetweenpowder– packing properties and roll press compact heterogeneity. Powder Technology, 2003, 130,pp.282–287.

15. KosturkiewiczB.:Badania identyfikacyjne zasila-czaślimakowegodopraswalcowych.Pracadoktor-ska.AGH.Kraków1997(inPolish).

16. KosturkiewiczB.:Matematycznymodelobciążeniaelementuroboczegozasilaczaślimakowego.Auto-matyka,2011,t.15,z.2,pp.247–254(inpolish).