1986 National Waste Processing Conference 28

8/10/2019 1986 National Waste Processing Conference 28

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THREE TYPES OF LOW SPEED SHREDDER DESIGN

DG M. HLL

Dallas, Texas

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This paper describes three basic designs o lowspeed(sometimes called shear) shredders which have evolvedto meet varying application requirements in shredding

dierent types o bulky, waste materials What hasemerged are three distinct congurations o shredder 'rotors and cutters, used in units with basically similarmechanical characteristics. The basic shredder can beeither electromechanically or electrohydraulicallydriven, with the preerence or either o the two beingentirely dependent on the nature and volume o thematerial to be reduced in size Thus, the evolution odierent types o low-speed shredders is the directresult o the need to shred various specialized subclasses o material separately rom, or in addition to,the general waste stream

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With very ew exceptions, lowspeed shredders areused or the size reduction o waste materials such as

(but not limited to) municipal solid waste, discardedtires, old appliancescommonly reerred to as white

goods, industrial and construction debris, and scrapelectrical wire and cable

There are two basic reasons or shredding any othese materials densication to reduce volume, or

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preparation or downstream processing operationsDensication, or simple size reduction, by itsel imposes ew restrictions on shredder design The bruteorce o the drive applied to the cutters can result inmore or less acceptable results being obtained with

dierent cutter designs.n contrast, preparation or downstream processing

operations may subject the shredder to stringent perormance requirements or the particle size and ormproduced Thus, a primary criteria in the design willbe the use, i any, o the shredder output t there aredownstream processing operations, the characteristicso the material being shredded then will impose secondary selection criteria on the shredder design. Homogeniety o the material or whether it contains a widevariety o materials, whether it needs to be cleanlysheared or can be to apart, and the material com

position all impose greater restrictions (than in densication applications) on the design required ordesired shredder perormance

Figur shows one o the rst types o shear shredders whih eolved over the past 0 years or a specicuse applicatOn the preshearing o scrap nonerrous


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FIG 1 TYPE I WIRE SH REDDER[Inp Torque Specificaons 38200 fb/Saf @ 19 p (51,800 N Shaf)]

insuated wire and cable to prepare it or eeding intoa mechanica reclamation system n this instance theraw material is relativey homogeneous (when compared to solid waste) in composition but varies in ormt may be in a typical scrap processing operation inthe orm o dense baes weighing up to 2 b 9

kg) (as shown in Photograph cois bundles or oosewire. This mass o materia then needs to be convertedinto relatively loose ree-owing pieces 62 in. (60 cm) ong that can be ed into the rst processingoperation a closetoerance radial knie granuator

Three actors had to be taken into consideration inthe design o this type o shear shredder

a The limitations o alteate processing methodssmal manualy-ed shears were quite aborintensive(as wel as unsae) whie hydraulic guillotine shearstended to compress the wire into dense blocks Neithero these methods could economicaly precut dense bales(a process actor).

b The sensitivity o the downstream granuatorsto surge or shock loads either o the above methodscoud result in overeeding the downstream system andthe compressed material rom hydraulic shears causedmore rapid wear in the granuator (again a processactor)

c The nature o the eed the dense baes neededto be to apart yet the individua wires needed to becut not stretched and to

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The resultant design shown in Fig incorporatestwo counter-rotating shats that do not intermesh witheach other. nstead they cut against a stationary anvibar equipped with replaceable and adjustabe knivesAt the same time the knives have sucient projectionto pul apart the dense mass o wire and cabe As the

knives on the two rotors pass between the stationaryknives they pul through and cut into short engthsthe tanged mass o raw material.

n Photograph 2 the rotor conguration is shown;in the center can be seen a portion o the stationaryanvil which supports the stationary knives The twoshats re independenty driven and can independentyreverse should an obstruction or thick mass o materia be present. The resut is a uniorm ow o wireand cabe cut into short lengths (see Photograph 3which can be ed to the downstream processing system.

The unique eature o this type o shear shreddermakes it idea or this one purpose. That same eaturerotor knives cutting against stationary knives on acenter anvil make it impractical or such materials asmunicipal soid waste tires "white goods and otherbuky waste For those the center anvi wi resut ina drastic reduction in capacity due t bridging o materia on the anvi Additionaly the nip ange or lineo attack o the cutters onto the material being shredded is not sucient to pul bulky items into the interace o the cutters


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he reultig deig illutrate the adaptio of thebaic mechaical characteritic of the hear hredderto a pialized applicatio

he ecod baic hredder deig how i Fig 2,i the oe mot commoly thought of whe dicuig hear hredder ypical applicatio iclude

hreddig:a muicipal olid wateb tire where the oly objective i ize ructio

for ladllc overized bulky wate uch a fuiture mat

tree rolled carpet etc(d) demolitio ad cotructio debrie crap part from a maufacturg proce where

the reductio i eceary prior to dipoal or ale toa crap dealer

documet detructio

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hi type of hear hredder may be coidered a ageeralpurpoe deig for either imple ize reductioor hreddig prior to rther proceig Becaue ofthe variety of applicatio the baic eed which guidethi deig i exibility Limitatio are ot impoed

by either pecic applicatio or the ature of aypecic feed tream; itead the rage of feed materaldee the rage of performace that mut be availablehe baic deig the i for a uit that hred adtear material apart with cutter havig a much deeper

ip agle to accommodate overize bulky materal.I almot all cae thi type of hredder ue two

cotrarotatig haft which itermeh with eachother he material i draw ito the pich poit adheared or to apart rather tha cut here i o

ceter avil ad typically the two ha ru at differet peed ad torque output A typical M adtorque dieretial i how i Fig 2 hi dieretialrpm give dieret relative tip velocitie betwee cutter o adjacet rotor. It i believedad appear tobe upported by eld experiecethat thi feature will


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provide better shearing action for shredding the multitude of materials that may be fed to this type of

shredder.It is understandable, given the wide range of appli

cations and the exibility of the basic design, that thistype of shredder is manufactured in a wide range ofcutting chamber sizes, cutter congurations, width andnumber of cutters, connected horsepower, and rpmranges on the individual cutting shas However, a

common thread to l the models of dierent manufacturers is the dierential rpm of the two shas

Shredders of this ty are currently manufacturedby a number of companies and utilize either a directdrive, from an electric motor or diesel engine driving

through a gear box, or a hydraulic dive Hydrauicallypower units may use either eltric motors or aninteal combustion ene to supply power to thehydraulic pump(s) Horsepower ranges-from 7X to60 (56 kW3 kW)attest to the wide variety ofapplications of this basic shear shrder design

Regardless of the size of the shrder, the width ofthe cutting segments, or the connected horsepower, lunits use a similar, helical conguration of the cuttingsegment Photograph , shows the interior of a 65 in

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76 in (165 cm 93 cm) cutting chamr in a4 hp (3 kW) shredder Please note that the seg

ments shown are split into two halves and boltaround a key or hexagonal sha However, the samegeneral conguration would apply i the segments werestacked on the shas from one end

This type of shrder, because of its versatility, andthe ide range of materials that it will press suc

cesslly, wbe the most common design spied inthe future Its low maintenance (per ton pressed)cost, apparent reduced power consumption, and thereduction of explosion hazards when processing municipal solid waste, make it very attractive when compared to the traditional high speed hamermills for

reduction of MSW and demolition wasteAnother advantage of the low speed shredder, when

shrding to produce refusederived fuel for bgin a dedicated boiler, is the relatively large mean size

of the discharge material The larger mean size createsvoidages in the F bed, thus allowing for a morecomplete combustion, with closer temrature control

Photograph 5 shows a typical municipal watestream feeding into a Type II shredder. This particushredder was equipped with in (10 cm) wide cutig


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sgmnts haing a 4 in. cutt poction. Th sutantsi distibution of th shddd matia is shown inFig 3 What is signcant is that an aag of ony83% of th dischag passd a X in (635 mm) siingscn Th minimum was 5% and th maximumwas 03% Th man si of th dschag was 2 in(508 mm) which woud sut in th cas of ingin a ddicatd boi in a y unifom combustion ow with suting cos conto on combustion

tmpatuThis si distibution points out a th adantag

of th sha shdd compad to a highspd impactmi fo th pimay duction of soid wast That isth coas man si of gass and camic paticsf it is dsiab to ha a ow ash contnt in th RFthn this ath coas gass faction is not ony asito spaat it is not imbddd in th oganic matiasby high ity impacts in th shdd Thus spaation of gass and camics fom RF pio to combustion boms mo cint.

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Whi th Typ shdd psnts what w bi to b th stat of th at in MSW shdsspcic componnts of th gna wast stam mayqui a dint appoach if thy a to b pocssdas a spaat matia stam Tis whn incudd inMSW psnt no pobm fo a Typ shddHow th incas intst in us of shdd tisas a incas ubb amation and gisationpohibiting th andg of ti in any fom ha

catd a nw -incasing wast stam composdony of tis Th sut thn is th thid typ ofshdd sha discuss tay

Lik a Typ shd this thid typ is dsigndwith a spcic wast stam in mind and with a spcicnd us obcti fo th poduct gnatd Th dsignmust tak into account th downstam pocs


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FIG 2 TYPE I MSW SHREDDER[Input Torqe Specifcations: 1 @ 32,000 ft-b/ Shaft @ 32 rpm 43,400 N. m Shaft @ 32 rpm);

1 @ 57,000 ftb / Shaft @ 16 rpm 77,306 N. m Shaft @ 16 rpm)]

SCREEN PERCENT RETAINED

SZE NAVG MN MAX

+4 193 97 329

+2 307 230 350

+1 192 149 239

+1/2 132 89 174

+1/4 93 62 120

PAN 83 51 103

FIG 3 0203 DECEMBER 190 SZE DISTRBUTION OFSHREDDER OUTPUT: ELEVEN SAMPLINGS FROM 112

TO 24 b; AVERAGE SIZE 1 b; AVERAGE BUKDENSITY 54 pcf

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qurmts ad t spcc atur of t fd matraSpccally:

a T srddr output must b rasoaby uform sap of a sz tat ca rady budad fr of og strps of rubbr

T raw matral s buky xb lastc adot asy to gag t trfac btw t cuttrs

As a rsut ts Typ III srddr dsg corporats faturs from t rst two typs ad k TypI, adds som ry uqu faturs to mt t rqurmts of ts spcc fd matra Fgur 4 lustrats

a typca cross-scto troug t cuttg cambr ofts dsg

Frst bcaus of t lastcty of t fd matralad to g bttr cotrol or t partcl s producd t borrows t da of rplacab cuttg dgsfrom t Typ I srddr Nxt fro a Typ II srddr t borrows t da of t trmsg rotors admats t ctr a to as t trac of tbuky fd matra to t cuttg trfac ad rduc t possblty of matra brdgg


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ROTATION ROTATION -

ROTATION ROTATION

FIG TYP III TIR SHRDDR[Inpt Torqe Speciication: 26,500 tb/Shat @ 19 rpm (35,900 N Sat]

These two features, by themselves, however will noteliminate the possibility of producing the long stripsof rubber which interfere with downstream processingoperations Additionally, tires would still be free to

bounce around on top of the rotating cutters, greatlyreducing net throughput To solve this specic materalhandling problem, the design incorporates a set of starshaped feed rolls which push the individual tire carcasses one at a time into cutting zone. These feedersengage the tire carcass and feed it into the cutters ata feed rate less than the peripheral speed of the cutters.As the tires are fed into the cutting zone the cuttersengage them with a true shearng action It is notpossible for the tires to be extruded through the intereshed cutters. This cuts the tires into more uni-

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form pieces and eliminates the production of long stripsof rubber. A typical Type III Shredder is shown inPhotograph 6.

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As has been illustrated in the previous gures andphotographs, the basic concept of a lowspeed shreddercan be subject to a number of design varations. Theseadapt the basic advantages of low-speed shredding tospecic problems in waste processing and provide userswith a wider choice in equipmentor even the optionof "customized unitsto meet specic applicationproblems This, of course, will also require closer def


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PHOOGRAPH 6

inition o shedde peomnce euiements nd stute evlution o poposed shedde etues by systemdesignes nd uses Thee cn be ovelps in ppliction betwn the dieent etues vilble Theeoe shedde selection must tke into ccount ll thectos which dene the behvio o the ineed mteils it is shedded s well s the euied peomnce

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Fom the bsic Type shedde nd the two vitionspesented heein, it is ppent tht thee cn be nlmost innite viety o cutte styles, sie ndthoughput These povide the industy with milyo sie eduction mchines o use in cuent pplictions nd on which to bse utue development ospecilied wste pocessing pplictions

1986 National Waste Processing Conference 28

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Transcript of 1986 National Waste Processing Conference 28