Mechanical Handling in the Chemical Industry
iir~y operate at qx:cds u p to ti00 feet per minute (or Easkr), aiid inny liave its cnrrying-run supporting idlers
Eruni 3 to 5 feed apart., dcpciidintj upon the capacity required, tlic siac r,i tlic lumps, mil tire weight OS tile rriaterial per cubic foot. T!ie roturn idlers irmy be Srom 9 to 10 feet nptrt,. Today's idler i i crjiiippeti with tapered ruller bearings and with grease-seal rcservoirs tlint iieed rer:lrarging only at very iiifreqireiit intervals by a grease gorr. Attention necess w y ior i,iaintenani!e is reiiiiccil to a ininiriium. Accurately inadc, well-balanced, wll-lubricated, free-turning rolls mlt i n luiig lifts of thc cquipmmt. Grease seals are important tokeep thegrease in the reservoir and
t o e x c l u d e dirt and grit from the moving parts. The hcit- c o LL v c y or
instdlilt.ion :it I h i t of
FIGIJRE 2.
BELT CONYEYOR 1'08 WOO"
28
CtZn.s
gqouod deliveriiig to II belt c o n v e y o r , 30 inches wide, running ,,p,v:mi at a 20" :Logle. The idlers fur thiseonveyor m e grnrribised to p"""ent tho %,It irom st,ickirig to thein. The belt cunreyor, 36 inclres wide, shown in Figure 2, runs river t h e digester bins xt t h e p l a n t oi a p u l p a n d lumber corngany. 'l'his conveying unit disbributes the wood Chip8 to the
liornetiirrw tirere art: si: I disclisrgc opm. ings witti no g&s, with tiif? rcsult tlyat the t i l a terinl discliargcs t~irrn2ghthc first. opeiiing until the iiciglit of the pile renclies and closcs the opcnirig. T h e d i s c h a r g e will then 1x: through tlic next o p i i i i i in ~ the troiigfi, and so on, irrrtil the storage is full. Screw eiinveyors are used fur moriiir; materials Irorinontnlly UT at inclines not cxceeilirq about IO". A s a role, t h i r use is confincd to tire sses of smmiec. Wlien oiiplq~edfor abrasive oiiitcrials tending to CR:W r, the wrem and tmiigli sliuuld 1x: construated of cast iron, ruarigiiiicsc steel, or lJeat-tru!atiYl i;ttu.l. The screw wiivnyor is freqilontly uuid i n sand iirid gravel vrasiiiiig plan vire. TIE screw l i a i ii soriiihiiig sctiori 011 t,he sand and keeps tire l w m arid other foreign inatcrial iit siispetrsirn~,to Le carried awng in the
terial in bulk, such as cement., grain, chrtiiicals, sugar, OT similar materials, Hcrcw conveyurs are Ioxv iii first cost, heirig cxcecdingly simple in construction and requiririg very little fiead room. In fact, tlic screw conveyor easi often he placed in close quarters where otlicr forms of conveyors will riot work efficiently. The conveying rnedium consis t r of a spirid moiioted o n a cciit,ral shaft or pipe, aial sorwi to piisli the nmterial ahead i i i an all-stecl or wiiodcn s t e e l - l i n e d trough i n wliich the spiral is rotatcd by siiitahle driving m a c h i n e r y . From the top of the conveyor trooglr the ciids of the 8-, io-,or 1Pfoat seatirrns of standard screw conveyor we supported at i n t e r t n c d i a t e points by rii(:ans of lisnger lieariiigs. Tire diairieter of the coiivcym or spiral may he its small us 3 incfics and as largc as 24 inches. The material is dist:iiarged eitlter over t.lte end of the conveying trough, or tlimugh gates fitted in the trough boitoni where desired.
AIW,S ('n\-iEY"ns
s h o w s a diatrihit,ing eanveyur, G inchcx iii dismeter, in a d o s t sealed t r o u a h with s ecial dust-tight dis. cinrgo elmt,t?s, i i * l , ~ dlirig red lead from tire elevator to t i l e storage I k over the iunmes. A t t h e p l a n t of u rubber oompnoy :L S C I B O C I , I I Y U ~ Ois~ u s d Si,r handling shredded ruther, :mid I"i;ure t i pictures how this is srrtmged to h k c m r e of 61 long stomge pile. A screw conveyor drive with overhead nioi.w mounting on a 9-inch lieliciiid conveyor is used f o r distributing the d ~ r e ~ l d m riihiicr l OYW drying racks. The spccial typo of positivc drive for this vcyor gives il positive, continuous flow of mn a t a prwletcrmincd speed. 'Tho eIevat~,rilri shown iii the Imckgrouod. Screv r,onveyora are often umil i n specirtl f i r mixing :and a g i t a t i n g m a t e r i a l s . l'igii 8 h W S the slurry agitator tnnk used at a ccmcnt plant; the insert pictures the rihbon screw coiiveyor used in the tnnk. Many similar in tims BIB made in the chemienl industry. sections are often used ior stirring, such as on a cement mixer used in urermrinp mix for a cnncretoblock plant.
There arc inany applications of this typr of conveyor that are in use, not only in tliv
chemical industries, but in many varied industries. Cottonsced-oil mills and cotton gins are among the important users of t h i ~type of conveyor.
A p r o n conveyors for h a n d l i n g b u l k m a t e r i a l s , SUCII 8s coal, sand, c r u s h e d stone, ores, and other lieavy materials uscd io p r o d u c t i o n , are u s u a1I y constructed with twir strands of roller chain traveling on s u i t a b l e tracks on both tile top and 1)iittom runri. Overl a p p i n g s k e l pans tie the t w o c h a i n s t o g e t h e r and serve :IS t h e a p r o n o n which the materials are conveyed. Stat ion a r y r e t a i lling sides, or skirt h a r d s , are wed t o pcrinit
w greator drptli i o he carried.
iii
material
Apron couveyora may /IC: installed either liorioomttllly, or a t inclines up t o about, 2.5". O w i n g to t h e i r subs t iLnt ial steel eonstruclioli. tlre pans witlistand the slioek ( i f d u m p i n g liea s y ~ i r i i s s c ~ US inatcriai upon tlicnr. A s tlre conrepor operates at 11 s h + - speed, tisiia1l.s froiii IO t,u 100 feet per minuie, t h niiriirtenance cost is lorn. The m e t a l -mi i i i n g fidd esiieciailg requires a heavy and very ruggcd rrnd diEltreiri typc OS a p r o n f e e d e r , as l u r n p s t i p t.0 t i f e e t in diinensioir and weighing ii tun ur morc are sometimes dropped in the pans froni considerable height. Tu meet s u c h eonilitirms, the
pans, c h a i n s , s u p p u r t i n g rollers, and spro&et ivheeis, are all made of manganese steel and are of very rugged design. The chains which operate this type of feeder arc constructed so that they cannot articulate, bend, or sag helow horizontal clii%iiicenters of the material-carrying run, brit are frec to flex in the opposite direction and bend a r o u n d s p r o c k e t s . The t o p - c a r r y i n g r u n i s the nun-sagging p o r t i o n of the fceder, and is the feature of this type of feeder. One of the rniirry typical rxamplcs of an aproii-feeder i n s t a l l a t i o n is depicted in Figure 8. This steel apron f e e d e r or c o n v e y o r , with rvidtli of 36 inches and pitch of 12 inches, handles limcstone from the p r i m a r y to the s e c o n d a r y crusher. l'~1,lGHTcosvtiYolIs
' i kflight, or pusher i,ypc of conveyor was devekjpcd as a means of distributing non-abrasive materials lioriaoniailp: or elevat.ing up to appr~iximately4.5". The material is received in it trough, pushed along by flights attached to the a i d u s u a l l y discharged 11 the bottom of the trough, being ~irovidetlwith gates to he upened or elused as the conditions reqiiire. In the early days t,he flight c o n v e y o r was made only with one strand of chain, tlic flight being fastened to it centrally, aiid ~ v usually a ~ made of malleable iriiii with a thiokcned scraping edge, as well a8 with wearirrg pads for sliding the fliglits on st,eel tracks on the bottrnn run. In the Right conveyor the bottom run usually does the conveying. The nerd fur greater capacity vas met by
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32
N G1N
inuyiding two strands of chair! xttached t o the erids of the flights. A further irnprovenient is the use of rollers suspendiiig the chains and Higlits, instead of permitting the latter to drag on tlie bottom of the trough; the use of double strands of cliaiii with rollers at the articulation poiots to carry tlic chains and flights is also an improveinent. The Higlit conveyor is not expensive in first cost, but should be avvided for handling abrasive materials, such as sand, etc., as tlie sliding or scraping action rapidly wears the trough lining. The conveyor operates at speeds up to 150 feet per minute, and is siiitable for either lumpy or small materials.
1’: 1s I1 I
N G C €5 E M I S T I1Y
Vol. 21, No. I
the load from tlre elinin links tlienrselves, when ireiirg dragged through a trough. An example of this type of conveyor is depicted in Figure 10, showing the metal drums being coliveyed in the plant of an eastern oil company. Pronial is especially suitable for conveyor use. A description of this chain occurs in a 1at.w paragraph.
The overhead trolley conseyor saves fiwr space, inakes ceilings or roof trusses pay dividends, arid travels irregular paths tis conditions may demand. This type of conveyor often turns obsolete plant layouts into struighb-line nietlioda without costly rebuilding. Its main features, besides Hesihility, itre low power ctirr;mnption, initial w s t , aiid maintcnance. A typical example c d this type
