Matflow 2 v2-Ok (1)wfwf

7/22/2019 Matflow 2 v2-Ok (1)wfwf

1/13

Bucket elevators are for transport of light flowing solid bulk materials if the height difference

between the starting and end points is big. This difference can be even up to 150 meters and

above. There are two basic version of this machine: the pitched bucket elevator (having

distance / pitch / between the buckets! and continuous bucket elevators. There are four main

differences between the two versions. "itched bucket elevators have a distance between the

buckets for continuous the buckets are closel# after each other. "itched elevators are mainl#

for free flowing materials continuous are for handling larger lumps or fragile material.

$aterial from pitched elevators is discharged using the centrifugal principle! continuous ones

using the gravit# principle. %peed of the pitched version is high! for the continuous ones slow.


2/13

Belt bucket elevators have higher speeds and therefore higher capacit#. The operation is

smoother and &uieter. 't has high abrasion resistance to materials. 't has also higher corrosion

resistance. The# cannot be used however at higher temeratures.

or higher temperatures and for more damaging (e.g. sharp particles materials chain bucket

elevators can be used advantageousl#. )ound steel chain is easier to be replaced and cheaper

then the central chain! but the e*pected life is shorter. +entral chain has longer service time!

but is more e*pensive and abrupt mechanical failures can also happen.

%coop,feeding is used for handling non,sensitive materials and for pitched bucket elevators.

)e&uired additional power because of scooping can be calculated appro*imatel#. 'n additionin case of overloading the resistance can increase significantl# causing possible malfunctions.


3/13

l#,feeded elevators picks up materials from the air! therefore it is a more gentle solution for

sensitive materials. 'n addition loading resistance can be calculated more e*actl#. The onl#

disadvantage is that implementation of an additional conve#or (screw conve#or or loading

bucket elevator is necessar#.

Busket elevators operating at greater speed discharge material using the centrifugal principle.

'n this case the material slides at the outer side of the buckets. or the case of the perfect

discharge the buckets are led so that the material discharges from the bucket with almost no

friction at the bucket. %low moving bucket elevators discharge materials sliding at the back

plate of the previous bucket. This means more gentle handling but a significant wear as well.

'nside discharge is implemented in compact machines.


4/13

The slide shows forces on the particle in the bucket. These are - gravitational force and

centrifugal force. The resulting force is designated b# -es. 'f the direction of this force

shows above of the level of the rear plate of the bucket! the material will be discharged

centrifugall#! if shows under the level of the rear plate the material will flow out

gravitationall#.

Bucket elevators can be calculated onl# appro*imatel# using empirical diagrams as well. efte&uation can be used for calculating capacit# of the belt conve#or in m 2/h. v is the velocit# of


5/13

the bucket elevator in m/s! 3Bis the 3olume of a single bucket in dm2! tBis the distance of the

buckets. 4 is the filling grade of a bucket in percent (it is about 0!5 ... 0!. )ight e&uation

describes the necessar# force for the motion of the bucket elevator (circumferential force at

the drive sprocket is u. f-esis an empirical resistance coefficient which can be calculated

using the right diagram (area 1 and 2 are for deep and flat buckets! area 6 and 7 are for

triangle shaped buckets! area 1 and 6 are for belt bucket elevators! area 2 and 7 are for chainbucket elevators. & is the weight of the empt# chain or belt 8 buckets /m. 't can be read from

the left diagram for different t#pes. +urves a .. d correspond curves 1 .. 7 of the right diagram!

curves e and f are for two chains verison for deep and flat buckets and triangle shaped

buckets.


6/13

The figure shows different possible material flows inside the trough. The top figure is the

basic version with one input and one output. 'f the screw is divided into two and the pitch of

the two halves are opposite than the single rotation of the screw transfers the material into

opposite direction! like on the second and the third figure. The fourth figure is a multiple input

/ output version.

The figure shows calculating e&uations for horiontal screw conve#ors. 't must be mentioned

that particularl# the e&uation for the re&uired power is ver# appro*imate because of thegeneral resistance factor which needs a great practice to appl# an appropriate value.


7/13

igure presents basic construction of a horiontal screw conve#or. 9epending on the direction

of the rotation and the art of the bearings the screw can be pushed or pulled. The later ones are

more advantageous because pushed screws have greater deformation.


8/13

igure presents operational principle of vertical screw conve#ors. owever the construction is

similar to the horiontal screw the operation is different. oriontal screw conve#ors have a

ma*imal speed of rotation! above which no material transport is possible because it will rotate

together with the screw. 3ertical conve#ors however need a minimal speed of rotation in

order to raise sufficient centrifugal force which pushes the material to the wall of trough so it

will not fall back.

)oller conve#or is for the conve#ance of unit loads. 't re&uires stable unit loads with flat

under surface.


9/13

-ravitational roller conve#ors transport unit loads along mainl# straight directions where the

end point is lower than the start. The potential energ# of the unit load is converted into

kinetical energ#! frictional heat and into kinetical energ# because of the speeding up of the

rollers. ;s the two later losses increase with the speed of the unit load! there e*ists a

theoretical limit speed for the unit load.


10/13

"owered roller conve#ors can be driven in various wa#s. or straight sections a low noise

solution can be implemented using a drive belt! which runs between transport and tensioning

rollers. The small changes in the direction of the belt result the necessar# pushing force on the

rollers to achieve frictional drive. or shorter conve#ors it is a more compact solution to use

individuall# driven rollers. 'n this case a small motor is placed inside the roller.

+urved conve#or section cant have belts. or these modules it is common to use chains

which connect sprockets of two neighbouring rollers. 'n this case each roller must have two

sprockets.


11/13

rom the modules of roller conve#ors comple* s#stems can be built. 'f the diverting of

selected unit loads is necessar#! it can be solved using several e&uipment. The simplest

solution is the use of a pusher which uses a pneumatic c#linder to remove ob=ects at the side.

't can be used onl# for light and stable loads because of the friction at the rollers. +hain

transfers use transversal chain conve#ors which are lifted in the case of diversion is needed.

The former two e&uipment causes the unit load travel further in cross direction as the unit

loads are not rotated at the same time. These solution are therefore not appropriate fore*ample for >?) pallets. or these heavier unit loads turntables come into application which

rotates the whole unit load into an# desired direction. The disadvantage of this solution is low

capacit# as it stops the unit load full#. "op,up belt and sliding shoes dont stop the unit load

and the unit load is rotated as well. owever the angle of the diversion and the unit loads

weight is limited.


12/13

The ne*t surve#ed machines belong to lifting devices with enclosure. That means the#

undergo less strict regulations than elevators for persons! which save costs. 't means certainl#

that no persons are allowed in it during operation.

3ertical transfer machines can be classified into two basic groups non,continuous and

continuous operating e&uipment. @on,continuous machines have three main constructional

parts: the static structure including the guiding rails! the lifting carriage which is e&uipped

with the driven roller conve#or section. The third main part is the lifting device which can bemechanic with steel ropes! belts! but h#draulic or even pneumatic versions are e*ist as well!

for smaller height differences. $ain advantages of non,continuous lifting devices is the lower

cost and the fle*ible construction. 9isadvantage is the lower capacit#! as the machine cannot

input further unit loads before the previous one reaches output and the table gets back to the

original position.

+ontinuous elevators run continuousl#! having multiple tra#s to carr# multiple unit loads at

the same time. This allows achieving great capacities but the input of unit load must be

s#nchronied with the machine.


13/13

Top left figure show a spiral conve#or using a special linked cleeking chain. 't is used not

onl# for gentle transport of unit loads but for process intern storage as well. )ight solution is a

continuous elevator however it can connect different relations as well as it cane have multiple

input and output stations as well. The light weight unit loads are transported on tra#s which

are mechanicall# compatible with the small conve#or sections which can be turned

horiontall# if material transfer is needed and can be turned down is no transfer is necessar#.

Documents

Matflow 2 v2-Ok (1)wfwf