破碎机英文

ABSTRACT

Low

reduction

ratios

and

high

wear

rates

are

the

two

characteristics

ntost

commonh

are

not

often

considered

Jor

use

in

mineral

processing

circuits,

attd

many

of

their

advantages are being largely overlooked. This paper describes a novel roll crusher that

has

been

developed

ipt

order

to

address

these

ed

to

as

the

NCRC

(Non-Cylindrical Roll Crusher), the new crusher incorporates two rolls comprised qf

an alternating arrangement

of platte attd convex or concave su@wes. These unique

roll prqfiles improve the angle qf nip, enabling the NCRC to achieve higher reduction

ratios

than

conventional

roll

crushers.

Tests

with

a

model

prototype

have

indicated

thar

evell

fi)r

very

hard

ores,

reduction

ratios

exceeding

lO:l

can

be

attained.

In

addition,

since

the

comminution

process

in

the

NCRC

combines

the

actions

of

roll

arM jaw crushers there is a possibili O' that the new profiles may lead to reduced roll

wear rates.2001 Elsevier Science Ltd. All rights reserved.

Keywords:

crushing

INTRODUCTION

Conventional

roll

crushers

suffer

from

several

disadvantages

that

have

lcd

to

their

lack

of

popularity

in

mineral

processing

applications.

In

particular,

their

low

reduction

ratios

(typically

limited

to

about

3:1)

and

high

wear

rates

make

them

unattractive when compared to other types of comminution equipment, such as cone

crushers.

There

are,

however,

some

characteristics

of

roll

crushers

that

are

very

desirable from a mineral processing point of view. The relatively constant operating

gap in a roll crusher gives good control over product size. The use of spring- loaded

rolls make these machines tolerant to uncrushable material (such as tramp metal). In

addition, roll crushers work by drawing material into the compression region between

the

rolls

and

do

not

rely

on

gravitational

feeci

~like

cone

and

jaw

crushers.

This

generates

a

continuous

crushing

cycle,

which

yields

high

throughput

rates

and

also

makes the crusher capable of processing wet and sticky ore. The NCRC is a novel roll

crusher

that

has

been

dcveloped

at

the

University

of

Western

Australia

in

ordcr

to

address

some

of

the

problems

associated

with

conventional

roll

crushers.

The

new

crusher incorporates two rolls comprised of an alternating arrangement of plane and

convex

or

concave

surfaccs.

These

unique

roll

profiles

improve

the

angle

of

nip,

enabling the NCRC to achieve higher reduction ratios than conventional roll crushers.

Preliminary tests with a model prototype have indicated that, even for very hard oics,

reduction

ratios

exceeding

10:I

can

be

attained

(Vellelri

and

Weedon,

2000).

These

initial

findings

were

obtained

for

single

particle

feed.

where

there

is

no

significant

interaction

between

particles

during

comminution.

The

current

work

extends

the

existing results bv examining inulti- particle comminution inthe NCRC. It also looks at

various othcr factors that influencc the perli~rmance of the NCRC and explores

the effectiveness of using the NCRC for the processing of mill scats.

PRINCIPLE OF OPERATION

The angle of nip is one of the main lectors effccting the performance of a roll

crusher.

Smaller

nip

angles

are

beneficial

since

they

increase

tl~e

likelihood

of

parlictes bcing grabbed and crushed by lhe rolls. For a given feed size and roll gap,

the

nip

angle

in

a

conventional

rtHl

crusher

is

limited

by

the

size

of

thc

rolls.

The

NCRC attempts to overcome this limitation through the use of profiled rolls, which

improve the angle of nip at various points during one cycle (or revolution) of the rolls.

In addition to the nip angle, a number of other factors including variation m roll gap

and mode of commmution were considered when selecting Ille roll profiles. The final

shapes

of

the

NCRC

rolls

are

shown

in

Figure

I.

One

of

the

rolls

consists

is

an

alternating arrangement of plane and convex surfaces, while the other is formed from

an alternating arrangement of phme and concave surlaccs.

The shape of the rolls on the NCRC result in

several

unique characteristics.

Tile

most

important

is

that,

lk)r

a

given

particle

size

and

roll

gap,

the

nip

angle

generated

m

the

NCRC

will

not

remain

constant

as

the

rolls

rotate.

There

will

be

times

when

the

nip

angle

is

much

lower

than

it

would

be

for

the

same

sized

cylindrical

rolls

and times

when it will be much highcr. The actual variation in

nip

angle over a 60 degree roll rotation is illustrated in Figure 2, which also shows the nip

angle generated under similar conditions m a cylindrical roll crusher of comparable

size. These nip angles were calculated for a 25ram diameter circular particle between

roll of approximately 200ram diameter set at a I mm minimum gap. This example can

be used to illustrate the potential advantage of using non-cylindrical rolls. In order for

a particle to be gripped, the angle of nip should normally not exceed 25 °

. Thus, the

cylindrical

roll

crusher

would

never

nip

this

particle,

since

the

actual

nip

angle

remains constant at approximately 52 °

. The nip angle generated by the

NCRC,

however,

tidls

below

25

°

once

as

the

rolls

rotate

by

(0

degrees.

This

means that the non-cylindrical rolls have a possibility of nipping the particlc 6 times

during one roll rewHution.

EXPERIMENTAL PROCEDURE

The

laboratory

scale

prototype

of

the

NCRC

(Figure

3)

consists

of

two

roll

units, each comprising a motor, gearbox and profiled roll. Both units are mounted on

linear

bearings,

which

effectively

support

any

vertical

componcnt

of

force

while

enabling

horizontal

motion.

One

roll

unit

is

horizontally

fixed

while

the

other

is

restrained

via

a

compression

spring,

which

allows

it

to

resist

a

varying

degree

of

horizontal load.

The pre-load on the movable roll can be adjusted up to a maximum of 20kN.

The two motors that drive the rolls are electronically synchronised through a variable

speed

controller,

enabling

the

roll

speed

to

be

continuously

varied

up

to

14

rpm

(approximately 0.14 m/s surface speed). The rolls have a centre-to-centre distance at

zero gap setting) of I88mm and a width of 100mm. Both drive shafts are instrumented

with

strain

gauges

to

enable

the

roll

torque

to

be

measured.

Additional

sensors

are

provided to measure the horizontal force on the stationary roll and the gap between

the

rolls.

Clear

glass

is

fitted

to

the

sides

of

the

NCRC

to

facilitate

viewing

of

the

crushing zonc during operation and also allows the crushing sequence to bc recorded

using a high- speed digital camera.

Tests

were

performed

on

several

types

of

rocks

including

granite,

diorite,

mineral

ore,

mill

scats

and

concrete.

The

granite

and

diorite

were

obtained

from

separate commercial quarries; the former had been pre-crushed and sized, while the

latter was as-blasted rock. The first of the ore samples was SAG mill feed obtained

from

Normandy

Mining's

Golden

Grove

operations,

while

the

mill

scats

were

obtained from Aurora Gold's Mt Muro mine site in central Kalimantan. The mill scats

included

metal

particles

of

up

to

18ram

diameter

from

worn

and

broken

grinding

media. The concrete consisted of cylindrical samples (25mm diameter by 25ram high)

that

were

prepared

in

the

laboratory

in

accordance

with

the

relevant

Australian

Standards.

Unconfined

uniaxial

compression

tests

were

performed

on

core

samples

(25mm

diameter

by

25mm

high)

taken

from

a

number

of

the

ores.

The

results

indicated strength ranging from 60 MPa for the prepared concrete up to 260 MPa for

the Golden Grove ore samples.

All of the samples were initially passed through a 37.5mm sieve to remove any

oversized particles. The undersized ore was then sampled and sieved to determine the

feed size distribution. For each trial approximately 2500g of sample was crushed in

the

NCRC.

This

sample

size

was

chosen

on

the

basis

of

statistical

tests,

which

indicated that at least 2000g of sample needed to be crushed in order to estimate the

product P80 to within +0.1ram with 95% confidence. The product was collected and

riffled into ten subsamples, and a standard wet/dry sieving method was then used to

determine the product

size distribution. For each trial, two of the sub-samples were

initially

sieved.

Additional

sub-samples

were

sieved

if

there

were

any

significant

differences in the resulting product size distributions.

A number of comminution tests were conducted using the NCRC to determine

the effects of various parameters including roll gap, roll force, feed size, and the effect

of

single

and

multi-particle

feed.

The

roll

speed

was

set

at

maximum

and

was

not

varied

between

trials

as

previous

experiments

had

concluded

that

there

was

little

effect of roll speed on product size distribution. It should be noted that the roll gap

settings quoted refer to the minimum roll gap. Due to the non- cylindrical shape of the

rolls, the actual roll gap will vary up to 1.7 mm above the minimum setting (ie: a roll

gap selling of l mm actually means 1-2.7mm roll gap).

RESULTS

Feed material

The performance of all comminution equipment is dependent on the type of

material

being

crushed.

In

this

respect,

the

NCRC

is

no

different.

Softer

materials

crushed

in

the

NCRC

yield

a

lower

P80

than

harder

materials.

Figure

4

shows

the

product size distribution obtained when several different materials were crushed under

similar conditions in the NCRC. It is interesting to note that apart from the prepared

concrete

samples,

the

P80

values

obtained

from

the

various

materials

were

fairly

consistent.

These

results

reflect

the

degree

of

control

over

product

size

distribution

that can be obtained with the NCRC.

Multiple feed particles

Previous trials with the NCRC were conducted using only single feed particles

where there was little or no interaction between particles. Although very effective, the

low throughput rates associated with this mode of comminution makes it unsuitable

for

practical

applications.

Therefore

it

was

necessary

to

determine

the

effect

that

a

continuous feed would have to the resulting product size distribution. In these tests,

the NCRC was continuously supplied with

feed

to

maintain a bed of material level

with the top of the rolls. Figure 5 shows the effect that continuous feed to the NCRC

had

on

the

product

size

distribution

for

the

Normandy

Ore.

These

results

seem

to

show a slight increase in P80 with continuous (multi- particle) feed, however the shift

is

so

small

as

to

make

it

statistically

insignificant.

Similarly,

the

product

size

distributions would seem to indicate a larger proportion of fines for the continuously

fed

trial,

but

the

actual

difference

is

negligible.

Similar

trials

were

also

conducted

with

the

granite

samples

using

two

different

roll

gaps,

as

shown

in

Figure

6.

Once

again

there

was

little

variation

between

the

single

and

multi-particle

tests.

Not

surprisingly, the difference was even less significant at the larger roll gap, where the

degree of comminution (and hence interaction between particles) is smaller.

All of these tests would seem to indicate that continuous feeding has minimal

effect on the performance of the NCRC. However, it is important to realise that the

feed particles used in these trials were spread over a very small size range, as evident

by the feed size distribution shown in Figure 6 (the feed particles in the Normandy

trials were even more uniform). The unilormity in feed particle size results in a large

amount

of

free

space,

which

allow:s

for

swelling

of

the

broken

ore

in

the

crushing

chamber, thereby limiting the amount of interaction between particles. True

feeding of the NCRC with ore having a wide distribution of particle sizes (especially

in the smaller size range) is likely to generate much larger pressures in the crushing