2. SIZE REDUCTION
SIZE REDUCTION INVOLVES REDUCING THE SIZE OF PARTICLES SO AS TO GET
MORE PRODUCTS.
LAWS INVOLVED IN SIZE REDUCTION ARE : RITTENEGER’S LAW ,KICK’S LAW
AND BOND’S LAW .
FORCES INVOLVED IN SIZE REDUCTION ARE IMPACT, COMPRESSION,
ATTRITION AND SHEARING.
3. TYPES OF CRUSHERS
Crushers are classified according to the stage of crushing which they
accomplish, such as: Primary,Secondary,Tertiary
A primary crusher receives the stone directly from a quarry after blasting,
and produces the first reduction in size.
The output of the primary crusher is fed to a secondary crusher, which
further reduces the stone size. Some of the stone may pass through four or
more crushers before it is reduced to the desired size.
The degree of breakage is spread over several stages as a means of
closely controlling product size and limiting waste material.
As stone passes through a crusher, the reduction in size may be expressed
as reduction ratio.
The reduction ratio is the ratio of crusher feed size to product size.
4. ROLL CRUSHER
Roll crushers are used for producing additional reductions in the sizes of stone after the
output of a quarry has been subjected to one or more stages of prior crushing.
Roll crushers have a theoretical MAXIMUM reduction ratio of 4:1. If a 2 inch particle is fed to
the roll crusher the absolute smallest size one could expect from the crusher is 1/2 inch. Roll
crushers will only crush material down to a minimum particle size of about 10 Mesh (2 mm). A
roll crusher crushes using compression, with two rolls rotating about a shaft, towards the gap
between the rolls
5. The particles are drawn into the gap between the rolls by their rotating motion and a
friction angle formed between the rolls and the particle, called the nip angle.
The two rolls force the particle between their rotating surface into the ever smaller gap
area, and it fractures from the compressive forces presented by the rotating rolls.
Some major advantages of roll crushers are they give a very fine product size distribution
and they produce very little dust or fines.
Rolls crushers are effectively used in minerals crushing where the ores are not too
abrasive and they are also used in smaller scale production mining of more abrasive
metal ores, such as gold.
Coal is probably the largest user of roll crushers, currently, though. Coal plants will use roll
crushers, either single roll or double roll, as primary crushers, reducing the ROM coal.
8. DOUBLE ROLL CRUSHER
Working Principle and Structure of Double Roller Crusher
1.this series of roll crusher is mainly formed by the roller, roller support bearing, compression
and adjusting device, drive components etc.
2.the adjustment of the particle size: between the two rollers equipped with adjustment
device like pads or wedge.The wedge-shaped device has a adjusting bolt on top, when the
adjustment bolt pull up the wedge, the wedge will push the
movable roller away from the fixed roller,then the gap
between two rollers is larger and produce larger particle
size. When the wedge falls down, with the effect of the
compression springs, the movable roller makes the gap
become smaller between two rollers and thus produce
the smaller particle size. Pad device can adjust the output
size by changing the quantity of the pads or its thickness,
Adding more pads,larger gap between two rollers, and
when reducing the pads,it comes the smaller gap and
smaller output size.
9. 3.drive device is composed of two electric motors.V-belt drags the rollers
through drive of the grooved pulley, move and rotate in the relative direction.
In the crushing, the materials enter the feed opening and through the rollers,
rolled and grinded, the finished products will discharge from under the
chassis.
4.for safety, drive part should install the security cover according to the actual
situation respectively.
Application of Double Roller Crusher
The double roll crusher is applied in the industry of cement, chemical,
electric power, metallurgy, building materials, refractories and other sectors
for crushing medium hard materials such as medium and fine crushing of
limestone, slag, coke, coal and other materials.It is more superior than
ordinary crushers especially in the construction Materials Industry like pisolite
and greenbean shake production
12. TOOTHED ROLL CRUSHER
CONTAIN 1 OR 2 CURVED ROLL WORKING AGAINST A STATIONARY CURVED
BEAKER PLATE
THEY ARE MORE VERSATILE THAN SMOOTH ROLL CRUSHER BUT CANNOT
HANDLE VERY HARD SOLIDS
THEY OPERATE BY COMPRESSION,IMPACT AND SHEAR AND SO IT CAN
REDUCE MUCH LARGER PARTICLES
SUITABLE FOR FRIABLE AND BRITTLE MATERIALS LIKE COAL, SOFT LIMESTONE,
SLAG,CLAY ETC
13. CAPACITY OF ROLL CRUSHER
The capacity of a roll crusher will vary with:
The kind of stone
The size of feed
The size of the finished product
The width of rolls
The speed at which the rolls rotate
The extent to which the stone is fed uniformly into the crusher.
14. POWER CONSUMPTION OF ROLL CRUSHERS
WITHIN THE SAME REDUCTION RATIO POWER CONSUMPTION OF ROLL CRUSHER VARY WIDELY
THE POWER REQUIRED COULD BE GIVEN BY GENERAL EQUATION :
18. PROBLEM
QUESTION
IF CRUSHING ROLLS, 1M IN DIAMETER ,ARE SET SO THAT THE
CRUSHING SURFACES ARE 12.5mm APART AND THE ANGLE OF NIP IS
31.WHAT IS THE MAXIMUM SIZE OF PARTICLES THAT SHOULD BE FED TO
THE ROLLS ?
19. ANSWER
THE PARTICLE SIZE MAY BE OBTAINED FROM :
cos ∞ =(r1+b)/(r2+b)
In this case, 2 ∞ = 31
cos ∞ = 0.964
b = 12.5/2 =6.25 mm = 0.00625 m
r1 = ½ = 0.5 m
0.964 = (0.5 + 0.00625)/(0.5+r2)
r2 = 0.025 m = 25mm
