Aggregates required for a given job are generally specified by a full set of gradation limits and other relevant properties of the material. When rock is crushed, the product includes material of the size of the crusher setting, some slightly larger and the rest of the material smaller than the crusher setting. Crusher manufacturers publish grid charts, particle size cumulative distribution curves, and/or product size distribution tables to help predict the gradation of the crusher product. These charts, curves, and tables give the percentages passing or retained on standard size screens for each given setting of the crusher.

Screen Analysis of Product from Jaw Crusher, Percent Passing Screen Opening

Product

Size

(in.)

Closed Side Setting of Crusher (in.)

Product

Size

3/4

11.522.533.5456

(in.)

Over 10

Over 10

-10 +9

0-10 +9

-9 +8

02-9 +8

-8 + 7

07

-8 +7

-7 +60810

-7 +6

-6 +5

0051212-6 +5
-5 + 4411131414

-5 +4

-4 + 3.5077988

-4 + 3.5

-3.5 +3

077101198-3.5 +3

-3 + 2.5

0512131210108

-3 +2.5

-2.5 +231516141311118

-2.5 +2

-2 +1.5

0017171716141376

-2 +1.5

-1.5 +1

21926201915111076

-1.5 +0.75

-0.75 + 0.5

20201311865443

0.75 +0.5

-0.5 +0.25

40251311764443

-0.5 +0.25

Under 0.25

2016128767633

Under 0.25

Setting

0.75″1″1.5″2″2.5″3″3.5″4″5″

6″

The distribution of product sizes given in the table above is based on crushed limestone weighing 100 lb/cu ft with a specific gravity of 2.6. This same sort of information may be presented by the manufacturer in a set of curves for the various settings of the crusher. Typical screen analysis from primary crusherThe curves, one for each closed side setting, will give an estimate of the cumulative percentage of material passing a given screen size on the horizontal scale with the screen opening in inches on the vertical scale.

Percentage of Product Passing Square Opening Equal to Crusher Open Side Setting

Feed (%)

Type of Crusher

Run of Quarry

Scalped Percent

Scalped and  Recombined with Fines

Limestone

Jaw

 90 85 88

Gyratory

 90 85 88

Granite

Jaw

 75 75 75

Gyratory

 82 75 80

Trap rock

Jaw

 70 70 70

Gyratory

 75 70 85

 

A jaw crusher, like that of the Table below, is set with an open circuit (no recirculation) at 2 in. to produce 60 tons per hour (tph) of crushed limestone aggregate.

(a) How much of the output will pass a 1½-in. screen (i.e., minus 1½-in. material), and (b) how much of the material—percentage and tonnage—will pass the 1½-in. screen and be retained on the ¾-in. screen?

Screen Analysis of Product from Jaw Crusher, Percent Passing Screen Opening

Product

Size

(in.)

Closed Side Setting of Crusher (in.)

Product

Size

3/4

11.522.533.5456

(in.)

Over 10

Over 10

-10 +9

0-10 +9

-9 +8

02-9 +8

-8 + 7

07

-8 +7

-7 +60810

-7 +6

-6 +5

0051212-6 +5
-5 + 4411131414

-5 +4

-4 + 3.5077988

-4 + 3.5

-3.5 +3

077101198-3.5 +3

-3 + 2.5

0512131210108

-3 +2.5

-2.5 +231516141311118

-2.5 +2

-2 +1.5

0017171716141376

-2 +1.5

-1.5 +1

21926201915111076

-1.5 +0.75

-0.75 + 0.5

20201311865443

0.75 +0.5

-0.5 +0.25

40251311764443

-0.5 +0.25

Under 0.25

2016128767633

Under 0.25

Setting

0.75″1″1.5″2″2.5″3″3.5″4″5″

6″

The solution to each part, using the above table, is:

(a) Following the vertical column for the 2 in. setting shows that 63% of the output passes the 1½ in. screen. So the – 1½ in. material output will be 0.63 x 60 = 37.8 tph.

(b) In the column for a 2 in. setting, it is found that 20% of the output is between 1½ in. and 1 in. size (i.e., -1½ +1 in.) and 13% is between 1 in. and ¾ in. ( – 1 +¾). Therefore, the quantity of output passing the 1½ in. screen and retained on the ¾ in. screen is 33%. The rate of production in the 1½ in. to ¾ in. size range is 0.33 x 60 = 20 tph.

Typical screen analysis from primary crusher