FIELD OF INVENTION:
The present invention relates to a process for determination of grinding energy required for
grinding of ores in ball milling process. More particularly, the determination is based on
Knoop hardness no.
BACKGROUND OF THE INVENTION:
There is a huge demand for iron orefine (1-10 mm) to ultra-fine powders (0-0.15 mm) in
many industrial applications. They are used in bricks, paints and pigment manufacturing and
pharmaceutical & cement industry etc. Apart from the aforementioned positive impacts of
these fines, there are also negative impacts e.g. in iron and steel industry if they are directly
charged into iron making furnaces, namely blast furnaces, will result in packing of these
fines into voids, permeable areas and thus, decreasing the bed permeability. This in turn will
decrease the gas flow inside the blast furnace. So, agglomeration of such ultra-fines is an
essential task that is widely done on commercial scale by Palletisation process.
Pelletisation process involves rolling of moist iron ore fines ( <0.15 mm) with or without
binder to produce spherical balls of size 9 to 16 mm usually for charging into blast furnace
to produce hot metal. Quality of pellets so produced depends on various factors like
chemistry of ores (iron ore, flux etc.), granulametry of ore, dosage of flux, types of binder,
firing temperature of pellets etc. Among the aforementioned factors, one of the most
important factors that determine the green pellet quality is the granulametry of ore in terms
of ore fineness and suitable size distribution of the raw materials. For ensuring the right
granulometry of ore for production of good quality green pellets, grinding of raw materials is
carried out in ball mill at pellet plant. But fluctuation in feed ore characteristics due to
mechanized mining, use of advanced tools in handling and transportation of the fines,
deterioration of ore quality etc. result in frequent changes in granulometry of ore, and
destabilization of the plant thereby, resulting in deterioration of green pellet quality and
thus, decrease in quality of indurated pellet. Therefore, ascertaining the feed ore
characteristics for grinding process, in terms of grindability, is an imperative task.

Considerable research has been carried out for determination of grindability in terms of
grinding energy required to decrease the size of the particles in ball mill.
Patents in this field are as follows:
1. JP2879679: Method of testing hardness of micro region : It claims to develop a
testing method for determining the hardness of a micro region, into which an
indenter is pushed, from an indentation curve indicating a relation between a
penetration depth observed when an indenter in an arbitraty shape is pushed in and
an in indenting force.
2. JPH0353144:The grindability evaluation method which uses the grindability test
equipment of the solid raw materials: It claims that The load applied to per unit
vertical area of the solid raw material (4) by pressurizing unit (50) or roller (1) is set
to 0.03-0.30 Kgf/mm2. Based on the applied load, crushability level of roller or
pulverizing ball is estimated.
3. SU539260:Method of determining the grindability of ore materiailov: It claims to use
shatter test for determining the grindability of ore.
4. JPS61139745:Method for testing grindability: The purpose is to estimate the mill
capacity or grinding power of a grinding machine with good accuracy, by using a
substance to be ground obtained during the grinding of the substance to be ground
by the grinding machine or a substance to be ground simulating this grinding state
as a specimen.
5. TW201035545: vickers- hardness testing system and method: A vickers-hardness
testing system to be executed by a computer is provided in the patent.
6. US2005223798: Testing method for ball mills: The invention relates to a testing
method for designing a semiautogenous or an autogenous grinding circuit with at
least one ball mill for grinding ore.
7. US4026479: Method and system for maintaining optimum throughput in a grinding
circuit : In it a method and a system are disclosed for maintaining optimum
throughput in a grinding circuit of the type in which fresh ore is fed to a rod mill and
the ground ore from the rod mill, together with the ground ore from a ball mill
operated in a reversed circuit, are combined in a pump box and pumped to a cluster
of hydrocyclone classifiers.

8. F.C bond, the third theory of comminution: Test method to determine grinding
energy of ore: This widely used Bond work index is based on the principle that the
work input is proportional to the new crack tip length produced and equals the work
represented by product minus that represented by feed. This method requires a
closed-cycle grinding of the ore and uses a mill of size 30.5 cm X 30.5 cm rotating at
70 rpm with a ball charge of 20.125 kg as shown in the FIG. 1. But, this BWI
determination method is an iterative process and is very tedious & time consuming
and normally 40 to 50 hours if worked continuously. It also assumes that the ores
tested is not ductile in nature. This assumption implies that there are no variations in
material elasticity and thus, can lead to a certain degree of error.
None of the above mentioned patents are helpful in determining the grinding energy
required in ball mills in a fast and a high accuracy way.
OBJECTS OF THE INVENTION:
In view of the foregoing limitations inherent in the prior-art, it is an object of the invention
to develop a process for determination of grinding energy in fast and highly accurate
manner.
SUMMARY OF THE INVENTION
In one aspect, the invention provides a process for determining grinding energy of an iron
ore fines comprising steps of determining phases of an iron ore sample in percent,
encapsulating the iron ore sample in a mold using cold setting epoxy resin, determining
Knoop hardness no. (K) of the various phases of the iron ore sample at 50 gm. load, taking
weighted mean of the Knoop hardness number (K) of the various phases to calculate Knoop
hardness no. of the entire iron ore sample and determining the grinding energy of the iron
ore sample using a formula: Grinding Energy (KWH) = 0.000125K2 - 0.21856K + 106.024
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
FIG. 1showsa Bond's ball mill for determination of grinding energy.
FIG. 2shows series of steps of a process for determining grinding energy of ore fines in
accordance with an embodiment of the invention.

FIG. 3 shows the Knoop elongated diamond indenter shapein accordance with an
embodiment of the invention.
FIG. 4iltustrates graphical correlation between BWI and Knoop hardness in accordance with
an embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION:
Various embodiments of the invention providea process for determining grinding energy of
an iron ore fines, the process comprising steps of:determining phases of an iron ore sample
in percent; encapsulating the iron ore samplein a mold using cold setting epoxy
resin;determiningKnoop hardness no.{K) of the various phases of the iron ore sample at 50
gm. load;taking weighted mean of the Knoop hardness number (K) of the various phases to
calculate Knoop hardness no. of the entire iron ore sample; anddetermining the grinding
energy of the iron ore sample using a formula:Grinding Energy (KWH) =0.000125K2 -
0.21856K + 106.024
Shown in FIG. 2 is series of steps of a process (200) for determining grinding energy of iron
ore fines in kWH/ton.
At step (204), variousphases of a sample of iron ore fines are determined in percent. The
phase determination can be done in reflective ray optical microscopy or XRD.
At step (208),the iron ore sampleis encapsulated in a mold using cold setting epoxy
resin.10 gm. of the sample can be used for encapsulation in a mold.
The sample is polished using diamond solution.
At step (212), the encapsulated sample is mounted over the Leica microhardness tester for
determining the Knoop hardness number (K).Knoop hardness number (K) of various phases
of the iron ore sample is determinedat 50 gm. load.

The Knoop indenter is a diamond ground to a pyramidal form that produces a diamond-
shaped indentation with the long and short diagonals in the approximately ration of 7:1
resulting in a state of plane strain in the deformed region. The Knoop Hardness Number
(KHN) is the applied load divided by the unrecovered projected area of the
indentation.Shown in FIG. 3 is the Knoop elongated diamond indenter shape.
K=F/A = P/CL2
where:
F= applied load in kgf,
A = the unrecovered projected area of the indentation in mm2,
L = measured length of long diagonal indentation in mm,
C=0.07028 = constant of indenter relating projected area of the indentation to the square of
the length of the long diagonal.
The special shape of the indenter makes it possible to place indentation much closer
together than with a square Vickers indentation.
At step (216), weighted mean of the Knoop hardness number (K) of the various phases is
taken to calculate Knoop hardness no. of the entire sample. The weighted mean is the sum
of various multiplications of the Knoop hardness number (K) of various phases with
theircorresponding area percentage.
At step (220),the grinding energy of the iron ore sample is determined using the formula:
Grinding Energy (KWH) =0.000125k2 - 0.21856K +106,024 eq. 1
Generation of Grinding Energy Formulation:
Various samples of iron were takenand their Knoop hardness was calculated as per the step
204 to step 216. Later, their BWI were also calculated and plotted against their
corresponding Knoop hardness as shown in FIG. 4.
Thereby the relation is established between the Grinding Energy and the Knoop hardness
no. as eq. 1.

Experimental Analysis:
The effectiveness of the above mentioned process can be validated by the following
example. The following example should not be construed to limit the scope of invention.
The following samples 1 and 2 have been taken for determining grinding energy of ore fines
using the process (200), Grinding Energy (KWH), and conventional bond working index
(BWI).
Case study sample 1:

BWI: 9.76; Grinding Energy-KWH: 10.61; Error: 8.7%
Case study for sample 2 :

BWI: 11.46; Grinding Energy-KWH: 10.48; Error: 8.78%
Since in both case studies it is found that the error is less than 10%, therefore the process
(200) is effective.
Advantages
Using theprocess (200) it is possible to determine the grinding energy in a fast and a high
accuracy way. It takes maximum 10 hours todetermine the grinding energy.

We claim:
1. A processfordetermining grinding energy of an iron ore fines, the process comprising
steps of:
determining phases of an iron ore sample in percent;
encapsulatingthe iron ore samplein a mold using cold setting epoxy resin;
determiningKnoop hardness no.(K) of the various phases of the iron ore
sample at 50 gm. load;
taking weighted mean of the Knoop hardness number (K) of the various
phases to calculateKnoop hardness no. of the entire iron ore sample; and
determining the grinding energy of the iron ore sample using a formula:
Grinding Energy (KWH) =0.000125K2- 0.21856K +106.024
2. The process as claimed in claim 1, wherein the phase determination is done in
reflective ray optical microscopy.
3. The process as claimed in claim 1, wherein the phase determination is done by XRD.
4. The process as claimed in claim 1, wherein the Knoop hardness number (K) is
determined in Leica microhardness tester.