the analysis of cuttability properties of model

8/12/2019 The Analysis of Cuttability Properties of Model

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The Analysis of Cuttability Properties of Model

Samples Prepared with Different StrengthNiyazi Bilim and Bilgehan KekeSelcuk University, Mining Engineering Department, Konya, Turkey

Abstract. Energy saving is very important parameter in the industry. Rock

excavation (cutting) machines represent a major cost item in the mining and tunnel

sector. Therefore, determining the optimum cutting conditions is major

importance in the sector. Otherwise prediction of the performance and selecting of

the rock cutting machines is very important. In literature, there are studies usually

related to the prediction of cutting performance referring to materials with

adjustable properties.

Specific energy is defined as the amount of energy required to cut a unit

volume of rock. In this study, rock cutting experiments were performed on eight

concrete samples which indicates model rock samples in-situ with small scale

linear cutting machine. During the cutting the specific energy value was calculated

from the electric energy required of machine was measured by using power

analyzer. In addition, physical and mechanical properties of the model concrete

blocks were determined then relationships between specific energy values

obtained from cutting tests and the model samples mechanical properties were

analyzed.In this study, concrete samples with different concrete class were used owing to

heterogeneous properties of concretes. Thus, mechanical properties of samples

were adjusted as required. Eight different concrete samples with using EN 206-1

standard C8/10, C12/15, C16/20, C20/25, C25/30, C30/37, C35/45, C40/50

concrete class were used as model specimens. These specimens were cut same

condition and calculated specific energies of samples. In addition, some

mechanical properties were carried out on these specimens with different concrete

class. In conclusion, the relation between specific energy and mechanical

properties of samples were determined.

Keywords: Cuttability, performance prediction, cutting theory, specific energy.

1 IntroductionExcavation cost is very high in mining and similar operations. Rock excavation

(cutting) machines represent a major cost item in the mining and tunnel sector.Therefore, determining the optimum cutting conditions is major importance in the

sector. Otherwise, prediction of the performance and selecting of the rock cutting

machines is very important. The rock cutting tests carried out in the laboratory is272 N. Bilim and B. Keke

also the most successful, reliable and efficient method to observe toolrock

interaction and estimate the tool forces [1]. Balc et al. [2] rock cutting test carried

out on rock samples, mineral and ore samples with different mechanical

properties. They used both the full-scale cutting tests and the small scale rock

cutting tests. Also, they analyzed to the relation between specific energy and

physical and mechanical properties of rocks as statistically. Fowell and McFeat-

Smith [3, 4] performed experimental studies to correlate specific energy obtained

by the small scale rock cutting tests to some rock properties such as cone indenter

index, cementation coefficient, Schmidt hammer rebound value and compressivestrength.

Specific energy is one of the parameters that describe the cutting efficiency in

laboratory and in field. In mechanical excavation studies, some rock properties

affecting the SE were investigated by different researchers [5, 6]. But, the

estimation of the cutting efficiency by using a single rock property is impossible.

Since many rock properties affect the cuttability of rocks specific energy values

were correlated, in the past, with rock properties by different researchers [4,11].

Bilim [12] calculated to specific energy (kWh/m), amount of excavation (m/h),

and feed rate (m/dk) values for performing analyses of cutting machines in


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ayrhan coal mining and derived to mathematical model for estimation of

specific energy. Copur et al. [13] searched for relations between optimum specific

energy obtained by the full-scale cutting tests and laboratory tests included

compressive and tensile strength, they also looked for relations between a

brittleness index obtained from macro-scale indentation tests and rock cutting

efficiency, including specific energy and cutter forces.

Cuttability is very important parameter for tunnel and ore excavation.

Cuttability are affected by many parameters. However, the most important

parameter affected to rock cuttability is rock properties. The most effective

parameter of rock properties can be regarded as mechanical properties of the

rocks. Therefore, in this study, it is aimed that mechanical properties of the rock is

determined to the effect on rock cuttability. Also, it is planned to derive a

mathematical equation for practically estimation of rock cuttability. In accordance

with this purpose, the tests were carried out by preparing model rock samples.

In this study, rock cutting experiments were performed on different seven

model samples with small scale linear cutting machine during the cutting the

specific energy value was calculated from using with load cell. In addition,

physical and mechanical properties of model samples were determined.

Relationships between specific energy values obtained from cutting tests and

model samples mechanical properties were analyzed.

2 Preparation of Model SamplesMany study carried out for estimation of cutting machine performance and

cuttability have been carried out to cutting tests in the laboratory on different rock

samples. Hence, estimation models derived for estimation of cuttability giveThe Analysis of Cuttability Properties of Model Samples 273

accurate results at similar rocks used in the tests. Thus, there is no definitive

accepted model for estimation of rock cuttability, nowadays. The biggest cause of

this condition is heterogeneous of rock units. In other words, rock units have many

parameters affecting to cuttability. To derive accurate model for heterogeneous

rock units, an estimation model including whole parameters affecting to cuttability

is required. For example, there are good estimation models accepted by scientist

for heterogeneous rock mass in mining (RMR and Q etc.). These models have

been formed by using many parameters determining rock mass properties to

analyze of rock mass and good results have been obtained. If an estimation modelis formed by evaluating many parameters affecting cuttability, this model will be

very useful. However, a sophisticated study carried out for estimation of rock

cuttability is required to effort, time and cost. It may be appropriate in large

project such as a tunnel project excavated with TBM. Eventually, the models to be

derived for estimation of rock cuttability can be performed easily by scientist and

it should require less effort. With all this information, these studies were

conducted to derive an estimation model by using two different properties

affecting rock cuttability.

The model samples for cutting tests have been prepared in concrete classes that

stated in EN-206-1 test Standard. Different cement, water and aggregate ratio have

been prepared for each concrete class. The aim of this is to form model samples in

different endurance properties. 5 cube samples have been prepared from each

concrete class, so 35 cube concrete samples have been prepared in total. All ofmodel samples are 7*7*7 cm. these model samples have been firstly left in water

along 28 days. Later, tests have been started. As shown in Fig. 1 preparations of

model samples.Fig. 1 Preparation of model samples

274 N. Bilim and B. Keke

3 Mechanical Properties of Model SamplesUniaxial compressive strength (UCS) and Schmidt hardness tests carried out on

the model samples. Then, the results as shown in Table 1.Table 1 Mechanical test results of model samples


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Concrete

class

Test Results

UCS

(MPa)

Schmidt

Hardness

Density

(gr/cm3)

C12/15 18.7 21.5 2.35

C16/20 22.1 22.7 2.35

C20/25 30.2 24.6 2.40

C25/30 41.9 32 2.40

C30/37 50.2 32.3 2.39

C35/45 48.5 32.5 2.37

C40/50 55.9 33.4 2.38

4 Cutting Tests and Determining of Cutting Energy

4.1 Linear Cutti ng TestsThe small-scale cutting test is discussed in detail by McFeat and Fowell [3, 4 and

7]. The test results are classified as index values and evaluated according to

previously accumulated field performance data. The basic disadvantage of this test

is that the predictions using this method are based on an index cutter instead of a

real life cutter. This test has been developed by McFeat Smith and Fowell [3] and

then using Bilgin and Shariar [14] to simulate the cutting action of chisel tools and

to measure the corresponding cutting properties of model rock materials. It is

suggested a standard laboratory rock cutting test by international rock mechanic

commission (ISRM) [15] to measure the cuttability of rocks. Specific energy is

defined as the amount of energy required to cut a unit volume of rock. Specific

energy value is the most popular method in order to predict the efficiency of

cutting machines. In this test a cubic of 7 cm. in length is fixed in a table of a

shaping machine and cut by a chisel pick having a rake angle of5 degrees, a

clearance angle of 5 degrees, tool width of 12.5 cm and a cutting depth of 2 mm.

as a standard conditions. The tool forces in three orthogonal directions are

recorded using a force dynamometer and the specific energy in MJ/m3 iscalculated by dividing the mean cutting force FC by the yield Q (the volume ofThe Analysis of Cuttability Properties of Model Samples 275

rock or mineral obtained by unit distance of cut). The test results, which may be

classified as index values, are evaluated according to previously accumulated field

performance data. As shown in Fig. 2 linear cutting test set.Fig. 2 Linear cutting test set

5 Development of Cutting Theory for RockIn cutting theory, firstly, the relations between the cuttability and some

mechanical properties of model rock samples have been evaluated. Later, the

meanings of these relations have been evaluated as statistical. As meaningful,

resulting (in the light of this study, and the data obtained from digger) is derived

from a theory of rock cutting use of relationships. The biggest difference from the

other cutting of the theory is that is made by creating a model of rock samples.The biggest advantage of this kind of rock samples be homogeneous, hence many

physico-mechanical property of the fixed order of rock has been. In this way, the

rocks cuttability, the evaluation of the parameters affecting the hardness and

resistance has been more easy and correct. The resulting equations are given

below the graphics and showing the relationships created (Figs. 3 and 4).

As you can see from the Figs. 3 and 4 between specific energy and uniaxial

compressive strength, Schmidt hardness meaningful relationships has been

achieved. This is obtained from the relations in the light of the theory of multiple

regression were applied in order to develop a mathematical model. Cutting


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prediction model for rock (cutting theory) is presented in equation 1 which was

obtained by multiple regressions.276 N. Bilim and B. KekeFig. 3 Relation between Schmidt hardness and specific cutting energyFig. 4 Relation between Uniaxial compressive strength hardness and specific cutting energy

SE=32.45+0.59UCS-0.71SH

SE: Specifik energy (MJ/m3)

UCS: Uniaxial Compressive StrengthSH: Schmidt HardnessThe Analysis of Cuttability Properties of Model Samples 277

6 ConclusionsHomogeneous model samples have been prepared in this study and have been

researched the influence of rock properties in conclusion of cutting tests. it has

been determined that the most effective parameter in rock cuttability is hardness

and strength. The aim of this study is to estimate the most correct rock cuttability,

so an estimation model has been developed. The rock cuttability has been

estimated easily with this model.

the analysis of cuttability properties of model

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