ORIGINAL PAPER

Prediction of sawing performance based on indexproperties of rocks

Fatih Bayram

Received: 2 December 2011 /Accepted: 22 August 2012# Saudi Society for Geosciences 2012

Abstract Performance analysis of all systems used in indus-trial production is very important subject in terms of capturingthe low production cost. This subject is also important forchoosing production methods in natural stone processing.Circular sawing is a commonly used method in natural stoneprocessing. The preliminary prediction of circular sawingperformance is very useful for stone producers. In this study,the prediction of sawing performance from some index prop-erties of stones was conducted. The unit wear on diamondsegments was evaluated as performance criteria. The statisti-cal analysis was carried out, and this performance parameterwas predicted from some index properties including coneindenter hardness, Shore hardness, Böhme surface abrasion,and brittleness. The most suitable prediction equation derivedfrom regression analysis was selected. It was determined thatthis equation was statistically reliable for prediction of unitwear for natural stone processing.

Keywords Natural stone . Circular sawing . Unit wear .

Index properties . Regression analysis

Introduction

Natural stones are widely used for construction and decora-tion purposes. Natural stone blocks should pass some oper-ations in order to offer for human usage. Differentprocessing methods and machines are used in natural stoneprocessing operations. One of the machines used in produc-ing and processing of natural stones is a circular sawingmachine. Circular sawing machines have been widely used

in a variety of applications, including sawing, cutting, split-ting, grinding, and trimming of stone. These machines canbe successfully used in these applications because they sawprecisely and rapidly. Furthermore, they are flexible, eco-nomical, and easy to operate.

The most important subject in circular sawing system isthe more effective and more economical usage of diamondsawblades. Therefore, the prediction of sawing performanceis very important in cost evaluation and process planning.Unit wear is the most convenient parameter to determine thesawing performance. It is the amount of wear on diamondsegment occurring by sawing of definite stone surface. Thepreliminary prediction of circular sawing performance isvery useful for stone producers.

Circular sawing method was investigated by a number ofresearchers. The first studies on circular rock sawing systembegan in the late 1960s, and further early studies were donebetween 1960 and 1980 with the technology of those years.However, more detailed and professional studies on circularsawing system have been performed since 1980s. Especial-ly, the mechanism and processing of the circular sawinghave been well-documented. General applications, principalguidelines, sawing mechanism and sawability, saw design,materials and manufacture, and friction in sawing are amongthe topics that have received attention for circular sawing(Ertingshausen 1985; Luo and Liao 1995; Luo 1996, 1997;Konstanty 2000, 2002; Brook 2002; Xu et al. 2003; Wei etal. 2003; Ilio and Togna 2003; Delgado et al. 2005; Poliniand Turchetta 2005, 2007).

Wright and Cassapi (1985) found that rock hardness wasclosely related with wear and energy consumption underconstant sawing conditions on different granitic hard rocks.Cassapi et al. (1987) performed experimental studies withbridge sawing machine and correlated the sawing forceswith engineering properties of rocks. Pai (1987) stated thatspecific energy and power consumption were dependent on

F. Bayram (*)Department of Mining Engineering, Aksaray University,68100 Aksaray, Turkeye-mail: fbayram@aksaray.edu.tr

Arab J GeosciDOI 10.1007/s12517-012-0668-5

several parameters at the grinding stage of sawing process.Wright and Tagg (1998) emphasized that sawability andabrasivity were the two important elements in selectingcircular saw properties. Xu (1999) examined the frictioncharacteristics in granite sawing with diamond segmentedcircular saws. The researcher measured the sawing forcesand determined the specific sawing energies. Li et al. (2002)explained that the wear on circular sawblade depended onmachine parameters and their combination with each other.Eyuboglu et al. (2003) examined the statistical relationshipsbetween rock parameters and wear on segments and devel-oped a wear model. Ersoy and Atici (2004) examined thesawing forces and specific energies by changing advancerate and depth of saw at constant peripheral speed on circu-lar sawing machine. Ersoy et al. (2005) performed sawingexperiments by changing advance rate and depth of saw atconstant peripheral speed with two different sawblade andcorrelated with rock properties. Buyuksagis and Goktan(2005) performed experimental studies on sawing perfor-mance with real marble samples. Buyuksagis (2007) inves-tigated the effects of sawing mode (up and down sawing) ingranite sawing. Kahraman and Gunaydin (2008) found astrong linear correlation between indentation hardness indexvalues and the hourly production of the circular saws.Buyuksagis (2010) determined the effects of diamond seg-ment characteristics (diamond concentration, matrix compo-sitions, matrix hardness, etc.) on sawing performance. Ucun etal. (2011) investigated the effects of diamond concentration onsawing forces, power consumption, and specific energy at aconstant sawing condition. Guney (2011) derived the modelsthat include surface hardness and crystal size for the predictionof hourly slab production of carbonate rocks using large-diameter circular saws. Sengun and Altindag (2012) predictedthe specific energy of rocks in cutting process using somephysical and mechanical properties.

In previous studies, there is no study related to predictionof unit wear from index properties. The aim of this study isto investigate the correlations between sawing performanceparameter (unit wear) and index properties (cone indenterhardness, Shore hardness, Böhme surface abrasion, andbrittleness) and to conduct statistical models for predictionof sawing performance parameter. These index properties ofrocks were selected for statistical analysis due to relationswith sawing mechanism. The most suitable statistical modelwas selected for prediction of unit wear according to bestsubsets regression. These obtained models have been veryimportant for stone producers.

Experimental studies

Sawing experiments were performed by fully automaticcomputer assisted circular sawing machine. This machine

was designed and developed in Hacettepe University, Min-ing Engineering Department. The machine parameters ef-fective on sawing (reactional sawing forces in X, Y, and Zdirections; vibration; consumed energy, etc.) can be mea-sured and sawing conditions (advance rate, peripheralspeed, sawing depth, etc.) can be controlled accurately onthis machine (Fig. 1). The sawing head of the machine canmove upward–downward on the vertical axis, and the wag-on of the machine can move rightward–leftward on thehorizontal axis mechanically. These machine movementsare supplied by linear guideway and ball screws. Sawingprocess is realized with four AC motors, and their powersvary 0.37–11 kW. The main motor giving rotational move-ment to the circular saw has an 11-kW power. It is possibleto settle circular saws having diameters of 400, 500, and600 mm on the machine. Two inverters were employed tocontrol the peripheral speed and advance rate, respectively.Three-dimensional reactional sawing forces were measured

Fig. 1 A fully automatic computer assisted circular sawing machine

Fig. 2 A special designed wear measurement equipment

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by means of platform-type (single point) load cells. Alloperations in the machine could be controlled by computersand recorded in 250-ms intervals.

The wear was measured using special designed measureequipment (Fig. 2). This equipment consists of three lineargauges (one of them for vertical measurements, the others forhorizontal measurements), platform specially produced forthese gauges, digital signal converter, software for transferringmeasured data, and computer for collecting measured data.The wear measure equipment is a new design and techniquefor determining the wear on segments accurately.

In this study, six different types of real marbles wereused. The mini-blocks from these natural stones were pre-pared as in 20×30×50 cm dimensions. The sawing opera-tions were performed under constant sawing conditions at50 m/s peripheral speed and 900 mm/min advance rate for

each natural stone in 60 mm constant depth of saw. Thesawing operations were repeated five times for each stone.The amount of water used in sawing was arranged as 20–22 l/min considering the saw blade diameter. A circular sawblade used in this study had a diameter of 500 mm and 30impregnated diamond segments with C24 concentration.The dimensions of the each segment are 40 mm in length,5.5 mm in width, and 7 mm in height.

Index properties of natural stones

In this study, index properties of natural stones (cone in-denter hardness, Shore hardness, Böhme surface abrasion,and brittleness) were determined using different test meth-ods. The index properties of these natural stones tested aregiven in Table 1.

Cone indenter hardness

The cone indenter hardness test was developed by the Na-tional Coal Board (NCB) in UK. The test procedure wasdescribed by NCB (1977). It is usually used to determinesawability, cuttability, drillability, and for the estimation ofuniaxial compressive strength of intact rock. The dimen-sions of test specimen were 12×12×6 mm.

Shore hardness

The Shore hardness test measures relative hardness of rocksin terms of the elasticity of the material. The Shore hardnessof natural stones was determined according to ISRM (2007)

Table 1 Some mechanical and index properties of natural stonestested

Commercialnames of stones

CIH SH BSA UCS TS B

Afyon White 4.33 49 37.09 51.45 6.22 12.64

Afyon Violet 4.54 42 33.85 73.94 5.49 14.24

Afyon Tigerskin 4.87 56 35.73 40.95 7.8 12.64

Muğla White 4.17 42 30.85 65.31 4.77 12.48

Afyon Pink 5.68 58 23.09 46.71 6.32 12.14

Afyon Grey 4.17 51 36.35 49.65 6.53 12.73

CIH cone indenter hardness, SH Shore hardness, BSA Böhme surfaceabrasion (cm3 /50 cm2 ), UCS uniaxial compressive strength (MPa), TStensile strength (MPa), B brittleness [preferred by Altindag (2008) asB ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiðUCS� TSÞ=2p

]

Fig. 3 The relationshipsbetween unit wear and indexproperties

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standards. The minimum test specimen volume of 80 cm3

was prepared for each natural stone in this test.

Böhme surface abrasion

The Böhme surface abrasion test measures the amount ofabrasion on the material surface through friction. These testswere carried out according to Turkish Standard, TS 699(TSE 1981). The dimensions of test specimen were 71×71×71 mm.

Brittleness

Brittleness index is one of the important index properties ofrocks, but there is no universally accepted brittleness defi-nition. Brittleness is generally defined as the function ofuniaxial compressive strength and tensile strength of therocks. In this study, brittleness concept suggested by Altin-dag (2008) was used.

The uniaxial compressive strength and tensile strengthtests were realized according to ISRM (2007). Uniaxialcompressive strength tests were conducted on core sampleshaving a diameter of 54 mm and length/diameter ratio of2.5. Brazilian tensile strength test was used for determiningthe tensile strength of natural stones. These tests were per-formed on core samples having a diameter of 54 mm andheight/diameter ratio of 0.5.

Statistical analysis

The data obtained from this studywere analyzed usingMinitab15 statistical software. The sawing performance parameter andindex properties were initially correlated. The relationshipsbetween them were investigated graphically, and results weregiven in Fig. 3. As seen in Fig. 3, unit wear is well correlated toindex parameters. The quadratic model was conducted todetermine the correlations among the variables. Unit wear ondiamond segment positively related to cone indenter hardnessand Shore hardness, and the coefficients of determination were0.86 and 0.91, respectively. Unit wear inversely related toBöhme surface abrasion and brittleness, and the coefficientsof determination were 0.86 and 0.91, respectively.

The relationships between unit wear on diamond segmentand index properties of natural stones were also investigatedstatistically. For the statistical evaluation, each parameterincluded in the research was taken as a variable. Unit wearwas defined as dependent variable, and cone indenter hard-ness, Shore hardness, Böhme surface abrasion, and brittle-ness were categorized as independent variables. Thedescriptive statistics of variables were given in Table 2.

The selection of variables for the most suitable statisticalmodel was carried out using the best subsets regressionmethod. The adjusted R2 and Mallows’ Cp were used in thisregression method for selecting the most adequate subset.Adjusted R2 is a modification of R2 that adjusts for thenumber of explanatory terms in a model and is computedby taking the sample size into consideration. Mallows’ Cp is astatistic used as an aid in choosing between multiple regres-sion models that are compared. The Cp statistic is defined as

Table 2 Descriptive statistics ofvariables used in analysis Variables Data Mean Standard deviation Variance Minimum Maximum

Unit wear (UW) 6 0.02253 0.00578 0.00003 0.01614 0.03297

Cone indenterhardness (CIH)

6 4.627 0.580 0.336 4.170 5.680

Shore hardness (SH) 6 49.67 6.77 45.87 42.00 58.00

Böhme surfaceabrasion (BSA)

6 32.83 5.27 27.76 23.09 37.09

Brittleness (B) 6 12.816 0.731 0.534 12.149 14.247

Table 3 The results of best subsets regression

Adjusted R2 Mallows’ Cp Coneindenterhardness

Shorehardness

Böhmesurfaceabrasion

Brittleness

81.3 12.7 X

79.4 14.2 X

93.0 4.1 X X

87.3 7.5 X X

97.2 3.1 X X X

93.6 4.5 X X X

94.9 5.0 X X X X

Table 4 The analysis of variance of regression model for unit wear

Source Degree offreedom

Sum ofsquares

Meansquare

Fvalue

p(probability)

Regression 3 1.6534E−04

5.5115E−05

59.79 0.016

Residual 2 1.844E−06

9.22E−07

Total 5 1.6718E−04

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a criterion to assess fits when models with different numbersof parameters are being compared. The results of best subsetsregression is given in Table 3.

The model having the highest adjusted R2 and the lowestCp values should be preferred as the most suitable regressionmodel when taking into account the coefficient of determi-nation and Mallows’ Cp criteria. According to results ofanalysis given in Table 3, the italic written choice wasselected as the most suitable regression model for predictingthe unit wear. The unit wear could be predicted more reli-able from cone indenter hardness, Shore hardness, andbrittleness.

The multiple regression equation for this model is formu-lated as follows,

UW ¼ 0:0252þ 0:0131CIH� 0:000596SH� 0:00264B ð1ÞThe coefficient of determination (R2) of this equation was

0.99, and this model can be accepted as a highly reliableestimation model for unit wear values.

The analysis of variance for the validation of Eq. 1 wasperformed, and the results are given in Table 4. According toTable 4, the model based on the regression coefficients isstatistically significant at 95 % confidence level.

The relationship between actual and calculated values ofunit wear is given in Fig. 4. It can be seen from Fig. 4 thatthe calculated values reflect the real values very well (R20

0.988).

Conclusions

In this study, unit wear on diamond segments in circularsawing operation based on the rock index properties wasanalyzed using the method of multiple regression and thebest subsets regression methods. The following results wereput forward:

1. Unit wear values were correlated with some index prop-erties of natural stones. According to high correlations,these index properties could be used for predicting theunit wear.

2. Cone indenter hardness, Shore hardness, and brittlenesswere selected by the best subsets regression for predic-tion of unit wear.

3. The derived estimation equation is highly reliable forpredicting the unit wear (R200.99).

This derived estimation equation is only valid for realmarbles, but similar studies can be performed for othernatural stones (limestones, granites, etc.). Consequently,the index properties of natural stone can be easily used forpredicting the sawing performance. This study is very usefulfor stone producers.

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