In situ diamond wires diameter determination of the external cutting rope

In situ diamond wires:diameter determinationof the external cutting ropeMarcello Filgueiraa,*,Daltro Garcia PinattibaLaborato ´rio de Materiais Avanc ¸ados (LAMAV),Universidade Estadual do Norte Fluminense (UENF),Av.Alberto Lamego,2000,Pq.Califo´rnia,28013-600Campos dos Goytacazes,RJ,Brazil bDepartamento de Engenharia de Materiais (DEMAR),FAENQUIL,CP116,12600-000Lorena,SP,BrazilReceived 11May 2004;accepted 13September 2004AbstractDiamond wires are cutting tools used in the slabbing of dimension stones.This tool consists of a steel cable B 5.0mm in diameter on which annular metal–diamond pearls (B ext 10.0mm,length 6.0mm)are mounted,with spacings of 20mm between them.The use of this technology has been expanded all over the world due to its advantages on the other slabbing techniques.Besides this,it is recognized that the spacings between diamond pearls are prematurely weared out,leading to a catastrophic steel cable rupture.To prevent this problem,a new technology to process diamond wires was proposed,called ‘‘in situ’’Technology (involves powder met-allurgy and rotary forging),which is composed of a braiding array of diamond composite wires over a Cu–Nb strength cable.This work deals with the determination of the optimum diameter for the external cutting rope.Ó2004Elsevier Ltd.All rights reserved.Keywords:Sintering;Diamond composite;Optimum diameter;Tensile tests;Cutting rope1.IntroductionDiamond wires are cutting tools for rocks (marble,granite,etc.),concrete and substitutes of saws in general [1–3].They are composed of an AISI 316stainless steel cable over which are assembled diamond sintered pearls (beads)with 10–12mm in diameter spaced 25mm be-tween each other.The slabbing operation is carried out with a driven pulley coupled to a motor which pro-motes the diamond wire rotation.The wire is passed through coplanar holes previously made in the rock,and the tension imposed to the wire is made by a motor mounted on trails,coupled to the cutting system.The utilization of this slabbing technology has been ex-panded allover the world,due to its advantages on the other techniques.Some of the disadvantages of the commercial dia-mond wires are:(1)the diamonds are concentrated only in the beads,evidencing a low specific diamond concen-tration along the wire;(2)it is observed a large amount of diamond pull-outs during cutting operations,evi-dencing a low adhesion of the pair diamond-bonding matrix;(3)it is affirmed elsewhere [4]that the AISI 316stainless steel cable breaks down mainly due to the erosion caused by the rock friction,as well as by the gen-erated scrap.To overcome these disadvantages,it was conceived the ‘‘in situ’’diamond wire,whose fabrication involves mechanical conformation processes such as rotary forg-ing and wire drawing,copper tubes restackings,and thermal treatments of sintering and recrystalization,as well explained in previous works [4–8].It was idealized the use of Cu–15vol.%Nb composite wires as the high tensile strength cable,covered with a external cutting rope made in bronze 4wt.%diamond composite,along0263-4368/$-see front matter Ó2004Elsevier Ltd.All rights reserved.doi:10.1016/j.ijrmhm.2004.09.004*Corresponding author.Tel./fax:+552227261533.E-mail address:marcello@uenf.br (M.Filgueira).International Journal of Refractory Metals &Hard Materials 23(2005)85–90/locate/ijrmhmthe overall wire surface(continuous diamond volume). This new diamond wire exhibits a higher specific cutting surface,because the diamonds are impregnated in all the bulk and surface of the wire,thus eliminating the spac-ings between beads of the commercial diamond wires.It is also eliminated the possibility of the cable failure by erosion.The so called‘‘in situ’’technology enables the diamond impregnation of the tool in the same time in which the wire is processed—a novelty.Table1gives the comparison of geometric data of diamond wires fabricated by pearls and‘‘in situ’’tech-niques.Diamond composite volume and surface in the ‘‘in situ’’wire are30and5times larger than pearls wire, respectively,and the cutting section of rocks are de-creased by36%.In the studied system the mechanism of failure of the external cutting rope is by the matrix wear,because the diamond crystals are sintered together with the bronze matrix,thus,one canfind diamonds into the entire wire bulk.Other matter of great importance is that when wiresÕrupture occurs,it is very easy to joint them to-gether by silver welding(enabling UTS and diamond adhesion maintenance)—a rapid and simple way to re-use the wires until its end of cutting capacity(1.23mm in diameter for this cutting rope—as measured and discussed in Ref.[6]).The braided wire shown in Fig.1is composed of127filaments of Cu–15vol.%Nb(/=0.36mm each)forming a core of4.68mm in diameter.In the sequence12wires of bronze4wt.%diamond(/=1.65mm eachfilament) are braided around the core giving afinal diameter of 8.00mm.The Cu–15vol.%Nb combines a resistance close to the steel wire and theflexibility of stainless steel, as shown by Filgueira and Pinatti[8].The Refs.[4,5]ex-plain how to process and arrange the Cu–Nbfilaments of the Fig.1(a)with guaranteed strength.In this sense, this work deals with the determination of the optimum diameter of the external cutting rope made of bronze 4wt.%diamond.2.ExperimentalThe bronze4wt.%diamond external cutting rope of the‘‘in situ’’diamond wires were processed as shown in Refs.[6,8],in diameters ranging from2.9to1.0mm. It was used a diamond concentration50(2.2carat/cm3;0.44g/cm3;0.1264cm3of diamond/cm3of tool)since this is the concentration used to cut dimension stones.Fig.2 shows the processingflow chart of the bronze4wt.% diamond external cutting rope.The materials used in this work are:De Beers SDA+6540/50mesh uncoated high quality diamonds—mean particle size350l m,com-mercial atomized bronze powder(75/60l m),and OFHC copper tubes.It is recognized that the diamond wires operates under traction,thus the tensile strength measurements of the external cutting rope is mandatory,and acts as a strong tool to the determination of the optimumTable1Comparative geometric data between pearls and‘‘in situ’’diamond wireData Pearls‘‘In situ’’/e(external diameter)10mm8mm/i(internal diameter)7mm5mmWidth5mm(pearls)1000mm(length/m) Spacing25mm Continuous Diamond volume/m a1000mm330,630mm3 Diamond surface/m b5,027mm325,133mm3Relation between ‘‘in situ’’/pearls Volume30 Surface5a Diamond composite volume/m:p=4Âð/2e À/2iÞ·width·num-ber of pearls/m.b Diamond composite surface/m:p·/e·width·number ofpearls/m.diameter of the cited rope.In this sense,groups of ten samples of each diameter was then submitted to tensile tests—the results were taken as a mean value.This was carried out in a MTS Universal Testing Ma-chine—mod.810.23M—cap.250kN,according to the ASTM E8M-97standard.Tensile velocity was of 1mm/min for all samples.Fatigue tests were also con-ducted for groups of 4samples of /=1.65mm in diam-eter,according to the standard ASTM E466-82.The loading levels were of 120–50MPa,150–50MPa,170–50MPa and 200–50MPa,at a frequency of 60Hz.It is also worth to say that all samples were tested at the an-nealed condition to ensure the possibility to compare the results.3.Results and discussionThe determination of the optimum external cutting rope depends on three parameters:(1)it must be desig-nated as optimum diameter the smaller as possible,to ensure that the final diameter of the ‘‘in situ’’diamond wires (diameter of the Cu–Nb inner core +diameter of the bronze–diamond cutting rope—see Fig.2)be de-signed for the maximal scrap generation in the quarry;(2)the minimal diameter must be adequate to the cut-ting conditions with diamond wires,it means that is not enough to process the external cutting rope with a very reduced diameter,because the tool must also to at-tend the conditions of mechanical strength;and (3)it must be designed according to the braided array of the Cu–Nb inner core.Fig.3shows the graph of the external cutting rope behavior when submitted to tensile tests,for various diameters.One can observe that for /=2.90mm,the angular coefficient of the curve changes.If an adjust-ment line is put between the points /=2.90mm and /=1.65mm until attain the point in which the rupture load is zero,the diameter /=1.20mm is found—linear regression (dashed line).Nevertheless,the rupture load for the bronze–4wt.%diamond wire measured for this diameter was F =180N.It leads to the affirmation that the initial three values of the curve indicate the tensions of adhesion diamond–bronze.Fig.4(a)and (b)show the fracture surfaces of a /=1.20mm bronze–4wt.%diamond wire.It is observed the contact diamond-diamond,consequently the bronze resistant section is very small when compared to the wire section,being strongly influenced by the presence of the diamond crystals.Therefore,the force F =180N is attributed to the adhesion between the pair bronze–diamond.In other words,for diameters down to /=1.65mm the bronze resistant section is not an important parameter,and rather it reflects the diamond–bronze bonding strength.Mixture of bronze 4 wt% diamond↓Cold isostatic pressing at 200 MPa, rubber matrix, ∅initial =12.87mm,∅final =8.00mm↓Sintering at 850°C/20 min., vacuum 2.10-4 mmHg ↓Capping into OFHC copper tube, ∅ext.=13.70mm,∅int.=9.20mm↓Rotary forging from ∅=11.45mm down to ∅=1.20mm↓Annealing at 650°C/20min., vacuum 2.10-4 mmHg, at each areareduction of 30%↓Pickling of the copper capping in a HNO 3+ H 2O solution at each desired diameterFig.2.Processing flow chart of the bronze/diamond external cap.M.Filgueira,D.G.Pinatti /International Journal of Refractory Metals &Hard Materials 23(2005)85–9087In Fig.5is verified that the rupture tension (ultimate tensile strength—UTS)remain constant at 230MPa,from /=2.90mm to 1.84mm,and then it diminishes drastically due to the effect of the presence of diamonds crystals,as discussed previously.This effect can also be seen in Figs.6–8,that show,respectively,the fractogra-phies of the bronze–diamond composite for diameters of /=2.44mm,/=1.84mm,and /=1.40mm,aftertensile tests.In all micrographs are seen that the dia-mond crystals are well distributed,and that with the diameter reduction a diamonds approximations take place,leading to the reduction inUTS.Fig.4.(a,b)Bronze–diamond wire fractographies./=1.20mm.Fig. 6.Bronze–diamond composite fractography./=2.44mm.UTS =230MPa.Fig.7.Bronze–diamond composite fractography./=1.84mm.UTS =230MPa.Fig.8.Bronze–diamond composite fractography./=1.40mm.UTS =155MPa.88M.Filgueira,D.G.Pinatti /International Journal of Refractory Metals &Hard Materials 23(2005)85–90As a comment,it is worth to observe from Figs.4, and6–8,that the adhesion bronze–diamond crystals is very low.This is attributed to the fact that the diamond used was the uncoated type—it influences strongly on the adhesion.Future works will be conducted using metal or ceramic coated diamonds,to improve adhesion to the metal matrix.The coatings on diamonds are usu-ally carried out by chemical vapor deposition(CVD), forming a surroundingfilm—strongly bonded to the diamondÕfaces,which reacts with the metal matrix dur-ing sintering,forming new phases or compounds at the interfaces—thus increasing the adhesive force.According to the optimized array shown in Fig.2,the inner core of Cu–Nb responsible for the high UTS (960MPa),andflexibility,presents diameter of/= 4.68mm—see Refs.[4,5].To complete the array with the cutting rope,it must be guaranteed that the overall surface of the Cu–Nb core is completely covered by the diamond composite of the cutting rope.According to this request,and considering the possibility of thebraiding array with12cutting rope wires for a reduced diameter—as explained in Ref.[4],one canfinally to determine the optimum diameter of the cutting rope, through the perimeter(p)equation:p¼pÂ/total)ð4:68þ/br–diam:ÞÂp¼12Â/br–diam: )/br–diam:¼1:66mmwhere B total is thefinal diameter of the diamond wire after braiding;B br–diam.is the diameter of the bronze–diamond external cutting rope.To ease the assembly,it should be considered the diameter of B br–diam.=1.65mm,providing a gap of 12·(1.66À1.65)=0.12mm.In this sense,thefinal diameter of the‘‘in situ’’diamond wire is/total¼/Cu–Nbþð2Â/br–diam:Þ¼4:68þð2Â1:65Þ)/total¼800mmFor this arrangement,the external cutting rope must operate at a maximum tension of60MPa.One can ob-serve from Fig.4that the UTS of the bronze–diamond composite for the diameter of/br–diam.=1.65mm is by 180MPa—3times higher.It means that the external cut-ting rope can operate with security.Finally,it is recognized that the diamond wires work under dynamic tensile loading.Thus samples of the bronze–diamond external rope were submitted to fati-gue tests,as explained in the experimental part.Fig.9 shows that the diamond composite fails at bout500cy-cles for a loading of200–50MPa.However,at the load-ing of120–50MPa,the diamond composite fails at7.106 cycles,thus indicating that the cutting rope,for the diameter of/br–diam.=1.65mm will not fail by fatigue, because it would probably fail previously by wear, during rock cutting operation(slabbing).4.ConclusionsThis work deals with the development of a new tech-nology to process diamond wires for slabbing of dimen-sion stones,the so called‘‘in situ’’technology.Here,was shown the important step of the external cutting rope determination.As result,one could conclude that the optimum diameter of the cutting rope for the designed arrangement was of/br–diam.=1.65mm,because is pre-sented an UTS=180MPa,which is3times superior to the tension of operation when cut rocks.Other impor-tant factor is that for the cited diameter,the external rope can sustain the fatigue imposed by dynamic loading.AcknowledgmentsThe authors would like to express their gratitude to the Materials Science and Engineering Department/ Faenquil—Lorena/SP—Brazil,for all the equipment used in the experiments.References[1]Thoreau B.Diamond impregnated wire for sawing hard abrasivestones.IDR1984;2:94–5.[2]Daniel P.More granites succumb to diamond wire.IDR1986;5:187–94.[3]Daniel P.Granite quarrying—cut waste and costs.IDR1986;1:1–4.[4]Filgueira M.In situ diamond wires production.PhD thesis.StateUniversity of North Fluminense,Advanded Materials Lab.,2000.153p[in Portuguese].[5]Filgueira M,Pinatti DG.In situ diamond wires.Part I.The Cu–15vol.%Nb high strength cable.J Mater Process Technol 2002;128:191–5.M.Filgueira,D.G.Pinatti/International Journal of Refractory Metals&Hard Materials23(2005)85–9089[6]Filgueira M,Pinatti DG.In situ diamond wires.Part II.Thebronze4wt.%diamond composite cutting rope.J Mater Process Technol2003;132:132–7.[7]Filgueira M,Bobrovnitchii G,Pinatti DG.A new route to processdiamond wires.Mater Res2003;63:327–33.[8]Filgueira M,Pinatti DG.Production of diamond wire byCu–15vol.%Nb insitu process.In:Proc of the15th Int Plansee Seminar,Reutte,Austria.Plansee Holding AG,vol.1,2001.p.360–74.90M.Filgueira,D.G.Pinatti/International Journal of Refractory Metals&Hard Materials23(2005)85–90。