Significant producers of diamond grains
Modern, composite materials: non-ferrous metal alloys reinforced with hard particles, wood composites, plastic composites reinforced with glass fibers, nickel super-alloys (Hastalloy, Waspalloy, Inconel 718, Udimet720) and titanium Ti6Al4V, TiAl) [1-5] requires the development of technology taking into account abrasive tools with new binders [6-9].It is emphasized that provided affective work tools in the optimal adjustment of the characteristics of grinding machines, machining parameters, the characteristic of tools and a method of cooling and dressing. Typical bonded abrasive tool includes: super hard grains (diamond cubic boron nitride, mono-or microcrystalline microstructure), filler(corundum, silicon carbide, boron nitride etc.), binder (sintered metal, electroplated, resin, ceramic, hybrid), modifiers (homogenizers, greases), body (metal, ceramic, polymer). Currently as bonded abrasive products are mainly used synthetic diamond or cubic boron nitride grains. Significant diamond grains producers were shown in table 1 
|Producer||Trade name of diamond||Grains morphology||Application|
|Sandvic Hyperion, USA||MBG 600||Irregular, sharp, friable||Coarse and fine grinding ceramics, glass and precious|
|MBG 640||Cubooctahedral crystals with high|
impact and fracture strength,
free cutting capability
|RVG||Irregular shapes, medium friable crystals||Precision grinding and finishing of tungsten carbide and carbide, grinding of|
|RVG 800||Irregular shape, superior free capabilities due to controlled micro fracturing mode of crystals|
|RBI - uncoated||Irregular shape, medium friable crystals||grinding of tungsten carbides and PCD inserts|
|SPR||Uncoated economic grade grain, the friability of SPR enables controlled diamond fracturing, wheel self- sharpening and free cutting action|
|Element Six, USA||PDA 657||It is suited for used in less applications where sharp cutting characteristic are important|
|microchipping structure, friable||Grinding of cermets and elements of technical ceramic|
|Gems Superabrasives, China||GRD 10|
|Multi crystal shape, consisting of many micro crystals with slight friability enable excellent self- sharpness||Grinding of soft Stones cutting,, sharpening, grinding ceramics and rubber|
|Lands, USA||LS 070||Ultra friable, irregular shape||Specialized grinding benefiting from free cutting crystals|
|LS 100||Friable, irregular shape|
|LS 600F||Uniform, blocky friable||Grinding lapping, polishing of cemented carbide, special steels, glass, natural stone|
|Kingray New Materials & Science Technology Co., China||JRI – typ A|
JRI – typ B
|irregular shape||Grinding of nonferrous hard alloys|
|Changha 3 better ultra HARD MATERIALS, China||SMD 690||Premium grade grain with high strength and great thermal stability|
|Sharp crystal shape||Grinding stones ,ceramics, polishing of hard materials optical glass grinding|
|RVD||Irregular crystal shape preferably self-sharpness||Grinding of hard alloy, non-ferrous metal, polishing of natural diamond|
|RVE||Friable and strong self-sharpness, policrystallic shape, low hardness||Fine processing ceramics, optical glasses, grinding, polishing of nonferrous metals and nonmetallic materials, PCD, carbide, granite|
|SF Diamond, China||SFD 10||Irregular shape, rough surface low strength||For grinding tools, which work with low load|
|Irregular crystal shape, rough surface, low strength|
|Comparatively regular crystal shape, medium strength||For grinding wheels, which work with medium and low load|
|SDM-c||Dark green color, medium tough, micro-friable multinano crystal, irregular shape, perfect self-sharpen ability|
|The Institute of Super Hard Materials Kiev Ukraine||AC 4|
|Irregular shape, friable, low strength||Grinding of brittle materials (ceramic, hard alloys, glass)|
|Irregular shape, less friable, medium strength|
|Comparatively regular crystal shape, medium strength|
In general, monocrystalline grains, used for tools with vitrified bond are assigned for grinding of flat and shaped surfaces, for example grinding of internal surfaces of Titan alloys and sharpening (fig. 2). Microcrystalline grains are complexes consisting of collection of small microcrystals with sizes ranging from one to a few microns, characterized by a higher mechanical strength, and higher ductility of monocrystalline grains (fig. 3)
The microcrystalline grains are recommended for grinding operations, where surface quality is the main processing criterion. The fillers can be alumina, silicon carbide, tungsten, zirconium silicate etc. It is assumed that the filler, introduced into the binder, protects the seed prior to the dynamic action of chips (typically having a higher temperature) and that increases the strength properties of the sinter, the thermal resistance and wear resistance, also taking part in the grinding process. The binder is a factor connecting the embankment of grain in the wheel causes the maintenance work until the grains have sharp edges, thereby induced on the self-sharpening effect of the grain. The efficiency of binders application provide features such as adequate strength of fixing force of particles in the binder, wear resistance, the possibility of sintering of the tools below temperature of graphitization (diamond) or active oxidation (CBN), having long thermal conductivity allowing for intense heat removing from the grinding zone without accumulation, the coefficient of thermal expansion close or identical with the coefficient of thermal expansion of the abrasive grain, proper hardness and strength, no reaction with work-piece material [6-8, 11-13]. Vitrified binders are primarily glass or devitrificate from the multicomponent system, received from synthetic chemicals with very high purity [6, 9].
They are divided into a low-melting binder (sintering temperature up to 730o C), medium (sintering temperature up to 880oC) and a high-melting (sintering temperature above 900oC). The most characteristic systems are borosilicate glasses modified with various oxides (Na20, Li20), calcium-silicate glasses, modified by V205, Fe203 or P205, lead-borosilicate devitrificates, barium-borosilicate with the addition of bismuth oxide. The most famous research centers dealing with binders for super hard tools including vitrified bond are located in Worceaster (GE company-USA), Aachen(RWTH-Germany), Sankt Petersburg (Ilyich company –Russia), Kiev (Institute of Super hard Materials –Ukraine), Zhengzhou (Zhengzhou Concern Hongtuo Superabrasive Products Co.-China). The Institute of Advanced Manufacturing Technology is conducting researches aiming at obtaining ceramic binders for super abrasives tools with controlled physical and mechanical properties and testing tools containing these binders. This publication shows the results of research of new vitrified (ceramic) binders and testing of grinding tools with these binders for the latest generation of composite BNDCC (boron nitride dispersive in cemented carbide) of various grit size of cubic boron nitride grains.
2. Experimental section
2.1. Part I Preparation and study of some physical and mechanical properties of glasses
2.1.1. The starting materials and methods of research
The study selected five variants of glasses from the Si02-Al203-B203-Na20-Ba0 system. The following were used as starting materials:
silicon dioxde -Si02 pure
hydrated aluminum nitrate Al (N03)3 x9H20 of high purity or aluminum hydroxide Al (0H) 3
barium carbonate BaC03-pure
boric acid H3B03-pure
sodium carbonate Na2C03-pure
After accurate grinding, sieving through a 0.63mm sieve and mixed, raw materials were placed in corundum crucibles and heated at a temperature above 1,350° C. After fritting (hot melt glass pouring into cold water) and once again the glass was milled and sieved. All glass frits were completely transparent with bluish color. On the received materials the following tests were carried out:
the density of helium, on Accu Pyc II 1340V10 helium pycnometer using 5 parallel samples;
the X-ray diffractometer of Panalytical Empiriam with copper lamp in the range of 2 theta angle of 5 to 90 degrees;
calculation of thermodynamic stability using algorithm VCS for sets of glasses in temperatures of 700, 900, 1300 and 1500° C on two assumptions: the total miscibility of liquid and vapor phases or total immiscibility liquid and vapor phases;
the reactivity of raw materials of glasses and the melt glasses using differential scanning calorimetry (DSC-device STA-449 F3 Jupiter)
the wettability of glasses to the substrate of silicon carbide or sintered alumina (cubitron) on the high-temperature microscope of Leitz -Watzler type by sessile-drop method.
microscopic observation (SEM)of transverse specimens after testing the wettability
the Young's modulus of glass using a flaw with the head broadband
the three-point bending strength of trabecular glass, describing the work of destruction by using a machine Zwick Roell Z2.5
2.1.2. Results and discussion
Test glass belonged to the group of light, characterized by a low density, ranging between 2.34 (W4), and 2.69 g/cm3 (Ba23bis). It was evident that with the reduction of silicon dioxide content in the glass, decreasing the density of the glass increased A slight increase in the content of barium oxide, the constant of silicon dioxide and reduced alumina content did not affect significantly the increase in density. The results are summarized in Table 2
|The variant of glasses||Density [g/cm3]|
|Ba 23 bis||2,6912|
2.1.3. Calculations of thermodynamic stability of the glasses by algorithm VCS
Chemical stability of the connections between components of the glasses was determined by calculation of the thermodynamic potential of components by VCS algorithm, which takes into account the probable stability of the reaction products. Equilibria calculations were performed for the four variants of the glasses of the SiO2-Al2O3-BaO-B2O3-Na2O system in temperatures 700° C, 900° C, 1,350° C, 1500° C at atmospheric pressure 1013 hPa. The molar ratios of the components were adopted taking into account their actual values. It was assumed that the component of glass within these ranges of temperatures may occur: in a multicomponent gas phase and condensed phase pure (liquid and solid). It is not known whether the active phase pure liquid form (that are immiscible with each other) or a liquid phase formed of unlimited miscibility, therefore, the calculation was performed by two assumptions out. Of the approximately 100 likely stable compounds there were 10, of which the solid 3. Summary of solid stable compounds glass as an example of option 2 are shown in Tables 3 and 4.
|Name of compounds in solid phase||700o C||900o C||1350 o C||1500 o C|
According with the first assumption at high temperatures (1350, 1500° C) there should be stable three compounds: an aluminum borosilicate (Al6BSi2O13), barium silicate (BaSi2O5) and silicon dioxide (SiO2). In the second assumption the second barium silicate (BaSi2O5) presented only one. Similarly were in the other glasses. The verification of the existence of these compounds in the glass was carried out on the basis of X-ray examination.
|Name of compounds in solid phase||700oC||900oC||1350oC||1500oC|
2.1.4. X-ray research of the glasses
The study of X-ray glasses clearly showed amorphous structure, as evidenced increase in the background at low angles and lack of educated, sharp peaks throughout the angular range. (fig. 4-X-ray glasses of W1). The existence of crystalline barium silicate (Al6BSi2O13) was not found.
2.1.5. Differential scanning calorimetry research
Thermal analysis of the five types of the glass raw materials and glass of W1 variant was based on differential scanning calorimetry. This method consisted of recording energy required to bring to zero the difference in temperature of the test sample and the reference material as a function of temperature or time. The shape of the DSC curve showed a good agreement with the DTA curve. Endothermic peak was created when the sample temperature was below the standard, and the exothermic peak, when the temperature of the sample was higher than the reference. Samples containing a mixture of raw materials (precursors) of glass heated at a rate of 5° C/min to a temperature of 1400° C. When analyzing the plots, it can be concluded that the incomplete decomposition of the raw materials with the separation of water or CO2 to a temperature of 350°C occurred, as reflected by the different endothermic peaks. The earliest release of the water of hydration of aluminum nitrate (variant W2-71,0o C, 80,0o C), followed by water coming from the decomposition of boric acid (W1-127,3o C) and CO2 from the decomposition of sodium carbonate. At a temperature of 548o C on curves of W2 and Ba23 bis inflection appeared to indicate polymorphic transitions of silicon dioxide with the appearance of high gamma phase. For all graphs at about 1230° C and above the melting peak of barium carbonate was observed. Full homogenization mixture of precursors occurred above 1,350° C (W1-DSC chart in fig. 5 and 6)
Analyzing the DSC plot of W1 glass could be seen of his amorphous. The inflection of the curve reported that there was at 542oC vitrification and 649,8oC started the process of softening. On the thermogravimetric curve TG were not visible weight loss upon heating the glass.
2.1.6. Wettability research of glasses
The study of wettability of glasses to substrates of silicon carbide or submicrocrystalline sintered corundum is performed using high-temperature microscope of Leitz- Watzler, type using sessile drop method. Silicon carbide is used as a filler in diamond grinding wheels or supporting grain. SiC substrate, there was degassed under vacuum, and therefore contain adsorbed gases from the air (oxygen, nitrogen), and chronic alcohol bath defatted not entirely surface. Therefore, the observed high temperature sintering (for all variants within 620-670o C glasses) and the temperature drops propagation (920-970o C).
Contact angle theta ranged less than 40 degrees. All the tested glass wetted submicrocrystalline sintered corundum (cubitron) substrate better than the silicon carbide substrate, at lower temperatures (880-930o C), although the same procedure of degreasing were conducted.
2.1.7. Mapping of the surface of glass-substrate microsection
Microscopic observation of transverse cross-sectional views of the glass –SiC substrate or glass-submicrocrystalline sintered corundum substrate carried out using a scanning electron microscope JSM 6460LV and starters EDS (Energy – dispersive X-ray spectroscopy analyzer) revealed the presence of a small transition layer in the system glass- submicrocrystalline sintered corundum (pictures of the glass Ba23 bis-submicrocrystalline sintered corundum) contains barium elements. The phenomena of interlayer (fig. 9) in the case of specimens glass-silicon carbide substrate comprising this was much wider probably resulted from the presence of silicon, both in the glass and substrate.
2.1.8. Testing the strength of glass
Flexural testing was performed on the four groups of glasses for Zwick Roell Z2.5 machine, at the test speed of 0.5 mm/min, and the spacing supports 34 mm The flexural modulus was determined for all samples by the secant, taking reference points as a force of 50 N and 100 N start the end (Table 5). Maximum bending strength in the range of 100 MPa was obtained for the samples of glass W1 and Ba23 bis. For a group of glasses W4 and W3 it was lower by half. This can be explained by the reduced content of primarily silicon dioxide in these glasses. Similar behavior was observed in the samples of the destruction operation. The largest value of the work of destruction (W1-19,27 N/mm) was obtained for samples W1 and three times lower for samples W3.
|Names of samples||Bending strength [MPa] average value||Work of destruction [N/mm] average value||Bending modulus [GPa] average value|
|W1 glass||105,72 +-2||19.27||25,945|
|Ba23 bis glass||101,35||16,49||27,195|
2.1.9. Young modulus measurement of glasses
The measurements were carried out on the test bench equipped with a flaw, heads broadband and a PC with installed software. Young's modulus and Poisson's ratio of the samples based on the determined velocity of the longitudinal wave and transverse density of the material. All calculations were performed using the program Modulus 1.0. The highest values obtained of glass Ba23 bis (87 GPa) (Table 6). Poisson's ratio for all glasses were the same (0.38).
|Name of samples||Poisson’s ratio||Young modulus [GPa]||Modulus uncertenainty [%]|
|Ba 23 bis glass||0.38||87||5,8|
2.2. Part II Operational tests of grinding wheels containing the newly developed glass
2.2.1. The starting materials and methods of research
After summarizing the results of studies on the physical and mechanical properties of the newly developed glass, two of them with the best value properties (Ba23 bis and W1) were selected and used to develop the recipe wheel. Test wheels were prepared to carry out grinding tests. Grinding of flank surface of BNDCC composite samples was performed using wheels 6A2 100x10x4 mm type, containing uncoated diamond grain, Lands LS120 (D46-45-38 microns) type or LS 600F (D25-20-30 microns) with higher concentration of diamond (C125%) and a W1 or Ba23 bis binder (Fig. 9b).
Using DOE, influence on surface roughness and process efficiency of following parameters was derived:
grinding wheel peripheral speed, vs = 12, 15, 20 m / s
working engagement ae: 0.002, 0.005, 0.01 mm / double stroke of the table
diamond grain D46, D25
Constant parameters during experiments were:
a research position with the universal tool grinder 3E642,
the characteristics and dimensions of the grinding type 6A2 100x10x4 mm
the type of coolant-fed Synkom PGA
the method by pouring coolant
maschining time of the one cycle, t = 600 s,
number of the table double strokes – 3
table feed speed, vf = 210 mm / min
The study was carried out on a modernized grinding universal tool grinder 3E642 (fig. 10a), equipped with stepless speed control of the wheel and the cooling system. Grinding process was carried out with cooling by spraying a 2% solution of PGA Synkon coolant concentrate in tap water.
To test of the efficiency of grinding process of custom BNDCC composite sample (boron nitride dispersive in cemented carbide), comprising weight 20% of the grains of cubic boron nitride, with granulation 4-8 mm and dimensions 19x5,7 mm from the edge intersected at a distance of 1 mm from the end, were made at the Warsaw Univeristy of Technology, at the Faculty of Materials Science and Engineering. Before attempts to work the sample was adhered to the brackets in order to attach them to the machine (fig. 10c). Below the picture shows the position of the test, the wheel and bonded composites (fig. 10b).
Measured: the height of abraded material m, height of wheel. Calculated: the volume of abraded material Vw, consumption volume Vs wheel, radial wheel wear Vrs, grinding ratio G, yield losses of (volumetric) Qw, proper performance defects Q'w (deficient performance attributable on the active wheel width).
Sample mass measurements were carried out before and after each treatment using a laboratory scale with an accuracy of measurement 0.001 g. Measurements of the height of wheels and work-before and after each test was performed using electronic calipers accurate to 0.01 mm.
For the measurement of surface topography work-pieces profiler workshop was used. Before and after test were performed via research work on modul profilometer TOPO 01vP designed for measurement and analysis of surface roughness and waviness profiles and the profile of the actual surface without filtration with the program PROFILE. Images of 2D, 3D, marked elevation values Rz, Rt, Ra and horizontal parameters W, St, Sa in accordance with PN-EN ISO 4287th were conducted. The microscopic observations (SEM) of the samples before and after grinding were made. The designated function of the object of research in the form of a polynomial of the second degree of interaction, allowed to determine the statistical relationship between the basic parameters of the treatment and its effects (surface roughness).
2.2.2. Results and discussion
The results of grinding tests of D46 diamond grinding wheels with newly developed binders worked at a peripheral speed of 12, 15, 20 m / s and depth of grinding 0.002, 0.005 mm/double stroke of the table. were presented in Tables 7-8 and figures (fig. 11-16). It was evident that both: the D46 Ba23 bis wheel andW1 D46 wheel were best operating at a depth of 0.005 mm grinding/double stroke. The uniform wear of diamond grains and their self-sharpening were demonstrated.
The grinding wheels with D25 grit size of diamond grains worked at a speed of 15m/s and depth of grinding 0.002 and 0.005 mm/double stroke. All the grinding performance parameters were comparable for both types of wheels. Better results were obtained by D25 grinding wheels with Ba23 bis binder. For the depth of the grinding process the surface roughness of machined BNDCC composites varied within the same limits 0.02-0.03 µm. Comparing the results of performance parameters of the process of grinding wheels with the D46 and D25 granulation can state that they were very similar. Slightly better results were obtained with the wheels with lower diamond grit size (D25).
|Kind of wheel||Working engagement ae, mm||Peripheral speed of wheel vs, m/s||Qw, x10-3 mm3/s||Q'w, x10-3 mm3/mm·s||G [-]||Ra, µm|
|D46 Ba23 bis||1,35||0,14||3,41||0,03|
|Kind of wheel||Working engagement ae, mm||Peripheral speed of wheel vs, m/s||Qw, x10-3 mm3/s||Q'w, x10-3 mm3/mm·s||G||Ra, µm|
|Kind of wheel||Working engagement ae, mm||Peripheral speed of wheel vs, m/s||Qw, x10-3 mm3/s||Q'w, x10-3 mm3/mm·s||G, [-]|
|D25 Ba23 bis||0,002||2,31||0,23||31,60||0,02|
|D25 Ba23 bis||0,005||2,22||0,22||27,65||0,03|
2.2.3. Research of geometric structure of BNDCC composites
The study of geometric structure of the samples before and after grinding showed that the assumed test conditions are properly selected (Figure 20a). Machining by grinding the assumed operating parameters of wheel allowed to obtain roughness parameters (Ra, Rz, Rt) times better than the initial (Ra before 1.28-1.40 µm, Ra after-0,018-0,04 µm, Rz before 7,05-7,890 µm, Rz after 0,126-0,150 µm). Image of 3D surface of the BNDCC composite before grinding process showed the presence of significant inequalities (fig. 20a). After grinding process the surface was completely inequalities (fig. 20b).
2.2.4. The microscopic image of BNDCC composite
The samples of BNDCC composites were observed under a scanning microscope before and after the grinding tests. For all composite samples before grinding process parallel scratches were visible on the surface of the samples. These were probably established through their mechanical treatment after sintering. Microscope image of the samples after grinding showed sharply defined edges with blunted of blade grains in carbide matrix.
2.2.5. The mathematical model of the function of research object
The mathematical model describing the change in the surface roughness Ra of the treated object as a function of the depth of grinding and peripheral speed of grinding wheel was shown in graphic form (fig. 22, 23). The function of the object of research was determined for the grinding process of D46 Ba23 bis wheel and D25W1 wheel BNDCC composite of grit size 4-8 m assuming independent parameters (depth of grinding, ae and grinding wheel peripheral speed vs) and the dependent parameter (surface roughness of the composite). For DOE purposes and analysis of experimental results, STATISTICA was used [15,16]. The range of variability was low. Statistical analysis of the results of experimental studies included
Approximation of object function tests,
Statistical verification of the adequacy of the function approximating,
Statistical verification of significance approximating function coefficients.
The function of the object of research adopted in the form of a polynomial of the second degree of interaction is described by the following formula:
ae, vs – the size of the input,
a0 ÷ a5– polynomial coefficients.
The results of preliminary calculations showed that the best fit regression equations to the results of the experiment allows the second degree polynomial model of interaction, and therefore the calculated regression equation stepwise regression presented in this form. Analysis of individual regression equations fit to the experimental results was based on multivariate correlation coefficient R and also based on function values and Student's t-value of F-Snedecor. The level of significance p = 0.05.
Analysis of relationship shown in Figure 22 and 23 confirmed that the minimum value of surface roughness BNDCC samples was obtained at the peripheral speed of grinding wheels in the range 14-16 m/s and 0.005 mm depth of grinding/double stroke of table. These data verified the results of performance tests of these samples.
3. Summary and conclusion
Based on the survey it can be concluded that:
the research glass fulfilled their utility criteria as binders for super hard abrasive tools;
glass received by frytting method belonged to the group of light glasses (ρ <2.64 g / cm 3). It was completely transparent with a bluish tint;
thermodynamic calculation of chemical stability of glass precursors were conducted by VCS algorithm. It was shown in accordance with first assumption that the three compounds were stable in solid states at high temperatures: barium silicate, silicon dioxide, aluminum borosilicate; in the second assumption only one (barium borosilicate). X-ray crystallographic studies have not confirmed the presence of compounds. Investigated samples were in pure amorphous form;
differential scanning calorimetry of precursor glasses showed their distribution with the separation of water or CO2 to a temperature of 350oC. The whole sets underwent complete homogenization above 1,350° C;
substrates were wetted well by all variants of glasses, although in all cases submicrocrystalline sintered corundum was wetted better than silicon carbide. Microscopic observation of samples transverse glass-substrate systems contains submicrocrystalline sintered corundum after the wettability studies showed the presence of narrow interlayer contained barium. In -case of transverse specimens with silicon carbide substrates were much wider, probably resulted from the presence of -silicon in glass and substrate;
the flexural strength showed the highest values was obtained by W1 and Ba23 bis glass. The work of destruction was tree times lower for W3 glass than W1 glass;
diamond wheels with D46 or D25 grains and Ba23 bis or W1 binders fulfilled the criteria of utility in the flat grinding process;
analysis of grinding process efficiency Qw [x10-3mm3/s] Q'w [x10-3mm3/mm⋅s], G (listed in Tables 3, 4) showed a very good result under the processing conditions. It was observed that the most favorable results are obtained when the samples of BNDCC composite was machining in – the grinding depth of 0.005 mm/double stroke of table and the peripheral speed of the wheel of 15 m/s;
the results of the geometrical structure of the surface of the BNDCC composites showed that the grinding surface roughness was Ra 0.018 -0.04 µm compared to the initial roughness of Ra 1.248 -1.4 µm, Rz after grinding 0.12-136 µm compared to the initial value of Rz 7,096-7,96 µm;
the mathematical model of grinding process properly describes the working condition necessary to obtain the lowest roughness.
the use of diamond wheels with newly developed vitrified (ceramic) binder in conventional grinding technology has allowed to obtain a mirror of BNDCC composites.
Presented research results were obtained within the project: “Application of modern BNDCC and DDCC composites for cutting tools”, Applied Research Program – Contract No. PBS1/A5/7/2012 financed by The National Centre for Research and Development in Poland