COMPLETE SPECIFICATION

A Resinoid bonded in-situ TiB2 based ceramic grinding wheel and method of making the same

Field of Invention:

The present invention relates to a synthesis of grinding wheel. The invention relates more specifically to the method of synthesis of in-situ TiB2 and blended with AI2O3 for the development of grinding wheel, which can be used to grind hard materials like steel.

Background of the Invention:

This invention relates to abrasive particles essentially consisting of in-situ titanium di-boride and Alumina. In the method of producing grinding wheel the abrasive particles are mixed thoroughly .The conventional abrasive particles of the trade are aluminium oxide and silicon carbide. These wheels are brittle and exhibit poor shock resistance. Therefore, their application is limited where impact and large temperatures differentials are involved. The present invention relates to ceramic grinding wheel with in-situ T1B2- AI2O3 system particularly suitable for use as grinding wheel for grinding hard material like hardened steel. Titanium diboride (TiB2) has attracted much attention for applications such as cutting tools, armours and wear-resistant materials. Applications of TiB2 are limited due to cost, reduced diffusion coefficient and mass transport during densification. Keeping these facts in mind and using the reaction between halides known in the literature, cheaper in-situ TiB2 powder is produced and subsequently resin bonded, which has high hardness, increased service life and enhanced performance.

Brief description of the prior art;

No prior art such as/ closely related to the present one is already available.

U.S. Patent No 4076506 describes about transition metal carbide and boride abrasive particles. This invention relates to abrasive particles and a process for their preparation. The particles consist essentially of a matrix of titanium carbide and zirconium carbide, at least partially in solid solution form and grains of crystalline titanium diboride dispersed throughout the carbide matrix.

U.S. Patent No 5431704 relates to the invention of ceramic abrasive grains, method of producing the same and abrasive products made of the same, wherein the resinoid bonded grinding wheels using Al203-Er203 particles showed a high G-ratio compared with the conventional fused Alumina-Zirconia eutectic abrasives.

U.S. Patent No 2952529 relates to the invention of resinoid bonded abrasive wheels, wherein this invention relates to resinoid bonded abrasive wheels and is particularly concerned with abrasive wheels of the type described, which are adapted for grinding of stainless steel billets and at the same time contain no sulphur or metallic sulphides.

U.S. Patent No 4385907describes about resinoid-bonded grinding wheel employing the ultra-hard abrasives such as cubic boron nitride or diamond are formed with a support member which' is made of a heat insulating material such as ceramics for preventing thermal expansion of the grinding wheel and maintaining a precision grinding operation.

U.S. Patent No 4657563 discloses an improved resin-bonded grinding wheel composition and is shown making use of a kyanite or sillimanite or andalusite filler or mixtures thereof. More particularly, the grinding wheel is a hot pressed phenol formaldehyde wheel having an alumina-zirconia abrasive with a kyanite additive therein. These wheels can be used for heavy duty metal grinding and have been determined to be especially useful for the snag grinding of titanium metal.

U.S. Patent No 5711774 describes -about the silicon carbide abrasive wheel, wherein a vitreous bonded abrasive grinding wheel comprises silicon carbide abrasive grain, hollow ceramic spheres and a low temperature, high strength bond.

U.S. Patent No 6440185B2 relates to a resinoid grinding wheel wherein a typical resinoid grinding wheel of the present invention includes 25 parts by volume of AI2O3 abrasive grains with grain size of #150, 20 parts by volume of organic hollow material, with average particle diameter of 80 µm, and 10 parts by volume of pores having 1 mm in size. They are all dispersed in 40 parts by weight of a bond made of cured epoxy resin.

U.S. Patent No 6669747B2A grinding wheel: According to this invention cubic boron nitride (CBN) or other abrasive particles such as diamond are secured to a substrate by an electroplated, electroless plated or brazed layer of nickel, chrome or nickel or chrome based alloy, a first antioxidation layer of, for example, vapour deposited titanium aluminium nitride (TiAIN) and a second hard lubricant layer of, for example, vapour deposited molybdenum disulfide (M0S2), diamond graphite, tungsten carbide carbon, carbon nitride, titanium carbide carbon or titanium carbon nitride. The hard lubricant layer acts as a release agent and lubricant, which reduces clogging of the wheel by lowering adhesion and facilitating the release of ground material from the wheel thereby providing improved grinding performance.

U.S. Patent No 6264719 Titanium based metal matrix composites r-einforced with ceramic particulates are well known, based on a blend of titanium alloy powders with ceramic powders, e.g., aluminium oxide powders, utilizing a low energy ball milling process, followed by cold compacting and sintering to produce an appropriate composite. In order to produce a titanium base alloy alumina metal matrix composite, titanium dioxide powder is blended with aluminium powder and subjected to dry high-energy intensive milling until the separate particle phases achieve a size of 500 nanometers maximum. The intermediate powder product is then heated to form the titanium alloy/alumina metal matrix composite in which the ceramic particles have an average diameter of no more than 3 um, and the oxide consists of more than 10% and less than 60% by volume fraction of the total composite.

WO1996030550(Al) claims two methods for producing a ceramic reinforced Al-alloy metal-matrix composite. The first one comprises the steps of dispersing a ceramic phase (of titanium diboride) in a liquid aluminium or aluminium alloy, mixing the ceramic phase with a cryolite or other fluoride flux powder and melting the mixture together with the aluminium or aluminium alloy phase at a temperature of between 700° and 1000°C. In the second method, the fluoride flux is reduced in situ by either molten aluminium or its alloying elements (Mg, Ca) to yield T1B2 crystallites of different size and size distribution that can be predetermined by fixing the flux and alloy composition and the processing temperature.
WO1981001144 describes the tough and wear-resistant ceramic materials based on reactive metal bonded alumina-titanium nitride. The ceramic composite body contains a metal phase with reactive metal components such as Zr, Ti, Hf, or Y to obtain the characteristic of toughness. The compositions were extremely useful for applications such as metal cutting operations where improved toughness is required in addition to the exceptional wear resistance, which ceramics usually possess.

Dirk Biermann, Evelyn Wurz, A study of grinding silicon nitride and cemented carbide materials with diamond grinding ^wheels, Prod. Eng. Res. Devel. (2009) 3:411-416, DOI 10.1007/sll740-009-0183-z, Resinoid bonded wheels have been well proven for grinding cemented carbides and silicon nitride based materials. The processes of grinding silicon nitride and cemented carbide materials differ in material removal and the damage mechanism due to their different material properties.

C. F. Yao, Q. C. Jin, X. C. Huang, D. X. Wu, J. X. Ren, D. H. Zhang, Research on surface integrity of grinding Inconel 718, Int J Adv Manuf Technol, DOI 10.1007/s00170-012-4236-7, have studied the effect of different grinding parameters. The surface integrity of Inconel 718 was assessed by vitrified single alumina and resin bonded CBN wheel. It was concluded that better surface integrity is produced by alumina wheel and the grinding depth had predominant effect on the same.
S.Y. Luo, Y.C. Liu, C.C. Chou, T.C. Chen, Performance of powder filled resin-bonded diamond wheels in the vertical dry grinding of tungsten carbide, Journal of Materials Processing Technology 118 (2001) 329-336: The results showed that the resin bonded diamond with the greatest amount of copper filler resulted in relatively high proportions of protrusive particles and breakage grits resulting in the production of high forces and temperature. The resulting G ratio is low.

Objective of the Invention:

1. The Main objective of the present invention is to synthesize in-situTiB2 and blend it with AI2O3 for development of a grinding wheel.

2. The secondary objective of the present invention is to fabricate resinoid bond in-situ T1B2 - AI2O3 grinding wheel.

3. The third objective of the present invention is fabrication of grinding wheel with high wear resistance.

4. The fourth objective of the present invention is that the grinding wheel has enhanced performance for grinding hard materials like hardened steel.

5. The fifth objective of the present invention is that the resinoid bond in-situ T1B2 - AI2O3 grinding wheel has increased G-ratio and provides good surface finish during the grinding operation.

6. The final objective of the present invention, the resinoid bond in-situ T1B2 - AI2O3 grinding wheel, is economically viable.

Summary of the invention:

The present invention is about a resinoid bonded in-situ T1B2 based ceramic grinding wheel and method of making the same, wherein the T1B2 is prepared from in-situ salt-metal reaction between halide salts with Al alloy. The TiB2 particles are separated by treating the Al-TiB2 composite dissolving in an acidic medium. The extracted T1B2 particles are further reduced to a particle size of 4-5um by ball milling. The T1B2 powders obtained from ball milling are thoroughly blended with AI2O3 particles to form abrasive matrix. The Resinoid bonded grinding wheel is fabricated by blending the powdered phenol formaldehyde resin with the abrasive grains. The mixture is then hydraulically pressed and subsequently cured. The grinding wheel is machined to final size and dressed with a single point diamond dresser.

Brief Description of the Drawings:

Fig 1 XRD pattern of in-situ TiB2 particles prepared using scrap Al alloy Fig 2 shows the tangential force for Mill annealed and Hardened EN31steel at 3000 RPM

Fig 3 shows the normal force for Mill-annealed and Hardened EN31 steel at 3000 RPM

Fig 4 shows the dynamometer output for developed in-situ T1B2 grinding wheel at 0.05mm DOC (mill-annealed)

Fig 5 shows the dynamometer output for commercial alumina grinding wheel at 0.05mm DOC (mill-annealed)

Fig 6 shows the average Surface roughness and RMS roughness for Mill annealed EN31 steel at 3000 RPM

Fig 7 shows the average Surface roughness and RMS roughness for Hardened EN31 steel at 3000 RPM

Detailed description of the invention:

The inventors have developed a ceramic grinding wheel which has high wear resistance and provides better surface finish and eliminates some of the demerits of the previous inventions. The method used to synthesize in situ T1B2 powders is unconventional, but economically viable. Present invention provides resinoid bonded ceramic grinding wheel composed of AI2O3 and TiB2 synthesized by in-situ reaction. Formation of in-situ TiB2 has been confirmed thorough XRD using Cu-Ka radiation. Grinding experiments were carried out on steel (EN31) in both mill annealed and hardened conditions, which would give an idea about the effect of hardness on the wear resistance at various depths of cut (DOCs) and a constant speed of 3000 RPM. Forces during grinding were recorded using a dynamometer. Surface finish was measured for all machining conditions. The above process outputs were compared with those of commercially available Alumina grinding wheels.

Fig.1 shows the XRD pattern characterised using Cu-Ka radiation of the in-situ T1B2 particles extracted from the matrix metal. Careful control over the process parameters resulted in the absence of other brittle intermetallic phases.The chemistry underlying a patented process called Flux assisted synthesis, developed by London Scandinavian Metallurgical Company (LSM), is used in the generation of T1B2 powders. But/ as is demonstrated here, further developments of this idea, which have led to the present invention, are novel and original. An analogy in this regard is that the same Newton's second law is used to develop two entirely different products of aeroplane and rocket. Each of these has been patented. Aluminium scrap is melted at 750 °C, after which the two salts (see below) were added to the molten aluminium alloy. KBF4 was added first and stirred followed by the addition of K2T1F6 into the melt and sodium cryolite, which prevents agglomeration within the matrix. The stirrer used was of stainless steel, coated with zirconia. Coating was applied to prevent contamination of the molten metal by iron. Since aluminium produces dross, degassing was done by passing argon. Chemical reaction between the salts and the molten aluminium alloy takes place to form an in-situ T1B2 particulates matrix. The AI-T1B2 synthesized through the in-situ reaction is subjected to mechanical crushing followed by leaching in an acidic medium. The metal phase dissolves leaving behind the T1B2 particles, which are filtered and dried followed by ball milling for 8h at 240 rpm with a Ball to Powder Ratio of 10:1 and adding acetone at regular intervals to prevent agglomeration.

Hardness
Rockwell hardness indentations were made using the C scale .The results tabulated below are the mean value of 5 individual indentations.

Resinoid Bonding
The resinoid bond in the present invention essentially consists of commercial Alumina particles (4-5um) and Titanium diboride (4-5um), which is produced through the in-situ reaction. The boride matrix is approximately 60 to 63% by volume and the Alumina content is 18 to 25%. In addition to these, the grinding wheel consists of the resin, mufferlite, and the filler, which are added in definite proportions varying from 20-25%. The grinding wheel is prepared by thorough mixing of resin oil with the abrasive grains followed by sieving. The powdered phenol formaldehyde resin (Bakelite BR-2417) along with mufferlite and the filler is blended with the sieved mixture (abrasive grains'and resin oil). The mixture is then hydraulically pressed to size (250x20x76 mm) with periodic compaction loads of 41.3 MPa and a holding time of 3 minutes. Subsequently it is cured from 70°C -190°C for 24 hours followed by cooling for 2 hours in the oven. After cooling, the wheels were checked for distortion in shape and size. The wheels are then machined to final size and dressed with a single point diamond dresser. The major criteria for evaluating the performance of the abrasive particles in the abrasive wheel are the following:

(1) The Grinding ratio or G-ratio, i.e. the ratio of the volume of material removed to the volume of the wheel consumed.

(2) Surface finish, i.e. ability of the wheel to produce a smooth surface on the work-piece, which is determined from the microscopic peak to valley variations.

(3) Tangential and Normal grinding forces.

The experimental conditions used for the grinding wheel performance evaluation are given below:

Work-Piece Material: EN31 steel (Mill annealed and Hardened conditions)

Speeds : 3000 RPM
Table speed : 4.5m min-1
Depth of Cut (DOC) : 0.025,0.05,0.1mm
Coolant : (None) Dry

The grinding wheel is tested in surface grinding operation with respect to the above mentioned performance indicators. The invention is compared with commercial Alumina ceramic wheels. The temperatures at the work-piece/ wheel interface were measured using a non-contact Fluke® Infra¬red thermometer for all the DOCs.

Grinding Ratio or G-Ratio

G ratio is calculated by grams of material removed, per gram of wheel used. The G-ratio for both the ceramic wheels and the work specimens are listed below. The experiments were carried out at 0.1 mm depth of cut and 3000 RPM for 5 minutes. The unused grinding wheels and the work-pieces were weighed. It was ground for the set period of time (5 minutes). The used wheels and work-pieces were weighed after grinding.

G-ratio (TiB2, Hardened) = 5.2
G-ratio (TiB2, mUl annealed) = 4
G-ratiO (A1203, Hardened) = 4
G-ratio (A12C8, mill annealed) = 2.33

From the above determined G-ratios it is evident that the developed in-situ TiB2 based grinding wheel has higher wear resistance with higher material removal. Higher the number, the more work the wheel will do. It will take 1.3 commercial alumina wheels to do the work of 1 T1B2 based newly developed wheel for the work-piece in the mill annealed condition. And 1.72 alumina wheels are required to do the work of 1 T1B2 wheel while grinding the hardened material. It can therefore be concluded that the newly developed wheel performs better than the commercial wheel in both the cases and can be recommended for use in mill annealed as well as hardened conditions of steels. In addition, it is emphasized that even though the idea is established here using steel as the work-piece, similar considerations are also applicable to grind other hard work-pieces.

Comparison of costs between developed in-situ TiB2 and Commercial TiB2 In-situ TiB2

The grinding wheels developed by using commercial T1B2 powders costs 6 folds more than the developed in-situ T1B2 wheel. Therefore, it can be said based on the calculations that the wheel developed by in-situ reaction, followed by the filtration method of extracting T1B2 particles, is financially viable. Though the cost of developed in-situ TiB2 wheel is 1.6 times greater than commercial Alumina based wheel, the life of the former is high by 1.5 times and provides ~ 55% better surface finish than the latter at same machining conditions. The cost estimates are based on current Indian market rates.

Grinding Forces
The tangential and normal grinding forces can be substituted for horizontal and vertical forces respectively. Fig. 2 shows the Grinding forces plotted for different DOCs and constant speed for both the ceramic grinding wheels and the work-pieces. In case of mill-annealed steel, the tangential force of the developed grinding wheel increases with an increase in the DOC. This could be due to the presence of hard and strong bonds. Due to weak bonding in the alumina wheel, as the depth of cut increases, the force decreases and comes back to the initial value, which means that the rate of material removed is less than at a lower (0.05mm) DOC. This leads to rapid plucking out of the abrasive grains, in turn leading to wheel wear at a very short time, which is also evident from the G-ratio (2.33). Generally increased DOC should enhance the material removal, which can be correlated with the forces. In addition, the force produced at 0.05 mm DOC is high. Thereafter it reduces drastically, which is not preferred for ideal grinding. A hard surface'facilitates material removal with ease, as a result of which the forces generated during the grinding of hardened EN31 steel* with the developed T1B2 wheel are less compared with that present in the mill annealed condition. Weak bonds of alumina get chipped with an increase in DOC resulting in more grinding force. Wear of the TiB2 wheel while machining hardened steel is less than the mill-annealed steel which can be visualized from the magnitude of the tangential forces.

Fig.3 shows that the Normal grinding force for the commercial Alumina wheel is found to be higher for both the mill-annealed and hardened conditions. In case of the alumina wheel, the temperature at the interface is found to be high (720°C) at 0.1mm DOC, which leads to faster wear. This could be due to the effect of heat dissipation from the grinding wheel work-piece interface (point contact) to outwards along both sides of the grinding wheel and tangential force arising from dry grinding. This rise in temperature causes the resin bond to degrade severely, which results in distortion and reduces the grit retention in the wheel. Worn surfaces display more roughness than a burnished and smooth face, when machining is done with alumina wheel. This implies that there are significant merits with T1B2 as the major constituent. Depth of cut followed by work-piece velocity has great influence on the forces. Ductile and brittle removal modes exist in case of mill-annealed and hardened steels respectively. A different trend is" observed for the cutting forces. For the developed wheel, initially the forces are high as the wheel gains momentum to initiate metal removal. As time progresses it remains almost constant, indicating uniform material removal and wear. From the figures, it is found that the magnitude of cutting forces for the alumina wheel is twice that of the developed wheel and this indicates rapid wear in case of the former. For clarity, the actual outputs from the dynamometer are provided in Fig.4 and Fig.5.

Surface Finish
Fig. 6 shows an average surface roughness and RMS roughness for Mill annealed EN31 steel at 3000 RPM. For mill-annealed work-pieces surface roughness of the ground specimens is plotted for different depths of cut at a constant spindle and table speed. It is found that the developed in-situ TiB2 based grinding wheel performs better than the commercial alumina wheel. Surface roughness was measured using a contact type profilometer according to JIS 2001 standards with 0.8 mm cut-off length from Taylor Hobson. Alumina-based wheel gives rise to relatively poor finish at all depths of cut compared with the present in-situ TiB2 wheel. In general, both the wheels give poor finish at high DOC than at lower DOC, but the newly developed wheel is found to be the better one.

Fig. 7 shows an average surface roughness and RMS roughness for Hardened EN31 steel at 3000 RPM. In case of the alumina wheel there is a sudden increase in the roughness value at 0.05 mm DOC during the grinding of the hardened work-pieces. Thereafter the roughness decreases with an increase in the depth of cut. The magnitude of surface roughness is low for alumina wheel at the lowest depth of cut. On the contrary, at 0.5 mm DOC the surface finish is found to be the best while grinding with the developed TiB2 wheel. But at a high DOC the finish is poorer in both the cases. The alumina wheel also produces slight burns at high DOC; this is because at the work-piece-wheel -interface temperatures produced during dry grinding at high DOC are quite high compared with dry grinding at low depths of cut. At 0.1 mm DOC temperatures reach 700°C, while the average temperatures at 0.025 mm and 0.05 mm DOC are 360°C and 550°C respectively.

Claims:
We Claim:

1. A process for preparation of resinoid bonded in-situ TiB2 based ceramic grinding wheel, comprising: abrasive material which essentially consists of in-situ TiB2- AI2O3 resin, mufferlite, filler, sieve mixture and resin oil.

2. As claimed in claim1, the TiB2 is extracted by salt metal reaction of halide salts with Aluminum alloy, thus leaching the AI-T1B2 in acid

3. As claimed in claim 1, the TiB2 particles extracted by acid leaching is ball milled for 16 hours at 240 RPM to reduce the particle size to 4-5 urn and is blended with AI2O3 to form in-situ TiB2- AI2O3 abrasive grains

4. As claimed in the claim 1, wherein the said in-situ T1B2- AI2O3 abrasive grains comprise particles with a grain size of 4-5 um in the ratio of 60:40 by weight.

5. As claimed in claim 1, wherein the said grinding wheel is prepared by thorough mixing of resin oil with abrasive grains, followed by sieving.

6. As claimed in claim 1, wherein the resinoid bonded grinding material is prepared by adding resin along with mufferlite and filler to the sieve mixture.

7. As claimed in claim 1, wherein the resinoid bonded grinding mixture is hydraulically pressed to the size (25x20x76) mm with a compaction load of 41.3 MPa and holding time 3 minutes.

8. As claimed in claim 1, wherein the said mixture is cured at 70°C for 24 hours followed by cooling in 2 hours.

9. As claimed in claim 1, wherein the said, grinding wheel comprising resinoid bonded in-situ TiB2- AI2O3 abrasive material exhibits high hardness and good wear resistance.

10. As claimed in claim 1,

a. wherein the resinoid bonded grinding wheel is characterized by Kistler dynamometer to correlate the wear resistance with the commercially available grinding wheels.

b. wherein the resinoid bonded grinding shows increased G-ratio, which indicates / provides good surface finish compared with commercial AI2O3.