Subsequent Grinding Research Articles

Sustainable machining of molds for tile industry by minimum quantity lubrication

Abstract Nowadays, to reduce water pollution, soil contamination, and human health hazards, the environmental legislation is forcing manufacturing companies to avoid the use of metalworking fluids. Thus, the adoption of the dry machining and minimum quantity lubrication (MQL) techniques is becoming essential. However, small and medium companies are having difficulties and are skeptical about the adoption of these new techniques. In this study, a methodology is proposed to implement an MQL system for sustainable machining with a step-by-step procedure that facilitates its industrial application. The methodology is divided into three steps: i) MQL configuration to verify its effect on surface roughness, considering the effective flow rates and nozzle position; ii) process modeling based on the Box–Behnken design of experiments (DoE) to model surface roughness, power consumption, and tool life; and iii) process optimization for minimizing cost and environmental impact in terms of water usage and kg of CO2 equivalent. The methodology is applied in the manufacturing process of a component of a mold for the tile industry. Different alternatives are analyzed and the best alternative in both economic and environmental aspects is the use of the MQL system with optimal cutting parameters and an early tool change strategy that ensures part quality without subsequent grinding operations.

RESEARCH OF THE SCRAP VEHICLE TIRE GRINDING PROCESS

The problem of scrap tires and out-of-service rubber products recycling is relevant and has great environmental and economic importance The most popular tire recycling methods in Russia are pyrolysis and grinding. According to the laws of several western countries, pyrolysis technologies are prohibited as environmentally unsafe. Therefore, the of scrap tires grinding method can be considered the most promising and more environmentally friendly. The aim of the study was to develop an effective technology for scrap tires recycling in terms of energy consumption and depth by pretreatment in solvents of various types and subsequent grinding. The use of methods of mechanical action on the material, in particular the operation of aggressive media, is substantiated. The results of experimental studies have shown that crushing when exposed to various corrosive media (solvents) reduces energy consumption, improves the separation of metal and textiles from rubber, improves rubber yield.

Experimental study of chip shapes in grinding by unique quick stop method and the ground subsurface layers micro-hardness

The paper analyses deformation and heat flow aspects of chip formation in grinding process by developed unique quick stop method and properties of ground surfaces, mainly micro-hardness. The cutting speed of the grinding process is within the range of high-speed turning and milling, so the chip formation is characterized by a high contact temperature and intensive plastic deformation. Moreover, the grinding wheel is a cutting tool of undefined geometry and the dimensions of grinding grains are several orders lower in comparison with the defined geometry cutting tools. The mentioned features make the research of the grinding process very specific. The paper provides the obtained micro-section of the chip forming process and the special chip shapes obtained by quick stop method in the grinding process. Furthermore, the paper analyses the special properties of the ground surface and even subsurface layers through the micro-hardness analysis, discusses performance in subsequent operating conditions and subsequent grinding of that layers. The experiments were carried out for the steel workpieces, ceramics grinding wheels and grinding without cooling.

Design and validation of a kinematic numerical dressing model of conventional grinding wheels

Dressing is one of the most critical parameters that determine the efficiency of subsequent grinding processes. In this study, the analysis and validation of a kinematic dressing model for the case of corundum wheels is done. The accuracy of the model is evaluated by predicting the abrasive surface after the dressing operation for the case of a single-point dresser, observing the deviations between simulations and experimental results. These results show deviations of 19.2%, 7.57% and 19.69% for the roughness parameters root mean square height (Sq), density of peaks (Spd), and reduced peak height (Spk) respectively, which are indicators of the cutting ability of the grinding wheel and have influence on subsequent grinding processes in terms of the surface finish on the ground parts. These results show the way of future research work, giving useful information for optimising this numerical model and extending the analysis for different types of dressing tools.

Electrical Discharge Machining and Grinding of SiC Single Crystal Using a Disc-type Hybrid Tool of Polycrystalline Diamond

Silicon carbide (SiC) single crystal was machined using a disc-type hybrid tool of polycrystalline diamond (PCD). The tool can be used to perform electrical discharge machining (EDM) as a roughing process and grinding as a finishing process. The width of the discharge gap and the thickness of the resolidified layer caused by EDM were measured, the results of which were then used to optimize the subsequent grinding conditions. As a result, ductile mode grinding was realized by removing the EDM-induced resolidified layer completely. In addition, a low surface roughness was obtained after grinding by utilizing the electrical discharges in EDM to dress the PCD tool surface. Finally, high surface integrity and productivity were successfully sustained by optimizing the EDMgrinding cycles.

Evaluation of Mechanical Properties of Sealing Mortar with Partial Replacement of Portland Cement by Stone Crusher Waste

Civil construction is one segment responsible for major environmental and social impacts. Among its raw materials, Portland cement, which is produced by the burning and subsequent grinding of a composition of clays and limestones. This manufacturing process causes great environmental damage, both by the exploitation of deposits and by the process of clinkering (burning of raw materials), which emits a significant amount of CO2 in the atmosphere. Therefore, there is a need for research on materials that reduce these impacts on the environment and that can be used by civil construction to the partial replacement of cement. Thus, this research had as objective to produce settlement mortar through the partial replacement of the Portland cement by filler powder, in different proportions and to study its mechanical properties. The results show that the partial replacement of the cement by the residue has acceptable behavior in the mortar.

Design and validation of a kinematic numerical dressing model of conventional grinding wheels

Dressing is one of the most critical parameters that determine the efficiency of subsequent grinding processes. In this study, the analysis and validation of a kinematic dressing model for the case of corundum wheels is done. The accuracy of the model is evaluated by predicting the abrasive surface after the dressing operation for the case of a single-point dresser, observing the deviations between simulations and experimental results. These results show deviations of 19.2%, 7.57% and 19.69% for the roughness parameters root mean square height (Sq), density of peaks (Spd), and reduced peak height (Spk) respectively, which are indicators of the cutting ability of the grinding wheel and have influence on subsequent grinding processes in terms of the surface finish on the ground parts. These results show the way of future research work, giving useful information for optimising this numerical model and extending the analysis for different types of dressing tools.

Application of repetitive high power (high voltage) nanosecond electromagnetic pulses to improve technological properties of diamond-bearing kimberlites

In this paper we used Fourier transform infrared spectroscopy (FTIR), analytical electron microscopy, microhardness measurements and other methods to study changes in the morphological, structural defects, hydrophobicity, mechanical and technological properties of rock constituents of kimberlite igneous rocks and crystals of natural diamonds exposed to nonthermal action of the repetitive nanosecond electromagnetic pulses. The destruction of secondary mineral surface films, their removal from the diamond surfaces, the growth of crystal hydrophobicity, and an increase in the number of B2 defects were observed after 30-50 seconds of electrical pulse treatment. The obtained result indicates possibility of applying pulsed energy effects to intensify the diamond flotation and to advance efficiency of the weakening of kimberlite rock constituents without damaging the precious crystals and ensuring their preservation by the subsequent grinding of refractory ores.

Comparative study of methods for producing gum arabic powder and the impact of DIC treatment (instant controlled pressure drop) on the properties of the product

In this study, gum arabic powder was produced according to four methods by inserting a restructuring stage by DIC treatment (instant controlled pressure drop) in the classic process of grinding and spray drying. Properties of the final product were compared, and the results show that DIC treatment enables to control and improve the properties of the powder. The DIC treatment can cause a controlled increase in the tapped bulk density, filling rate, compressibility, porosity; and a reduction in interstitial air volume and the loose bulk density. It also facilitated the subsequent grinding and intensified the drying kinetics. The impacts of pressure and DIC treatment time were examined. Pressure was the strongest factor influencing the properties of the gum arabic powder. Selecting an optimal pressure and treatment time plays a decisive role in controlling the properties of powders.

Impact of pressure in static and dynamic pressing of ultrafine plasmochemical ZrO2 (Y)-Al2O3 powders on compact density and compaction efficiency during sintering

The effect of different methods of pretreatment and compacting of ultrafine alumina-zirconia powders of composition (in mass%): 20 Al2O3-80 (ZrO2-Y2O3) on densification processes during pressing and subsequent calcination has been studied. Ultrafine powders were prepared by plasma-chemical method. It was found that the initial nanocomposite is a mechanical mixture made up of zirconia nanoparticles and amorphous alumina in a thermodynamically nonequilibrium state. Grinding of powders did not affect their phase state. Powder compacts were produced by means of uniaxial static pressing and magnetic pulse compaction. The impact of mechanical processing of powders on ceramics density was studied. It was shown that dry grinding of powders in a planetary ball mill does not increase the ceramics density. The best and virtually identical results were obtained using preliminary static pressing of powders at increased pressure P = 900 MPa and their subsequent grinding in a ball mill. Dilatometric studies showed that double-action magnetic pulse compaction provides the maximum shrinkage rate at lower temperatures in comparison to that observed under static pressing. The ceramic density achieved is higher than that obtained using other pressing methods.

Influence of Mechanical Treatment on Consolidation Processes of Ultradisperse Powders of Stabilized Zirconium Oxide

The effect of preliminary machining of ultradisperse powders of stabilized zirconium dioxide and its composite on consolidation in compacts under uniaxial static pressing and subsequent sintering is studied. The investigations were carried out with powders of compositions (in mol %) 97ZrO2–3Y2O3 and 80Al2O3–20(ZrO2–Y), which were obtained by the sol-gel and the plasma-chemical method, respectively. Mechanical processing of powders was carried out in two ways. The first method consisted in preliminary static pressing of powders at elevated pressure of 900 MPa and their subsequent grinding in a ball mill. The second method consisted in grinding the initial powders in an Activator-2SL planetary mill with drums and grinding balls of zirconia. It is established that mechanical treatment significantly affects the density of compacts. In this case, there is no strict correlation between the density of the sintered ceramic and the density of compacts. With increasing density of compacts, their expansion can be observed at the isothermal holding stage, which leads to a decrease in density of the ceramic. It is shown that, in dry grinding to improve the technological properties of ultradisperse powders obtained by the sol-gel and plasma-chemical methods, the most suitable is the method of mechanical treatment, which consists in pre-pressing the powders at elevated pressure and then grinding them in a ball mill.

Development of a TEM Compatible Nanowire Characterization Platform With Self-Forming Contacts

A nanowire characterization platform is designed and fabricated in MEMS-technology for the thermoelectric and structural characterization of single nanowires. The latter is achieved by making the chip compatible to TEM holder, by restricting its thickness to less than 160 μm and its diagonal dimensions to less than 3 mm. Two different fabrication technologies are presented for the realization of such platform, based on a design reproducing the functional requirements. Our first fabrication technique is based on ICP etching, using (100)-silicon wafers, and a subsequent rear grinding. However, as the design includes a vertical wall trench structures, ICP etching of such deep recesses is time-consuming and expensive. Therefore, a second fabrication process is developed, making use of wet-etched (110)-silicon. With these substrates a challenge arises from the intersection of inclined {111} facets. To solve this natural limitation, we introduce a novel fabrication process. Our technique relies on damaging the intersecting {111} planes, to make them etchable again and to produce deeper trenches with vertical walls in a wet-chemical etching process. Additionally, the electrical contacts at the platform are made from porous metal to increase the surface-to-volume ratio, to increase the possibility of a spontaneous electrical contact between the electrodes and nanowires.

Formation of the surface roughness during grinding with flap wheels after shot peening

Shot peening is widely used in forming long panels and sheaths. Due to impact by shot on the processed surface, a specific microgeometry is formed, the characteristic feature of this microgeometry are the numerous dimples as the traces of shot impact with different diameters and depths. A presence of these dimples causes deterioration of the surface roughness parameters. Therefore, after shot peening the mandatory requirement is the implementation of surface grinding with flap wheels for partial removal of the dimples. The size of the assigned allowance for grinding depends on the quality requirements of the part surface. At the same time, the depths of the remaining dimples are determined by the part surface roughness requirements. After grinding, the new surface microgeometry is formed, as a combination of micro-roughness from previous types of processing and the remained dimples in result of shot peening. In this work the microgeometry formation of surface layer of the samples after shot peen forming and subsequent grinding with flap wheels was analysed. The parameters of surface roughness were measured by the method of three-dimensional optical scanning. In the measurement result, the mathematical model of the surface micro-profile formation was formulated, the analytical dependences of the position of the center plane and the arithmetic mean deviation of profile were obtained.

Initial examination of fuel compacts and TRISO particles from the US AGR-2 irradiation test

Post-irradiation examination was completed on two as-irradiated compacts from the US Advanced Gas Reactor Fuel Development and Qualification Program’s second irradiation test. These compacts were selected for examination because there were indications that they may have contained particles that released cesium through a failed or defective SiC layer. The coated particles were recovered from these compacts by electrolytic deconsolidation of the surrounding graphitic matrix in nitric acid. The leach-burn-leach (LBL) process was used to dissolve and analyze exposed metallic elements (actinides and fission products), and each particle was individually surveyed for relative cesium retention with the Irradiated Microsphere Gamma Analyzer (IMGA). Data from IMGA and LBL examinations provided information on fission product release during irradiation and whether any specific particles had below-average retention that could be related to coating layer defects or radiation-induced degradation. A few selected normal-retention particles and six with abnormally-low cesium inventory were analyzed using X-ray tomography to produce three-dimensional images of the internal coating structure. Four of the low-cesium particles had obviously damaged or degraded SiC, and X-ray imaging was able to guide subsequent grinding and polishing to expose the regions of interest for analysis by optical and electron microscopy. Additional particles from each compact were also sectioned and examined to study the overall radiation-induced microstructural changes in the kernel and coating layers.

Modeling and Analysis of Contact Conditions during NC-Form Grinding of Cutting Edges

Due to increasing demands on cutting tools, cutting edge preparation is of high priority because of its influence on the tool life. Current cutting edge preparation processes are mostly limited to generating simple roundings on the cutting edge. Multi-axis high precision form grinding processes offer great potential to generate defined cutting edge microgeometries. Knowledge about the relation between grinding strategy and material removal rate can achieve improved work results with regard to higher precision of shape and dimensional accuracy as well as enhanced cutting edge quality. Therefore, a kinematic-geometric model was developed in order to analyze the complex contact conditions during grinding cutting edge microgeometries by using a simulation approach based on the intersection of geometric bodies. The subsequent grinding tests largely validated the utilized simulation approach.

Enhanced Recovery Process of Calcium Oxide and Metals from Steelmaking Slag with Net Carbon Sequestration

The iron and steel making (ISM) industry is one of the largest CO2 emitters in the world. Despite a sustained global research effort, utilization of best available technologies will not result in CO2 reductions for the industry that are sufficient to meet the Paris Climate Agreement. One area of the ISM process that still contains a large untapped potential for CO2 reduction is the recycling of slag. Currently ∼46% of ISM slag in Japan is used as an additive in cement production, reducing CO2 emissions. However, substantial grinding of slag is necessary prior to usage, which reduces the net CO2 offset of this process.We propose an alteration to current cooling methods in order to reduce the grinding energy of slag. Additionally, this new method recovers more low entropy metallic species than current processes. Molten slag is poured into shallow trays and allowed to settle in order to increase the separation of accidentally entrained metals from the calcium silicate melt. Upon reaching the solidification temperature the slag is cooled rapidly enough to induce the amorphous structure necessary to use slag as a cement additive. After solidification, the slag is quenched from high temperature in an ambient temperature water bath to create fractures throughout the slag due to high thermal stresses. These fractures reduce the subsequent grinding energy and liberate disparate species. This method results in a potential reduction of CO2 emissions for the Japanese ISM industry of ∼12.4 Mt/year; an increase of 3.0 and 2.1 times that of water-based and air-based cooling methods that include heat recovery, respectively. The process is validated by simulation and experimental results.

SPECIFIC FEATURES OF SPS-SINTERING OF BORON CARBIDE POWDERS PRODUCED BY DIFFERENT METHODS

Mechanochemical and SHS methods are up-and-coming ways to produce finely dispersed boron carbide nano powder. With optimal process conditions the synthesized phases have ultra dispersed state with well-developed surfaces of the boundaries of grains and subgrains that have either a nano or microcrystalline structure, and that ensures its higher density after vibrocompaction treatment, which in its turn can result in a reduced burn-out rate and a slow-down absorption activity under the influence of neutron irradiation. The products of mechanochemical synthesis and SHS have specified composition and specific structural state and are related with fast solid-phase reactions. The presented research dealt with boron carbide powders that had been produced by mechanochemical or SHS methods, as well as by carbon char or amorphous boron reduction, or the reduction of boron carbide that had been produced by SPS sintering. The purpose of the research was to determine the most optimal SPS sintering modes and to investigate the structure and properties of the sintered boron carbide workpieces made from the powders produced by the above mentioned methods. Source materials for boron carbide synthesis by mechanochemical method or carbon reduction with subsequent crushing and grinding, as well as for SHS treatment were carbon char of PM-15 grade and amorphous boron of A grade taken in stoichiometric composition. SPS sintering of boron carbon powders produced as above mentioned took place at Spark Plasma Sintering (SPS) - Labox 650 plant in graphite dies of 15 mm in diameter in vacuum under 25… 50 MPa pressure. The study of В4С powder workpieces that had been produced by mechanical synthesis, SHS or carbon reduction or SPS sintering of carbon char and amorphous boron mixture, yielded the most efficient modes of SPS sintering for each powder under research. The highest relative density was observed with SPS sintering of В4С powders produced by mechanosynthesis or SHS.

Fate of Salmonella throughout Production and Refrigerated Storage of Tahini

Tahini, a low-moisture food that is made from sesame seeds, has been implicated in outbreaks of salmonellosis. In this study, the fate of Salmonella was determined through an entire process for the manufacture of tahini, including a 24-h seed soaking period before roasting, subsequent grinding, and storage at refrigeration temperature. Salmonella populations increased by more than 3 log CFU/g during a 24-h soaking period, reaching more than 7 log CFU/g. Survival of Salmonella during roasting at three temperatures, 95, 110, and 130°C, was assessed using seeds on which Salmonella was grown. Salmonella survival was impacted both by temperature and the water activity (aw) at the beginning of the roasting period. When roasted at 130°C with a high initial aw (≥0.90) and starting Salmonella populations of ∼8.5 log CFU/g, populations quickly decreased below detection limits within the first 10 min. However, when the seeds were reduced to an aw of 0.45 before roasting at the same temperature, 3.5 log CFU/g remained on the seeds after 60 min. In subsequent storage studies, seeds were roasted at 130°C for 15 min before processing into tahini. For the storage studies, tahini was inoculated using two methods. The first method used seeds on which Salmonella was first grown before roasting. In the second method, Salmonella was inoculated into the tahini after manufacture. All tahini was stored for 119 days at 4°C. No change in Salmonella populations was recorded for tahini throughout the entire 119 days regardless of the inoculation method used. These combined results indicate the critical importance of aw during a roasting step during tahini manufacture. Salmonella that survive roasting will likely remain viable throughout the normal shelf life of tahini.

Effect of the Structure of TiB2–(Fe–Mo) Plasma Coatings on Mechanical and Tribotechnical Properties

The structure, mechanical properties, and wear-resistance of TiB2–(Fe–Mo) plasma coatings are investigated. Composite powders in the TiB2–(Fe–Mo) system with 20, 40, 60, and 80 wt.% of the Fe–13 wt.% Mo alloy were produced by vacuum sintering with subsequent grinding. The developed powders are conglomerates that contain both refractory and metallic phases. During plasma spraying of developed coatings, a coating with heterophase structure, which consists of Fe-based metal alloy and titanium diboride grains, is formed. The effect of the microstructure of plasmasprayed coatings on the wear-resistance under abrasive wear and dry sliding friction conditions is studied. The scratch hardness testing revealed an insufficient strength of TiB2–20 wt.% (Fe–13 wt.% Mo) coatings and their poor adhesion to the coating base, resulting in the extremely gross wear, when friction. It is found out that, due to the optimal ratio of refractory and metallic phases, the TiB2–40 wt.% (Fe–13 wt.% Mo) coating possesses high wear-resistance under abrasive wear and dry sliding friction conditions.

Investigation of Thermal Treatment Processes for Dissimilar Wafer Bonding

Wafer bonding, also termed as “direct bonding” or “wafer direct bonding”, has one of the main advantages for its ability to integrate dissimilar materials in various areas of microelelctronics, optoelectronics, micro/nanoelectromechanical systems (M/NEMS). Silicon is the most extensively used material for semiconductor industry. To meet demands on superior electrical, optical and acoustic applications, it is important to combine silicon with appropriate materials, such as GaAs, quartz glass, and LiTaO3. In general, two wafers are brought into contact at room temperature (~25ºC) and followed by thermal treatment processes (>100ºC) enabling reliable bonding strength to withstand subsequent mechanical grinding or polishing processes. During thermal treatments, the major concern in dissimilar bonded wafer pairs is the thermal stress originating from a mismatch in thermal expansion coefficients. Higher thermal stresses above a critical temperature may cause sliding, debonding, cracking or misfit dislocation between two bonded wafers. It is therefore highly desirable to predict the critical temperatures and optimize the thermal steps for dissimilar bonded wafer pairs with various materials and thicknesses. In this paper, a thermal stress model is developed based on analytical as well as finite element methods. To ensure a good bonding, the thermal stress should be smaller than the critical yield stress of the bonded materials. Meanwhile, the deformation energy should be lower than the bonding energy so that no sliding or debonding occurs during the thermal treatments. Under these two conditions, the critical temperatures for various dissimilar bonded wafer pairs (Si/GaAs, Si/Quartz and Si/LiTaO3) are calculated and predicted. The effects of wafer thickness are also demonstrated. To verify our calculation results, 100-mm silicon wafers are combined to LiTaO3 wafers by plasma activated bonding process. The bonded wafer pairs are heated at different temperatures to strengthen bonding. Experimental results show the critical temperature value is in agreement with our calculation. We believe our model provides a tool to optimize the thermal treatment processes during the dissimilar wafer bonding. It has great potentials to improve the bonding processes for wafer-level hybrid integration.