Abrasive Capacity Research Articles

In vitro evaluation and comparison of the abrasive capacity of zirconia whitening toothpaste at different concentrations on the radicular dentin surface of human teeth

In vitro evaluation and comparison of the abrasive capacity of zirconia whitening toothpaste at different concentrations on the radicular dentin surface of human teeth

Effect of nozzle wear on mechanical properties of 3D printed carbon fiber-reinforced polymer parts by material extrusion

A widespread problem of manufacturing processes is represented by the occurrence of tool wear that can lead to both poor surface finish and poor mechanical properties in the workpiece. This issue affects also additive manufacturing technologies such as the material extrusion technique. In this process, the wear mechanisms of the extrusion nozzle can be severe, in particular when materials with a high abrasive capacity, such as carbon fiber-reinforced polymers, are 3D printed. Despite the significance of this problem, scientific literature lacks systematic evaluations of nozzle wear and its correlation with parts mechanical properties. In this framework, the present paper aims at investigating the effect of the nozzle wear evolution on the mechanical properties of additively manufactured parts in short carbon fiber-reinforced polyamide. To this purpose, 3D printing processes were performed. The time dependence of the nozzle wear was analyzed by interrupting the additive manufacturing process at fixed time intervals. To analyze the effect of nozzle wear on the mechanical performances of printed parts, tensile specimens were 3D printed and tested at room temperature. A reduction in mechanical performances of the printed samples and a worsening in the surface quality were observed with increasing the nozzle wear. Optical microscopy investigation and X-ray computed tomography were used to monitor the external and internal nozzle wear evolution. The surface roughness measurements were performed to evaluate the surface quality of the 3D printed parts. Furthermore, the scanning electron microscopy was used to observe the three-dimensional topography of the longitudinal sections of filament in Carbon PA, at different printing time values, and fractured surfaces of tensile samples. This study can help to better understand nozzle wear and to predict tool service life for industrial applications. In addition, it can prompt future studies focused on the reduction of tool wear.

Beyazlatıcı Diş Macunlarının Kompozit Rezinlerin Mikrosertliğine ve Yüzey Pürüzlülüğüne Etkisi: Bir İn Vitro Çalışma

Objective: This study aimed to assess the effect of different types of whitening toothpastes on the microhardness and surface roughness of composite resins. Material and Methods: 120 discshaped samples each of Clearfil Majesty Esthetic and Gradia Direct Anterior composite resins were randomly assigned to 4 groups, based on the toothpaste used [three whitening toothpastes: Signal White Now (SWN), Colgate Optic White (COW), Ipana 3D White Luxe (IWL), and one non-whitening toothpaste: Sensodyne Promine (SP)]. The samples were brushed using an electrical toothbrush for 4 minutes. Before and after toothbrushing surface roughness (n=15) and Vickers microhardness (n=15) values were measured and the topography of the composite resins was observed using scanning electron microscopy. Data were analyzed using repeated measures analysis of variance and Bonferroni correction (p˂0.05). Results: The surface roughness was significantly affected by the toothpastes (p=0.013) and there was a significant interaction between toothpastes and composite resins (p˂0.001). The surface roughness of composite resins significantly increased after toothbrushing with all toothpastes. SWN and IWL showed significantly higher surface roughness values than SP (p=0.024 and p=0.028, respectively). There was a significant increase in the microhardness values for Gradia Direct Anterior after toothbrushing with SWN, IWL and SP (p=0.003, p˂0.001 and p=0.029, respectively). Conclusion: In this study, it was determined that all toothpastes increased the surface roughness values of Clearfil Majesty Esthetic and Gradia Direct Anterior, and all toothpastes (except COW) increased the microhardness values of Gradia Direct Anterior. Clinicians should notify patients of the abrasive capacity of all toothpastes, especially those that are whitening.

Stone Tools from Prehistoric Mining Sites in North Tyrol, Austria: Typology – Terminology – Material Properties

Mining archaeological field prospections and excavations conducted by the Research Center HiMAT at the University of Innsbruck yielded proof of extensive copper ore mining from the late Middle Bronze Age to the Early Iron Age (1300 - 700 BC) in the mining regions of Kitzbühel-Jochberg and Schwaz-Brixlegg in Northern Tyrol. This paper deals with stone tools collected at prehistoric mining sites and focusses on their typology, material properties and the problem of terminology. Petrographic analyses show a conscious selection of special stone materials for different applications. Typically, hard and tough metamorphic rocks collected from river gravel banks or glacial deposits of alpine valleys were used as raw materials for tool production. In general, well-rounded pebbles and boulders of amphibolite, garnet-amphibolite and eclogite were the preferred rock type used for percussion tools. According to the archaeological evidence, such stone tools were mostly used in the ore beneficiation process (crushing, to some extend also grinding) and have only rarely been found in connection with underground mining activities. For further beneficiation processes (grinding), other properties of the stone material such as abrasive capacity were required. In this context, boulders of orthogneiss/gneiss were the favoured rock material for netherstones (anvil stones and lower grindstones) and upper grindstones. The investigation of hafting modifications visible on stone tools shows that several hafting methods can be discussed, and that cords from plant fibres as well as straps of animal skin/leather could have been used for this purpose. Analysis of traces of wear provide information on the former function of the stone tools as well as on their practical application.

Case study: Abrasive capacity of Limnoperna fortunei (golden mussel) shells on the wear of 3 different steel types

The impact of particles suspended in the water is responsible for the wear of mechanical surfaces in hydraulic systems. The characteristics and concentrations of these particles in the flow directly influence the intensity of the abrasion processes. Within this context, knowledge of the abrasive power of a particle is of great importance. It is known that an invasive species, known as golden mussel shell, has become embedded in several hydroelectric plants of the South and Southeast of Brazil, provoking an increase of the wear caused by shells that pass through the hydraulic system. In this context, the abrasive capacity of ground golden mussel shells on the three metallic materials used in the labyrinth component of the hydraulic turbines was analyzed. To determine the wear pattern and the relationship of the specific wear coefficient of the material (k), due to the increased concentration of golden mussel shell, micro-scale abrasive wear tests were performed on three different steel plates using abrasive suspensions at different concentrations of ground golden mussel shell in distilled water. The abrasivity of the golden mussel shell was also compared with the abrasivity of silicon carbide (SiC), commonly used as standard material in microabrasion tests. The analyses showed that the golden mussel shell is around 16 times less abrasive than the silicon carbide, taking into account the average obtained for the three different materials tested. In addition, the wear mechanisms acting on the SiC tests and those with the golden mussel shell were the same.

The effect of the plastic behavior of clay particles on LCPC abrasive coefficient

In mechanized excavation projects, the major part of feasibility studies includes predicting the lifetime of cutting tools. Estimating the required numbers of tools for excavating a certain length of a section, under defined geologic conditions, and assessing the cost and downtimes needed for tools replacement are the other important issues in the preliminary studies of these projects. Presently, there are several experimental models used to study the abrasive capacity of soil materials in mechanized tunneling applications. In this paper, the effect of plastic behavior of clay particles on the abrasivity of soil materials was studied using the results of LCPC abrasivity tests. The results showed that the rheological behavior of abrasive samples changes considerably with the change of the clay particles mineralogy and the dominant water content. These changes have a significant effect on recorded wear amounts. Based on the obtained results, the plastic limit and the liquid limit of the clay part can be used to predict the appeared abrasive trends in LCPC tests. Moreover, during performing the LCPC tests, the consumed power of the electromotor of the testing device was recorded. The obtained power graphs confirmed the effect of the mineralogy and the water content of the clay part on the rheological and abrasive behavior of the testing samples.

Case study: Effects of sediment concentration on the wear of fluvial water pump impellers on Brazil's Acre River

The most important factor causing surface wear in hydraulic systems is the impact produced by abrasive particles suspended in the water flow. The impact conditions, such as mean particle velocity; particle mass; abrasive particle concentration in the liquid flow (number of particles per unit of liquid volume, size distribution of the particles); angle of attack at which the particles collide with the surface; and duration of the effect produced by the particles on the surface contribute to the development of the abrasion process. The wear resistance of the centrifugal pump impellers depends on the characteristics of the materials used in their manufacture and the abrasiveness of the suspended sediments in the pumped water. Despite special care in choosing the material used in its manufacture, abrasive wear is practically impossible to totally avoid. This work analyses the wear of ductile cast iron impeller blades of a centrifugal pump, used at the Fluvial Water Elevation Station (FWES) of the Acre River sedimentary basin in Brazil, due to the sediment concentration variation and the river water level. To determine the wear pattern and the relationship between the material and specific wear coefficient (k) due to increased sediment concentration, a ball-cratering microscale abrasive wear test was performed on samples of ductile cast iron, withdrawn from a used impeller, and abrasive suspensions at concentrations of 1, 2, 3, 5 and 10 g L−1 of river sediment in distilled water. The wear volume to the impeller blades due to the relative velocity of the mixture (water + sediment) and the wear accumulated in an annual hydrological cycle were estimated mathematically. The results showed that: i) the k remains constant regardless of the normal force (FD) applied in the tests in the abrasometer; ii) the wear tests showed the abrasive capacity of the sediments at different concentrations; and iii) the rotational control of the pump speed based on the sediment concentration and the river water level can contribute to a reduction in wear of up to 30% considering the hydrological cycle.

On the development and evolution of wear flats in microcrystalline sintered alumina grinding wheels

Wheel wear is a critical issue for grinding process optimization. This is why it receives so much attention both from Academia and industry. The development of new generations of abrasive wheels requires improving the understanding of the mechanisms involved in the loss of abrasive capacity of the wheels. In the case of alumina wheels, which are largely used in many grinding operations, the development of microcrystalline sintered alumina grains is one of the most important innovations to emerge since the early 1980’s. In comparison with white fused alumina this grains are characterized by higher ductility and have approximately 5% more hardness. However, the mechanisms of occurrence of wear flats in these new abrasives are still to be fully understood. In this work, a novel approach to the study of the underlying phenomena that occur during the development of wear flats in microcrystalline sintered alumina grains is presented. Experimental results in terms of grinding forces, friction coefficient and surface analysis are presented and compared to those obtained with conventional white fused alumina. The value of wear flat area is as much as 25% higher in the case of microcrystalline sintered alumina grains. Results will be useful to prevent the development of grinding burns resulting from wear flat development in these new alumina wheels.

Experimental and numerical analysis of thermal phenomena in the wear of single point diamond dressing tools

Grinding technologies represent a critical step in the production of high added-value and high precision parts for strategic industrial sectors such as aerospace, automotive, biomedical, and wind generation. Whilst a number of factors related to the grinding wheel are important for optimizing the grinding process, there is no doubt that the wheel surface topography is the most influential factor. Surface topography is induced not only by the nature of the wheel itself, but also, more importantly, by the dressing process. Dressing is periodically carried out in order to recover the abrasive capacity of the wheel once excessive wear of abrasive grits has occurred. The high temperatures and contact forces present in dressing lead to wear of the diamond dressing tool, which in turn damages the topography of the wheel surface. Although the scientific literature has paid attention to the phenomena involved in dressing tool wear, some issues are still in need of explanation. Thus, the aim of the present study was to address the unresolved issue concerning the relationship between dressing temperatures and dressing tool wear. Using a combined empirical and modeling approach, the work reported here shows that temperatures on the surface of the dressing tool can be reduced by as much as 35% when using high conductivity materials in the tool holder. In addition, a methodology has been devised in order to estimate accurate values of the heat partition ratio towards the diamond dressing tool. The results show that the heat partition depends primarily on the dressing mechanism involved. Its values range from 0.97 (when friction between the dressing tool and the grinding wheel prevails) to 0.54 when grain breakage and pull-out occur at higher dressing depths. It has been analyzed and measured the wear suffered by the diamond under interesting designed tests. It has been demonstrated that the effective reduction of temperatures during process led us to take a lower wear rate of the diamond.

In vitro and in vivo evaluation of diamond-coated strips.

To test in vitro and in vivo the wear performance of diamond-coated strips by means of tribological testing and scanning electronic microscope (SEM). To evaluate the in vitro wear performance, a tribological test was performed by a standard tribometer. The abrasive strips slid against stationary, freshly extracted premolars fixed in resin blocks, at a 2-newton load. At the end of the tribological test, the residual surface of the strip was observed by means of SEM analysis, which was performed every 50 meters until reaching 300 meters. For the in vivo analysis, the strip was used for 300 seconds, corresponding to 250 meters. The strips presented a fenestrated structure characterized by diamond granules alternating with voids. After the first 50 meters, it was possible to observe tooth material deposited on the surface of the strips and a certain number of abrasive grains detached. The surface of the strip after 250 meters appeared smoother and therefore less effective in its abrasive power. After 300 seconds of in vivo utilization of the strip, it was possible to observe the detachment of diamond abrasive grains, the near absence of the grains and, therefore, loss of abrasive power. Under ideal conditions, after 5 minutes (30 meters) of use, the strip loses its abrasive capacity by about 60%. In vivo, a more rapid loss of abrasive power was observed due to the greater load applied by the clinician in forcing the strip into the contact point.

Influence of the matrix composition, structure and properties on the service life of diamond drills

The study covers microstructure and mechanical properties of 4 matrices with complex chemical composition: VK15–Cu, VK15–Cu–Sn, VK20–Cu, and VK20–Cu–Sn used in the production of diamond drilling tools. The sample matrices was produced by infiltration of hard-metal mouldings with copper at t = 1100 °C and with bronze at t = 1000 °C. Thin sections of diamond-free matrices were prepared, their metallographic and microprobe analyzes were made, their hardness, micro-hardness, density and porosity were found. The hardness of matrices was measured according to the HRC scale, their microhardness was measured using the PMT-3 device under the 2N load. As a result it was revealed that 1) infiltration of the VK15 and VK20 hard-metal mouldings with copper and brass based melts produces hard and strong matrices for diamond tools with maximum 3 % apparent porosity, and the infiltration process is more complete when using bronze; 2) the most hard are the matrices obtained by infiltration of the VK15 hardmetal mouldings with bronze. The use of the VK20 hard-metal based mouldings matrices when manufacturing diamond drilling tools is inadvisable because of the sharp decrease in its abrasive capacity when drilling hard materials.

Effect of High Pressure Waterjet Peening on Surface Strengthening Properties of 7075-T651 Aluminum Alloy

The high pressure waterjet peening (WJP) was adopted to strengthen the surfaces of 7075-T651 aluminum alloy. The results demonstrate that the processing parameters such as shooting distance, holding time and water pressure affected the abrasive capacity of gas cavities significantly. Compared with non-peening and shot peening (SP) specimens, the fatigue life of as-WJPed specimens was improved by 22% and 6.6%, respectively. The maximum residual compressive stress generated by WJP and SP was approximately equivalent, which is −350 ≤ σ ≤ −400MPa. While the residual compressive stress near the strengthened surface introduced by WJP was higher than that of SP, hence the fatigue life of WJPed specimen increased much more. The surface roughness strengthened by WJP was also better than that of SP. Because the surface profile was well protected in WJP, the good surface qualities also insured a long fatigue life.

Tribological behaviour of composites made of carbon fibres and ceramic matrix in the Si–C system

Thanks to their low density, good thermal, mechanical and tribological properties, composites made of carbon fibres and carbon matrix (C/C) are particularly adapted to the manufacturing of aircraft brake discs. Several methods have been developed to improve their performance. For instance, the introduction of silicon carbide within the matrix notably increases the friction coefficient. While carbon fibres enhance the toughness of the matrix, silicon carbide shows high hardness, thermal stability and low chemical reactivity, leading to superior friction properties. The purpose of the present study was to evaluate the influence of such matrix modification on the friction behaviour and to identify the related mechanisms. With C/C as a reference, four different hybrid matrix composites were elaborated. For the first one, the matrix consisted in carbon (C) and silicon carbide (SiC), deposited in alternated layers around the fibres. For the second one, it was constituted of C, SiC and free silicon (Si), randomly distributed. For the third one, the matrix was made of SiC only. For the fourth one, it was similar to the third one but with some additional free Si. These samples were submitted to structural and mechanical characterization, then to friction and wear tests using a pin-on-disc tribometer, at variable temperatures and humidity. Compared to C/C, they exhibited higher friction coefficients and wear rates, in line with the abrasive capacity of silicon carbide. For severe conditions, the friction coefficient sometimes dropped abruptly, through the occurrence of a mechanism close to lubrication. These results highlight both mechanical and physico-chemical effects of silicon carbide on the tribological properties of hybrid matrix composites at various energies. Finally, the influence of some free silicon within the matrix was discussed.

A genetic base of utilisation of maize cob as a valuable naturally renewable raw material

The original technological method of the maize cob processing has been developed at the Maize Research Institute, Zemun Polje, by which lignocellulose granules of different particle sizes are produced from the cob. Different chemical composition and physical and chemical properties of these fractions, and especially a great capacity of binding liquids particularly oil and water determine, their usage as degreasing and drying means. Due to their great hardness and abrasive capacity, products made from ground cobs are usable for polishing in the metal processing industry, while the composition of certain compounds (pento-san) are of a particular importance in the chemical industry for the pro duction of furfural and its derivates. As these products are inert, of neutral pH and free of heavy metals they are used as organic carriers in the pro duction of pesticides and agro-chemicals, as well as, in cosmetics and the pharmaceutical industry.

Abrasive capacity of ß’-sialons synthesized by hot pressing

The abrasive capacity of s’-sialons synthesized by hot pressing of a mixture of powder Si3N4 AI2O3, and A1N is studied as a function of the microstructure and the chemical and phase compositions.

Glacial Sediment Production and Development of Hydro-Electric Power in Glacierized Areas

This paper discusses the results of a sediment-monitoring programme carried out in connection with hydro-electric power development plans in the river basins surrounding the Jostedalsbreen ice cap in Norway. Whereas the highest suspended-sediment transport rates occur during years with several flash-flood events, the bed load is more dependent upon the duration of large magnitude flood events. Bed-load transport has been obtained from annual measurements of deltaic growth in small lakes at the front of glaciers. During the years 1968–86, the mean ratio of bed load to total load amounted to 0.30–0.50% of the total load, but in years with large magnitude floods this ratio decreased. The mean annual suspended sediment yield of Norwegian glaciers ranges from 100 tonnes km2 a−1 to 1300 tonnes km2 a−1. Valley glaciers cause the highest erosion rates, with the exception of the small cirque glacier, Trollbergdalsbreen, which is thought to be a soft bed glacier. The investigation programme undertaken involved monitoring the volume of suspended sediments, together with the size distribution, mineralogy and shape of grains. In general, the valley glaciers supply more sand than the smaller cirque glaciers, whereas particles in the fine sand and silt-size ranges in almost all of the glaciers are angular in shape. Methods of comparing the abrasive capacity of the sediment load at various intakes in a power plant are discussed. Long-term sediment supply from the glaciers was investigated by studies of varves and rythmites in sediment cores from glacier-fed lakes.

Glacial Sediment Production and Development of Hydro-Electric Power in Glacierized Areas

This paper discusses the results of a sediment-monitoring programme carried out in connection with hydro-electric power development plans in the river basins surrounding the Jostedalsbreen ice cap in Norway. Whereas the highest suspended-sediment transport rates occur during years with several flash-flood events, the bed load is more dependent upon the duration of large magnitude flood events. Bed-load transport has been obtained from annual measurements of deltaic growth in small lakes at the front of glaciers. During the years 1968–86, the mean ratio of bed load to total load amounted to 0.30–0.50% of the total load, but in years with large magnitude floods this ratio decreased. The mean annual suspended sediment yield of Norwegian glaciers ranges from 100 tonnes km2 a−1 to 1300 tonnes km2 a−1. Valley glaciers cause the highest erosion rates, with the exception of the small cirque glacier, Trollbergdalsbreen, which is thought to be a soft bed glacier. The investigation programme undertaken involved monitoring the volume of suspended sediments, together with the size distribution, mineralogy and shape of grains. In general, the valley glaciers supply more sand than the smaller cirque glaciers, whereas particles in the fine sand and silt-size ranges in almost all of the glaciers are angular in shape. Methods of comparing the abrasive capacity of the sediment load at various intakes in a power plant are discussed. Long-term sediment supply from the glaciers was investigated by studies of varves and rythmites in sediment cores from glacier-fed lakes.

Measurement of the abrasive capacity of powders of carbides and borides of refractory metals

The abrasive capacity of carbides and borides of titanium, zirconium, hafnium, vanadium, chromium, tantalum, molybdenum, and tungsten was investigated.