Larger Specific Gravity Research Articles

DETERMINATION OF THE SIZE OF MEDIUM GRANULES IN FREE ABRASIVE PROCESSING TECHNOLOGY AND THE SIZE OF THE RESERVOIR OF A MACHINE FOR VIBRATION PROCESSING OF PARTS

It is noted that the process of vibration processing of parts is carried out by the relative movement and mutual pressure of granules of the medium and the parts being processed circulating in the oscillating reservoir. It is noted that the removal of defects from the surface of a part is carried out by the processes of microcutting and elastoplastic deformation. It is indicated that despite the effectiveness of vibration processing, its capabilities are limited to performing simple operations and have not been sufficiently studied. The effectiveness of vibration processing depends on a number of factors, among which the size of the medium granules and the size of the machine reservoir play a significant role. To determine these factors, the kinematics of the finishing and grinding process was considered, and the joint movement of the medium granule and the part was taken into account. The removal of microchips along the entire length of the machined surface during one period of oscillation of the machine reservoir and the damping properties of the material of the working medium used were also taken into account. It has been established that, depending on the shape of the part, its position and direction of movement in the reservoir, the angle of contact with the granules can vary from 0 to 90º. In this regard, cases of encounters between granules and parts are considered. It has been established that the unfavorable case of a meeting occurs at the right angle of their collision. It is concluded that the removal of microchips from the surface of parts is theoretically inversely proportional to the size of the medium granules. It has been determined that the increase in damping of the medium caused by a decrease in the size of the granules can be compensated by increasing the amplitude of the oscillations of the reservoir and the use of granules with a large specific gravity. The choice of granule size is also limited by the conditions of their access to the surfaces being treated, while the conditions for eliminating the possibility of granules jamming are met. It has been experimentally confirmed that the reservoir with a “U” – shaped cross-section turned out to be the best, due to the absence of stagnant zones in it. It has been established that as the cross-section of the reservoir increases, the productivity of the machine will decrease. Intensifying the process by increasing the amplitude is unacceptable, since this causes the appearance of deep defects on the treated surfaces. To increase processing efficiency, it is necessary to increase the volume of the reservoir by lengthening it, rather than increasing its cross-section.

Perceived Obstacles in Land Use Change for Hybrid Sweetgum Plantations: Landowner Opinions from the South Central United States

Abstract Hybrid sweetgum (Liquidambar styraciflua × L. formosana) has received considerable attention as a potential feedstock for traditional and nontraditional forest-based enterprises due to its fast growth and large specific gravity. However, the perceptions of landowners are important to understand the degree of acceptance concerning land use change to consider this opportunity in the United States. We administered a survey instrument to three thousand landowners representing the states of Texas, Oklahoma, Louisiana, and Arkansas where hybrid sweetgum plantations would be feasible. A seemingly unrelated regression analysis was used to explore the attributes that may influence the environmental and economic obstacles in land use change for hybrid sweetgum plantations. Study results suggest that landowners who perceived higher importance of marketing aspects of hybrid sweetgum expressed greater economic concerns for land use change. In contrast, those having higher planted pine acres had higher environmental concerns about land use change. Female landowners were more concerned than their male counterparts. Landowners need access to accurate information from their trusted sources to make informed management decisions, especially when making decisions to adopt new opportunities such as hybrid sweetgum. Study Implications: Study results reveal the need for outreach to landowners in the south central United States, as many were not aware of fast-growing hardwood species such as hybrid sweetgum. Information on growth potential, economics, and management techniques can help facilitate the adoption of hybrid sweetgum. Field visits and peer-to-peer learning facilitated by early adopters can be effective strategies for outreach.

Corrosion Behavior of Al Alloy A6061 Jointed with High-Tensile Strength Steel By Friction Stir Welding in NaCl Solution

In recent years, weight reduction of automobile bodies has been effective in reducing carbon dioxide emissions. For this reason, the replacement of steel, which has a large specific gravity, with aluminum alloys and carbon fiber reinforced plastics is being promoted for the right materials in the right places. In this case, an appropriate dissimilar material joining method is needed in terms of ease of assembly, joining performance, and cost. Friction stir welding (FSW) has emerged as a promising joining method for a variety of engineering applications. FSW is a solid-phase joining technique that has been shown to have significant advantages over conventional welding in terms of the strength and quality of the joints produced. However, during joining of metallic materials by FSW, microstructural changes may occur that affect their corrosion degradation. In this study, the corrosion behavior of A6061 jointed with high-strength steel (SPCC980) by FSW in aqueous NaCl solution and the effect of Al alloy microstructural changes on it were investigated.In this study, FSW was performed on A6061 and SPCC980 steel plates, and galvanic corrosion behavior was investigated by immersion tests and surface observations, as well as electrochemical measurements of Al alloys. Immersion tests were performed in 1 M NaCl solution. Micro electrochemical polarization tests of A6061 were also performed to investigate the corrosion behavior.In the immersion test of the galvanic couple of A6061 and SPCC980 steel plates in NaCl solution, galvanic corrosion occurred with the Al alloy as the anode and the steel plate as the cathode, and hydrogen evolution was observed mainly from the BM site on A6061 in the initial stage of immersion. This is due to the hydrogen evolution reaction occurring inside the pitting corrosion of the A6061. The pits was formed near Fe-rich inclusions in the BM site. In the HAZ site, corrosion propagated from Fe-rich inclusions along grain boundaries, but no pitting corrosion was formed. In the NZ site, minor localized corrosion was developed. These results indicate that the susceptibility to localized corrosion and its morphology differ in each site on the A6061. The difference in localized corrosion susceptibility on the A6061 was considered to be caused by the difference in the distribution of Fe-rich inclusions. However, the fact that the size and number of Fe-rich inclusions in each site did not differ suggests that the difference in anodic dissolution activity near Fe-rich inclusions affects pitting corrosion susceptibility in each site. A6061 alloy is a precipitation-strengthened Al alloy reinforced by β'' phase, which is a metastable phase of Mg2Si, and dense precipitation of β'' phase was observed in the BM site. Therefore, the reason for the higher localized corrosion susceptibility of BM is related to the precipitation of the β'' phase.This paper is based on results obtained from a project, JPNP14014, commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Experimental Study on Lead-Smelting Slag as Paste Filling Cementing Material

Under the current pressure of mineral product price and market competition, as well as the tightening of ecological and environmental protection policies, energy saving, emission reduction and cost reduction, and efficiency increase have become inevitable trends. Lead-smelting slag of smelter, as an industrial byproduct, is harmful solid waste to be eliminated. In this research, a series of experiments on substitute for cement were done for filling cost reduction under premise of guaranteeing the filling strength, using PC32.5 cement as reference cementing material. Meanwhile, with Portland cement clinker, water quenching slag of BF ironmaking, and lead-smelting slag of smelter in different ratios, four cementing materials were made and named as cementing material I, cementing material II, cementing material III, and cementing material IV. Then, the above five cementing materials including PC32.5 cement were mixed, respectively, with tailing and water to prepare paste backfill slurry with different binder-tailing ratio and concentration. Backfill block was made and cured at 20°C; their uniaxial compressive strengths in different curing ages were measured. The result shows the strength of backfill test block using cementing material I (cement clinker and water quenching slag) without lead-smelting slag is far higher than that of test block using PC32.5 cement as cementing material. The strength of block with 16% lead-smelting slag increased dramatically, which was higher than the strength of block using PC32.5 as cementing material. However, the strength of test block decreased when the content of lead-smelting slag reached 32% and 40%. The more lead-smelting slag was added, the worse influence on strength of backfill would be. Because of large specific gravity of lead-smelting slag and low content of CaO, the hydration activity of lead-smelting slag is far lower than that of water quenching slag. Therefore, using moderate lead-smelting slag as substitute for cement will lead to increase of backfill strength and decrease filling cost.

Numerical study on hydrodynamic load and vibration of pipeline exerted by submarine debris flow

Submarine debris flow, as one of the natural phenomena of marine disasters, often occurs in different sea areas, which has a strong impact on marine structure due to its large specific gravity and high velocity. Submarine pipeline is an important submarine structure which is extremely vulnerable to the marine environment, especially under the submarine debris flow. Many studies have been conducted on the interaction between the debris flow and the pipeline. Based on previous studies, the effects of the debris flows under the water-air interface on the pipeline with degree of freedom are investigated in this study where the debris flow volume, density, slide slope angle, the spring stiffness coefficient, pipeline location and tandem pipeline are considered. According to the computational fluid dynamics theory, a numerical tank is established using the Immersed Boundary (IB) method, in which the three-phase media (air, water and debris flow) are embedded. The results demonstrate that when the debris flow occurs, the water-air free surface is affected by the debris flow propagation, generating a surface wave. When the debris flow passes through the pipeline, with the increase of debris flow density and volume, the force on the pipeline increases, but the vibration frequency of pipeline decreases. Meanwhile, the vibrating pipeline will cause strong turbulence to the debris flow. In addition, the force and the vibration frequency of the pipeline are closely related to the flow pattern of debris flow reaching the pipeline. When the debris flow passes through the tandem pipeline, the closer the distance between the two pipelines is, the more significant the mutual influence between two pipelines is, because the negative pressure area formed behind the upstream pipeline can affect the downstream pipeline to a certain extent.

Study of Self Compacting Concrete performance with addition of nylon fiber

Self Compacting Concrete (SCC) is a plastic concrete that is easy to flow because of its own weight, fulfils all the desired concrete molds, and has the properties to compose itself. Very suitable applied to conventional concrete construction work that has a large specific gravity and compaction or vibration of concrete is needed. The purpose of compaction itself is to minimize the air trapped in fresh concrete, hence the concrete becomes homogeneous and voids do not occur. To increase the flexural strength of concrete, the addition of nylon fibers can be a solution. Nylon fiber is a material with polymer fibers that have fiber, film and plastic properties. The objective of this study is to evaluate the compressive strength and modulus of elasticity, tensile strength and flexural strength of concrete with the addition of nylon fiber. The percentage of nylon fiber addition of 0.5% and 1% of the weight of cement with a diameter of 0.35 mm and 0.65 mm and a length of 15 mm and 20 mm. With the addition of 1% nylon fiber, compressive strength increases 126% in variation of 0.65 mm diameter and L = 15 mm, tensile strength increases 56.27% in variations diameter of 0.65 mm and a fiber length of 20 mm and flexural strength increases 5.390% in variations a diameter 0.65 mm in the length of 20 mm. The diameter, length and volume of the addition of nylon fibers affect the concrete mechanical behavior. It is proven that the greater the diameter of the nylon and the percentage of the addition of nylon can increase the strength of concrete.

Fe THIN FILMS GROWN ON SURFACE OF SrFe12O19 BY MOCVD METHOD AND ITS ABSORBING PROPERTIES

Nowadays, more and more researchers pay attention to the microwave absorbing materials with the increase of electromagnetic pollution and the development of stealth technology for military platforms. Traditional microwave absorbers, such as ferrite, metal powder, conductive magnetic fibers, magnetic flake powder, and nanoparticles and so on, are facing some common problems such as large specific gravity, narrow absorption bandwidth, large match thickness and poor absorption performance. Composites with core-shell structures are becoming promising microwave absorbing material because such structure can exhibit magnetic and dielectric characteristics through the proper selection of core and shell materials. Thus, Fe(CO)5 deposition on the SrFe12O19 surface has been considered for the fabrication of a new composite that possesses the advantages of these two materials. This new composite might also obtain remarkable microwave absorption through thin layer absorbers in the entire 2~18 GHz frequency range. The Fe-SrFe12O19 composites with core-shell structures were prepared by metal organic chemical vapor deposition (MOCVD) using the SrFe12O19 and iron pentacarbonyl [Fe(CO)5] as the precursors. XRD, SEM, EDS and a vector network analyzer were used to characterize the structure and electromagnetic properties of the samples. The structure and morphology analyses show that the composites have complete core-shell structures with SrFe12O19 as core and Fe layers as shell. Fe nanoparticles were uniformly deposited on the surface of SrFe12O19 with *陕西省自然科学基金资助项目 2012SXJJ005 收到初稿日期: 2013-11-27,收到修改稿日期: 2014-04-21 作者简介:刘渊,男, 1986年生,博士生 DOI: 10.11900/0412.1961.2013.00774 第1095-1101页 pp.1095-1101

Characteristics and provenance implication of detrital minerals since Marine Isotope Stage 3 in Core SYS-0701 in the western South Huanghai Sea

The previous studies of the sedimentology and chronology of sediment core SYS-0701, which was recovered from the western South Huanghai Sea (Yellow Sea), have revealed the changes in the sea-level and sedimentary evolution during the late Quaternary in the region. The present study used mineralogical data from the section of the core deposited since Marine Isotope Stage (MIS) 3, to decipher the provenance of sediments of the paleo-delta deposited during MIS 3 and MIS 1. Based on the lithologic features and the variations with depth of the concentrations of carbonates and both heavy and light minerals in bulk samples, the upper part of Core SYS-0701 can be divided into three units designated DU1, DU4, and DU5, in accord with previously used terminology. Sub-units of unitsDU1 (DU1-1 andDU1-2) andDU4 (DU4-1 andDU4-2) have also been identified. DU1 was deposited during MIS 1, and DU4 and DU 5 were formed during MIS 3. All data pertaining to dominant heavy mineral assemblages, diagnostic minerals, ratios of diagnostic minerals, light mineral associations, textural maturities, and carbonate contents, indicate that the sediments of Core SYS-0701 are comparable with Huanghe River (Yellow River) sediments. Moreover, the mineralogy of the sediment evidenced its dependence on supply rates and hydrodynamic conditions. Weak hydrodynamics (DU5 and DU4-2) and/or low sediment supply (DU1-2) led to sediment containing less hornblende and epidote, with a large specific gravity and high content of flaky minerals, and vice versa in cases of strong hydrodynamics (DU4-1) and very large sediment supply (DU1-1).

Caracterização e uso de madeiras de galhos de árvores provenientes da arborização de Brasília, DF.

Este trabalho objetivou a caracterização da madeira de galhos provenientes de poda de árvores da arborização de Brasília e constou da investigação da possibilidade de seu uso como lenha e carvão vegetal. Foram estudadas 12 espécies de maior presença na arborização de Brasília. As espécies Persea americana, Spathodea campanulata, Ficus sp, Chorisia speciosa e Ochroma pyramidale foram caracterizadas como madeiras moles, com massa específica abaixo de 0,44 g/cm3. Caesalpinea leiostachya, com 0,73 g/cm3 caracterizou-se como madeira dura e Pterogyne nitens, Peltophorum dubium, Mangifera indica, Syzygium jambolana, Ligustrum lucidum e Paquira aquática, com valores entre 0,5 e 0,7 g/cm3 estão no grupo das madeiras moderadamente duras. As espécies: Caesalpinea leiostachya, Syzygium jambolana, Ligustrum lucidum e Peltophorum dubium apresentaram os maiores valores para contração volumétrica, entre 13 e 15,5%, enquanto os menores valores foram encontrados para Ficus sp. e M. indica com, respectivamente, 6,70 e 7,41%. Uma característica favorável para o uso da madeira para produção energética é a maior quantidade de massa por unidade de volume, dessa forma, as espécies de maiores massas específicas seriam as mais indicadas. As demais espécies poderiam ser transformadas em briquetes, aumentando assim a quantidade de calor por unidade volumétrica. Outros usos seriam como: composto orgânico (compostagem) e para a confecção de pequenos objetos (cinzeiros, cabos de ferramentas, enfeites, porta-jóias).

Improvement of the fatigue strength of aluminium alloy welded joints by high hardness and large specific gravity shot peening

The shot peening method, which requires simple equipment and treatment, is extensively employed as a method to improve fatigue strength. However, conventional steel ball shot material has a low specific gravity, so high speed projection is required in order to improve fatigue strength; thus, the accompanying noise and high air flow are problems. Accordingly, in order to improve these aspects, high hardness and high specific gravity shot material has been developed with 1.7 times the hardness (HV1400) and approximately 1.9 times the specific gravity (approximately 14) compared with a conventional steel ball.1,2

FRP防水用樹脂の硬化途中の収縮力測定方法の開発と収縮力測定

Unsaturated polyester resin for FRP waterproofing membranes have a disadvantage of shrinking in the process from liquid to solid state. It is fundamentally needed to estimate induced contraction stress of the resin for designing a good waterproofing membrane system. A new technique, in which the resin is poured in a floating frame on liquid of large specific gravity and induced contraction stress is measured, was proposed in the paper. The technique was applied for some resin samples and it was made clear that contraction stress mainly developed in a few ten hours and reached to the levels of 0.1-0.4N/mm^2.

Treatment of slaughterhouse wastewater using an activated sludge/contact aeration process

This study combines a two-phase biological treatment system of activated sludge/contact aeration process by adding biological contact filters into the rear sector of the activated sludge aeration tank of the slaughterhouse wastewater treatment plant. This system keeps the advantages of complete mixing of substrates and microorganisms and flexible operation of the activated sludge process, and increased biological phase, less sludge, process stability and good settleability of sludge of the contact aeration process. This system could avoid the defects of sludge bulking, increased sludge production and difficult operation of the activated sludge process, and system clogging and rigid operation of the contact aeration process. Because suspended microorganisms are flowing into the contact aeration system, which then degrade or suspend within the biological contact filters after being adsorbed by the fixed biological film, on which partial bio-solids will act as seeding microorganisms. Suspended microorganisms and the dropped biological film will settled in the secondary settling tank, then reflux into the activated sludge aeration tank. The partial dropped biological film will decompose in the activated sludge aeration tank to achieve the function of decreasing sludge. Large specific gravity and good settling ability of biofilm sludge will provide better effluent quality. It has been proven through a practical experiment at a slaughterhouse wastewater treatment plant in Taiwan, that the activated sludge process effluent COD value of 150-200 mg/L and SS value of 80-100 mg/L were decreased to around 40 mg/L and 22 mg/L, respectively, after changing its system to the two-phase biological treatment system of activated sludge/contact aeration process.

高硬度・大比重ショットピーニングによるＳＭ４９０Ａ溶接継手の疲れ強さ改善

In this study, we have developed new shot materials of tungsten carbide (150 and 100 μm in average diameter) with high hardness and large specific gravity, which is about 1.7 times (HV1400) in hardness and about 1.9 times in specific gravity (specific gravity 14) compared with the conventional one. And we have examined the improvement in the fatigue strength of SM490A welded joint, the outbreak of noise and the use of projection air when this shot material is used. The following experimental results were obtained : 1) The fatigue strength of welded joint was improved very well even in low projection air pressure 0.2 MPa when the peening was performed with the tungsten carbide shot materials of 150 μm in diameter, which has higher hardness and larger specific gravity than the conventional steel ball shot materials. 2) When the tungsten carbide with 100 μm in diameter or the conventional steel ball with 177 μm in diameter was used as the shot material, the higher projection air pressure above 0.4 MPa was needed in order to obtain the same fatigue strength improvement when the tungsten carbide with 150 μm in diameter was applied. 3) This improvement of the fatigue strength was mainly an effect of hardness increase by peening, but there was an additional effect of the compressive residual stress, too. 4) It was possible to reduce the noise value by approximately 10 dB and also the amount of projection air by more than 50 %, when the shot material with the high hardness and large specific gravity in particle diameter 150 μm was used in order to obtain the similar peening effect of the conventional steel ball shot materials.

A study of iron mineral transformation to reduce red mud tailings

This study examines the effects of iron mineral transformation in an aluminum extraction process on the settling behavior, and the physical and chemical properties of the resulting red mud slurry that must be disposed of. By producing a red mud with a higher solid content, the total volume of mud slurry will also be reduced for a given alumina production rate and more caustic soda will be recovered. The settling behavior and the mineralogical, physical, and physico-chemical properties of one bauxite and three red muds processed under varying conditions were analyzed based on examination of the iron mineral transformations. The properties of red muds derived from the same bauxite can differ markedly due to variations in operating conditions of the Bayer process, such as temperature and the addition of a reducing agent. The settling of red mud can be improved by converting goethite into hematite and/or magnetite to produce a mud of larger particle size, smaller specific surface area, and larger specific gravity, characteristics which reduce the total volume of mud slurry to be disposed of and which allow for less potential contamination from caustic soda. This study also found that the by-product — Bayer sodalite — has the high exchange capacity for Na + that might contribute to the long-term environmental problems.

太平洋炭の接触ガス化におよぼすチャー形態の影響

Each maceral of Taiheiyo coal was concentrated under a density separation technique and was carbonized under a quick heating in a fluidized bed.The char prepared from exinite-and vitrinite-rich part of coal has pores with a thick wall, while the char with more minerals, specific gravity of < 1.40, showed an opposite tendency.The catalyst dispersion state in the catalyzed char was as follows.The concentration of the catalyst in the mineral-poor char was high on the macropore surface and low in the wall. In the mineral-rich char, the catalyst dispersion was better than the above.Therefore, the catalytic reactivity of a char with a larger specific gravity is higher than that with a smaller specific gravity.

Specific gravity and tracheid length variation of white spruce in Alberta

Specific gravity and tracheid lengths were measured for increment cores from 10 trees in each of four selected white spruce (Piceaglauca (Moench) Voss) stands in Alberta. The data show large specific gravity differences among sample stands and from tree to tree within stands. Longer tracheids were found in mature wood of trees grown in the more northern stands sampled. A few trees were intensively examined to determine the variation of properties within the stem. The complex variation patterns from pith to bark and stump to crown are reported with comments on the importance of these variation patterns to breeding programs for the improvement of the wood properties. A somewhat unusual finding was that white spruce produces wood in top logs that is of equal or greater specific gravity and tracheid length than wood produced in butt logs.

Emergence and Organ Elongation of Seedling of Paddy Rice Sown under Upland Field Condition as Affected by Specific Gravity and Weight of Seed

This experiment was carried out to see the influence of the specific gravity and weight of seed on seedling emergence of paddy rice sown under upland field condition. Variety used was Norin No.23 and seeds were covered with soil of 5cm in depth. Results obtained were as follows. 1. The weight and the uniformity of seeds increased with the increase in specific gravity 0f seed. 2. The ungerminated seeds were found considerably in the seeds with the smaller specific gravity (below 1.05), but not found in the larger ones (beyond 1.10). And the correlation co-efftcient between the specific gravity of seed and the time of seedling emergence was not significant. 3. At the 122nd hour after seeding, the length f coleoptile and primary leaf was longer in the seeds with the larger specific gravity (beyond 1.OO) than in the smaller ones (below 1.O0). But at the 208th hour after seeding, such a relationship was not observed. And the length of mesocotyl was longer in the seeds with the smaller specific gravity (below 1.05) than in the larger ones (beyond 1.10), when both results at the 122nd and 208th hour after seeding were combined. 4. The time of seedling emergence became earlier with increasing of seed weight. 5. At the 122nd hour after seeding, the length of coleoptile and the total length of mesocotyl and coleoptile and the diameter of coleoptile was correlated positively with seed weight. At the 208th hour after seeding, the length of coleoptile, primary leaf, leaf sheath of first leaf and second internode was correlated positively with seed weight. And the length of mesocotyl was correlated negatively with seed weight, when both results at the 122nd and 208th hour after seeding were combined

Properties of Glasses in the Systems K&lt;sub&gt;2&lt;/sub&gt;O-BaO-V&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt;, K&lt;sub&gt;2&lt;/sub&gt;O-ZnO-V&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt; and BaO-ZnO-V&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt;

The glass-forming regions in three vanadate systems were determined and some physical properties and the ratio of V4+ state to total vanadium, i.e. V4+/Vtotal, were investigated.The remarkable features of these glasses are as follows: dark and opaque in color, poor chemical durability, devitrification tendency on heating, large thermal expansion coefficient, low transformation and softening temperatures, large specific gravity, and low Vickers hardness. In the BaO-ZnO-V2O5 glass which has stable and wide glass-forming region ranging 33 to 70mol% of V2O5, the remarkable nonlinear relations between the compositions and its properties were observed. The chemical analysis of vanadium in these glasses indicated that vanadium in 5+ state was predominant and the value of V4+/Vtotal was less than 4 percent.From the contribution of N. W. M., i.e. K2O, BaO, and ZnO, to the properties of glasses, it is considered that the character of each N. W. M. in these vanadate glasses is similar to that in the silicate glasses and the coexistence of two kinds of N. W. M. is effective for the stabilization of vanadate glasses.

Grindability of Coal by Hardgrove's Method

In determinating the grindability of coal by Hardgrove's method, the volume of sample in the testmachine pot will be different owing to the speaific gravity of sample, so that the determined data will be influeneed by the specific gravity of sample.And the grindability index of sample, larger specific gravity than standard coal, is inclined to larger than true value. When the grindability index of coal is calculated by the weight of sample through No.200 screen, it is better to calculate as following;G.I.=13+6.93w× (γ0/r)-bwhere, w: weight through No.200 screenγ0: specific gravity of standard coalγ: specific gravity of sampleb: constant.