High-speed grinding of isophthalic resin glass fibre reinforced plastic pipes

Abstract

In an experimental investigation some of the parameters affecting the efficiency of cylindrically grinding glass fibre reinforced plastic pipe section have been examined. For a range of grinding conditions, 70% glass isophthalic resin workpieces were ground, using a variety of aluminium oxide and silicon carbide grinding wheels. Such parameters as grinding forces, specific energy, and wheel wear are collated. Also examined was the effect on the grinding parameters and workpieces when the infeed rate is increased, for grinding both with and without coolant.

MST/383     

Impact of grinding aids on dry grinding performance,bulk properties and surface energy

In dry fine grinding processes the relevance of particle-particle interactions rises with increasing product fineness. These particle-particle interactions reduce the grinding efficiency and complicate the process control. The adsorption of grinding aid molecules on the product particle surface is a common measure to handle these effects. To ensure an efficient grinding aid application, the impacts of additives on particle and bulk properties, which influence the micro-processes inside the mill, need to be understood. Within this study the effects of several grinding aids on dry fine grinding of limestone in a laboratory vibration mill were investigated. Unlike in many other scientific works, the impacts of grinding aids were analyzed on different levels simultaneously: Grinding success and agglomerate size distributions were evaluated by wet and dry particle size measurements, respectively. Additionally, material coating on the grinding media, powder flowabilities and particle specific surface energies were measured. It was shown that all of the investigated grinding aids influence the grinding efficiency. However, the formation of agglomerates is not necessarily linked to the product fineness. Furthermore, a strong impact of certain grinding aids on the flowability of the product powder was determined. Thereby, the bulk flow behavior also determines the grinding result as it affects the stress mechanism inside the mill. Moreover, a direct relation between surface energy and powder flowability as well as agglomeration behavior could be demonstrated.     

Issues of Fine Coal Grinding in the Heat and Powder Plant Industry

ABSTRACT

Fine powder processing is of interest for reducing emissions such as NO_x, CO, and for improving the combustion efficiency in coal fired heat and power plants. Within the presentation, first a short overview will be given about recent developments of fine coal grinding technologies in the German power plant industry. Afterwards, bench scale test results with a coal impact mill and a 0.5 MW_th, pf-fircd coal combustion chamber will be shown; these results demonstrate the effect of fine coal grinding on NO_x, -emissions, and especially on burnout. Also, the necessary milling energy for fine goal grinding was of particular interest. Based on these results, the application of fine coal grinding technologies in full scale power plants will be assessed.     

Use of Wet Grinding and Aging to Produce Narrow Particle Size Distribution

An experimental study on the improvement of particle size distribution of calcite powder (d₅₀ = 3.23 μm) was carried out. Ultrafine grinding of calcite powder was studied under batch wet conditions in a laboratory stirred mill. After grinding, the suspension was allowed to age at 30°C for 12 and 24 h. The results indicated that the fineness narrow particle size distribution is influenced to a small extent by altering some operating parameters, such as suspension temperature and aging time. Further increase in the fineness narrow particle size distribution is likely with additional optimization work on the operating parameters of aging process.     

A study on the effect of process parameters in stirred ball mill

An experimental study on the fine grinding of calcite powder (d₅₀ = 62.16 μm) using a 0.75 l laboratory stirred ball mill has been carried out. The effects of various operating factors, such as grinding time (min), stirrer speed (rpm), slurry density (wt.%) and ball filling ratio on fine grinding was studied under batch wet conditions using alumina balls, 95% purity with diameters 3.5–4.0 mm. A series of laboratory experiments using 2⁴ full factorial designs was conducted to determine the optimum grinding parameters. The test results showed that the stirrer speed and grinding time have strong effects on the grinding efficiency, based on the value of specific surface area (m²/g).     

Effect of Various Operating Factors on Wet Stirred Mill Performance

In this study, the effects of various operating factors, such as initial particle size, feed quantity, filling volume of the ball, and ball size distribution on fine grinding of calcite powders (CaCO₃) were studied using a laboratory stirred mill under wet conditions. A series of laboratory experiments using 2⁴ full factorial designs was conducted to determine the optimum grinding parameters. The main and interaction effects on the specific surface area (m²/g) of the ground product were evaluated using Yates' analysis. The test results showed that the main factors that influence the mill grinding performance are the feed quantity and the ball size distribution.     

High performance stainless steel via powder metallurgy hot isostatic pressing

Abstract

Argon atomised austenitic stainless steel (AISI 304) powder was characterized for its physical properties such as particle shape, microstructure, median particle size, particle size distribution, apparent density, tap density, and jlowrate. Subsequently, the tap density of the as received powder was improved to the desired level by adjusting the powder distribution followed by mixing and blending. This powder was subjected to hot isostatic pressing (hipping) at two different combinations of temperature and pressure to optimise the microstructure and mechanical properties. Mechanical properties of the stainless steel obtained by the powder metallurgy (PM) hipping route were found to be superior to those of conventionally processed wrought steel. The superior performance of PM hipped steel is attributed to its low oxygen content, fine grain size, and high degree of chemical homogeneity. Although the production of billets by the hipping route does not appear to be economical owing to the high capital cost of the hot isostatic press, the added advantage of obtaining a nearnet shape makes the process economically viable for production of intricate shapes.     

Analysis of ball mill grinding operation using mill power specific kinetic parameters

With a view to developing a sound basis for the design and scale-up of ball mills, a large amount of data available in the literature were analyzed for variation of the two key mill performance parameters: power specific values of the ‘absolute breakage rate of the coarsest size fraction’, S^*, and ‘absolute rate of production of fines’, F^*, with some of the important operating and design variables such as the mill speed, ball load, particle load, ball diameter and mill diameter. In general, values of both the mill performance parameters were found to vary significantly with the mill operating conditions. The nature and relative magnitude of variation for the two parameters also differed significantly. Moreover, the effect of any particular variable on the S^* and F^* values was found to be significantly different for different sets of operating conditions. It has been emphasized that, as the purpose of grinding is to produce fine particles, the mill design and scale-up work should be based mainly on the F^* parameters. Moreover, it is not correct to regard the S^* values to be independent of the mill design and operating variables as a general rule, especially for a fine analysis of the performance of the grinding systems.     

Appropriate selection of an aggregation inhibitor of fine particles used for inhalation prepared by emulsion solvent diffusion

Abstract

Context: Dry powder inhaler (DPI) formulations have been developed to deliver large amounts of drugs to the lungs.

Objective: Fine particles of a poorly water-soluble drug, the model drug ONO-2921, were prepared by the emulsion solvent diffusion (ESD) method for use in a DPI.

Methods: The effects of additives on the fine particle formation of ONO-2921 were estimated when droplets of an ethanolic drug solution were dispersed into aqueous media containing various additives. Subsequently, the suspensions were freeze-dried to create powdered samples to estimate the inhalation properties using a twin impinger and an Andersen cascade impactor.

Results: This simple ESD method produced submicron-sized ONO-2921 particles (approximately 600?nm) in combination with suitable additives. In addition, the freeze-dried powder produced using additives exhibited superior in vitro inhalation properties. Among these methods, the freeze-dried powder produced with 0.50% weight/volume one type of polyvinyl alcohol (PVA-205) displayed the most efficient features in the fine particle fraction (FPF). These results could be explained by the stabilization of the ONO-2921 suspension by PVA-205, indicating that PVA-205 acts as an aggregation inhibitor of fine particles.

Conclusions: The ESD method, in combination with appropriate types and amounts of additives, may be useful for preparing a DPI suitable for delivering drugs directly to the lungs without the assistance of carrier particles.     

Studying the effect of different operation parameters on the grinding energy efficiency in laboratory stirred mill

In this study, considering different operational parameters for stirred media mill, change in specific energy was compared to the change in R_x values, i.e. the cumulative weight of the material undersized to a specific sieve. R values, namely R₃₈, R₇₅, R₁₀₆, were measured before and after grinding in stirred mill. The change in R_x (ΔR_x, %) values were calculated and they were used to evaluate the certain unit of effectual energy (Ecb). This abovementioned calculation is performed by proportioning the Specific Energy (SE) to ΔR_x values. The effectual part of SE is considered to be the ratio of the energy needed only for size reduction in grinding and it should be related to the ΔR_x. The relative Ecb ratios of different grinding conditions give the relative specific energy efficiency ratio (SEe). The relative specific energy efficiency ratio is inversely proportional to specific grinding parameters and ground product particle sizes. The relative specific energy efficiency can be considered as the relative amount of energy for various grinding conditions. The variation between relative energy amount and the previously specified particle size provides a realistic comparison of different grinding parameters. The abovementioned variation could be employed to understand the resistance particle size which is a new concept to describe the particle size at which the maximum effectual SE is directly used. In the context of this study, it was aimed to figure out the interrelation between specific energy efficiency and PSD variation along with the resistance particle size.     

Investigation of the cyanide leaching optimization for ultrafine grinding gold–silver ore

ABSTRACT

In recent years, the ultrafine grinding (UFG) process has become increasingly important for the recovery of precious metals (especially for Au and Ag) from raw ores. It is well known that cyanide leaching of gold–silver ore has been an accepted process in the world. In the current study, UFG was proposed as a pretreatment method prior to cyanide leaching of a gold–silver ore. First, the ore was crushed and ground by jaw, cone crusher, and ring mill, respectively. Particle size of ground product was 75 µm based d₈₀. Second, the fine product was subjected to the grinding process by vertical wet stirred ball mill, and the final ultrafine product was used as leach feed material. The leach feed material had about d₈₀ = 20 µm and d₅₀ = 6.02 µm particle size. Some important leaching parameters were optimized by using the ultrafine powder in the study. The final leach experiments demonstrated that the recoveries of Au and Ag were 91.92% and 82.15% under optimum leaching conditions such as 150 kg/t quicklime dosage, 25% pulp density, 85°C leach temperature, 500 g/t cyanide concentration, and 90 h leaching time.     

Results with a High-G Cyclomill™

ABSTRACT

A Cyclomill with a 2.5” diameter grinding tube has been constructed that operates at about 100 g's. This device is being used to grind a super abrasive to the very small average mean particle size of.25 microns. The media for such grinding is hardened steel shot of between.5 and 1 millimeter diameter. The device is currently being used daily by a major manufacturer of superfine, super-hard abrasives for production. It has been found that, as expected, the rate of wear of the grinding tube is low. The fact that the Cyclomill can achieve such low particle sizes wjih reasonable efficiency would appear to have significant implications for the production of sub-micron grinds in various fields.     

Continuous Grinding Kinetics of Ethenzamide Particles by Fluidized-Bed Jet-Milling

ABSTRACT

Continuous grinding kinetics of Ethenzamide powder, as a model active pharmaceutical ingredient (API) was investigated by fluidized-bed jet-milling. Because the oversize fractions after the classification were well fitted by a modified Rosin-Rammler distribution function, an equation of grade efficiency curve was obtained, which was also characteristic of API. A continuous grinding model was developed on the basis of a batch model by using 1st Kapur function relating grinding rate, the grade efficiency curve, and the overall process flow model consisting of grinding, classification, and mixing zones. The residual ratio obtained was well fitted to the experimental results except for the particle size range smaller than 4 μm and larger than 100 μm. Furthermore, because the volume of the active grinding zone adopted as the fitting parameter was found to be 5 cm³ in all experiments and the value was considered to be appropriate dimensionally, this result supports the reliability of the model.     

Influence of Stress Intensity on the Comminution of Ceramics in Stirred Ball Mills

ABSTRACT

Experimental investigations on the comminution of white fused alumina and silicon carbide in stirred ball mils show that the circumferential velocity of the stirrer disks, the size and density of the grinding beads, as well as the Young's moduli of the grinding beads and of the product, affect the specific energy required for a certain product fineness. The influence of all these operating parameters on the relationship between the product fineness and the specific energy can be described by the stress intensity. The stress intensity is a measure of the energy that can be transferred from the grinding beads to the product particles. Stress intensity and specific energy are the comprehensive influencing parameters on the comminution of ceramic materials in stirred ball mills. For each stress intensity, a certain relationship between specific energy and product fineness exists.     

Analysis of grinding aid performance effects on dry fine milling of calcite

The control mechanism in the production of fine particles is important in dry grinding processes, which are popular in the grinding of some minerals. The behavior of the fine particles with each other and with the mill environment is complex and needs to be investigated in detail (on a micro-scale) in every application. One of the parameters controlling the fine particles in a mill is the use of the correct amount and type of grinding aid. Mechanisms of action must be understood well to develop grinding aids and fully utilize their positive effects. As a general explanation, with the use of grinding aids, the production tonnage can be increased at the desired product fineness, as well as achieving a finer product at the same production tonnage. However, it is necessary to know other mechanisms and effects to increase efficiency and correct use. The influence of grinding aids on the dry fine grinding of calcite using several analysis methods was revealed in the present study. Within the context, the results were assessed considering grinding performance (particle size distribution and size reduction ratio), product quality (color properties), flowability, adsorption properties (FTIR), and agglomeration behavior (SEM). Moreover, the tested effect of each grinding aid was discussed for each analysis, and the collected results were combined around a summary core diagram.     

Influence of dry and wet grinding conditions on fineness and shape of particle size distribution of product in a ball mill

The influence of grinding conditions on the production of fine particles and the width of the particle size distribution produced during ball mill grinding was investigated. The grinding experiments were carried out varying the grinding ball diameter under dry and wet conditions. The relation between the weight passing size observed in an arbitrary cumulative undersize fraction and the grinding time was expressed by modifying Tanaka’s semi-theoretical equation for the grinding limit. The fineness of the product was evaluated by the median particle size in undersize distribution, and the shape of the particle size distributions by three different size ratios calculated using 10%, 20%, 50%, 80% and 90% cumulative weight passing sizes, that showed the width of the particle size distribution. The median particle sizes of product obtained for the grinding limit in wet and dry conditions were around 0.5–0.6 μm and 2 μm, respectively. The width of the particle size distribution in wet grinding decreased with decreasing median particle size of the ground product, and the size distribution in dry grinding became nearly constant. The particle size distribution width was lowered by using smaller grinding balls in wet condition and larger grinding balls in dry condition.     

Novel synthesis of TiN fine powders by nitridation with ammonium chloride

TiN fine powders were prepared by the reaction of TiH₂ with ammonium chloride at various temperatures under a flow of N₂/H₂ mixed gas. In a temperature range of 500-800°C, the powder samples obtained had a particle size of 3-20 nm, and a specific surface area of 30-60 m²/g. The particle size increased with the increase of the reaction temperature. The lattice parameters and the chemical analysis data showed that the TiN powder had the stoichiometric composition. The TiN powder prepared at temperatures of 600-800°C showed superconductivity with a transition temperature of 4.0-4.5 K.     

Aluminium powder particles produced by SAMD technique: typical characteristics and correlations between processing conditions and powder size

Abstract

The present paper consists of two parts. In the first part the principles of a new method of metal powder production, termed 'solid assisted melt disintegration (SAMD)' are discussed and the typical characteristics of the produced powder are outlined. In the second part the effects of some processing parameters on the size distribution and mean diameter of the powder are reported. The SAMD method involves mixing solid particles (i.e. alumina) with the liquid aluminium alloy aided by mechanical agitation. The shear force induced by the impeller is transferred to the metal via the non-wetting solid medium and results in melt disintegration. The resulting mixture of aluminium droplets and alumina particles are subsequently cooled in air and screened through 300 μm sieve to separate alumina from solidified aluminium powder particles. The SAMD technique has demonstrated the capability to produce a wide particle size distribution. The small sized particles (i.e. <53 μm) exhibited irregular shapes, but larger ones were mostly spherical. These powder particles were dense (pore free) without attached satellite particles and exhibited a relatively coarse microstructure. The processing parameters investigated include the size of Al₂O₃ particles, Al₂O₃/Al weight ratio, stirring speed and stirring time. It was concluded that there exists an optimum value for each of the aforementioned parameters corresponding to a minimum in the mean particle size.     

Thermoelectric properties of a Pb0.2Sn0.8Te solid solution prepared through thermal decomposition of salts

We have studied the thermoelectric properties of microcrystalline samples of the Pb_0.2Sn_0.8Te solid solution prepared by hot-pressing fine powders obtained through the thermal decomposition of lead acetate trihydrate and tin oxalate in the presence of tellurium powder. The electrical conductivity, Seebeck coefficient, and thermal conductivity of the samples have been measured at room temperature and in the temperature range 300–700 K and correlated with the particle size of the powders and heat-treatment conditions. We have compared the thermoelectric properties of hot-pressed samples from powders prepared through the thermal decomposition of salts and by mechanical grinding of ingots.     

Evaluation of size reduction and power requirement in ambient and cryogenically ground fenugreek powder

This comparative study on particle size analysis of ambient and cryogenically ground fenugreek powder shows the change in different grinding parameters such as a function of varying moisture content. Comparatively finer powder was found in case of cryogenic grinding as analyzed using MaScontrol as well as through sieve analysis. Grinding time (found more for normal grinding), number of revolutions (less for cryogenic grinding), specific energy requirement (more for ambient grinding), specific surface area (higher for cryogenic grinding) were found to be increasing with increasing moisture content for both ambient and cryogenic grinding but feed rate was found to be decreasing in nature with increasing moisture content for both the grinding processes. Statistical analysis of mean, mode median, variance, variation, Skewness, Curtosis, and Span is also reported.