Nature of corrosive and abrasive wear in ball mill grinding

Laboratory results of marked-ball wear tests are used to discuss the relative significance of corrosive and abrasive wear in wet grinding. The electrochemical mechanism was investigated by correlating the corrosive wear with the corrosion current obtained from polarization curves under abrasion. Slurry rheology governs the manner in which ground slurries coat grinding balls, thereby influencing not only the grinding efficiency but also abrasive wear. The effects of percent solids and a grinding aid are illustrated.

Francis Watsonin teologinen hermeneutiikka

Tämän tutkimuksen tehtävänä on selvittää Francis Watsonin käsitys teologisesta hermeneutiikasta. Tutkielmassa käytetään kolmea tarkentavaa tutkimuskysymystä: Miten Watson hahmottaa tieteellisen raamatuntutkimuksen ja Raamatun teologisen tulkinnan suhteen? Miten Watson näkee raamatuntutkimuksessa historiallisen ja kirjallisen lähestymistavan suhteen toisiinsa? Miten Watson suhtautuu postmodernismiin teologisessa hermeneutiikassaan? Tutkimusmetodina on systemaattinen analyysi. Watsonin teologista hermeneutiikkaa ei ole tutkittu suomeksi ennen tätä työtä ja kansainvälistäkin tutkimusta aiheesta on hyvin vähän. Sen vuoksi tutkimuksessa on pyritty käsittelemään Watsonin teologista hermeneutiikkaa mahdollisimman kattavasti, mutta samalla on jouduttu rajaamaan työn ulkopuolelle osa Watsonin käsittelemistä teemoista, kuten Raamatun feministinen kritiikki ja VT:n ja UT:n suhde. Tutkimuksen päälähteinä ovat Watsonin kirjat Text, Church and World ja Text and Truth, joissa hän analysoi modernia historiallis-kriittistä raamatuntutkimusta, postmodernismia ja kirjallista lähestymistapaa Raamattuun. Watson kritisoi niissä näkemiään ongelmia ja kritiikkinsä pohjalta rakentaa omaa teologista hermeneutiikkaansa. Toissijaisina lähteinä tutkimuksessa on useita Watsonin artikkeleja, jotka tuovat lisävalaistusta Watsonin hermeneuttiseen ajatteluun. Päälähteiksi valitut teokset ja toissijaisiksi lähteiksi valitut artikkelit kattavat laajasti Watsonin hermeneutiikkaa käsittelevät kirjoitukset. Johdannon ja loppukatsauksen lisäksi tutkimus on jaettu neljään päälukuun. Tutkielman toisessa luvussa selvitetään Watsonin näkemys tieteellisen raamatuntutkimuksen ja Raamatun teologisen tulkinnan suhteesta ja havaitaan, että Watsonin mukaan raamatuntutkimuksen tulisi palvella teologista tulkintaa. Watson näkee ongelmallisena modernin raamatuntutkimuksen taipumuksen pitää erillään raamatuntutkimus ja -tulkinta ja luoda vastakkainasetteluja yliopiston ja kirkon, eksegetiikan ja systemaattisen teologian sekä neutraalin ja teologisen tulkinnan välille. Kolmannessa luvussa tarkastellaan Watsonin kritiikkiä historiallis-kriittistä tutkimusta kohtaan ja hänen perustelujaan päätökselle käyttää raamatuntulkinnassa ensisijaisesti tekstien lopullista, kanonista muotoa. Watson tukeutuu perusteluissaan Brevard Childsin kanoniseen lukutapaan ja tekstien yhteisölliseen käyttöön. Havaitaan, että Watson kuitenkin kritisoi kanonista lukutapaa sekä formalismista että sen teologisista sidonnaisuuksista. Watson hakee tukea myös Hans Frein narratiivisesta lähestymistavasta, jota Watson samalla kritisoi totuuskysymyksen ohittamisesta. Lopuksi käsitellään Watsonin yritystä liittää tekstin maailma ja sen taustalla oleva sosio-poliittinen todellisuus toisiinsa. Neljännessä luvussa käsitellään Watsonin yritystä yhdistää historiallinen ja kirjallisuustieteellinen lähestymistapa Raamatun teksteihin. Havaitaan, että Watsonin mielestä historiallis-kriittinen tutkimus polkee paikallaan ja siksi tarvitaan kirjallinen lähestymistapa, joka painottaa tekstin lopullista muotoa. Luvussa osoitetaan, ettei Watson kuitenkaan halua korvata puhtaasti historiallista lähestymistapaa puhtaasti kirjallisuustieteellisellä lähestymistavalla, sillä hän näkee ongelmallisena myös narratiivisen kritiikin taipumuksen käsitellä raamatunkertomuksia fiktiivisinä narratiiveina. Watson pyrkii ratkaisemaan ongelman yhdistämällä historiallisen ja kirjallisuustieteellisen lähestymistavan toisiinsa käsittelemällä evankeliumeja kerrottuna historiana. Viidennessä luvussa selvitetään miten Watson suhtautuu postmodernismiin teologisessa hermeneutiikassaan. Siinä havaitaan, että Watson näkee postmodernismin tarjoavan hyödyllisiä näkökulmia useissa hermeneuttisissa kysymyksissä. Samalla Watson vastustaa postmodernismin näkemystä, ettei teksteillä ole yhtä määrättyä merkitystä ja postmodernin teologian taipumusta viedä Raamatun kertomukselta sen universaali merkitys. Luvussa kuitenkin osoitetaan, että Watsonin antama kuva George Lindbeckin ja Stanley Hauerwasin postmodernista teologiasta on yksipuolinen ja osittain virheellinen.

Laboratory studies on ball wear in the grinding of a hematite-magnetite ore

Marked-ball grinding tests were carried out under different grinding conditions and environments. Three types of balls were used, namely, cast hyper steel, high chrome cast iron and EN-31 (forged), which cover a wide range of chemical composition, microstructure and media hardness. The effect of pulp density on ball wear and grinding efficiency was also studied. Relative pulp viscosities at different percent solids for the ore slurry were also determined. As the Kudremukh ore contained about 0.2% pyrite, the effect of addition of pyrite on ball wear was studied separately. Results of marked-ball grinding tests indicated that ball wear increased with time and showed a sharp increase for wet grinding over dry grinding. Ball wear under wet grinding conditions was also influenced by the gaseous atmosphere in the mill. At 70% solids, the best results in terms of reduced ball wear coupled with satisfactory grinding efficiency were obtained. The influence of oxygen on the corrosive wear of grinding balls was increasingly felt only if sulphide minerals such as pyrite were also present in the ore. The various ball materials could be arranged in the following order with respect to their overall wear resistance: high chrome cast iron > EN-31 (forged) > cast hyper steel.Possible ball wear mechanisms involved in the grinding of Kudremukh ore are discussed.

A new approach to the kinetics of size reduction in ball milling

The rate of breakage of feed in ball milling is usually represented in the form of a first-order rate equation. The equation was developed by treating a simple batch test mill as a well mixed reactor. Several case of deviation from the rule have been reported in the literature. This is attributed to the fact that accumulated fines interfere with the feed material and breaking events are masked by these fines. In the present paper, a new rate equation is proposed which takes into account the retarding effect of fines during milling. For this purpose the analogy of diffusion of ions through permeable membranes is adopted, with suitable modifications. The validity of the model is cross checked with the data obtained in batch grinding of ?850/+600 ?m size quartz. The proposed equation enables calculation of the rate of breakage of the feed at any instant of time.

Ball wear and its control in the grinding of a lead-zinc sulphide ore

Marked ball grinding tests were carried out in the laboratory with a lead-zinc sulphide ore under different experimental conditions using high carbon low alloy steel (cast and forged) and high chrome cast iron balls. Relative ball wear as a function of grinding period and milling conditions was evaluated for the different types of ball materials. The role of corrosion and abrasion-erosion in the wear of grinding media is brought out. Methods to minimise ball wear through control of mill atmosphere and addition of reagents are discussed.

Effect of microstructure and hardness on the grinding abrasive wear resistance of a ball bearing steel

Grinding media wear appears to be non-linear with the time of grinding in a laboratory-scale ball mill. The kinetics of wear can be expressed as a power law of the type w=atb, where the numerical constant a represents wear of a particular microstructure at time t = 1 min and b is the wear exponent which is independent of the particle size prevailing inside a ball mill at any instant of time of grinding. The wear exponent appears to be an indicator of the cutting wear mechanism in dry grinding: a plot of the inverse of the normalised wear exponent (Image ) versusHs (where Hs is the worn surface hardness of the media) yields a curve similar to that of a wear resistance plot obtained in the case of two-body sliding abrasive wear. This method of evaluating the cutting wear resistance of media is demonstrated by employing 15 different microstructures of AISI-SAE 52100 steel balls in dry grinding of quartz in a laboratory-scale ball mill.

Ball wear mechanisms and control in the grinding of sulfide and phosphate ores

Marked ball grinding tests were carried out in the laboratory using high carbon low alloy steel (cast and forged) and high chrome cast iron balls. Relative ball wear as a function of grinding period and milling conditions was evaluated for the different type of ball materials in the grinding of lead-zinc sulphide and phosphate ores. Results indicated that ball wear increased with time and showed a sharp increase for wet grinding over dry grinding. Ball wear under wet grinding conditions was also influenced by the gaseous atmosphere in the mill. The influence of oxygen on the corrosive wear of grinding balls was increasingly felt in case of sulphide ore grinding. The grinding ball materials could be arranged in the following order with respect to their overall wear resistance:

Combined Cryo and Room-Temperature Ball Milling to Produce Ultrafine Halide Crystallites

The combined milling at cryogenic temperature as well as room temperature (RT) has been carried out to prepare ultrafine NaCl crystallites. The milling has been done in evacuated tungsten carbide vials backfilled with high-purity Ar. The results indicate the effect duration of cryomilling prior to RT milling has a strong effect on the final crystallite size. The deformation aided sintering of NaCl crystallites during RT milling and leads to the formation of bimodal distribution of crystallites. The cuboidal-shaped NaCl crystallite undergoes a roughening transition due to plastic deformation. The experimental results are explained using the temperature-dependent mechanical properties of NaCl single crystals and plastic-deformation-induced roughening.

Laboratory studies on ball wear in the grinding of a chalcopyrite ore

Wear of high carbon low alloy (HCLA) cast steel balls during the grinding of a chalcopyrite ore was evaluated under different experimental conditions. The role of oxygen in enhancing ball wear during wet finding is brought out. The influence of pH on ball wear was also examined from the view point of acid production during grinding and reactivity of sulphides. Contributions from corrosion and abrasion towards ball wear are quantified in terms of ball wear rates as a function of time, particle size and gaseous atmosphere in the mill.

Preparation of ultrafine CsCl crystallites by combined cryogenic and room temperature ball milling

The present investigation reports the preparation and microstructural characterization of ultrafine CsCl crystallites using combined cryogenic and room temperature (RT) mechanical milling. The milling has been performed in evacuated WC vials under high purity argon atmosphere. The low temperature milling has been utilized as an effective means of rapid fracturing of the CsCl crystallites. This was followed by RT milling for different time durations. The final crystallite size obtained is 10 +/- 6 nm for sample cryo-milled for 11 h and subsequently RT milled for 35 h. The experimental findings indicate the strong effect of duration of cryo-milling on the final size of the crystallites. The prolonged room temperature milling leads to increase of the crystallite size due to deformation-induced sintering. The results have been discussed in the light of currently available literature. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Friction between a Steel Ball and a Steel Flat Lubricated by MoS2 Particles Suspended in Hexadecane at 150 degrees C

A steel ball was slid on a steel flat lubricated by molybdenum disulfide (MoS2) particles suspended in hexadecane oil at 150 degrees C. The friction data is compared with that obtained when the ball was slid on the flat sprayed apriori with nominally dry MoS2 particles. The friction in the dry experiment was found to increase with temperature while the friction in wet condition was found to decrease with increasing temperature. Micro-Raman and Fourier transform IR spectroscopy are used to explore the roles of environmental moisture and chemical degradation of oil on the formation of antifriction film on the steel substrate.

Synthesis of free standing nanocrystalline Cu by ball milling at cryogenic temperature

This paper reports for the first time synthesis of free standing nano-crystalline copper crystals of a similar to 30-40 nm by ball milling of copper powder at 150 K under Argon atmosphere in a specially designed cryomill. The detailed characterization of these particles using multiple techniques that includes transmission electron microscopy confirms our conclusion. Careful analysis of the chemistry of these particles indicates that these particles are essentially contamination free. Through the analysis of existing models of grain size refinements during ball milling and low temperature deformation, we argue that the suppression of thermal processes and low temperature leads to formation of free nanoparticles as the process of fracture dominates over possible cold welding at low temperatures. (C) 2012 Elsevier B.V. All rights reserved.

Optical and dielectric study of strontium modified barium zirconium titanate ceramic prepared by high energy ball milling

Strontium modified barium zirconium titanate with general formula Ba1-xSrxZr0.05Ti0.95O3 ceramics have been prepared by solid state and high energy ball milling technique. The X-ray diffraction and Rietveld refinement studies show that all the compositions have single phase symmetry. The composition BaZr0.05Ti0.95O3 shows orthorhombic symmetric with space group Amm2. The structure changes from orthorhombic to tetragonal with strontium doping up to x = 0.3 and with further addition, changes to cubic. The scanning electron micrographs show that the grain size decreases with increase in strontium content. The temperature dependent dielectric behavior shows three phase transition in the parent material which merges with an increase in Sr content The transition temperature and dielectric constant decreases with an increase in Sr concentration. The phase transition becomes more diffused with increment in doping concentration. The ferroelectric behavior of the ceramics is studied by the hysteresis loop. The optical behavior is studied by the UV-visible spectroscopy and found that the optical band gap increases with Sr concentration. (C) 2015 Elsevier B.V. All rights reserved.

Magnetohydrodynamics equilibrium of a self-confined elliptic plasma ball

A variational principle is applied to the problem of magnetohydrodynamics (MHD) equilibrium of a self-contained elliptical plasma ball, such as elliptical ball lightning. The principle is appropriate for an approximate solution of partial differential equations with arbitrary boundary shape. The method reduces the partial differential equation to a series of ordinary differential equations and is especially valuable for treating boundaries with nonlinear deformations. The calculations conclude that the pressure distribution and the poloidal current are more uniform in an oblate self-confined plasma ball than that of an elongated plasma ball. The ellipticity of the plasma ball is obviously restricted by its internal pressure, magnetic field, and ambient pressure. Qualitative evidence is presented for the absence of sighting of elongated ball lightning.

Magnetohydrodynamic equilibrium of plasma ball lightning

Thin foil observations using transmission electron microscopy reveal that the density of dislocations within the band is extremely high and the tangled arrangement of dislocations tends to align along the length of the shear band. The grains in the band were also elongated along the shear band and clearly exhibited a crystallographic nature.