Coarse Dust Research Articles

The Removal of Dust and Trash from Cotton Sliver by Segmental Drafting

Segmental drafting makes use of a roll with a discontinuous surface, located in the front, bottom position of a two zone drafting system. Segmental drafting removes more coarse trash and dust (larger than 43 μm) and slightly less fine dust than a continuous drafting roll used in the same position. Segment roll design, sliver production rate, drafting force, and draft ratio all have an effect on dust removal.

The Continuous Monitoring of Particulate Emissions

Particulate emission from the combustion of fuel must be monitored by two types of instrument. The fine end of the spectrum, which causes visibility problems in the atmosphere, can be checked by smoke recorders. The inherent inaccuracies of these instruments can be greatly reduced by the use of a steel tube to maintain alignment, by the use of Everclean Windows, and by the automatic use of purging air to record the effective instrument zero (British Patent Application No. 44785/69). The coarse end of the spectrum, which tends to pollute surfaces at ground level, can be checked by the CERL Flue Dust Monitor which is particularly sensitive to the coarser dust. This instrument has been made extremely simple and reliable by intensive development. It is particularly suitable for checking the performance of electrostatic precipitators.

The personal Centripeter--a particle size-selective personal air sampler.

A size-selective air sampler suitable for the measurement of personal exposure to radioactive dust is described. Sampling at 21/min, it separates coarse dust from the finer particles which are collected separately on discs of high efficiency glass fibre filter paper suitable for direct radiation counting. Suction is provided by a diaphragm pump, the rapid variation of air flow-rate being suppressed by a pulsation damper. The collection characteristic of the first stage (the cone) is such that 50 per cent of the mass associated with unit density spherical particles of diameter above 5 µm is collected; the remainder is deposited on a filter paper in the second stage. Wall losses as a function of particle size have been measured. The maximum loss (∼14 per cent) occurs on the nozzle of the cone for particles of diameter about 3 μm.

A Gravimetric Dust Sampling Instrument (Simpeds): Preliminary Results

An extremely portable gravimetric airborne dust sampling instrument, which is built into a miner's cap-lamp and battery assembly, is described. The instrument (Simpeds) samples at 1·85 l/min, uses a cyclone elutriator to separate coarse dust, and collects the fine airborne dust on a membrane filter for subsequent weighing and analysis. Results with a prototype instrument suggest that it over-samples by about 10 per cent compared with the Mre and Simgard gravimetric dust sampling instruments. Simpeds has been designed to satisfy safety requirements for use in British coal mines, where it could be used for research purposes.

熔接衛生に関する研究 (その2) : 熱応力が熔接時の発塵に及ぼす影響

Coating materials of electrodes are rapidly heated during arc-welding. In order to study how thermal stress generated by the are-welding effects the production of dusts, samples of coating materials were rapidly thrown into an electric furnace kept at constant temperatures (every 100°C, from 100°C to 1000°C) and were heated for 20 minutes. Obtained results were shown by the time-differential value of weight change curves. Whether the heating temperature was high or low, the thermal stress was generated ad maximum 30∼40 seconds after the beginning of heating the samples and caused to produce a lot of dusts. Heatings at 300°C∼400°C and 500°C∼800°C generated extreme thermal stresses. These temperatures were in accordance generally with those (below 300°C and 450°C∼670°C) already reported. When the coating materials was rapidly heated, the thermal stress generated even below 1, 000°C could be a thermal shock, producing dusts. The thermal shock at 300°C∼400°C caused mainly by the vaporization of hygroscopic water, which acts between structures and between crystals, developing coarse dusts. The dusts produced at 500°C∼800°C are caused by decreasing glutinosity of the coating materials and by various changes of the crystal system. This thermal shock acts between crystals and between the internal parts of the crystal, producing fine dusts.

The Variability of Dustfall Analysis Due to the Container and the Collecting Fluid

As part of their air pollution control program, many communities monitor the coarse dust content of the atmosphere by simply exposing an open vessel to the atmosphere for an extended period of time. The material collected and retained by a fluid layer is then weighed and chemically analyzed. In this study a statistical approach was used to separate the real and significant effects of different container-fluid combinations on both the magnitude of dustfall and its composition.

Dust Control in Living Rooms by the Air Filter Cleaner.

Dust controling effect of the air filter cleaner was tested in chemical laboratories and a residence. The coarse dust impactor, the Roken dust counter and the electrostatic dust sampler were used for dust determinations. Air borne dust was decreased to one third∼one tenth of the control tests by the air filter cleaner, if the number air changes of caused by the apparatus was 5∼6/hr. This air filter cleaner was more effective on fine dust particles than on coarse dust particles, and most effective on the total dust concentration in weight.

DUST IN CARD ROOMS: A CONTINUING PROBLEM IN THE COTTON-SPINNING INDUSTRY.

The results are given of environmental and clinical investigations in four card rooms where one of the latest systems of exhaust ventilation to control dust has been installed. The concentration of air-borne coarse dust particles, larger than 2 mm., was reduced by between 80% and 90% around the carding engines. The card rooms consequently looked less dusty. However, the concentrations of medium and fine sized dust particles were not always reduced and were actually increased in some places. In one mill, when the new control system had been running for three years, there was found to be no reduction in the prevalence of non-specific chest symptoms, and there was an increase in the number of those with chest tightness on Mondays, a symptom characteristic of byssinosis. Evidence is given of a similar failure to reduce the dust sufficiently in three other mills where the same exhaust system is installed. There is an urgent need to extend the limited investigations reported here to a larger number of mills. Meanwhile there is a continuing morbidity and mortality from byssinosis. Until work in card rooms has been made safe and proved to be so, it is necessary to have regular measurement of dust conditions and for the workers to have periodical medical examinations to enable managements to be advised about the hazards in their mills and advice to be given to the individuals affected by the dust.

The Cascade Impactor: An Instrument for Sampling Coarse Aerosols

A new instrument is described which will sample windborne and stationary aerosols such as natural fogs and clouds, fine sprays, insecticidal mists, coarse dusts, pollen and spores, etc. By means of four progressively finer jets impinging on glass slides in series the sample is split up into size-graded fractions in a form suitable for microscopic analysis. The greatest efficiency of sampling is achieved for particles in the range 50 μ-1.5μ diameter. The size-grading greatly facilitates the detailed microscopic examination of heterogeneous samples and in some cases enables approximate size-distributions to be obtained by bulk estimations of the samples without the need for microscopic sizing. Experimental results for the efficiency of jets in impacting particles are correlated by dimensional analysis, and a parameter of general applicability for estimating impaction efficiencies of jets is derived. Descriptions are given of new methods of dealing with volatile droplets and of analysing the samples.

Earth-Currents and the Occurrence of Gold

GOLD has been so large a factor in the prosperity and greatness of Australia, that the interesting subject of the origin of gold drifts and reefs must always possess to us something more than a purely scientific attraction. In the earlier days of the goldfields there was among the diggers much speculation, of a scientific and semi-scientific nature, as to the processes by which Nature had produced the accumulations of coarse and fine gold dust which it was their business to extract from the alluvial drifts. The most obvious explanation, of course, was that the grains of gold had an origin similar to that of the debris and detritus of various characters which made up the alluvium itself; and this explanation seemed to harmonize so completely with the general processes of Nature that at one time it was almost universally accepted as the correct one. But many thoughtful mining authorities had their doubts upon the subject, and these doubts were not founded, as so frequently happens, upon mere prejudice, but were fortified by the fact that certain phenomena characteristic of the occurrence of drift gold were not only not explained by the “detrital hypothesis,” as it is called, but were absolutely inconsistent with it. Chief among these objections may be mentioned the undoubted generalization that drift gold is nearly always purer than the gold in the reefs of the neighbourhood in which it occurs. No explanation as to the long distances to which grains of gold might be conveyed, or to the possible purifying effects of natural chemical action, made up any satisfactory explanation of the known facts, and accordingly under the detrital theory these facts had to remain shrouded in mystery. Then, again, it was a frequent occurrence for gold to be found so peculiarly embedded in pieces of wood, or in conjunction with natural crystals of minerals, such as the sulphides, that those who were constantly being brought into contact with such phenomena were firmly convinced that at all events there was a certain proportion of the gold found in alluvial drifts which had its origin in some other source than the breaking down of quartz reefs by the ordinary processes of Nature. The majority of those who held to this belief had at first but little scientific knowledge of natural reactions; and when questioned as to their theory on the subject, they were accustomed to say of the alluvial drift-gold, that it appeared to be actually growing—a statement which sometimes provoked, not unnaturally, a smile of pity for misplaced credulity.