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By Tâmisa Eleutério Silva

Ligas de alumínio possuem, dentre diversas propriedades, uma atrativa combinação entre resistência mecânica e densidade, característica que leva à utilização cada vez maior desses materiais em setores estratégicos, como as indústrias aeronáutica e automobilística. O aumento da resistência dessas ligas, por sua vez, está associado ao tratamento de endurecimento por precipitação, podendo ainda ser influenciado pelo encruamemto do metal, esse último decorrente da eventual realização de deformação plástica entre as etapas de solubilização e envelhecimento do referido processamento. Dentro desse contexto, neste trabalho foi avaliado o comportamento mecânico de amostras da liga de alumínio 7.075 submetidas à compressão monotônica e cíclica após a etapa de solubilização do tratamento de endurecimento por precipitação. O comportamento do material foi analisado através de ensaios de dureza. Os resultados evidenciaram os efeitos das características e da magnitude da deformação na propriedade mecânica da liga.

Aug 8, 2018

Detailed underground mine design and optimisation studies undertaken by the author over the past few years have clearly demonstrated that additional value can be created by varying the cut-off grade (COG) spatially throughout a deposit as well as over time. This additional value can be particularly significant for marginal operations. This paper, by way of worked examples, illustrates the conceptual and practical considerations of applying a differential cut-off policy for an underground mine to both maximise value and manage risks associated with production and metal price volatility. Consideration is given to both the design stage of a new mine and to the strategic and practical application of a differential cut-off policy in an operating mine.

Jan 1, 2005

By T. Banerjee, R. deS. Almeida, D. Gudgeon, F. C. F. Batista, L. deÁ. Silva

"Yamana Chapada’s mine is one of the larger copper-gold mines in Brazil. The mine is located in Goiás state, in the central part of Brazil. The mine has estimated Mineral Reserves of 4.1 million ounces of gold and 3.2 billion pounds of copper as of December 31, 2016. While gold and silver are significant, Chapada’s process flowsheet is configured closer to that of copper facilities. This includes a SAG/Ball configuration for grinding followed by flotation. In the case of Chapada, the mineralogy results in higher-than-normal complexity, notably a significant circulating load both in the grinding and flotation circuits. From an operating perspective, the complexities are controllable, but require careful attention to ensure that circulating loads are effectively managed and gold is not lost to tailings. Chapada created an automation roadmap in 2016 designed to increase plant performance (tonnage, recovery and efficiency). Based on strong potential, the project was fast tracked and within 4 months instruments were installed, control algorithms implemented, and training sessions took place to ensure sustainability at site. This paper will follow the Chapada journey from identifying the opportunities through to implementation and testing.IntroductionYamana Chapada mine is a Copper-Gold mine located in Goiás State, Brazil. Although the mine contains large quantities in Mineral Reserve of gold (4.1 million contained oz as of December 31, 2016), Chapada is primarily a copper mine with copper principally found as chalcopyrite. Accordingly, the processing flowsheet at Chapada is comparable to that of other copper mines with a SAG and Ball mill each partnered with a cyclopack, followed by a flotation circuit. While the overall design is conventional, the mineralogy at Chapada results in significant circulating loads both in the grinding and flotation circuits. This does introduce certain complexities for operating strategies and practices, but, importantly, favourable recoveries and elevated processing rates can be maintained, albeit they need to be closely managed. Plant automation helps in this regard."

Jan 1, 2018

By Livia Mara Candido

As reservas de minério de ferro, apresentam tendências de menores teores de Fe, tornando maior a necessidade da redução da fração granulométrica inferior a 150µm, o que torna o processo viável tecnicamente por meio concentração. O método mais comum utilizado é a concentração através da flotação. Flotação é uma técnica de separação baseada na afinidade das espécies minerais com as moléculas de água. Na flotação reversa de minério de ferro, utilizam-se agentes que reforçam o caráter hidrofílico das partículas de Ferro, chamados de depressores. O mais comumente utilizado é o amido de milho em forma de solução, gelatinizado com a adição de soda cáustica. Dentro desse contexto e afim de aumentar o poder de gelatinização do depressor, foram realizados através do planejamento fatorial estatístico, ensaios de flotação em bancada, com diferentes concentrações iniciais e finais de amido de milho presente na solução e ainda a relação de amido/soda para avaliar o impacto sobre a recuperação metalúrgica da flotação, concluindo-se que recuperação metálica foram fortemente influenciados pela concentração inicial da solução de amido.

Oct 30, 2017

By C. Robinson

The Diavik Diamond Mine is located in one of the most remote and forbidding places in the world, 220 kilometres south of the Arctic Circle and on the bed of a vast northern lake, Lac de Gras. A single road, built out of ice and crossing frozen lakes, connects the mine with other operations and Yellowknife, the capital of the Canada's Northwest Territories. Diamonds were first discovered in the Lac de Gras region in the early 1990s, and construction of the Diavik Diamond Mine was completed in 2003. Diavik currently mines three kimberlite pipes. Open pit mining has now concluded and all three pipes are mined using underground mining methods. In early 2010, Diavik began mining and processing initial ore from its new underground mine; underground mining operations are expected to continue beyond 2020. The initial mine ventilation system was an exhausting (pull) system with fresh air supplied by a fresh air raise and a main ramp. Return air was exhausted via two raises and a secondary ramp. The system had a total flow capacity approximating 401-411 m3/s. With planned increased production and with changes in mining method, it has been proposed to change the mine ventilation system to a positive (forcing) ventilation system in order to meet projected increases in flow requirements of 566-708 m3/s. Extensive engineering work was developed in order to successfully achieve the changes in system configuration. In the proposed configuration, the main ramp is in an exhaust configuration and exhaust raises are converted to fresh air raise. A number of system implementation options were investigated and phased plans for system execution have been developed. The proposed changes to the ventilation system are substantial and involve extensive construction work. Work was commenced in 2011, each planned phase has been successfully completed to date, and system changes continue today in order to achieve complete system flow reversal and increased flow distribution. This paper details the design of the modified ventilation system and commissioning work which will allow the mine to meet its future production targets.

Aug 1, 2013

By Daniel Mapa Clemente

Processing of tin slags in reduction furnaces was studied in order to optimize tin recovery and reduce recirculation rates of slags containing thorium and uranium oxides. A theoretical approach considering a mass balance of the process was developed and adjusted by experimental results in order to predict the final slag composition. A metallic phase (FeSnSi) was discovered trapped in the slag due to high apparent viscosity, raising the FeO and SnO2 contents of the slag sample. This FeSnSi alloy is rich in tin and its recovery would help to reduce the slags recirculation. High contents of ZrO2 were found in the slag, restricting it from reaching complete fluid phase. Through an analysis of the slag in the CaO-FeOx-SiO2 and ZrO2-CaO-SiO2 phase systems it can be concluded that final slags should be modeled aiming fluid phase at working conditions and additions should be planned in order to control ZrO2 levels.

Oct 30, 2017

By Jing Zhong, Yugang Li, Chen Yan, Shaoda Zhang, Qian Wang

Online surface quenching technology has been developed for the hot charging process to prevent the surface cracks in high strength low-alloy steel slabs. In this paper, a two-dimensional heat transfer model of surface quenching process was presented. This finite element model includes nonlinear thermodynamic properties, by which the slab temperature distributions were computed. The model predicted temperatures show reasonable agreement with the measurements. The effects of the water flow rate and slab movement velocity on temperature variation during the quenching and subsequent tempering process were investigated. The result shows that the temperature drop increases but the tempering temperature changes slightly with increasing water flow rate and decreasing slab velocity. Keeping the slab movement velocity at 1.2-2.1m/min and the water flow rate at 55-70m3/h, the slab surface experiences a temperature drop of 400-600 firstly, then recovers above 650, the quenching and energy-saving effect are remarkable.

Jan 1, 2015

By Walter Luiz Corrêa Junior

O fósforo é um dos elementos mais importantes do processo de produção de aço em convertedores a oxigénio, devido à dificuldade de remoção durante o processo de sopro de oxigénio e depois do vazamento para panela de aço. Este trabalho mostra resultados obtidos através da alteração em variáveis de processo como o consumo de cales, teor de FeO na escória e uso de fluorita, durante o sopro e a avaliação da partição de fósforo com base em modelos de autores como Healy, Turkdogan, Basu e Suito, foi realizada utilizando os dados industriais da aciaria da ArcelorMittal Tubarão, com objetivo de comparar estes dados com as abordagens citadas. Um software termodinâmico foi usada para cálculo das atividades, da fração de líquido e do fósforo em equilíbrio, com a finalidade de auxiliar a identificação das principais diferenças termodinâmicas entre os dados experimentais e correntes. O resultado final mostra que as alterações realizadas no processo foram significativos para melhorar a taxa de partição de fósforo.

Jul 30, 2018

By M Yahyaei, F Vos, J Siliezar

Site-based case studies (including data collected from industrial surveys) and their application in evaluating circuit performance, have a significant role in developing reliable process models. Such models are useful to both plant metallurgists and researchers. Appropriate process models enable the plant metallurgist to assess the impact of different operational parameters on the overall circuit performance. They also provide the researcher with a detailed understanding of process behaviour in response to changes in ore characteristics and process conditions (ie plant throughput, ore competence, ore type). Thus enabling the identification of effective operating factors, and allowing them to be ranked in order of their influence on the process response, which eventually develops into a process control tool in the hands of plant operators.The above approach has been developed and applied at the Julius Kruttschnitt Mineral Research Centre (JKMRC) separately for both comminution and flotation processes. In recent years, the JKMRC has attempted an integrated approach by developing process models that incorporate the impact of upstream processes on downstream processes. This is not possible using the traditional approach of separate comminution and flotation surveys, so conducting integrated plant surveys is crucial for success in developing integrated process models. This paper summarises industrial experience gained while conducting such an integrated plant survey at Glencore’s Ernest Henry Mining operation near Cloncurry in north Queensland. An appropriate approach should be taken to enable the alignment of different requirements from different processes during the plant survey. This, as well as the challenges faced in integrating comminution process models with flotation process models, are identified.CITATION:Yahyaei, M, Vos, F, Powell, M S, Siliezar, J and Perkins, T, 2014. Challenges in developing integrated process models based on industrial survey data, in Proceedings 12th AusIMM Mill Operators’ Conference 2014 , pp 437–446 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 1, 2014

By C. P. Lowes

"The REFLUX™ Classifier (RC™) consists of a fluidized bed housing, with a system of parallel inclined channels above. This system performs a simultaneous gravity separation and desliming of the feed material, utilising the inclined channels in order to retain the relatively fine dense particles. These particles promote the formation of an autogenous dense medium within the fluidized bed. Relatively large, low density particles are displaced from the fluidized bed and conveyed upwards through the inclined channels reporting to the overflow with other finer particles. Given the hydrodynamic role of both the particle size and density in determining the particle transport through a water based suspension, all gravity separators operate over a limited size range. In the case of the REFLUX™ Classifier, efficient separations can be produced across a very broad size range, from nearly 10 mm down to 10 m, however, for a given application the size range is much more limited. This study was concerned with the processing of dense minerals over a broad size range, and the need for multistage processing. Here the overflow from the first stage cascades to the second stage, incorporating coarse gangue rejection. This approach is shown to deliver remarkably high grades and recovery.INTRODUCTION The performance of the REFLUXTM Classifier (RC™) in beneficiating fine coal is well documented (Galvin, 2012). Although the technology can be applied to relatively fine particles below 0.1 mm, or coarser particles below 2.0 mm or even 8.0 mm (Galvin et al., 2010), in each case the technology is applicable to limited particle size ranges. In coal preparation, the most common size range is 0.25 to 2.0 mm, covering an eight-fold range in the particle diameter. Coal has a relatively low density, typically below 1600 kg/m3, with a significant portion below 1400 kg/m3. In water, the buoyant density difference (~ 400 kg/m3) is therefore low compared to that of gangue minerals (1600 kg/m3) by a factor of 4, enhancing the potential for separation. Thus, in coal preparation, the technology can be applied over a commensurately broader size range, typically up to eight-fold."

Jan 1, 2018

By Rodrigo Estay Huidobro, Andrés Martinoli, Claudia Pavez-Orrego

The effects of induced seismicity caused by mining activities are one of the main problems that the mining industry faces. Although it has been documented by countries with a great mining tradition (United States, Canada, Australia and Chile) for over a century, the problem has been intensified throughout the years due to the greater depths that mineral extraction reaches, where the stress levels and environmental conditions increase the possibility of a rockburst occurrence. Seismic events inside the mine cause important losses of human lives and infrastructure damage. To deal with this problem it is necessary to implement several kinds of safety protocols. For example, seismic indicators allow to identify, through the analysis of a set of seismic parameters -magnitude, energy, time, decay rate, among others-, periods of time when a seismic event of considerable magnitude is most likely to occur. The objective of this work is to use the frictional energy generated by a microearthquake inside the mine as a seismic indicator, linking it with the occurrence of large magnitude seismic events which are outer the background activity. Thus, we seek to determine the set of seismic parameters which allow the best performance of the frictional energy/heat indicator. In the present study, we considered magnitude, frictional energy, and time as seismic parameters to study the efficiency of the proposed indicator. The optimal set of parameters was determined using two different methodologies: accumulated thermal energy and alert bands. The Piece Skill Score and the Accuracy indexes were used to evaluate each set of parameters. Both approaches show a high rate of true positive and true negative hits. Furthermore, it was concluded that both methods show complementary results in terms of the detection of critical events (Mw > 3.0).

Apr 26, 2022

By Michael McClintock, Bern Klein

"The high pressure grinding roll (HPGR) is a relatively new comminution technology that is gaining popularity for providing energy efficient solution to hard rock mining operations. A significant barrier to increased adoption of HPGRs is the present requirement for large amounts (excess of 2 tonnes) of sample for pilot testing, which may not be possible for most early stage projects. Three methodologies have been developed at NBK Institute of Mining Engineering at the University of British Columbia that may be used for sizing design optimization of HPGR circuits. All three methodologies use a MTS pistonpress to simulate HPGR comminution. These tests are capable of providing information regarding energy consumption, energy breakage relationship, reduction ratio, and product size distributions. In a period of slow economic development, these methodologies are critical to allow the industry to cost effectively understand the operational benefits of HPGR implementation. This paper examines previous test work done at UBC, as well as the development of an HPGR and piston press database for use in sizing and budgeting of HPGR circuits.INTRODUCTIONCurrently, the mining industry faces several challenges due to falling commodity prices and escalating costs. This has applied pressure for operations and projects to reduce costs and improve project economics. In addition engineering and metallurgical budgets have shrunk as companies try to conserve cash. Improvements and optimization of milling and comminution circuits is one area project economics may be significantly improved. By considering alternative comminution technologies such as the high pressure grinding roll (HPGR), energy operating costs may be greatly lowered. Many have begun to implement HPGR crushing as an alternative to semi-autogenous grinding (SAG) mills, including KGHM and, Sierra Gorda, and Freeport Mc-MoRan’s Cerro Verde operation. However, implementing new technology for companies with little or no HPGR experience may not be practical. An operator must consider both feasibility and economics of a circuit. Currently, consideration of the HPGR requires expensive pilot scale testing for which large sample sizes are needed. In addition, few laboratories are equipped for running pilot scale HPGR test programs. Furthermore, the results of pilot HPGR testing are dependent on the quality of the sample, which cannot represent variations across a deposit. In contrast, ball mills and SAG mills can be sized using the Bond Mill Work Indexes that require a small amount of sample which enable a number of different geological blocks to be tested to allow engineers to have a complete understanding of how the comminution circuit will perform for the life of mine."

Jan 1, 2016

By Todd Burchett

Mining engineers spend countless hours and resources when designing a new underground coal mine. Their primary objective is to design the safest and most efficient operating mine with regards to coal production. A key variable often overlooked in this design stage is the slope conveyor. Typically, a slope conveyor is expected to operate with a 98-percent or higher availability. However, too often little effort is put forth by the mining engineer to optimize its design. Coal companies will rely on engineering, procurement, construction and management (EPCM) companies for the preliminary design, because the slope conveyor will be considered part of the surface material handling processes. This preliminary design will be used when soliciting quotations for the slope conveyor. Unfortunately, EPCMs may not have enough expertise with conveyors to optimize the design. This expertise is available with an original equipment manufacture (OEM) of conveyors, which ultimately may be responsible for supplying the slope conveyor. Each OEM will provide a bid package that represents what it considers to be the optimal design.

Jan 1, 2013

By S. B. Robertson, D. R. Dolinar, G. E. Hinshaw, G. M. Molinda, D. M. Pappas

Rock falls in coal mines cause many injuries each year. Most of these injuries are not caused by major roof collapses, but from falls of smaller rocks from the immediate top or roof skin. Even though safety professionals and mine operators strive to reduce these types of injuries, there has not been a substantial decrease in the rock fall injury rate over the past decade. Various surface controls are used in mines to control the roof skin. One control that has proven to be very effective is roof screening. Roof screen effectively controls roof skin and provides a high roof surface coverage. Although many mines are reluctant to use screen for primary skin control because of the additional costs of time and materials, others are having great success at controlling both the costs and surface rock. In this study, injury data are presented that show a dramatic reduction in roof skin injuries when screening is used. Much of this success is due to the protection from falling rock that the operators receive from roof screen. Five case studies in which roof screen was used are presented along with the associated costs of materials, impact on bolting advance rates, and potential ergonomic risks. The effects of roof screening on skin control and safety are also included. Finally, this paper provides information about best practices and features of roof bolting machines that affect production and safety.

By Ferry Belisario Benique

A empresa Aceros Arequipa S.A. no seu complexo siderúrgico situado na cidade de Pisco, no Perú, está reutilizando os finos das pelotas de minério de ferro na fabricação de aglomerados (briquetes) para uso no processo de redução direta em forno rotativo na fabricação de ferro esponja (DRI). Dessa forma, testes no laboratório foram realizados com o objetivo de encontrar um ligante ou mistura de ligantes que proporcione um aglomerado com boa resistência à compressão a frio e boas propriedades mecânicas a quente que garantam sua integridade dentro do forno durante o processo de redução. No presente trabalho apresenta-se a metodologia desenvolvida e os resultados obtidos na fabricação dos briquetes em laboratório e na planta piloto de briquetagem de finos. Adicionalmente, resultados dos briquetes após redução no forno rotativo a escala industrial também são apresentados.

Aug 1, 2018

By Fernando Zevallos

Las metodologías actuales para el procesamiento topográfico en las minas subterráneas peruanas pueden ser mejoradas. En el mercado se encuentran módulos de topografía subterránea dentro del entorno de los softwares especializados de minería que integran y automatizan el procesamiento topográfico, la generación de reportes y el manejo de la información topográfica. Este proceso integrado asegura resultados correctos en cuanto a los entregables (sólidos con volumen, planos y reportes). Asimismo, permite reducir el tiempo de procesamiento, que puede ser usado para elevar el nivel de detalle del levantamiento topográfico y realizar una correcta gestión de la información topográfica.

Sep 20, 2019

By M Spiteri, S Woth, J Caratti, K Henley

Blasting is an essentially violent process aimed to disrupt and loosen rock for productive excavation and downstream processing. Dilution of the orebody to some extent is the inevitable result, particularly in narrow vein gold mines. A small change in gold recovery is usually a strong lever on revenue generation. As a result blast designs are carefully engineered to both minimise and control the direction of rock movement. Traditionally blast designs in gold mines have used the minimum powder factor that will still permit rock excavation. This now conflicts with the recent industry trend to optimise the total process flowsheet from the mine to the mill. Numerous mines have achieved success in reducing total mining cost by increasing powder factors. Not only is explosive energy cheaper than mechanical comminution energy requirements, the increased blasting effect may deliver benefits across all downstream processes of digging, hauling, crushing and milling. Kalgoorlie Consolidated Gold Mines (KCGM) Fimiston operation is the largest gold mine in Australia, located in the heart of the Kalgoorlie Goldfields. Blast dilution has been reduced at KCGM by managing location of blast boundaries and by firing along strike to choked faces. Significant economies of scale have resulted from application of a bulk mining methods. The bench height of 10 m is the largest in the Western Australian Goldfields, and is typically mined in a single pass with large face shovels. Recent increases in production rates in both the mine and mill has been partly attributed to a 30 per cent increase in powder factor. KCGM then examined the benefit of a further 18 per cent increase in powder factor to 1.0 kg/BCM. A concern though was the impact of very high powder factors resulting in excessive blast movement and subsequently ore dilution. This was the subject of a project conducted with Orica Explosives. OricaÆsDMC(Distinct Motion Code) blast model was applied to understand the effect of not just further increases in powder factor but also blast geometry and explosive type. The modeling work demonstrated that high powder factors may be applied with minimal increase in ore dilution provided the combination of blast geometry and explosive type is optimised. These results are currently being implemented to achieve further reductions in total mining costs without a significant impact on recovery.

Jan 1, 2001

By B Zhao

Gas and coal dust, as potential harmful elements (PHEs) produced during mining, are considered two serious threats to the safe mining and the health of miners because of its explosive and pathogenic properties. To solve this problem, compound reagents enhanced water spraying technology was used to control the gas and coal dust in excavation working face in this study, and spray testing platform and wind tunnel were used to investigated the suppression effect for gas and coal dust. In addition, sink test, and agglomeration experiments were also used to analyse its suppression mechanism. Testing results show that the dust reduction efficiencies of compound reagents enhanced water spraying technology for four different particle sizes were 80 per cent, 91.43 per cent, 94.74 per cent and 94.46 per cent, and improved by 14 per cent, 10.86 per cent, 8.42 per cent and 4.25 per cent compared to water spraying. Moreover, the gas suppression efficiency also can be increased more than 20 per cent. Sink test, and agglomeration experiments results show that compound reagent improves the spreading efficiency of the liquid on the surface of the coal by changing its wettability, and this process can not only slow down the desorption rate of gas by forming a water-sealing effect in the coal surface indicated, but also promote the agglomeration of fine-grained coal dust.

Oct 12, 2022

By Congling Shi, Marek Borowski, Yue Wang, Jianwei Cheng, Xixi Zhang, Xuan Xu

As the first barrier to prevent accidents caused by explosions in underground coal mines, the integrity and stability of mine seals have great effects on mine workers’ lives and underground production safety. In this paper, the mechanical responding performance of typical mine seals under the impact load are studied by using numerical simulation method. By such simulation studies, the safety of different seals subjected to the explosion load is evaluated. Seals’stability are also investigated under effects caused by various influence factors including thickness of mine seal, cutting depth into surrounding rocks, rock type, and the roof-tofloor convergence under given the explosion load. The research results can provide theoretical basis and reasonable improvements for mine seal’s construction practices for improving its anti-explosion performance.

By F. Calizaya, S. Bhattacharyya

"INTRODUCTION Mechanized underground mines often suffer from noise overexposure. Noise levels are usually above the Permissible Exposure Limit (PEL) where underground fans are used. Sound levels in active workings can reach 121 dB(A), especially when fans are not equipped with silencers. Use of silencers seldom ensure PEL for various reasons. Overexposure of noise induces permanent hearing loss among mine workers. Recent field studies by a NIOSH-funded research project at six coal and non-coal mines revalidated the findings. The University of Utah has undertaken laboratory studies to reduce fan noise at the source. A new silencer prototype with varying noise dampening material has been designed and tested. The silencer and an associated extension which can be repacked with different dampening materials were used in various configurations. Attempts were made to simulate field conditions where installations are quick and not perfect. The test results are presented here. NOISE IN UNDERGROUND MINES Noise induced hearing loss (NIHL) is a chronic problem in the mining industry. In spite of regulations being in place and elaborate hearing protection programs under way, hearing loss is prevalent among the mine workers (Bise, 2001). All production and support machinery in mining generate loud noise often beyond the approved exposure level. Researchers in the U.S. have identified auxiliary fans as one of the major sources of noise that can create noise exposure levels up to 121 dB(A), which is one of the highest in the mining operation (Bauer, 2006). Studies have demonstrated substantial reduction of noise level by using silencers. Adequate fan selection and proper utilization of silencers in auxiliary fans have great potential of abating the problem. In hard rock mines, auxiliary fans are used in blower configuration to ventilate development headings and large production stopes, and also to ventilate underground shops, crushers, conveyor transfer points, etc. Typical duct diameters in hard rock mines vary from 0.91 m to 1.21 m. Silencers are often omitted for cost reduction. In coal mines auxiliary fans are used in exhaust configuration with rigid ducts 0.61- 0.76 m in diameter (Hagood, 1982 and Moreby, 2009) to ventilate working faces in gate-roads and main entry developments. Sometimes, stone dusters are added at the discharge end to dust the roof, ribs and floor. AUXILIARY FANS AND SILENCERS Auxiliary fans are relatively smaller in size than the main fans and often have high rotational speeds (1800 -3000 rpm). Fans are selected based on pressure-quantity requirements and space restrictions only. Noise emissions are rarely considered during the selection stage. Installation of fans, ducts and other accessories is mainly based on best practices, which often do not include noise control. As a result, the operation of an auxiliary or local ventilation system normally produces excessive noise."

Jan 1, 2018