Hard Metal Manufacturing Research Articles

Dermal and inhalable cobalt exposure-Uptake of cobalt for workers at Swedish hard metal plants.

PurposeCobalt exposure is known to cause adverse effects on health. A major use of cobalt is in the manufacture of hard metal. Exposure can lead to asthma, hard metal lung disease, contact allergy and increased risk of cancer. Cobalt is mainly absorbed from the pulmonary tract, however penetration through skin may occur. The relationships between exposure to inhalable cobalt in air and on skin and the uptake in blood and urine will be investigated, as well as the association between dermal symptoms and dermal exposure.MethodsCobalt exposure in 71 workers in hard metal production facilities was measured as inhalable cobalt in the breathing zone and cobalt found on skin with acid wash. Uptake of cobalt was determined with concentrations in blood and urine. Correlations between exposure and uptake were analysed.ResultsInhalable cobalt in air and cobalt in blood and urine showed rank correlations with coefficients 0.40 and 0.25. Cobalt on skin and uptake in blood and urine presented correlation coefficients of 0.36 and 0.17. Multiple linear regression of cobalt in air and on skin with cobalt in blood showed regression coefficients with cobalt in blood (β = 203 p < 0.0010, and β = 0.010, p = 0.0040) and with cobalt in urine (β = 5779, p = 0.0010, and β = 0.10, p = 0.60).ConclusionsOur data presents statistically significant correlations between exposure to cobalt in air with uptake of cobalt in blood and urine. Cobalt on skin was statistically significant with cobalt in blood but not with urine.

Mortality Among Hardmetal Production Workers: UK Cohort and Nested Case-Control Studies.

The aim of this study was to characterize the mortality at two hardmetal production factories in the United Kingdom as part of an international study. Standardized mortality ratios (SMRs) were calculated on the basis of mortality rates for England and Wales, and local rates. A nested case-control study of lung cancer was undertaken. The cohort comprised 1538 workers, with tracing complete for 94.4%. All-cause mortality was statistically significantly low for all cancers and nonmalignant respiratory disease, and for lung cancer was nonsignificantly low. The SMR for lung cancer for maintenance workers was elevated, based on only six deaths. The odds ratio for lung cancer per year of exposure to hardmetal was 0.93 (0.76 to 1.13). In this small study, there is no evidence to support that working in the UK hardmetal manufacturing industry increased mortality from any cause including lung cancer.

Biological monitoring of dermal and air exposure to cobalt at a Swedish hard metal production plant: does dermal exposure contribute to uptake?

SummaryBackgroundOccupational exposure to cobalt is well established in hard metal manufacture. Cobalt is known to cause contact allergy, asthma, hard metal lung disease, and lung cancer. The relationship between skin exposure and uptake determined in blood has not been extensively investigated.ObjectiveTo examine whether skin and inhalable air exposure to cobalt contributes to uptake, determined as cobalt in blood, in a hard metal manufacturing factory.MethodsThe amount of cobalt on the skin found with an acid wash technique, the air concentrations of inhalable cobalt and cobalt blood concentrations were determined and correlated in exposed workers.ResultsWe found a significant rank correlation for cobalt concentrations on the skin, in inhalable air, and in blood (0.376–0.498). Multiple linear regression showed significant regression coefficients for cobalt skin exposure and blood (B = 0.01, p < 0.05) and for inhalable cobalt in air and blood (B = 49.1, p < 0.001). According to our model based on data from the regression analyses, a twofold increase in skin exposure levels at different air concentrations caused a 3–14% increase in blood levels.ConclusionsOur data suggest that skin exposure to cobalt in the hard metal industry could affect the total uptake at the same order of magnitude as air exposure.

Biological monitoring of cobalt in hard metal factory workers.

The main aim of this study was to investigate the cobalt (Co) concentrations in urine along 4months and their relationship with Co concentrations in blood and haemoglobin (adducts) in 34 workers from a hard metal manufacturing plant where metallic Co and Co oxide were used. Furthermore, the excretion kinetics of Co was investigated and the half-lives of Co in blood, plasma and urine were calculated along 18days of non-exposure in the same workers. Co was analysed, in all biological samples, by ICP/MS. Wide fluctuations in the urinary Co concentration were observed throughout the work shift and during the work week. A highly significant linear correlation was found between Co concentration (geometrical mean) in urine samples provided each Thursday (end shift) during 16 subsequent weeks and levels of Co-haemoglobin adducts or blood Co concentrations at the end of the same period. The Co elimination kinetics in globin calculated along 18days without Co exposure was slow, being related to the physiological metabolism of haemoglobin, while in blood, plasma and urine Co half-lives were 12.3, 9.1 and 5.3days, respectively. Co concentrations in haemoglobin or blood are highly related to the geometrical mean concentration of urinary Co when samples are collected weekly for several subsequent weeks. The biological monitoring of occupational exposure to Co in hard metal facilities provides reliable results by using the Co concentrations in haemoglobin or in whole blood. The urinary findings, though, do not show the same reliability because of their wide daily and weekly fluctuations.

Nanotoxicity: emerging concerns regarding nanomaterial safety and occupational hard metal (WC-Co) nanoparticle exposure.

As the number of commercial and consumer products containing engineered nanomaterials (ENMs) continually rises, the increased use and production of these ENMs presents an important toxicological concern. Although ENMs offer a number of advantages over traditional materials, their extremely small size and associated characteristics may also greatly enhance their toxic potentials. ENM exposure can occur in various consumer and industrial settings through inhalation, ingestion, or dermal routes. Although the importance of accurate ENM characterization, effective dosage metrics, and selection of appropriate cell or animal-based models are universally agreed upon as important factors in ENM research, at present, there is no “standardized” approach used to assess ENM toxicity in the research community. Of particular interest is occupational exposure to tungsten carbide cobalt (WC-Co) “dusts,” composed of nano- and micro-sized particles, in hard metal manufacturing facilities and mining and drilling industries. Inhalation of WC-Co dust is known to cause “hard metal lung disease” and an increased risk of lung cancer; however, the mechanisms underlying WC-Co toxicity, the inflammatory disease state and progression to cancer are poorly understood. Herein, a discussion of ENM toxicity is followed by a review of the known literature regarding the effects of WC-Co particle exposure. The risk of WC-Co exposure in occupational settings and the updates of in vitro and in vivo studies of both micro- and nano-WC-Co particles are discussed.

The history of the technological progress of hardmetals

The impressive history of hardmetals starts with the search for a proper and cheaper material for drawing dies for the drawing of non-sag tungsten (NS-W) after the First World War. The OSRAM R&D group tried to reduce the brittleness of pure WC by adding nickel at first and soon thereafter cobalt, which was utterly successful. Hence, a project aimed to find the solution to a specific problem can unexpectedly lead to a much more important application: The classical hardmetal was born at the OSRAM Studiengesellschaft in Berlin. The famous respective Schröter patent was issued in 1923. Since nobody at OSRAM was realizing the significance of this invention, the patent was offered to the Krupp Company where the development of a production technology for the manufacture of hardmetals was started. Especially in the prewar and war-years (1935–1945) the hardmetal production at KRUPP increased exponentially from ca. 30t/year to 500t/year.The further development of hardmetals is characterized by other carbide and binder combinations. TiC-based hardmetals are a great step forward in the machining of steels and so are fine-grained hardmetals for a wide spectrum of applications. Coating technologies have greatly increased the wear resistance of hardmetals.With the rising tendency of automation in metal cutting, indexable inserts with quite complex geometries were developed for the application in lathes and milling centers working with computer numerical control (CNC). Coating technologies by chemical vapor deposition (CVD) and physical vapor deposition (PVD) have greatly increased the wear resistance of hard metals. Coating with aluminum oxide multilayers and with diamond was devised as well as compact nonmetallic hard materials such as cubic boron nitride, oxide and nitride ceramics and mixed ceramics. Cermets are only briefly discussed here.Hence, after a period of almost 90years, cemented carbides have evolved from a temporary solution in industry (as a substitute for diamond in W-wire-drawing in the lighting industry) to a very successful and almost irreplaceable material for the manufacturing industry. It is also one of the best characterized materials and makes for 36% of global PM-production.The authors of this presentation consider it remarkable that from the very beginning of hardmetals, the optimal combination of WC and Co was chosen. Even today, 90years later, there is no better combination of hard carbide and metallic binder in sight.Finally, a short survey of the literature of hardmetals and hard materials is given.

Hard Metal Lung Disease Diagnosed on a Transbronchial Lung Biopsy Following Recurrent Contact Dermatitis

A 63-year-old man employed in a hard metal manufacturing company for 40 years presented with a chronic dry cough and exertional dyspnea 20 years after the onset of recurrent exanthemas. A chest radiograph revealed bilateral reticular shadows in the upper lung field. Pathological specimens in which tungsten was detected were obtained via a transbronchial lung biopsy. Patch tests were positive for cobalt and other metals. The patient was diagnosed with hard metal lung disease (HMLD) concurrent with contact dermatitis and treated with corticosteroids. This case suggests that allergies to metal may play a role in the onset of HMLD.

55 An historical cohort study of workers in the UK hard-metal industry

ObjectivesA feasibility study has shown that a scientifically rigorous and comprehensive epidemiological study of workers involved in the manufacture or production of tungsten carbide with a cobalt binder is feasible,...

SPS Method for Manufacturing Carbide Materials

Due the rapid heating rate combined with high pressure by the Spark Plasma Sintering (SPS) technologies possible manufacture a wide range of novel materials with exceptional properties that cannot be achieved using conventional sintering techniques. Hard metals are, from a technical point of view, one of the most successful composite materials. An overview of the metallurgical reactions during the SPS sintering process of powder mixtures for the manufacture of hard metals is presented. The relatively complex phase reactions in the multi-component system TiC-Mo-W-Ni are discussed. There were elaborated a new technology for the fabrication of nanocrystalline hard metals of a new class assigned for the production of articles with high different characteristics. Elaborated materials are characterized by high melting temperature, hardness, wear-resistance, and satisfactory strength at high temperature and corrosive resistance. Through the use of developed technology and the appropriate structural condition gives possibility to achieve high physical-mechanical characteristics. Obtaining of composite materials via elaborated technology is available from the corresponding complex compounds and directly consisting elements too. In this case High-temperature Self-propagation Synthesis (SHS) and spark plasma sintering/synthesis (SPS) process are united and during a single operation it is possible to get not only the powder materials but at the same time obtain required details.

Upper Lobe-Dominant Pulmonary Fibrosis Showing Deposits of Hard Metal Component in the Fibrotic Lesions

We present a 54-year-old man employed in the field of hard metal manufacturing who complained of progressive dyspnea and weight loss. His chest radiograph showed bilateral fibrosis predominantly distributed in the upper lobes with bilateral pleural effusions, and a strong reduction in lung volume. Lung histopathology showed apical cap-like fibrosis but no giant cell interstitial pneumonia. Electron probe microanalysis detected tungsten deposits in the fibrotic region: we therefore considered this to be a case of hard metal disease. Hard metal disease should be considered as one possibility in the differential diagnosis of upper lobe-dominant pulmonary fibrosis.

Toxicity of Tungsten Carbide and Cobalt-Doped Tungsten Carbide Nanoparticles in Mammalian Cells in Vitro

BackgroundTungsten carbide nanoparticles are being explored for their use in the manufacture of hard metals. To develop nanoparticles for broad applications, potential risks to human health and the environment should be evaluated and taken into consideration.ObjectiveWe aimed to assess the toxicity of well-characterized tungsten carbide (WC) and cobaltdoped tungsten carbide (WC-Co) nanoparticle suspensions in an array of mammalian cells.MethodsWe examined acute toxicity of WC and of WC-Co (10% weight content Co) nanoparticles in different human cell lines (lung, skin, and colon) as well as in rat neuronal and glial cells (i.e., primary neuronal and astroglial cultures and the oligodendro cyte precursor cell line OLN-93). Furthermore, using electron microscopy, we assessed whether nanoparticles can be taken up by living cells. We chose these in vitro systems in order to evaluate for potential toxicity of the nanoparticles in different mammalian organs (i.e., lung, skin, intestine, and brain).ResultsChemical–physical characterization confirmed that WC as well as WC-Co nanoparticles with a mean particle size of 145 nm form stable suspensions in serum-containing cell culture media. WC nanoparticles were not acutely toxic to the studied cell lines. However, cytotoxicity became apparent when particles were doped with Co. The most sensitive were astrocytes and colon epithelial cells. Cytotoxicity of WC-Co nanoparticles was higher than expected based on the ionic Co content of the particles. Analysis by electron microscopy demonstrated presence of WC nanoparticles within mammalian cells.ConclusionsOur findings demonstrate that doping of WC nanoparticles with Co markedly increases their cytotoxic effect and that the presence of WC-Co in particulate form is essential to elicit this combinatorial effect.

Biological monitoring of cobalt exposure: results in a non-exposed population and on workers of a hard metal manufacture

Biological monitoring of cobalt exposure: results in a non-exposed population and on workers of a hard metal manufacture

Effects of Co magnetism on Co/TiC( [formula omitted]) interface adhesion: a first-principles study

First-principles plane-wave pseudopotential calculations of the electron structure and energetics of the interfaces between the (0 0 1) surfaces of ferromagnetic fcc Co and TiC are reported. A detailed comparison with the case of the paramagnetic Co(0 0 1)/TiC(0 0 1) interface demonstrates that the Co magnetism lowers the adhesion work and increases the interface energy significantly, but practically does not affect the nature and strength of the interface Co–C bonds. The magnetic contribution to the interface energetics originates from the interface-induced changes in the magnetization energy of the interface Co layer. This contribution can be adequately described within the Stoner model of itinerant ferromagnetism, taking the paramagnetic density of electronic states as an input. The found effects are expected to be important during the solid-state sintering stage of the hardmetal manufacturing process.

Exposure assessment in the hard metal manufacturing industry with special regard to tungsten and its compounds

OBJECTIVESTo assess the exposure to tungsten, cobalt, and nickel in a plant producing hard metals. The main components of hard metals are tungsten carbide and cobalt metal. According to recent...

Nitrogen-containing hardmetals and cermets

First-principles plane-wave pseudopotential calculations of the electron structure and energetics of the interfaces between the (0 0 1) surfaces of ferromagnetic fcc Co and TiC are reported. A detailed comparison with the case of the paramagnetic Co(0 0 1)/TiC(0 0 1) interface demonstrates that the Co magnetism lowers the adhesion work and increases the interface energy significantly, but practically does not affect the nature and strength of the interface Co–C bonds. The magnetic contribution to the interface energetics originates from the interface-induced changes in the magnetization energy of the interface Co layer. This contribution can be adequately described within the Stoner model of itinerant ferromagnetism, taking the paramagnetic density of electronic states as an input. The found effects are expected to be important during the solid-state sintering stage of the hardmetal manufacturing process.

Activity and passive-avoidance learning in cobalt-injected rats

A wide range of cognitive-behavioral sequelae, including memory deficits, results from hard metal disease in humans. Cobalt is a common component in the manufacture of hard metals and is a biologically active, toxic substance. This study examined the effects of cobalt exposure in rats. Results showed decreased exploratory behavior and a trend for higher-dose subjects to show decreased passive avoidance learning. No significant differences in active maze learning were found. These results indicate the value of further explorations of the cognitive-behavioral effects of cobalt exposure and suggest a number of methodological cautions.

A practical guide to hardmetal manufacture: S.G. Moseley et al.(Edgar Allen Danite Ltd, Sheffield, UK)

In order to increase the production efficiency of powder injection moulding for SiC parts, thermal debinding was performed in air furnace without gas shield. Bending tests were performed to evaluate the strength of samples debound under different temperatures. The effects of oxidation on debinding process were also analyzed. Analysis indicates that air could accelerate the debinding rate of green parts without defects occurring. The bending strength of debound samples increases from 6.55 MPa to 11.58 MPa as the pre-sintering temperature increases from 550 °C to 850 °C. On the other hand, the bending strength of the samples pre-sintered at 1200 °C in argon atmosphere is only 11.52 MPa. It was found that, blanks have enough strength for transport after being pre-sintered in air atmosphere at 850 °C. The technology could reduce the requirement for heating equipment and enhance the efficiency of debinding for SiC parts.

Preliminary data on hard metal workers exposure to tungsten oxide fibres

The first personal exposure data for tungsten oxide fibres, in two hard metal manufacturing industries is presented. Occupational exposure was studied by static and personal measurements during tungsten metal production. Three different initial materials were used, ammonium-paratungstate (APT), blue oxide and tungsten trioxide. In both factories, airborne tungsten oxide fibres were detected both in static and personal samples. Fibre exposure varies for different activities. Charging of raw material, changing the hammer, cleaning-work on the cyclone and the micro-filter were found to be among the most high dusty operations. However, as workers use respirators during cleaning operations, these filters could not be related to personal exposure. The calcination of APT to the blue oxide generates fibrous dust. The raw material imported as blue oxide is also fibrous material and both charging it into the calcination furnace and re-charging it into the reduction furnace generates unnecessarily additional dusty periods. A single reduction-stage is, therefore, preferable. Furthermore, the tungsten trioxide raw material is non-fibrous, therefore, calcination of APT to tungsten trioxide and its reduction to tungsten metal is preferable with respect to minimising workers exposure to tungsten oxide fibres.

Aspects and limits of ultrafine tungsten carbide powder and hardmetal manufacture: W.D. Schubert et al. (Technical University of Vienna, Vienna, Austria). Int. J. Refractory Metals and Hard Materials, vol 13, no 5, 1995, 281–296

Aspects and limits of ultrafine tungsten carbide powder and hardmetal manufacture: W.D. Schubert et al. (Technical University of Vienna, Vienna, Austria). Int. J. Refractory Metals and Hard Materials, vol 13, no 5, 1995, 281–296

General aspects and limits of conventional ultrafine WC powder manufacture and hard metal production

Ultrafine WC/Co hard metals (average WC grain sizes ≤ 0.5 μm) can be successfully and reliably obtained by conventional hard metal manufacturing techniques. In this paper, some of the crucial aspects of conventional powder manufacture, powder milling and liquid phase sintering are discussed. Conventional ultrafine WC powder manufacture is based on the production of tungsten powder by hydrogen reduction of tungsten oxides and subsequent carburization. Alternatively, direct carburization can be carried out. However, inherent to the powder processing techniques used and the particle growth mechanisms involved (oxide precursors used, reduction and carburization history), there exists a lower limit beyond which-finer WC powders cannot be produced. This limit lies in the particle size range of 50–150 nm (0.05–0.15 μm). Powder milling is carried out to obtain an even dispersion of the Co binder in the ultrafine WC matrix. The more uniform the phase distribution (WC, Co, grain growth inhibitor) within the green powder compact, the more uniform will be the material transport during sintering, and hence the uniformity of the WC grain growth/growth inhibition during sintering. Enhanced WC grain growth occurs early in the sintering cycle, even below the temperature at which the liquid phase is formed. This growth can be largely restricted by the addition of VC. However, effective grain growth inhibition has to take place already during this early period of solid-state sintering. The ‘early’ availability of the grain growth inhibitor at the WC/Co interface can, therefore, determine the degree of growth inhibition. Ultrafine hard metals are in particular prone to discontinuous grain growth of the WC. Different reasons for this local growth mode are propounded relating to both the chemical as well as the geometrical departures from uniformity in the green powder compact. While it is still not possible to predict exactly an ultimate WC grain size limit, below which WC grain growth can no longer be restricted, even with proper inhibitor additions, experimental evidence indicates that this average WC grain size limit lies in the range of 200–300 nm. This limit is inherent to the existing conventional processing techniques (powder manufacture, milling, liquid phase sintering) and the WC growth mechanisms involved and can be overcome only by establishing a completely new route in hard metal manufacture.