Hard Metal Tools Research Articles

Diamond coatings and cBN coatings for tools

The introduction of diamond-coated tools for industrial machining of materials, formerly hampered mainly by coating adhesion difficulties, has, in the recent years, found considerable success, thanks to solutions of this main problem worked out in several R&D laboratories. Compared with the state of the art as to the diamond coating of hard metal and ceramic tools, coating of steel with diamond or cubic boron nitride (cBN) still needs a considerable amount of R&D work to be done, before field testing of tools can actually be started.

Degassing of gas atomized aluminium-lithium alloy powders: S.J.Davis et al. (University of Surrey, Guildford, UK.) Int. J. Rapid Solidification, Vol 9, No 3, 1996, 187–209

Producers of hardmetal tooling face a number of challenges from the increasing use of high-performance materials in many engineering applications and the introduction of new forming and cutting processes. This has seen intensive efforts in the development of hardmetal cutting materials and tools in the last few years. Klaus Dreyer and Hen van den Berg of Widia GmbH in Essen, Germany, outline recent trends in the manufacture of hardmetal tooling and wear parts.

Electrochemical etching of diamond containing hardmetal tool steels and diamond recovery : M. Meszaros, K. Vadasdi. (Hungarian Academy of Sciences, Budapest, Hungary). Int. J. Refractory Metals Hard Mater., vol 14, no 4, 1996, 229–234

Electrochemical etching of diamond containing hardmetal tool steels and diamond recovery : M. Meszaros, K. Vadasdi. (Hungarian Academy of Sciences, Budapest, Hungary). Int. J. Refractory Metals Hard Mater., vol 14, no 4, 1996, 229–234

Formation of diamond coatings on tungsten carbide-cobalt hardmetal tools : R. Haubner, B. Lux (Technical University of Vienna, Vienna, Austria). Int. J. Refractory Metals Hard Mater., vol 14, no 1/3, 1996, 111–118

Formation of diamond coatings on tungsten carbide-cobalt hardmetal tools : R. Haubner, B. Lux (Technical University of Vienna, Vienna, Austria). Int. J. Refractory Metals Hard Mater., vol 14, no 1/3, 1996, 111–118

Epidemiological study of hard metal asthma.

To elucidate factors contributing to hard metal asthma, the entire workforce of a corporation producing hard metal tools (n = 703) was examined. The variables evaluated were the atopy reflected by immunoglobulin E (IgE) antibody against mite allergen, history of exposure to hard metal, smoking, concentration of airborne cobalt, specific IgE antibody reaction against cobalt, and the respiratory symptom of attacks of reversible dyspnoea with wheeze (asthmatic symptoms). Univariate analysis showed that the prevalence of the asthmatic symptoms was significantly higher in formerly and currently exposed male workers than in non-exposed male workers. Positive IgE reaction against cobalt was found in seven men (2.0%), all of whom had asthmatic symptoms. Furthermore, it was found that atopy, positive IgE antibody against cobalt, and age of 40 or older were significantly correlated with asthmatic symptoms. Multilogistic analysis on the same factors and smoking in all of the workers showed that the age, experience of hard metal exposure, and atopy were significant risk factors associated with the asthmatic symptoms. Multilogistic analysis of data for currently exposed and non-exposed workers also showed that age and atopy were risk factors, and that the exposure to cobalt at the low concentration (at or below 50 micrograms/m3) but not at the higher concentration was a significant risk factor. Exposure to mist of coolants containing ionic cobalt, used during grinding, was not found to be any more hazardous in terms of onset of asthmatic symptoms than exposure to hard metal dust containing metallic cobalt. Accordingly, it is concluded that both environmental factors and individual susceptibility should be taken into consideration in efforts to reduce the prevalence of hard metal asthma.

On the formation of diamond coatings on WC/Co hard metal tools

Composite cutting tools having wear-resistant superhard surface coatings (diamond) on a stiff and ductile substrate as base material exhibit excellent performances. A prime requirement for the successful production of such tools is a strong interfacial adhesion of the coating onto the substrate. Industry requires high reproducibility, reliability of each individual tool tip, and an economical mass production process. Hard metal substrates are the obvious choice for most industrial applications of diamond-coated tools. Thus the use of an appropriate hard metal grade and the application of a surface pretreatment — applied to the hard metal prior to the deposition of the diamond coating — are equally important in order to obtain a reproducible diamond coating adhesion. In order to achieve the reliable adhesion necessary for industrial tools, the appropriate interfacial modification must be made. These modifications control possible interactions which can occur at the diamond/hard metal interface. This includes a number of parameters which contribute to optimal bonding of the diamond coating to the substrate, e.g. cobalt mobility (diffusion), cobalt binder effects, diamond nucleation and growth conditions and interfacial roughness of the hard metal/diamond interface, etc. Obviously, the diamond synthesis method applied and the correct choice of deposition parameters are important to achieve a usable and economical product.

Optical emission spectroscopy on an industrial PACVD system for titanium nitride

The optical emission spectra of an industrial PACVD process for coating of hard metal and HSS tools with titanium nitride (TiN) layers by a micro-pulsed d.c. discharge were investigated. For recording of the spectra a simple and economy-priced spectrometer with an resolution of about 0.5 nm was used. Atomic lines of H, Ar and Ar +, and some molecular bands of H 2, N 2, N 2 + and NH were found. With the resolution and sensitivity available it was not possible to clearly identify atomic lines of titanium, nitrogen or chlorine and bands of titanium nitride or titanium chlorides. Because the optical emission of the discharge comes only from species made up of five elements one can expect that many of the spectral lines are highly correlated. For that reason, principal component analysis should offer a good tool to identify those parts in the optical emission spectra which distinguish the single spectra, and which would be relevant for plasma monitoring. However, factors describing species responsible for TiN formation were not found within our experimental limits.

Warm compaction's magnetic attraction

Producers of hardmetal tooling face a number of challenges from the increasing use of high-performance materials in many engineering applications and the introduction of new forming and cutting processes. This has seen intensive efforts in the development of hardmetal cutting materials and tools in the last few years. Klaus Dreyer and Hen van den Berg of Widia GmbH in Essen, Germany, outline recent trends in the manufacture of hardmetal tooling and wear parts.

Environmental Contamination by Cobalt in the Vicinity of a Cemented Tungsten Carbide Tool Grinding Plant

Surface soil and dust samples have been collected from the vicinity of a hard metal (cemented tungsten carbide) tool grinding factory. As a result of poor waste management practices, dusts generated by the grinding operation were, for the most part, swept from the interior of the building onto open ground at the rear of the plant. The potential for contamination of the local environment with cobalt, tungsten, and other metals as a result of dust being either resuspended from the resulting uncontrolled mound of debris or emitted from the factory vents was considerable. Levels of cobalt in local soils were found to be as high as 12,700 mg kg−1; almost 2000 times higher than the average value for in the United States. Scanning electron microscopy and energy dispersive X-ray microanalysis examination of the waste dust particles revealed that the individual particles were, in general, composites containing variable quantities of tungsten, cobalt, calcium, titanium, and iron. Individual particles in soil samples collected at some distance from the plant were less heterogenous, and fewer particles contained detectable quantities of cobalt. This would suggest that a degree of disassociation had occurred in the soil environment resulting in a mobilization of the cobalt.

Occupational exposure to metallic cobalt in the province of Beragmo. Results of a 1991 survey

The results of a survey on workers potentially exposed to cobalt in the Bergamo Province are reported. Its aim is to assess the number of workers at risk of developing respiratory disease due to the inhalation of metallic cobalt. Interest was shown after an examination of 11 cases of ‘hard metal disease’, which we diagnosed, in workers who came from different production areas and had different degrees of exposure. A first group of 45 factories with potential cobalt exposure was identified by consulting the archives of the Local Sanitary Units (USSL) and of the Chamber of Commerce, and by use of the telephone directory and requesting information from the producers and users of Widia tools. A second group of 2039 factories was selected from those industrial activities where we had previously ascertained the presence of grinding operations using hard metal tools with diamond wheels. This study is related to all the factories in the first group and 10% of the factories in the second group. More than 304 inspections were carried out. In this context 403 exposed workers were identified. Workplace air measurements (250 samples) and biological monitoring (>600 samples) to determine the exposure levels to cobalt were performed. The results show an unexpected diffuse occupational exposure in different production areas where the airborne cobalt is frequently underestimated and higher than the TLV.

Trace metal lung disease: a new fatal case of hard metal pneumoconiosis

Four subjects who work at sharpening and grinding hard metal tools were examined. Only one worker, a 37-year-old female exposed for 7 years to hard metal dusts, developed hard metal pneumoconiosis which rapidly progressed to death. Cytology of the bronchoalveolar lavage (BAL) showed a high number of eosinophils, more than 30% of the cell population. Biopsy of the lung revealed interstitial fibrosis with hyperplasia of pneumocyties of the second type and inflammatory cellular infiltration of the interstitium. Obvious abnormal amounts of tungsten (W) and tantalum (Ta) were determined in the BAL and in the lung biopsy by neutron activation analysis (NAA) while cobalt (Co) levels were near the normal values. The Co and W content in blood and urine and particularly in pubic hair and toenails of the patients was significantly higher than the normal values. This suggests that these biological specimens could be used as indicators of chronic exposure to hard metal dusts. The other three workers investigated did not develop the lung disease. They also had obvious abnormal metal levels in the biological specimens analyzed suggesting that there is no correlation between internal dose, length of exposure and the development of interstitial fibrosis.

Hard metal disease: eight workers with interstitial lung fibrosis due to cobalt exposure

Eight hard metal workers exposed to cobalt containing dust (four producers of stone-cutting cobalt-diamond wheels and four grinders of hard metal tools) and affected by interstitial lung fibrosis have been examined. A close relationship between cobalt exposure and clinical findings was observed in six patients who were still working. The clinical picture ranged from minor symptoms to manifestations resembling those of hypersensitivity pneumonitis, with fever, weightloss, non-productive cough and dyspnea. A restrictive impairment of the ventilatory function was prevalent. The chest roentgenogram of one patient showed a diffuse reticular nodular pattern, while the others presented a mild reticular accentuation of the interstitium. In five patients, bioptic specimens of the lung parenchima showed interstitial collagenic fibrosis with inflammatory cells infiltrating the alveolar septa. An increased number of lymphocytes and polymorphs was reported in the bronchoalveolar lavage (BAL) fluid from seven patients. Giant multinucleated cells were present in the BAL of four subjects while an inversion of the helper-suppressor ratio was evident in those patients who were still exposed to cobalt when BAL was performed. In this study, the causal role of metallic cobalt inhalation in the etiology of the lung disease is examined and discussed.

Evaluation and comparison of the levels of occupational exposure to cobalt during dry and/or wet hard metal sharpening. Environmental and biological monitoring

To investigate risks to hard metal tool sharpeners, 80 factories in the Lombardia Region (North Italy) were selected and examined. The scope of the survey consisted of verifying and quantifying that risk, so as to be able to control it and reduce it as far as is possible. We singled out a group of 12 factories, comprising ∼750 workers 60 of whom were exposed to cobalt, in which operations such as sharpening with diamond grinding stones are normally carried out. In those factories, the risk was quantified by determining the concentration of cobalt in dust, collected by means of personal and fixed samplers (23 measurements) during sharpening operations. The station had no local ventilation device; sharpening is mainly performed wet and has been found to present a greater risk than those where sharpening is exclusively performed dry. Results were confirmed by biological monitoring which showed the presence of cobalt excreted in exposed workers' urine collected at the end of the work shift.

Cobalt exposure in wet grinding of hard metal tools for wood manufacture

The authors examined exposure to cobalt during the wet grinding of hard metal tools (Widia tools) used in the wood industry, usually in small specialized workshop which can produce exposure to cobalt > TLV-TWA (50 μg/m 3) if carried out with no protective devices. Local exhausts near the grinding wheel can reduce the exposure to cobalt by as much as 20 times. Nevertheless, some technical problems often hamper the effectiveness of these protective devices, so that the plant situation, examined by the forecasting OTL test as proposed by Tuggle (Am. Ind. Hyg. Assoc. J., 43 (1982) 338), does not appear to be completely acceptable. Other technical solutions are therefore necessary for a complete control of the exposure to cobalt. A more effective water stream, a greater air velocity near the grinding wheel and a protective shield between the wheel and the worker are some suggestions.

Diamond as a wear-resistant coating

Refractory chemical vapour deposition (CVD) coatings strongly improve the performances of hard metal tools. Low-pressure diamond synthesis permits bothin situCVD diamond coating and freestanding low-pressure diamond sheet fabrication. The performance of coated and freestanding bonded diamond layer tools approaches those of commercial polycrystalline diamond (PCD) products. Low-pressure diamond grits and new composite powders could provide new and extraordinary grinding powders of raw materials for novel types of PCD composites. Commercial production is now mainly a scaling-up problem. Reliable and low-cost fabrications are among the most important requirements. As these applications tolerate the use of poly crystalline layers, they are likely to be between those industrial low-pressure diamond products having soon a significant market share.

Research, development and performance of cemented carbide tools coated by plasma-activated chemical vapour deposition

The basic research and the development of a plasma-activated chemical vapour deposition (PCVD) process to coat hard metal tools is described. With the new process, coatings of TiN, TiC and Ti(C,N) can be produced. Because of the low deposition temperature, any loss in toughness of the substrates can be avoided. Even complex-shaped inserts can be coated very uniformly without any movement of the substrates during the coating process. Properties such as deposition rates, hardness, composition, adherence and surface performance have resulted in a wide range of applications, some of which are discussed. The PCVD technique has now been introduced as a standard coating technology for hard metal inserts. As a new development the deposition of alumina coatings by the pulsed PCVD process is described. In addition to the coatings of the TiCN system the fine-grained alumina layers open up a wide range of new applications for PCVD technology.

AEM-investigation of ceramic coatings on hard metals

To improve their working life, hard metal tools are coated with ceramic protective coatings by means of chemical vapour deposition (CVD). Generally, several layers are deposited, e.g. titaniumcarbide, titaniumnitride, titaniumcarbonitride and aluminiumoxide with thicknesses ranging from some 10 nm to some μm.The understanding of mechanical properties of the coatings is dependent on gaining a knowledge of both the interfaces and the structure of the coatings involved. The coating properties are, in turn, dependent on the coating deposition parameters. A detailed understanding of the influence of these parameters on the mechanical and chemical properties of the multilayer/substrate combination is therefore required.The structure and morphology of the multilayer coatings have been already investigated by using optical and scanning electron microscopy (SEM), whereas transmission electron microscopy (TEM) was hitherto only applied to the study of single TiC or Al2O3coatings.For TEM-investigations cross-sections must be taken through the multilayer coating and the cemented carbide substrate. In our investigations, a method of preparation described by Newcomb et al.

Trace Metal Lung Diseases: A New Fatal Case of Hard Metal Pneumoconiosis

Four subjects working in sharpening and grinding operations of hard metal tools were examined. Only 1 worker, a 37-year-old female exposed for 7 years to hard metal dusts, developed hard metal pneumoconiosis, which rapidly progressed to death. Cytology of the bronchoalveolar lavage (BAL) showed a high number of eosinophils, more than 30% of the cell population. Biopsy of the lung revealed interstitial fibrosis with hyperplasia of the pneumocytes of the second type and inflammatory cellular infiltration of the interstitium. High tungsten (W) and tantalum concentrations were determined in the admission BAL and in the biopsy 4 months later by neutron activation analysis while cobalt (Co) levels were near to normal values. The content of Co and W in blood and urine and particularly in pubic hair and toe nails of the patients was significantly higher than the normal values. This suggests that these biological specimens could be used as indicators of chronic exposure to hard metal dusts.

Tantalum—processing, properties and applications

Tantalum— the Earth’s 49th most abundant element— is frequently produced as a by-product of tin smelting. The metal is also extracted from concentrates by reduction with sodium or fused-salt electrolysis; tantalum carbide is produced by carburization of Ta2O5 or tantalum hydride. Sintering, electric-arc melting and electron-beam melting are used to refine and purify raw tantalum. Tantalum’s unique properties make it suitable for a number of diverse applications, including capacitors, chemical equipment, hard-metal tooling and alloys. Tantalum consumption is expected to increase in the capacitor market, because of the demand for electronics equipment.

Bronchopulmonary diseases due to ultra-hard metal dust, with special reference to the result of the dust analysis

In order to clarify the relationship between exposure to hard metal dust containing cobalt and bronchopulmonary diseases, cross-sectional medical and occupational hygienic investigations were conducted in a hard metal tool manufacturing factory. As a part of the environmental investigation, general air concentrations and personal exposure to both total dust and cobalt dust were measured. The highest total dust and cobalt concentrations in general atmosphere and personal samples were found in a powder handling room among all departments. The highest personal exposure concentration of cobalt was 1.29 mg/m3 (arithmetic mean value) in the dry grinder using diamond wheels. Powder handlers were exposed to cobalt 0.56 mg/m3, press operators to 0.66 mg/m3, shapers to 0.19 mg/m3, wet grinders to 0.07 mg/m3, and sintering workers to 0.03 mg/m3. In Japan TLV for cobalt has not yet been established. Dust exposure measurement should be carried out in all hard metal industries. TLV for cobalt is discussed by means of literature.