Adipose tissue concentrations of persistent organic pollutants and total cancer risk in an adult cohort from Southern Spain: Preliminary data from year 9 of the follow-up

There is an increasing trend in the incidence of cancer worldwide, and it has been accepted that environmental factors account for an important proportion of the global burden. The present paper reports preliminary findings on the influence of the historical exposure to a group of persistent organic pollutants on total cancer risk, at year 9 in the follow-up of a cohort from Southern Spain. A cohort of 368 participants (median age 51 years) was recruited in 2003. Their historical exposure was estimated by analyzing residues of persistent organic pollutants in adipose tissue. Estimation of cancer incidence was based on data from a population-based cancer registry. Statistical analyses were performed using multivariable Cox-regression models. In males, PCB 153 concentrations were positively associated with total cancer risk, with an adjusted hazard ratio (95% confidence interval) of 1.20 (1.01–1.41) for an increment of 100 ng/g lipid. Our preliminary findings suggest a potential relationship between the historical exposure to persistent organic pollutants and the risk of cancer in men. However, these results should be interpreted with caution and require verification during the future follow-up of this cohort.This study was supported in part by research grants from the Spanish Ministry of Health (FIS 02/974, EUS2008-03574), CIBER de Epidemiología; Junta de Andalucía (01/264, P09-CTS-5488 Project of Excellence, PI-0675-2010, and PI-0513-2012), and the Instituto de Salud Carlos III (FIS PI11/0610)

High temperature tribology of high strength boron steel and tool steels

There are many tribological interfaces that are exposed to elevated temperatures. Typical examples are the interfaces of various moving assemblies, for examples in aerospace industry, power generation and metalworking processes. The exposure of materials to elevated temperatures results in highly complex interfaces due to changes in morphology, microstructure and mechanical properties coupled with the occurrence of oxidation and diffusion. All of these changes will influence the tribological behaviour of materials at elevated temperatures. Another major concern is lubrication at elevated temperatures since conventional lubricants do not perform at temperatures above ~300ºC. High strength steels are commonly used as structural reinforcements or energy absorbing systems in automobile applications due to their favourable strength to weight ratios. The high strength of these steels leads to several problems during forming such as poor formability, increased spring back, and tendency to work-harden. In view of these difficulties, high strength steels are usually formed at elevated temperatures with a view to facilitating forming and simultaneous hardening by quenching of complex shaped parts. A review of published literature has revealed that only a few studies pertaining to high temperature tribology (including those of hot metalworking) have been carried out so far. The understanding of the high temperature tribological behaviour of high strength steels and tool steel pairs is also highly inadequate. The aim of this work is therefore to obtain a better understanding of the friction and wear mechanisms of tool steel and high strength boron steel tribological pairs at elevated temperatures. The experimental studies were carried out by using a high temperature version of the Optimol SRV reciprocating friction and wear test machine. The tribological studies were performed at temperatures ranging from 40ºC to 800ºC. The experimental materials were tool steels of three different alloying compositions (with and without nitriding) and high strength boron steel (unhardened, hardened, with and without Al-Si coating). The results have shown that both friction and wear of tool steel and high strength steel pairs are temperature dependant. An increase in temperature has resulted in lower friction for all the material pairs. Tool wear increased when the temperature increased from 40 to 400ºC during sliding against uncoated high strength steel but remained unchanged when the temperature increased further to 800ºC. When sliding against Al-Si coated high strength steel, tool wear increased with increasing temperature. Plasma nitriding of tool steels has been effective in reducing friction as well as in providing protection against severe adhesive wear. The Al-Si coating on the high strength steel has resulted in high friction at low temperatures and low friction at elevated temperatures. It has also shown an increased wear resistance at elevated temperatures. The coating undergoes significant surface morphological changes when exposed to elevated temperatures which are likely to influence its tribological behaviour. Hardening of the high strength steel has resulted in decreased friction at all temperatures. It led to higher tool wear at low temperatures and lower tool wear at elevated temperaturesGodkänd; 2007; 20070820 (pafi

Tribology of hot forming tool and high strength steels

Tribological research pertaining to moving machine components operating at elevated temperatures has so far received only limited attention despite the fact that many technological applications encounter high-temperature conditions. Examples of such applications can be commonly found in the aerospace, power generation and hot metal working industries. In the metal working field, thermo-mechanical forming of high-strength steel components has grown very rapidly in recent years. The increased usage of such components has its driving forces in improved crashworthiness, reduced fuel consumption and conservation of natural resources. These processes, invented about 30 years ago in northern Sweden, enable the forming of complex shaped components at elevated temperatures and the simultaneous control of complex microstructures. Despite the fact that more than 30 years of research has gone into developing and optimising these thermo-mechanical processes there are several aspects which have not been adequately studied or understood. One of these aspects is the tribology of the tool-workpiece interaction at the high temperatures encountered during hot metal forming. This is where tribological research can contribute greatly in improving the hot sheet metal forming processes. The main tasks involved are the understanding, prediction and control of friction as well as wear during the interaction of tool and workpiece at elevated temperature. Future research also needs to consider the tribology of rapidly emerging surface engineering technologies that have potential for high temperature applications such as hot metal forming. This work has focussed on investigating the friction and wear characteristics of different tool steels during sliding against ultra high strength boron steel at different temperatures ranging from room temperature to 900 °C. Tribological studies have also been conducted on surface treated/coated tool steels during sliding against coated workpiece material with a view to explore the potential of surface engineering in controlling friction and minimisation of wear at elevated temperatures.The results have shown that friction and wear characteristics of these material pairs are temperature dependant and generally the tribological interaction of the tool-workpiece pair at elevated temperatures result in reduced friction and increased wear of the tool material. The main wear mechanisms at elevated temperatures are adhesive and abrasive and interaction with oxidised wear debris has a significant influence on the tribological behaviour of the system. Plasma nitriding of the tool steel has resulted in reduced and more stable friction and also improved resistance against severe adhesive wear at elevated temperatures. The best wear resistance has been achieved by applying a duplex surface modification system on the tool steel (nitriding + PVD coating). Application of a surface coating on the ultra high strength boron steel, Al-Si or Al-Si with graphite, has been shown to have a much greater effect on the frictional behaviour compared to that on the tool surface. This, however, has an effect on tool wear owing to the abrading action of the hard intermetallic layer formed on the Al-Si coated UHSS surface when exposed to high temperatures.Godkänd; 2009; 20091102 (jenhar); DISPUTATION Ämnesområde: Maskinelement/Machine Elements Opponent: Professor & Director nCAST Robert J. K. Wood, University of Southampton, UK Ordförande: Professor Braham Prakash, Luleå tekniska universitet Tid: Måndag den 7 december 2009, kl 09.30 Plats: E 246, Luleå tekniska universite

Tribology in Cold Pilgering

The lubricants that are used today by Sandvik Materials Technology AB in the cold pilger process contain chlorinated paraffins. Due to environmental, economic and health reasons, these lubricants have to be replaced. The method for trying out new pilger lubricants today is full scale trials in cold pilger mills. The main aim of this thesis has been to investigate whether it is possible to evaluate pilger lubricants by using some standard laboratory tribological test methods. In addition to this, a review of published literature and a description of the cold pilger process in tribological terms have also been conducted. The literature review included the published work pertaining to cold pilgering in tribology related scientific journals and books. This review indicated that only very limited information is available in open literature and the survey was therefore broadened to include other similar metal working processes. The test methods that have been used are the sliding four ball test machine and the SRV (Schwingung Reibung Verschleiß) reciprocating friction and wear tester. The test specimens for the four ball machine were standard bearing steel balls. In the SRV tests, cylinder on disc and a ball on disc test specimen configurations were used. The cylinder specimens were manufactured from the tube material and the disc specimens were made of mandrel material. The balls for the SRV were made of standard stainless steel. In the four ball machine, both the wear preventive characteristics and extreme pressure properties have been evaluated. In the SRV Optimol machine, seizure and wear tests have been performed. To analyse the surfaces, Wyko 1100 NT optical surface profiler has been used. A more thorough analysis of test specimen surfaces was also carried out by using SEM/EDS at SMT. The results show that the SRV cylinder on disc and ball on disc seizure tests are very representative of the cold pilger process. The ranking of various lubricant formulations from these tests correlate very well to the ranking from the full scale cold pilger trials. The surface damage modes and material transfer in the tests correspond well with those observed in the actual process. The SRV wear test corresponds only to a limited extent and the reason for this is that the ranking of cold pilger lubricants is not based on wear.The four ball EP tests do not correlate that well with the real ranking. This is attributed to the use of different test specimen material in four ball tests as compared to that actual tube/mandrel materials and the test method may not reproduce the conditions prevalent in the cold pilger process. The four ball wear tests do not correlate at all to the actual ranking of lubricant formulations owing to the same reasons and also in view of the fact that the ranking is not based on wear.Validerat; 20101217 (root

Tribological performance evaluation of cold pilgering lubricants

Godkänd; 2010; 20100920 (jenhar

Tribological performance evaluation of cold pilgering lubricants

Godkänd; 2010; 20100920 (jenhar

High temperature friction and wear of post-machined additively manufactured tool steel during sliding against AlSi-coated boron steel

In recent years, additive manufacturing (AM) of metallic materials has achieved the production of virtually fully dense parts, extending the range of potential applications. There is a growing interest in the use of AM to produce forming tools for hot stamping. The possibilities of locally tailoring the die material to tackle wear challenges and producing more complex geometries to improve die cooling are key-features driving that interest. However, there is a lack of knowledge concerning the tribological behavior of AM materials, particularly at high temperature, as well as the influence surface finishing processes after additive manufacturing. The aim of this study is to investigate the high temperature friction and wear behavior of a tool steel, produced by selective laser melting, within the context of hot forming of AlSi-coated boron steel. A high temperature strip drawing tribometer was used to perform sliding tests at 600 °C and 700 °C. Three different surface finishes were used for the AM samples: ground, milled and shot-blasted. A conventionally produced steel with the same chemical composition and a ground surface finish was used as a reference. At 600 °C, a similar stable coefficient of friction of 0.4 was observed for both materials and all surface topographies. At 700 °C, all tests resulted in a sudden increase in friction up to 0.9 due to local rupture of the AlSi-coating, severe material transfer and ploughing. The wear mechanisms observed for the ground surfaces, both AM and reference tool steel, were a combination of adhesive material transfer and abrasive material removal that promotes material pile-up, resulting in wedge formation on the tool steel surface. The characteristic wedge formation was not common in the milled surface. This is attributed to strain-hardening and topographical features from the finishing process. For the shot-blasted AM surface, deformation and flattening of the large asperities was observed, as well as material transfer. Subsurface deformation associated with high adhesion during sliding was observed, mainly for the ground surfaces. The milled surface resulted in the least amount of tool steel transfer onto the counter body, while the shot-blasted one resulted in the largest amount. AM and reference ground tool steel showed very similar friction and wear behavior in this tribosystem.Validerad;2023;Nivå 2;2023-04-14 (joosat);Licens fulltext: CC BY License</p

Embeddability behaviour of some Pb-free engine bearing materials in the presence of abrasive particles in engine oil

One of the tribological requirements on engine bearing material is its ability to safely embed contaminant particles onto its surface and minimise damage to both the bearing and crankshaft surfaces. In this work, a journal bearing test rig that operates under constant load has been employed to investigate the embeddability behaviour of selected multi-layered Pb-free engine bearing materials at three different rotational speeds using engine oil contaminated with SiC particles. Experimental results have shown that third-body abrasive wear is influenced by the lubricant film thickness. There was also difference in embeddability of the different materials. Bismuth-based overlay and MoS2 containing polyamide-imide-based overlay-coated materials show higher wear compared to tin-based overlay and a polyamide-imide-based composite overlay-coated material. Steel counter surfaces sliding against bismuth-based overlay and MoS2 containing polyamide-imide-based overlay exhibited higher wear than those sliding against tin-based overlay and polyamide-imide-based composite overlay. Validerad;2019;Nivå 2;2019-04-12 (oliekm)</p