Shrinkage and warpage behaviour on injection moulding parts

Dissertação de mestrado em Engenharia de Polímeros (área de especialização em Projecto e Fabrico de Moldes)O processo de moldação por injecção é caracterizado pela elevada taxa de produção e qualidade nos seus produtos. Sendo perfeitamente viável a produção de peças com geometrias complexas a baixo custo, tendo em conta as excelentes propriedades que advêm do material polimérico. Contudo o material é sujeito a sucessivas transformações que dependem de diversas variáveis relacionadas com as propriedades do material, projecto do molde, performance do equipamento e dos parâmetros de processamento. Como resultado, as dimensões finais dos produtos resultantes do processo de moldação por injecção, infelizmente diferem das dimensões da cavidade do molde (fenómeno da contracção). A indústria de plásticos pertence a uma nova era de processamento automatizado, estando neste momento preparada para ser competitiva devido a uma enorme diversidade de opções. O uso de instrumentação é uma prova viva da importância da automatização, uma vez que sem instrumentação não é possível o controlo do processo. Hoje em dia, a elevada exigência e parâmetros apertados de qualidade nos produtos torna com que o interesse neste assunto seja cada vez mais relevante e presente. Por esta razão é fundamental um conhecimento exaustivo, do que na realidade acontece dentro da cavidade durante os ciclos de moldação. O objectivo deste trabalho é fornecer informação sobre o efeito da segunda pressão e temperatura do molde na contracção e empeno, em diferentes materiais, com peças moldadas por injecção. Um molde foi manufacturado sendo posteriormente instrumentado e a leitura dos respectivos sinais foi monitorizada continuamente através de um sistema de aquisição de dados. Simulações em Moldflow foram efectuadas para validar os resultados experimentais. Os resultados da contracção/empeno foram comparados com medições de orientação de fibras. Quatro materiais como o PC, PP, PP com 20% e 30% de fibras de vidro, foram usados nas moldações.Injection moulding is characterised by its high production rates and accurately sized products. It is possible to produce inexpensive complex geometry composite products with stiffness properties. However the material is subjected to successive transformations that depends on several variables related to material properties, the mould design, equipment performance and moreover process variables. As a result, the final dimensions of injection moulded products unfortunately differ from those of the mould cavity (shrinkage occurs). The plastics industry has entered in the world of automated processing and it is now sorting out available options in order to be competitive. The use of instrumentation is very important in the automation, because without instrumentation, there is no process control. Nowadays the products require higher demands on dimensional accuracy and stability, so the interest in this subject is more and more present. For this reasons an approach is need to a complete understanding of what happens inside the cavity during and after the moulding cycle. The propose, of this work is to provide information about the effect of holding pressure and mould temperature on shrinkage and warpage on different materials in injection moulding parts. An instrumented mould was manufactured and sensors signals were continuously monitored by a Data Acquisition System. In order to validate the experimental results, simulations in Moldflow were done. The results of shrinkage/warpage were compared with the fibre orientation measurements. Four materials were used for the mouldings: PC, PP, PP with 20% and with 30% of Glass Fibres

Ecology and diversity of Solanum trisectum Dunal from Madeira Island: implications for Its conservation

Solanum trisectum Dunal is an endemic Solanaceae of Madeira Island (Portugal), considered critically endangered due to its extreme rarity. Since its discovery this species has shown a narrow distributional range mainly on the northern side of the island, with scattered and small populations and large time gaps between sightings. The present work aimed to understand the underlying ecological underpinnings for this species rarity towards an effort to increase the success of conservation actions. Data on historical locations, environmental conditions field surveys, reinforcement in situ and ex situ germination trials were obtained. The species was found to currently occur only in two wild populations and two reinforcement sites, amounting to twenty-four plants in total. Statistical analysis of these data related wild populations and successful reinforcement sites, separating them from other sites where the reinforcement did not succeed. This suggests that the successful reinforcement sites showed conditions more similar to wild population sites compared to non-successful ones. The data obtained supports the hypothesis that S. trisectum distribution and rarity is determined by species specific habitat needs, i.e., abiotic conditions, which have been for the first time assessed during the present work. Further, this study also reinforces the classification of S. trisectum as a top priority species for conservation.Prospecting, Monitoring and Conservation of Normania triphylla in Madeira (Mohamed bin Zayed Species (project number 13255498)) and Madeira PO 14-20, contract CASBIO (ref M1420-01- 0145-FEDER-000011 ).info:eu-repo/semantics/publishedVersio

Characterisation of microbial attack on archaeological bone

As part of an EU funded project to investigate the factors influencing bone preservation in the archaeological record, more than 250 bones from 41 archaeological sites in five countries spanning four climatic regions were studied for diagenetic alteration. Sites were selected to cover a range of environmental conditions and archaeological contexts. Microscopic and physical (mercury intrusion porosimetry) analyses of these bones revealed that the majority (68%) had suffered microbial attack. Furthermore, significant differences were found between animal and human bone in both the state of preservation and the type of microbial attack present. These differences in preservation might result from differences in early taphonomy of the bones. © 2003 Elsevier Science Ltd. All rights reserved

Evaluation of a quality improvement intervention to reduce anastomotic leak following right colectomy (EAGLE): pragmatic, batched stepped-wedge, cluster-randomized trial in 64 countries

Background Anastomotic leak affects 8 per cent of patients after right colectomy with a 10-fold increased risk of postoperative death. The EAGLE study aimed to develop and test whether an international, standardized quality improvement intervention could reduce anastomotic leaks. Methods The internationally intended protocol, iteratively co-developed by a multistage Delphi process, comprised an online educational module introducing risk stratification, an intraoperative checklist, and harmonized surgical techniques. Clusters (hospital teams) were randomized to one of three arms with varied sequences of intervention/data collection by a derived stepped-wedge batch design (at least 18 hospital teams per batch). Patients were blinded to the study allocation. Low- and middle-income country enrolment was encouraged. The primary outcome (assessed by intention to treat) was anastomotic leak rate, and subgroup analyses by module completion (at least 80 per cent of surgeons, high engagement; less than 50 per cent, low engagement) were preplanned. Results A total 355 hospital teams registered, with 332 from 64 countries (39.2 per cent low and middle income) included in the final analysis. The online modules were completed by half of the surgeons (2143 of 4411). The primary analysis included 3039 of the 3268 patients recruited (206 patients had no anastomosis and 23 were lost to follow-up), with anastomotic leaks arising before and after the intervention in 10.1 and 9.6 per cent respectively (adjusted OR 0.87, 95 per cent c.i. 0.59 to 1.30; P = 0.498). The proportion of surgeons completing the educational modules was an influence: the leak rate decreased from 12.2 per cent (61 of 500) before intervention to 5.1 per cent (24 of 473) after intervention in high-engagement centres (adjusted OR 0.36, 0.20 to 0.64; P < 0.001), but this was not observed in low-engagement hospitals (8.3 per cent (59 of 714) and 13.8 per cent (61 of 443) respectively; adjusted OR 2.09, 1.31 to 3.31). Conclusion Completion of globally available digital training by engaged teams can alter anastomotic leak rates. Registration number: NCT04270721 (http://www.clinicaltrials.gov)