Influence of salt support structures on material jetted aluminum parts

Like most additive manufacturing processes for metals, material jetting processes require support structures in order to attain full 3D capability. The support structures have to be removed in subsequent operations, which increases costs and slows down the manufacturing process. One approach to this issue is the use of water-soluble support structures made from salts that allow a fast and economic support removal. In this paper, we analyze the influence of salt support structures on material jetted aluminum parts. The salt is applied in its molten state, and because molten salts are typically corrosive substances, it is important to investigate the interaction between support and build material. Other characteristic properties of salts are high melting temperatures and low thermal conductivity, which could potentially lead to remelting of already printed structures and might influence the microstructure of aluminum that is printed on top of the salt due to low cooling rates. Three different sample geometries have been examined using optical microscopy, confocal laser scanning microscopy, energy-dispersive X-ray spectroscopy and micro-hardness testing. The results indicate that there is no distinct influence on the process with respect to remelting, micro-hardness and chemical reactions. However, a larger dendrite arm spacing is observed in aluminum that is printed on salt

Analysis of salts for use as support structure in metal material jetting

Material jetting (MJT) is a category of additive manufacturing processes where the build material is deposited in the form of individual droplets. MJT has recently been expanded into the field of metal processing due to a potentially high printing speed at low equipment and raw material cost. For full 3D capability, support structures are needed that have to be removed after the print job. We examine water soluble salts and suitable nozzle materials to realise the printing of molten salt in a MJT process. Here, the wetting characteristics of the melt and nozzle are crucial because pronounced wetting is problematic for the ejection of droplets. A sessile-drop contact angle test stand was set up to evaluate the wetting characteristics of three salts or salt mixtures (NaCl, KCl–NaCl and NaCl–Na2CO3) on six different nozzle materials (various ceramics and graphite), i.e. potential nozzle materials. The results indicate a high wetting tendency of most of the examined samples with the exception of KCl-NaCl on graphite. Application of these materials on a MJT test stand confirm the feasibility of our findings

Nafenopin-induced rat liver peroxisome proliferation reduces DNA methylation by N-nitrosodimethylamine in vivo

The hypolipidaemic drug nafenopin (NAF) has been shown to enhance the hepatocarcinogenic effect of N-nitrosodimethylamine (NDMA) and N-nitrosodiethylamine in rats. We have investigated whether the NAF-induced peroxisome proliferation in hepatocytes interferes with NDMA's metabolism and interaction with DNA. Adult male Wistar rats received a single i.p. injection of [14C]NDMA (2 mg/kg) and were killed 4 h later. DNA was isolated from liver and kidney, hydrolysed in 0.1 N HCI and analysed by Sephasorb chromatography. In rats pre-treated with NAF (0.2% in the diet over a period of 3 weeks), the concentration of N7-methylguanine in hepatic DNA (μmol/mol guanine) was 46% below control values. This is probably due to the greater amount of target DNA, as NAF caused a marked hepatomegaly with a 50% increase in total liver DNA content. Concentrations of N7-methylguanine in kidney DNA were twice as high in NAF-pre-treated animals when compared to control rats. This is unlikely to result from a shift in the metabolism of NDMA from liver to other rat tissues since the time course and extent of the conversion of [14C]NDMA to 14CO2 and 14C-labelled urinary metabolites were identical in NAF-treated and control animals. There was no indication that NAF inhibits the activity of the hepatic O6-alkylguanine-DNA alkyltransferas

Binder content and storing conditions of inorganically-bound foundry cores determine the intensity and onset time of gas release in metal casting

Organically-bound foundry cores are substituted by inorganically-bound cores increasingly. This trend is due to regulatory efforts, workplace safety issues, and increasing costs for waste deposits. Changing the binder system reduces the emissions to mostly water vapor, solving health and safety issues. Yet, the difference in the behavior of the gas phase, namely, the condensation potential of water, changes the casting process drastically. In contrast with the continuous generation and discharge of combustion products in the case of organic binders, water accumulates within the foundry core. Only once the cold spots of the core reach boiling temperature noteworthy amounts of vapor are created, increasing the chance for gas defects of the cast parts. Countermeasures have to be taken when designing the core’s geometry. We conducted the following research to improve the understanding of core gas release and its interactions with the foundry core’s binder content and storage conditions. Both binder content and relative humidity during storage were varied in three steps. Their influence on the core gas amount, time of gas generation, and gas permeability of the cores were investigated. The experiments were performed in the institute’s Induction Analysis Furnace and an aluminum melt bath. We found a strong dependency of storage humidity, further increased by increasing binder content on the gas amount and time of the gas release

A test stand for quantifying the core gas release and the gas permeability of inorganically-bound foundry cores

Environmental and work safety aspects necessitate a radical change in the foundry industry. Organic binder systems for foundry sand cores create toxic combustion products and are, therefore, more and more often substituted by inorganic binder systems. While providing an environmental advantage by mainly releasing water vapor, inorganic binder systems impose new challenges for the casting process. The gas release of inorganically-bound foundry cores can lead to increased gas porosity in the cast parts and thus to high scrap rates. The present work aims to gain more understanding of the gas generation and transport in inorganic sand binder systems. We developed a test stand to measure the temperature-dependent core gas release in inorganically-bound foundry cores and their gas permeability. Samples were prepared in a core blowing process and analyzed using the test stand. The measurement results are in good agreement with validation experiments and existing literature

Feasibility of acoustic print head monitoring for binder jetting processes with artificial neural networks

The clogging of piezoelectric nozzles is a typical problem in various additive binder jetting processes, such as the manufacturing of casting molds. This work aims at print head monitoring in these binder jetting processes. The structure-born noise of piezoelectric print modules is analyzed with an Artificial Neural Network to classify whether the nozzles are functional or clogged. The acoustic data are studied in the frequency domain and utilized as input for an Artificial Neural Network. We found that it is possible to successfully classify individual nozzles well enough to implement a print head monitoring, which automatically determines whether the print head needs maintenance

LIQUID METAL JETTING OF ALUMINUM PARTS WITH SALT SUPPORT STRUCTURES

Liquid metal jetting (LMJ) bears the potential of being a fast part manufacturing technology while using a cheap raw material. LMJ is a subtype of material jetting (MJT) and the parts are built by successively depositing droplets of molten metal onto a build platform. For full 3D capability, support structures are necessary, which must be removed in subsequent processes. In previous investigations, we proposed the usage of water-soluble salt as a support material, selected a suitable salt, and analyzed the influence of this material on aluminum parts made in LMJ. The present work shows a duplex MJT print head for processing aluminum alloys and KClNaCl salt. Various printing sequences and support structure strategies are compared. The results show that the sequence of printing aluminum and salt is crucial. Furthermore, using thin layers of the support material as a release layer appears promising.Mechanical Engineerin

Murine Features of Neurogenesis in the Human Hippocampus across the Lifespan from 0 to 100 Years

BACKGROUND: Essentially all knowledge about adult hippocampal neurogenesis in humans still comes from one seminal study by Eriksson et al. in 1998, although several others have provided suggestive findings. But only little information has been available in how far the situation in animal models would reflect the conditions in the adult and aging human brain. We therefore here mapped numerous features associated with adult neurogenesis in rodents in samples from human hippocampus across the entire lifespan. Such data would not offer proof of adult neurogenesis in humans, because it is based on the assumption that humans and rodents share marker expression patterns in adult neurogenesis. Nevertheless, together the data provide valuable information at least about the presence of markers, for which a link to adult neurogenesis might more reasonably be assumed than for others, in the adult human brain and their change with increasing age. METHODS AND FINDINGS: In rodents, doublecortin (DCX) is transiently expressed during adult neurogenesis and within the neurogenic niche of the dentate gyrus can serve as a valuable marker. We validated DCX as marker of granule cell development in fetal human tissue and used DCX expression as seed to examine the dentate gyrus for additional neurogenesis-associated features across the lifespan. We studied 54 individuals and detected DCX expression between birth and 100 years of age. Caveats for post-mortem analyses of human tissues apply but all samples were free of signs of ischemia and activated caspase-3. Fourteen markers related to adult hippocampal neurogenesis in rodents were assessed in DCX-positive cells. Total numbers of DCX expressing cells declined exponentially with increasing age, and co-expression of DCX with the other markers decreased. This argued against a non-specific re-appearance of immature markers in specimen from old brains. Early postnatally all 14 markers were co-expressed in DCX-positive cells. Until 30 to 40 years of age, for example, an overlap of DCX with Ki67, Mcm2, Sox2, Nestin, Prox1, PSA-NCAM, Calretinin, NeuN, and others was detected, and some key markers (Nestin, Sox2, Prox1) remained co-expressed into oldest age. CONCLUSIONS: Our data suggest that in the adult human hippocampus neurogenesis-associated features that have been identified in rodents show patterns, as well as qualitative and quantitative age-related changes, that are similar to the course of adult hippocampal neurogenesis in rodents. Consequently, although further validation as well as the application of independent methodology (e.g. electron microscopy and cell culture work) is desirable, our data will help to devise the framework for specific research on cellular plasticity in the aging human hippocampus

Temporal transcriptomic analysis of the Listeria monocytogenes EGD-e σB regulon

<p>Abstract</p> <p>Background</p> <p>The opportunistic food-borne gram-positive pathogen <it>Listeria monocytogenes </it>can exist as a free-living microorganism in the environment and grow in the cytoplasm of vertebrate and invertebrate cells following infection. The general stress response, controlled by the alternative sigma factor, σ^B, has an important role for bacterial survival both in the environment and during infection. We used quantitative real-time PCR analysis and immuno-blot analysis to examine σ^Bexpression during growth of <it>L. monocytogenes </it>EGD-e. Whole genome-based transcriptional profiling was used to identify σ^B-dependent genes at different growth phases.</p> <p>Results</p> <p>We detected 105 σ^B-positively regulated genes and 111 genes which appeared to be under negative control of σ^Band validated 36 σ^B-positively regulated genes <it>in vivo </it>using a reporter gene fusion system.</p> <p>Conclusion</p> <p>Genes comprising the σ^Bregulon encode solute transporters, novel cell-wall proteins, universal stress proteins, transcriptional regulators and include those involved in osmoregulation, carbon metabolism, ribosome- and envelope-function, as well as virulence and niche-specific survival genes such as those involved in bile resistance and exclusion. Ten of the σ^B-positively regulated genes of <it>L. monocytogenes </it>are absent in <it>L. innocua</it>. A total of 75 σ^B-positively regulated listerial genes had homologs in <it>B. subtilis</it>, but only 33 have been previously described as being σ^B-regulated in <it>B. subtilis </it>even though both species share a highly conserved σ^B-dependent consensus sequence. A low overlap of genes may reflects adaptation of these bacteria to their respective environmental conditions.</p