Search Results (7)

Injection moulding (IM) is a manufacturing technique used to produce intricately detailed plastic components with various surface finishes, enabling the production of high-tolerance functional parts at scale. Conversely, stereolithography (SLA) three-dimensional (3D) printing offers an alternative method for fabricating moulds with shorter lead times and reduced costs compared to conventional manufacturing. However, fabrication in a layer-by-layer fashion results in anisotropic properties and noticeable layer lines, known as the stair-step effect. This study investigates post-processing techniques for plaques with contrasting stair-step effects fabricated from commercially available SLA high-temperature resin, aiming to assess their suitability for IM applications. The results reveal that annealing significantly enhances part hardness and heat deflection temperature (HDT), albeit with a trade-off involving reduced flexural strength. Experimental findings indicate that the optimal stage for abrasive surface treatment is after UV curing and before annealing. Plaques exhibiting contrasting stair-step effects are characterized and evaluated for weight loss, dimensional accuracy, and surface roughness. The results demonstrate that abrasive blasting effectively removes the stair-step effect without compromising geometry while achieving polished surface finishes with roughness average (RA) values of 0.1 μm through sanding. Overall, a combination of abrasive blasting and sanding proves capable of precisely defining surface roughness without significant geometry loss, offering a viable approach to achieving traditional IM finishes suitable for both functional and aesthetic purposes. Full article

This article presents the results of research on alkali-phenolic binders used in moulding sands. The results of the presented experiments are part of a search for the optimum conditions to implement the thermal regeneration of spent alkali-phenolic binder moulding sands. The cured binders were subjected to thermogravimetric analysis in aerobic and anaerobic atmospheres. On the basis of the resin decomposition curves, the integral polymer decomposition temperature was determined, and the required thermal regeneration temperature for the alkali-phenolic binder moulding sands that were used was determined according to a specific procedure. The spent moulding sand was subjected to roasting procedures at different temperatures in order to confirm the necessary regeneration temperatures. The effects of the procedures that were carried out were evaluated by means of weight losses and ignition losses, microscopic pictures were taken, and using scanning microscopy, an analysis of the chemical composition in the micro areas on the surfaces of the matrix grains was carried out using scanning microscopy. The indicators for the comparisons between the individual binders were also calculated from the mass losses. The research and analysis that were carried out made it possible to indicate the required temperature for the thermal regeneration of the spent alkali-phenolic binder moulding sand to reduce the involved energy expenditure. The factors that can determine the successful implementation of the process and the obtaining of the best possible grain matrix for reuse were also indicated. Full article

A series of studies related to the production of organobentonite, i.e., bentonite-poly(acrylic acid), and its use as a matrix grain-binding material in casting moulding sand is presented. In addition, a new carbon additive in the form of shungite was introduced into the composition of the moulding sand. Selected technological and strength properties of green sand bond with the obtained organobentonite with the addition of shungite as a new lustrous carbon carrier ($R_c^w$, $R_m^w$, $P^w$, $P^w$, $P_D$) were determined. The introduction of shungite as a replacement for coal dust in the hydrocarbon resin system demonstrated the achievement of an optimum moulding sand composition for practical use in casting technology. Using chromatographic techniques (Py-GC/MS, GC), the positive effect of shungite on the quantity and quality of the gaseous products generated from the moulding sand during the thermal destruction of its components was noted, thus confirming the reduced environmental footprint of the new carbon additive compared to the commonly used lustrous carbon carriers. The test casting obtained in the mould of the organobentonite moulding sand and the shungite/hydrocarbon resin mixture showed a significantly better accuracy of the stepped model shape reproduction and surface smoothness compared to the casting obtained with the model moulding sand. Full article

This paper presents the outcomes of extensive research targeting the development of high-performance alkyd and polyester resins used as binders in mould- and core-making permeable composite materials designated for large-size/complex-shape, heavy alloy-steel and cast-iron castings (0.5 to 50 tonnes): steam turbine casings (e.g., 18K360 condensing turbine), naval engine blocks and heavy machinery. The technology was implemented by Zamech/ALSTON Power. The key issues discussed here are: (1) control of resin crosslinking kinetics; slow or rapid strength development, (2) shelf-life control of pre-mixed composite, (3) improved thermo-mechanical stability; (4) kinetics of gaseous by-product emission. Optimised composite formulations (resins, crosslinkers and catalysts) allow for the flexible control of material properties and mould-/core fabrication, i.e.,: shelf-life: 10–120 min; mould stripping time: 10 min to 24 h; compressive strength: 4–6 MPa (with post-cure: 10–12 MPa); tensile strength: up to 3 MPa (after post-cure). The moulding sands developed achieved thermal resistance temperatures of up to 345 °C, which exceeded that of 280 °C of comparable commercial material. The onset of the thermal decomposition process was 2–3 times longer than that of furan or commercial alkyd/polyester resin. The technology developed allows for the defect-free manufacture of castings (no pinholes) and binder contents minimisation to 1.2–1.5% with quartz and 1.2% with zirconium or chromite sand. Full article

Electrically melted and over-heated (>1500 °C) grey cast iron at less than 0.04%S, as commonly used, solidifies large amounts of carbides and/or undercooled graphite, especially in thin wall castings; this is necessary to achieve a stronger inoculation. The efficiency of Ce-bearing FeSi alloy is tested for lower ladle addition rates (0.15 and 0.25 wt.%), compared to the base and conventional inoculated iron (Ba,Ca-bearing FeSi alloy). The present work explores chill and associated structures in hypoeutectic grey iron (3.6–3.8%CE, 0.02%S, (%Mn) × (%S) = 0.013–0.016, Al_res < 0.002%), in wedge castings W₁, W₂ and W₃ (ASTM A 367, furan resin sand mould), at a lower cooling modulus (1.1–3.5 mm) that is typically used to control the quality of thin wall iron castings. Relatively clear and total chill well correlated with the standard thermal (cooling curve) analysis parameters and structural characteristics in wedge castings, at different wall thickness, displayed as the carbides/graphite ratio and presence of undercooled graphite morphologies. The difference in effects of the two inoculants addition is seen as the ability to decrease the amount of carbides and undercooled graphite, with Ce-bearing FeSi alloy outperforming the conventional inoculant, especially as the wall thickness decreased. It appears that Ce-bearing FeSi alloy could be a solution for low sulphur, electric melt, thin wall iron castings production. Full article

The assessment of the harmfulness of moulding and core sands is mainly based on investigations of compositions of gases emitted by liquid casting alloys during the mould pouring. The results of investigations of moulding sands obtained under industrial conditions are presented in this paper. A unique research stand was designed and built for this aim. It allowed us to determine emissions of gases at individual stages of casting a mass up to 50 kg. This approach enables simulation of foundry conditions. Moulding sands bound by organic binders (phenol-formaldehyde; furan), inorganic binders and green sand, were subjected to investigations. The composition of gases that evolved during the individual stages, pouring, cooling and knocking out, was tested each time, and the contents of Polycyclic Aromatic Hydrocarbons (PAHs) and benzene, toluene, ethylbenzene, and xylenes (BETX) were analysed. Investigations indicated that the emission of gases from sands with inorganic binders is negligible when compared with the emission of gases from sands with organic binders. The emission of gases from green sand is placed in the middle of the scale. As an example: the sand with furan resin emitted 84 mg of BTEX (in recalculation for 1 kg of sand) while from sands with inorganic binders there was a maximum of 2.2 mg (for 1 kg of sand). In the case of sands with inorganic binders, MI and MC sands indicated comparable and very low emissions of gases from the PAHs group, at the level of 0.018 mg and 0.019 mg for 1 kg of sand, respectively. The higher emission of PAHs from MG sand is the result of its different way of hardening (a binder was of an organic character) than of sands MI and MC. Full article

Having established that sulphur presence in the mould materials appears to have an important contribution in graphite degeneration at least in the casting surface layer, a research program is undertaken to explore the possible beneficial effect of sulphur diffusion blocking at the metal–mould interface. Test samples, with and without a thin steel sheet (up to 3 mm thickness) application on the inner surface of the mould cavity, before iron melt pouring, are considered for structure analysis. A higher nodulizing potential (0.048% Mg_res, 0.015% Ce_res, and 0.006% La_res) decreases the occurrence of surface graphite degeneration in castings obtained in rigid chemically bonded resin sand moulds, using P-toluol sulfonic acid (PTSA) hardener (S-including), but it is not enough to avoid this phenomenon (200–400 μm skin in present experimental conditions). The casting skin appears to have different values, depending on the evaluation technique (un- and Nital-etching direct measurement, or graphite parameters variation on the casting section). In the presence of a thin steel sheet at the metal–mould interface, the casting skin thickness decreases or is just excluded. It is supposed that it acts as a barrier, blocking S-diffusion from the mould media into the iron melt. Without this S-diffusion, the graphite degeneration in the casting surface layer could be avoided, or at least diminished. For industrial application, the increasing of residual content of nodulizing elements is a limited solution, and it is recommended to use barriers to block S transfer on the mould/metal surface, such as dense coatings or coatings with desulphurization capacity. Full article