Gypsum Mold Research Articles

Structure of Gypsum and Polymer Molds for Slip Casting

The microstructure of gypsum and polymer molds for slip casting of ceramic articles is investigated. Analysis of the microstructure of porous molds showed that gypsum molds have a more fine-porous and uniform structure than polymer molds. It was determined that gypsum molds are expedient to use in small-lot production and manufacture of objects of fine art.

Monitoring of the Structure and Quality of Aluminium Castings in Moulds of Gypsum Mixtures

The paper deals with the production of dimensionally accurate castings of aluminum alloys in moulds of gypsum moulding mixture. This manufacturing process is very important for the production of castings for radio technology. Castings have high dimensional accuracy and high - quality of surface. Production of aluminum alloy castings in moulds of gypsum mixtures belong to a group of non-traditional methods of casting and foundry practice, this method is used for the production of special castings. Moulds and cores from gypsum mixture have specific application not only in the production of aluminum alloy castings but cast alloys with low melting temperature (tin, zinc, lead). In these days this method produces dimensionally accurate parts with high surface smoothness such as those used for radio-communication systems or propeller small blowers. Under the conditions of the Czech foundry at our institution, the Department of Engineering Technology - TU of Liberec, we devote this method for many years. The main attention is paid to the methodology for the production of gypsum moulds and their heat treatment and the correct choice of the chemical composition of the aluminum alloy in order to obtain high-quality castings.

Surface Coating of Gypsum-Based Molds for Maxillofacial Prosthetic Silicone Elastomeric Material: The Surface Topography.

This study aimed to compare the surface roughness of maxillofacial silicone elastomers fabricated in noncoated and coated gypsum materials. This study was also conducted to characterize the silicone elastomer specimens after surfaces were modified. A gypsum mold was coated with clear acrylic spray. The coated mold was then used to produce modified silicone experimental specimens (n = 35). The surface roughness of the modified silicone elastomers was compared with that of the control specimens, which were prepared by conventional flasking methods (n = 35). An atomic force microscope (AFM) was used for surface roughness measurement of silicone elastomer (unmodified and modified), and a scanning electron microscope (SEM) was used to evaluate the topographic conditions of coated and noncoated gypsum and silicone elastomer specimens (unmodified and modified) groups. After the gypsum molds were characterized, the fabricated silicone elastomers molded on noncoated and coated gypsum materials were evaluated further. Energy-dispersive X-ray spectroscopy (EDX) analysis of gypsum materials (noncoated and coated) and silicone elastomer specimens (unmodified and modified) was performed to evaluate the elemental changes after coating was conducted. Independent t test was used to analyze the differences in the surface roughness of unmodified and modified silicone at a significance level of p < 0.05. Roughness was significantly reduced in the silicone elastomers processed against coated gypsum materials (p < 0.001). The AFM and SEM analysis results showed evident differences in surface smoothness. EDX data further revealed the presence of the desired chemical components on the surface layer of unmodified and modified silicone elastomers. Silicone elastomers with lower surface roughness of maxillofacial prostheses can be obtained simply by coating a gypsum mold.

S2010205 ものづくり教育のための卓上プラスチック成形機の開発([S201-02]技術教育・工学教育(2),技術と社会部門)

The plastics mold machine which could use for engineering education was developed. Developed plastics mold machine is the small desk top injection molding machine. The operation is very easy, because the structure of the injection molding machine is very simple. This machine heats the plastic to the over melting point, and it injects the plastic by the pressure in the mold. The mold for injection molding was manufactured in the gypsum. However, the mold made in the gypsum is easy to be broken for the brittleness. In the experimental result, though the injection molding with gypsum mold is possible, it is necessary to improve the brittleness of the gypsum mold. The injection molding machine and gypsum mold become the useful teaching material.

Molding Gypsums in the Production of Ceramic Sanitary and Table Ware. Adapted Porosity With Optimal Strength

The new improved molding gypsums are used for casting ceramic articles by the conventional and multiple casting (spagless) technologies. Such gypsums increase casting productivity and extend the life cycle of gypsum molds and copies.

Forming properties of bodies for casting sanitary ware ceramics

The coagulation structural and technological properties of slip bodies for casting ceramics on stands in gypsum molds and under pressure in polymer molds are shown. Body compositions that optimize water systems with differentiation of casting methods and porcelain structure during firing are presented.

Molluscs from the fossil site of "Lo Hueco" (Upper Cretaceous, Cuenca, Spain): Palaeoenvironmental and sequential implications

In the exceptional site of Lo Hueco (Cuenca, Spain) more than 8500 macroremains of plants, invertebrates and vertebrates, including titanosaur sauropod dinosaurs, have been collected in a succession of Upper Cretaceous Garumn facies. This work describes the molluscs found together, interpreting their palaeoenvironmental and sequential meaning. The sample is comparatively scarce due to the urgency of the excavation, and to constraints of the preservational scenario, seemingly not ideal for the fossilization of carbonated remains. Thus, the absence of well preserved shells has motivated the use of open nomenclature. Bivalves are recorded by unarticulated marly mudstone moulds of Margaritifera sp., Anodonta sp., ?Corbicula sp. and Pisidium sp., and most gastropods by gypsum moulds of Faunus sp. This association indicates a typical freshwater palaeofauna, where the presence of Melanopsidae gastropods can suggest the sporadic influence of moderately brackish-water episodes. These data confirm previous palaeoenvironmental interpretations proposed for the site. Additionally, the presence of the terrestrial gastropod Palaeocyclophorus sp. in underlying beds with high proportion of vegetal terrestrial organic matter, and situated over an important erosive discordance, has allowed to locate the beginning of the depositional sequence of Lo Hueco.

The Temperature Distribution Research of Foaming Gypsum Mold in the Fabrication and Pouring Process

This paper describes study of temperature variation in the gelling and hardening, thermal baking and pouring stage of foaming gypsum mold. The temperature difference curve in the gelling and hardening process shows an rapid decline, tending to the placid downward eventually after a clipping rise. During the thermal baking stage, owing to the low heat conduction coefficient of the foaming gypsum mold, the actual temperature of each thermocouple lags behind the craft temperature, lag degree increases gradually with the extension of baking temperature and holding time. At the initial period of pouring process for molten aluminum, the temperature of center position in the mold increases fast by absorbing lots of heat in the solidification process, whereas, slower temperature rising curve occurs in the edge and intersection position. Coupled with the ongoing of air convection heat transfer, resulting in a continuous falling of temperature, therefore the temperature difference curve of each point inside the mold shows a successive upward trend with the solidification process of molten aluminum alloy.

Influence of thermal storage on microstructure and properties of Sn–9Zn–xIn alloys

This study investigated the solidification behaviour and microstructural properties of Sn–9Zn–xIn alloys cooled under various crucible environments (i.e. gypsum or graphite moulds). Sn–9Zn–xIn solder specimens were prepared with the addition of In ranging from 0 to 0·5 wt-%. The specimens were melted at 200°C, poured into gypsum or graphite moulds and then allowed to cool in air. The microstructure, chemical composition and hardness properties of various specimens were then systematically examined. It was found that the microstructure (and hence the mechanical properties) of the solder samples can be controlled by manipulating the variables of the solidification process, such as cooling rate, element diffusion rate, solubility among elements and the crucible environment.Cette étude a examiné le comportement de solidification et les propriétés de la microstructure des alliages Sn–9Zn–xIn refroidis dans divers creusets (c’est-à-dire des moules en plâtre ou en graphite). On a préparé des spécimens de soudure de Sn–9Zn–xIn avec des additions d’In variant de 0 à 0·5% en poids. Les spécimens étaient fondus à 200°C, coulés dans des moules en plâtre ou en graphite, et ensuite refroidis à l’air. Ensuite, on a systématiquement examiné la microstructure, la composition chimique et la dureté des divers spécimens. On a trouvé que l’on pouvait contrôler la microstructure (et ainsi les propriétés mécaniques) des échantillons de soudure en manipulant les variables du procédé de solidification, comme la vitesse de refroidissement, la vitesse de diffusion de l’élément et la solubilité entre les éléments ainsi que la nature du creuset.

Effect of Different Grinding Time on the Performance of Gypsum Mould

In order to improve the performance of gypsum mould, dry grinding process was applied to the pretreatment of gypsum powder and the effect of the ball-milling time on the performance of gypsum powders was mainly studied in our work. X-Ray powder diffraction (XRD) and scanning electron microscope (SEM) were employed to characterize the phase compositions and microstructures of gypsum mould. The results show that the initial and final setting time of gypsum slurry reduces with the increasing of ball-milling time. But the initial and final setting time changed slightly when the ball-milling time was extended to 1 hour or more. Furthermore, the water absorption of gypsum moulds made by the pre-grinded gypsum powders was increased by 42.0 percent in the case of 2 hours’ grinding time, yet the flexual strength of the mould was slightly decreased by 12.5 percent. The main phase of gypsum powder was unchanged, but decrystallization degree increased after dry grinding process. Meanwhile, the crystal orientation and particle aggregation of the gypsum powders were destroyed, and the particle length of that was shortened. As a result, the gypsum moulds obtained by the as-treated gypsum powders have high porosity and water absorption.

Shear bond strength between light polymerized hard reline resin and denture base resin subjected to long term water immersion

The effect of long-term water immersion on the shear bond strength between denture base resin and Triad visible-light-polymerized (VLP) direct hard reline resin is not known. The aim of this study was to investigate the bonding characteristics of Triad VLP direct hard reline resin to heat-polymerized denture base resin subjected to long-term water immersion. Ninety circular disks, 15mm in diameter and 3mm thick, of denture base resin were polymerized from a gypsum mold. Sixty specimens were subjected to water immersion and 30 were stored at ambient room temperature for 4months. Thirty water-immersed specimens were dried with gauze (group 1), while the other 30 water-immersed specimens were dried with a hair dryer (group 2). The dry specimens (n=30) represented the control group (group 3). All specimens were air abraded and painted with bonding agent before packing Triad VLP direct hard-reline resin. Specimens in each group were subjected to thermal cycling for 50,000 cycles between 4°C and 60°C water baths with 1-min dwell time at each temperature. The bond strength at which the bond failed under stress was recorded using a universal testing machine. One-way ANOVA and Tukey post hoc comparison were applied to find significant differences between groups (α=0.05). Significant differences in mean shear bond strength among the specimens existed because of variable water content in the denture base resin (P<0.05). Group 3 (dry) was higher than group 2 (desiccated), and the lowest was group 1 (saturated). The shear bond strength of Triad VLP direct hard reline resin to denture base resin depended on the water content in the denture base resin. The dry denture base resin demonstrated superior bond strength compared with the desiccated and water-saturated denture base resins.

Researches on Alloy form Characteristic Based on Gypsum Molding

With the rapid development of economic, gypsum is widely used in casting and other industry areas. In this paper, the result is obtained that the performance of plaster mold is better when gypsum-water ratio is 0.5. If the composition of gypsum slurry mixture (� -hemihydrate, mullite powder, zirconium powder, reinforcing fibers) is mullite powder: zircon flour: enhancing fiber = 1:0.25:0.2:0.02-0.04, the mixture will be optimum property. The temperature influencing on bending-strength of plaster and the influence of gypsum-water ratio, filler types and calcination temperature on gypsum bending-strength has been analyzed by means of experiments. Spiral-shaped gypsum mold was made by gypsum molding material and mobility experiment was conducted on Pb-Sn alloys. Compared with pure gypsum, gypsum mixture had better mechanical properties. The fluidity of the alloy in the gypsum mold was effected by casting pressure, pouring temperature and alloy ratio. The research results have benefit to the application of gypsum casting technology.

Replication of specifically microstructured surfaces in A356-alloy via lost wax investment casting

A common way of realizing microstructural features on metallic surfaces is to generate the designated pattern on each single part by means of microstructuring technologies such as e.g. laser ablation, electric discharge machining or micromilling. The disadvantage of these process chains is the limited productivity due to the additional processing of each part. The approach of this work is to replicate microstructured surfaces from a master pattern via lost wax investment casting in order to reach a higher productivity. We show that microholes of different sizes (∅ 15–22 µm at depths of 6–14 µm) can be replicated in AlSi7Mg-alloy from a laser-structured master pattern via investment casting. However, some loss of molding accuracy during the multi-stage molding process occurs. Approximately 50% of the original microfeature's heights are lost during the wax injection step. In the following process step of manufacturing a gypsum-bonded mold, a further loss in the surface quality of the microfeatures can be observed. In the final process step of casting the aluminum melt, the microfeatures are filled without any loss of molding accuracy and replicate the surface quality of the gypsum mold. The contact angle measurements of ultrapure water on the cast surfaces show a decrease in wettability on the microstructured regions (75°) compared to the unstructured region (60°).

Comparison of cranioplasty implants produced by machining and by casting in a gypsum mold

Cranioplasty is a medical technique used to correct craniofacial defects. Depending on the size and location of the defect, a bone substitute to replace the deformed or missing tissue can be manufactured. With the advances in computer-based systems and the invention of new biomaterials, the production of customized implants with good cosmetic and functional results has now become widespread. However, little research has been undertaken into the quality of prefabricated specimens in terms of dimensional and form errors. Because of the geometric complexity involved, measurement of this kind of object is a complicated process. The aim of this paper is to describe two different manufacturing processes used to produce a large polymethylmethacrylate (PMMA) implant for use in cranioplastic surgery and to discuss the results of the evaluation of the dimensional errors and lead times associated with these methods. In the first method, the specimen was directly machined from an acrylic block. In the second, the implant was cast in a machined gypsum mold. Both processes were based on a digital model of a dried human skull scanned by computer tomography. Dimensional errors were evaluated with a coordinated measurement machine. Despite their complexity, the PMMA specimens produced were measured and their dimensional differences established. Compared with direct machining, casting results in a longer lead time and, because of shrinkage, a larger dimensional deviation.

Molding of conical ceramic articles from aqueous slurry

Results of design and construction developments focused on the problem of centering of a core in the cavity of a gypsum mold, the production of ceramic blanks with thickness variability and specified shape, and ways of increasing the uniformity of articles in molding of large sheathing for antenna radomes by means of aqueous slurry casting are presented.

Study on Gypsum Molding Material Properties and Alloy Liquidity

In this paper the influence of gypsum-water ratio, filler types and calcination temperature on gypsum bending strength were analyzed by the means of experiments. Spiral-shaped gypsum mold was made by gypsum molding material and mobility experiment was conducted on Pb-Sn alloys. Compared with pure gypsum, gypsum mixture had better mechanical properties. The fluidity of the alloy in the gypsum mold was prone to casting pressure, pouring temperature and alloy ratio. The research results have benefit to the development of gypsum casting technology.

Increase in the service life of forming surfaces of molding units. Part 2. Study of the effect of operating properties of molding units on their operating life

The effect is considered of such operating properties as the design of a molding unit and the method of drying gypsum molds, on the life of the forming surface of molding units. Avoidance of the disadvantages revealed combined with results obtained in part 1 (E. I. Sudal’tsev, D. V. Kharitonov, and A. A. Anashkina, “Increase in the service life of forming surfaces of molding units. Part 1. Study of the improvement of molding unit forming surface material quality,” Novye Ogneupory, No. 2, 30 - 38 (2010).) of this work make it possible to increase the service life of molds by more than a factor of three

Linear dimensional change in acrylic resin disinfected by microwave energy

The purpose of this study was to characterize the linear dimensional change in specimens made in aluminum rectangular dies (65.0x12.0x3.5mm), with 4 reference demarcations, using the Clássico, Onda-Cryl and QC-20 brands of acrylic resin. Wax patterns with 67.0x15.0x5.0mm were embedded in metallic or plastic flasks with stone gypsum, according to the conventional technique. After stone gypsum setting, the wax molds were removed and the aluminum dies impressed in the stone gypsum mold with silicone material. The powder/liquid proportion and acrylic resin were manipulated according to manufacturer’s instructions. The metallic flask pressure was achieved using the RS tension method. After polymerization in water at 74OC for 9 hours, ebullition water for 20 minutes or microwave energy (900 W) for 10 minutes, the specimens were cooled at room temperature and then removed from the flasks and submitted to conventional finishing. The distances between the A-B, C-D, A-C, and B-D reference points were measured before and after disinfection by microwave energy (650W for 3 minutes). The linear dimensional evaluation of the distances was performed by the same operator with an Olympus optical comparator microscope, with an accuracy of 0.0005mm. Obtained data were submitted to ANOVA and Tukey’s test (α=.05%). The disinfection by microwave energy did not alter the original linear dimensions of the specimens.

Improvement of the rheological properties of clayey suspensions treated with Bacillus mucilaginosus culture liquid

The effect of Bacillus mucilaginosus culture liquid on the rheological properties of clayey suspensions is investigated. It is established that the culture liquid acts as a surfactant and promotes fluidization of a clayey suspension while lowering the moisture content and increasing its sedimentation stability, which makes it possible eliminate the use of electrolytes without degrading the basic technological parameters of the slip and the properties of the intermediate product. This expands the fluidized state interval of slip, lowers the viscosity and thickening factor, and increases the rate of ceramic cast accumulation in a gypsum mold.

Increase in the service life of forming surfaces of molding units. Part 1. Study of the improvement of molding unit forming surface material quality

Materials are reviewed that are used in manufacturing the forming surfaces of molding units. Choice of the optimum water and gypsum ratio for a gypsum paste is provided and methods are considered for improving gypsum mold quality.