SUITABILITY OF MOULDING MATERIALS FOR Al-Li ALLOY CASTING

The paper describes the production of an AlSi7Mg cast alloy with Li additions and the reactions of the melt with different moulding materials. It is known that Li is very reactive and tends to form various reaction products such as oxides, gases, etc., which can influence the casting quality. The aim of the research was to find a suitable way to produce such an alloy and to describe the reaction products that are formed between the melt and the moulding material and thus to find a suitable moulding material for processing Al cast alloys with Li additions. The melt was produced in an induction furnace under an inert atmosphere. After melting, 1 w/% Li was added and the melt was cast into five different mould materials consisting of graphite, steel, a CO2 sand mixture, Croning mixture and calcium silicate materials. In the last three cases, various alcohol-based coatings were also used, such as graphite, zirconium oxide-graphite coating and aluminate-graphite filler coating. The results showed that the reaction products in the form of powder on the casting surfaces and the gas porosity in the castings occurred in the cast of a calcium silicate mould and sand mould mixtures. In the case of graphite and steel moulds, the casting surfaces were not oxidised, with no reaction products, and no gas porosity.

ASSESSMENT OF LOCAL CHROMITE SAND AS ‘GREEN’ REFRACTORY RAW MATERIALS FOR SAND CASTING APPLICATIONS IN A POST-PANDEMIC WORLD

In a post-pandemic world, health and environmental safety will become a more important issue than it was before the COVID-19 pandemic. Several fields of engineering, including the foundry industry, have already adopted health and safety measures in the workplace. The risk of pulmonary disease caused by the inhalation of fine particles of silica sand, the main moulding material used in the foundry industry, is rampant in that industry. In terms of environmental protection, the new regulatory restrictions on the disposal of used sand create the need for moulding aggregates to be more recyclable than silica. Chromite sand is an alternative refractory sand for metal casting applications, and is abundant in South Africa. The present study investigated whether this aggregate has better overall reusability than silica. The focus of this study is on the use of chromite sand in foundries as a contribution to improving health in the workplace and to reducing the environmental impact of foundry sand.

Application of the Numerical Model to Design the Geometry of a Unit Tool in the Innovative RTH Hydroforming Technology

The article presents a newly patented rapid tube hydroforming (RTH) manufacturing method, perfectly suited to single-piece production. The RTH technology significantly complements the scope of hydroforming processes. Due to the unusual granular material of the die tool, in particular moulding sand or mass, the process design requires the use of numerical modelling calculations. This is related to the complexity and the synergistic effect of process parameters on the final shape of the product. The work presents the results of numerical modelling studies of the process, including the behaviour of the die material and the material of the hydroformed profile. The numerical calculations were performed for a wide range of parameters, and can be used in various applications. The significant properties of moulding material used for the RTH tests were determined and one was chosen to build the die in RTH experiments. The results of the numerical modelling were compared with the results of the experiments, which proved their high compatibility. The final conclusions of the analyses indicate that the RTH technology has many possibilities that are worth further development and research.

Characterization of Southwestern Nigeria River Sand for foundry use

The greater number of castings produced globally are made by using sand casting techniques that utilize sand as major moulding material. This paper characterizes Isasa River sand based on its physical and chemical properties with the aid of Tandem pelletron electrostatic accelerator, trinocular microscope, mechanical sieve shaker, and box furnace, for Foundry application. Results obtained revealed that the River sand has moisture content of 4.30%, clay content of 2.22%, grain fineness number (GFN) of 49, Silica (SiO2) content of 93%, and sintering point of 1400oC. The River sand is a 4-screen sand, having angular grains with medium sphericity. Isasa River sand will be suitable for casting of gray iron and non-ferrous metals, with the addition of binding agent in suitable proportion.

Application of Surface Layer Inoculation Processes to Solid Solution-Strengthened Ductile Cast Iron

Within the present investigations, an in-mould inoculation method for ductile cast iron with elevated silicon contents was developed. The inoculation process takes place at the interface between the mould’s surface and the melt. The application of a mould wall inoculation process allows inoculation at the latest possible point in time, which means high efficiency due to reduced fading effects. For this purpose, various inoculant suspensions are produced, containing inoculants in different amounts and grain fractions. The inoculant is applied to the surface of a PEP SET™-bonded moulding material by means of an air-pressurized spraying pistol. The specimen geometry used in the tests is a 5-stepped wedge, which represents wall thicknesses in the range of 5–40 mm. For a total of 8 castings, inoculant fractions in the spectrum of 0–25 and 0–45 μm are used to produce the solid solution-strengthened grade EN-GJS-500-14 that is specified in the European standard EN 1563. Metallographic investigations show that a complete solidification according to the stable system can be adjusted in the investigated wall thicknesses by inoculation with grain fractions of 0–25 μm.

A comparative evaluation of border molding using two different materials in mandibular edentulous arches- an in-vivo study

Brief Background The purpose was to compare and evaluate border moulding using two different materials on mandibular edentulous arches. Materials and Methods This clinical study was performed on 15 healthy edentulous subjects who reported to the department of Prosthodontics. All the subjects were first given complete dentures, fabricated with low fusing compound as the border moulding material, followed by complete dentures with putty as the border moulding material. Retention was measured at 3 stages: Border moulding; Complete denture insertion; 6 weeks follow up. Patient’s satisfaction was measured with a 10 point visual analogue scale for both the dentures pre treatment and at the follow up visit. Results Putty border moulding showed higher retention as compared to low fusing compound border moulding with significant difference at all stages- stage 1 (p=0.011), stage 2 (p=0.009) and stage 3 (p=0.0054). The time taken for border moulding was significantly lower in Group 2 than Group 1(P=1.6E-48). According to VAS scores, in terms of aesthetic and comfort parameters, patients were satisfied in both groups without any significant difference, however, retention in Group 2 was higher as compared to group 1(P=0.05) Summary and Conclusions There was a statistically significant difference in the retention, between the groups. Group 2( Putty) had higher retention compared to Group 1(low fusing compound).Time taken for border moulding was significantly lower for Group 2( putty). No significant difference in patient’s satisfaction was observed for aesthetic and comfort parameters. In functional parameter, retention was better in Group 2(putty) subjects. Key Words: Low fusing compound, PVS (putty), border molding, mandibular edentulous arch.

Decoring Behaviour of Chosen Moulding Materials with Alkali Silicate Based Inorganic Binders

This paper contains basic information about new processes for cores for cylinder heads production with alkali silicate based inorganic binders. Inorganic binders are coming back to the foreground due to their ecologically friendly nature and new technologies for cores production and new binder systems were developed. Basically these binder systems are modified alkali silicates and therefore they carry some well-known unfavourable properties with their usage. To compensate these disadvantages, the binder systems are working with additives which are most often in powder form and are added in the moulding material. This paper deals with decoring behaviour of different moulding sands as well as the influence of chosen additives on knock-out properties in laboratory terms. For this purpose, specific methods of specimen production are described. Developed methods are then used to compare decoring behaviour of chosen sands and binder systems.

Determination of Heat Accumulation Coefficient for Oil Bonded Moulding Sands

The possibility of controlling the solidification and cooling time of castings creates prospects of improving their structure and by the same their properties. Thermal properties of the mould constitute therefore an important factor which is necessary to consider while seeking for the mentioned improvement. The presented work illustrates the method of determining some basic thermal coefficients of moulding material, i.e. the coefficient of temperature equalisation a2, known also as the temperature diffusivity, and the heat accumulation coefficient b2, which characterises the ability of moulding material to draw away the heat from a casting. The method consists in experimental determining the temperature field within the mould during the processes of pouring, solidification and cooling of the casting. The performed measurements allow for convenient and exact calculations of the sought-after coefficients. Examinations were performed for the oil bonded moulding sand of trade name OBB SAND ‘E’. The experiment showed that the obtained value of b2 coefficient differs from the value calculated on the basis of theoretical considerations available in publications. Therefore it can be stated that theoretical calculations of the heat accumulation coefficient are thus far not sufficient and not quite reliable, so that these calculations should be verified experimentally.