The moulding sand must have enough refractoriness property to produce excellent quality of casting free from defects.
The sand with lack of refractoriness melts and gets fuse in the casting and spoils the quality of the cast metal. The refractoriness is the measure of sinter point of the sand not its melting point. This is all about the six properties of moulding sand. Every types of moulding sand used in the casting process must have these six properties. If you find anything missing comment us. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment.
Skip to content. Table of Contents. In this study, effects of sawdust, coal dust and iron filling additives at varied proportions on some selected properties of moulding sand were investigated. Consequently, cylindrical specimens with different percentages of additives were prepared based on standard procedures. The prepared specimens were subjected to basic moulding sand testing including moisture content, bulk density, porosity, permeability, green compression strength and green shear strength using standard methods and equipment.
From the obtained test results, all the experimental additives were found to improve the selected moulding properties of the base silica sand. Moulding sand specimen with sawdust additive revealed a relatively better compaction as compared to moulding sand specimens with coal dust and iron filling additives respectively. The moisture absorbing strength of the moulds was also found to increase with increasing percentage of sawdust.
Addition of coal dust to the moulding sand was found to improve sand porosity and permeability which results in less casting defects, and due to improved moisture absorbing strength of sawdust, moulding sand specimens that contained sawdust were equally found to exhibit good compaction with maximum green compressive strength of The most common casting process used in the foundry industry is the sand cast system [1].
The principal constituents of moulding sands are: silica sand grains, clay bond , moisture, and organic additives. Virtually all sand cast moulds for ferrous castings are of the green sand type [2]. Green sand consists of high-quality silica sand, about 10 percent bentonite clay, 2 to 5 percent water and about 5 percent sea coal; other materials may be added to the sand mixture to enhance certain properties [3] , and for defects free cast products, foundry sand for mould making must be carefully prepared to meet certain basic requirements such as refractoriness, cohesiveness, permeability, collapsibility, green strength dry strength, thermal stability and reusability [1].
Moulding sands are specified based on average size and shape. Finer grains lead to more intimate contact and lower the permeability, but tend to fortify the mould and lessen its tendency to get distorted and the shapes of the grain may vary from round to angular [4].
A good moulding sand always represents a compromise between conflicting factors, and to obtain an acceptable compromise of the four basic requirements, the size of the sand particles, the amount of bonding agent such as clay , the moisture content, and the percentage of organic matter are all selected [3].
Moulding material is often reclaimed and recycled, the organic material that has to be added again as a portion of it will burn during the pour [5]. When moulding sands are used for mould making without additives, some important characteristic may be absent in the sand [6].
When additives are added to moulding sands, certain properties including high temperature plasticity, metal penetration property and surface finish are improved [2]. Additives are mixed during sand preparation based on the requirement of molten metal and base sand to obtain specific characteristics in the sand [3].
In spite of the property-enhancing influence of additives on castings from sand cast system, it is regrettable to note that while efforts by researchers on inoculation practice are on the increase, only scanty information on sand additives is available in literatures. Hence, qualities of cast products from the local foundries are found to come with some defects that are preventable when some specific properties are introduced into the base sand through additives.
This study, therefore examines the influence of sawdust, iron filling and coal dust which are cheap and available at varied proportions on the moisture content, permeability, porosity, bulk density, green compressive strength and green shear strength of the base sand that is silica sand with a view to determining the best mould s with correct additives proportion for sand cast system.
This is traced to higher solubility of Fe in molten aluminium [ 13 ]. Fine grained aluminium alloy was obtained which has better strength by inoculating the melt with MgFeSi powder which forms insoluble compound particles, thus helping to increase the rate of nucleation. The grain refinement of Al and its alloys using inoculants that boost heterogeneous nucleation is an important structure modification method used in many industries.
A fine grain size in metal alloy castings guarantees i homogeneous mechanical properties, ii distribution of second phases and microporosity on a fine scale, iii superior machinability because of ii , iv enhanced uniform anodizable face, v improved strength, toughness, and fatigue life, and vi superior corrosion resistance. The literature has quite a lot of mechanisms proposed for grain refinement and critical reviews exist in reports of Perhpezko [ 19 ] and McCartney [ 20 ].
In the present study, the initial scrap charge invariably contains significant amounts of iron in addition to MgFeSi inoculant, which takes an imperative function in the nucleation process.
High Fe content in the charge also encourages the formation of Al-Si-Fe phase. The varying degrees of properties of cast samples at different pouring temperatures using coarse-fine sand particle sizes mixtures are reported in Figures 3 a — 3 d. Meanwhile, in Figure 3 d , there is increase in the trend of the cast porosity as the sand permeability reduces Figure 3 d. The casting voids most frequently called porosity are caused by gas formation, solidification shrinkage, or nonmetallic compound formation in the molten metal.
Blows or blowholes are bulky gas-related voids caused by entrapped mould or core gases in the molten metal. They are large enough and resemble bubbles with smooth internal surfaces and are buoyant and float close to the top of the casting; they can also get trapped on the bottom surface of a core lower in the mould.
Moreover, pinholes are caused by gases atoms dissolved in molten metal that connects and become molecules. In recent times, there are increasing interests in research on performance of castings with porosity. Most notable research is on the fracture mechanics of microplasticity models of fatigue and failure to incorporate effects of inclusions, microporosity, macroporosity, and microstructure to cast aluminium alloy components [ 22 ].
The pores are large enough to be seen even with the naked eyes on some specimen as observed in Figures 7 — 9. To really calculate the fraction and size of porosity after solidification is finished, a more complex analysis may be necessary. Reports have it that the quantity and size of the porosity produced in Al The porosity of cast aluminium alloy obtained at different pouring temperatures and moulding sand mixing ratios are also presented in Figures 7 — 9. The microstructures obtained from the scrap and the cast Al substrates using higher resolution metallurgical microscope with digital camera under magnification are shown in Figures 10 — The analyses of the mechanical properties hardness, strength based on combination of the composition and microstructures revealed the presence of voids and inclusions in the metal cast.
The primary inclusions include solids in the melt above the liquidus temperature of the alloy such as i the exogenous inclusions dross, entrapped mould material, slag, and refractories ; ii salts and fluxes suspended in the melt resulting from a previous melt-treatment processes; and iii suspended oxides of the melt entrapped within by turbulence or on top of the melt.
Secondary inclusions include those formed after the solidification of the main metallic phase. In addition to the microphotographic examinations of the materials, the purpose of the XRD analyses in the present study is to make a distinction among the phases and the grain sizes of the microstructure with the view of appreciating and elucidating reasons for their mechanical properties hardness and strength and forecasting their wear behaviour.
The grain size is also related to the diffraction angle by where is the grain size and is the wavelength; is the diffraction angle. The parameters such as peak values, the diffraction angles, grain sizes, and the crystal structures are analysed and illustrated in Tables 5 and 6 and diffractograms Figures 15 - The phases of compounds at diffraction angles and peak values which are found to be present in the samples are shown in Tables 5 and 6 and diffractograms Figures 15 - At a constant wavelength, the grain sizes of different phase compounds are calculated from 3.
Tables 5 and 6 present the XRD analyses for the scrap and cast aluminium alloy samples. By comparing the results in Tables 5 and 6 , it is clear that fine grains are present more than coarse grains in the cast sample than in the as-received scrap sample. Fine grains are usually characterised by high BHN values and tensile strength properties as obtained in Figures 3 a — 3 d.
Hence, there is no doubt that such cast material will possess better wear resistance property than the as-received scrap Al alloy material as compared with the previous findings [ 14 , 16 , 28 ]. Relatively, sets of 0. Higher fraction was obtained from the 0. The overall effects of variation in the pouring temperatures in combination with the moulding sand mixing ratios on the surface morphology, porosity, hardness, and strength of cast samples are illustrated Figures 3 — 9.
Higher casting temperature causes gassing resulting from the boiling of molten Al alloy and escape of some volatile oxides which increased the metal cast porosity hence producing porous cast with corresponding reduction in strength and hardness measured. Under this condition, there are sufficient pores in the mould which allow the timely escape of heat, reducing the possibility of gases being entrapped in the metal cast.
This explains the reasons for the wear behaviour of the cast Al alloy samples previously reported by the authors [ 29 ]. The effects of moulding sand particles mixing ratio with respect to sand permeability and the pouring temperatures on the hardness, porosity, and microstructures of cast aluminium pistons used in hydraulic brake master cylinder have been studied.
Higher BHN and strength values were also obtained by inoculating the melt with MgFeSi which forms insoluble compound particles.
The authors declare that there is no conflict of interests regarding the publication of this paper. The authors acknowledge the staff and management of the Premier Wings Engineering Services, Ado Ekiti, for providing the workshop services for the production and preparation of materials used for the study.
Dry compressive strength of a moulding-sand mixture increases as moisture is added, until the sand is too wet to be workable Fig. We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits. Do not sell my personal information. Cookie Settings Accept. Manage consent. Close Privacy Overview This website uses cookies to improve your experience while you navigate through the website. Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website.
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