Sand Mould Design for Casting an Aluminium PotA Basic Procedure of Supplementing Artisanal Practices

Artisanal green sand casting of aluminum pots is a notable flourishing business in many urban areas of west and central Africa but seen to be typified by labor-intensive and subjective control of a large number of variables to successfully cast. Correct mold designs with in-flow and cooling rates of molten aluminum are fundamental in reducing labor and defects in the castings. The paper presents sand mold design for casting 30litre-capacity cylindrical aluminum pot of internal diameter 314.7mm, depth 386mm, and wall thickness 4mm with  handling lugs alongside its cover using unpressurized gating system ratio of 1:3:3. The design provides suitable specifications of the ladle position, mass and pouring time and in-flow rate of molten aluminum, layout for the mold components, means of compensating process cooling shrinkages of aluminum during solidification, patterns for the castings, and molding box. The motive behind the paper was to emphasize and exemplify the use of basic engineering design procedure for supplementing artisanal green sand molding practices for improving consistency and productivity, and minimizing laboriousness and casing defects with improved profitability in the business.


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Abstract-Artisanal green sand casting of aluminum pots is a notable flourishing business in many urban areas of west and central Africa but seen to be typified by labor-intensive and subjective control of a large number of variables to successfully cast.Correct mold designs with in-flow and cooling rates of molten aluminum are fundamental in reducing labor and defects in the castings.The paper presents sand mold design for casting 30litre-capacity cylindrical aluminum pot of internal diameter 314.7mm, depth 386mm, and wall thickness 4mm with handling lugs alongside its cover using unpressurized gating system ratio of 1:3:3.The design provides suitable specifications of the ladle position, mass and pouring time and in-flow rate of molten aluminum, layout for the mold components, means of compensating process cooling shrinkages of aluminum during solidification, patterns for the castings, and molding box.The motive behind the paper was to emphasize and exemplify the need for using basic engineering design procedure to supplement artisanal green sand molding practices for improving consistency and productivity, minimizing laboriousness and casing defects, and higher profitability in the business.Index Terms-Consistency; Engineering Supplementation; Green Sand Casting Business; Improvement.

I. INTRODUCTION
Casting is the process of making desired solid product by pouring molten metal into a refractory mold that is made with a cavity that has the shape and size of the product and allowing the metal to solidify in the cavity to form the product.Various patterns which are replicas of the final products to be made are used to create the requisite cavities in the molds.Sand castings are produced in specialized factories called foundries.A foundry consists of design, pattern shop, molding, heating and heat treatment, machining, inspection and testing sections.Over 70% of all metal castings are produced via sand casting process [1][2][3][4].Sand molds are designed to have their components arranged with different specifications for producing various castings.The mold is made up of two halves-the cope (upper half) and the drag (bottom half), which meet along a parting line.Both mold halves are contained inside a box called a flask which itself is divided along the parting line.The two halves of the mold are placed together by using pins called dowel pins.The mold cavity is formed by packing sand around the pattern in each half of the flask.After the sand has been packed and the pattern removed, a cavity that forms the external shape of the casting remains.Some internal surfaces of the casting may be formed by cores.Sand casting involves use of green or dry sand molds.Cores are additional pieces that form the internal holes and passages of the casting.Cores are typically made of sand so that they can be shaken out of the casting [5].Fig. 1 shows a typical mold arrangement for sand casting.Molds made of sand are relatively cheap, and sufficiently refractory even for heavy-metal foundry use.The advantages of sand casting include: use of simple and easily available materials, suitability for high production rate, feasibility for producing objects with intricate shapes, and ability to be used to produce very small parts weighing few grams to large complicated components weighing several metric tons.Metals that can be sand-cast include ferrous metals such as steel and cast iron and many non-ferrous metals but aluminum is the most commonly used metal in the metal casting industries due to its comparatively far more properties of casting merit than other metals [5,6].
Sand casting is nevertheless attended with a number of problems such as lower dimensional accuracy of products, labor-intensiveness involved in the process, and various defects products are prone to compared to some other production processes like machining.Successful sand casting therefore requires meticulous control of a large number of metallurgical and mold design variables.Correct mold design with flow and cooing rate controls of the molten metal in the mold cavities is the basic for successful casting and reducing the labor involved.Mold design requires establishing requisite specifications of the pouring basin, sprue, sprue well, runner, gating system, product cavity, and cooling means to achieve satisfactory products of various types and sizes.Improper mold design can cause oxidation of molten metal, misruns, mold erosion and failure with attendant costs.In foundries, greater engineering skills and creativity are used to control many process variables to eliminate or minimize defects in castings and achieve higher Sand Mould Design for Casting an Aluminium Pot-A Basic Procedure of Supplementing Artisanal Practices Thomas N. Guma and Lilian O. Uche production rates with less labor compared to artisanal casting practices which are mostly carried out at shop level [3,4].
Artisanal green sand casting of aluminum pots has been a highly thriving business for decades in some west and central African urban areas with total worth estimated to be several millions of Nigerian Naira.Many people find gainful employment in the business and many more profitably trade with the cast pots.The major buyers and end users of the pots are people from some African native communities where firewood is the only available energy source to meet cooking and other heating needs.Most of the pot users prefer them to industry-produced ones which are also available in markets for sale because of their relative affordability at cheaper rates and designs in the traditions of the natives or ability of custom-making them to various desired sizes and shapes.Most of the artisans involved in the pot casting are not engineers or holders of degrees or advanced certificates in foundry technology but people who once worked in foundries where they experientially acquired some casting knowledge or technical school leavers and trade centre trainees who also acquired the knowledge through years of experience in the pot business itself.Such workers are seen to lack in-depth engineering control of the casting variables particularly mold design with correct control of aluminum flow and cooling rates in spite of their highly commendable skills.The workers compete with one another to produce better quality pots and profiteer more so often use contrasting subjective skills in controlling many variables in order to achieve their aims [7,8].Visually, their successfully cast-produced pots look good but many of them do end up as scraps during the casting process as was fieldobserved and shown for example in Figs. 2, and 3 [9].to be consulting government-employed professionally competent foundry engineers charged with the responsibility of making inputs in all their main designs before any production.The aim in this paper is to highlight the economic importance of artisanal green sand pot casting business and attendant problems and emphasize the need for using basic engineering principles to supplementing basic production practices for improving consistency and productivity, minimizing laboriousness and scraps, and maximizing profits in the business.The objective is to exemplify use of the principles by presenting the mold design for casting 30litre-capacity aluminum pot with handling lugs alongside its cover.Material make for the pattern was dry mahogany wood.

D. Riser for the Pot Casting
A cylindrical open riser with volume greater than that of the pot and cover casting was considered suitable for compensating shrinkages of molten aluminium in the pot casing cavities.The design specifications of the riser in accordance to Chvorinov's rule [9,10,12] were as follows: a. Surface area of the pot casting together with its cover and handling lugs (  ).g. Location of the riser.The riser is specified to be located between the main pot and its cover plate castings 10mm above them as shown in Fig. 6.The design results give complete specifications of the mold and aluminum for optimally casting 30litre-capacity cylindrical aluminum pot with nominal dimensions of 314.7mm internal diameter, 386mm depth, and 4mm wall thickness alongside its cover and three semi-circular handling lugs of 10mm solid thickness and 20mm-radius as can be seen from subsections A, B and C of section II.The specifications are in terms of dimensions and components arrangement of the mold in relation with one another and quantity of aluminum to flow through them as can be seen from subsections B, C, and Fig. 6 of section II.To cast the pot and its cover to accurate dimensions, dry mahogany wood patterns were found suitable and recommended to be making with specified dimensions for molding for the castings [10].
A tapered sprue was considered suitable for the mold and its dimensions duly design-specified as can be seen from subsection C of section II and Fig. 5.Other design specifications of the mold were one sprue and well, one runner and four in-gates with their cross sectional sizes.The mold design was based on unpressurized gating system ratio of 1:3:3 with the centre parting line type as can also be seen in subsection C and Fig. 6 under section II.The in-gates were designed to enable both the pot and its cover to be cast from the same mold.Two of the in-gates provided the means of feeding molten aluminum into the main pot cavity and its two handling lugs at mid-length on two outer opposite diametrical positions of the cavity and the other two in-gates for the pot cover cavity at two outer opposite diametrical middle positions of its handling lug as can be seen from Fig. 4.An open cylindrical riser with location shown in Fig. 6 and dimensions given in subsection D of section II was designed for compensating shrinkages of molten aluminum in the casting cavities during solidification time.A steel box of 650 by 650 by 650mm dimensions was found suitable and recommended for green sand molding for the pot castings.

IV. CONCLUSION
The importance and production problems of artisanal aluminum pot casting business have been highlighted.A green sand mold with a tapered sprue, un-pressurized gating system ratio of 1:3:3, and an open riser for compensating cavity shrinkages of molten aluminum during solidification has been designed in accordance to engineering theoretical practicalities for casting 30litre-capacity cylindrical aluminum pot alongside its cover and three semi-circular handling lugs.The design specified the requisite ladle position, sprue and well sizes, runner and in-gates dimensions, pattern make and allowances, total mass and insprue flow rate and pouring time and cost of aluminum as well as molding box for optimally producing the pot castings.The work was intended to emphasize with exemplification the need for using basic engineering design procedures to supplement artisanal green sand molding practices to improving consistency and productivity, minimizing laboriousness and scraps, and increasing profits in the pot casting business for any entrepreneurial, educational and research interests.

Fig. 6 :
Fig. 6: The design layout for the casting

Dr
Thomas Ndyar Guma received B. Eng, M.Sc and Ph.D degrees in mechanical engineering from Ahmadu Bello University Zaria, Nigeria.His research interests are vast and include design and production, manufacturing automation and corrosion protection of mechanical systems Mrs Lilian Ogboi Uche received her Post Graduate Diploma in Mechanical Engineering in 2018 from Nigerian Defence Academy Kaduna where she worked under Dr Thomas Ndyar Guma for her research project.Her research interest is in the area of computer aided design with application to foundry engineering