ALTERNATIVE MATERIALS FOR SILICA SAND, BINDERS AND ADDITIVES IN SAND CASTING PROCESS A REVIEW

Transcription

1 ALTERNATIVE MATERIALS FOR SILICA SAND, BINDERS AND ADDITIVES IN SAND CASTING PROCESS A REVIEW Prabhushankar.N Assistant Professor, Department of Mechanical Engineering, SVS College of Engineering, Coimbatore Rajesh Krishna Raj.N, Sivapraksh.M, Sreenath.J.K, Sujithkumar.M & Midhun Krishna.A UG Scholars, Department of Mechanical Engineering, SVS College of Engineering, Coimbatore Abstract: Foundries all over the world consume silica sand, clay binders and additives to some proportion for production of green sand castings. Silica sand apart from being used for mould making and core making, it is also used in many areas such as glass making, and construction etc., Consumption of silica sand in large quantities will lead to the depletion of these resources. If an alternative source is identified, the demand on single source will be avoided and the cost of the sand can be lowered drastically. Apart from conventional binders and additives for sand moulding different organic binders and additives are also available by which the sand mould properties can be improved according to the material cast like cast iron, steel, aluminum, brass etc. The search for different alternative sources in sand moulding can lead to good quality sand casting at reduced production cost. Keywords - alternative sources; silica sand; sand mould properties; binders; additives. 1. INTRODUCTION Silica sand used in foundry contains high proportion of SiO 2, (more than 95%) and less than that are used as construction aggregates. Silica sand also serves as raw material for glass making and Page No: 399

2 wide range of other industrial and horticultural applications. Silica sands are costlier than the construction sands and this encourage serving wide geographical market, including exports. Naturally available silica sands used in the past are of less economic importance today and the demand is for clay free silica sand which has high silica content. The binding agents like bentonite, chemicals and resins are added for mould and core making which increases the production cost of castings. The quality of castings in green sand moulding depend on various process parameters and input parameters like sand grain size, shape, binder, clay which are complex in nature. Additives play a very important role in green sand mould to enhance specific mould properties. 2. ALTERNATIVE SOURCES FOR MOULDING MATERIALS Some of the alternative sources that have been used as a moulding material are listed below, Tailing Sand Silica free Sand Fly Ash Chromite Sand Olivine Sand Ferro Chrome Sand Blast furnace slag Alumina Cassava starch Soluble Sodium Silicate binder Gum Arabic Tamarind powder and Coconut shell powder Corn Cob and Rice Husk Ashes 2.1 Tailing Sand After tin extraction the residue minerals obtained is called tailing sand. The silica content of tailing sand is between 94% to 99.5%. It is available in large quantity at the Kinta Valley, Page No: 400

3 Malaysia. It has high permeability. It is an important property for sand casting process where the gases formed after pouring molten metal into moulds finds passage for escaping to produce defect free casting. Fig.1 Tailing sand 2.2 Silica free Sand Silica-free minerals obtained as by-products from the manufacture of construction aggregates are cost-effective replacements for foundry silica sand. The major health and safety issues associated with using silica sand can be rectified by using silica free sand with suitable binders and additives. Sand reclamation technology will enable foundries to change to silica-free sand and/or reduce minimize total sand costs per unit of good casting produced. Fig.2 Fly ash Page No: 401

4 2.3 Fly Ash Fly Ash is a residue resulting from the combustion of pulverized coal or lignite in thermal power plants. It is a fine powdery residue of spherical particles generally in the size range of 0.5 to 100 micron. Generally the fly ash consists of nearly 50% silica. Fly ash can be mixed with silica sand for mould making. Fly ash have very high melting point, can absorb and transmit heat during pouring and have the ability to allow gases to pass through a compacted mass. 2.4 Chromite Sand Chromite sand occurs naturally and it consists of oxides of chrome and iron. It has sub-rounded grain structure with highly polished surfaces with 85 AFS fineness number and it does not require crushing and can be used directly in the mould. High thermal conductivity which gives good chilling properties to casting, low thermal expansion property produces good dimensional stability castings and also it has a high refractoriness. When chromite sand is used as moulding sand wide range of resin bonding systems and inorganic binders can be used. Fig.3 Chromite sand 2.5 Olivine Sand Olivine sand is special sand used to maximize the bond performance and it can produce strong chemically bonded mould. The casting defects like shrinkage cavities can be eliminated in both ferrous and non-ferrous green sand castings. Burn-in penetration defects are reduced and lower cleaning casts are achieved. Page No: 402

5 Fig.4 Olivine sand 2.6 Ferro Chrome Slag Fe-Cr slag is an industrial solid waste generate from the Ferro alloys plant. Globally, Fe-Cr slag is producing around 6.5 to 9.5 million tons per annum and likely to be increased by 2.8 to 3%. Since by the large amount of availability and having similar physical and chemical properties with silica sand, investigations can be carryout to find out the suitability of this Fe-Cr slag as alternative mould materials in ferrous and non ferrous foundry industry. Fig.5 Ferrochrome slag 2.7 Blast Furnace Slag Slag is a partially vitreous by-product of smelting ore to separate the metal fraction from the unwanted fraction. It can usually be considered to be a mixture of metal oxides and silicon dioxide. However, slag can contain metal oxides and metal atoms in the elemental form. While slag are generally used as a waste removal mechanism in metal smelting, they can also serve Page No: 403

6 other purposes, such as assisting in the temperature control of the smelting ; and also minimizing any re-oxidation of the final liquid metal product before the molten metal is removed from the furnace and used to make solid metal. Every ton of pig iron produces four tons of Blast Furnace Slag (BFS) and tons of blast furnace gas. Blast furnace slag can partially substitute basic foundry matrix, i. e., sand as a backup. Fig.6 Blast furnace slag 2.8 Alumina Alumina which is a refractory material is added to the green sand mould which improves green, dry compression strength and permeability of the recycled sand. The foundry sand should be recycled for economical reasons and by adding additives like bentonite the green compressive strength is increased. To improve dry and hot compression strength of recycled green sand, addition of alumina improves the mechanical properties. Fig.7 Alumina powder Page No: 404

7 2.9 Cassava Starch Cassava is a cheap source of starch abundantly found in Kenya. It has excellent bonding characteristics. It poses no health hazard and is environment-friendly for the production of sand cores. It also reduces dependence on imported, costlier sources as moulding materials for production of castings. Fig.8 Cassava starch 2.10 Soluble Sodium Silicate Binder The new inorganic binders like soluble sodium silicate binder will provide a good knocking out properties of moulding sands, while maintaining an appropriate level of strength properties. Collapsibility is an important property for moulding sand and especially for cores where the sand materials should be free to collapse after the casting has been solidified to prevent cracks and tear in final casting. Fig.9 Soluble Sodium Silicate Binder Page No: 405

8 2.11 Gum Arabic Gum Arabic also called as acacia gum, is a natural gum made of the hardened sap of two species of the acacia tree. It has adequate bonding strength, hardness and shatter index but the green permeability by using this as binder is very low. Fig.10 Gum arabic 2.12 Tamarind powder and Coconut shell powder Tamarind powder is used as an additive to silica sand mould and it is produced by pulverizing the tamarind seeds to a powder form, it is an agricultural waste available abundantly. Coconut shell powder is produced by grinding the coconut shell to a fine powder form. The tamarind powder gives the better green compression and green shear strength for the moulding sand due to its fineness. The permeability number also shows the higher number. Fig.11 Tamarind powder Page No: 406

9 Fig.12 Coconut shell powder (natural type) Fig.13 Coconut shell powder (dry type) 2.13 M. Rice husk and corn cob Rice husk and corn cob are waste by products of agricultural processing industries. Research has shown that rice husk and corn cob materials have high silica contents. The ashes from these agricultural wastes are also of high binding properties. In addition, since the pulverized form of these materials have very fine grain sizes; they can therefore act as good blend to the coarse sized silica sand. Fig.14 Rice husk powder Page No: 407

10 Fig 15: Corn Cob powder 3. LITERATURE SURVEY A.Abdullah et al. (2012) [1] investigated the samples of tailing sands gathered from four identified tin mines located at the Perak State, Malaysia by the standards and testing procedures. The sand mixture bonded with 4% clay found to have higher permeability number compared to mixture bonded with 8% clay due to the amount of fine particles of the binder. Test on green compression strength is necessary to determine the working range and the potential for tailing sand as aggregate for making green sand casting mould. Kenneth P. Harris (2005) [2] investigated that there is a possibility that foundries can change to silica-free foundry sand. Silica-free fine minerals are readily available as by-products from the manufacture of construction aggregates. Installing advanced mechanical sand reclamation systems employ variable energy attrition and multi fraction techniques in which the silica free sand can be converted in to foundry quality sand. Foundries can optimize their use of these new foundry sands and reduce specific sand and binder consumption. The organic binders can be replaced with low cost inorganic binders and the levels of volatile organic compounds (VOC's) in foundry air can be reduced drastically. Jerzy Sobczak and Mr. Robert M. Purgert (2002) [3] researched to use Fly ash wasted from the thermal power plant with various binders to make the mould. The prime properties like green compression strength and permeability were carried out to find the viability of alternative. Investigation carried out reveals that maximum of 20% can be used for mould making. Further tests are carried out to check the applicability of using 100% fly ash for core production, for this Page No: 408

11 purpose, the binder used and the system has to be optimized to reduce the problems associated with core friability and permeability. Daryl F. Hoyt [4] found that O chromite sand can be used to produce high quality cores with either the phenolic urethane nobake or coldbox binders. The cores produced by this sand have high properties when compared to other speciality sand. Blending of finer chromite sand with other aggregates can produce properties higher than other sands. Tataram.K. Chavan and H.M.Nanjundaswamy (2013) [5] found that Olivine sand has lower free silica content, good refractory properties and strong resistance to metal attack. Olivine sand is less stable under thermal shock conditions than zircon sand or chromite sand, but its thermal expansion is much less than silica sand. The presence of hydrous magnesium silicates (serpentine) may contribute to pin holing or pock marking when olivine sand (uncalcined) is used in the production of low carbon steel castings. Olivine sand particles are less durable than other non silica sands, although it has comparable hardness. I. Narasimha Murthy et al. (2016) [6] investigated that High silica sand is commonly used in foundry industry for sand moulds making. Various efforts are being made to use the industrial wastes as an alternate molding material in foundry to conserve the natural resources; and effective utilization of the industrial waste to sustain the industrialization. Ferro chrome (Fe- Cr) slag has many of the same attributes of the sand. In this paper investigations were carried out on comparative mould and casting properties of high silica sand and Fe-Cr slag for foundry applications. A series of sand tests were carried out on silica sand, Fe-Cr slag individually and various combinations of these two. The process parameters considered for this investigation were % of Sodium silicate, CO2 gassing time, and mould setting time. Two types of moulds were made with 100%Fe-Cr Slag and 100% Silica Sand individually with 8%Sodium Silicate and 15Seconds CO2 gassing time. The mould permeability, compression and shear strength results showed Fe-Cr Slag will be a suitable candidate for either partial or full replacement of molding sand. Enhanced mould properties were observed for Fe-Cr slag than silica sand. Good surface finish castings with enhanced mechanical properties and fine grain microstructures were produced by Fe-Cr slag moulds. Page No: 409

12 K. Thirupathi Rao and A.SureshBabu (2015) [7] investigated that Now a day, utilization of silica sands for foundry purpose in hundreds of tons. Industrialization and globalization leads to high production rates, which in turn increased the demands in multiples. It is the time to use the materials in an effective way and minimize its utilization by looking for alternative. With this thought find an alternative solution for the future generation for the reduction in usage of moulding sand.around 13-15% of blast furnace slag can be mixed with sand in the preparation of mould as the percentage of slag increases the hardness of the moulds made through CO 2 process is increasing. But this high hardness is not required, since poor collapsibility. Hence 13-15% of slag can be recommended. Surface finish of the casted products is poor, so more machining allowance is to be provided. Hence we can't go beyond 15% of slag. It is observed that the moulds made with slag have more permeability than the sand moulds. A.K. Birru et al. (2014) [8] investigated that Alumina, which is a refractory material, have the possibility to improve the green, dry compression strength and permeability of the recycled sand. The results were compared with green sand and recycled green sand and found that addition of alumina improves the mechanical properties. Experiments were conducted at 0.2%, 0.4%, 0.6% alumina addition, it is found that in 0.2% alumina addition the permeability was 2450; Green compression strength was 880 and Dry compression strength 3300 gm/cm2, which is found to be optimum. Oyetunji et al. (2013) [9] investigated that Good quality cores can be successfully produced using cassava starch in combination with Iyoloko clay. Core is produced by mixtures containing 8-12% starch, 5% clay and 6-10% water after baking between 150 o and 180 o C for 2 hours. It is found that cores with optimum properties were from mixtures containing 10% starch, 5% clay and 10% water. The green and baked shear strength values from these tested cores were 31.1 KN/m 2 and KN/m 2 respectively. The strength values obtained from these tested cores show that they are suitable for the production of iron and non-ferrous castings. I. Izdebska-Szanda et al. (2012) [10] investigated that Soluble sodium silicate binders which are inorganic binders are non-toxic in nature but knocking-out properties of moulding sand with inorganic binders are very low. The new generation of binders allows for significant improvement knocking-out properties of moulding sand with those binders. The study confirmed that the proposed method of modification and obtained in this way selected binders allow Page No: 410

13 achieving reclamation of elevated temperatures. moulding sands with these binders, at ambient temperature and Nuhu A. Ademoh, and A.T. Abdullahi. (2009) [11] investigated the Sand specimens bonded with the gum Arabic at different proportions with standard foundry test like green and dry compressive strength, hardness and permeability, shatter index and moisture content tests. The result showed that % binder content in powdered form is suitable for casting non-ferrous alloys, malleable and grey iron whereas 8-13% is suitable for light steel. In solution form, it is suitable for non-ferrous alloy. Tataram K Chavan and H.M.Nanjundaswamy (2013) [12] investigated the effect of fly ash, tamarind powder and coconut shell powder as an additive to silica sand in different proportion on green sand mold. It is found that green compression strength and green shear strength with the tamarind powder as additive gives the higher strength as compare to fly ash and coconut shell powder. Tamarind powder has high fineness so higher green and shear strength can be obtained by using tamarind powder. Sunday Aribo (2011) [13] investigated the use of rice husk and corn cob ashes as aggregates for foundry moulding sand weight percent of rice husk and corn cob ashes were added to the sand mixture and the sand properties determined. A mixture of equal proportion of rice husk and corn cob ashes was also used. The results showed that the green compression strength, green shear strength, moisture content and permeability decrease with increase in the additives (rice husk ash, corn cob ash, and (50% rice husk and 50% corn cob ashes). While dry compression strength and dry shear strength increase with increase in weight percent of the additives. 4. CONCLUSION The proposed work focuses on listing some of the possible alternative sources as moulding materials for production of green sand casting. The consumption of silica sand to some proportion can be reduced by replacing it with suitable moulding materials without compensating quality and further production cost of casting can be lowered. The health issues associated with silica sand in foundry can also be rectified if it is replaced by silica free minerals with suitable binder and additives. Moreover depending on a single source for casting production can be Page No: 411

14 avoided which gives flexibility for selecting various moulding materials to reduce the demand for the particular material. 5. FUTURE SCOPES The construction aggregates are to be tested for green sand mould making application along with silica sand and if possible to replace silica sand to some proportion or fullness in the sand mould. Further silica free sand, tailing sand, chromite sand, olivine sand, alumina and other waste powders like fly ash, tamarind powder, coconut shell powder can be mixed in suitable proportion with different combination along with suitable binders and additives to create a standard AFS specimen and to check the properties like, green compression strength, dry compression strength, permeability, shatter index, etc., If the suitable combination of these alternative sources is found, then casting is to produced from standard material and tests to be carried out to confirm the suitability of this alternative material for mould and core making. 6. REFERENCES [1] A.Abdullah,S.Sulaiman,B.T.H.T.Baharudin,M.K.A.Ariffin, T.R.Vijayaram, M.Sayuti Effect of Moisture Content on the permeability of Tailing Sand Samples gathered from Ex Tin Mines in Perak State Malaysia, Advanced Materials Research Vol 445 (2012) pp , December [2] Kenneth P. Harris, Silica-Free Foundry Sand At Silica Sand Prices, Shape Casting: The John Campbell Symposium,The Minerals, Metals, & Materials Society, [3] Jerzy Sobczak and Mr. Robert M. Purgert, The use of Fly Ash as an aggregate For Foundry Sand Mould and core production, Final Report June 1, 2001 thru April 30, [4] Daryl F. Hoyt, A new Chromite Sand that offers unique characteristics to the metal casting industry Foundry Sand Technology, Marseilles, Illinois, USA. [5] Tataram. K. Chavan, H.M.Nanjundaswamy, Effect of variation of different additives on green sand mould properties for Olivine sand, International Journal of Research in Engineering & Advanced Technology, Volume 1, Issue 4, Aug-Sept, [6] I. Narasimha Murthy, N. ArunBabu, J. Babu Rao,High Carbon Ferro Chrome Slag Alternative Mould Material for Foundry Industry, Procedia Environmental Sciences 35, , 2016 Page No: 412

15 [7] K. Thirupathi Rao and A.SureshBabu, Usage of Blast furnace slag in moulding sand to produce Al-mg alloy castings, Proceedings of International Conference on Recent Trends in Mechanical Engineering-2K15(NECICRTME-2K15), 20th 21st ovember,2015 [8] A.K. Birru, L. Dharam Singh, P. Arun kumar, Enhancement of mechanical properties of recycled Green Sand by addition of Alumina, 5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014), IIT Guwahati, Assam, India. December 12th 14th, [9] Oyetunji, S.O. Seidu, A. I. Opaluwa, Study on the Shear strength of Foundry sand cores using Clay and Cassava Starch as Binder,International Journal Of Engineering,2013 [10] I. Izdebska-Szanda, M. Angrecki, S. Matuszewski, Investigating of the knocking out properties of moulding sands with new inorganic binders used for castings of non-ferrous metal alloys in comparison with the previously used, Archives of Foundry Engineering, Volume 12 Special Issue 2/2012. [11] Nuhu A. Ademoh, A.T. Abdullahi, Assessment of foundry properties of steel casting sand moulds bonded with the grade 4 Nigerian Acacia species (gum arabic), International Journal of Physical Sciences Vol. 4 (4), pp , April, [12] Tataram K Chavan, H.M.Nanjundaswamy, Comparison of Fly ash with Coconut shell powder and Tamarind powder on Green sand mould properties, International Journal of Latest Trends in Engineering and Technology, Vol. 2 Issue 4 July [13] Sunday Aribo, Effect of Varying Corn Cob and Rice Husk Ashes on Properties of Moulding Sand, Journal of Minerals & Materials Characterization & Engineering, Vol. 10, No.15, pp , 2011 Page No: 413