Applied Clay Science, 5 (1990) Elsevier Science Publishers B.V., Amsterdam- Printed in The Netherlands

Transcription

1 Appied Cay Science, 5 (1990) 8597 Esevier Science Pubishers B.V., Amsterdam Printed in The Netherands 85 Anaysis and Deveopment of gbokoda Cay as a Binder' for Synthetic Mouding Sand n \U C.A. LOTO and E.O. OMOTOSO Department of Metaurgica and Materias Engineering, ObafemiAwoowo University, efe (Nigeria) (Received May 19, 1988; accepted after revision December 22, 1988) \) ABSTRACT f: u Loto, C.A. and Omotoso, E.O., Anaysis and deveopment of gbokoda cay as a binder for synthetic mouding sand. App. Cay Sci., 5: Cay obtained from gbokoda in the southwestern part of Nigeria has been anaysed and deveoped as a binder for synthetic mouding sand. The anaysis was compared with the anaytica resuts obtained for the pretreated bentonite cay imported from the U.S.A. and used by the Nigerian Foundries Ltd. (NFL). Xray anaysis indicated the presence of kaoin, iite and montmorionite (parent minera of bentonite), with kaoin having the highest percentage in the gbokoda cay and montmorionite was further confirmed by the fame test which shows the existence of exchangeabe cations not present in kaoin. The effects of mixing varying amounts of cay, tempering water and sand on mouding properties were investigated. The green and dry strength and shatter index of the mixtures were determined. The green and the dry strength (both in shear and compression) of the gbokoda test cay, mixed with the subanguar agoon siica sand and determined at optimum water content, give good vaues for synthetic mouding sand. The shatter index test shows a decrease in coapsibiity as the water content decreases at constant cay addition. gbokoda cay is more coapsibe but ess tough than bentonite as shown by the shatter index. ~. ~ NTRODUCTON n genera practice, mouding sand and dry sand are most commony bonded with cay. n the natura mouding sands the cay occurs in association with the sand grains, whist the synthetic sands are bonded with seected cays from separate deposits. Testing techniques for moudingsand have been deveoped and the constitution and properties of foundry bonding cays have been comprehensivey examined (Grim and Cuthbert, 1945; Tayor and Diran, 1952; Heine et a., 1958; Lawrence, 1961; Wenninger, 1963, 1968; Sanders and Doeman, 1967, 1969). However, the present work concerns the anaysis and deveopment of an avaiabe oca cay deposit. n this work, the composition of the cay was determined by Xray diffrac 1m 11 ' /90/$ Esevier Science Pubishers B.V.

2 86, C.A. LOTO AND E.O. OMOTOSt tion and chemica anayses. Further to determine its suitabiity for use as ~ binder in synthetic mouding sand, mechanica and physica tests were carrieci out on green and dry sand test sampes without any other additives. Efforts are sti being made in the deveopment of avaiabe oca raw materias for industria use, wordwide and particuary in the deveoping countries. This, no doubt, wi contribute to the research interest created in this paper. Though cay is avaiabe in arge quantities in different riverine areas of Nigeria, no, particuar industria use has been made of it. There is aso no known research on the anaysis and deveopment of the avaiabe cay to determine its suitabiity for industria use. This investigation is therefore a part of an ongoing effort to deveop an efficient foundry sand binder from avaiabe oca cay deposits. The cay used in this study was coected from gbokoda in the riverine area of Ondo State iri the southwestern part of Nigeria. The vast reserves of siica sand (Si0 2 > 98%) at gbokoda make the area sefsufficient in mouding sand. A foundry industry using 100% oca sand/cay is thus considered viabe in the area if the avaiabe cay coud be deveoped and found suitabe as an efficient foundry sand binder. Further research work in the deveopment of this cay for foundry use is anticipated. EXPERMENTAL PROCEDURES Preparation of test sampes The asreceived cay contains a arge amount of coarse partices, mainy quartz. Because of their widey varying size ratios, the cay and the quartz were separated using gravity sedimentation techniques, foowed by wetsieving to remove ight, coarse partices that might foat in the suspension. The asreceived wet cay was dissoved in water and thoroughy dispersed by 1.5 g/dm 3 Cagon (sodium hexametaphosphate). After stirring for about 30 min, the content of the jar was aowed to sette for about 5 min. The quartz was observed to be sedimenting and the cay partices to be in suspension. The quartz sediments and the cay in suspension were separated by decantation. The sediment was discarded whie the suspension was retained for subsequent separation. The suspension, which was 100% cay and sit, was sedimented using centrifuga sedimentation methods. The separation was carried out in a aboratory centrifuge. This consists of four 55cm 3 tubes radiay arranged and traces a 7 em radius when rotating. The tubes were fied with the surry obtained from the gravity separation suspi;!nsion and aowed to rotate at 15,000 rev./min for 30 min. The centrifuga force was cacuated to be 19 kn. The cear water on top was then decanted and the thickened surry removed from the bows for subsequent dewatering operations. '

3 :;)!'.. ;...:.', GBOKODA CLAY AS A BNDER FOR SYNTHETC MOULDNG SAND 87 This surry was dried in an oven at 50 o C for 16 h. t was virtuay impossibe to increase the temperature so as to reduce the drying time because of the characteristic changes that might occur at higher temperatures. The dried mass was crushed in a aboratory mi and subsequenty sieved (90 J1m sieve) to further ensure the purity of the cay. \ Loss on ignition test ~ Five grams of the dry materia was heated for 2 hat 1000 C in a gass crucibe, using the aboratory muffe furnace. After ensuring constant weight after ignition, the residua cay was measured and the ignition oss cacuated (Tabe ~. Xray anaysis J Xray diffraction patterns of gbokoda cay and NFL bentonite were obtjined using a Phiip's diffractometer and chart recorder. ron Ka radiations. with a Mn fiter were used. The scanning conditions were.28 kv and 12 rna, ~~2 28/min scanning speed, 1 em/min recording speed and a time constant of 4.0. The range was cps. The resuts obtained were anaysed (Tabes, ). Cassica anaysis Comparative tests were carried out on the bentonite and gbokoda cay (Tabe V ) with the aim of determining the intensity of the emitted radiation based on Na+, K+ and Ca 2 +. n the fame photometer, a suitaby diuted soution of the cay sampes was sprayed into a fame producing the characteristic r,adiation. The intensity of radiation was measured with a photomutipier. TABLE Physica properties of gbokoda cay Property Vaue %Cay bond (1) as received 78% (2) quartzfree 100% $pecific gravity 2.22 Coour grey Loss on ignition %at 100 C 15.7

4 J/ 88 C.A. LOTO AND E.O. OMOTOSO TABLE Diffraction anges and corresponding dvaues of gbokoda cay Peak eo d( ) Reated cay nm sine mineras dvaues of known mineras (nm) Montmorionite Montmorionite Montmorionite ite Kaoinite ite Kaoinite Montmorionite , TABLE ) Diffraction anges and corresponding dvaues of NFL bentonite Peak eo d( ) Reated cay nm sine mineras Montmorionite Montmorionite ite 4! Kaoin Kaoin Kaoin Kaoin TABLE V Chemica composition of NFL bentonite and gbokoda cay A (bentonite) K+ (ppm) (%) Na+ (ppm) 13, (%) Ca 2 + (ppm) (%) Fe (ppm) (%) B (gbokoda cay) dvaue of known mineras (nm) ~!! ~ 'D i '. '' ' j rn!.', ' ~ :~.! i. j J

5 ~ 1 D j i ' GBOKODA CLAY AS A BNDER FOR SYNTHETC MOULDNG SAND 89 Testing of mouding sand Detais of the tests,' testing procedures and equipment used have been described in the AFS Foundry Sand Handbook (Anonymous, 1963). The siica sand (80, 85, 89, 91, 93, 95 and 98% by weight), cay binder (20, 15, 11, 9, 7, 5, 3% by weight), and tempering water were thoroughy mixed manuay for 10 min and stored in covered pastic jars to prevent airdrying. At each addition of an amount of sand mixture adequate to form standard 50 mm diameter and 50 mm high, test pieces after three rams was measured out. After ramming th:qee times, the test pieces were then used in standard green compres~ion and shatter index test (Anonymous, 1963). The oading rate in the compression tests was 13.6 kg/min. The tests were repeated on three simiar sampes and th~ average determined. Aso, three standard test pieces were made for the dry compression and shear tests. They were baked for 2 hat 160 C and cooed in air to ambient temperature for about 30 min before testing on a universa str ngth test machine. Averages of the test resuts were recorded. RE ULTS AND DSCUSSON f J J u u Xray anaysis The Xray diffraction pattern obtained (28 is 2 40 ) confirmed the presence of highquaity montmorionite with sma amounts of kaoin and iite (Tabes and ). gbokoda cay (Tabe ) was shown to contain kaoin as the predominant minera with appreciabe quantities of montmorionite and iite. The imported bentonite (Tabe ) possessed the typica pattern of a threeayer minera, whie the gbokoda cay diffractogram presented the typica pattern of a twoayer minera. The degree of crystainity and dspacing varied in both cases due to random orientation of the grains and suppression of some peaks by impurities, especiay in the quartzfree untreated gbokoda cay. Chemica anaysis 'the chemica anaysis (Tabe V) shows the presence of N a +, K +, Ca 2 +, anq Fe 2 + in both cays aong with the aumina and siicates pecuiar to a cays. Sodium is the most potent exchangeabe cation in gbokoda cay even though proportionatey ess than in the bentonite. t was not observed to swe when water was added (as does bentonite). K+ and Ca 2 + are aso present in esser quantities. ts iron (Fe) content is greater than that of bentonite, presumaby due to the fact that the gbokoda cay was not pretreated to eiminate.iron compounds and other ikey impurities that do not contribute to the bonding

6 90 C.A. LOTO AND E.O. OMOTOSO abiity of the cay. But the bentonite, being a standard bonding cay, had been chemicay treated to remove these impurities. The high sodium content in the bentonite confirmed its sweing characteristic. Thus it can be cassified as a sweing or sodium montmorionite. Sweing is broady due to two main causes; adsorption of water in the surface ayers of the attice, which is hydration concerned with the exchangeabe cation; and a second stage in which the unit ayers are forced apart as a resut of repusion which is simiar to the forces due to osmotic pressure and known as osmotic sweing (Grim, 1953; Stephens and Waterworth, 1968). The cacium ion Ca 2 +, present in cays as an exchangeabe cation, does not possess the sweing quaity of N a+. Therefore, the montmorionite present in gbokoda cay is probaby Ca 2 + based, whie the Na + ocked within the iite is aso present. The anaysis cassifies the gbokoda cay as sodium (cacium) auminium iron hydroxide siicate. However, it coud be said that kaoin, the predominant minera in gbokoda cay, is A(Si ) (0H) 4, which shows the degree of substitution and cation exchange capacity to be ow. However, iitic cays usuay contain more than 37% K + (Wora, 1975). Anaysis of gbokoda cay indicates a very ow iite content (0.03% K+ ). This then shows that it is not iitic cay. i 1 n, Green strength The green strength of a cay test materia is the compressive stress in kn / m 2 necessary to cause rupture of a standard cyindrica specimen using a compressiontesting machine. A green sand contains cay and water, as we as the principa sand constituent, Si0 2 Figs. 1, 2 and 3 show the effect of the various cay and tempering water contents on the green and shear strength of both the gbokoda cay and bentonitebonded sands. Both increased steadiy as the cay content increased, but decreased after reaching an optimum as the tempering water increased. For each cay type there was an optimum water content. Too much water causes excessive pasticity, and too itte fais to deveop adequate strength. These effects coud be attributed to the poar characteristics of cay, as a resut of which they are abe to adsorb strong poar moecues, especiay water moecues. The adsorption resuts in the formation of thin water ayers around the cay partices and is thus responsibe for the pasticity of cay (Tayor et a., 1966). The first ayer adjusts to the eectric fied of the cay and a second ayer may be attracted to the first and so on. The attraction becomes weaker from the second ayer on and is progressivey weaker for successive ayers. Sodium montmorionite reaches its maximum strength when the fim is about three moecues thick, an excess of which makes the system ose its strength (Tayor et a., 1966). Cacium montmorionite attains a maximum strength when the fim is about four moecues thick. This confirms the higher water sensitivity T! n : ~ o ~ :1

7 92 C.A. LOTO AND E.O. OMOTOSO r ''(( ~10.0 z 9.0 = C c: < V 5.0 L. "' <11.c: V c: < <11... J % cay 11 20% ay Log% of op timum (peak point) temper ing wa ter. Fig. 3. Effect of optimum tempering water on the green shear strength of Lagos agoon sand bonded with gbokoda and NFL imported bentonite cays. = gbokoda cay; o = bentonite cay. of bentonitebonded sand compared with the gbokoda caybonded sands. However, the higher strength of the former for a particuar cay content wi be due to its better cation exchange capacity and hence higher bonding strength. As the cay content increased, the differences in the green compressive and shear strengths of both cay bonds increased. This is probaby due to the fact that with more cay the exchange capacity increased more rapidy in the bentonite than in gbokoda cay, thereby enhancing the better bonding property in the former than in the atter. t coud aso be expained that the increasing discrepancy at high cay contents is due to the reduction in the dependence of the strength of the sand/ cay mixture upon the sand strength. t was aso observed that the gbokoda cay ost its moisture faster than bentonite when paced in the open. This seems to suggest that the bentonite cay has a comparativey higher adsorption and retentive abiity than the gbokoda cay. Dry strength The dry compression strength of the materias was obtained by drying the specimens in an oven at 100OoC for 2 has previousy indicated. The universa testing machine was used to determine the strength foowing the same procedure?s for the green strength, but with higher oads used. Fig. 4 shows the effect of cay additions on the dry compressive and shear strengths of both sampes. Both increased as the tempering water was increased. This drystrength behaviour, in particuar, is the reverse of that for the green strength which diminished with increasing water content after (

8 ( 1 _;J GBOKODA CLAY AS A BNDER FOR SYNTHETC MOULDNG SAND o c 1600 "' c 0 "iii "' ' E 0 u~ ~: c +'Z g':><: ~ ;;, "' 600 ' o '"' : E"' :J E 200 ';:i Percent cay Fig. 4. The effect of percentage cay addition on the optimum dry compression and shear strength of Lagos agoon sand bonded with gbokoda and bentonite cays. X =compression strength curve (gbokoda cay); =shear strength curve ( gbokoda cay); 6. =compression strength curve (bentonite cay); o =shear strength curve (bentonite cay). rkaching an optimum. That this behaviour of the dry strength was argey due to improved distribution of the binder and the higher buk densities attainabe (Beey, 1982), seems reasonabe. Athough the dry strength of bentonitecay bonded sand was generay higher than that of gbokoda cay bonded sand, differences at higher cay content did not increase as in the green strength. This was the case since water content does not contribute primariy to dry strength. A possibe source of bond strength is the surface tension of the water surrounding the cay and sandcay partices (Caine and Toepke, 1967, 1968; Wenninger and Lang, 1969), and fiing the capacity interstices, particuary those of the cay partices. t coud thus be inferred that the bond strength is caused by the surface ayers of water acting on a stretched membrane, forcing the partices together. As the water ayer becomes thinner by drying, the forces hoding the partices together increase (Tayor et a., 1966). This aso expains the higher dry strength of the mouding sands than their green strength. A decrease in the dry shear strength of bentonitebonded sand was obtained at 11% cay addition (Fig. 4). Repeated tests gave the same resut. This trend was considered to be due to cay saturation for a particuar water content in which the transverse fracture on the stretched interpartice membrane easiy overcame the poar bonds.

9 ( 94 C.A. LOTO AND E.O. OMOTOSO Shatter index Fig. 5 shows the effect of cay additions on the coapsibiity of the green sands, whie Fig. 6 shows the effect of cay additions on toughness, a as a measure of the shatter index. The gbokoda cay showed a continuous decrease in coapsibiity (Figs. 5 and 6 ), both with the cay content and tempering water percentage. Simiary, the toughness increased with increasing cay and tempering water addition, changing from a concave shape to a convex curve. The gbokoda cay did not reach saturation within the imit of the experimenta period. With the bentonites with ow cay contents ( 3, 5, 7%), the coapsibiity decreased with moisture content whie toughness increased. At higher cay percentages, however, the coapsibiity passed through a maximum. The deformation or pasticity of mouding sand is determined from the green compression test (Beey, 1982). The property can be reated to the potentia resistance of mouds to hydrostatic pressure and to casting contraction. The product of deformation and green strength has been used as an index of toughness (Beey, 1982). That is: mouding sand toughness number=dxsx100, where d=deformation (.urn), and s=green compression strength (kn/m 2 ). Hence, considering this direct reationship of green strength to toughness, the curves obtained both for the bentonite and gbokoda cay bonded sands were not unexpected. Coapsibiity measures the fragiity of the mouding sand. Since coapsibiity is the inverse of toughness, its tendency to increase with decreasing cay content coud be justified. QJ L.. :J "' QJ E 5.0 't c: ro 4.0 "'X c: QJ ~~ 3. 0 L.. ~....._QJ o::: >.c:.~f)... "' a.,eo 1.0 ~ Q 0 3 u Percent c ay Fig. 5. The effect of cay addition on the coapsibiity (shatter index measure) of Lagos agoon sand bonded with gbokoda and the NFL bentonite cays. = gbokoda cay; o =bentonite cay. r [ r [,.!!!!.! r Li c

10 J GBOKODA CLAY AS A BNDER FOR SYNTHETC MOULDNG SAND ( X Q) ""0 c:... ~ ro.r::... 0 Q)... ::J ro Q) E Q) c:.r:: 01 ::J 0 f L Percent cay Fig. 6. The effect of cay addition on the toughness (measure of shatter index ) of Lagos agoon sand bonded with gbokoda and the NFL bentonite cays. 0 =bentonite cay; o = gbokoda cay. n the drystrength anaysis of bentonitic sand, the dryshear strength passed through a maximum, as aso the toughness. This phenomenon coud be due to an optimum condition being reached in the sandcay water saturation system. The excess moisture increased the pasticity which made it easiy deformabe and hence a decrease in toughness with an attendant increase in coapsibiity. Thus, potting the optimum shatter index against cay content showed an increase in coapsibiity of up to 5% and a gra_dua decrease as the cay content was increased. There was a steeper increase in toughness for bentonitebonded sand because of its greater sensitivity to water additions. CONCLUSONS rr1 ij ( 1) gbokoda cay consists of shae mineras such as iite, kaoinite, montmorionite, with kaoinite being the base cay and montmorionite, most responsibe for good mouding properties, present in a smaer quantity. Chemica anaysis showeda fairy high iron content. (2) The imported bentonite contains more sodium (sweing) montmorionite than cacium (nonsweing) montmorionite as is evident from the chemica and Xray anaysis and the high dry strength not attainabe by cacium montmorionite. (3) Optimum green strength for the bentonite addition to subanguar agoon sand occurred at 9% cay addition and 2% tempering water. gbokoda J

11 L.\ i r 96 C.A. LOTO AND E.O. OMOTOSO cay exhibits an optimum green strength at 15% cay addition, and 3% tempering water. ( 4) The shatter index properties of both cays are comparativey suitabe as binders for synthetic mouding sand. ( 5) The practica impication of these findings woud seem to be that with a higher cay content, the gbokoda cay coud be substituted for the bentonite. With pretreatment of the cay, the optimum green strength coud be attained with a ower percentage of cay addition; and a bend of both the bentonite and the gbokoda cay woud aso give good mouding properties. r.. 1 ACKNOWLEDGEMENTS ( The authors acknowedge the cooperation of the Department of Metaurgica and Materias Engineering, Obafemi Awoowo University, efe, Nigeria and the Department of Mechanica Engineering, University of Lagos, Nigeria, for making avaiabe the research faciities used for this investigation. REFERENCES ( Anonymous, Foundry Sand Handbook, 7th ed., American Foundrymen Society, Des Paines,. Beey, P.R., Foundry Technoogy. Butterworth, London. Caine, J.B. and Toepke, R.E., An exporatory investigation of some bondwater systems. Am. Foundrymen Soc. Trans., 75: Caine, J.B. and Toepke, R.E., Waterbond ratios and modabiity of moding sands. Am. Foundrymen Soc. Trans., 76: Grim, R.E., Cay Mineraogy. McGrawHi, New York, N.Y. Grim, R.E. and Cuthbert, F.L., The bonding action of cays: cays in green mouding sands. inois State Geo. Surv. Rep., 102: Heine, R.W., King, E.H. and Schumacher, J.S., Correation of green strength, dry strength and moud hardness of moding sands. Am. Foundrymen Soc. Trans., 66, 59 pp.. Lawrence, W.G., Factors infuencing moding sand properties. Foundry, Oct., pp Sanders, C.A. and Doeman, R., Durabiity of bonding cays. Parts, and. Am. Foundrymen Soc. Trans., 75: Sanders, C.A. and Doeman, R., Durabiity of bonding cays, Part V, and: Durabiity of twentynine commercia cays. Am. Foundrymen Soc. Trans., 76: Sanders, C.A. and Doeman, R.L., Cay technoogy, durabiity of bonding cays, Parts V X. Am. Foundrymen Soc. Trans., 77: Stephens, H.A. and Waterworth, A.N., Significance of the exchangeabe cation in foundry bentonite. Br. Foundryman, May Tayor, H.F. and Diran, L.M., The nature of bonding in cays and sandcay mixtures. Am. Foundrymen Soc. Trans., 52: 163. Tayor, F.H., Feminas, M.C. and Wuff, J., Foundry Engineering. Wiey, New York, N.Y. Wenninger, C.E., Some newy deveoped concepts for green sand bondings. Am. Foundrymen Soc. Trans., 71: 177. ' i "!,

12

13 .\ j Wood Sci. Techno!. 24: (1990) Wood S cience and Te chnoogy SpringerVerag ;. 1.. '. 1 Determination of cations and anions in the ashes of ~orn e medicinay used tropica woods * 0. A. Fakankun; C. A. Loto, efe, Nigeria Summary. The ashes of some medicinay used tropica woods were characterised. These were Af ze/ia africana, Astonia congensis, Antiaris africana, Terminaia ivorensis, Azadirachta indica, Ricinodendron heudeotti, Chorophora excesa and Danieia ogea. The ashes were obtained by treating wood in a muffe furnace, after which the ashes dissoved in distied water. The very akaine soutions obtained were anaysed for Na +, K +, Ca2+, Mg 2 +, Mn 2 +, Fe 2 +, Cu2+, C1, SO~ and PO!. Due to wide medicina appication of these wood species experiments were made to determine the cations and anions which may be active ingredients in the compounds (drugs) used in the treatment of differet aiments. _j ntroduction (. J i...j J 1 J 1...J ~ About onethird of the word's and surface is covered with forests with the equatoria rain forest accounting for about 18%. Among the arge number of direct uses, the use of wood for fue has probaby been the most significant. Of the uses of industria wood, umber is the most important especiay in construction of housing; furniture industry is aso a major market for both softwoods and hardwoods. Besides these uses, most of these woods are of medicina importance in the tropics where the bark, root and eaves are used in making drugs to cure severa types of aiments. t is aso possibe to synthesize drugs from these compounds or intermediate compounds that may be extracted from the wood. (rvine 1961; Tedder eta!. 1975). The preparation of macrocycic compounds that may be of medicina importance was found to be unsuccessfu except in the presence of meta ions (Conon eta!. 1973). Yieds of modified porphyrins are ow in the absence of meta ions, whie the use of a meta ion as a tempate is ony appicabe provided they can form meta compexes (Broadhurst eta!. 1972). Transformation of these arge macrocyces may invove the use of centra meta ions as found for magnesium in chorophy and iron in haemogobin. The introduction or presence of metas into or in macrocyces can cause striking variations in reactivity, and this may seriousy affect the potency of the drug from such macrocyces. * The authors are thankfu to A. Amusan of Soi Science Department, Obafemi Awoowo University, efe for technica assistance J

14 ......

15 ......,...,