VES SSN (18 Yolu . . .

.E FOUNDRY GINEERING kc W E

Published quarterly as the organ of the kuur~u~y wmmission of the Polish Academy d Sciences

Specla! Issue 11zu08

The influence of microwave heating and water glass kind on the properties

of molding sands K. Granata'*, D. Nowaka, M. Pigiela, M. Stachowicza, R. wikierab

" Zaklad OdIewniclwa i Automatyzacj i, Politechnika Wrodawska, ul. Lukasiewicza 5, 50-37 I WrocEaw, Polska Ronal Polska Sp. z o.o., ul. Inzynierska 3,55-221 Jelcz Lnskowice, Polska

*~ontakt korespondencyjny: e-mail: kazimierz.granat@pw.woc.pl

Otrzymano 07.03.2008; zaakceptowano do druku 22.03.2008

Abstract This work presents rcsults of research on thc influcncc of microwave heating time on the process of hardening of warcr glass molding

sands. Essential influence of this drying process on basic properties such as: cornprcssion, bcnding mind tcnsitc strcng~h as well as pcrrneabili~y and w a r resistance, has bccn found. I t has bccn proved, that at1 thc investigated sorts of sodium water glass could be uscd as binding material of molding sands intended for curing with the microwave process healing. It has bccn found, while analyzing the rcsults of property studics or microwavc heated molding sands with 2.5% addition of water glass, that aIl available on the markct kinds of this binding agent (inctuding the most frequently uscd in foundry 145 and 149 kinds) after microwave heating guarantee very good compression, bending and tensile strength as well as permeability and wcar resistance. Moroovcr, it has bccn dctcrmined that the optimal curing powcr of molding sands containing various kinds of water gIass is 560 W. AII values exceeding this rcsult in stabilization of basic propcrtics of molding sands. The use of microwave curing of water glass molding sands results in a significant decrease of hardening process time. full stabilization of molding sands as well as much lower energy consumption.

Key words: Innovative foundry materials and technologies, heating power, microwaves, moIding sand, water glass

1. Introduction 2. Measuring position

Microwaves arc brodIy applied in such fields as telecommunications, rne~eorology or chemistry. Microwave encrgy rnighl also be used. among others, in foundry engineering and curing process of molding sands, including watcr glass molding sands [ 1 4 1 . Microwave hardening process time is 10- 200 t imcs shortcr in comparison to conventional heating. Also, cnergy consumplion in microwavc heating is 10 up to even I00 times lower. The above mentioned bencfi~s encouraged thc Authors, expccting additional positive effects related to irnplcrncntation of this innovative method of molding and core sands containing watcr glass, to undertake cffons of microwavc encrgy application in hardening process of this sands.

Hardening process studies (curing, dehydration [ 6 ] ) of molding sands conducted with commonly used rnicrowavc ovcns do not guarantee repeatability of parameters and FuIl process control. These devices have a very simple power supply unit. not allowing for a steady magnetron output powcr control. In our studics we used a microprocessor control led device. a1 lowing for magnetron power supply control and microwaves' amp1 ilude regulation (which allows for a steady power control) as well as the possibility of hcating time duration and numbcr of cyclcs selection matching a degree of working chamber filIing with stack [2, 71. Thc studics have been conducted at it research station described by earlier publications 115, 171.

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3. Preparation of molding sands

It has bccn dctcmincd, basing on litetatun data and analysis of thc initial study rcsults [2], that - rrotn fhc viewpoint of rnicrowavc hardening process - i t is beneficial to introducc a 0.5% addition of watcr to a mass consisting of high-silica sand and watcr glass. A standard high-silica sand From N o w o g d I3obrza1iski sand mine of 0.32/0.2/0. E 6 main Srac~ion and sodium watcr glass rnanu~aclured by Zaklady Chcmicznc ..RudnikiW S.A., whose properties (according to ccrtificatc) arc prcscntcd in tabkc I, have been used For preparation on molding sands uscd in our studics. Thc molding sands have bccn preparcd according to thc folEowing formula: A portion of high-silica sand (4 kg) was put into a taboratory mixer and, aftcr its start, 20 ml (0.5%) or watcr were poured in. Water glass (2.5%) was doscd in during the mixing pmccss, which took 4 minutcs. Thc samples for determination of comprcssion, bcnding and tcnsilc strcngth as wcll as pcrmcability and wcar rcsistnacc wcrc forrncd in a standard rammcr from molding sands prcparcd in this way [g-101.

Consolidarion degrcc of thc tcstcd samplcs was determined on the hasis of the initial sludics. which dcmonsrratcd that a triplc ramming oh ~ h c mxsscs guarantees their sufficient consolidation atlowing for taking them out. without damagc to btocks, from molds and operating, rcgardlcss of watcr glass kind used For their prcpanrioo, A constant, apparcnt density of the mass, playing an important rok in our studics, wits also determined in this way [3].

4. Sample hardening process

Thc szudies havc bccn conduct4 for molding sand samplcs containing five different kinds of waler glass Ctablc 1). Thc samples were subject to microwavc effccts. Thm samplcs havc been simultaneously put into thc heating chamkr and thcir compression, bending and rcnsilc strcngth dctcrmincd. This number of samples ensured propr owration of rnagnctron and identical research conditions. It has bccn dctcrmincd that optimal curing rime should bc 240 scconds [ 151. Thc samples have h e n [eft to cool down to arnhicnt tcrnpraturc, aftcr hdcning. Microwave powcr rangcd from 240 up to 720 W basing on the analysis of the prcviously coaductcd cxpcrimcnts.

Sincc cornprcssion slrcngth of thc microwave c u d samples cxccedcd measurement rancc of a univcrsal lahorntory apparatus, this valuc was dclcrmincd using a univcrsal strcnelh -hachine lnstron 1126, cnsusing idcnticnl prcssurc incrcnsc spccd, cqual to 0.25 ~krn'.

5. Research rwults

Comparison of research results of curing p w c r influcncc on molding sands containing fivc diffcrcnt watcr glass kinds on comprcssion, bcnding and tensiIc strength as wcll as pcrrncability md wcar rcsistancc has bccn prcscntcd in figurcs 1 to 5. Mcasuting points constitute mean values or rhrcc mcnsurcmcnls.

As appcars from figure 1 analysis, cornprcssion strcngth in case of 240 W power i s very low and fluctuntcs around 1 MPn value. regardless of watcr glass kind. Such a low srrcngzh rcstrlts From insufficient curing of the samplcs, which has bccn shown in tigurc 6. A vcry subslantlal (tenfold) szrcnpth incrcimc is obscrvcd with powcr incteax up to 400 W. Only in cnsc of walcr glass of 137 kind {or thc highest rndulc) thc strcngth incrcascd vcly slighrly. At 560 W a funher incrcasc of comprcssion srrcngth is observed, howcver, ir is not so grcat as in casc of 400 W pwcr. Cornprcssion strcngth stahitization Tor all Ihc uscd water glass kinds takcs placc with powcr incrcxe lo ovcr 560 W. Compression srrcngth diffcrcncc of watcr glass of 145 kind in comparison to 137 kind is almost 40%.

Figurc 2 prcscnts micmwavc hcaring p w c r influcncc on tcnsilc strength. Its incrcasc is observcd within pwcs rangc of 240 - 560 W. Tcnsilc strength stabilizes abovc this valuc. The grcatcst tcnsile slrcngth charactcrizcs molding sand wirh watcr glass of 150 kind and i t is 40% higher than that of 137 kind molding sand prcparcd with addition of water glass of.

Ilcating power influence on bending strcngth is prcscn~d in figurc 3. In this casc also, an incrcasc of bcnding stscngth has bccn observed in case of power exceeding 400 W. Similarly as in cm of compression and tcnsiic strength. bending slrcngth srabjlizcs under these conditions, Also in this cilsc. a 40% difference of bcnding strcngth of two watcr glass kinds - 145 snrl 137 - is observed.

Tablc 1. Physical-chemical propmics of sodium watcr glms

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Murnyu*. [W]

Fig. I . Influcncc of microwavc hcaring power and warcr glass kind on compression strcngih of molding sand

Fig. 2. Influcnce of microwave heating pwer and water glass kind on !ensile strength of molding sand

I ~ ~ * Y P ~ F N I

Fig. 3. Influence: of microwave heating power and water glass kind on bcnding strength o f molding sand

n watsr glwl l40 watar glarl I45

'4 wte~ glasl 149 '0- water alasl 150

Fig. 4. Influcncc o f microwavc hcating powcr and watct glass kind on pmneabili~y of molding sand

Fig. 5. Influcncc of microwave heating power and water glass kind on wcar rcsistsncc of molding sand

Pig. 6. The sample sthjcct to curing at niicmwave power of 240 W

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As appears from thc analysis of figure 4, presenting microwave heating power influcncc on permeability, thc microwave proccss duration has practicalIy no influence on this value, regardless of thc uscd water glass kind.

Heating power innuencc on wear rcsistancc of the investigated molding sands has been presented in fjgure 5. Wear resistance is reduced until rcaching 560 W (while abrasion strength of thc mass increases), Abovc this valuc, wear resistancc remains at a practicaIly unchanged level for all the usdl watcr glass kinds.

6. Final conclusions

While anaIyzing thc results of microwavc hcating p o w r influence on basic properties of water glass molding sands it might bc stated that:

all kinds of water glass available on the markct and used in our research (including the most frequently uscd in foundry engineering kinds of 145 and 149) after microwave heating guarantee very good campression, bending and tensile strength as well as permeability and wear resistance, the greatest influence of microwave heating power has been found in case of compression, bcnding and tensile strength of all kinds of water glass, from among alI the investigated water glass kinds, the greatest sensitivity of basic properties to microwave heating power change has been observed in case of water glass kinds of 145 and 150. the smallest influence of microwave heating p w e r has been observed for water glass 137 kind, no heating power influence on permeability and wear resistance of the investigated molding sands containing all kinds of water glass has been obsewed in case of its values exceeding 560 W, the optimal microwave hcating power of rnoIding sands with at1 kinds of water gIass is 560 W. Further increase or power has no influence on basic properties of molding sands and their stabilization is observed, application of microwave curing process for water glass molding sands ensures notablc economic benefits resulting from a significant reduction of curing time as well as from reduction of energy consumption, while simultaneously ensuring excellent properties of motding and core sands.

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