2 Livarski vestnik, letnik 68, št. 1/2021 S. Ramrattan 1 , L. Wells 1 , R. Tuttle 2 , J. Medved 3 1 Western Michigan University, ZDA, / Western Michigan University, US; 2 Univerza Saginaw Valley State University, ZDA, / Saginaw Valley State University, US; 3 Univerza v Ljubljani, Slovenija / University of Ljubljana, Slovenia Karakterizacija površin z ognjeobstojnim premazom za diskaste vzorce s kemično vezanim peskom – 2. del Refractory Coated Surface Characterization for Steel using Disc- Shaped Chemically Bonded Sand Specimens – Part II Izvleček Jekleni ulitki se z globalnega trga vračajo v kovinsko livarsko industrijo v ZDA. Kemično vezani peščeni sistemi so pomemben in rastoč del livarske tehnologije in njihova interakcija na fronti med formo in jeklom se proučuje v študiji – 1. del. Za kvalitativne spremembe oz. izboljšanje površinske kakovosti na mejnih površinah med jeklenim ulitkom brez premaza v litem stanju in kemijsko vezanimi peščenimi sistemi (1. del) je morda potrebna uporaba ognjeobstojnih premazov. Ob današnjem poudarku na izdelavi kompleksnih jeklenih ulitkov in vedno strožjih dimenzijskih zahtevah med proizvodnjo obstaja potreba po hitri in cenovno ugodni karakterizaciji kakovosti površine v litem stanju z uporabo ognjeobstojnega premaza kemično vezanega peščenega sistema. Štiri ognjeobstojne premaze, zasnovane za jeklene ulitke, smo nanesli na diskaste vzorce (jedra) v proizvodnem obratu z uporabo tehnik za nanašanje, ki se uporabljajo v vsakodnevni livarski proizvodnji. Preprosto in praktično preskusno litje malega obsega z uporabo vzorcev jeder oblike diska je bilo razvito na univerzi Western Michigan University (WMU). Preizkus omogoča sočasno omočenje vzorcev jeder pri znani tlačni višini, temperaturi in kemijski sestavi jekla. Preskusno litje je bilo izvedeno na univerzi Saginaw Valley State University (SVSU) in rezultati nakazujejo, da različni kemično vezani pečeni sistemi z ognjeobstojnimi premazi zagotovijo različne površine jeklenih ulitkov v litem stanju. Rezultati dokazujejo, da lahko nove tehnologije ognjeobstojnih premazov zagotovijo boljšo površinsko kakovost jeklenih ulitkov v litem stanju v primerjavi s kremenčevimi in keramičnimi peski. Vendar pa so za zmanjšanje in/ali odpravo pripekanja peska/veziva potrebni ustrezni ognjeobstojni premazi. Nazadnje lahko ognjeobstojni premazi vplivajo na razformanje oz. sposobnost razpada peščene mešanice po litju, kemično vezanih peščenih sistemov. Ključne besede: pripekanje (med drugim obsega pripekanje, penetracijo in sprijemanje premaza), diskasti vzorec, preskusno litje, kemijsko vezivo za pesek, ognjeobstojni premaz, površinska hrapavost Abstract Steel castings are returning to the U.S. Metal Casting Industry from the Global Market Place. Chemically bonded sand systems are an important and growing part of foundry technology and their interaction at the mold-steel interface is in question based on a study - Part I. The qualitative changes in surface quality found at uncoated as-casted steel/chemically bonded sand interfaces (Part I) may require refractory coating (wash) technology to warrant improvement. With today’s emphasis on near-net-shape steel Zaščiteno z avtorskimi pravicami / Copyrights 2020 3 Livarski vestnik, letnik 68, št. 1/2021 1 Uvod in namen 1.1 Podlaga Kemično vezani pesek in jedra predstavljajo pomemben del livne tehnologije jekla in njihovo vedenje ob stiku s staljenim jeklom je še posebej pomembno. V 1. delu te raziskave nakazujemo, da enostavna rešitev ne obstaja, ko gre za izbiro zrnastega medija, namenjenega uporabi z jeklenimi ulitki [1]. Zanimanje za učinke ognjeobstojnih premazov za zaščito fronte med jeklom in kemijskim vezivnim sredstvom za pesek je v industriji jekla še vedno izrazito [1]. Vsako leto v industriji za ognjeobstojne premaze za kemijske sisteme livarskega peska porabijo milijone evrov. Ognjeobstojni premazi se uporabljajo kot pomoč pri izboljšanju zaključnega sloja površine, zmanjševanju napak zaradi toplotnega raztezanja, kot je nastanek žil, in napak zaradi nevezanega peska, kot je erozija ulitkov iz sivih litin [2-4]. Vendar pa ta 1 Introduction and Purpose 1.1 Background Chemically bonded sand cores and molds are an important part of steel casting technology and their behavior in contact with molten steel is of great interest. Part I of this research suggests there is no panacea when selecting granular media for use with steel castings [1]. Interests in the effects of refractory coatings to protect the steel/chemical sand binder interface remain high in the metal casting industry [1]. Every year, the industry spends millions of dollars on refractory coatings for chemically bonded sand systems. The refractory coatings have been used to aid in surface finish improvements, reduce thermal expansion defects such as veining, and un- bonded sand defects such as erosion in cast iron castings [2-4]. However, the same issues for steel castings are less understood. Assessing the addition of refractory coatings in terms of productivity castings, and with ever more stringent casting dimensional reproducibility requirements, there is a need to quickly and affordably characterize as-cast surface quality as a function of the refractory coated chemically bonded sand system. Four refractory coatings designed for steel castings were applied to disc-shaped specimens (cores) by industry using the application techniques used in normal foundry production. A small, simple, and practical casting trial using disc-shaped specimen cores was developed at Western Michigan University (WMU). The test allows several core specimens to be wetted simultaneously from a known steel head pressure, temperature, and chemistry. The casting trials were conducted at Saginaw Valley State University (SVSU) and results show that various refractory coated chemically bonded sand systems provide different as- cast steel surfaces. Results show that new refractory coatings technology can provide a superior as-cast surface quality to silica and ceramic sands in a steel casting. Still, adequate refractory coatings are required to reduce and/or eliminate sand/binder burn-on. Finally, the refractory coatings can affect the shakeout/collapsibility of the chemically bonded sand system. Keywords: burn-on (to include terms such-as burn-in, penetration, and adhering coating), disc-shaped specimens, casting trial, chemical sand binder, refractory coating, surface roughness 4 Livarski vestnik, letnik 68, št. 1/2021 področja niso tako dobro poznana, ko gre za jeklene ulitke. Ocena dodajanja ognjeobstojnih premazov z vidika težav v povezavi s produktivnostjo je ključnega pomena, še posebej pri odstranjevanju sistemov z ognjeobstojnimi premazi iz ulitka. Prav tako bi bilo mogoče v novem preskušanju litja oceniti kakovost površine ulitka v litem stanju [1]. Usmerjeno segrevanje peščenih kompozitnih materialov (medij za forme in ulitke) v materialih povzroča anizotropne toplotne gradiente. Ko pridejo oblikovani peščeni kompoziti v stik s staljeno kovino, povzroči prenos toplote termo- kemično reakcijo, posledica katere so dimenzijske spremembe kompozitnega materiala. Pri poljubni temperaturi je mogoče te dimenzijske spremembe oz. toplotne deformacije pripisati sočasnim spremembam tako peska kot veziva [1,5]. Pri ocenjevanju livarskih ognjeobstojnih premazov na diskastih vzorcih je mogoče učinek izmeriti na mejnih površinah med formo in kovino.1 Večina livarn kupuje ognjeobstojne premaze na vodni osnovi v obliki koncentrata, bodisi paste ali pa visoko viskozne suspenzije [3,4]. Na takšen način se zmanjša količina vode med transportom, kar pomaga pri suspenziji ognjeobstojnega premaza med prevozom. Po prejemu ognjeobstojnega premaza v obliki koncentrata morajo v livarni premaz razredčiti skladno s specifikacijami za uporabo, najpogostejši preizkus za določanje končne točke redčenja pa je preizkus na podlagi Baumejeve lestvice.3,4 Odbor društva AFS za reakcije na fronti forma-kovina (4-F) je izvedel in objavil raziskavo, ki nakazuje, da uporaba preizkusa na podlagi Baumejeve lestvice za kontrolo redčenja ognjeobstojnih premazov poveča variabilnost z vidika odstotka trdnih delcev v premazu [4]. Mnogo let so v ZDA lokalni proizvajalci ognjeobstojnih premazov issues is important, especially in terms of how refractory coated sand systems shakeout of the casting. Additionally, the as- cast surface quality can be addressed using in a new casting trial [1]. Directional heating of sand composites (mold and core media) generate anisotropic thermal gradients in the materials. When shaped sand composite comes in contact with molten metal, the heat transferred causes thermo-chemical reactions that result in dimensional changes in the composite. At any given temperature these dimensional changes or thermal distortions are attributable to simultaneous changes in both the sand and the binder [1,5]. When evaluating foundry refractory coatings, the effect of different refractory coating types placed on a disc-shaped specimen can be accessed at the mold/metal interfaces.1 Most foundries purchase their water based refractory coatings in a concentrated form, either as a paste or a high viscosity slurry.3,4 This practice reduces the weight of water shipped and assists the suspension of the refractory coating during shipment. Receiving the refractory coating in a concentrated form necessitates the in-foundry dilution of the coating to application specifications and the most common test used to determine the end point during dilution is the Baume’ test [3,4]. The AFS Mold-Metal Interface Reactions Committee (4-F), has conducted research and has since published paper indicating that the use of the Baume’ test to control the dilution of refractory coatings adds variability to the % Solids of the coating [4]. For many years in the United States the domestic refractory coating manufacturers have recommended that foundries not use Baume’ as a singular coating control test during the dilution of refractory coatings. Many foundries still used the Baume’s test (Mold & Core Test Handbook, AFS 4409- 5 Livarski vestnik, letnik 68, št. 1/2021 priporočali, naj livarne ne uporabljajo preizkusa na podlagi Baumejeve lestvice kot edini kontrolni preizkus med redčenjem ognjeobstojnih premazov. V številnih livarnah se še vedno uporablja preizkus na podlagi Baumejeve lestvice (priročnik Mold & Core Test Handbook, AFS 4409-00-S) kot edini kontrolni preizkus za ognjeobstojne premaze na vodni osnovi. Društvo AFS prav tako financira celovite raziskave tehnologije za kontrolo premazov od mokrega do suhega stanja [3]. Osnovna hipoteza proizvajalcev premazov in Odbora 4-F je, da naravna variabilnost rezultatov na podlagi Baumejeve lestvice poveča variabilnost odstotka trdnih delcev v premazu med redčenjem. Povečanje variabilnosti odstotka trdnih delcev vodi v spremembe suhih ognjeobstojnih usedlin na jedrih in formah, zaradi česar nastaja povečano število napak med litjem, prav tako pa se spremenijo tudi dimenzije ulitka [3, 4]. Običajna debelina livarskega ognjeobstojnega premaza pri litem železu je pribl. 0,15 mm, vendar pa je natančnost meritev debeline premaza pri jeklu vprašljiva. Zato so bili vzorci v tej raziskavi z ognjeobstojnim premazom premazani v tovarni ter nato poslani v preskusno litje. Po preskusnem litju je bil preskusni vzorec uničen, kar omogoča pridobivanje informacij o odstranjevanju livarskega peska in kakovosti v litem stanju na podlagi fronte med vzorcem in jeklom [1]. 1.2 Namen Ta raziskava je bila zasnovana za proučitev ognjeobstojnega premaza in kvantifikacijo kakovosti površine ulitka v litem stanju na fronti med jeklom in vzorcem s pomočjo preprostih in praktičnih preskusnih litij 00-S) as the singular control test of a water based refractory coating. Moreover, AFS sponsored research addresses complete wet to dry coating control technology [3]. The underlying hypothesis of the coating manufacturer’s and the 4-F Committee’s position is that the inherent variability of the Baume’s test increases the variability of the % Solids of a coating during dilution. Increasing the variability in the % Solids translates to changes in the refractory dry deposit on cores and molds which ultimately results in an increased number of casting defects and changes to the dimensions of the casting [3, 4]. A typical foundry refractory coating thickness used with cast iron is 0.006 inches; however, the accuracy of thickness measurement is suspect for steel. Thus, specimens used in the study were refractory coated in industry and shipped to the casting trial. After the casting trials, the test specimen is destroyed allowing information such as shakeout and as-cast surface quality to be gained from the specimen/ steel interface [1]. 1.2 Purpose This research was designed to study the effect of refractory coating and to quantify as-cast surface quality at a steel/specimen interface using as small, simple and practical casting trial. The questions of the study were twofold: • Is there a difference in as-cast surface quality among the refractory coating types used with steel casting? • Is there a difference for refractory coatings shakeout at steel fill temperature? In the present work, various refractory coated chemically bonded sand disc-shaped 6 Livarski vestnik, letnik 68, št. 1/2021 malega obsega. Raziskava je želela odgovoriti na dve vprašanji: • ali obstaja razlika v kakovosti površine ulitka v litem stanju glede na različne vrste ognjeobstojnih premazov, ki se uporabljajo za jeklene ulitke? • ali obstaja razlika v povezavi z odstranjevanjem ognjeobstojnih premazov med polnjenjem kalupov z jeklom? V tem delu smo kemijsko spojena peščena jedra v obliki diskov (piškotke) z različnimi ognjeobstojnimi materiali uporabili v litju in jih proučili pri temperaturi jekla. Ta dvodelna raziskava se osredotoča na analizo dejanskega preskusnega litja z uporabo diskastih vzorcev z ognjeobstojnim premazom (2. del) in brez njega (1. del), proizvedenih skozi različne postopke z uporabo kemičnih veziv za pesek, in sicer iz kremenčevega peska in še enega medija za forme. Preskusno litje običajno imenujemo »piškotki v krofu« (Sl. 1). V 1. delu te raziskave smo dognali, da površinski pogoji in zaključni sloj jeklenih ulitkov v litem stanju niso dobro poznani in da so z njimi povezani znatni stroški končne obdelave. Potrebna je strategija za kvalifikacijo kemično vezanih peščenih sistemov, namenjenih uporabi v specimen cores (cookies) were poured and studied at steel temperatures. This two part study is focused on an analysis of an actual casting trial using refractory coated (Part II) and uncoated (Part I) disc-shaped specimens produced from various chemical sand binder processes using silica sand and alternative molding media. The casting trial is normally referred to as “cookies-in- doughnut” (Fig. 1). Slika 1. Prikaz modela okrogle oblike z luknjo z diskastimi vzorci Figure 1. Transparent view of doughnut-shaped model with disc-shaped specimens Part I of this research identified as- cast surface condition and finish in steel castings is not well understood and often incurs significant finishing costs. A strategy Preglednica 1. Najboljša mejna površina med diskastim vzorcem brez premaza in jeklom (1. del) Table 1. Best Uncoated Disc-Shaped Specimen/Steel Interface (Part I) Vzorec / Specimen Posnetek vzorca v litem stanju / As-Cast Image Ugotovitve in površinska hrapavost / Observation & surface roughness 2 (Keramika A: / Ceramic A: 68 GFN, 3% RCS) Razformanje diskastih vzorcev je bilo odlično. Pesek se je prijel na fronto – težko ga je odstraniti. Hrapavost površine Sa = 130 µm. Shakeout of the disc-shaped specimens was excellent. Sand stuck to the interface – hard to remove. Surface roughness Sa = 130 µm. 7 Livarski vestnik, letnik 68, št. 1/2021 jeklenih ulitkih. Potreben je nov standard »površinske kakovosti pri litju v pesek« [1]. Najboljša površinska hrapavost v litem stanju, dosežena v 1. delu, je opredeljena in prikazana v Preglednici 1 [1]. Cilj avtorjev je opredeliti, kako močno lahko ognjeobstojni premaz izboljša površino jeklenega ulitka v litem stanju. 2 Metodologija V tej raziskavi smo proučili učinek ognjeobstojnih premazov na različne sisteme peščenih sistemov na podlagi majhnih, preprostih in praktičnih preskusnih litij namesto bolj zahtevnih in dalj časa trajajočih procesov zbiranja konvencionalnih livarskih preizkusnih ulitkov z namenom pridobivanja informacij o njihovi površinski kakovosti. V tem projektu smo proučili različne kemično vezane peščene sisteme z različnimi vrstami ognjeobstojnih premazov, zasnovanih za uporabo z jeklom. Premazi so bili pridobljeni in naneseni na diskaste vzorce v proizvodnem obratu. Preskusno litje je bilo izvedeno na univerzi Saginaw Valley State University (SVSU). Ulitki so bili pregledani v laboratoriju za litje kovin univerze Western Michigan University (WMU). Postopek je bil sestavljen iz 5 glavnih korakov: 1. proizvodnja diskastih vzorcev, 2. nanos ognjeobstojnega premaza na vzorce, 3. razvoj modela in izdelava forme No-bake iz furanske smole z ozkim okvirjem z dovajalnim sistemom z ognjeobstojnim premazom, 4. preskusno litje in 5. proučitev površinske kakovosti. is needed to qualify chemically bonded sand binder systems for to use with steel castings. A new “Sand Casting Surface Quality” standard is needed [1]. The best as-cast surface roughness achieved in Part- I is identified and shown in Table 1 [1]. The authors aim is to determine how much improvement refractory coating technology can provide an as-cast steel surface. 2 Methodology This research study examines the effects of refractory coatings on a variety of sand binder systems using a small, simple, and practical casting trial as opposed to the more laborious and time-consuming processes of collecting conventional foundry test castings to obtain information regarding castings surface quality. In this project, various chemically bonded sand systems were studied with different types of refractory coatings designed for a steel application. The coatings were sourced and applied to disc- shaped specimens in industry. Casting trials were conducted at Saginaw Valley State University (SVSU). Castings were inspected at Western Michigan University (WMU) Metal Casting Laboratory. The procedure consisted of 5 major steps: 1. Disc-shaped specimen production, 2. Refractory coating specimens, 3. Model development and fabrication of Furan No-bake tight-flask molds with the gating system refractory coated, 4. Casting trials, and 5. Surface quality observations 8 Livarski vestnik, letnik 68, št. 1/2021 2.1 Priprava diskastih vzorcev Diskasti vzorci (premer 50 mm, debelina 8 mm) so bili pripravljeni v obratu s pomočjo naslednjih procesov: oplaščeni pesek (RCS – Resin Coated Sand), PUR Cold Box (PUCB) in No-Bake anorganski natrijev silikat (IONB). Raziskovalci so se osredotočili na sisteme, povezane s slabo površinsko kakovostjo oz. težavami z razformanjem iz 1. dela. V Preglednici 2 so prikazane 2.1 Pr epar a tion of Disc Shaped Specimens Disc shaped specimens (50 mm dia. by 8 mm thick) were prepared in industry using the following chemical sand binder processes: shell resin-coated-sand (RCS), phenolic urethane cold box (PUCB) and inorganic sodium silicate no-bake (IONB). The researchers focused on systems that showed poor surface quality and/or were unable to shakeout in Part I. Table 2 shows Preglednica 2. Diskasti vzorci z ognjeobstojnim premazom za preskusno litje Table 2. Refractory Coated Disc-shaped Specimens for Casting Trial Št. / # Proces / Process AFS-GFN [sito] / [screens] Odstotek veziva / % Binder Peščeni sistem / Sand Systems A PUCB 65 [3] 1,4 Kremenčev pesek z okroglimi zrni IL / IL Round Grain Silica B RCS 65 [3] 3,0 Kremenčev pesek z okroglimi zrni IL / IL Round Grain Silica C E ISOCURE 65 [3] 3,0 Evropski kremenčev pesek / European Silica Sand D E PEPSET 65 [3] 3,0 Evropski kremenčev pesek / European Silica Sand E IONB 65 [3] 3,5 Keramični B (sintrani Al 2 O 3 ) / Ceramic B (sintered Al 2 O 3 ) F IONB 87 [4] 3,5 Keramični B (sintrani Al 2 O 3 ) / Ceramic B (sintered Al 2 O 3 ) ravni oz. odstotki veziva v primerjavi s težo peska, vrsta peska, AFS-GFN in zrnatost za sisteme, ki so bili v tej raziskavi premazani z ognjeobstojnimi premazi. Pomembno je izpostaviti, da so bili vsi peščeni sistemi (naravni kremenčev in sintetični keramični), uporabljeni za izdelavo diskastih vzorcev, v obratu izdelani, premazani z ognjeobstojnim premazom ter poslani na WMU za merjenje in preskušanje. Dodatne informacije o teh kemično vezanih peščenih sistemih so navedene v 1. delu [1, 6]. the percent binder levels based on weight of sand, the sand types, the AFS-GFN and screen distributions for the systems that are refractory coated in this study. It is important to point out that all sands (natural silica or synthetic ceramic) used in this study to produce disc-shaped specimens were produced in industry, refractory coated in industry and shipped to WMU for measurement and testing. Additional information regarding these sand binder systems can be found in Part I [1, 6]. 9 Livarski vestnik, letnik 68, št. 1/2021 2.2 Ognjeobstojni premaz za diskaste vzorce Izbrana vzorčna jedra z ognjeobstojnim premazom so bila transportirana na univerzo SVSU za preskusno litje. V industriji zasnovani, pripravljeni in naneseni so bili štirje ognjeobstojni premazi za jeklene ulitke, in sicer na različne diskaste vzorce (Preglednica 3). Tehnologija ognjeobstojnih premazov na vodni osnovi je v livarski industriji pogosta. To tehnologijo je raziskovalo društvo AFS in prehod iz mokrega v suho stanje je dobro poznan in evidentiran [2-5]. Manj poznana tehnologija ognjeobstojnih premazov se imenuje sol- gel, opisana pa je spodaj. Sol-gel je mešanica majhnih delcev dveh (ali več) snovi, ki so očitno homogeni, kar imenujemo disperzijski sistem. Snov, ki je v majhni količini prisotna v mešanici, je disperzijska faza; porazdeljena je po disperzijskem mediju. Velikost delcev trdne disperzijske faze meri med 1 in 100 nm. Koloidni delci sol nastanejo s hidrolizo prehodnih molekul, ki nato kondenzirajo. Pod specifičnimi pogoji se lahko koloidni delci vežejo v tridimenzionalno neurejeno in razvejano mrežo po celotni prostornini – in tvorijo gel. Obstajata dva osnovna procesa sinteze sol-gela: anorganski (koloidni) ter organski (polimerni ali alkoksidni). Po koloidni poti nastaja gel skozi aglomeracijo gostih koloidnih delcev [7,8]. V najnovejših študijah tehnologije premazov so ugotovili, da sol-gel bistveno izboljša površino ulitkov v nekaterih postopkih uporabe [7,9]. Tehnologija premazov igra pomembno vlogo pri razmerju dodanih komponent sol-gela drugim sestavinam. Zaradi takšnega vpliva na viskoznost premaza in njegove lastnosti rasti, kot je npr. mazanje, se izboljša površina ulitka. Za naše potrebe smo pripravili premaz za ulitek sol-gel na 2.2 Refractory Coating of Disc Shaped Specimens Selected refractory coated specimen cores were delivered to SVSU for the casting trials. Four refractory coatings for steel casting were designed, prepared and applied by industry to various disc-shaped specimen (Table 3). Water based refractory coating technology is common placed in the foundry industry. This technology has been studied by the AFS and wet to dry controls are well understood and documented [2-5]. A less common refractory coating technology is sol-gel and this approach is described below. Sol-gel is a mixture of small particles of two (or more) substances that is apparently homogeneous and is called the dispersion system. The substance which is in the mixture in a small amount is the dispersed phase; it is distributed in the dispersion medium. The particle size of the solid dispersed phase is between 1-100 nm. Colloidal sol particles are formed by hydrolysis of precursor molecules which then condense. Under certain conditions, the colloidal particles can bind into a three- dimensional disordered and branched network throughout the volume - forming a gel. There are two basic processes for sol-gel synthesis: inorganic (colloidal) and organic (polymeric or alkoxide). By the colloidal route, the gel is formed by agglomeration of dense colloidal particles [7,8]. Recent studies in coatings technology, indicate the sol-gel additive significantly improve the surface of the castings in some application processes [7,9]. The coating technology itself plays an important role in the ratio of the added sol-gel component to the other components. Because of this affects the viscosity of the coating and with its growth properties such as lubrication and, 10 Livarski vestnik, letnik 68, št. 1/2021 osnovi komercialnega premaza na podlagi cirkonija Aquadur ZP – 85 % (Exoterm-it d.o.o) in komponento sol-gel (HCl, TiCl4) – 15 %. 2.3 Razvoj modela V tem poskusu smo diskaste vzorce primerjali na podlagi modela »površinskih napak«.1 Zasnovali smo okrogel model z luknjo, primeren za diskaste vzorce pod enakomernim metalostatičnim tlakom (Sl. 1), in sicer za izvedbo niza preskusnih litij jekla. 1 Namen tega modela je ugotoviti, ali obstajajo razlike med površinsko kakovostjo front jeklenih ulitkov v litem stanju. 2.4 Preskusno litje Postopek preskusnega litja je sestavljala proizvodnja ulitkov iz furanske smole ter nato taljenje, litje in končno razformanje ulitkov. Forme so bile izdelane na univerzi WMU pri naslednjih okoljskih pogojih: temperatura 20±1 °C in relativna zračna vlažnost 50±2 %. Litje je potekalo na univerzi SVSU. Ulitki so se pred razformanjem strdili, nato so bili zapakirani in poslani v laboratorij za litje kovin univerze WMU. consequently, the surface of the casting are improved. For our purposes, we prepared a sol-gel casting coating from a commercial zirconium-based coating Aquadur ZP – 85 % (Exoterm-it d.o.o) and sol-gel (HCl, TiCl 4 ) component - 15%. 2.3 Model Development In this experiment chemically bonded disc-shaped specimens were compared using an experimental “surface defect” model. 1 The doughnut-shaped model that accommodates disc-shaped specimens under an equal metallostatic pressure was designed (Fig. 1) to perform a series of steel casting trials. 1 The purpose of this model is to identify if there are differences in as-cast steel interfacial surface quality. 2.4 Casting Trials The casting trial procedure consisted of Furan mold fabrication followed by melting, pouring, and shakeout. Molds were fabricated at WMU where ambient conditions were temperature controlled at 20±1°C and relative humidity was controlled at 50±2 %. Pouring occurred at SVSU. Castings were allowed to solidify before Preglednica 3. Nanos ognjeobstojnega premaza na diskaste vzorce Table 3. Refractory Coatings Applied to Disc-shaped Specimens Podjetje / Company Osnovni material / Base Material Proces / Process Način apliciranja / Application I (ASK, Španija) / (ASK, Spain) Cirkon / Zircon Vodna osnova / Water Based Pršenje / Sprayed II (ASK, ZDA / (ASK, USA) Cirkon / Zircon Vodna osnova / Water Based Pomakanje / Dipped III (Refcotec) Cirkon / Zircon Vodna osnova / Water Based Pomakanje / Dipped IV (U, Slovenija) / (U, Slovenia) ? Sol-gel / Sol Gel Nanos s čopičem / Brushed 11 Livarski vestnik, letnik 68, št. 1/2021 Priprava form No-bake iz furanske smole z ozkim okvirjem Na tri forme No-bake iz furanske smole z ozkim okvirjem smo namestili jeklen lijak premera 114,3 mm (4.5 in.) in filter za zagotavljanje konstantne tlačne višine in hitrosti polnjenja. Dovajalno votlino forme okrogle oblike z luknjo smo premazali z ognjeobstojnim premazom, da bi vzorec zaščitili pred nesprijetim peskom in preprečili pokanje form. Vsak spodnji del forme je vseboval jedrne nastavke, da v ulitku ne bi prišlo do pozicijskih učinkov. Takšen pristop je omogočil pripisovanje razlik v kakovosti ulitka izključno diskastim vzorcem jeder z ognjeobstojnim premazom. Postopek Postopek izdelave forme je potekal v naslednjih korakih: • zgornji in spodnji del forme sta bila izdelana skladno z vzorcem modelne plošče, ki obsega preprost dovajalni sistem za neposredno dovajanje brez tlaka. • Po izdelavi smo zgornjemu delu forme dodali lijak za neposredno litje, da bi zagotovili tlačno višino 23 cm (9 palcev) za vsak vzorec. • Pred sestavljanjem obeh polovic forme smo diskaste vzorce postavili na jedrne nastavke (Sl. 2). Visokotemperaturni lepilo smo nanesli na delilno ravnino. Formo smo zaprli ob delilni ravnini in na zgornji del forme pred litjem postavili uteži. Taljenje in litje Forme so bili označene in vanje je bilo litih dvanajst diskastih vzorcev po naključnem redu. Dvanajst diskastih vzorcev je bilo simetrično razporejenih po vzorcu z namenom preprečevanja pozicijskih učinkov litja. Ta pristop je shakeout then packaged and shipped to WMU Metal Casting Laboratory. Preparation of Furan No-Bake Tight- Flask Molds Three furan no-bake tight-flask molds were fitted with a 114.3 mm (4.5 in.) dia. steel pouring sleeve and a filter for constant head-pressure and fill velocity. The doughnut-mold gating cavities were refractory coated to protect specimen interface from loose sand and to prevent molds from cracking. Each drag mold contained core-prints where no positional effects exist in the casting. This approach allows possible variation in casting quality to be attributed to only refractory coated disc-shaped cores specimens. Procedure The mold making procedure consisted of the following steps: 1. Cope and drag mold halves were fabricated according to a match plate pattern that is comprised of a simple non- pressurized direct pour gating system. 2. After fabrication a direct pouring sleeve is added to the cope mold in order to obtain 9 inches (23 cm) pressure head on each of the specimens. 3. Prior to assembling the cope and drag, disc-shaped specimens were set in the core-prints (Fig. 2). A high temperature adhesive was used at the parting line. The mold was closed to secure the parting line and weights were placed on the cope prior to pouring. Melting and Pouring The molds were labeled and poured where twelve disc-shaped specimens were randomized. The twelve disc- shaped specimen cores were arranged 12 Livarski vestnik, letnik 68, št. 1/2021 omogočil raziskavo, s katerim sistemom peščenih veziv je povezana določena površinska kakovost (mejna površina med vzorcem in kovino). Razmerje med peskom in kovino za vse forme No-bake je bilo 2:1. Taljenje in litje je potekalo v laboratoriju za litje kovin univerze SVSU. V vse forme je bilo ročno lito malolegirano jeklo 4130 pri temperaturi 1.600 °C, povprečno trajanje litja za vsako formo je bilo ~15 sekund. Jeklo se je dovajalo skozi lijak za neposredno litje s filtrom iz keramične pene. Jeklo je bilo v vse forme lito do višine 23 cm (9 palcev). Pomembno je izpostaviti, da je bilo jeklo v vse forme vlito pri isti temperaturi in da je bila kemijska sestava enaka kot v 1. delu. 1 2.5 Raziskava površinske kakovosti Jekleni ulitki so se pred razformanjem iz form strdili. Za razformanje smo ulitek postavili na kovinsko mizo z jekleno mrežo, spodnji del forme je bil obrnjen navzdol. Razformanje smo izvedli s pnevmatskim kladivom s prilagojenim topim sekačem. Pnevmatsko kladivo smo uporabili na zunanjem obodu in ga premikali ob robu ulitka vnaprej določen čas (45 s). Ves pesek smo iz jedrnega nastavka iztresli s pomočjo gravitacije. Po razformanju ulitka je bilo mogoče na podlagi znanega vnosa energije določiti fronto med diskastim vzorcem in kovino. Določeni vzorci so se zlomili in padli iz jedrnega nastavka, zato jih ni bilo treba razformati, odstranjevanje drugih vzorcev symmetrically in a mold so that no positional effects on the casting should be present. This approach allowed possible variation in casting surface quality (specimen/metal interface) to be attributed to sand binder systems. The sand-to-metal ratio for all no-bake molds was 2:1. Melting and pouring took place at SVSU Metal Casting Laboratory. All molds were manually poured with 4130 low alloyed steel at 1600 °C where the average pouring time on each mold was ~15 sec. The steel was delivered through a direct pouring sleeve fitted with a ceramic foam filter. All molds were poured to 23 cm (9 in.) head-height. It is important to point out all molds were poured from the same heat and was the same metal chemistry poured in Part I. 1 2.5 Surface Quality Observation The steel castings were allowed to solidify prior to shakeout from molds. For shakeout, the casting was placed on a steel- grated metal table with the drag side down. Shakeout was conducted using a pneumatic air-chisel with a modified blunt-tip. More specifically, the air-chisel was brought in Slika 2. Diskasti vzorci na jedrnih nastavkih v spodnjem delu forme s premazom Figure 2. Disc shaped specimens set on core prints in coated drag mold 13 Livarski vestnik, letnik 68, št. 1/2021 pa je bilo zahtevno. Ocene razformanja so bile izdelane s pomočjo Preglednice 4. Ulitki so bili prerezani blizu fronte diskastega vzorca/jeklo in nato preiskani s 3D-makroskopijo, če je bilo mogoče vzorec razformati. Ravnina na Sl. 3 prikazuje prerez ulitka, ki razkriva fronto vzorec/ jeklo. 3D-posnetki fronte vzorec/kovina in površinska hrapavosti so bili izmerjeni in poročani v rezultatih. Ocene površine fronte v litem stanju so bile izdelane s pomočjo Preglednice 4. Ta analiza se je v prvi vrsti osredotočala na karakterizacijo površinske kakovosti contact with the outer circumference and moved along the periphery of the casting for a predetermined amount of time (45 secs.). All sand that was shook out was free to flow out of the core-prints. After casting shakeout, with a known energy input, observations could be made of the disc-shaped specimen/metal interface. Certain specimens collapsed and fell out the prints without need for shakeout while other specimens were difficult to remove. Shakeout ratings were made using Table 4. The castings were sectioned near the disc shape specimen/steel interface and then examined using a 3D Macroscope if the specimen was able to shakeout. The plane in Fig. 3 shows a section cut performed on the casting to reveal the specimen/steel Preglednica 4. Lestvica ocen za razformanje in pogoje fronte med ognjeobstojnim premazom/ jeklom Lestvica ocen Razformanje Pogoji fronte pri ognjeobstojnem premazu 1 (nizka – najslabša) Slaba – brez razformanja, brez odstranitve Ni na voljo – zavržen ulitek 2 Zmerna – potrebno mehansko odstranjevanje – težko kopanje Pesek se je prijel na premaz – težko ga je odstraniti 3 Dobra – potrebno mehansko odstranjevanje – enostavno kopanje Pesek se je prijel na premaz – enostavno ga je odstraniti 4 Zelo dobra – potrebno razformanje s stresanjem (najm. 45 s) Prijel se je tanek sloj premaza 5 (visoka – najboljša) Odlična – premaz/pesek odstranjena z minimalno tresenja oz. brez njega Čista površina jekla – brez premaza Table 4. Rating Scale for Shakeout and Refractory Coated/Steel Interfacial Condition Rating scale Shakeout Coating interfacial condition 1 (low – worst) Poor – No shakeout, no removal NA - Scrapped casting 2 Fair – Requires mechanical removal – hard to dig Sand stuck to coating – hard to remove 3 Good – Requires mechanical removal – easy to dig Sand stuck to coating – easy to remove 4 Very Good – Requires vibratory shake (min. – 45 sec.) Thin layer of coating adhering 5 (high – best) Excellent – Coating/ Sand removed with little to no vibration Clean Steel Surface – free of coating 14 Livarski vestnik, letnik 68, št. 1/2021 fronte vzorcev z ognjeobstojnim premazom/ jeklom. 3D-makroskopijo smo uporabili zaradi digitalne nekontaktne tehnologije meritve površin ter za zajemanje posnetkov in podatkov. Avtorji so površinsko kakovost v litem stanju prikazali kot celoto z naslednjimi sestavinami: Površinski pogoji: ocena učinkovitosti razformanja in odsotnost površinskih napak, npr.: pripekanje, površinske anomalije, kot so razjede, penetracije, luske, brazgotine itd., kot je opredeljeno v Preglednici 4, Površinska hrapavost: digitalna nekontaktna meritev površine, označena z R a (µm). 3 Rezultati in razprava V tem poglavju so navedeni rezultati v povezavi s površinsko kakovostjo in ugotovitve, ki izhajajo iz preskusnega litja jekla. Pomniti je treba, da so bili diskasti vzorci, premazani z ognjeobstojnim premazom, liti pri temperaturi za jeklo (1600 °C). Društvo AFS ne opredeljuje razlike med kakovostjo površine ulitka in končno površino ulitka. Prav tako so opredeljeni interface. 3D images of the specimen/metal interfaces and surface roughness were measured and reported as results. As-cast interfacial finish ratings were made using Table 4. This analysis was focused primarily on characterizing the as-cast surface quality of refractory coated specimen/steel interface. A 3D Macroscope was considered for its digital noncontact surface measurement technology, imaging, and data capture. Further, the authors depict an as-cast surface quality as being comprised of both: Surface Condition: A rating of the ability to shakeout and freedom of surface issue such as: Burn-on, surface anomalies such as erosions, veins, penetration, scabs, scars, etc. as defined in Table 4; and Surface Roughness: A digital noncontact surface finish measure as R a (µm) 3 Results and Discussion This section will relate the surface quality observations and findings from the steel casting trials. It is important to reiterate that refractory coated disc-shaped specimens used for casting were poured at steel temperatures (1600 °C). The AFS does not define a difference between casting surface quality and casting surface finish. Further, the conspicuous results related to surface condition and finish as it may relate to pouring temperature and binder type are Slika 3. Prosojna ravnina, prikazana nad ulitkom s postavljenimi jedri Figure 3. Transparent cutting plane imposed on the casting with cores in place 15 Livarski vestnik, letnik 68, št. 1/2021 jasni rezultati, povezani s površinskimi pogoji in končno površino, saj so lahko povezani z livno temperaturo in vrsto veziva. Raziskovalci so primerjali končne površine ulitkov v litem stanju in površinske pogoje na podlagi lestvice ocen, kot je opredeljena v Preglednici 4. Diskasti vzorci brez premaza so povezani z majhnim razponom hrapavosti (Preglednica 5). Peščeni sistem z najdrobnejšimi zrni 3 je bil najgladkejši s 40 µm in hrapavost peščenega sistema z grobimi zrni 5 je merila 69 µm. Ognjeobstojni premaz lahko izboljša površinsko hrapavost diskastih vzorcev, vendar se lahko rezultati razlikujejo glede na način nanosa. Sol-gel je bil najbolj raskav ognjeobstojni premaz zaradi načina nanosa. Sledovi čopiča so bili jasno vidni v obliki potez na vzorcih z ognjeobstojnim premazom sol-gel. Tipična površinska hrapavost nepremazanih in z ognjeobstojnim premazom premazanih vzorcev je prikazana v Preglednicah 5 in 6. Rezultati so bili dosledni med preskusnimi litji z vidika hrapavosti površine in drugih ugotovitev. Kvalitativna ocena kovinskih površin front vzorcev s premazom je pokazala, da vse površine s premazom niso enake. Zanimivo je, da je v Preglednici 4 prikazano, da višje ocenjeni pogoji fronte niso povezani z boljšo hrapavostjo površine niti pri nepremazanih vzorcih niti pri vzorcih z ognjeobstojnim premazom. To pomeni, da površinske kakovosti ulitka v litem stanju ne določa niti velikost peščenih zrn niti proces peščenih veziv. Vendar pa je bila površinska kakovost, dosežena z ognjeobstojnim premazom sol-gel, boljša v primerjavi z ognjeobstojnimi premazi na vodni osnovi. Rezultati za ognjeobstojne premaze na vodni osnovi so prikazani v Preglednici 7, vendar podatki o hrapavosti površine niso navedeni, saj so bile tudi najboljše fronte jekla mnogo preveč raskave (>100 µm). identified. The researchers have compared the as-cast surface finishes and surface condition using a rating scale as defined in Table 4. Uncoated disc-shaped specimens showed a narrow range of roughness Preglednica 5. Hrapavost površine tipičnih diskastih vzorcev brez premaza Table 5. Surface Roughness of Typical Uncoated Disc-Shaped Specimen Vrsta vzorca / Specimen type Hrapavost površine (µm) / Surface roughness (µm) Optično / Optical Površina S a (premer 35 mm) / S a Area (35 mm dia.) 1 (Keramika A / Ceramic A: 68 GFN, 3 % RCS) 52 4 (Kremenčen pesek z okroglimi zrni / Round Grain Silica: 65 GFN, 1,4 % PUCB) 57 5 (Pesek iz jezera: / Lake Sand: 65 GFN, 1,4 % PUCB) 69 3 (Keramika B / Ceramic B: 80 GFN, 3 % RCS) 40 16 Livarski vestnik, letnik 68, št. 1/2021 Rezultati preskusnega litja vzorcev z ognjeobstojnim premazom sol-gel so prikazani v Preglednicah 8 in 9 ter razvrščeni glede na sistem veziv za pesek. Razlike v površinski hrapavosti je mogoče opredeliti tudi med vzorci z ognjeobstojnim premazom sol-gel v litem stanju. Najboljša površinska hrapavost front vzorcev z ognjeobstojnim premazom sol-gel, prikazana v Preglednici 8, je mnogo boljša od katere koli predhodno opredeljene površinske hrapavosti. Zanimivo je, da površinska hrapavost jeklenih ulitkov v litem stanju ni povezana s površinsko hrapavostjo diskastega vzorca brez premaza niti vzorcev z ognjeobstojnim premazom. (Table 5). The finest sand system 3 was the smoothest 40 µm and a coarser sand system 5 was 69 µm. Refractory coating can improve the surface roughness of the disc-shaped specimens but this depends on the method of application. The sol-gel was the roughest refractory coating due to the method of application. The brush strokes were clearly visible and wavy on the sol-gel refractory coated specimens. Typical surface roughness from uncoated and refractory coated specimens are shown in Tables 5 and 6. Results were consistent casting trial to casting trial by surface roughness and observations. Qualitative evaluation of the coated specimen metal interfaces indicated that all coated surfaces were not the same. More interestingly, Table 4 shows that a higher rated interfacial condition did not relate to superior surface roughness in either uncoated or refractory coated specimens. This points out that neither the sand fineness nor a sand binder process dictates as-cast surface finish. Yet, the as- cast surface quality achieved with the sol-gel refractory coating process was superior to the water based refractory coating process in surface quality. The results for the water based refractory coatings are shown in Table 7 but no surface roughness data is reported because the best steel interfaces were far too rough (>100 µm). The results from the casting trials for Sol-Gel refractory coated specimen interfaces are pictured in Tables 8 and 9 and laid out according to sand binder system. Moreover, surface roughness differences can be identified among the as- cast Sol-Gel refractory coatings. The best surface roughness for Sol-Gel refractory coated specimen interfaces shown in Table 8 are far superior to any surface roughness identified previously. Interestingly, the as- cast steel surface roughness does not Preglednica 6. Hrapavost površine tipičnih diskastih vzorcev z ognjeobstojnim premazom Table 6. Surface Roughness of Typical Refractory Coated Disc-Shaped Specimen Vrsta vzorca / Specimen type Hrapavost površine (µm) / Surface roughness (µm) Optično / Optical Površina S a (premer 35 mm) / S a area (35 mm dia.) Nanos s pomakanjem / Dip Coated [B1155] 40 Nanos s pršenjem / Spray Coated [B1755] 34 Nanos sol- gela / Sol-Gel Coated 85 17 Livarski vestnik, letnik 68, št. 1/2021 relate to the surface roughness of either the uncoated disc-shaped or refractory coated specimens. Tables 8 and 9 show the same specimen/ steel interfaces, however the area from which the surface roughness is measured are is dissimilar and different Sa values are reported for the same interface. Fig. 4 addresses how a surface condition such as sand/coating adhering to the steel interface compromises the surface roughness by pointing out the height changes among sand grains, refractory coating, and steel. Logically, the smaller best surface area Table 8 reveal superior Sa values. Using a larger area more waviness and surface issues are captured in the measures and rougher Sa values are shown in Table 9. With a better application method for the Sol- Gel refractory coating a superior as-cast steel interface is possible. Furthermore, a new standard for measuring as-cast steel surface quality with and without refractory coating is essential. V Preglednicah 8 in 9 so prikazane iste fronte med vzorcem in jeklom, vendar se površine, na podlagi katerih so izmerjene njihove hrapavosti, razlikujejo in različne vrednosti Sa so bile izmerjene za isto fronto. Na Sl. 4 je prikazano, kako površinski pogoji, kot je pesek/premaz, ki se prime na fronto jekla, poslabša hrapavost površine, in sicer z izpostavitvijo sprememb višine med peščenimi zrni, ognjeobstojnim premazom in jeklom. Logično je, da so najmanjše najboljše površine iz Preglednice 8 povezane z ugodnejšimi vrednostmi Sa. Ob uporabi večje površine je v meritvah zajetih več nepravilnosti oz. površinskih napak in manj ugodne vrednosti Sa so prikazane v Preglednici 9. Ob uporabi boljšega načina nanašanja ognjeobstojnega premaza sol- gel je mogoče zagotoviti boljšo fronto jeklenega ulitka v litem stanju. Prav tako je ključnega pomena določitev novega standarda za merjenje površinske kakovosti v litem stanju z ognjeobstojnim premazom in brez njega. Preglednica 7. Ugotovitve v povezavi s površino ulitkov v litem stanju na fronti diskastih vzorcev z ognjeobstojnim premazom na vodni osnovi/jeklo Table 7. As-Cast surface observations from water based refractory coated disc-shaped specimen/ steel interface Podjetje / Company Način apliciranja / Application Razformanje / Shakeout Pogoji fronte pri ognjeobstojnem premazu / Coating interfacial condition I (ASK, Španija / Spain) Pršenje / Sprayed 3–4 Dobra – potrebno mehansko odstranjevanje – enostavno kopanje / 3-4 Good – Requires mechanical removal – easy to dig 2–3 Pesek se je prijel na premaz – težko ga je odstraniti / 2-3 Sand stuck to coating – hard to remove II (ASK, ZDA / USA) Pomakanje / Dipped 2 Zmerna – potrebno mehansko odstranjevanje – težko kopanje / 2 Fair – Requires mechanical removal – hard to dig 2 Pesek se je prijel na premaz – težko ga je odstraniti / 2 Sand stuck to coating – hard to remove III (Refcotec) Pomakanje / Dipped 2 Zmerna – potrebno mehansko odstranjevanje – težko kopanje / 2 Fair – Requires mechanical removal – hard to dig 2 Pesek se je prijel na premaz – težko ga je odstraniti / 2 Sand stuck to coating – hard to remove 18 Livarski vestnik, letnik 68, št. 1/2021 Preglednica 8. Presek ulitka, ki prikazuje najboljšo površinsko hrapavost ulitka v litem stanju, in ugotovitve v povezavi s površino ulitkov v litem stanju na fronti diskastih vzorcev z ognjeobstojnim premazom sol-gel/jeklo Table 8. Casting sections showing best area for as-cast surface roughness and observations from various sol-gel refractory coated disc-shaped specimen/steel interface Vrsta vzorca / Specimen type Hrapavost površine / Surface roughness (µm) Ugotovitve / Observations Optično / Optical Najboljša površina S a / Best area S a Razformanje / Shakeout Pogoji fronte / Interfacial condition A Kremenčen pesek z okroglimi zrni / Round Grain Silica (65 GFN, 1,4 % PUCB) 19 3 Dobra – potrebno mehansko odstranjevanje – enostavno kopanje / Good – Requires mechani- cal removal – easy to dig 4 Prijel se je tanek sloj premaza / Thin layer of coating adhering B Kremenčen pesek z okroglimi zrni / Round Grain Silica (65 GFN, 3% RCS) 17 3 Dobra – potrebno mehansko odstranjevanje – enostavno kopanje / Good – Requires mechani- cal removal – easy to dig 3 Pesek se je prijel na premaz – enostavno ga je odstraniti / Sand stuck to coating – easy to remove C (E ISOCURE ) 21 4 Zelo dobra – potrebno razformanje s stresanjem (najm. 45 s) / Very Good – Requires vibratory shake (min. – 45 sec.) 4 Prijel se je tanek sloj premaza / Thin layer of coating adhering D (E PEPSET ) 24 4 Zelo dobra – potrebno razformanje s stresanjem (najm. 45 s) / Very Good – Requires vibratory shake (min. – 45 sec.) 4 Prijel se je tanek sloj premaza / Thin layer of coating adhering E (Keramika B: 87 GFN, 3,5 % anorganskega veziva) / (Ceramic B: 87 GFN, 3.5% Inorganic Binder) 33 1 Slaba – brez razformanja, brez odstranitve / Poor – No shakeout, no removal 3 Pesek se je prijel na premaz – enostavno ga je odstraniti / Sand stuck to coating – easy to remove F (Keramika B: 65 GFN, 3,5 % anorganskega veziva) / (Ceramic B: 65 GFN, 3.5% Inorganic Binder) 24 3 Dobra – potrebno mehansko odstranjevanje – enostavno kopanje / Good – Requires mechani- cal removal – easy to dig 3 Pesek se je prijel na premaz – enostavno ga je odstraniti / Sand stuck to coating – easy to remove 19 Livarski vestnik, letnik 68, št. 1/2021 Preglednica 9. Presek ulitka, ki prikazuje ENOTNO površinsko hrapavost ulitka v litem stanju, in ugotovitve v povezavi s površino ulitkov v litem stanju na fronti diskastih vzorcev z ognjeobstojnim premazom sol-gel/jeklo Table 9. Casting Sections Showing Uniform Area As-Cast Surface Roughness and Observations from various Sol- Gel Refractory Coated Disc-Shaped Specimen/Steel Interface Vrsta vzorca / Specimen type Hrapavost površine / Surface roughness (µm) Ugotovitve / Observations Optično / Optical Enotna površina S a / Best area S a [963 mm 2 ] Razformanje / Shakeout Pogoji fronte / Interfacial condition A Kremenčen pesek z okroglimi zrni / Round Grain Silica (65 GFN, 1,4 % PUCB) 157 3 Dobra – potrebno mehansko odstranjevanje – enostavno kopanje / Good – Requires mechanical removal – easy to dig 4 Prijel se je tanek sloj premaza / Thin layer of coating adhering B Kremenčen pesek z okroglimi zrni / Round Grain Silica (65 GFN, 3% RCS) 289 3 Dobra – potrebno mehansko odstranjevanje – enostavno kopanje / Good – Requires mechanical removal – easy to dig 3 Pesek se je prijel na premaz – enostavno ga je odstraniti / Sand stuck to coating – easy to remove C (E ISOCURE ) 915 4 Zelo dobra – potrebno razformanje s stresanjem (najm. 45 s) / Very Good – Requires vibratory shake (min. – 45 sec.) 4 Prijel se je tanek sloj premaza / Thin layer of coating adhering D (E PEPSET ) 287 4 Zelo dobra – potrebno razformanje s stresanjem (najm. 45 s) / Very Good – Requires vibratory shake (min. – 45 sec.) 4 Prijel se je tanek sloj premaza / Thin layer of coating adhering E (Keramika B: 87 GFN, 3,5 % anorganskega veziva) / (Ceramic B: 87 GFN, 3.5% Inorganic Binder) 462 1 Slaba – brez razformanja, brez odstranitve / Poor – No shakeout, no removal 3 Pesek se je prijel na premaz – enostavno ga je odstraniti / Sand stuck to coating – easy to remove F (Keramika B: 65 GFN, 3,5 % anorganskega veziva) / (Ceramic B: 65 GFN, 3.5% Inorganic Binder) 864 3 Dobra – potrebno mehansko odstranjevanje – enostavno kopanje / Good – Requires mechanical removal – easy to dig 3 Pesek se je prijel na premaz – enostavno ga je odstraniti / Sand stuck to coating – easy to remove 20 Livarski vestnik, letnik 68, št. 1/2021 4 Zaključek in priporočila Društvo AFS potrebuje novo metodo za merjenje površinske kakovosti ulitkov, litih v pesek. Nov digitalni standard mora obsegati digitalni indeks tako za površinske pogoje ulitka kot tudi površinsko hrapavost ulitka. Uporaba preprostih diskastih vzorcev v enostavnem in stroškovno učinkovitem preskusnem litju je omogočila kar največje zmanjšanju vpliva geometrije na ulitek, kar omogoča izvedbo smiselne analize toplotno-mehanskih interakcij in napak, ki nastajajo na fronti med formo in jeklom. Pomembne in koristne ugotovitve je mogoče iz preizkusnega litja potegniti na podlagi zgolj osnovnih predpostavk. Preskusno litje jekla je pokazalo, da obstajajo razlike med ocenjevanimi peščenimi vezivnimi sistemi z ognjeobstojnimi premazi. Preskusno litje je prav tako pokazalo, da lahko tehnologija ognjeobstojnih premazov, še posebej sol-gel, zagotovi zaščito ter izboljšanje površinske kakovosti na fronti jeklo/vzorec. Noben preiskovan ognjeobstojni premaz na vodni osnovi ni zagotovil površinske kakovosti ulitka v litem stanju <100 µm na fronti jeklo/vzorec. Priporoča se preiskava izbočenega sloja ognjeobstojnih premazov na vodni osnovi za zagotavljanje boljše 4 Conclusion and Recommendation The AFS requires a new standard for measuring sand cast surface quality. A new digital standard must consider a digital index for both casting surface condition and casting surface roughness. The use of the simple disc-shape in a simple cost- effective casting trial allowed for minimizing the effect of geometry on casting, allowing a meaningful analysis of the thermo- mechanical interactions and issues resulting at mold/steel interface. Important and useful findings can be extracted from the casting trial with just basic assumptions. The steel casting trial showed there were differences observed among the refractory coated sand binder systems evaluated. The casting trial showed that refractory coating technology, especially Sol-Gel can offer protection and more notably an improvement in surface quality at the steel/specimen interface. No water based refractory coating technologies studied were able to provide an as-cast surface finish <100µm at the steel/specimen interface. It is recommended that the proud layer thickness of water based refractory coating technology be investigated to better protect as a steel interfacial barrier. This work identified sand-binder system that Sprijeti material / Adhering material Jeklo / Steel Optično / Optical Višina / Height 3D-posnetek / 3D Image Slika 4. Povečava (Vzorec B), ki prikazuje pesek/premaz, ki se je prijel na fronto jekla Figure 4. Magnified views (Specimen B) showing sand/coating adhering to the steel interface 21 Livarski vestnik, letnik 68, št. 1/2021 zaščite kot bariera na fronti jekla. V prispevku smo opredelili peščene vezivne sisteme, katerih razformanje je bilo oteženo ali nemogoče, ob uporabi ognjeobstojnega premaza pa je bilo razformanje mogoče. V prispevku smo prav tako razkrili da lahko sam način nanašanja (s čopičem, pomakanjem ali pršenjem) ognjeobstojnega premaza močno vpliva na površinsko kakovost jeklenih ulitkov. Omejitve V tej raziskavi so predstavljeni podatki nekaterih ognjeobstojnih premazov pri temperaturah za jeklo in tlačni višini, običajni za srednje velike jeklene ulitke. Obstajajo tudi drugi sistemi ognjeobstojnih premazov, iz katerih je mogoče pridobiti dodatne podatke in bolje spoznati toplotne lastnosti in vedenje drugih peščenih sistemov. Zahvale Avtorji se želijo zahvaliti študentom univerz SVSU (H. Towalski, K. Konwinski in I. Portice) in WMU (A. Patel, M. Patel, K. Pathak in K. Shenoy) za pomoč pri preskusnem litju in laboratorijskem testiranju. were difficult or unable to shakeout from steel were possible with refractory coating technology. Further, the work reveals that the mere technique (brush, dip, or spray) of applying the refractory coating can significantly impact steel casting surface quality. Limitations The work in this paper represents the data for a few refractory coating systems at steel temperatures and a head pressure representative of a medium size steel casting. There are other refractory coating systems and aggregates from which additional data could be gathered to learn more about thermal properties and behaviors of other sand systems. Acknowledgments The authors thank the metal casting students at SVSU (H. Towalski, K. Konwinski, and I. Portice) and WMU (A. Patel, M. Patel, K. Pathak, and K. Shenoy) for their support with casting trials and laboratory testing. Viri / References Ramrattan, S., Wells, L., and Tuttle, R., “As-Cast Surface Characterization for Steel using Disc-Shaped Chemically Bonded Sand Specimens”, International Journal of Metalcasting, (2020). Ramrattan, S. N., Cheah, S. F., Guyer, O. 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