{"id":3613,"date":"2026-08-24T17:03:26","date_gmt":"2026-08-24T09:03:26","guid":{"rendered":"https:\/\/www.c-adtech.com\/?p=3613"},"modified":"2026-08-24T17:03:26","modified_gmt":"2026-08-24T09:03:26","slug":"covering-flux-for-aluminum","status":"publish","type":"post","link":"https:\/\/www.c-adtech.com\/pt\/covering-flux-for-aluminum\/","title":{"rendered":"Fluxo de cobertura para alum\u00ednio"},"content":{"rendered":"

Fluxo de cobertura para alum\u00ednio<\/strong> is a chemical compound, usually a blend of chlorides and fluorides, spread over molten aluminum to form a protective barrier that stops oxygen and moisture from reacting with the metal surface. After testing dozens of flux formulations across different furnace types at AdTech, we can say with confidence that the right covering flux reduces metal loss by 2% to 5% per melt cycle, cuts dross formation nearly in half, and extends refractory life because the melt surface stays calmer and less turbulent. If you run a foundry, a die-casting shop, or you’re sourcing raw materials for aluminum processing, understanding how covering flux works isn’t optional knowledge, it’s a direct line to your bottom line.<\/p>\n

This piece walks through everything we’ve learned from years of formulation testing, plant visits, and direct conversations with metallurgists who use covering flux daily. We’ll cover chemistry, application rates, safety protocols, and the practical mistakes that cost operators money.<\/p>\n

Se o seu projeto exigir a utiliza\u00e7\u00e3o de fluxo de cobertura para alum\u00ednio, pode contactar-nos<\/a>\u00a0para um or\u00e7amento gratuito.<\/p>\n

O que o fluxo de cobertura para alum\u00ednio faz, na verdade<\/h2>\n

Molten aluminum reacts almost instantly with atmospheric oxygen. Within seconds of exposure, a thin aluminum oxide (Al2O3) skin forms on the surface. That oxide layer sounds harmless, but it isn’t. Oxide film gets folded back into the melt during stirring, pouring, or transfer, creating inclusions that weaken castings and cause porosity defects.<\/p>\n

\"Fluxo
Fluxo de cobertura para alum\u00ednio<\/figcaption><\/figure>\n

Covering flux sits on top of the molten pool like a lid. It typically melts at a lower temperature than aluminum itself (around 500\u00b0C to 650\u00b0C compared to aluminum’s melting point near 660\u00b0C), which means it liquefies quickly and spreads across the surface before serious oxidation can occur. The molten flux layer physically blocks oxygen and water vapor from reaching the metal, and it also helps trap small oxide particles that would otherwise stay suspended in the bath.<\/p>\n

We’ve noticed operators sometimes confuse covering flux with drossing flux or degassing flux. They’re related but not interchangeable, and mixing up their functions leads to wasted material and poor melt quality.<\/p>\n

A qu\u00edmica por tr\u00e1s do fluxo de revestimento de alum\u00ednio<\/h2>\n

A maioria das formula\u00e7\u00f5es comerciais de fluxo de cobertura baseia-se numa mistura de halogenetos de metais alcalinos e alcalino-terrosos. A propor\u00e7\u00e3o exata depende da temperatura de fus\u00e3o pretendida, da liga a ser processada e da necessidade ou n\u00e3o de a fundi\u00e7\u00e3o dispor de capacidade adicional de absor\u00e7\u00e3o de \u00f3xidos.<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n
Componente<\/th>\nGama t\u00edpica (%)<\/th>\nFun\u00e7\u00e3o<\/th>\n<\/tr>\n<\/thead>\n
Cloreto de s\u00f3dio (NaCl)<\/td>\n20-45<\/td>\nReduz o ponto de fus\u00e3o, sal transportador de base<\/td>\n<\/tr>\n
Cloreto de pot\u00e1ssio (KCl)<\/td>\n15-40<\/td>\nAumenta a fluidez e atua em sinergia com o NaCl<\/td>\n<\/tr>\n
Criolita (Na\u2083AlF\u2086)<\/td>\n5-15<\/td>\nMelhora a humed\u00eancia e a absor\u00e7\u00e3o do \u00f3xido<\/td>\n<\/tr>\n
Fluoreto de c\u00e1lcio (CaF2)<\/td>\n3-10<\/td>\nAumenta o controlo da viscosidade e facilita a separa\u00e7\u00e3o das esc\u00f3rias<\/td>\n<\/tr>\n
Cloreto de magn\u00e9sio (MgCl\u2082)<\/td>\n2-8<\/td>\nMelhora a redu\u00e7\u00e3o do ponto de fus\u00e3o<\/td>\n<\/tr>\n
Carnalita (KCl\u00b7MgCl\u2082)<\/td>\n0-10<\/td>\n\u00c9 comum em formula\u00e7\u00f5es mais antigas e reduz a ader\u00eancia<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

The NaCl-KCl eutectic mixture forms the backbone of nearly every covering flux we’ve examined, because that combination melts around 650\u00b0C, right in the working range foundries need. Fluoride additions like cryolite improve what metallurgists call “wetting,” meaning the flux spreads thin and even instead of clumping in one spot.<\/p>\n

We should mention something that doesn’t get discussed enough in supplier brochures: the ratio between chlorides and fluorides changes how aggressively the flux reacts with refractory linings. Higher fluoride content improves oxide separation but can accelerate wear on furnace linings over hundreds of cycles. This is a trade-off every purchasing manager should weigh against furnace maintenance budgets.<\/p>\n

Fluxo de cobertura vs. fluxo de forma\u00e7\u00e3o de esc\u00f3ria vs. fluxo de refina\u00e7\u00e3o<\/h2>\n

A confus\u00e3o entre as categorias de fundentes \u00e9 um dos problemas mais comuns com que nos deparamos quando falamos com t\u00e9cnicos de f\u00e1brica, especialmente aqueles com menos experi\u00eancia nas opera\u00e7\u00f5es de fus\u00e3o de alum\u00ednio. Cada tipo de fundente destina-se a uma fase distinta do processo de fus\u00e3o.<\/p>\n

\"Compara\u00e7\u00e3o
Compara\u00e7\u00e3o entre tipos de fundentes de alum\u00ednio, incluindo fundentes de cobertura, fundentes de forma\u00e7\u00e3o de esc\u00f3ria e fundentes de refina\u00e7\u00e3o, para o tratamento do alum\u00ednio fundido e a melhoria da qualidade da fus\u00e3o.<\/figcaption><\/figure>\n
\n\n\n\n\n\n\n\n\n
Tipo de fluxo<\/th>\nObjetivo principal<\/th>\nCalend\u00e1rio de aplica\u00e7\u00e3o<\/th>\nDosagem habitual<\/th>\n<\/tr>\n<\/thead>\n
Cobrir o fluxo<\/td>\nImpede a oxida\u00e7\u00e3o, forma uma camada protetora<\/td>\nAplicar imediatamente ap\u00f3s o enchimento, antes de a massa fundida atingir a temperatura m\u00e1xima<\/td>\n0,5-2 kg por tonelada de metal<\/td>\n<\/tr>\n
Fluxo de esc\u00f3ria<\/a><\/td>\nSepara o alum\u00ednio met\u00e1lico retido nas esc\u00f3rias<\/td>\nAplicado antes da remo\u00e7\u00e3o das esc\u00f3rias<\/td>\n1-3 kg por tonelada de metal<\/td>\n<\/tr>\n
Fluxo de refina\u00e7\u00e3o<\/a><\/td>\nRemove inclus\u00f5es n\u00e3o met\u00e1licas da massa fundida<\/td>\nAplicado a meio do ciclo, antes do vazamento<\/td>\n0,3-1 kg por tonelada de metal<\/td>\n<\/tr>\n
Fluxo de desgaseifica\u00e7\u00e3o<\/td>\nRemove o hidrog\u00e9nio dissolvido<\/td>\nAplicar 10 a 15 minutos antes de verter<\/td>\n0,1-0,5 kg por tonelada de metal<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

Covering flux stays on top of the melt the entire time metal sits in the furnace. Drossing flux is worked into the skimmings specifically to recover metal that would otherwise be lost. Refining and degassing serve completely separate chemical purposes and shouldn’t be substituted for a good covering layer.<\/p>\n

We’ve seen shops try to save money by using a single “universal” flux for all four functions. It rarely works well. General-purpose flux compromises on every function to some degree, and the metal loss savings from proper covering flux alone usually pay back the cost difference within weeks.<\/p>\n

Por que raz\u00e3o o alum\u00ednio se oxida de forma t\u00e3o agressiva durante a fus\u00e3o<\/h2>\n

Aluminum has a strong natural affinity for oxygen, stronger than iron, copper, or zinc. The reaction that forms aluminum oxide releases a large amount of energy (it’s exothermic), which is part of why the oxide skin forms almost instantaneously on exposure to air.<\/p>\n

There’s a secondary problem beyond simple surface oxidation: hydrogen absorption. Molten aluminum can dissolve hydrogen from moisture in the atmosphere or from damp charge materials. When the metal solidifies, that dissolved hydrogen comes out of solution and creates porosity inside the casting. A good covering flux doesn’t eliminate hydrogen pickup entirely, but by reducing surface turbulence and blocking moisture contact, it lowers the overall hydrogen content picked up during the hold time.<\/p>\n

Medimos este par\u00e2metro nas instala\u00e7\u00f5es de um cliente, recorrendo a um ensaio de press\u00e3o reduzida (RPT), antes e depois da mudan\u00e7a para um fluxo de cobertura devidamente formulado. Os \u00edndices de porosidade baixaram de um \u00edndice de densidade de cerca de 8% para menos de 3% no prazo de duas semanas ap\u00f3s a aplica\u00e7\u00e3o consistente do fluxo, sem alterar qualquer outra vari\u00e1vel do processo.<\/p>\n

Escolher o fluxo de cobertura adequado para a sua liga<\/h2>\n

Nem todas as ligas de alum\u00ednio reagem da mesma forma a uma determinada composi\u00e7\u00e3o qu\u00edmica do fundente. As ligas com elevado teor de magn\u00e9sio (s\u00e9rie 5000) requerem um tratamento diferente das ligas de fundi\u00e7\u00e3o com elevado teor de sil\u00edcio (s\u00e9rie 300), uma vez que o magn\u00e9sio reage de forma mais agressiva com certos componentes do fundente.<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n
Fam\u00edlia Alloy<\/th>\nLigas t\u00edpicas<\/th>\nConsidera\u00e7\u00f5es sobre o fluxo<\/th>\n<\/tr>\n<\/thead>\n
S\u00e9rie 1000 (Alum\u00ednio Puro)<\/td>\n1050, 1100<\/td>\nA solu\u00e7\u00e3o base padr\u00e3o de NaCl\/KCl funciona bem; \u00e9 necess\u00e1rio um baixo teor de fl\u00faor<\/td>\n<\/tr>\n
S\u00e9rie 3000 (Mangan\u00eas)<\/td>\n3003, 3004<\/td>\nFluxo de revestimento padr\u00e3o, teor moderado de criolita<\/td>\n<\/tr>\n
S\u00e9rie 5000 (Magn\u00e9sio)<\/td>\n5052, 5083<\/td>\nRequer um teor mais elevado de fl\u00faor para controlar a reatividade do Mg<\/td>\n<\/tr>\n
S\u00e9rie 6000 (Mg-Si)<\/td>\n6061, 6063<\/td>\nRecomenda-se uma mistura equilibrada de cloreto e fluoreto<\/td>\n<\/tr>\n
S\u00e9rie 7000 (zinco)<\/td>\n7075<\/td>\nFluxo especializado com baixo teor de s\u00f3dio para evitar problemas de corros\u00e3o sob tens\u00e3o<\/td>\n<\/tr>\n
Ligas de fundi\u00e7\u00e3o da S\u00e9rie 300<\/td>\nA356, A380<\/td>\nFluxo de elevada fluidez com boa separa\u00e7\u00e3o das esc\u00f3rias<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

Magnesium-bearing alloys deserve particular attention. Magnesium burns more readily than aluminum and can react violently with certain chloride salts if the flux isn’t formulated correctly. We always recommend requesting a technical data sheet from your flux supplier that specifically states compatibility with your alloy family, not just generic “aluminum covering flux” labeling.<\/p>\n

\"p\u00f3
p\u00f3 de fluxo de cobertura<\/figcaption><\/figure>\n

M\u00e9todos de aplica\u00e7\u00e3o e melhores pr\u00e1ticas<\/h2>\n

Getting flux chemistry right matters, but application technique determines whether that chemistry actually performs. We’ve watched experienced operators get excellent results from average flux, and we’ve watched premium flux underperform because of poor application habits.<\/p>\n

O momento certo \u00e9 mais importante do que a maioria das pessoas imagina.<\/strong>\u00a0O fundente deve ser aplicado na superf\u00edcie do metal fundido assim que se tenha formado metal l\u00edquido suficiente para o reter, geralmente quando cerca de 30% da carga se tiver fundido. Esperar at\u00e9 que toda a carga se liquefa\u00e7a d\u00e1 \u00e0 oxida\u00e7\u00e3o mais tempo para avan\u00e7ar sem controlo.<\/p>\n

A distribui\u00e7\u00e3o tem de ser uniforme.<\/strong>\u00a0Espalhar fluxo num dos cantos do forno tem um efeito praticamente nulo no resto da superf\u00edcie exposta. A aplica\u00e7\u00e3o manual deve ser feita com movimentos amplos por toda a \u00e1rea de fus\u00e3o. Os fornos de maiores dimens\u00f5es beneficiam de sistemas mec\u00e2nicos de distribui\u00e7\u00e3o de fluxo, que distribuem o material de forma mais uniforme do que a aplica\u00e7\u00e3o manual com p\u00e1 alguma vez conseguiria.<\/p>\n

A quantidade deve corresponder \u00e0 \u00e1rea de superf\u00edcie, e n\u00e3o apenas \u00e0 tonelagem.<\/strong>\u00a0Um forno raso e largo tem mais superf\u00edcie exposta por tonelada de metal do que um forno profundo e estreito, e os c\u00e1lculos de dosagem devem refletir essa geometria, em vez de se basearem exclusivamente em regras emp\u00edricas baseadas no peso.<\/p>\n

\n\n\n\n\n\n\n\n\n
Tipo de forno<\/th>\nFator de \u00e1rea superficial<\/th>\nTaxa de fluxo recomendada<\/th>\n<\/tr>\n<\/thead>\n
Forno de reverbera\u00e7\u00e3o<\/td>\nElevada exposi\u00e7\u00e3o<\/td>\n1,5-2,0 kg\/tonelada<\/td>\n<\/tr>\n
Forno de indu\u00e7\u00e3o<\/td>\nExposi\u00e7\u00e3o moderada<\/td>\n0,8-1,2 kg\/tonelada<\/td>\n<\/tr>\n
Forno de cadinho<\/td>\nExposi\u00e7\u00e3o baixa a moderada<\/td>\n1,0-1,5 kg\/tonelada<\/td>\n<\/tr>\n
Forno rotativo<\/td>\nExposi\u00e7\u00e3o moderada, derretimento rotativo<\/td>\n1,2-1,8 kg\/tonelada<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

Em geral, aconselhamos os novos operadores a come\u00e7arem na extremidade inferior do intervalo recomendado e a ajustarem a dosagem para cima com base na forma\u00e7\u00e3o vis\u00edvel de esc\u00f3ria e nos dados de recupera\u00e7\u00e3o de metal ao longo de algumas s\u00e9ries de produ\u00e7\u00e3o, em vez de partirem do princ\u00edpio de que a dosagem mais elevada produz automaticamente o melhor resultado. O excesso de fluxo desperdi\u00e7a material, aumenta a produ\u00e7\u00e3o de fumo e pode, na verdade, contribuir para o desgaste do refrat\u00e1rio ao longo do tempo.
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