{"id":2045,"date":"2015-02-19T18:00:52","date_gmt":"2015-02-19T16:00:52","guid":{"rendered":"http:\/\/www.cookson-clal.com\/le-blog\/?p=2045"},"modified":"2018-02-16T10:55:24","modified_gmt":"2018-02-16T08:55:24","slug":"fusion-et-solidification-du-metal","status":"publish","type":"post","link":"https:\/\/www.cookson-clal.com\/le-blog\/fusion-et-solidification-du-metal\/","title":{"rendered":"Fusion et Solidification des alliages de bijouterie"},"content":{"rendered":"<p>La fonderie est un proc\u00e9d\u00e9 qui permet d\u2019obtenir des pi\u00e8ces de formes et de dimensions vari\u00e9es, par coul\u00e9e d\u2019un m\u00e9tal ou alliage liquide dans un moule.\u00a0C\u2019est dans le moule, qui pr\u00e9sente la forme voulue, que le m\u00e9tal liquide se refroidit et se solidifie.<\/p>\n<p><strong>\u00a0La fonderie met en \u0153uvre\u00a0:<\/strong><\/p>\n<ul>\n<li>un moyen de fusion : le four<\/li>\n<li>une empreinte \u00e0 la forme d\u00e9sir\u00e9e : le moule<\/li>\n<li>un dispositif pour faire passer le m\u00e9tal du four au moule.<\/li>\n<\/ul>\n<p>Le ph\u00e9nom\u00e8ne essentiel en fonderie est la <strong>solidification du m\u00e9tal.<\/strong>\u00a0La solidification d\u2019un m\u00e9tal pur s\u2019effectue \u00e0 une temp\u00e9rature constante appel\u00e9e \u00ab\u00a0temp\u00e9rature de solidification\u00a0\u00bb (c\u2019est la m\u00eame que la temp\u00e9rature de fusion).<\/p>\n<h2><span style=\"color: #ff9900;\">\u00a0Solidification d&rsquo;un m\u00e9tal pur<\/span><\/h2>\n<p>Le passage de l\u2019\u00e9tat liquide \u00e0 l\u2019\u00e9tat solide s\u2019accompagne d\u2019un d\u00e9gagement de chaleur qui est caract\u00e9ristique de chaque m\u00e9tal, cette chaleur est appel\u00e9e <strong>chaleur latente de solidification<\/strong>. (fig. 1)<\/p>\n<p><a href=\"http:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/solidification-du-metal.jpg\" data-rel=\"lightbox-image-0\" data-rl_title=\"\" data-rl_caption=\"\" title=\"\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-5525 size-medium\" src=\"http:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/solidification-du-metal-300x205.jpg\" alt=\"courbe de solidification du m\u00e9tal\" width=\"300\" height=\"205\" srcset=\"https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/solidification-du-metal-300x205.jpg 300w, https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/solidification-du-metal.jpg 738w, https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/solidification-du-metal-300x205@2x.jpg 600w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><br \/>\nLorsqu\u2019une masse de m\u00e9tal liquide se refroidit dans un moule, on voit appara\u00eetre, \u00e0 la temp\u00e9rature de solidification, des fragments de solide qui grandissent \u00e0 partir de germes.\u00a0Pour que ces germes grossissent, c\u2019est-\u00e0-dire pour que la <strong>solidification<\/strong> progresse, il faut que la chaleur qui se d\u00e9gage soit \u00e9vacu\u00e9e par les parois du moule.<\/p>\n<p><span style=\"text-decoration: underline;\">Les germes qui amorcent la solidification d\u2019un m\u00e9tal peuvent avoir deux origines\u00a0:<\/span><\/p>\n<ul>\n<li>soit \u00eatre constitu\u00e9s de groupements d\u2019atomes du m\u00e9tal qui prennent l\u2019arrangement du r\u00e9seau cristallin du solide.<strong> C\u2019est la germination homog\u00e8ne.\u00a0<\/strong><\/li>\n<li>soit \u00eatre des fragments de corps \u00e9trangers (impuret\u00e9s) insolubles dans le m\u00e9tal liquide.<strong> C\u2019est la germination h\u00e9t\u00e9rog\u00e8ne<\/strong>.<\/li>\n<\/ul>\n\n\t\t<style type=\"text\/css\">\n\t\t\t#gallery-1 {\n\t\t\t\tmargin: auto;\n\t\t\t}\n\t\t\t#gallery-1 .gallery-item {\n\t\t\t\tfloat: left;\n\t\t\t\tmargin-top: 10px;\n\t\t\t\ttext-align: center;\n\t\t\t\twidth: 50%;\n\t\t\t}\n\t\t\t#gallery-1 img {\n\t\t\t\tborder: 2px solid #cfcfcf;\n\t\t\t}\n\t\t\t#gallery-1 .gallery-caption {\n\t\t\t\tmargin-left: 0;\n\t\t\t}\n\t\t\t\/* see gallery_shortcode() in wp-includes\/media.php *\/\n\t\t<\/style>\n\t\t<div id='gallery-1' class='gallery galleryid-2045 gallery-columns-2 gallery-size-medium'><dl class='gallery-item'>\n\t\t\t<dt class='gallery-icon landscape'>\n\t\t\t\t<a href='https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/germinaison-homogene.jpg' title=\"\" data-rl_title=\"\" class=\"rl-gallery-link\" data-rl_caption=\"\" data-rel=\"lightbox-gallery-1\"><img loading=\"lazy\" decoding=\"async\" width=\"162\" height=\"61\" src=\"https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/germinaison-homogene.jpg\" class=\"attachment-medium size-medium\" alt=\"germinaison homogene\" aria-describedby=\"gallery-1-5527\" \/><\/a>\n\t\t\t<\/dt>\n\t\t\t\t<dd class='wp-caption-text gallery-caption' id='gallery-1-5527'>\n\t\t\t\tGerminaison homog\u00e8ne\n\t\t\t\t<\/dd><\/dl><dl class='gallery-item'>\n\t\t\t<dt class='gallery-icon landscape'>\n\t\t\t\t<a href='https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/germinaison-heterogene.jpg' title=\"\" data-rl_title=\"\" class=\"rl-gallery-link\" data-rl_caption=\"\" data-rel=\"lightbox-gallery-1\"><img loading=\"lazy\" decoding=\"async\" width=\"195\" height=\"73\" src=\"https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/germinaison-heterogene.jpg\" class=\"attachment-medium size-medium\" alt=\"germinaison heterogene\" aria-describedby=\"gallery-1-5526\" \/><\/a>\n\t\t\t<\/dt>\n\t\t\t\t<dd class='wp-caption-text gallery-caption' id='gallery-1-5526'>\n\t\t\t\tGerminaison h\u00e9t\u00e9rog\u00e8ne\n\t\t\t\t<\/dd><\/dl><br style=\"clear: both\" \/>\n\t\t<\/div>\n\n<p>Quelle que soit la nature des germes, la solidification du m\u00e9tal liquide commence toujours \u00e0 une temp\u00e9rature inf\u00e9rieure \u00e0 la temp\u00e9rature de solidification, c\u2019est le ph\u00e9nom\u00e8ne de surfusion. (fig. 2 a et b)<\/p>\n\n\t\t<style type=\"text\/css\">\n\t\t\t#gallery-2 {\n\t\t\t\tmargin: auto;\n\t\t\t}\n\t\t\t#gallery-2 .gallery-item {\n\t\t\t\tfloat: left;\n\t\t\t\tmargin-top: 10px;\n\t\t\t\ttext-align: center;\n\t\t\t\twidth: 50%;\n\t\t\t}\n\t\t\t#gallery-2 img {\n\t\t\t\tborder: 2px solid #cfcfcf;\n\t\t\t}\n\t\t\t#gallery-2 .gallery-caption {\n\t\t\t\tmargin-left: 0;\n\t\t\t}\n\t\t\t\/* see gallery_shortcode() in wp-includes\/media.php *\/\n\t\t<\/style>\n\t\t<div id='gallery-2' class='gallery galleryid-2045 gallery-columns-2 gallery-size-medium'><dl class='gallery-item'>\n\t\t\t<dt class='gallery-icon landscape'>\n\t\t\t\t<a href='https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/courbe-de-solidification-theorique.jpg' title=\"\" data-rl_title=\"\" class=\"rl-gallery-link\" data-rl_caption=\"\" data-rel=\"lightbox-gallery-2\"><img loading=\"lazy\" decoding=\"async\" width=\"300\" height=\"177\" src=\"https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/courbe-de-solidification-theorique-300x177.jpg\" class=\"attachment-medium size-medium\" alt=\"courbe de solidification theorique\" aria-describedby=\"gallery-2-5529\" srcset=\"https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/courbe-de-solidification-theorique-300x177.jpg 300w, https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/courbe-de-solidification-theorique.jpg 737w, https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/courbe-de-solidification-theorique-300x177@2x.jpg 600w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a>\n\t\t\t<\/dt>\n\t\t\t\t<dd class='wp-caption-text gallery-caption' id='gallery-2-5529'>\n\t\t\t\tcourbe de solidification th\u00e9orique\n\t\t\t\t<\/dd><\/dl><dl class='gallery-item'>\n\t\t\t<dt class='gallery-icon landscape'>\n\t\t\t\t<a href='https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/courbe-de-solidification-reelle.jpg' title=\"\" data-rl_title=\"\" class=\"rl-gallery-link\" data-rl_caption=\"\" data-rel=\"lightbox-gallery-2\"><img loading=\"lazy\" decoding=\"async\" width=\"300\" height=\"200\" src=\"https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/courbe-de-solidification-reelle-300x200.jpg\" class=\"attachment-medium size-medium\" alt=\"courbe de solidification reelle\" aria-describedby=\"gallery-2-5528\" srcset=\"https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/courbe-de-solidification-reelle-300x200.jpg 300w, https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/courbe-de-solidification-reelle.jpg 677w, https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/courbe-de-solidification-reelle-300x200@2x.jpg 600w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a>\n\t\t\t<\/dt>\n\t\t\t\t<dd class='wp-caption-text gallery-caption' id='gallery-2-5528'>\n\t\t\t\tcourbe de solidification r\u00e9elle\n\t\t\t\t<\/dd><\/dl><br style=\"clear: both\" \/>\n\t\t<\/div>\n\n<p>La surfusion permet la cr\u00e9ation de germes stables dans le liquide lorsque ces germes ont atteint une certaine grosseur, la temp\u00e9rature remonte \u00e0 la valeur T A et la solidification se poursuit \u00e0 la temp\u00e9rature constante, jusqu\u2019\u00e0 la derni\u00e8re goutte de liquide.<\/p>\n<h2><span style=\"color: #ff9900;\">\u00a0Solidification d&rsquo;un m\u00e9lange<\/span><\/h2>\n<p>Except\u00e9 certains alliages particuliers (eutectique, p\u00e9ritectique, compos\u00e9 d\u00e9fini, etc\u2026), la plupart des alliages se solidifient dans un intervalle de temp\u00e9rature qui est celui compris entre le liquidus et du solidus. La solidification d\u00e9bute, comme pour les m\u00e9taux purs, par la formation de germes qui croissent au fur et \u00e0 mesure que s\u2019\u00e9liminent les calories du m\u00e9tal liquide.<\/p>\n<p><strong>Figure 3 :<\/strong><br \/>\nCes courbes de refroidissement pour une s\u00e9rie d\u2019alliages or-argent (Au-Ag) indiquent l\u2019intervalle de fusion des alliages. Le point \u00ab\u00a0S\u00a0\u00bb repr\u00e9sente le d\u00e9but de la solidification. A noter que l\u2019or pur et l\u2019argent se solidifient \u00e0 des temp\u00e9ratures fixes, contrairement \u00e0 leurs alliages.<\/p>\n<div id=\"attachment_5530\" style=\"width: 310px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/courbe-de-refroidissement-alliages.jpg\" data-rel=\"lightbox-image-5\" data-rl_title=\"\" data-rl_caption=\"\" title=\"\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-5530\" class=\"wp-image-5530 size-medium\" src=\"http:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/courbe-de-refroidissement-alliages-300x275.jpg\" alt=\"courbe de refroidissement alliages\" width=\"300\" height=\"275\" srcset=\"https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/courbe-de-refroidissement-alliages-300x275.jpg 300w, https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/courbe-de-refroidissement-alliages.jpg 683w, https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/courbe-de-refroidissement-alliages-300x275@2x.jpg 600w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><p id=\"caption-attachment-5530\" class=\"wp-caption-text\">Figure 3<\/p><\/div>\n<h2><span style=\"color: #ff9900;\">Structure cristalline d&rsquo;une pi\u00e8ce coul\u00e9e<\/span><\/h2>\n<p>Les germes qui apparaissent dans le liquide se d\u00e9veloppent dans certaines directions en donnant naissance \u00e0 des arborescences appel\u00e9es dendrites. Au fur et \u00e0 mesure que progresse la solidification, les dendrites croissent jusqu\u2019\u00e0 rencontrer d\u2019autres voisines, la solidification se poursuit alors dans les espaces interdendritiques jusqu\u2019\u00e0 la derni\u00e8re goutte de liquide environnant (figure 4).<\/p>\n<p>Lorsque la solidification est termin\u00e9e, l\u2019aspect dendritique a g\u00e9n\u00e9ralement disparu, il a fait place \u00e0 des grains juxtapos\u00e9s.<\/p>\n<p><a href=\"http:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/figure4.jpg\" data-rel=\"lightbox-image-6\" data-rl_title=\"\" data-rl_caption=\"\" title=\"\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-2050 size-medium\" src=\"http:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/figure4-300x267.jpg\" alt=\"m\u00e9tal\" width=\"300\" height=\"267\" srcset=\"https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/figure4-300x267.jpg 300w, https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/figure4.jpg 336w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><\/p>\n<p>&nbsp;<\/p>\n<p><strong>La grosseur et la forme des grains d\u2019un m\u00e9tal coul\u00e9 d\u00e9pendent\u00a0:<\/strong><\/p>\n<ul>\n<li>du nombre de germes qui apparaissent dans le liquide<\/li>\n<li>de la vitesse de croissance de ces germes<\/li>\n<\/ul>\n<p><strong>Si le refroidissement est rapide\u00a0:<\/strong><\/p>\n<p><span style=\"text-decoration: underline;\">La surfusion est importante\u00a0<\/span>\u00a0\u2192 il y a un grand nombre de grains\u00a0: les grains sont petits<br \/>\n<span style=\"text-decoration: underline;\">Si le refroidissement est faible\u00a0<\/span>\u2192 le nombre de germes est petit\u00a0: les grains sont grossiers<\/p>\n<p>Lorsqu\u2019on fait la coupe longitudinale d\u2019un bloc de m\u00e9tal coul\u00e9 dans un moule (figure 5), on remarque trois couches cristallines d\u2019aspect tr\u00e8s diff\u00e9rent\u00a0:<\/p>\n<ul>\n<li><strong><span style=\"text-decoration: underline;\">1<sup>\u00e8re<\/sup> couche\u00a0:<br \/>\n<\/span><\/strong>Couche mince de grains tr\u00e8s fins form\u00e9s au contact des parois du moule. Dans cette zone, le refroidissement est brutal, les germes sont nombreux, ils donnent naissance \u00e0 des grains fins.<\/li>\n<li><strong><span style=\"text-decoration: underline;\">2<sup>\u00e8me<\/sup> couche\u00a0:<br \/>\n<\/span><\/strong>Elle est constitu\u00e9e de gros grains orient\u00e9s qui se sont d\u00e9velopp\u00e9s perpendiculairement \u00e0 la paroi du moule. Cette couche correspond \u00e0 un refroidissement moins brutal, d\u2019o\u00f9 le nombre de grains plus faible.<\/li>\n<li><strong><span style=\"text-decoration: underline;\">3<sup>\u00e8me<\/sup> couche\u00a0:<br \/>\n<\/span><\/strong>Elle est form\u00e9e de grains moyens, diversement orient\u00e9s. Cette couche s\u2019est refroidie lentement, il y a donc eu peu de germes.<\/li>\n<\/ul>\n<p><a href=\"http:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/figure5.jpg\" data-rel=\"lightbox-image-7\" data-rl_title=\"\" data-rl_caption=\"\" title=\"\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-2052 size-medium\" src=\"http:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/figure5-300x252.jpg\" alt=\"m\u00e9tal\" width=\"300\" height=\"252\" srcset=\"https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/figure5-300x252.jpg 300w, https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/figure5.jpg 328w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><\/p>\n<p>&nbsp;<\/p>\n<p><strong>Nota\u00a0:<br \/>\n<\/strong>Toutes les pi\u00e8ces de fonderie refroidies dans des moules m\u00e9talliques pr\u00e9sentent des ces 3 couches. Le volume occup\u00e9 par chacune d\u2019elle d\u00e9pend de plusieurs param\u00e8tres, notamment la temp\u00e9rature de coul\u00e9e, la temp\u00e9rature du moule, le rapport masse m\u00e9tal liquide\/masse du moule, etc<\/p>\n<h2><span style=\"color: #ff9900;\">S\u00e9gr\u00e9gation<\/span><\/h2>\n<p>Lorsqu\u2019un alliage se solidifie dans un intervalle de temp\u00e9rature, il faudrait, pour que les compositions du liquide et du solide suivent le liquidus et le solidus, une diffusion des atomes dans chaque phase. En pratique, cette diffusion se fait mal, le solide qui se d\u00e9pose est form\u00e9 de couches successives de compositions diff\u00e9rentes de celle de l\u2019\u00e9quilibre.<\/p>\n<p><strong><span style=\"text-decoration: underline;\"><span style=\"text-decoration: underline;\">1. Formation d\u2019un grain<\/span><\/span><\/strong><\/p>\n<p>Soit un grain de l\u2019alliage X (figure 6) qui se solidifie.<\/p>\n<p>A\u00a0 \u00a0 t1 appara\u00eet le 1<sup>er<\/sup> germe de composition s1<br \/>\nt2 le solide qui se d\u00e9pose \u00e0 la composition s2<br \/>\nt3 le solide qui se d\u00e9pose \u00e0 la composition s3<br \/>\nt4 le solide qui se d\u00e9pose \u00e0 la composition s4<\/p>\n<p>Bien que la diffusion des atomes tende \u00e0 faire \u00e9voluer chaque couche d\u00e9pos\u00e9e vers la composition d\u2019\u00e9quilibre, il subsiste dans le grain, en fin de solidification, une h\u00e9t\u00e9rog\u00e9n\u00e9it\u00e9 de composition qu\u2019on appelle\u00a0: <strong>s\u00e9gr\u00e9gation mineure<\/strong>.\u00a0Le centre d\u2019un grain a donc une composition diff\u00e9rente de celle du bord.<\/p>\n\n\t\t<style type=\"text\/css\">\n\t\t\t#gallery-3 {\n\t\t\t\tmargin: auto;\n\t\t\t}\n\t\t\t#gallery-3 .gallery-item {\n\t\t\t\tfloat: left;\n\t\t\t\tmargin-top: 10px;\n\t\t\t\ttext-align: center;\n\t\t\t\twidth: 50%;\n\t\t\t}\n\t\t\t#gallery-3 img {\n\t\t\t\tborder: 2px solid #cfcfcf;\n\t\t\t}\n\t\t\t#gallery-3 .gallery-caption {\n\t\t\t\tmargin-left: 0;\n\t\t\t}\n\t\t\t\/* see gallery_shortcode() in wp-includes\/media.php *\/\n\t\t<\/style>\n\t\t<div id='gallery-3' class='gallery galleryid-2045 gallery-columns-2 gallery-size-medium'><dl class='gallery-item'>\n\t\t\t<dt class='gallery-icon landscape'>\n\t\t\t\t<a href='https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/couches-de-solidification.jpg' title=\"\" data-rl_title=\"\" class=\"rl-gallery-link\" data-rl_caption=\"\" data-rel=\"lightbox-gallery-3\"><img loading=\"lazy\" decoding=\"async\" width=\"300\" height=\"134\" src=\"https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/couches-de-solidification-300x134.jpg\" class=\"attachment-medium size-medium\" alt=\"couches de solidification\" srcset=\"https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/couches-de-solidification-300x134.jpg 300w, https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/couches-de-solidification.jpg 501w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a>\n\t\t\t<\/dt><\/dl><dl class='gallery-item'>\n\t\t\t<dt class='gallery-icon landscape'>\n\t\t\t\t<a href='https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/Formation-dun-gran.jpg' title=\"\" data-rl_title=\"\" class=\"rl-gallery-link\" data-rl_caption=\"\" data-rel=\"lightbox-gallery-3\"><img loading=\"lazy\" decoding=\"async\" width=\"300\" height=\"244\" src=\"https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/Formation-dun-gran-300x244.jpg\" class=\"attachment-medium size-medium\" alt=\"Formation d&#039;un grain\" srcset=\"https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/Formation-dun-gran-300x244.jpg 300w, https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/Formation-dun-gran.jpg 596w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a>\n\t\t\t<\/dt><\/dl><br style=\"clear: both\" \/>\n\t\t<\/div>\n\n<p><strong><span style=\"text-decoration: underline;\">2. Rem\u00e8de \u00e0 la s\u00e9gr\u00e9gation<\/span><\/strong><\/p>\n<p>Il n\u2019est pas possible de supprimer les s\u00e9gr\u00e9gations mineures et majeures en agissant sur les param\u00e8tres de coul\u00e9e.<\/p>\n<h2><span style=\"color: #ff9900;\">Retrait<\/span><\/h2>\n<p>Lorsqu\u2019un m\u00e9tal est coul\u00e9 dans un moule, sa densit\u00e9 varie constamment au cours du refroidissement. Pour la plupart des m\u00e9taux, la densit\u00e9 \u00e0 l\u2019\u00e9tat solide est plus \u00e9lev\u00e9e que celle de l\u2019\u00e9tat liquide (tableau ci dessous), cela entra\u00eene, apr\u00e8s solidification compl\u00e8te, une contraction appel\u00e9e retrait (Quelques \u00e9l\u00e9ments, comme le Si, Ge, Sb, Bi\u2026 se contractent \u00e0 fusion.)<\/p>\n<p><a href=\"http:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/Densite-et-changement-de-volume-des-metaux-point-de-fusion.jpg\" data-rel=\"lightbox-image-10\" data-rl_title=\"\" data-rl_caption=\"\" title=\"\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-medium wp-image-5534\" src=\"http:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/Densite-et-changement-de-volume-des-metaux-point-de-fusion-300x191.jpg\" alt=\"Densit\u00e9 et changement de volume des metaux point de fusion\" width=\"300\" height=\"191\" srcset=\"https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/Densite-et-changement-de-volume-des-metaux-point-de-fusion-300x191.jpg 300w, https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/Densite-et-changement-de-volume-des-metaux-point-de-fusion.jpg 758w, https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/Densite-et-changement-de-volume-des-metaux-point-de-fusion-300x191@2x.jpg 600w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><\/p>\n<p><strong>Cons\u00e9quences du retrait<br \/>\n<\/strong>Le retrait est \u00e0 l\u2019origine de plusieurs d\u00e9fauts, nous ne citerons que les plus courants.<\/p>\n<ul>\n<li><strong><span style=\"text-decoration: underline;\">Micro-retassure<\/span> (retassure mineure) :\u00a0<\/strong>En fin de solidification, il peut rester, entre les dendrites, des poches que le liquide final n\u2019a pu combler. Ces trous sont appel\u00e9s <strong>micro-retassures<\/strong> lorsque leurs dimensions n\u2019exc\u00e8dent pas quelques dixi\u00e8mes de millim\u00e8tres, ou <strong>retassures<\/strong> <strong>mineures<\/strong> dans le cas de cavit\u00e9s de plusieurs millim\u00e8tres.<\/li>\n<\/ul>\n<ul>\n<li><strong><span style=\"text-decoration: underline;\">Retassure majeure<\/span> :\u00a0<\/strong>La solidification du m\u00e9tal liquide dans un moule et le retrait qui en r\u00e9sulte entra\u00eenent la formation d\u2019un creux \u00e0 la partie sup\u00e9rieure de la pi\u00e8ce coul\u00e9e. Ce d\u00e9faut porte le nom de retassure majeure, sa formation est illustr\u00e9e en figure 7.<\/li>\n<\/ul>\n<p style=\"text-align: center;\"><a href=\"http:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/retassure-majeure.jpg\" data-rel=\"lightbox-image-11\" data-rl_title=\"\" data-rl_caption=\"\" title=\"\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-medium wp-image-5536\" src=\"http:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/retassure-majeure-300x189.jpg\" alt=\"retassure majeure\" width=\"300\" height=\"189\" srcset=\"https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/retassure-majeure-300x189.jpg 300w, https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/retassure-majeure.jpg 753w, https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/retassure-majeure-300x189@2x.jpg 600w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><\/p>\n<ul>\n<li><strong><span style=\"text-decoration: underline;\">Rem\u00e8de aux d\u00e9fauts r\u00e9sultant du retrait<br \/>\n<\/span><\/strong>La retassure majeure peut-\u00eatre diminu\u00e9e par la cr\u00e9ation d\u2019une masselotte dans le haut du lingot. La masselotte constitue une r\u00e9serve de m\u00e9tal liquide. Maintenue dans une cavit\u00e9 isolante, elle permet de compenser la contraction qui r\u00e9sulte du retrait.\u00a0<span style=\"line-height: 1.5;\">On r\u00e9alise une masselotte en utilisant, dans la partie sup\u00e9rieure du moule, un mat\u00e9riau peu conducteur de la chaleur qui retarde la solidification du m\u00e9tal dans cette zone.\u00a0<\/span><span style=\"line-height: 1.5;\">Une masselotte bien calcul\u00e9e doit se solidifier en dernier , apr\u00e8s solidification compl\u00e8te de la pi\u00e8ce.<\/span><\/li>\n<\/ul>\n<hr \/>\n<p><a href=\"http:\/\/bit.ly\/2o2Qejr\" target=\"_blank\" rel=\"noopener\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-5538 size-full\" src=\"http:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/materiel-et-accessoire-pour-fonte.jpg\" alt=\"mat\u00e9riel et accessoires pour fonte\" width=\"855\" height=\"165\" srcset=\"https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/materiel-et-accessoire-pour-fonte.jpg 855w, https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/materiel-et-accessoire-pour-fonte-300x58.jpg 300w, https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/materiel-et-accessoire-pour-fonte-848x165.jpg 848w, https:\/\/www.cookson-clal.com\/le-blog\/wp-content\/uploads\/2015\/02\/materiel-et-accessoire-pour-fonte-300x58@2x.jpg 600w\" sizes=\"(max-width: 855px) 100vw, 855px\" \/><\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>La fonderie est un proc\u00e9d\u00e9 qui permet d\u2019obtenir des pi\u00e8ces de formes et de dimensions vari\u00e9es, par coul\u00e9e d\u2019un m\u00e9tal ou alliage liquide dans un moule.\u00a0C\u2019est dans le moule, qui&#8230;<\/p>\n","protected":false},"author":5,"featured_media":2065,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[247,246],"tags":[176,175,178,147,145,177],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v21.8 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\r\n<title>Fusion et Solidification des alliages de bijouterie | L&#039;atelier - Le blog des cr\u00e9ateurs de bijoux Cookson CLAL<\/title>\r\n<meta name=\"description\" content=\"La fonderie est un proc\u00e9d\u00e9 qui permet d\u2019obtenir des pi\u00e8ces de formes et de dimensions vari\u00e9es, par coul\u00e9e d\u2019un m\u00e9tal ou alliage liquide dans un moule. 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