{"id":7996,"date":"2026-01-02T09:00:00","date_gmt":"2026-01-02T09:00:00","guid":{"rendered":"https:\/\/uplastech.com\/silicone-post-curing\/"},"modified":"2026-01-02T09:00:00","modified_gmt":"2026-01-02T09:00:00","slug":"silicone-post-curing","status":"publish","type":"post","link":"https:\/\/uplastech.com\/id\/silicone-post-curing\/","title":{"rendered":"Post-Curing Silicone: Removing Volatiles and Setting Compression Set"},"content":{"rendered":"<style>\n.upl-blog{font-size:17px;line-height:1.78;color:#1f2937}\n.upl-blog p{margin:0 0 18px}\n.upl-blog h2{font-size:26px;line-height:1.3;color:#0b2b33;margin:46px 0 14px;font-weight:700;letter-spacing:-.015em}\n.upl-blog h3{font-size:19.5px;color:#0d3b47;margin:28px 0 10px;font-weight:700}\n.upl-blog ul,.upl-blog ol{margin:0 0 20px;padding-left:22px}\n.upl-blog li{margin:0 0 9px}\n.upl-blog figure{margin:0 0 34px}\n.upl-blog figure img{width:100%;height:auto;display:block;border-radius:10px}\n.upl-blog figcaption{font-size:13px;color:#6b7280;margin-top:10px;line-height:1.5}\n.upl-blog .toc{background:none;border:0;border-radius:0;padding:0;margin:0 0 34px}\n.upl-blog .toc .lwptoc{margin:0}\n.upl-blog .toc h4{margin:0 0 10px;font-size:13px;letter-spacing:.1em;text-transform:uppercase;color:#0d5563}\n.upl-blog .toc ol{margin:0;padding-left:18px;font-size:14.5px}\n.upl-blog .toc li{margin-bottom:6px}\n.upl-blog table{width:100%;border-collapse:collapse;font-size:14.5px;margin:0 0 10px}\n.upl-blog th{background:#0d3b47;color:#fff;text-align:left;padding:11px 13px;font-weight:600;font-size:13.5px;border:0}\n.upl-blog td{padding:11px 13px;border:0;border-bottom:1px solid #e8ebed;vertical-align:top}\n.upl-blog tbody tr:nth-child(even){background:#fafbfc}\n.upl-blog .tablecap{font-size:12.5px;color:#6b7280;margin:0 0 30px}\n.upl-blog .myth{background:#fff8ef;border:1px solid #f6ddbd;border-radius:8px;padding:16px 20px;margin:0 0 26px;font-size:15.5px}\n.upl-blog .myth b{color:#a85c10}\n.upl-blog .callout{background:#f2f8f9;border-radius:8px;padding:18px 22px;margin:0 0 26px;font-size:15.5px;border-left:3px solid #14707f}\n.upl-blog .faq h3{border-top:1px solid #eceff1;padding-top:22px;margin-top:0;font-size:18px}\n.upl-blog .faq h3:first-of-type{border-top:0;padding-top:0}\n.upl-blog .cta{background:linear-gradient(135deg,#0b2b33,#0d5563);color:#fff;border-radius:12px;padding:34px;margin:48px 0 30px}\n.upl-blog .cta h2,.upl-blog .cta .cta-h{color:#fff;margin:0 0 10px;font-size:24px;font-weight:700;line-height:1.3}\n.upl-blog .cta p{color:#c9dee3;margin:0 0 20px;font-size:16px}\n.upl-blog .btn{display:inline-block;background:#e07a1f;color:#fff;text-decoration:none;font-weight:700;padding:13px 26px;border-radius:8px;font-size:15.5px}\n.upl-blog .rel{border-top:1px solid #e8ebed;margin-top:40px;padding-top:26px}\n.upl-blog .rel h4{font-size:13px;letter-spacing:.1em;text-transform:uppercase;color:#6b7280;margin:0 0 14px}\n.upl-blog .rel ul{list-style:none;padding:0;margin:0}\n.upl-blog .rel li{padding:11px 0;border-bottom:1px dashed #e8ebed}\n.upl-blog .rel a{text-decoration:none;font-weight:600;font-size:15.5px}\n@media(max-width:640px){.upl-blog h2{font-size:22px}.upl-blog table{font-size:13px}.upl-blog .cta{padding:24px}}\n\/* \u5355\u7bc7\u9875\u9690\u85cf WhatsApp \u95ee\u5019\u5361\uff0c\u53ea\u4fdd\u7559\u5706\u5f62\u6c14\u6ce1\uff0c\u907f\u514d\u906e\u6321\u4fa7\u680f\u8be2\u76d8\u63d0\u4ea4\u6309\u94ae\u3002\n   \u6ce8\u610f\uff1aClick to Chat \u7684\u70b9\u51fb\u903b\u8f91\u662f\u300c\u95ee\u5019\u5361\u5143\u7d20\u5b58\u5728\u5c31\u4e0d\u8df3\u8f6c\u300d\uff0c\u53ea\u9760 CSS \u9690\u85cf\u4f1a\u8ba9\u6c14\u6ce1\u53d8\u6210\u6b7b\u94fe\u63a5\u3002\n   Code Snippets #9\u300cUPL single post: WhatsApp bubble jumps straight to chat\u300d\u8d1f\u8d23\u628a\u8be5\u8282\u70b9\u4ece DOM \u79fb\u9664\uff0c\n   \u4e0b\u9762\u8fd9\u6761 CSS \u53ea\u662f\u79fb\u9664\u524d\u7684\u89c6\u89c9\u515c\u5e95\u3002\u5220 #9 \u524d\u5fc5\u987b\u5148\u5220\u8fd9\u6761\u89c4\u5219\u3002 *\/\nbody.single-post .ht_ctc_chat_greetings_box{display:none !important}\n<\/style>\n<div class=\"upl-blog\">\n<figure>\n<img fetchpriority=\"high\" decoding=\"async\" src=\"https:\/\/uplastech.com\/wp-content\/uploads\/2026\/10\/silicone-post-curing.jpg\" alt=\"Volatiles remaining against post-cure time, and compression set against post-cure temperature\" width=\"1536\" height=\"909\"><figcaption>Volatiles fall from 1.8 to 0.35 percent in four hours at 200 C, while compression set bottoms out at 16 percent at 225 C and rises again at 250.<\/figcaption><\/figure>\n<div class=\"toc\"><\/div>\n<h2 id=\"why\">What a post-cure actually does<\/h2>\n<p>A press-cured silicone part is cured enough to be handled, not cured enough to be finished. Two things are still wrong with it. It contains volatile material, which is unreacted low-molecular-weight polymer and the fragments of any peroxide, and its network is not fully developed, so its compression set is higher than it will be after a few hours at temperature.<\/p>\n<p>A post-cure is a second, longer bake in an oven without pressure. It drives off the volatiles and completes the crosslinking, and it changes three properties: the volatile content, the compression set, and the hardness, which rises slightly as the network tightens.<\/p>\n<p>It is required for anything that touches food, skin or a patient, because the volatiles are the extractables that a compliance test looks for. It is also standard for optical parts, because the volatiles fog a lens, and for thick parts, because the press cure cannot reach the core.<\/p>\n<h2 id=\"volatiles\">Volatiles leave fast, then slowly<\/h2>\n<p>At 200 C the volatile content falls from 1.8 percent in the as-cured part to 1.0 after one hour, 0.6 after two, 0.35 after four, 0.2 after eight and 0.15 after sixteen. The first four hours remove 80 percent of what is removable, and the rest is a slow diffusion tail.<\/p>\n<p>The shape of the curve is set by diffusion, not by reaction. The volatiles near the surface leave quickly and the ones in the middle have to travel out through the rubber, and that path lengthens as the concentration gradient flattens. That is why a thick part needs much longer than a thin one at the same temperature.<\/p>\n<p>The practical schedule for a thin part is four hours at 200 C, which takes the volatile content below 0.5 percent, the level most compliance tests accept. A thick part of 10 mm or more needs eight to sixteen hours, or a higher temperature with the risk of over-cure on the surface.<\/p>\n<table>\n<thead>\n<tr>\n<th>Post-cure at 200 C<\/th>\n<th>Volatiles<\/th>\n<th>Removed<\/th>\n<th>Typical use<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>None<\/td>\n<td>1.8 percent<\/td>\n<td>0<\/td>\n<td>Mechanical parts only<\/td>\n<\/tr>\n<tr>\n<td>1 hour<\/td>\n<td>1.0 percent<\/td>\n<td>44 percent<\/td>\n<td>Handling<\/td>\n<\/tr>\n<tr>\n<td>2 hours<\/td>\n<td>0.6 percent<\/td>\n<td>67 percent<\/td>\n<td>General purpose<\/td>\n<\/tr>\n<tr>\n<td>4 hours<\/td>\n<td>0.35 percent<\/td>\n<td>81 percent<\/td>\n<td>Food and medical<\/td>\n<\/tr>\n<tr>\n<td>8 hours<\/td>\n<td>0.20 percent<\/td>\n<td>89 percent<\/td>\n<td>Thick sections<\/td>\n<\/tr>\n<tr>\n<td>16 hours<\/td>\n<td>0.15 percent<\/td>\n<td>92 percent<\/td>\n<td>Optical, critical<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 1 \u2014 Volatile content against post-cure time at 200 C.<\/p>\n<h2 id=\"set\">Set falls, then rises<\/h2>\n<p>Compression set improves with post-cure temperature and then gets worse. With no post-cure the set is 38 percent, at 150 C it is 30, at 175 C 24, at 200 C 18 and at 225 C 16. At 250 C it climbs back to 20.<\/p>\n<p>The improvement is the network completing. The reversal is degradation: at 250 C the polymer chains start to break as fast as they crosslink, and the network that results is less able to recover. The material also discolours and its tear strength falls, which is why a post-cure above about 230 C is a specialist operation rather than a default.<\/p>\n<p>The optimum is material-specific. A general-purpose HCR peaks around 200 to 225 C; a high-temperature grade can go to 250 without reversing, and a fluorosilicone is more sensitive. The compound data sheet usually gives a recommended post-cure, and it is worth following rather than inventing a schedule.<\/p>\n<h2 id=\"oven\">The oven and the fixture<\/h2>\n<p>A post-cure oven needs forced air and a uniform temperature, because a 10 C gradient across the chamber produces a 10 C difference in set across the batch. A laboratory oven with a fan and a calibrated controller is adequate; a home-made cabinet with a thermostat is not.<\/p>\n<p>Ventilation matters as much as temperature. The volatiles have to leave the oven, or they re-deposit on the parts as an oily film. A through-flow oven with an extraction duct is the right arrangement, and the duct should be sized for the volatile load rather than for the oven volume.<\/p>\n<p>Parts are usually post-cured loose on a perforated tray, in a single layer, because stacking traps volatiles between parts. A part that has to hold a dimension during the post-cure goes on a fixture, because the material softens at the post-cure temperature and will sag under its own weight.<\/p>\n<div class=\"callout\">A part that sags in the post-cure oven was not supported, not overcured. Support it, or post-cure it at a lower temperature for longer.<\/div>\n<h2 id=\"effect\">What else changes<\/h2>\n<p>Hardness rises by 2 to 5 Shore A during a post-cure, because the network tightens and the volatiles leave. A compound specified at 50 Shore A can come out at 53, and if the tolerance is plus or minus 3 that is the whole allowance.<\/p>\n<p>Dimensions shrink by 0.2 to 0.5 percent, for the same reason. On a moulded part with a tight dimension the shrinkage has to be allowed for in the tool, or the part has to be post-cured on a fixture that holds the dimension.<\/p>\n<table>\n<thead>\n<tr>\n<th>Properti<\/th>\n<th>Change after post-cure<\/th>\n<th>Mengapa<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Hardness<\/td>\n<td>+2 to 5 Shore A<\/td>\n<td>Network tightens as volatiles leave<\/td>\n<\/tr>\n<tr>\n<td>Dimensi<\/td>\n<td>-0.2 to 0.5 percent<\/td>\n<td>Same shrinkage<\/td>\n<\/tr>\n<tr>\n<td>Compression set<\/td>\n<td>Falls by 15 to 20 points<\/td>\n<td>Crosslinking completes<\/td>\n<\/tr>\n<tr>\n<td>Colour<\/td>\n<td>Slightly darker<\/td>\n<td>Thermal history<\/td>\n<\/tr>\n<tr>\n<td>Tear strength<\/td>\n<td>Unchanged below 230 C<\/td>\n<td>Degradation above it<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 2 \u2014 What a post-cure changes, and by how much.<\/p>\n<p>Colour changes slightly, usually a little darker or yellower. On a white or a translucent part this is visible, and it is the reason a post-cured part and an as-cured part should never be mixed in one assembly.<\/p>\n<h2 id=\"specify\">What to specify<\/h2>\n<p>A post-cure is a process specification, and it belongs on the drawing when the part has a compliance or a set requirement.<\/p>\n<ul>\n<li>Post-cure temperature and time, with the tolerance on both.<\/li>\n<li>Whether the part is supported during the post-cure.<\/li>\n<li>The volatile content or extractable limit the part has to meet.<\/li>\n<li>Compression set at the service temperature, after post-cure.<\/li>\n<li>Hardness after post-cure, not before, if the tolerance is tight.<\/li>\n<li>Whether the oven is through-flow and extracted.<\/li>\n<\/ul>\n<p>Hardness after post-cure is the item that catches people out. A drawing that specifies 50 Shore A and a process that post-cures to 53 produces parts that fail an incoming inspection while being perfectly good parts.<\/p>\n<div class=\"faq\">\n<h3>Why is silicone post-cured?<\/h3>\n<p>To drive off volatiles and complete the crosslinking. It lowers the extractables, improves compression set and stabilises the hardness, and it is required for food, medical and optical parts.<\/p>\n<h3>How long should a silicone post-cure be?<\/h3>\n<p>Four hours at 200 C for a thin part, which takes volatiles below 0.5 percent. Thick sections need eight to sixteen hours.<\/p>\n<h3>Does post-cure improve compression set?<\/h3>\n<p>Yes, up to a point. Set falls from 38 percent with no post-cure to 16 percent at 225 C, then rises again at 250 as degradation starts.<\/p>\n<h3>Does post-cure change hardness?<\/h3>\n<p>It raises it by 2 to 5 Shore A and shrinks the part by 0.2 to 0.5 percent. Specify hardness after post-cure, not before.<\/p>\n<h3>Why did my parts sag in the post-cure oven?<\/h3>\n<p>Because they were unsupported. The material softens at the post-cure temperature, so parts that must hold a shape need a fixture.<\/p>\n<h3>Can a post-cure be done in any oven?<\/h3>\n<p>It needs forced air, a uniform temperature and extraction for the volatiles. A cabinet with a thermostat will give uneven set and re-deposit volatiles on the parts.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">Need a silicone part with a set or extractable limit?<\/p>\n<p>Tell us the service temperature and the compliance test. We will quote the post-cure schedule and the set and volatile figures we can certify.<\/p>\n<p><a class=\"btn\" href=\"https:\/\/uplastech.com\/id\/silicone-rubber-products\/\">Ask about silicone post-curing<\/a>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/id\/silicone-vulcanization-temperature\/\">Vulcanisation Temperature and Time: The Cure Curve Behind Every Part<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/id\/platinum-cure-vs-peroxide-cure\/\">Platinum Versus Peroxide Cure: Speed, Purity and Inhibition<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/id\/medical-grade-silicone\/\">Medical Grade Silicone: What the Certification Actually Covers<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/id\/food-grade-silicone\/\">Food Grade Silicone: Compliance, Cure and Extractables<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/id\/silicone-calendering\/\">Silicone Calendering: Sheet and Coated Fabric in One Pass<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>Volatiles fall from 1.8 percent to 0.35 in four hours at 200 C, and compression set falls from 38 to 16 percent between no post-cure and 225 C. Past that, set climbs back to 20 and the cure is doing damage.<\/p>","protected":false},"author":1,"featured_media":7995,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_seopress_titles_title":"Post-Curing Silicone: Volatiles and Set","_seopress_titles_desc":"Silicone post-curing explained: volatiles against time and temperature, compression set against post-cure temperature, over-cure, ovens and fixtures, and when a","_seopress_robots_index":"","_seopress_robots_follow":"","_seopress_robots_imageindex":"","_seopress_robots_snippet":"","_seopress_robots_primary_cat":"39","_seopress_robots_breadcrumbs":"","_seopress_robots_freeze_modified_date":"","_seopress_robots_custom_modified_date":"","_seopress_robots_canonical":"","_seopress_social_fb_title":"","_seopress_social_fb_desc":"","_seopress_social_fb_img":"","_seopress_social_fb_img_attachment_id":0,"_seopress_social_fb_img_width":0,"_seopress_social_fb_img_height":0,"_seopress_social_twitter_title":"","_seopress_social_twitter_desc":"","_seopress_social_twitter_img":"","_seopress_social_twitter_img_attachment_id":0,"_seopress_social_twitter_img_width":0,"_seopress_social_twitter_img_height":0,"_seopress_redirections_value":"","_seopress_redirections_enabled":"","_seopress_redirections_enabled_regex":"","_seopress_redirections_logged_status":"","_seopress_redirections_param":"","_seopress_redirections_type":0,"_seopress_analysis_target_kw":"","footnotes":""},"categories":[39],"tags":[],"class_list":["post-7996","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-silicone-rubber-products"],"meta_box":{"post-to-quiz_to":[]},"_links":{"self":[{"href":"https:\/\/uplastech.com\/id\/wp-json\/wp\/v2\/posts\/7996","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/uplastech.com\/id\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/uplastech.com\/id\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/uplastech.com\/id\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/uplastech.com\/id\/wp-json\/wp\/v2\/comments?post=7996"}],"version-history":[{"count":0,"href":"https:\/\/uplastech.com\/id\/wp-json\/wp\/v2\/posts\/7996\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/uplastech.com\/id\/wp-json\/wp\/v2\/media\/7995"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/id\/wp-json\/wp\/v2\/media?parent=7996"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/id\/wp-json\/wp\/v2\/categories?post=7996"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/id\/wp-json\/wp\/v2\/tags?post=7996"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}