{"id":7940,"date":"2025-12-05T09:00:00","date_gmt":"2025-12-05T09:00:00","guid":{"rendered":"https:\/\/uplastech.com\/silicone-extrusion-process\/"},"modified":"2025-12-05T09:00:00","modified_gmt":"2025-12-05T09:00:00","slug":"silicone-extrusion-process","status":"publish","type":"post","link":"https:\/\/uplastech.com\/de\/silicone-extrusion-process\/","title":{"rendered":"Silicone Extrusion: Cold Feed, Hot Cure and the Tunnel Behind It"},"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-extrusion-process.jpg\" alt=\"Vulcanisation time against tunnel temperature, and line speed against profile cross-section\" width=\"1536\" height=\"909\"><figcaption>A tunnel at 250 \u00b0C cures in 40 seconds against 180 at 180, and a 40 mm\u00b2 section runs at a third of the speed of a 5 mm\u00b2 one.<\/figcaption><\/figure>\n<div class=\"toc\"><\/div>\n<h2 id=\"line\">What a silicone extrusion line looks like<\/h2>\n<p>A silicone extrusion line is shorter than a thermoplastic one and stranger. There is no long water tank, no vacuum calibration, and no haul-off pulling against a solidifying melt. Instead there is a cold-feed extruder, a shaping die, a hot-air tunnel several metres long, and a haul-off that has to pull a soft, uncured profile without stretching it.<\/p>\n<p>The material arrives as a soft, uncured compound with the consistency of putty. It is pushed through the die by a screw that is cooled, because silicone cures with heat and any heat in the barrel would start the reaction before the material reached the die. The die shapes the profile, and the profile then enters the tunnel, where hot air at 200 to 250 \u00b0C vulcanises it in flight.<\/p>\n<p>The result is a continuous process with no mould and no cycle time, which is why silicone extrusion is the cheapest way to make a long silicone profile. The constraints are different from thermoplastic extrusion: the profile is soft until it is cured, so it cannot be calibrated, and it distorts under its own weight in the tunnel.<\/p>\n<h2 id=\"cold-feed\">Cold feed and the screw<\/h2>\n<p>The screw runs cold, usually with water through the barrel, and its job is to convey and compress rather than to melt. A silicone extruder is therefore short: a length-to-diameter ratio of 10 to 15 rather than the 25 to 30 of a thermoplastic machine, because there is no melting to do and a long barrel would only add heat and residence time.<\/p>\n<p>The compression ratio is low, typically 1.2 to 1.5, because the material is already soft and a high compression would overheat it. The screw is often a simple single-flight design with a deep channel, and the die pressure is low compared with thermoplastic extrusion.<\/p>\n<p>Temperature control on the barrel is critical and it is a cooling function, not a heating one. The mechanical work of the screw generates heat, and if the barrel cannot remove it the compound starts to scorch or cure on the screw. A silicone extruder that is running hot will show it as lumps in the profile or as a rough surface, and the fix is more cooling water rather than a different screw.<\/p>\n<h2 id=\"cure\">The tunnel sets the line speed<\/h2>\n<p>Vulcanisation is a time-at-temperature reaction, and the tunnel is where the time comes from. The line speed and the tunnel length together set the residence time, and the tunnel temperature sets how much time is needed. At 180 \u00b0C a typical HCR compound needs about 180 seconds, at 200 it needs 110, at 220 it needs 70 and at 250 it needs 40.<\/p>\n<p>That is a factor of four and a half across the practical range, which means the tunnel temperature is the main lever on output. A 6 metre tunnel at 180 \u00b0C running at 2 metres a minute produces 120 metres an hour; the same tunnel at 250 \u00b0C runs at 9 metres a minute and produces 540.<\/p>\n<p>The limit is not the cure chemistry but the material. Above about 250 \u00b0C the surface of the profile can degrade before the core is cured, and a profile with a hard skin and a soft core is worse than one that is uniformly under-cured because it looks acceptable and fails later. The practical ceiling for most compounds is 230 to 250 \u00b0C.<\/p>\n<table>\n<thead>\n<tr>\n<th>Tunnel temperature, C<\/th>\n<th>Vulcanisation time, s<\/th>\n<th>Line speed for a 6 m tunnel, m\/min<\/th>\n<th>Output, m\/h<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>180<\/td>\n<td>180<\/td>\n<td>2.0<\/td>\n<td>120<\/td>\n<\/tr>\n<tr>\n<td>200<\/td>\n<td>110<\/td>\n<td>3.3<\/td>\n<td>198<\/td>\n<\/tr>\n<tr>\n<td>220<\/td>\n<td>70<\/td>\n<td>5.1<\/td>\n<td>306<\/td>\n<\/tr>\n<tr>\n<td>250<\/td>\n<td>40<\/td>\n<td>9.0<\/td>\n<td>540<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 1 \u2014 Tunnel temperature against cure time, line speed and output.<\/p>\n<h2 id=\"section\">Section size limits the line<\/h2>\n<p>A thin profile cures quickly and a thick one does not, for the same reason as in moulding: heat has to conduct to the centre. A 5 mm\u00b2 cross-section runs at about 30 metres a minute, a 10 mm\u00b2 at 22, a 20 mm\u00b2 at 15 and a 40 mm\u00b2 at 9.<\/p>\n<p>The relationship is not the square law of a moulded part, because the profile is passing through a tunnel rather than sitting in a hot mould, and because the surface is being heated continuously. But the trend is the same, and it means that a line running a thin profile and a line running a thick one are effectively different machines even if the hardware is identical.<\/p>\n<p>This is why silicone extrusion lines tend to specialise. A line tooled for 6 mm cord runs at 30 metres a minute and needs a short tunnel; a line tooled for a 40 mm\u00b2 window gasket runs at a third of that and needs a longer tunnel or a hotter one. Trying to run both on one line means running the thin profile far below its capability.<\/p>\n<h2 id=\"distortion\">Distortion: the problem thermoplastic extrusion does not have<\/h2>\n<p>A thermoplastic profile is calibrated and cooled while it is stiff enough to hold its shape. A silicone profile is soft when it leaves the die and stays soft until it is cured, so it sags, flattens and twists in the tunnel. There is no vacuum calibration to hold it, because the material would be pulled into the vacuum slots.<\/p>\n<p>The industry answers are support, speed and formulation. Support means a conveyor or a belt that carries the profile through the tunnel so it does not hang. Speed means getting it through the tunnel before it sags. Formulation means a compound with enough green strength to hold its shape, which is a property of the base polymer and the filler loading rather than something the line can change.<\/p>\n<ul>\n<li>Support the profile on a moving belt or a bed of rollers through the whole tunnel.<\/li>\n<li>Keep the die close to the tunnel entry, so there is minimal unsupported span.<\/li>\n<li>Use a profile design with a thick base or a flat back, so it can be supported on a stable face.<\/li>\n<li>Avoid thin, unsupported legs and long horizontal flanges, which will droop regardless.<\/li>\n<li>Cure fast at the entry to the tunnel, so the surface sets before the profile has time to sag.<\/li>\n<\/ul>\n<div class=\"callout\">A silicone profile is designed around how it will be supported in the tunnel, not just around how it will be used. A shape that is elegant in service can be impossible to cure.<\/div>\n<h2 id=\"die\">Die design and the die swell<\/h2>\n<p>A silicone die is simpler than a thermoplastic die because there is no melt to balance and no shrinkage to compensate for in the same way. But it has its own problem: die swell. The compound is compressed in the die and expands when it leaves, so the die opening is smaller than the profile and the amount of swell depends on the compound, the screw speed and the die land length.<\/p>\n<p>In practice the die is cut by trial. A first die is made at 80 to 90 percent of the target dimension, a profile is run, and the die is opened up in stages until the profile is right. That is why silicone tooling is cheap but slow to develop, and why a compound change mid-project means a die change.<\/p>\n<table>\n<thead>\n<tr>\n<th>Die feature<\/th>\n<th>Typical value<\/th>\n<th>Effect<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Land length<\/td>\n<td>3 to 8 times the wall thickness<\/td>\n<td>Longer land reduces swell but raises pressure and heat<\/td>\n<\/tr>\n<tr>\n<td>Die opening<\/td>\n<td>80 to 90 percent of the target<\/td>\n<td>Compensates for swell; adjusted by trial<\/td>\n<\/tr>\n<tr>\n<td>Entry angle<\/td>\n<td>30 to 60 degrees<\/td>\n<td>A sharp entry creates dead spots where material cures<\/td>\n<\/tr>\n<tr>\n<td>Die material<\/td>\n<td>Steel or aluminium<\/td>\n<td>Silicone is not abrasive, so aluminium is often enough<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 2 \u2014 The die features that decide whether a silicone profile runs.<\/p>\n<h2 id=\"where\">Where silicone extrusion wins<\/h2>\n<p>Silicone extrusion is chosen for continuous profiles where the temperature resistance, the flexibility or the electrical properties matter, and where the length makes moulding impossible. Cord, tube, window gaskets, oven seals, cable insulation, and the bulb seals on doors and hatches are the classic applications.<\/p>\n<p>It loses to moulding whenever the part is short, complex in three dimensions, or needs tight tolerances. A silicone extrusion can hold plus or minus 0.1 mm on a cross-section and a few millimetres on a cut length, which is fine for a gasket and not fine for a precision part.<\/p>\n<div class=\"faq\">\n<h3>Why does a silicone extruder run cold?<\/h3>\n<p>Because silicone cures with heat. The barrel is water cooled so the compound does not start to vulcanise before it reaches the die, and the screw conveys rather than melts.<\/p>\n<h3>How is silicone extrusion cured?<\/h3>\n<p>In a hot air tunnel, continuously, at 200 to 250 \u00b0C. The line speed and tunnel length set the residence time, and the temperature sets how much time is needed.<\/p>\n<h3>How fast can a silicone profile run?<\/h3>\n<p>About 30 metres a minute for a 5 mm2 section and 9 for a 40 mm2 one, at a tunnel temperature that gives enough cure. The section size is usually the limit.<\/p>\n<h3>Why do silicone profiles distort in the tunnel?<\/h3>\n<p>Because the material is still soft until it cures, and there is no vacuum calibration to hold it. Support belts, a short unsupported span and a fast cure at the tunnel entry are the answers.<\/p>\n<h3>What is die swell?<\/h3>\n<p>The expansion of the compound as it leaves the die. Silicone dies are cut at 80 to 90 percent of the target and opened up by trial, because the swell depends on the compound and the screw speed.<\/p>\n<h3>Can silicone profiles be made to tight tolerance?<\/h3>\n<p>To about plus or minus 0.1 mm on a cross-section. For tighter tolerances or complex three-dimensional shapes, moulding is the right process.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">Need a continuous silicone profile?<\/p>\n<p>Send the cross-section, the length and the service temperature. We will tell you whether extrusion or moulding is the right route, what the die has to look like, and how the profile will be supported in the tunnel.<\/p>\n<p><a class=\"btn\" href=\"https:\/\/uplastech.com\/de\/custom-injection-molding\/\">Talk to a silicone engineer<\/a>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/de\/silicone-tube-extrusion\/\">Silicone Tube Extrusion: Cold Feed, Hot Cure and Tight Tolerance<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/de\/silicone-rubber-manufacturing-processes\/\">Silicone Rubber Manufacturing: LSR, HCR and the Five Processes<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/de\/hcr-solid-silicone-rubber\/\">HCR Solid Silicone Rubber: Mixing, Moulding and the Strength It Buys<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/de\/cable-wire-insulation-extrusion\/\">Cable and Wire Insulation Extrusion: Crosshead, Preheating and Concentricity<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/de\/extrusion-line-start-up-shutdown\/\">Extrusion Line Start-Up and Shutdown: The Sequence That Saves Scrap<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>A silicone extrusion line is a cold-feed extruder, a hot-air tunnel and a lot of patience about the section. Vulcanisation falls from 180 seconds at 180 \u00b0C to 40 at 250, and the line speed follows the mass.<\/p>","protected":false},"author":1,"featured_media":7939,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_seopress_titles_title":"Silicone Extrusion: Cold Feed and Hot Cure","_seopress_titles_desc":"Silicone extrusion explained: cold feed versus hot feed, the hot air tunnel and continuous vulcanisation, cure time against tunnel temperature, line speed again","_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-7940","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\/de\/wp-json\/wp\/v2\/posts\/7940","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/comments?post=7940"}],"version-history":[{"count":0,"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/posts\/7940\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/media\/7939"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/media?parent=7940"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/categories?post=7940"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/tags?post=7940"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}