{"id":7788,"date":"2025-10-03T09:00:00","date_gmt":"2025-10-03T08:00:00","guid":{"rendered":"https:\/\/uplastech.com\/rigid-pvc-injection-molding\/"},"modified":"2026-10-28T09:22:17","modified_gmt":"2026-10-28T09:22:17","slug":"rigid-pvc-injection-molding","status":"publish","type":"post","link":"https:\/\/uplastech.com\/tr\/rigid-pvc-injection-molding\/","title":{"rendered":"Rigid PVC Injection Molding: Corrosion, Residence Time and a Twenty-Degree Window"},"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\/rigid-pvc-injection-molding.jpg\" alt=\"PVC injection moulding working window and colour shift against residence time\" width=\"1536\" height=\"909\"><figcaption>Thirty minutes at 200 \u00b0C and the material is already brown. PVC does not tolerate a stopped machine.<\/figcaption><\/figure>\n<div class=\"toc\"><\/div>\n<h2 id=\"why\">Why anyone moulds PVC at all<\/h2>\n<p>PVC is cheap, flame retardant by nature, chemically resistant and dimensionally stable. Those four properties make it the default material for pipe fittings, electrical conduit boxes, cable glands, window hardware and a long list of industrial parts.<\/p>\n<p>It is also the most difficult commodity resin to injection mould. The processing window is 20 \u00b0C wide, the material releases hydrogen chloride when it overheats, that acid attacks the machine and the tool, and the compound contains plasticisers and stabilisers that migrate and plate out.<\/p>\n<p>A shop that moulds PVC successfully has made specific investments: corrosion-resistant screw and barrel, a tool with stainless or chrome surfaces, good extraction, and a discipline about residence time that other materials do not require.<\/p>\n<table>\n<thead>\n<tr>\n<th>Compound<\/th>\n<th>Plasticiser<\/th>\n<th>Typical use<\/th>\n<th>Moulding note<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Rigid (U-PVC)<\/td>\n<td>0 \u2013 5 phr<\/td>\n<td>Fittings, conduit, boxes<\/td>\n<td>Narrowest window, most corrosive<\/td>\n<\/tr>\n<tr>\n<td>Semi-rigid<\/td>\n<td>10 \u2013 25 phr<\/td>\n<td>Profiles, housings<\/td>\n<td>Slightly wider, still aggressive<\/td>\n<\/tr>\n<tr>\n<td>Esnek<\/td>\n<td>30 \u2013 70 phr<\/td>\n<td>Cable, seals, boots<\/td>\n<td>Plasticiser plate-out risk<\/td>\n<\/tr>\n<tr>\n<td>Chlorinated (CPVC)<\/td>\n<td>0 \u2013 5 phr<\/td>\n<td>Hot water fittings<\/td>\n<td>Runs 15 \u2013 20 \u00b0C hotter<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 1 \u2014 PVC compound types. phr is parts per hundred of resin; the plasticiser content decides both flexibility and how the material behaves in the barrel.<\/p>\n<h2 id=\"thermal\">The thermal problem<\/h2>\n<p>PVC melts at 160 to 180 \u00b0C and degrades above about 210 \u00b0C. That leaves a 30 \u00b0C band in theory, and 20 \u00b0C in practice once you account for the fact that shear heating adds to the barrel temperature and the melt is hotter than the set point.<\/p>\n<p>Degradation is autocatalytic. A chain breaks and releases HCl; the HCl catalyses further breakdown. The reaction accelerates, and the visible signs follow in order: yellow, then brown, then black. By the time you see black, the barrel is contaminated and the next three hours are cleaning.<\/p>\n<p>The stabiliser package exists to interrupt this. Calcium-zinc and organotin stabilisers scavenge the HCl as it forms. They are consumed in the process, which is why residence time matters: a compound held at temperature for 30 minutes has used up more stabiliser than one held for 5.<\/p>\n<p>This is why PVC moulding has a rule that no other material has: the machine must not be left sitting hot with PVC in the barrel. A lunch break with the barrel at 195 \u00b0C is enough to produce a degraded plug at the screw tip that will appear in the first parts after the break.<\/p>\n<h2 id=\"corrosion\">Corrosion: what it attacks and what to do<\/h2>\n<p>Hydrogen chloride in the presence of moisture forms hydrochloric acid, and hydrochloric acid attacks carbon steel, brass and most aluminium alloys. A standard nitrided screw and barrel will show pitting within months of running rigid PVC.<\/p>\n<p>The correct specification is a bimetallic barrel with a corrosion-resistant liner, a screw with a tungsten carbide or Colmonoy hard facing, and a non-return valve in a corrosion-resistant grade. This is not a premium option; it is the minimum for a machine that will run PVC regularly.<\/p>\n<p>Tooling is the same story. Cavities and cores in standard P20 will corrode and lose their polish. Through-hardened stainless, or a hard chrome plate over a suitable base, is the standard. Aluminium tools are acceptable only for prototypes and only with a coating.<\/p>\n<p>Extraction is part of the equipment, not a building afterthought. HCl vapour at the nozzle and at the mould opening must be extracted at source, or it will corrode the machine frame, the electrical panels and everything else in the bay.<\/p>\n<div class=\"callout\">If your machine has run PVC and is now running another material, purge thoroughly and inspect the screw. Residual PVC in a hot barrel will degrade and contaminate the next material with black specks.<\/div>\n<h2 id=\"residence\">Residence time: the limit that is not on the datasheet<\/h2>\n<p>The practical limit for rigid PVC at 195 \u00b0C is about 10 minutes of residence. Beyond that the stabiliser is depleted and the colour starts to shift. At 200 \u00b0C the limit is closer to 6 minutes; at 185 \u00b0C it can be 20.<\/p>\n<p>Residence time is calculated from the shot weight and the barrel capacity, not from the cycle time alone. A 20-gram part on a machine with a 500-gram shot capacity has 25 shots of material in the barrel; at a 30-second cycle that is over 12 minutes of residence before anything has even happened.<\/p>\n<p>This is why PVC parts are moulded on small machines. Oversizing the press for tonnage reasons is the most common cause of colour problems in PVC, and it is invisible on a setting sheet.<\/p>\n<table>\n<thead>\n<tr>\n<th>Erime s\u0131cakl\u0131\u011f\u0131<\/th>\n<th>Maximum residence<\/th>\n<th>Practical consequence<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>180 \u00b0C<\/td>\n<td>25 min<\/td>\n<td>Forgiving, but fusion may be incomplete<\/td>\n<\/tr>\n<tr>\n<td>185 \u00b0C<\/td>\n<td>18 min<\/td>\n<td>The lower end of normal production<\/td>\n<\/tr>\n<tr>\n<td>190 \u00b0C<\/td>\n<td>12 min<\/td>\n<td>Normal operating point<\/td>\n<\/tr>\n<tr>\n<td>195 \u00b0C<\/td>\n<td>8 min<\/td>\n<td>Upper end, watch the colour<\/td>\n<\/tr>\n<tr>\n<td>200 \u00b0C<\/td>\n<td>5 min<\/td>\n<td>Only for fast cycles on small shots<\/td>\n<\/tr>\n<tr>\n<td>205 \u00b0C<\/td>\n<td>3 min<\/td>\n<td>Marginal; degradation likely<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 2 \u2014 Residence time limits for rigid PVC. The number falls faster than the temperature rises, which is why the window is effectively 20 \u00b0C wide.<\/p>\n<h2 id=\"settings\">Settings that work<\/h2>\n<p>Barrel profile for rigid PVC is flat or slightly rising, 175 to 190 \u00b0C, with the nozzle at the low end. A hot nozzle is the most common cause of drool and of degradation at the gate.<\/p>\n<p>Injection speed should be moderate. PVC is shear-sensitive and a fast shot through a small gate generates enough shear heating to push the melt past the degradation threshold locally. The result is a brown streak that follows the flow from the gate.<\/p>\n<p>Mould temperature is 30 to 50 \u00b0C. Colder gives a better surface but more frozen stress; hotter gives better fusion and a longer cycle. For fittings that must pass a pressure test, hotter is safer.<\/p>\n<p>Packing pressure should be modest \u2014 40 to 60 percent of injection \u2014 and packing time short. PVC is nearly amorphous and does not shrink much, so there is little to compensate and over-packing builds stress at the gate.<\/p>\n<table>\n<thead>\n<tr>\n<th>Parametre<\/th>\n<th>Value<\/th>\n<th>Note<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Barrel temperatures<\/td>\n<td>175 \u2013 190 \u00b0C<\/td>\n<td>Flat profile, nozzle at the low end<\/td>\n<\/tr>\n<tr>\n<td>Mould temperature<\/td>\n<td>30 \u2013 50 \u00b0C<\/td>\n<td>Hotter for pressure-tight fittings<\/td>\n<\/tr>\n<tr>\n<td>Injection pressure<\/td>\n<td>60 \u2013 90 MPa<\/td>\n<td>Orta d\u00fczeyde<\/td>\n<\/tr>\n<tr>\n<td>Injection speed<\/td>\n<td>Orta d\u00fczeyde<\/td>\n<td>Fast shots cause local degradation<\/td>\n<\/tr>\n<tr>\n<td>Packing pressure<\/td>\n<td>40 \u2013 60%<\/td>\n<td>Low; PVC shrinks little<\/td>\n<\/tr>\n<tr>\n<td>Back pressure<\/td>\n<td>Low, 2 \u2013 5 bar<\/td>\n<td>High back pressure adds heat<\/td>\n<\/tr>\n<tr>\n<td>Vida h\u0131z\u0131<\/td>\n<td>D\u00fc\u015f\u00fck<\/td>\n<td>Shear heating is the enemy<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 3 \u2014 Rigid PVC injection moulding settings. Every parameter here is chosen to minimise shear heating.<\/p>\n<h2 id=\"defects\">Defects<\/h2>\n<table>\n<thead>\n<tr>\n<th>Kusur<\/th>\n<th>Neden<\/th>\n<th>First check<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Brown streaks from the gate<\/td>\n<td>Local shear degradation<\/td>\n<td>Slow the injection, enlarge the gate<\/td>\n<\/tr>\n<tr>\n<td>Yellow overall<\/td>\n<td>Residence time or barrel temperature<\/td>\n<td>Shot size against barrel capacity<\/td>\n<\/tr>\n<tr>\n<td>Black specks<\/td>\n<td>Carbon from a previous degraded run<\/td>\n<td>Purge and clean the screw<\/td>\n<\/tr>\n<tr>\n<td>Dull or matte surface<\/td>\n<td>Cold mould or incomplete fusion<\/td>\n<td>Raise mould temperature<\/td>\n<\/tr>\n<tr>\n<td>Weak weld lines<\/td>\n<td>Low mould temperature, poor venting<\/td>\n<td>Mould temperature, then venting<\/td>\n<\/tr>\n<tr>\n<td>Plate-out on the mould<\/td>\n<td>Plasticiser or stabiliser migration<\/td>\n<td>Clean the tool, review the compound<\/td>\n<\/tr>\n<tr>\n<td>Brittle parts<\/td>\n<td>Under-fusion from a cold barrel<\/td>\n<td>Raise the barrel profile 5 \u00b0C<\/td>\n<\/tr>\n<tr>\n<td>Corrosion marks on the part<\/td>\n<td>Tool corrosion<\/td>\n<td>Inspect the cavity surface<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 4 \u2014 PVC injection moulding defects. Three of the eight are degradation, which is the defining risk of the material.<\/p>\n<div class=\"faq\">\n<h3>What is the processing temperature for rigid PVC injection moulding?<\/h3>\n<p>185 to 205 \u00b0C melt temperature, with 190 \u00b0C the normal operating point. Below 185 the fusion may be incomplete; above 205 degradation starts and cannot be reversed.<\/p>\n<h3>Why does PVC corrode injection moulding machines?<\/h3>\n<p>Degradation releases hydrogen chloride, which forms hydrochloric acid with moisture. It attacks carbon steel, brass and aluminium. Bimetallic barrels and corrosion-resistant screws are the minimum specification.<\/p>\n<h3>How long can PVC sit in a hot barrel?<\/h3>\n<p>About 10 minutes at 195 \u00b0C, less at higher temperature. This is why PVC parts are run on small machines \u2014 the shot size relative to barrel capacity determines residence time, and oversizing the press causes colour problems.<\/p>\n<h3>Can I run PVC in a machine that also runs other plastics?<\/h3>\n<p>Yes, with a thorough purge and a screw inspection. Residual PVC in a hot barrel degrades and contaminates the next material with black specks and corrosion.<\/p>\n<h3>What mould temperature should PVC use?<\/h3>\n<p>30 to 50 \u00b0C. Higher gives better fusion and pressure tightness, which matters for pipe fittings; lower gives a better surface finish.<\/p>\n<h3>Why does my PVC part have brown streaks from the gate?<\/h3>\n<p>Local shear degradation. The injection speed is too high or the gate too small, and the melt overheats as it passes through. Slow the shot and enlarge the gate.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">Moulding rigid PVC and fighting colour or corrosion?<\/p>\n<p>Tell us the part, the compound and the machine you have. We will tell you whether the shot size is right, what the tool needs, and where the degradation is coming from.<\/p>\n<p><a class=\"btn\" href=\"https:\/\/uplastech.com\/tr\/custom-injection-molding\/\">Talk to an injection moulding engineer<\/a>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/tr\/pvc-profile-extrusion\/\">PVC Profile Extrusion: Formulation, Die and Calibration<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/tr\/pvc-thermoforming-guide\/\">PVC Thermoforming Guide<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/tr\/pvc-dry-blend-mixing\/\">PVC Dry Blend Mixing<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/tr\/injection-molding-material-selection\/\">Injection Molding Material Selection<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/tr\/injection-molding-defects\/\">Injection Molding Defects: Causes and Fixes<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>PVC is the only commodity resin that will destroy your machine if you get it wrong. The window is 185 to 205 \u00b0C, and the failure mode is hydrochloric acid.<\/p>","protected":false},"author":1,"featured_media":7787,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_seopress_titles_title":"Rigid PVC Injection Molding: Temperature Window and Corrosio","_seopress_titles_desc":"PVC injection moulding guide: 185-205 C melt window, HCl degradation, corrosion-resistant tooling, residence time limits, formulation and the defects each cause","_seopress_robots_index":"","_seopress_robots_follow":"","_seopress_robots_imageindex":"","_seopress_robots_snippet":"","_seopress_robots_primary_cat":"35","_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":[35],"tags":[],"class_list":["post-7788","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-injection-molding"],"meta_box":{"post-to-quiz_to":[]},"_links":{"self":[{"href":"https:\/\/uplastech.com\/tr\/wp-json\/wp\/v2\/posts\/7788","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/uplastech.com\/tr\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/uplastech.com\/tr\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/uplastech.com\/tr\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/uplastech.com\/tr\/wp-json\/wp\/v2\/comments?post=7788"}],"version-history":[{"count":1,"href":"https:\/\/uplastech.com\/tr\/wp-json\/wp\/v2\/posts\/7788\/revisions"}],"predecessor-version":[{"id":7858,"href":"https:\/\/uplastech.com\/tr\/wp-json\/wp\/v2\/posts\/7788\/revisions\/7858"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/uplastech.com\/tr\/wp-json\/wp\/v2\/media\/7787"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/tr\/wp-json\/wp\/v2\/media?parent=7788"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/tr\/wp-json\/wp\/v2\/categories?post=7788"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/tr\/wp-json\/wp\/v2\/tags?post=7788"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}