{"id":8912,"date":"2026-09-13T09:00:00","date_gmt":"2026-09-13T08:00:00","guid":{"rendered":"https:\/\/uplastech.com\/extrusion-residual-stress\/"},"modified":"2026-09-13T09:00:00","modified_gmt":"2026-09-13T08:00:00","slug":"extrusion-residual-stress","status":"publish","type":"post","link":"https:\/\/uplastech.com\/ru\/extrusion-residual-stress\/","title":{"rendered":"Residual Stress in Extruded Profiles: The Defect You Cannot See"},"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\/11\/extrusion-residual-stress.jpg\" alt=\"Two cut lengths of grey PVC window profile on a granite surface plate with a steel rule, a feeler gauge under one end and a dial indicator\" width=\"1536\" height=\"909\"><figcaption>Both sections came off the same line. The gap under the end is stress, released.<\/figcaption><\/figure>\n<div class=\"toc\"><\/div>\n<h2 id=\"state\">Stress is a state, not a defect<\/h2>\n<p>A profile that leaves the tank straight and in tolerance has passed every test the line can apply, and it can still be full of stress. Stress is not a dimension. It is a stored elastic energy that will do work later, when something gives it a reason.<\/p>\n<p>There are two kinds in an extrusion. Thermal stress comes from the outside cooling before the inside, so the skin sets while the core is still soft and the core then shrinks against it. Orientation stress comes from draw-down: the polymer chains are stretched in the haul-off direction and frozen there.<\/p>\n<p>Both are invisible at the saw and both are reversible, which is the awkward part. A stressed profile is in equilibrium only because nothing has disturbed it. Cut it, machine it, warm it or expose it to a solvent and the equilibrium goes, and the part moves.<\/p>\n<p>That is why the complaint usually arrives from the customer rather than from the line. The line measures dimensions. The customer machines a slot, and the slot closes.<\/p>\n<h2 id=\"cooling\">The cooling rate sets the number<\/h2>\n<p>The dominant variable is how fast the section goes through the glass transition. Cool it slowly and the skin and the core arrive at rigidity together, so the differential shrinkage is small. Cool it fast and the skin is rigid while the core is still mobile, and the core pulls the skin into compression when it finally sets.<\/p>\n<p>The chart on the left shows the shape of it: stress against cooling rate, roughly linear over the range a water trough actually runs at. Doubling the cooling rate does not double the stress, but it does not halve it either, and the difference between a trough at 20 degrees and one at 8 degrees is a different product.<\/p>\n<p>The right hand panel is the practical part: how much each remedy actually removes. Annealing is far and away the largest, and it is the one most shops do not have. The others help and none of them is a substitute.<\/p>\n<figure>\n<img decoding=\"async\" src=\"https:\/\/uplastech.com\/wp-content\/uploads\/2026\/11\/extrusion-residual-stress-chart.jpg\" alt=\"Residual stress against cooling rate through the tank, and a bar chart of how much stress each remedy removes\" width=\"1536\" height=\"909\"><figcaption>Cooling rate sets the number; annealing is the only remedy that removes most of it.<\/figcaption><\/figure>\n<h2 id=\"measure\">Cutting it up is the measurement<\/h2>\n<p>There is no gauge that reads residual stress on a finished profile. The measurement is destructive and it is simple: cut a length, measure it, remove material from one face, and measure again. What the part does when you take material away is the stress that was there.<\/p>\n<p>The commonest version is the slitting test. A length of profile is slit along one wall with a thin blade and the gap that opens is measured with a feeler gauge or a travelling microscope. A gap that opens means the wall was in tension on the outside and compression on the inside, and the size of the gap scales with the stress.<\/p>\n<p>The second version is layer removal. Milling away a known depth from one face and measuring the resulting bow gives a stress profile through the wall, not just a number. It is a laboratory job and it is worth doing once per die rather than per batch.<\/p>\n<p>A third version needs no instrument at all: put a length in an oven at 10 degrees below its service temperature for an hour and measure it cold. Anything that moves was stressed. It is a pass or fail rather than a value, and for a shop without a lab it is the most useful test there is.<\/p>\n<table>\n<thead>\n<tr>\n<th>\u041c\u0435\u0442\u043e\u0434<\/th>\n<th>What it gives you<\/th>\n<th>Effort<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Slitting one wall<\/td>\n<td>A gap, and a tension or compression verdict<\/td>\n<td>Minutes, a blade and a gauge<\/td>\n<\/tr>\n<tr>\n<td>Layer removal<\/td>\n<td>A stress profile through the wall<\/td>\n<td>Laboratory, once per die<\/td>\n<\/tr>\n<tr>\n<td>Free anneal and remeasure<\/td>\n<td>Pass or fail against a limit<\/td>\n<td>An oven and an hour<\/td>\n<\/tr>\n<tr>\n<td>Machining a slot<\/td>\n<td>How much the part moves in service<\/td>\n<td>Minutes, and it mirrors the complaint<\/td>\n<\/tr>\n<tr>\n<td>Solvent wipe<\/td>\n<td>Whether the surface is under strain<\/td>\n<td>Seconds, qualitative<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 1 \u2014 Five ways to find out, in order of how much they cost.<\/p>\n<h2 id=\"anneal\">Annealing, and why nobody does it<\/h2>\n<p>Annealing is holding the profile at a temperature where the polymer can relax, then cooling it slowly enough that it does not re-introduce the stress it just lost. For PVC that is around 70 to 80 degrees Celsius, well below the softening point, for a time that depends on wall thickness.<\/p>\n<p>The cooling half is the part that gets skipped. A profile annealed for two hours and then quenched in a cold trough has the same stress it started with, because the quench puts it back. The oven has to be followed by a controlled ramp down, which means either a long tunnel or a batch oven with a programmer.<\/p>\n<p>The cost is the reason it is rare. An oven is capital, it takes floor space, it adds a handling step and it lengthens the lead time by a day. Against that, it converts a class of customer complaints into nothing, and the complaints are the expensive part.<\/p>\n<p>Where annealing is genuinely hard to justify, the alternative is to reduce the stress at source: slower cooling in the tank, less draw-down, and a die that does not force the polymer through a sharp expansion. That is a line change rather than a process addition, and it is often cheaper than an oven.<\/p>\n<table>\n<thead>\n<tr>\n<th>\u041c\u0430\u0442\u0435\u0440\u0438\u0430\u043b<\/th>\n<th>Annealing temperature<\/th>\n<th>Soak<\/th>\n<th>Ramp down<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Rigid PVC<\/td>\n<td>70 to 80 C<\/td>\n<td>1 hour per 3 mm<\/td>\n<td>Under 10 C per hour<\/td>\n<\/tr>\n<tr>\n<td>uPVC foam<\/td>\n<td>60 to 70 C<\/td>\n<td>1 hour per 5 mm<\/td>\n<td>Under 8 C per hour<\/td>\n<\/tr>\n<tr>\n<td>PP and PE<\/td>\n<td>90 to 100 C<\/td>\n<td>1 hour per 4 mm<\/td>\n<td>Under 10 C per hour<\/td>\n<\/tr>\n<tr>\n<td>ABS<\/td>\n<td>70 to 80 C<\/td>\n<td>1 hour per 3 mm<\/td>\n<td>Under 10 C per hour<\/td>\n<\/tr>\n<tr>\n<td>\u041f\u041a<\/td>\n<td>120 to 125 C<\/td>\n<td>1 hour per 3 mm<\/td>\n<td>Under 5 C per hour<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 2 \u2014 Starting schedules, to be confirmed on the actual compound.<\/p>\n<h2 id=\"downstream\">What it does after it leaves you<\/h2>\n<p>Machining is the classic trigger. A window profile that is milled for a drainage slot releases the stress in the wall around the slot and the profile bows. The customer sees a bowed window and calls the fabricator, and the fabricator calls the extruder, and by then the evidence has been cut up.<\/p>\n<p>Solvent welding is the second. A solvent cement softens the surface, the stressed layer relaxes, and the joint either opens or pulls the assembly out of square. A stressed pipe fitting that is solvent-welded in cold weather is a reliable source of leaks that nobody can explain.<\/p>\n<p>Heat is the third. A profile stored in a container in summer, or a dark profile in direct sun, reaches a temperature where the stress relaxes on its own. What comes out of the container is not what went in, and the distortion is blamed on the lorry.<\/p>\n<p>The fourth is environmental stress cracking, which is stress plus a chemical that would be harmless on its own. A stressed profile in contact with a detergent, a release agent or a solvent develops cracks that a stress-free one does not. This is the failure mode that turns a dimensional argument into a warranty claim.<\/p>\n<h2 id=\"specify\">Specify the relief, not the stress<\/h2>\n<p>No customer asks for a stress value, because there is no standard test to quote one against. What a customer can ask for is behaviour: a length that does not move more than a stated amount after a stated anneal, or after a stated machining operation.<\/p>\n<p>That is a specification both sides can check. Write it as a test: a 300 mm length, annealed at 75 degrees for one hour, cooled at 10 degrees per hour, measured on a surface plate, bow not to exceed 1.5 mm. It is arbitrary, it is repeatable, and it is enforceable.<\/p>\n<p>The second thing worth writing is the cooling condition. A trough temperature and a vacuum calibration setting are process parameters that determine the product, and leaving them out of the specification means the next die trial can quietly change them.<\/p>\n<p>The third is a handling rule for the customer. If a profile must be machined, tell them to machine a test piece first and measure it. That single sentence prevents most of the arguments, because it moves the discovery from their production line to their sample bench.<\/p>\n<div class=\"faq\">\n<h3>What causes residual stress in an extruded profile?<\/h3>\n<p>Two things. Thermal stress comes from the skin cooling and setting before the core, so the core shrinks against a rigid skin. Orientation stress comes from draw-down, which stretches the polymer chains and freezes them in the haul-off direction.<\/p>\n<h3>How do I measure residual stress in a profile?<\/h3>\n<p>Destructively. Slit one wall and measure the gap that opens, or mill material off one face and measure the bow. A free anneal followed by a remeasure gives a pass or fail without any instrument beyond an oven.<\/p>\n<h3>Does annealing remove all the stress?<\/h3>\n<p>Most of it, if the cooling ramp is controlled. An anneal followed by a cold quench puts the stress back, which is why the ramp down matters as much as the soak.<\/p>\n<h3>Why does the profile bow after the customer machines it?<\/h3>\n<p>Because machining removes material that was carrying part of the stress balance. The remaining wall relaxes and the section moves. The bow was always there, waiting for the cut.<\/p>\n<h3>Can I reduce stress without an annealing oven?<\/h3>\n<p>Yes, at source. Slower cooling in the trough, less draw-down and a gentler die transition all reduce the frozen-in stress. It is a line change rather than an added process, and it is often cheaper.<\/p>\n<h3>At what temperature does a PVC profile anneal?<\/h3>\n<p>Around 70 to 80 degrees Celsius, which is well below the softening point. The soak is roughly an hour per three millimetres of wall, followed by a ramp down of under ten degrees per hour.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">Profiles that stay where you put them<\/p>\n<p>Tell us the section, the wall and what the customer does to it afterwards. We will tell you where the stress will come from and whether the answer is the trough, the die or an oven.<\/p>\n<p><a class=\"btn\" href=\"https:\/\/uplastech.com\/ru\/%d0%bf%d0%b2%d1%85-%d0%bf%d1%80%d0%be%d1%84%d0%b8%d0%bb%d0%b8\/\">Discuss a profile project<\/a>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/ru\/profile-straightness-bow\/\">Profile Straightness and Bow<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/ru\/extrusion-water-bath-cooling\/\">Water Bath Cooling for Extrusion<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/ru\/extrusion-dimensional-drift\/\">Dimensional Drift in Extrusion<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/ru\/extrusion-die-swell\/\">Die Swell and What It Tells You<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/ru\/extrusion-brittleness\/\">Brittleness in Extruded Profiles<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>An extruded profile can be straight, in tolerance and full of stress. It shows up when somebody machines it, solvent-welds it or leaves it in the sun, which is usually after it has been shipped.<\/p>","protected":false},"author":1,"featured_media":8910,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[17],"tags":[],"class_list":["post-8912","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-plastic-extrusion-process"],"meta_box":{"post-to-quiz_to":[]},"_links":{"self":[{"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/posts\/8912","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/comments?post=8912"}],"version-history":[{"count":0,"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/posts\/8912\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/media\/8910"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/media?parent=8912"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/categories?post=8912"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/ru\/wp-json\/wp\/v2\/tags?post=8912"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}