{"id":8924,"date":"2026-09-17T09:00:00","date_gmt":"2026-09-17T08:00:00","guid":{"rendered":"https:\/\/uplastech.com\/extrusion-inline-gauging\/"},"modified":"2026-09-17T09:00:00","modified_gmt":"2026-09-17T08:00:00","slug":"extrusion-inline-gauging","status":"publish","type":"post","link":"https:\/\/uplastech.com\/es\/extrusion-inline-gauging\/","title":{"rendered":"Inline Gauging on an Extrusion Line: What It Catches and What It Misses"},"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-inline-gauging.jpg\" alt=\"A white PVC profile running out of a cooling tank through a laser diameter gauge head on an aluminium frame, with a digital caliper on a bench\" width=\"1536\" height=\"909\"><figcaption>The gauge measures one section, one metre at a time, forever.<\/figcaption><\/figure>\n<div class=\"toc\"><\/div>\n<h2 id=\"delay\">Sampling is a delay, not a control<\/h2>\n<p>An offline check every twenty minutes is not a control. It is a measurement of what the line was doing twenty minutes ago, taken by a person who then has to walk back and tell somebody. Between the drift starting and the correction, the line keeps running and the product keeps moving.<\/p>\n<p>The chart on the left puts a number on it. At six metres a minute, with five minutes for a person to notice, walk, measure, agree and adjust, a one minute sampling interval costs about fifteen metres of out-of-tolerance product per event. A thirty minute interval costs a hundred.<\/p>\n<p>Whether that matters depends on what the profile is worth and what the customer does with it. Fifteen metres of window profile is a nuisance. A hundred metres of a medical tube is a batch. The interval should be chosen from that number rather than from habit.<\/p>\n<figure>\n<img decoding=\"async\" src=\"https:\/\/uplastech.com\/wp-content\/uploads\/2026\/11\/extrusion-inline-gauging-chart.jpg\" alt=\"Metres of out-of-tolerance product produced before detection against sampling interval, and a bar chart of where measurement uncertainty comes from\" width=\"1536\" height=\"909\"><figcaption>The interval sets the scrap per event, and the reaction time is half of it.<\/figcaption><\/figure>\n<h2 id=\"what\">What a gauge actually measures<\/h2>\n<p>A laser diameter gauge measures a silhouette. Two axes of shadow give a diameter and an ovality, and a three-axis head gives a shape. It is fast, non-contact and it sees the outside only, which is fine for a pipe and insufficient for a profile with a wall.<\/p>\n<p>Wall thickness needs something that can see inside: ultrasonic heads on a rotating ring, X-ray, or a computed relationship from weight per metre. Ultrasonic is the usual answer for pipe and tube; weight per metre is the usual answer for a profile where the density is known and stable.<\/p>\n<p>Weight per metre is underrated. It is a gravimetric measurement, it integrates the whole cross-section rather than one line, and it catches the fault that dimension gauges miss: a wall that is thin everywhere in a way the outer silhouette does not show. It is also the measurement that maps directly to material cost.<\/p>\n<p>What none of them measure is the material. Gel, unmelt, dispersion, moisture and stress are invisible to a dimension gauge, and they are the defects that generate the complaints a gauge cannot prevent.<\/p>\n<table>\n<thead>\n<tr>\n<th>Gauge<\/th>\n<th>Measures<\/th>\n<th>Blind to<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Laser diameter, 2 axis<\/td>\n<td>Diameter and ovality<\/td>\n<td>Wall, material, internal voids<\/td>\n<\/tr>\n<tr>\n<td>Laser, 3 axis or scanning<\/td>\n<td>Profile shape at one section<\/td>\n<td>Wall, and anything along the length<\/td>\n<\/tr>\n<tr>\n<td>Ultrasonic ring<\/td>\n<td>Wall thickness around the section<\/td>\n<td>Surface defects, material<\/td>\n<\/tr>\n<tr>\n<td>X-ray<\/td>\n<td>Wall and internal voids<\/td>\n<td>Colour, surface, cost<\/td>\n<\/tr>\n<tr>\n<td>Gravimetric, weight per metre<\/td>\n<td>Average cross-section<\/td>\n<td>Where on the section the error is<\/td>\n<\/tr>\n<tr>\n<td>Vision, surface<\/td>\n<td>Scratches, die lines, colour<\/td>\n<td>Everything dimensional<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 1 \u2014 What each gauge can see, and what it cannot.<\/p>\n<h2 id=\"budget\">Where the measurement error comes from<\/h2>\n<p>A gauge that reads to a hundredth of a millimetre is not measuring to a hundredth of a millimetre. The right hand panel is an uncertainty budget, and the largest single term is the instrument itself at 45 percent, which is the only one people think about.<\/p>\n<p>Temperature is 25 percent and it is the term that makes a gauge lie in a way nobody notices. A profile measured at 40 degrees is bigger than the same profile at 20, and the coefficient for PVC is around 0.00007 per degree, which is 0.7 mm on a metre over twenty degrees. On a tight tolerance that is the whole allowance.<\/p>\n<p>Fixturing and location is 18 percent. A gauge that measures a profile that is not located the same way each time is measuring the fixture as well as the part. On a moving line this is the term that varies most, because the profile moves.<\/p>\n<p>Operator technique is 12 percent, and it exists mainly on the offline checks that the gauge is supposed to replace. The way to reduce it is not more training, it is fewer manual measurements.<\/p>\n<h2 id=\"mount\">Where to put it<\/h2>\n<p>The gauge belongs where the profile is stable, cool and under the same tension it will be measured at. That usually means after the cooling tank and before the haul-off, or immediately after the haul-off and before the saw.<\/p>\n<p>Before the tank is wrong for a different reason: the profile is hot, soft and still changing. A gauge there measures a shape that will not exist in ten seconds. It is useful as a die diagnostic and useless as a production control.<\/p>\n<p>After the saw is the other common mistake. Measuring the finished length is measuring the product, which sounds right and gives you a number that is already history by the time the saw has cut it. The saw is the last place you can still do something about it, not the first place to look.<\/p>\n<p>The second placement question is access. A gauge mounted where a technician cannot reach it will be cleaned weekly and calibrated annually, and it will be wrong in between. If it cannot be reached in thirty seconds it will not be maintained.<\/p>\n<table>\n<thead>\n<tr>\n<th>Position<\/th>\n<th>What the number means<\/th>\n<th>Main error introduced<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Before the tank<\/td>\n<td>Die output, still hot<\/td>\n<td>Thermal contraction not yet applied<\/td>\n<\/tr>\n<tr>\n<td>After the tank<\/td>\n<td>The frozen shape<\/td>\n<td>Residual water, surface temperature<\/td>\n<\/tr>\n<tr>\n<td>After the haul-off<\/td>\n<td>Shape under line tension<\/td>\n<td>Tension varies with the coil<\/td>\n<\/tr>\n<tr>\n<td>Before the saw<\/td>\n<td>The shape about to be cut<\/td>\n<td>Almost none, best position<\/td>\n<\/tr>\n<tr>\n<td>After the saw<\/td>\n<td>The shape already cut<\/td>\n<td>It is too late to act on it<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 2 \u2014 Where a gauge can go, and what each position costs in meaning.<\/p>\n<h2 id=\"loop\">Closing the loop, or not<\/h2>\n<p>A gauge that displays a number is a monitoring device. A gauge that adjusts the haul-off or the die bolts is a control loop. The difference is not the gauge, it is the actuator, and most lines have the first and not the second.<\/p>\n<p>Closed loop on diameter is common and it works: the gauge drives the haul-off or the melt pump and holds a dimension. Closed loop on wall thickness is harder, because the actuator is a die bolt or a screw on the die and the response is slow and interacts with every other wall.<\/p>\n<p>The middle option is worth more than it sounds. An advisory system that alarms, logs and shows a trend gives the operator the one thing a manual check cannot: the direction and rate of a drift. A drift caught at 0.02 mm per minute is a correction. The same drift caught at the tolerance limit is a scrap coil.<\/p>\n<p>Whatever the loop, record the data. A gauge with no historian answers the question of the moment and none of the questions afterwards, and the questions afterwards are the ones that decide whether the customer's complaint was a line fault or a material one.<\/p>\n<h2 id=\"blind\">What inline gauging cannot do<\/h2>\n<p>It cannot see a defect that is not a dimension. Gel particles, unmelt, black specks, die lines, moisture streaks and colour drift all pass a laser gauge without a flicker, and several of them are visible to a camera for a fraction of the cost.<\/p>\n<p>It cannot see the inside of the wall. A void, a bubble or a weld line from a spider die is invisible to every external measurement. X-ray sees some of it, destructive sectioning sees all of it, and neither is a production control.<\/p>\n<p>It cannot see stress. A profile that is perfectly in tolerance can be full of frozen-in stress, and the gauge will report it as good right up to the moment the customer machines it.<\/p>\n<p>So a gauge is one instrument in a set, and the set has to match the defect that actually costs money. A shop that buys a laser gauge to fix a gel problem has bought the wrong instrument and will conclude that gauging does not work.<\/p>\n<div class=\"faq\">\n<h3>What does an inline laser gauge measure?<\/h3>\n<p>A silhouette. Two or three axes of shadow give diameter, ovality and a profile shape at one section. It does not measure wall thickness or anything about the material.<\/p>\n<h3>How often should a profile be measured?<\/h3>\n<p>As often as the cost of the scrap per event justifies. At six metres a minute a thirty minute interval produces about a hundred metres of out-of-tolerance product before anybody knows.<\/p>\n<h3>Can inline gauging control wall thickness?<\/h3>\n<p>Partly. Ultrasonic or X-ray heads can measure it, and closed loop is possible, but the actuator is a die bolt or screw with a slow response that interacts with every other wall. Advisory feedback is usually the better first step.<\/p>\n<h3>Where should the gauge be mounted?<\/h3>\n<p>After the cooling tank and before the saw, where the profile is stable, cool and under the tension it will be measured at. Before the tank it measures a shape that will not exist in ten seconds.<\/p>\n<h3>Why does a gauge read differently in summer?<\/h3>\n<p>Thermal expansion. PVC expands by about 0.00007 per degree, which is 0.7 mm on a metre over twenty degrees. A profile measured hot is bigger than the same profile measured cold.<\/p>\n<h3>What defects does a laser gauge miss?<\/h3>\n<p>Gel, unmelt, black specks, die lines, moisture streaks, colour drift, internal voids and residual stress. All of them pass a dimension gauge without a flicker.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">Measurement that shortens the scrap<\/p>\n<p>Tell us the profile, the tolerance and the defect that costs you most. We will tell you which instrument to buy, where to mount it and whether the loop is worth closing.<\/p>\n<p><a class=\"btn\" href=\"https:\/\/uplastech.com\/es\/perfiles-de-pvc\/\">Discuss a gauging project<\/a>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/es\/extrusion-profile-tolerance\/\">Profile Tolerance and How to Hold It<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/es\/extrusion-dimensional-drift\/\">Dimensional Drift in Extrusion<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/es\/extrusion-gels-and-unmelts\/\">Gels and Unmelts in Extruded Profiles<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/es\/extrusion-haul-off-speed\/\">Haul-Off Speed and Line Balance<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/es\/extrusion-gravimetric-dosing\/\">Gravimetric Dosing on an Extrusion Line<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>A laser gauge on the line does not improve the profile. It shortens the distance between a drift starting and somebody knowing, and that distance is measured in metres of scrap.<\/p>","protected":false},"author":1,"featured_media":8922,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[17],"tags":[],"class_list":["post-8924","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\/es\/wp-json\/wp\/v2\/posts\/8924","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/comments?post=8924"}],"version-history":[{"count":0,"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/posts\/8924\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/media\/8922"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/media?parent=8924"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/categories?post=8924"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/tags?post=8924"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}