{"id":9081,"date":"2026-11-07T01:00:00","date_gmt":"2026-11-07T01:00:00","guid":{"rendered":"https:\/\/uplastech.com\/?p=9081"},"modified":"2026-11-07T01:00:00","modified_gmt":"2026-11-07T01:00:00","slug":"profile-die-flow-balance","status":"publish","type":"post","link":"https:\/\/uplastech.com\/de\/profile-die-flow-balance\/","title":{"rendered":"Balancing a Profile Die: Equal Flow to Every Leg"},"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\/pvc-foam-extrusion.jpg\" alt=\"Foamed PVC profile emerging from an extrusion die head onto a roller conveyor in a factory\" width=\"1536\" height=\"909\"><figcaption>A foamed PVC profile leaving the die. Every leg in that cross-section is fighting the others for melt.<\/figcaption><\/figure>\n<div class=\"toc\"><\/div>\n<h2 id=\"symptom\">What imbalance looks like on the line<\/h2>\n<p>The first sign is usually a dimensional drift that will not settle. One leg of the profile is at the top of tolerance while another sits at the bottom, and no amount of haul-off or screw speed tuning brings them together.<\/p>\n<p>The second sign is a surface difference. The fast leg has a smoother surface because it sees higher shear at the die land, and the slow leg shows a dull band or a faint melt fracture line. Two different surfaces on one profile is a flow balance problem almost every time.<\/p>\n<p>The third is a shape problem downstream. If one leg is running hot and thin, it sags in the calibration sleeve and the finished profile bows. The bow gets blamed on cooling, but the cause is upstream at the die.<\/p>\n<p>The fourth is weight per metre that will not repeat. If the legs are fighting, small changes in melt temperature redistribute flow between them and the linear weight wanders within a run.<\/p>\n<h2 id=\"why\">Why a die is never balanced as built<\/h2>\n<p>Flow takes the path of least resistance. In a profile die the melt leaves a distribution channel and then passes a land whose length and gap set the resistance for that leg. Two legs with the same gap but different land lengths have different resistances, and the shorter land wins.<\/p>\n<p>Most new dies are built deliberately slightly unbalanced toward the heavy sections, because a heavy leg can be choked back with a choker bar or a die bolt, while a starved leg cannot be fed without cutting metal. It is easier to take flow away than to add it.<\/p>\n<p>Melt temperature adds a second variable. A leg close to the die body centre runs hotter and flows more easily than a leg at the edge, even when the geometry is identical. This is why symmetric dies still produce asymmetric output.<\/p>\n<p>The material matters too. A rigid PVC with a narrow processing window shows imbalance as a surface defect long before the dimensions drift. A filled or foamed compound shows it as density variation instead.<\/p>\n<figure>\n<img decoding=\"async\" src=\"https:\/\/uplastech.com\/wp-content\/uploads\/2026\/11\/profile-die-flow-balance-chart.jpg\" alt=\"Output share of the thin leg falling as its land length increases, and the land length correction needed on each leg\" width=\"1536\" height=\"909\"><figcaption>Land length is the control. The thin leg went from 34 percent of output to 19 percent over 25 mm of added land.<\/figcaption><\/figure>\n<h2 id=\"land\">Using land length as the control<\/h2>\n<p>Land is the parallel section at the end of the die where the melt is forced to flow straight. It generates most of the die's pressure drop, and because pressure drop scales with land length, it is the most predictable way to redistribute flow.<\/p>\n<p>The useful relationship is close to linear over a modest range. Doubling the land length on a leg roughly halves the flow through it, provided the gap stays constant and the melt stays at the same temperature.<\/p>\n<p>In practice, corrections are made in 2 to 5 mm steps. A leg that is 20 percent too heavy typically needs 8 to 12 mm of added land, and taking it in two steps lets you see the response before committing.<\/p>\n<p>Add land by inserting a shim or by replacing the land block, never by welding onto the die face. Welded land changes the surface finish locally and the seam becomes a flow disturbance that shows up as a line on the profile.<\/p>\n<h2 id=\"measure\">Measuring balance without a flow board<\/h2>\n<p>A flow board is the classic method: run the die without calibration, catch the extrudate for a fixed time, and weigh each leg. It is accurate and it costs a shutdown and a lot of scrap.<\/p>\n<p>The on-line alternative is to measure the finished profile. Cut sections at fixed intervals and measure wall thickness at the same four points on each. The leg whose wall is consistently thickest is the one getting the most flow.<\/p>\n<p>Linear weight is the fastest indicator. Weigh one metre every fifteen minutes for an hour. If the total varies by more than 2 percent at constant screw speed and haul-off, flow is moving between legs.<\/p>\n<p>Surface is the cheapest indicator of all. Photograph the profile under raking light and compare the gloss of each leg. A leg that is visibly duller is starved, and it will show a dimensional problem within a few hours.<\/p>\n<table>\n<thead>\n<tr>\n<th>Measurement<\/th>\n<th>Kosten<\/th>\n<th>What it tells you<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Flow board catch and weigh<\/td>\n<td>Shutdown plus scrap<\/td>\n<td>Absolute flow split per leg<\/td>\n<\/tr>\n<tr>\n<td>Section wall thickness<\/td>\n<td>A saw and a micrometer<\/td>\n<td>Which leg runs heavy<\/td>\n<\/tr>\n<tr>\n<td>Linear weight per metre<\/td>\n<td>A scale<\/td>\n<td>Whether flow is drifting<\/td>\n<\/tr>\n<tr>\n<td>Surface gloss under raking light<\/td>\n<td>A phone camera<\/td>\n<td>Which leg is starved<\/td>\n<\/tr>\n<tr>\n<td>Melt pressure at the die<\/td>\n<td>A pressure gauge<\/td>\n<td>Total restriction, not the split<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 1 \u2014 Ways to measure die balance, cheapest first.<\/p>\n<h2 id=\"iterate\">Iterating without ruining the die<\/h2>\n<p>Write down the starting state before you touch anything: land lengths, gaps, screw speed, haul-off, melt temperature and the measured wall at each point. Dies accumulate undocumented adjustments, and without a record you cannot go back.<\/p>\n<p>Change one leg at a time, and change it by the smallest amount that will produce a measurable response. A 2 mm land change on a 20 mm land is 10 percent, which is enough to see in a single section.<\/p>\n<p>Give the die time to stabilise. After a land change, run at least twenty minutes before measuring, because the die body has to reach a new thermal equilibrium and the flow split moves while it does.<\/p>\n<p>Stop when the spread is inside the tolerance band, not when it is perfect. Chasing the last 1 percent of balance on a PVC profile usually produces a die that is balanced at one temperature and unbalanced at another.<\/p>\n<table>\n<thead>\n<tr>\n<th>Change<\/th>\n<th>Typical effect<\/th>\n<th>Risiko<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Add 5 mm land to one leg<\/td>\n<td>Flow down 15 to 25 percent on that leg<\/td>\n<td>Low, reversible with a shim<\/td>\n<\/tr>\n<tr>\n<td>Close a die bolt<\/td>\n<td>Local flow down, surface marks<\/td>\n<td>Medium, bolt marks the land<\/td>\n<\/tr>\n<tr>\n<td>Raise melt temperature 5 C<\/td>\n<td>All legs up, edge legs up more<\/td>\n<td>Low, but affects cooling<\/td>\n<\/tr>\n<tr>\n<td>Enlarge the gap 0.1 mm<\/td>\n<td>Flow up sharply on that leg<\/td>\n<td>High, hard to undo<\/td>\n<\/tr>\n<tr>\n<td>Weld onto the land<\/td>\n<td>Unpredictable<\/td>\n<td>High, changes surface finish<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 2 \u2014 Correction options ranked by risk.<\/p>\n<h2 id=\"after\">What to check after the die is balanced<\/h2>\n<p>Re-check the calibration. A die that was balanced to compensate for a cold calibration sleeve will be wrong once the sleeve is fixed, and the two get tuned against each other until neither is right.<\/p>\n<p>Re-check the haul-off and the cut length. Flow balance changes the linear weight, and if the line was running at a haul-off speed chosen to hit weight with an unbalanced die, the length will now be off.<\/p>\n<p>Record the final land lengths on the die drawing. A balanced die is an asset, and the next person to open it needs to know which leg has 32 mm of land and why.<\/p>\n<p>Finally, run the profile for a full shift and measure at the start, middle and end. A die that is balanced cold and unbalanced hot is not balanced, and only a long run shows it.<\/p>\n<div class=\"faq\">\n<h3>How do I know my profile die is out of balance?<\/h3>\n<p>One leg sits at the top of tolerance while another sits at the bottom, the surfaces have different gloss, and linear weight drifts at constant screw speed. Two different surface finishes on one profile is the clearest sign.<\/p>\n<h3>Does adding land length reduce flow?<\/h3>\n<p>Yes. Land length is the main source of pressure drop in a profile die, so doubling the land on a leg roughly halves the flow through it at constant gap and melt temperature.<\/p>\n<h3>How much land should I add at a time?<\/h3>\n<p>Two to five millimetres. A leg that is 20 percent heavy usually needs 8 to 12 mm in total, taken in two steps so you can measure the response before committing more.<\/p>\n<h3>Can I balance a die by tightening the die bolts?<\/h3>\n<p>Only for small corrections. Bolts deflect the die locally and leave marks on the land, and they respond differently as the die heats. Land length is repeatable; bolt torque is not.<\/p>\n<h3>Why does balance change during a run?<\/h3>\n<p>The die body reaches thermal equilibrium over the first twenty to thirty minutes, and melt temperature redistributes flow between legs as it settles. Measure only after the die has stabilised.<\/p>\n<h3>Do I need a flow board to balance a die?<\/h3>\n<p>No. Section wall thickness, linear weight per metre and surface gloss under raking light will all show which leg is heavy. A flow board gives absolute numbers but costs a shutdown.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">Profile out of tolerance?<\/p>\n<p>Send the cross-section drawing and your measured wall thickness at each point. We will tell you which legs are heavy and how much land to add.<\/p>\n<p><a class=\"btn\" href=\"https:\/\/uplastech.com\/de\/losungen-fur-die-kunststoffextrusion\/\">Talk to our extrusion team<\/a>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/de\/extrusion-die-swell\/\">Extrusion Die Swell<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/de\/extrusion-vacuum-sizing\/\">Extrusion Vacuum Sizing<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/de\/sizing-sleeves-and-calibrators\/\">Sizing Sleeves and Calibrators<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/de\/extrusion-die-land-length\/\">Extrusion Die Land Length<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/de\/multi-cavity-profile-dies\/\">Multi-Cavity Profile Dies<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>A profile die is never balanced when it is first hung. Every leg gets a different share of the melt, and the fix is land length &#8211; not screwing the die bolts tighter.<\/p>","protected":false},"author":1,"featured_media":7614,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[17],"tags":[],"class_list":["post-9081","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\/de\/wp-json\/wp\/v2\/posts\/9081","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=9081"}],"version-history":[{"count":1,"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/posts\/9081\/revisions"}],"predecessor-version":[{"id":9451,"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/posts\/9081\/revisions\/9451"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/media\/7614"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/media?parent=9081"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/categories?post=9081"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/tags?post=9081"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}