{"id":9009,"date":"2026-10-23T09:00:00","date_gmt":"2026-10-23T08:00:00","guid":{"rendered":"https:\/\/uplastech.com\/crosshead-die-design\/"},"modified":"2026-10-23T09:00:00","modified_gmt":"2026-10-23T08:00:00","slug":"crosshead-die-design","status":"publish","type":"post","link":"https:\/\/uplastech.com\/es\/crosshead-die-design\/","title":{"rendered":"Crosshead Die Design: Concentricity Is Decided Before the Screw Turns"},"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\/cable-wire-insulation-extrusion.jpg\" alt=\"Plastic insulated cable emerging from an extrusion crosshead die\" width=\"1536\" height=\"909\"><figcaption>The wire goes through the middle. The plastic has to arrive evenly around it.<\/figcaption><\/figure>\n<div class=\"toc\"><\/div>\n<h2 id=\"problem\">The geometry problem<\/h2>\n<p>In a crosshead, the melt arrives from the extruder at right angles to the wire and has to turn and distribute evenly around a circle. That turn is the source of every concentricity problem, because the melt that arrives first has a shorter path than the melt that has to travel around the far side.<\/p>\n<p>The design has to equalise the flow path, either by shaping the manifold so the path lengths are equal or by introducing a restriction that forces redistribution. Every crosshead design is a different answer to that problem.<\/p>\n<p>The result is measured as wall eccentricity: the difference between the thickest and thinnest wall, expressed as a percentage of the nominal wall. It is the number the customer sees in a cross section and the number that determines whether the cable passes a voltage test.<\/p>\n<p>Eccentricity also costs material. A cable specified at 0.7 mm nominal wall with 12 percent eccentricity has to be run at a higher average wall to guarantee the minimum, and that extra compound is paid for on every metre.<\/p>\n<h2 id=\"designs\">Four designs, four eccentricities<\/h2>\n<p>A pressure crosshead uses a narrow annular gap and high melt pressure to force the polymer evenly around the wire. It gives the best concentricity, around 3 to 4 percent eccentricity in the chart, and it needs high pressure and careful temperature control.<\/p>\n<p>A tube-on crosshead extrudes a tube that is drawn down onto the wire. It is simple and tolerant and it gives about 9 percent eccentricity, because the draw-down amplifies any initial imbalance.<\/p>\n<p>A semi-tube crosshead sits between the two, at about 6 percent, and it is the common compromise for general purpose cable.<\/p>\n<p>A vacuum sizing crosshead pulls a vacuum in the die so the melt is drawn onto the wire and held there while it cools. It gives the best result of the four at about 3.4 percent, and it needs a vacuum system and a sealed die.<\/p>\n<figure>\n<img decoding=\"async\" src=\"https:\/\/uplastech.com\/wp-content\/uploads\/2026\/11\/crosshead-die-design-chart.jpg\" alt=\"Wall eccentricity by crosshead type, and line speed against die draw ratio\" width=\"1536\" height=\"909\"><figcaption>Concentricity is a design property, not an operator skill.<\/figcaption><\/figure>\n<h2 id=\"draw\">Draw ratio and the speed limit<\/h2>\n<p>Draw ratio is the ratio of the die opening to the finished insulation diameter. A draw of 1.2 means the insulation is drawn down to 83 percent of the die size; a draw of 2.8 means it is drawn to 36 percent.<\/p>\n<p>Higher draw gives more output per revolution and therefore more line speed. The right hand panel shows that: at a draw of 1.2 the line runs at 120 metres per minute, at 2.0 it runs at 305 and at 2.8 at 395.<\/p>\n<p>But high draw amplifies eccentricity and orientation. The melt is stretched in the draw-down cone, and any imbalance in the annular gap is multiplied. That is why a pressure crosshead at low draw gives better concentricity than the same crosshead at high draw.<\/p>\n<p>The curve also flattens. Going from 2.4 to 2.8 adds only 25 metres per minute, which is not worth the concentricity penalty. Most cable lines sit between 1.8 and 2.4 for that reason.<\/p>\n<table>\n<thead>\n<tr>\n<th>Crosshead<\/th>\n<th>Eccentricity<\/th>\n<th>Pressure need<\/th>\n<th>Lo mejor para<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Presi\u00f3n<\/td>\n<td>3.0%<\/td>\n<td>Alta<\/td>\n<td>Thin wall, tight tolerance<\/td>\n<\/tr>\n<tr>\n<td>Vacuum sizing<\/td>\n<td>3.4%<\/td>\n<td>Moderado<\/td>\n<td>Thin wall, high speed<\/td>\n<\/tr>\n<tr>\n<td>Semi-tube<\/td>\n<td>6.2%<\/td>\n<td>Moderado<\/td>\n<td>General purpose<\/td>\n<\/tr>\n<tr>\n<td>Tube-on<\/td>\n<td>9.0%<\/td>\n<td>Bajo<\/td>\n<td>Thick wall, tolerant cable<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 1 \u2014 Eccentricity by crosshead design.<\/p>\n<h2 id=\"tooling\">What to specify in the tool<\/h2>\n<p>The tip and die are a matched pair. The tip centres the wire in the die, and the annular gap between tip and die sets the wall thickness. A tip that is off centre by 0.05 mm produces an eccentricity that no amount of manifold tuning will remove.<\/p>\n<p>The tip bore has to match the wire diameter closely enough to centre it but loosely enough to allow it to pass. A tip that is too tight wears and scores the conductor; too loose and the wire wanders.<\/p>\n<p>The die land length affects the same trade as any other die: longer land gives better concentricity and higher pressure. Cable dies usually run shorter than profile dies because the draw-down helps and because pressure is limited.<\/p>\n<p>And the manifold has to be accessible for cleaning. A crosshead with a flow path that cannot be opened will accumulate degraded material in the dead spots, and the result is periodic lumps in the insulation that look like contamination from the resin.<\/p>\n<table>\n<thead>\n<tr>\n<th>Par\u00e1metro<\/th>\n<th>Typical setting<\/th>\n<th>Effect<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Tip to wire clearance<\/td>\n<td>0.05 to 0.15 mm<\/td>\n<td>Centring against wear<\/td>\n<\/tr>\n<tr>\n<td>Die land length<\/td>\n<td>3 to 6 times wall<\/td>\n<td>Concentricity against pressure<\/td>\n<\/tr>\n<tr>\n<td>Draw ratio<\/td>\n<td>1.8 to 2.4<\/td>\n<td>Speed against eccentricity<\/td>\n<\/tr>\n<tr>\n<td>Temperatura de fusi\u00f3n<\/td>\n<td>Per compound<\/td>\n<td>Viscosity and draw behaviour<\/td>\n<\/tr>\n<tr>\n<td>Vacuum<\/td>\n<td>0.2 to 0.5 bar<\/td>\n<td>Melt onto wire, vacuum sizing only<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 2 \u2014 Settings that decide whether the wall comes out even.<\/p>\n<h2 id=\"diagnose\">Diagnosing an eccentric wall<\/h2>\n<p>First check the tip centring. Measure the wall at four points around the circumference and see whether the thin side is consistent around the length. A consistent thin side is a centring problem; a thin side that rotates is a flow problem.<\/p>\n<p>Second check the temperatures. A cold spot on one side of the crosshead raises local viscosity and pushes flow to the other side. An infrared scan of the crosshead body will find it in minutes.<\/p>\n<p>Third check the screen pack and the melt pressure. A rising pressure with unchanged settings means a restriction, and a restriction upstream of the crosshead produces an imbalance that the manifold cannot correct.<\/p>\n<p>Fourth check the vacuum, if it is a vacuum sizing head. A leaking seal or a blocked vacuum port produces a local loss of contact between melt and wire, which shows as a thick patch rather than a thin one.<\/p>\n<h2 id=\"cost\">What eccentricity costs<\/h2>\n<p>The material cost is straightforward. If the minimum wall has to be 0.7 mm and eccentricity is 12 percent, the average wall has to be about 0.78 mm to guarantee it. That is 11 percent more compound on every metre.<\/p>\n<p>The quality cost is less obvious. An eccentric wall has a thin side that fails a voltage test first, so the failure rate is set by the worst point rather than the average. A cable that is electrically marginal will fail in service at the thin side.<\/p>\n<p>And the speed cost. Improving concentricity usually allows a higher draw or a higher line speed at the same eccentricity, so the capital in the crosshead is recovered through output rather than through material.<\/p>\n<p>That is why a pressure or vacuum sizing crosshead is worth its extra cost on any cable with a thin wall and a tight tolerance, and why a tube-on head is adequate for a thick-jacketed flexible cord.<\/p>\n<div class=\"faq\">\n<h3>What wall eccentricity is acceptable in cable insulation?<\/h3>\n<p>Under 5 percent for a tight tolerance cable, which needs a pressure or vacuum sizing crosshead. Tube-on heads typically give 9 percent and suit thick, tolerant jackets.<\/p>\n<h3>Why does a crosshead produce an eccentric wall?<\/h3>\n<p>The melt has to turn ninety degrees around the wire, so path lengths differ. Design, tip centring and temperature uniformity all affect how evenly it redistributes.<\/p>\n<h3>What is draw ratio and why does it matter?<\/h3>\n<p>The ratio of die opening to finished insulation diameter. Higher draw gives more line speed but amplifies any eccentricity, so most lines run between 1.8 and 2.4.<\/p>\n<h3>How do I tell a centring problem from a flow problem?<\/h3>\n<p>Measure the wall at four points along the length. A thin side that stays in the same place is centring; a thin side that rotates is flow or temperature.<\/p>\n<h3>Does eccentricity cost material?<\/h3>\n<p>Yes. To guarantee a 0.7 mm minimum with 12 percent eccentricity you have to run about 0.78 mm average, which is 11 percent more compound on every metre.<\/p>\n<h3>Is a vacuum sizing crosshead worth it?<\/h3>\n<p>For thin wall, high speed and tight tolerance, yes. It gives the best concentricity of the four designs and allows higher line speed, at the cost of a vacuum system.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">Cable wall eccentricity out of tolerance?<\/p>\n<p>Send the construction, the wall and the current crosshead type. We will tell you whether it is the tool, the temperatures or the draw.<\/p>\n<p><a class=\"btn\" href=\"https:\/\/uplastech.com\/es\/extrusiones-de-tubos-y-tuberias\/\">Discuss cable extrusion<\/a>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/es\/wire-insulation-extrusion\/\">Wire Insulation Extrusion<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/es\/cable-jacket-extrusion\/\">Cable Jacket Extrusion<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/es\/cable-concentricity\/\">Cable Concentricity<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/es\/cable-extrusion-defects\/\">Cable Extrusion Defects<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/es\/extrusion-die-flow-channel\/\">Extrusion Die Flow Channel Design<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>Wire and cable insulation is judged on wall concentricity, and concentricity comes from the crosshead, not from the operator. Four designs give four very different eccentricity figures.<\/p>","protected":false},"author":1,"featured_media":7649,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[17],"tags":[],"class_list":["post-9009","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\/9009","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=9009"}],"version-history":[{"count":0,"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/posts\/9009\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/media\/7649"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/media?parent=9009"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/categories?post=9009"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/tags?post=9009"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}