{"id":8204,"date":"2026-03-05T09:00:00","date_gmt":"2026-03-05T09:00:00","guid":{"rendered":"https:\/\/uplastech.com\/cable-jacket-extrusion\/"},"modified":"2026-03-05T09:00:00","modified_gmt":"2026-03-05T09:00:00","slug":"cable-jacket-extrusion","status":"publish","type":"post","link":"https:\/\/uplastech.com\/de\/cable-jacket-extrusion\/","title":{"rendered":"Cable Jacket Extrusion: Pressure Die, Drawdown and Surface Finish"},"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-jacket-extrusion.jpg\" alt=\"Thick black cable emerging from a pressure die head into a water trough, with a laser diameter gauge and a finished coil on a reel\" width=\"1536\" height=\"909\"><figcaption>A jacket coming out of a pressure die. The die sets the diameter; the drawdown sets how tight it grips.<\/figcaption><\/figure>\n<div class=\"toc\"><\/div>\n<h2 id=\"die\">Pressure die or tube die, and what each gives<\/h2>\n<p>A cable jacket is applied by one of two die types. A pressure die forces the melt against the core under pressure inside the die, so the melt fills the space and the jacket is formed by the die. A tube die extrudes a tube slightly larger than the core and draws it down onto the core outside the die, with vacuum applied between them.<\/p>\n<p>A pressure die gives better adhesion and a smoother surface, because the melt is in contact with the core while it is still under pressure. It is also less tolerant of core variation, because the die gap is fixed and a larger core means a thinner jacket.<\/p>\n<p>A tube die is more tolerant of core diameter variation and it can run at higher line speed, because the drawdown is doing the sizing rather than the die. It gives a looser jacket and a more matte surface, and it needs vacuum to pull the tube onto the core without trapping air.<\/p>\n<h2 id=\"drawdown\">Drawdown is what makes it tight, and what roughens it<\/h2>\n<p>Drawdown ratio is the ratio of the die gap to the finished jacket wall, or the ratio of the die diameter to the finished cable diameter. A ratio of 1.0 means the jacket leaves the die at its final size; a ratio of 2.0 means it is pulled to half that size after leaving the die.<\/p>\n<p>Some drawdown is necessary. It is what makes the jacket grip the core and what closes the die marks. But drawdown also stretches the surface, and past a point the stretch produces a rough, matte finish. Surface roughness goes from 0.4 microns Ra at a drawdown of 1.0, to 0.6 at 1.2, 1.1 at 1.5, 2.4 at 1.8 and 4.8 at 2.2.<\/p>\n<p>That is a factor of twelve across the range, and it is the reason a glossy jacket and a tight jacket are in tension. A jacket that is drawn down enough to grip is a jacket that has lost its gloss, and the compromise is usually somewhere around 1.2 to 1.5.<\/p>\n<figure>\n<img decoding=\"async\" src=\"https:\/\/uplastech.com\/wp-content\/uploads\/2026\/10\/cable-jacket-extrusion-chart.jpg\" alt=\"Surface roughness rising from 0.4 to 4.8 microns against drawdown ratio, and wall thickness deviation rising from 1.2 to 5.6 percent against line speed\" width=\"1536\" height=\"909\"><figcaption>Left: surface roughness against drawdown, 0.4 microns at 1.0 and 4.8 at 2.2. Right: wall thickness deviation against line speed, 1.2 percent at 20 m\/min and 5.6 at 100.<\/figcaption><\/figure>\n<h2 id=\"speed\">Line speed loosens the tolerance<\/h2>\n<p>Wall thickness deviation rises with line speed: 1.2 percent at 20 m\/min, 1.6 at 40, 2.4 at 60, 3.8 at 80 and 5.6 at 100. The cause is that the sizing and cooling have less time to work, and any variation in the melt or the core arrives at the finished cable with less damping.<\/p>\n<p>The wall tolerance matters because the jacket is a mechanical protection, not a dielectric. A thin spot is where the cable will fail in a bend or an abrasion test, and it is invisible from outside. The specification is usually a minimum wall, for the same reason as wire insulation.<\/p>\n<p>The way to run fast and hold tolerance is to cool harder and sooner. A longer trough, colder water or a spray ring right at the die all help, and they cost less than running slowly.<\/p>\n<h2 id=\"surface\">Getting a surface that looks right<\/h2>\n<p>A glossy jacket needs a hot die, a short air gap and low drawdown. The melt has to be fluid enough to flow out against the die wall and it has to be cooled quickly once it leaves, so that the surface it had in the die is the surface it keeps.<\/p>\n<p>A matte jacket is produced deliberately by raising the drawdown, lowering the die temperature, or adding a matte agent to the compound. It hides handling marks and it is easier to make consistent, which is why most industrial cable is matte and most visible cable is glossy.<\/p>\n<p>The third option is embossing, where a textured sizing sleeve or a wheel marks the surface with a pattern or text. That is a separate operation and it interacts with drawdown, because the pattern is stretched along with the jacket.<\/p>\n<table>\n<thead>\n<tr>\n<th>Die type<\/th>\n<th>Adhesion<\/th>\n<th>Surface<\/th>\n<th>Core tolerance<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Druck<\/td>\n<td>Best<\/td>\n<td>Glossy<\/td>\n<td>Schlecht<\/td>\n<\/tr>\n<tr>\n<td>Tube with vacuum<\/td>\n<td>Gut<\/td>\n<td>Matte to satin<\/td>\n<td>Gut<\/td>\n<\/tr>\n<tr>\n<td>Tube without vacuum<\/td>\n<td>Schlecht<\/td>\n<td>Matte<\/td>\n<td>Gut<\/td>\n<\/tr>\n<tr>\n<td>Semi-pressure<\/td>\n<td>Gut<\/td>\n<td>Satin<\/td>\n<td>M\u00e4\u00dfig<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 1 \u2014 Die types and what each gives<\/p>\n<h2 id=\"problems\">The defects and their causes<\/h2>\n<p>A loose jacket that slides on the core is a drawdown problem or a vacuum problem. If the drawdown is too low the jacket never grips; if the vacuum is too low, air is trapped between the jacket and the core and the jacket is loose in patches.<\/p>\n<p>A jacket with a visible seam or a stripe is a die problem, usually a damaged die land or a build-up of degraded material on one side. It appears as a line running along the cable, and it is fixed by cleaning or replacing the die.<\/p>\n<p>A jacket that is oval rather than round is a cooling problem. The jacket cools from the outside while it is still soft, and if the cooling is uneven, or if the cable is touching something before it is set, the section goes oval. A sizing sleeve and a straight water trough fix it.<\/p>\n<h2 id=\"spec\">Specifying a jacket<\/h2>\n<p>The drawing needs the core diameter and its tolerance, the jacket compound, the minimum wall, the overall diameter, the adhesion requirement and the surface finish. It also needs the bend and abrasion requirements, because those decide the compound and the wall more than the electrical requirements do.<\/p>\n<p>It should name the test for adhesion, because there are several and they do not agree. A strip test, a pull test and a ring test give different numbers, and a specification that says 'good adhesion' specifies nothing.<\/p>\n<table>\n<thead>\n<tr>\n<th>Eigentum<\/th>\n<th>Typical value<\/th>\n<th>Test<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Minimum wall<\/td>\n<td>0.8-2.0 mm<\/td>\n<td>Section<\/td>\n<\/tr>\n<tr>\n<td>Overall diameter<\/td>\n<td>\u00b10.2 mm<\/td>\n<td>Laser gauge<\/td>\n<\/tr>\n<tr>\n<td>Adhesion<\/td>\n<td>10-30 N<\/td>\n<td>Strip or pull<\/td>\n<\/tr>\n<tr>\n<td>Surface<\/td>\n<td>Gloss or matte<\/td>\n<td>Visual against master<\/td>\n<\/tr>\n<tr>\n<td>Ovality<\/td>\n<td>Under 3%<\/td>\n<td>Diameter gauge, two axes<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 2 \u2014 The five lines a jacket drawing needs<\/p>\n<div class=\"myth\">Myth: more drawdown makes a better jacket because it grips harder. Past about 1.5 the surface roughens, the wall tolerance loosens and the jacket can thin at the die marks. Grip comes from adhesion and vacuum as much as from drawdown.<\/div>\n<div class=\"faq\">\n<h3>What is a normal drawdown ratio for a cable jacket?<\/h3>\n<p>Between 1.2 and 1.5 for most jackets. Below that the jacket does not grip; above that the surface roughens and the wall tolerance suffers.<\/p>\n<h3>Why is my jacket loose on the core?<\/h3>\n<p>Either insufficient drawdown or insufficient vacuum between the tube and the core. A loose jacket in patches is usually trapped air, which points at the vacuum.<\/p>\n<h3>What is the difference between a pressure die and a tube die?<\/h3>\n<p>A pressure die forms the jacket inside the die under pressure, which gives better adhesion and a glossier surface but less tolerance of core variation. A tube die extrudes a tube and draws it down onto the core, which is more tolerant and gives a matte finish.<\/p>\n<h3>How fast can a jacket line run?<\/h3>\n<p>It depends on the wall and the cooling. Wall tolerance goes from 1.2 percent at 20 m\/min to 5.6 at 100, so running faster needs more cooling, not just more speed.<\/p>\n<h3>Why is the jacket oval?<\/h3>\n<p>Uneven cooling, or the cable touching something before the jacket has set. A sizing sleeve and a straight trough fix it.<\/p>\n<h3>Can a matte jacket be made glossy?<\/h3>\n<p>Usually by raising the die temperature and lowering the drawdown. If the compound contains a matte agent, the gloss will be limited by the compound rather than the process.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">A jacket that is loose, oval or too rough?<\/p>\n<p>Send the construction and the defect. We will tell you whether it is the die, the drawdown or the cooling, and what the line should be set to.<\/p>\n<p><a class=\"btn\" href=\"https:\/\/uplastech.com\/de\/losungen-fur-die-kunststoffextrusion\/\">Ask about cable jacketing<\/a>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/de\/wire-insulation-extrusion\/\">Wire Insulation Extrusion: Concentricity, Wall and the Spark Tester<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/de\/silicone-cord-profile\/\">Silicone Cord Profile: Extruding a Round That Stays Round<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/de\/sheet-surface-gloss\/\">Sheet Surface Gloss: The Roll, the Chill and the Number<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/de\/hdpe-sheet-extrusion\/\">HDPE Sheet Extrusion: Density, Stress and the Flat Sheet<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/de\/losungen-fur-die-kunststoffextrusion\/\">Plastic Extrusion Solutions: Profile, Sheet, Pipe and Tube<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>A cable jacket is pulled down onto the core, and drawdown is what makes it tight. It is also what roughens it: going from a 1.0 to a 2.2 drawdown ratio takes surface roughness from 0.4 to 4.8 microns and turns a gloss jacket matte.<\/p>","protected":false},"author":1,"featured_media":8202,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[17],"tags":[],"class_list":["post-8204","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\/8204","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=8204"}],"version-history":[{"count":0,"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/posts\/8204\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/media\/8202"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/media?parent=8204"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/categories?post=8204"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/de\/wp-json\/wp\/v2\/tags?post=8204"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}