{"id":36247,"date":"2024-11-25T15:56:05","date_gmt":"2024-11-25T07:56:05","guid":{"rendered":"https:\/\/zetarmold.com\/?p=36247"},"modified":"2026-05-02T17:53:04","modified_gmt":"2026-05-02T09:53:04","slug":"%e5%b0%84%e5%87%ba%e6%88%90%e5%bd%a2%e8%83%8c%e5%9c%a7%e3%81%ae%e8%aa%bf%e6%95%b4","status":"publish","type":"post","link":"https:\/\/zetarmold.com\/ja\/%e5%b0%84%e5%87%ba%e6%88%90%e5%bd%a2%e8%83%8c%e5%9c%a7%e3%81%ae%e8%aa%bf%e6%95%b4\/","title":{"rendered":"\u5c04\u51fa\u6210\u5f62\u306e\u80cc\u5727\u3092\u8abf\u6574\u3059\u308b\u306b\u306f\uff1f"},"content":{"rendered":"<p><a href=\"https:\/\/www.ptonline.com\/articles\/understanding-back-pressure-in-injection-molding\">\u80cc\u5727<\/a><sup id=\"fnref1:1\"><a href=\"#fn:1\" class=\"footnote-ref\">1<\/a><\/sup> 400\u7a2e\u985e\u4ee5\u4e0a\u306e\u30d7\u30e9\u30b9\u30c1\u30c3\u30af\u6750\u6599\u306b\u308f\u305f\u308b\u7d4c\u9a13\u3068\u81ea\u793e\u5185\u306e\u91d1\u578b\u88fd\u9020\u65bd\u8a2d\u3092\u6d3b\u304b\u3057\u3001\u5f53\u793e\u306e\u30a8\u30f3\u30b8\u30cb\u30a2\u30ea\u30f3\u30b0\u30c1\u30fc\u30e0\u306f\u3001\u3059\u3079\u3066\u306e\u91d1\u578b\u8a66\u4f5c\u30d7\u30ed\u30c8\u30b3\u30eb\u306e\u4e00\u74b0\u3068\u3057\u3066\u80cc\u5727\u30d1\u30e9\u30e1\u30fc\u30bf\u3092\u8abf\u6574\u3057\u307e\u3059\u3002\u306a\u305c\u306a\u3089\u3001\u6eb6\u878d\u54c1\u8cea\u304c\u4e00\u8cab\u3057\u3066\u3044\u306a\u3051\u308c\u3070\u3001\u3088\u304f\u4f5c\u3089\u308c\u305f\u91d1\u578b\u3067\u3082\u826f\u8cea\u306a\u90e8\u54c1\u3092\u751f\u7523\u3059\u308b\u3053\u3068\u306f\u3067\u304d\u306a\u3044\u304b\u3089\u3067\u3059\u3002<\/p>\n<div class=\"callout-key\" style=\"background:#f0f7ff; border-left:4px solid #2563eb; padding:1em 1.2em; border-radius:6px; margin:1.5em 0;\">\n<strong>\u8981\u70b9<\/strong><\/p>\n<ul>\n<li>Back pressure controls screw retreat speed during plasticization, directly affecting melt quality<\/li>\n<li>Typical back pressure ranges from 5 to 20 bar (0.5\u20132 MPa) for most engineering plastics<\/li>\n<li>Too-low back pressure causes air traps, color streaks, and shot-weight variation<\/li>\n<li>Too-high back pressure leads to material degradation, drooling, and longer cycle times<\/li>\n<li>Always start low and increase gradually while inspecting parts for defects<\/li>\n<\/ul>\n<\/div>\n<h2>What Is Back Pressure in Injection Molding?<\/h2>\n<p>\u5c04\u51fa\u6210\u5f62\u306b\u304a\u3051\u308b\u80cc\u5727\u306f\u3001\u3053\u306e\u30bb\u30af\u30b7\u30e7\u30f3\u3067\u8aac\u660e\u3055\u308c\u308b\u6a5f\u80fd\u3001\u5236\u7d04\u3001\u304a\u3088\u3073\u30c8\u30ec\u30fc\u30c9\u30aa\u30d5\u306b\u3088\u3063\u3066\u5b9a\u7fa9\u3055\u308c\u307e\u3059\u3002\u80cc\u5727\u306f\u30d7\u30e9\u30b9\u30c1\u30c3\u30af\u5316\u6bb5\u968e\u3067\u30b9\u30af\u30ea\u30e5\u30fc\u306b\u9069\u7528\u3055\u308c\u308b\u5236\u5fa1\u3055\u308c\u305f\u62b5\u6297\u3067\u3042\u308a\u3001\u901a\u5e3850\u301c200 bar\uff08725\u301c2,900 psi\uff09\u3067\u3001\u6eb6\u878d\u4f53\u3092\u5727\u7e2e\u30fb\u5747\u8cea\u5316\u3057\u307e\u3059\u3002\u3053\u308c\u306f\u6642\u306b <a href=\"https:\/\/www.sciencedirect.com\/topics\/engineering\/back-pressure\">plasticizing pressure<\/a><sup id=\"fnref1:2\"><a href=\"#fn:2\" class=\"footnote-ref\">2<\/a><\/sup> \u307e\u305f\u306f\u30b9\u30af\u30ea\u30e5\u30fc\u80cc\u5727 \u2014 \u56de\u5fa9\u6bb5\u968e\u3067\u30b9\u30af\u30ea\u30e5\u30fc\u304c\u5f8c\u65b9\u306b\u56de\u8ee2\u3059\u308b\u969b\u306b\u30b9\u30af\u30ea\u30e5\u30fc\u5f8c\u90e8\u306b\u9069\u7528\u3055\u308c\u308b\u62b5\u6297\u3002\u3053\u308c\u304c\u306a\u3044\u5834\u5408\u3001\u30b9\u30af\u30ea\u30e5\u30fc\u304c\u904e\u5ea6\u306b\u901f\u304f\u5f8c\u9000\u3057\u3001\u6eb6\u878d\u4f53\u304c\u7de9\u304f\u3001\u6c17\u6ce1\u304c\u591a\u304f\u306a\u308a\u307e\u3059\u3002<\/p>\n<p>In hydraulic machines, back pressure is set by adjusting the overflow valve on the injection cylinder. In all-electric machines, the servo motor controls it directly. The key point is that back pressure is not a single number you set once \u2014 it is a dynamic parameter you tune based on material, part geometry, mold design, and even ambient conditions.<\/p>\n<figure style=\"text-align:center;margin:2em 0;\">\n<img fetchpriority=\"high\" decoding=\"async\" width=\"800\" height=\"457\" src=\"https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/04\/injection-molding-machine-diag-800x457-1.jpg\" alt=\"Injection Molding Machine Diagram\" class=\"wp-image-53260 size-full\" style=\"max-width:100%;height:auto;\" srcset=\"https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/04\/injection-molding-machine-diag-800x457-1.jpg 800w, https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/04\/injection-molding-machine-diag-800x457-1-300x171.jpg 300w, https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/04\/injection-molding-machine-diag-800x457-1-768x439.jpg 768w, https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/04\/injection-molding-machine-diag-800x457-1-18x10.jpg 18w, https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/04\/injection-molding-machine-diag-800x457-1-600x343.jpg 600w\" sizes=\"(max-width: 800px) 100vw, 800px\" \/><figcaption style=\"font-size:0.78em; color:#888; font-style:italic; margin-top:4px; text-align:center;\">Injection molding machine components relevant<\/figcaption><\/figure>\n<h2>How Is Back Pressure Formed During Plasticization?<\/h2>\n<p>\u3053\u306e\u30bb\u30af\u30b7\u30e7\u30f3\u306f\u3001\u30d7\u30e9\u30b9\u30c1\u30c3\u30af\u5316\u5de5\u7a0b\u4e2d\u306b\u5f62\u6210\u3055\u308c\u308b\u80cc\u5727\u3068\u3001\u305d\u308c\u304c\u30b3\u30b9\u30c8\u3001\u54c1\u8cea\u3001\u6642\u9593\u3001\u307e\u305f\u306f\u8abf\u9054\u30ea\u30b9\u30af\u306b\u4e0e\u3048\u308b\u5f71\u97ff\u306b\u3064\u3044\u3066\u3067\u3059\u3002\u80cc\u5727\u306f\u3001\u30b9\u30af\u30ea\u30e5\u30fc\u5148\u7aef\u524d\u306b\u84c4\u7a4d\u3059\u308b\u6eb6\u878d\u30dd\u30ea\u30de\u30fc\u304c\u30b9\u30af\u30ea\u30e5\u30fc\u3092\u5f8c\u9000\u3055\u305b\u308b\u5341\u5206\u306a\u529b\u3092\u751f\u6210\u3057\u3001\u80cc\u5727\u30d0\u30eb\u30d6\u304c\u3053\u306e\u5f8c\u9000\u3092\u5236\u9650\u3057\u3066\u6eb6\u878d\u4f53\u3092\u5727\u7e2e\u30fb\u5747\u8cea\u5316\u3059\u308b\u3068\u304d\u306b\u5f62\u6210\u3055\u308c\u307e\u3059\u3002\u30b9\u30af\u30ea\u30e5\u30fc\u30fb\u30d7\u30e9\u30b9\u30c1\u30c3\u30af\u5316\u6bb5\u968e\u3067\u306f\u3001\u30b9\u30af\u30ea\u30e5\u30fc\u304c\u56de\u8ee2\u3057\u3066\u6750\u6599\u3092\u6eb6\u878d\u30fb\u8a08\u91cf\u3057\u307e\u3059\u3002\u6eb6\u878d\u30d7\u30e9\u30b9\u30c1\u30c3\u30af\u304c\u30b9\u30af\u30ea\u30e5\u30fc\u5148\u7aef\u524d\u306b\u84c4\u7a4d\u3059\u308b\u3068\u3001\u30b9\u30af\u30ea\u30e5\u30fc\u3092\u5f8c\u9000\u3055\u305b\u307e\u3059\u3002\u80cc\u5727\u30d0\u30eb\u30d6\u306f\u5c04\u51fa\u30b7\u30ea\u30f3\u30c0\u30fc\u6cb9\u306e\u6392\u51fa\u901f\u5ea6\u3092\u5236\u9650\u3057\u3001\u3053\u306e\u5f8c\u9000\u904b\u52d5\u306b\u5bfe\u3059\u308b\u62b5\u6297\u3092\u751f\u307f\u51fa\u3057\u307e\u3059\u3002<\/p>\n<p>\u30d7\u30ed\u30bb\u30b9\u306f\u6b21\u306e\u3088\u3046\u306b\u6a5f\u80fd\u3057\u307e\u3059\uff1a\u30b9\u30af\u30ea\u30e5\u30fc\u304c\u56de\u8ee2 \u2192 \u6750\u6599\u304c\u6eb6\u878d\u3057\u524d\u65b9\u306b\u79fb\u52d5 \u2192 \u6eb6\u878d\u5727\u529b\u304c\u5897\u52a0 \u2192 \u30b9\u30af\u30ea\u30e5\u30fc\u304c\u62bc\u3057\u623b\u3055\u308c\u308b \u2192 \u80cc\u5727\u30d0\u30eb\u30d6\u304c\u3053\u306e\u5f8c\u9000\u3092\u62b5\u6297 \u2192 \u6eb6\u878d\u4f53\u304c\u5727\u7e2e\u3055\u308c\u5747\u8cea\u5316\u3055\u308c\u307e\u3059\u3002\u30d0\u30eb\u30d6\u306e\u8a2d\u5b9a\u304c\u53b3\u3057\u3044\u307b\u3069\u3001 <a href=\"https:\/\/zetarmold.com\/ja\/%e3%82%b9%e3%82%af%e3%83%aa%e3%83%a5%e3%83%bc%e5%b0%84%e5%87%ba%e6%88%90%e5%bd%a2%e6%a9%9f\/\">\u5c04\u51fa\u6210\u5f62\u6a5f\u306e\u30b9\u30af\u30ea\u30e5\u30fc<\/a> \u5f8c\u9000\u901f\u5ea6\u304c\u9045\u304f\u306a\u308a\u3001\u6eb6\u878d\u4f53\u304c\u3088\u308a\u5fb9\u5e95\u7684\u306b\u6df7\u5408\u30fb\u5727\u7e2e\u3055\u308c\u307e\u3059\u3002<\/p>\n<div class=\"factory-insight\" data-fact-ids=\"equipment.injection_machines_47,equipment.tonnage_90_1850,company.experience_20_years\" style=\"background:#f0f7ff;border-left:4px solid #0066cc;padding:12px 16px;margin:1.5em 0;\"><strong>\ud83c\udfed ZetarMold Factory Insight<\/strong><br \/>In our Shanghai factory, we run 47 injection molding machines from 90T to 1850T. Over 20+ years of production, we have found that back pressure tuning accounts for roughly 30% of the defect-reduction gains when optimizing a new mold setup.<\/div>\n<h2>Where Do You Find the Back Pressure Adjustment Valve?<\/h2>\n<p>\u3053\u306e\u30bb\u30af\u30b7\u30e7\u30f3\u306f\u3001\u80cc\u5727\u8abf\u6574\u30d0\u30eb\u30d6\u306e\u4f4d\u7f6e\u3068\u3001\u305d\u308c\u304c\u30b3\u30b9\u30c8\u3001\u54c1\u8cea\u3001\u6642\u9593\u3001\u307e\u305f\u306f\u8abf\u9054\u30ea\u30b9\u30af\u306b\u4e0e\u3048\u308b\u5f71\u97ff\u306b\u3064\u3044\u3066\u3067\u3059\u3002\u80cc\u5727\u30d0\u30eb\u30d6\u306f\u6cb9\u5727\u5f0f\u6210\u5f62\u6a5f\u3067\u306f\u5c04\u51fa\u30b7\u30ea\u30f3\u30c0\u30fc\u306e\u5f8c\u90e8\u306b\u3001\u307e\u305f\u306f <a href=\"https:\/\/www.researchgate.net\/publication\/Injection_Molding_Screw_Design\">screw recovery<\/a><sup id=\"fnref1:3\"><a href=\"#fn:3\" class=\"footnote-ref\">3<\/a><\/sup> \u96fb\u6c17\u5f0f\u6210\u5f62\u6a5f\u306e\u30b3\u30f3\u30c8\u30ed\u30fc\u30e9\u30fc\u4e0a\u306e\u30e1\u30cb\u30e5\u30fc\u3002\u6cb9\u5727\u5f0f\u6210\u5f62\u6a5f\u3067\u306f\u3001\u30d7\u30e9\u30b9\u30c1\u30c3\u30af\u5316\u5de5\u7a0b\u4e2d\u306b\u30b9\u30af\u30ea\u30e5\u30fc\u304c\u5f8c\u9000\u3059\u308b\u969b\u306b\u5c04\u51fa\u30b7\u30ea\u30f3\u30c0\u30fc\u304b\u3089\u306e\u6cb9\u5727\u6cb9\u306e\u6392\u51fa\u901f\u5ea6\u3092\u30d0\u30eb\u30d6\u3067\u5236\u5fa1\u3057\u307e\u3059\u3002<\/p>\n<p>For all-electric machines, there is no hydraulic valve. Instead, the servo motor that drives the screw applies a programmable torque limit during retraction. You set this in the machine controller under screw recovery parameters. The principle is identical \u2014 you are controlling how much resistance the screw encounters while retreating.<\/p>\n<h2>How Do You Determine the Correct Back Pressure Value?<\/h2>\n<p>There is no single magic number. The typical-range for back pressure is between 5 and 20 bar (0.5 to 2 MPa) for most engineering plastics, but the exact value depends on several factors: the material being processed, the screw design, the part geometry, and the mold temperature. A good starting rule of thumb is to set back pressure at 10\u201320% of the maximum injection pressure and adjust from there.<\/p>\n<p>Material-specific starting points we use in our factory:<\/p>\n<p>- <strong>PP, PE (polyolefins):<\/strong> 5\u201310 bar \u2014 these materials melt easily and do not need high compaction<br \/>- <strong>ABS, PS:<\/strong> 8\u201315 bar \u2014 moderate pressure for consistent color mixing and density<br \/>- <strong>PC, PMMA (transparent resins):<\/strong> 10\u201320 bar \u2014 higher pressure ensures optical clarity and eliminates air bubbles<br \/>- <strong>PA (nylon), PBT:<\/strong> 8\u201315 bar \u2014 enough to compact the melt without causing degradation<br \/>- <strong>PVC, POM:<\/strong> 3\u20138 bar \u2014 keep it low, these materials are heat-sensitive and degrade quickly under high back pressure<\/p>\n<div class=\"claim claim-true\" style=\"background-color: #eff7ef; border-color: #eff7ef; color: #5a8a5a;\">\n<p><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"20\" height=\"20\" viewbox=\"0 0 24 24\" fill=\"none\" stroke=\"#16a34a\" stroke-width=\"2\"><path d=\"M9 16.17L4.83 12l-1.42 1.41L9 19 21 7l-1.41-1.41z\"\/><\/svg><b>\u300c\u30d0\u30c3\u30af\u5727\u529b\u3092\u4e0a\u3052\u308b\u3068\u3001\u6eb6\u878d\u6a39\u8102\u306e\u5747\u8cea\u6027\u304c\u5411\u4e0a\u3057\u3001\u6210\u5f62\u90e8\u54c1\u5185\u306e\u6c17\u6ce1\u304c\u6e1b\u5c11\u3057\u307e\u3059\u3002\u300d<\/b><span class=\"claim-true-or-false\">\u771f<\/span><\/p>\n<p class=\"claim-explanation\">Higher back pressure slows screw retreat, giving the material more time to mix and compress. This expels trapped air and creates a more uniform melt, which directly reduces bubbles and voids in the finished part.<\/p>\n<\/div>\n<div class=\"claim claim-false\" style=\"background-color: #f7e8e8; border-color: #f7e8e8; color: #8a4a4a;\">\n<p><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"20\" height=\"20\" viewbox=\"0 0 24 24\" fill=\"none\" stroke=\"#dc2626\" stroke-width=\"2\"><line x1=\"18\" y1=\"6\" x2=\"6\" y2=\"18\"\/><line x1=\"6\" y1=\"6\" x2=\"18\" y2=\"18\"\/><\/svg><b>\u300c\u6700\u9ad8\u306e\u90e8\u54c1\u54c1\u8cea\u3092\u5f97\u308b\u305f\u3081\u306b\u306f\u3001\u5e38\u306b\u30d0\u30c3\u30af\u5727\u529b\u3092\u53ef\u80fd\u306a\u9650\u308a\u9ad8\u304f\u8a2d\u5b9a\u3059\u3079\u304d\u3067\u3059\u3002\u300d<\/b><span class=\"claim-true-or-false\">\u507d<\/span><\/p>\n<p class=\"claim-explanation\">Excessive back pressure raises melt temperature, increases cycle time, and can cause material degradation \u2014 especially with heat-sensitive resins like PVC. It also causes nozzle drooling and flash. The correct approach is to start low and increase only until defects disappear.<\/p>\n<\/div>\n<h2>What Are the Proven Methods for Adjusting Back Pressure?<\/h2>\n<p>\u80cc\u5727\u306e\u8abf\u6574\u306f\u5358\u306b\u30c0\u30a4\u30e4\u30eb\u3092\u56de\u3059\u3053\u3068\u3067\u306f\u3042\u308a\u307e\u305b\u3093\u3002\u305d\u308c\u306f\u6750\u6599\u3092\u7406\u89e3\u3057\u3001\u6210\u5f62\u54c1\u3092\u89b3\u5bdf\u3057\u3001\u6bb5\u968e\u7684\u306a\u5909\u66f4\u3092\u884c\u3046\u4f53\u7cfb\u7684\u306a\u30d7\u30ed\u30bb\u30b9\u3067\u3042\u308a\u3001\u3088\u308a\u5e83\u7bc4\u306a <a href=\"https:\/\/zetarmold.com\/ja\/%e5%b0%84%e5%87%ba%e6%88%90%e5%bd%a2%e3%81%ae%e3%82%b9%e3%83%86%e3%83%83%e3%83%97\/\">\u5c04\u51fa\u6210\u5f62\u306e\u30b9\u30c6\u30c3\u30d7<\/a>. \u3053\u308c\u306f\u65b0\u3057\u3044\u91d1\u578b\u3092\u30bb\u30c3\u30c8\u30a2\u30c3\u30d7\u3059\u308b\u969b\u306b\u3001\u79c1\u305f\u3061\u306e\u751f\u7523\u73fe\u5834\u3067\u6bce\u56de\u5f93\u3046\u65b9\u6cd5\u3067\u3059\u3002<\/p>\n<h3>How Do You Adjust by Material Type?<\/h3>\n<p>Different polymers have vastly different viscosity curves, thermal stability windows, and sensitivity to shear heat. Low-melting-point materials like PE and PP need very little back pressure \u2014 5 to 10 bar is usually sufficient. Engineering plastics like PC and POM need more careful treatment: PC benefits from 10 to 20 bar for clarity and density, while POM and PVC should stay below 8 bar to avoid thermal degradation. Glass-filled materials often require slightly higher back pressure (15\u201320 bar) to break down glass fiber bundles and achieve uniform distribution.<\/p>\n<h3>How Do You Adjust by Part Size and Geometry?<\/h3>\n<p>Larger parts with thick walls benefit from higher back pressure because the increased melt density helps fill the cavity consistently and reduces shrinkage sinks. Thin-wall parts, on the other hand, need a balance \u2014 too much back pressure raises melt temperature and can cause flash at the parting line. For precision parts with tight tolerances (\u00b10.05 mm or tighter), we typically fine-tune back pressure in 1-bar increments while monitoring part weight and dimensions with a scale and calipers.<\/p>\n<figure style=\"text-align:center;margin:2em 0;\">\n<img decoding=\"async\" width=\"800\" height=\"457\" src=\"https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/02\/800x457_colored-plastic-storage-boxes.webp\" alt=\"colored-plastic-storage-boxes\" class=\"wp-image-52161 size-full\" style=\"max-width:100%;height:auto;\" srcset=\"https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/02\/800x457_colored-plastic-storage-boxes.webp 800w, https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/02\/800x457_colored-plastic-storage-boxes-300x171.webp 300w, https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/02\/800x457_colored-plastic-storage-boxes-768x439.webp 768w, https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/02\/800x457_colored-plastic-storage-boxes-18x10.webp 18w, https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/02\/800x457_colored-plastic-storage-boxes-600x343.webp 600w\" sizes=\"(max-width: 800px) 100vw, 800px\" \/><figcaption style=\"font-size:0.78em; color:#888; font-style:italic; margin-top:4px; text-align:center;\">ZetarMold injection molding factory<\/figcaption><\/figure>\n<h3>How Do You Use Dynamic Back Pressure Profiling?<\/h3>\n<p>Modern machines allow you to program back pressure in stages during the screw recovery phase. Instead of a single constant value, you can set, for example: Stage 1 at 5 bar for the first 30% of stroke (gentle start to avoid disturbing the cushion), Stage 2 at 15 bar for the middle 50% (main compaction and mixing), and Stage 3 at 8 bar for the final 20% (reduce pressure near the end to prevent drooling). This staged approach gives you better control over melt quality without the side effects of running high pressure through the entire recovery phase.<\/p>\n<div class=\"factory-insight\" data-fact-ids=\"materials.material_range_400_plus,facility.in_house_mold_manufacturing\" style=\"background:#f0f7ff;border-left:4px solid #0066cc;padding:12px 16px;margin:1.5em 0;\"><strong>\ud83c\udfed ZetarMold Factory Insight<\/strong><br \/>With experience across 400+ plastic materials and an in-house mold manufacturing facility, our engineering team tunes back pressure parameters as part of every mold trial protocol \u2014 because even a well-built mold cannot produce good parts if the melt quality is inconsistent.<\/div>\n<h2>What Happens If Back Pressure Is Set Incorrectly?<\/h2>\n<p><strong>\u30d0\u30c3\u30af\u30d7\u30ec\u30c3\u30b7\u30e3\u30fc\u8abf\u6574<\/strong> The screw retreats too fast, and the melt is loose and full of air. You will see gas marks (silver streaks) on the part surface, inconsistent shot weight, internal bubbles, and uneven gloss. Color mixing becomes patchy \u2014 especially with masterbatch \u2014 because the screw did not have enough resistance to properly blend the pigment into the melt. In severe cases, parts will show dimensional instability, with weight varying shot-to-shot by 2% or more.<\/p>\n<p><strong>When back pressure is too high:<\/strong> The melt temperature rises due to excessive shear, which can degrade heat-sensitive materials. You may notice discoloration (yellowing of white parts, dark streaks in colored parts), longer screw recovery times that extend cycle time, and nozzle drooling between shots. In extreme cases, excessive back pressure causes flash at the mold parting line because the melt is too hot and fluid. It also increases mechanical wear on the screw, barrel, and check ring.<\/p>\n<div class=\"claim claim-true\" style=\"background-color: #eff7ef; border-color: #eff7ef; color: #5a8a5a;\">\n<p><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"20\" height=\"20\" viewbox=\"0 0 24 24\" fill=\"none\" stroke=\"#16a34a\" stroke-width=\"2\"><path d=\"M9 16.17L4.83 12l-1.42 1.41L9 19 21 7l-1.41-1.41z\"\/><\/svg><b>\u300c\u30d0\u30c3\u30af\u5727\u529b\u304c\u4f4e\u3044\u3068\u3001\u6eb6\u878d\u6a39\u8102\u5185\u306b\u7a7a\u6c17\u304c\u9589\u3058\u8fbc\u3081\u3089\u308c\u3001\u90e8\u54c1\u8868\u9762\u306b\u9280\u6761\u3084\u6c17\u6ce1\u304c\u767a\u751f\u3059\u308b\u3053\u3068\u304c\u3088\u304f\u3042\u308a\u307e\u3059\u3002\u300d<\/b><span class=\"claim-true-or-false\">\u771f<\/span><\/p>\n<p class=\"claim-explanation\">Without sufficient back pressure, the screw retreats rapidly and does not compress the melt adequately. Air gets trapped in the molten polymer, and when the material is injected into the cavity, these air pockets create silver streaks (gas marks) and internal voids.<\/p>\n<\/div>\n<div class=\"claim claim-false\" style=\"background-color: #f7e8e8; border-color: #f7e8e8; color: #8a4a4a;\">\n<p><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"20\" height=\"20\" viewbox=\"0 0 24 24\" fill=\"none\" stroke=\"#dc2626\" stroke-width=\"2\"><line x1=\"18\" y1=\"6\" x2=\"6\" y2=\"18\"\/><line x1=\"6\" y1=\"6\" x2=\"18\" y2=\"18\"\/><\/svg><b>\u300c\u90e8\u54c1\u306b\u30b7\u30f3\u30af\u30de\u30fc\u30af\u304c\u767a\u751f\u3059\u308b\u5834\u5408\u306f\u3001\u5e38\u306b\u30d0\u30c3\u30af\u5727\u529b\u3092\u4e0a\u3052\u3066\u554f\u984c\u3092\u4fee\u6b63\u3059\u3079\u304d\u3067\u3059\u3002\u300d<\/b><span class=\"claim-true-or-false\">\u507d<\/span><\/p>\n<p class=\"claim-explanation\">Sink marks are primarily caused by insufficient holding pressure or cooling time, not back pressure. While back pressure affects melt density, adjusting holding pressure, packing time, and cooling parameters is the correct approach for sink marks. Increasing back pressure may actually worsen the issue by raising melt temperature.<\/p>\n<\/div>\n<h2>What Are the Benefits of Proper Back Pressure Adjustment?<\/h2>\n<p>The benefits of proper back pressure adjustment are the main categories or options explained in this section. Getting back pressure right pays off across every aspect of production. First, melt homogeneity improves dramatically \u2014 colors blend evenly, additives disperse properly, and you get consistent material properties throughout the part. Shot weight stabilizes to within 0.2\u20130.5% variation, which means part dimensions stay within tolerance shot after shot.<\/p>\n<p>Proper back pressure also eliminates a whole category of surface defects: gas marks, cold slugs, and gloss variation drop off significantly. For transparent parts made from PC or PMMA, the difference between 10 bar and 15 bar of back pressure can be the difference between a crystal-clear lens and one full of internal haze.<\/p>\n<figure style=\"text-align:center;margin:2em 0;\">\n<img decoding=\"async\" width=\"800\" height=\"457\" src=\"https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/03\/im-vs-cnc-tolerance.webp\" alt=\"Injection Molding Product vs CNC machining tolerance\" class=\"wp-image-52399 size-full\" style=\"max-width:100%;height:auto;\" srcset=\"https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/03\/im-vs-cnc-tolerance.webp 800w, https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/03\/im-vs-cnc-tolerance-300x171.webp 300w, https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/03\/im-vs-cnc-tolerance-768x439.webp 768w, https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/03\/im-vs-cnc-tolerance-18x10.webp 18w, https:\/\/zetarmold.com\/wp-content\/uploads\/2026\/03\/im-vs-cnc-tolerance-600x343.webp 600w\" sizes=\"(max-width: 800px) 100vw, 800px\" \/><figcaption style=\"font-size:0.78em; color:#888; font-style:italic; margin-top:4px; text-align:center;\">Proper back pressure adjustment directly impacts<\/figcaption><\/figure>\n<p>Finally, consistent back pressure reduces the need for downstream rework. Parts come out right the first time, which means less scrap, fewer quality holds, and shorter lead times \u2014 and that is where the real cost savings show up in production.<\/p>\n<h2>How Should You Approach Back Pressure Optimization?<\/h2>\n<p>Adjusting back pressure is not complicated, but it does require attention to detail. Start with the material-specific baseline values, observe your parts carefully, and adjust in small increments. Watch for the telltale signs: silver streaks mean increase back pressure; drooling and discoloration mean decrease it. Use dynamic profiling on modern machines for even better control.<\/p>\n<p>Need help dialing in your injection molding parameters? <a href=\"https:\/\/zetarmold.com\/ja\/injection-molding-complete-guide\/\">See our Injection Molding Complete Guide<\/a> for a comprehensive overview of all key process settings. For mold design and production support, <a href=\"https:\/\/zetarmold.com\/ja\/injection-mold-complete-guide\/\">check our Injection Mold Complete Guide<\/a>. \u90e8\u54c1\u8abf\u9054\u306e\u6e96\u5099\u306f\u3067\u304d\u3066\u3044\u307e\u3059\u304b\uff1f <a href=\"https:\/\/zetarmold.com\/ja\/injection-molding-supplier-sourcing-guide\/\">Our injection molding supplier sourcing guide<\/a> \u5de5\u5834\u306e\u9078\u629e\u3068\u8a55\u4fa1\u3092\u884c\u3046\u624b\u9806\u3092\u8aac\u660e\u3057\u307e\u3059\u3002<\/p>\n<h2>\u3088\u304f\u3042\u308b\u8cea\u554f<\/h2>\n<h3>What is the normal back pressure range for injection molding?<\/h3>\n<p>The normal back pressure range for most engineering plastics is 5 to 20 bar (0.5\u20132 MPa). Polyolefins like PP and PE typically run at 5\u201310 bar, while higher-performance materials such as PC and PMMA may require 10\u201320 bar to achieve adequate melt density. Heat-sensitive resins like PVC and POM should stay below 8 bar to avoid thermal degradation. A practical starting point is 10\u201320% of maximum injection pressure. From there, increase gradually in 1\u20132 bar increments while monitoring part quality \u2014 look for the elimination of silver streaks and consistent shot weight as indicators that you are in the right range.<\/p>\n<h3>How does back pressure affect part quality?<\/h3>\n<p>Back pressure directly controls melt density and homogeneity during screw recovery. Proper settings eliminate trapped air bubbles, ensure uniform color mixing with masterbatches, stabilize shot weight to within 0.2\u20130.5% variation, and reduce surface defects like silver streaks and gloss inconsistency. Too little back pressure causes voids, color streaks, and dimensional instability shot-to-shot. Too much raises melt temperature through excessive shear, leading to material degradation, nozzle drooling, flash, and longer cycle times. The impact is especially critical for transparent parts where even minor melt inconsistencies become visible defects.<\/p>\n<h3>Can back pressure be too high in injection molding?<\/h3>\n<p>Yes, excessive back pressure is a common production problem. It raises melt temperature through shear heating, which degrades heat-sensitive materials like PVC and POM \u2014 causing discoloration, dark streaks, or burning. It also causes nozzle drooling between shots, flash at the mold parting line, significantly longer screw recovery times that extend overall cycle time, and accelerated mechanical wear on the screw, barrel, and check ring. If you notice any of these symptoms, reduce back pressure in 3\u20135 bar increments and monitor whether the problems resolve within the next few shots.<\/p>\n<h3>How do you adjust back pressure for different plastics?<\/h3>\n<p>Start with material-specific baselines: 5\u201310 bar for PP and PE, 8\u201315 bar for ABS and PS, 10\u201320 bar for PC and PMMA, and 3\u20138 bar for PVC and POM. These ranges account for differences in melt viscosity, thermal stability, and shear sensitivity. After setting the baseline, observe the parts closely: increase back pressure if you see gas marks, silver streaks, or inconsistent color mixing; decrease if you see nozzle drooling, discoloration, or flash. Fine-tune in 1\u20132 bar increments, and always document your final settings for future production runs on the same mold.<\/p>\n<h3>What is the difference between back pressure and holding pressure?<\/h3>\n<p>\u30d0\u30c3\u30af\u5727\u529b\u3068\u4fdd\u5727\u306f\u3001\u5c04\u51fa\u6210\u5f62\u30b5\u30a4\u30af\u30eb\u306e\u5168\u304f\u7570\u306a\u308b\u6bb5\u968e\u3067\u4f5c\u7528\u3057\u3001\u305d\u308c\u305e\u308c\u7570\u306a\u308b\u76ee\u7684\u3092\u679c\u305f\u3057\u307e\u3059\u3002\u30d0\u30c3\u30af\u5727\u529b\u306f\u30b9\u30af\u30ea\u30e5\u30fc\u5fa9\u5e30\uff08\u53ef\u5851\u5316\uff09\u6bb5\u968e\u3067\u4f5c\u7528\u3057\u3001\u30b9\u30af\u30ea\u30e5\u30fc\u306e\u5f8c\u9000\u904b\u52d5\u306b\u5bfe\u3059\u308b\u62b5\u6297\u3092\u5236\u5fa1\u3057\u3001\u5c04\u51fa\u524d\u306e\u6eb6\u878d\u6a39\u8102\u306e\u6df7\u5408\u3001\u5727\u7e2e\u3001\u8131\u6c17\u306e\u7a0b\u5ea6\u306b\u76f4\u63a5\u5f71\u97ff\u3092\u4e0e\u3048\u307e\u3059\u3002\u4e00\u65b9\u3001\u4fdd\u5727\u306f\u30ad\u30e3\u30d3\u30c6\u30a3\u5145\u586b\u5f8c\u306b\u4f5c\u7528\u3057\u3001\u90e8\u54c1\u304c\u51b7\u5374\u30fb\u56fa\u5316\u3059\u308b\u969b\u306e\u4f53\u7a4d\u53ce\u7e2e\u3092\u88dc\u511f\u3057\u307e\u3059\u3002\u3053\u308c\u3089\u3092\u6df7\u540c\u3059\u308b\u3053\u3068\u306f\u521d\u5fc3\u8005\u306b\u3088\u304f\u3042\u308b\u9593\u9055\u3044\u3067\u3042\u308a\u3001\u8aa4\u3063\u305f\u30d1\u30e9\u30e1\u30fc\u30bf\u3092\u8abf\u6574\u3057\u3066\u3082\u3001\u5bfe\u8c61\u3068\u306a\u308b\u6b20\u9665\u306f\u4fee\u6b63\u3067\u304d\u307e\u305b\u3093\u3002<\/p>\n<h3>Does back pressure affect cycle time?<\/h3>\n<p>Yes, higher back pressure directly slows screw recovery because the screw must retreat against greater resistance. If screw recovery time exceeds cooling time, it becomes the cycle bottleneck and total cycle time increases proportionally. This is why dynamic (staged) back pressure profiling is preferred on modern machines \u2014 you can apply higher pressure during the middle portion of recovery for optimal melt quality, then reduce near the end to speed up the final stage. This approach maximizes both part quality and production throughput without the tradeoff of uniformly high back pressure.<\/p>\n<h3>Why does my injection molding machine drool from the nozzle?<\/h3>\n<p>Nozzle drooling typically indicates that back pressure is set too high or barrel temperature near the nozzle zone is excessive. The elevated pressure pushes molten material through the nozzle tip between shots, creating stringers or drools that cause cold slugs and blocked gates in the next cycle. Try reducing back pressure by 3\u20135 bar first. If drooling persists, lower the nozzle zone barrel temperature by 5\u201310\u00b0C. For materials prone to drooling, consider using a shut-off nozzle (spring-loaded or mechanically actuated) as a hardware solution to complement proper pressure settings.<\/p>\n<h3>Should I use staged back pressure for every mold?<\/h3>\n<p>Staged back pressure is most beneficial for parts requiring high melt quality that are also sensitive to drooling or thermal degradation. If you are running simple commodity parts with forgiving materials like PP or PE, a single-stage setting is usually sufficient and easier to manage. For engineering plastics, optical or transparent components, and precision molds with tight tolerances, staged profiling almost always improves results \u2014 the cost is just a few minutes of setup time. Consider it standard practice for any mold running PC, PMMA, glass-filled materials, or multi-cavity tools where consistency across cavities is critical.<\/p>\n<hr style=\"margin:2em 0;border:none;border-top:1px solid #e0e0e0;\" \/>\n<ol class=\"footnotes\">\n<li id=\"fn:1\">\n<p><strong>back pressure:<\/strong> Back pressure is a controlled resistance applied to the screw during the plasticization phase, ensuring that the molten polymer achieves consistent density and homogeneity inside the barrel before injection. <a href=\"#fnref1:1\" class=\"footnote-backref\">\u21a9<\/a><\/p>\n<\/li>\n<li id=\"fn:2\">\n<p><strong>plasticizing pressure:<\/strong> Plasticizing pressure refers to the same parameter as back pressure \u2014 it describes the resistance that slows screw retraction during the material recovery phase of injection molding. <a href=\"#fnref1:2\" class=\"footnote-backref\">\u21a9<\/a><\/p>\n<\/li>\n<li id=\"fn:3\">\n<p><strong>screw recovery:<\/strong> Screw recovery is an essential phase of the injection molding cycle in which the screw rotates and retreats to plasticize and accumulate a measured volume of molten material for the next injection shot. <a href=\"#fnref1:3\" class=\"footnote-backref\">\u21a9<\/a><\/p>\n<\/li>\n<\/ol>","protected":false},"excerpt":{"rendered":"<p>\u30d0\u30c3\u30af\u30d7\u30ec\u30c3\u30b7\u30e3\u30fc1\u306f\u3001\u826f\u54c1\u3068\u512a\u308c\u305f\u88fd\u54c1\u3092\u5206\u3051\u308b\u5c04\u51fa\u6210\u5f62\u30d1\u30e9\u30e1\u30fc\u30bf\u306e\u4e00\u3064\u3067\u3059\u3002\u6b63\u3057\u304f\u8a2d\u5b9a\u3059\u308c\u3070\u3001\u6eb6\u878d\u6a39\u8102\u306f\u5747\u8cea\u306b\u306a\u308a\u3001\u30b7\u30e7\u30c3\u30c8\u91cd\u91cf\u306f\u5b89\u5b9a\u3057\u3001\u6210\u5f62\u54c1\u306f\u304d\u308c\u3044\u306b\u4ed5\u4e0a\u304c\u308a\u307e\u3059\u3002\u8aa4\u3063\u3066\u8a2d\u5b9a\u3059\u308b\u3068\u3001\u6c17\u6ce1\u3001\u8272\u30e0\u30e9\u3001\u30b5\u30a4\u30ba\u30d0\u30e9\u3064\u304d\u3068\u4e00\u65e5\u4e2d\u683c\u95d8\u3059\u308b\u3053\u3068\u306b\u306a\u308a\u307e\u3059\u3002\u5f53\u793e\u306e\u4e0a\u6d77\u5de5\u5834\u3067\u306f\u300190\u30c8\u30f3\u304b\u30891850\u30c8\u30f3\u307e\u3067\u306e47\u53f0\u306e\u5c04\u51fa\u6210\u5f62\u6a5f\u3067\u6bce\u65e5\u30d0\u30c3\u30af\u30d7\u30ec\u30c3\u30b7\u30e3\u30fc\u3092\u8abf\u6574\u3057\u3066\u3044\u307e\u3059\u300220\u5e74\u4ee5\u4e0a\u306b\u308f\u305f\u308b\u7d4c\u9a13\u304b\u3089\u3001\u30d0\u30c3\u30af\u30d7\u30ec\u30c3\u30b7\u30e3\u30fc\u3092\u9069\u5207\u306b\u8a2d\u5b9a\u3059\u308b\u3053\u3068\u304c\u3001\u6162\u6027\u7684\u306a\u6210\u5f62\u4e0d\u826f\u3092\u89e3\u6d88\u3059\u308b\u6700\u3082\u65e9\u3044\u65b9\u6cd5\u3067\u3042\u308b\u3053\u3068\u304c\u5206\u304b\u308a\u307e\u3057\u305f\u3002\u91cd\u8981\u306a\u30dd\u30a4\u30f3\u30c8\uff1a\u30d0\u30c3\u30af\u30d7\u30ec\u30c3\u30b7\u30e3\u30fc\u306f\u53ef\u5851\u5316\u6642\u306e\u30b9\u30af\u30ea\u30e5\u30fc\u306e\u5f8c\u9000\u901f\u5ea6\u3092\u5236\u5fa1\u3057\u3001\u6eb6\u878d\u54c1\u8cea\u306b\u76f4\u63a5\u5f71\u97ff\u3092\u4e0e\u3048\u307e\u3059[\u2026]<\/p>","protected":false},"author":1,"featured_media":53260,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_seopress_robots_primary_cat":"none","_seopress_titles_title":"How to Adjust Injection Molding Back Pressure? | ZetarMold","_seopress_titles_desc":"Back pressure is one of those injection molding parameters that separates good parts from great ones. Set it correctly, and your melt is homogeneous, your shot.","_seopress_robots_index":"","_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[42],"tags":[387,386,388],"meta_box":{"post-to-quiz_to":[]},"_links":{"self":[{"href":"https:\/\/zetarmold.com\/ja\/wp-json\/wp\/v2\/posts\/36247"}],"collection":[{"href":"https:\/\/zetarmold.com\/ja\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/zetarmold.com\/ja\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/zetarmold.com\/ja\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/zetarmold.com\/ja\/wp-json\/wp\/v2\/comments?post=36247"}],"version-history":[{"count":0,"href":"https:\/\/zetarmold.com\/ja\/wp-json\/wp\/v2\/posts\/36247\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/zetarmold.com\/ja\/wp-json\/wp\/v2\/media\/53260"}],"wp:attachment":[{"href":"https:\/\/zetarmold.com\/ja\/wp-json\/wp\/v2\/media?parent=36247"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/zetarmold.com\/ja\/wp-json\/wp\/v2\/categories?post=36247"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/zetarmold.com\/ja\/wp-json\/wp\/v2\/tags?post=36247"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}