{"id":1516,"date":"2021-07-01T08:25:43","date_gmt":"2021-07-01T08:25:43","guid":{"rendered":"https:\/\/www.plastikcity.co.uk\/blog\/?p=1516"},"modified":"2021-08-11T08:41:13","modified_gmt":"2021-08-11T08:41:13","slug":"troubleshooting-common-pelletising-quality-issues","status":"publish","type":"post","link":"https:\/\/www.plastikcity.co.uk\/blog\/troubleshooting-common-pelletising-quality-issues\/","title":{"rendered":"Troubleshooting Common Pelletising Quality Issues"},"content":{"rendered":"<p><strong>In this blog, <a href=\"https:\/\/davis-standard.com\/\" target=\"_blank\" rel=\"noopener\">Davis-Standard<\/a>, a leader in high-performance converting and extrusion systems, has summarised thirteen common pellet quality issues with photo examples, defect names, possible causes and troubleshooting steps for correction. <\/strong><\/p>\n<p><!--more--><\/p>\n<p>Having issues with your pellets? The good news is there are some troubleshooting techniques to yield more uniform pellets.<\/p>\n<p>Under normal processing conditions and with properly designed equipment, underwater pelletising should yield pellets uniform in size, shape, weight, and other desired characteristics for subsequent processing or aesthetics. To ensure consistency, it\u2019s important to identify common issues that lead to pellet defects during start-up, including worn pelletising components and incorrect operating conditions. In most cases, pellet defects have multiple causes.<\/p>\n<p>Addressing one variable at a time and allowing time between adjustments will help you determine the full effect of each change before making additional modifications.<\/p>\n<h3>Issue 1: Agglomeration and Large Clusters<\/h3>\n<p><strong><img decoding=\"async\" class=\"alignnone wp-image-40973\" src=\"https:\/\/www.plastikcity.co.uk\/blog\/wp-content\/uploads\/2021\/08\/Collage-1-Issue-1-Agglomeration-and-Large-Clusters.jpg\" alt=\"Davis Standard - Issue 1: Agglomeration and Large Clusters\" width=\"450\" height=\"215\" \/><\/strong><\/p>\n<p><strong>Cause:<\/strong><\/p>\n<ul>\n<li>The product is too hot<\/li>\n<li>Quench water is too hot<\/li>\n<li>Low quench water flow<\/li>\n<li>The product is inherently tacky<\/li>\n<li>Die holes are too close<\/li>\n<\/ul>\n<p><strong>Troubleshooting:<\/strong><\/p>\n<ul>\n<li>Lower the product temperature<\/li>\n<li>Lower the water temperature<\/li>\n<li>Check water rate<\/li>\n<li>Check for proper surfactant levels, if applicable<\/li>\n<li>Make knife adjustment<\/li>\n<\/ul>\n<h3>Issue 2: Fines and Angel Hair<\/h3>\n<p><img decoding=\"async\" class=\"alignnone size-full wp-image-40974\" src=\"https:\/\/www.plastikcity.co.uk\/blog\/wp-content\/uploads\/2021\/08\/Issue-2-Fines-and-Angel-Hair.png\" alt=\"Davis Standard - Issue 2: Fines and Angel Hair\" width=\"222\" height=\"300\" \/><\/p>\n<p><strong>Cause:<\/strong><\/p>\n<ul>\n<li>Chipped or cracked orifice tips<\/li>\n<li>Die holes are partially blocked<\/li>\n<li>The shaft is not aligned properly<\/li>\n<li>Knife tracking issues<strong>\u00a0<\/strong><\/li>\n<\/ul>\n<p><strong>Troubleshooting:<\/strong><\/p>\n<ul>\n<li>Make knife-to-die adjustment<\/li>\n<li>Plug chipped holes<\/li>\n<li>Purge die and check flow uniformity<\/li>\n<li>Check ID\/OD knife coverage on orifice holes<\/li>\n<li>Realign pelletiser<\/li>\n<li>Refurbish die plate<\/li>\n<\/ul>\n<h3>Issue 3: Twins, Triplets and Chains<\/h3>\n<p><img decoding=\"async\" class=\"alignnone wp-image-40975\" src=\"https:\/\/www.plastikcity.co.uk\/blog\/wp-content\/uploads\/2021\/08\/Collage-2-Issue-3-Twins-Triplets-and-Chains.jpg\" alt=\"Davis-Standard - Issue 3: Twins, Triplets and Chains\" width=\"450\" height=\"216\" \/><\/p>\n<p><strong>Cause:<\/strong><\/p>\n<ul>\n<li>The product is too hot<\/li>\n<li>Quench water is too hot<\/li>\n<li>Low quench water flow<\/li>\n<li>Knife speed is too high<\/li>\n<li>The product is inherently tacky<\/li>\n<li>Die holes are too close<\/li>\n<\/ul>\n<p><strong>Troubleshooting:<\/strong><\/p>\n<ul>\n<li>Lower product temperature<\/li>\n<li>Lower temperature<\/li>\n<li>Check water flow rate<\/li>\n<li>Reduce knife speed<\/li>\n<\/ul>\n<h3>Issue 4: Dog bones and Dumbbells<\/h3>\n<p><img decoding=\"async\" class=\"alignnone size-full wp-image-40976\" src=\"https:\/\/www.plastikcity.co.uk\/blog\/wp-content\/uploads\/2021\/08\/Issue-4-Dog-Bones-and-Dumbbells.png\" alt=\"Davis-Standard - Issue 4: Dog bones and Dumbbells\" width=\"194\" height=\"300\" \/><\/p>\n<p><strong>Cause:<\/strong><\/p>\n<ul>\n<li>Low viscosity or high MI product<\/li>\n<li>Elastic\/stretchy product<\/li>\n<li>Blades are worn beyond the limit<\/li>\n<\/ul>\n<p><strong>Troubleshooting:<\/strong><\/p>\n<ul>\n<li>Make knife clearance adjustment<\/li>\n<li>Lower quench water temperature<\/li>\n<li>Ensure the blades\u2019 leading edges are sharp<\/li>\n<li>Replace knife hub<\/li>\n<\/ul>\n<h3>Issue 5: Tails<\/h3>\n<p><img decoding=\"async\" class=\"alignnone wp-image-40977\" src=\"https:\/\/www.plastikcity.co.uk\/blog\/wp-content\/uploads\/2021\/08\/Collage-3-Issue-5-Tails.jpg\" alt=\"Davis-Standard - Issue 5: Tails\" width=\"349\" height=\"250\" \/><\/p>\n<p><strong>Cause:<\/strong><\/p>\n<ul>\n<li>Chipped or cracked orifice tips<\/li>\n<li>The knife-to-die gap is too large<\/li>\n<li>Die surface is irregular<\/li>\n<li>The shaft is not aligned properly<\/li>\n<li>Knife tracking issues<\/li>\n<\/ul>\n<p><strong>Troubleshooting:<\/strong><\/p>\n<ul>\n<li>Plug chipped holes<\/li>\n<li>Make knife adjustment<\/li>\n<li>Check ID\/OD knife coverage on orifice holes<\/li>\n<li>Realign pelletiser<\/li>\n<li>Replace and refurbish die plate<\/li>\n<\/ul>\n<h3>Issue 6: Longs and Elbows<\/h3>\n<p><img decoding=\"async\" class=\"alignnone size-medium wp-image-40978\" src=\"https:\/\/www.plastikcity.co.uk\/blog\/wp-content\/uploads\/2021\/08\/Collage-4-Issue-6-Longs-and-Elbows-300x214-1.jpg\" alt=\"Davis-Standard - Issue 6: Longs and Elbows\" width=\"300\" height=\"214\" \/><\/p>\n<p><strong>Cause:<\/strong><\/p>\n<ul>\n<li>Knife speed is too slow<\/li>\n<li>The extrusion rate is too high<\/li>\n<li>Frozen die holes<\/li>\n<li>Low melt temperature<\/li>\n<li>Too few knives on the knife hub<\/li>\n<\/ul>\n<p><strong>Troubleshooting:<\/strong><\/p>\n<ul>\n<li>Complete pellet efficiency calculation<\/li>\n<li>Increase the knife speed<\/li>\n<li>Reduce the extrusion rate<\/li>\n<li>Increase the die temperature<\/li>\n<li>Increase the water temperature<\/li>\n<li>Restart the pelletiser<\/li>\n<li>Increase the number of knives<\/li>\n<\/ul>\n<h3>Issue 7: Internal Voids<\/h3>\n<p><img decoding=\"async\" class=\"alignnone size-full wp-image-40979\" src=\"https:\/\/www.plastikcity.co.uk\/blog\/wp-content\/uploads\/2021\/08\/Issue-7-Internal-Voids.png\" alt=\"Davis-Standard - Issue 7: Internal Voids\" width=\"253\" height=\"300\" \/><\/p>\n<p><strong>Cause:<\/strong><\/p>\n<ul>\n<li>Moisture in the polymer entering pelletiser<\/li>\n<li>Entrained gas or volatiles in polymer<\/li>\n<li>Quench rate is too fast<\/li>\n<\/ul>\n<p><strong>Troubleshooting:<\/strong><\/p>\n<ul>\n<li>Ensure the polymer is dry<\/li>\n<li>De-gas polymer upstream of pelletiser<\/li>\n<li>Strip polymer solvents<\/li>\n<li>Increase quench water temperature<\/li>\n<\/ul>\n<h3>Issue 8: Dimples<\/h3>\n<p><img decoding=\"async\" class=\"alignnone wp-image-40980\" src=\"https:\/\/www.plastikcity.co.uk\/blog\/wp-content\/uploads\/2021\/08\/Issue-8-Dimples.png\" alt=\"Davis-Standard - Issue 8: Dimples\" width=\"205\" height=\"280\" \/><\/p>\n<p><strong>Cause:<\/strong><\/p>\n<ul>\n<li>Shrinkage due to fast quenching<\/li>\n<\/ul>\n<p><strong>Troubleshooting:<\/strong><\/p>\n<ul>\n<li>Increase quench water temperature<\/li>\n<\/ul>\n<h3>Issue 9: Dust<\/h3>\n<p><img decoding=\"async\" class=\"alignnone wp-image-40981\" src=\"https:\/\/www.plastikcity.co.uk\/blog\/wp-content\/uploads\/2021\/08\/Issue-9-Dust.png\" alt=\"Davis-Standard - Issue 9: Dust\" width=\"204\" height=\"261\" \/><\/p>\n<p><strong>Cause:<\/strong><\/p>\n<ul>\n<li>Product is friable or brittle in solid-state<\/li>\n<\/ul>\n<p><strong>Troubleshooting:<\/strong><\/p>\n<ul>\n<li>Slow centrifugal dryer speed; no more than 10%<\/li>\n<\/ul>\n<h3>Issue 10: Surface or Melt Fracture<\/h3>\n<p><img decoding=\"async\" class=\"alignnone wp-image-40982\" src=\"https:\/\/www.plastikcity.co.uk\/blog\/wp-content\/uploads\/2021\/08\/Issue-10-Surface-or-Melt-Fracture.png\" alt=\"Davis-Standard - Issue 10: Surface or Melt Fracture\" width=\"205\" height=\"265\" \/><\/p>\n<p><strong>Cause:<\/strong><\/p>\n<ul>\n<li>The extrusion rate is too high<\/li>\n<li>High die-hole shear rate<\/li>\n<li>The product is too viscous<\/li>\n<li>Frozen die holes<\/li>\n<li>Orifice hole final land is scored<\/li>\n<li style=\"list-style-type: none;\"><\/li>\n<\/ul>\n<p><strong>Troubleshooting:<\/strong><\/p>\n<ul>\n<li>Reduce the extrusion rate<\/li>\n<li>Increase product temperature<\/li>\n<li>Use a larger hole diameter<\/li>\n<li>Use a shorter orifice hole final land length<\/li>\n<li>Increase die plate internal temperature<\/li>\n<li>Smooth final land surface<\/li>\n<\/ul>\n<h3>Issue 11: Trash or Shavings<\/h3>\n<p><img decoding=\"async\" class=\"alignnone wp-image-40983\" src=\"https:\/\/www.plastikcity.co.uk\/blog\/wp-content\/uploads\/2021\/08\/Issue-11-Trash-or-Shavings.png\" alt=\"Davis-Standard - Issue 11: Trash or Shavings\" width=\"170\" height=\"264\" \/><\/p>\n<p><strong>Cause:<\/strong><\/p>\n<ul>\n<li>The knife-to-die gap is too large<\/li>\n<li>Infrequent knife adjustment<\/li>\n<li>Die face has a build-up of smeared product<\/li>\n<li>Blades are not ground properly<\/li>\n<li>Die surface is worn irregularly<\/li>\n<li>Product is inherently stringy<\/li>\n<\/ul>\n<p><strong>Troubleshooting:<\/strong><\/p>\n<ul>\n<li>Make knife adjustment<\/li>\n<li>Blades are worn beyond the limit<\/li>\n<li>Ensure the blades\u2019 leading edges are sharp<\/li>\n<li>Replace the knife hub<\/li>\n<li>Refurbish the die plate<\/li>\n<\/ul>\n<h3>Issue 12: Popcorn<\/h3>\n<p><img decoding=\"async\" class=\"alignnone wp-image-40984\" src=\"https:\/\/www.plastikcity.co.uk\/blog\/wp-content\/uploads\/2021\/08\/Issue-12-Popcorn.png\" alt=\"Davis-Standard - Issue 12: Popcorn\" width=\"205\" height=\"215\" \/><\/p>\n<p><strong>Cause:<\/strong><\/p>\n<ul>\n<li>Moisture in polymer entering pelletiser<\/li>\n<li>Entrained gas or volatiles in polymer<\/li>\n<li>Quench rate is too fast<\/li>\n<\/ul>\n<p><strong>Troubleshooting:<\/strong><\/p>\n<ul>\n<li>Ensure the polymer is dry<\/li>\n<li>De-gas polymer upstream of pelletiser<\/li>\n<li>Strip polymer solvents<\/li>\n<li>Increase quench water temperature<\/li>\n<\/ul>\n<h3>Issue 13: Non-Uniform Pellets in Length, Size, or Shape<\/h3>\n<p><img decoding=\"async\" class=\"alignnone size-medium wp-image-40985\" src=\"https:\/\/www.plastikcity.co.uk\/blog\/wp-content\/uploads\/2021\/08\/Collage-5-Issue-13-Non-Uniform-Pellets-in-Length-Size-or-Shape-300x215-1.jpg\" alt=\"Davis-Standard - Issue 13: Non-Uniform Pellets in Length, Size, or Shape\" width=\"300\" height=\"215\" \/><\/p>\n<p><strong>Cause:<\/strong><\/p>\n<ul>\n<li>Temperature or viscosity change in product<\/li>\n<li>Die plate segments are not evenly heated<\/li>\n<li>Die plate heating manifold inlet\/outlet design<\/li>\n<\/ul>\n<p><strong>Troubleshooting:<\/strong><\/p>\n<ul>\n<li>Add static or another mixer<\/li>\n<li>Check condensate traps or other heating media restrictions at each die plate segment<\/li>\n<li>Refurbish die if insulation is lost<\/li>\n<\/ul>\n<p>Finally, use recommended calculations to determine if your die plate orifice holes are open before making other adjustments. This will ensure you are not adjusting your underwater pelletiser to produce optimum pellets at a sub-optimum rate.<\/p>\n<div id=\"attachment_40986\" style=\"width: 310px\" class=\"wp-caption aligncenter\"><img decoding=\"async\" aria-describedby=\"caption-attachment-40986\" class=\"size-full wp-image-40986\" src=\"https:\/\/www.plastikcity.co.uk\/blog\/wp-content\/uploads\/2021\/08\/Pellets-Uniform-and-Shape-and-Size.png\" alt=\"Davis-Standard: Pellets Uniform and Shape and Size\" width=\"300\" height=\"191\" \/><p id=\"caption-attachment-40986\" class=\"wp-caption-text\">Pellets uniform in shape and size<\/p><\/div>\n<p><strong>If you need assistance in calculating the percentage of open holes, get in touch with the team using the contact details below.<\/strong><\/p>\n<p>This guide was provided by the <a href=\"https:\/\/www.plastikmedia.co.uk\/?s=Davis-Standard\" target=\"_blank\" rel=\"noopener\">Davis-Standard<\/a> Connect Blog team. For more blog entries, visit the <a href=\"https:\/\/davis-standard.com\/blog\/\" target=\"_blank\" rel=\"noopener\">DS Blog Archive<\/a>.<\/p>\n<p><em><img decoding=\"async\" class=\"alignnone wp-image-28780\" src=\"https:\/\/www.plastikcity.co.uk\/blog\/wp-content\/uploads\/2021\/08\/davis-standard-logo-300x56-1.png\" alt=\"Davis-Standard Logo\" width=\"284\" height=\"53\" \/><br \/>\n<a href=\"https:\/\/davis-standard.com\/\" target=\"_blank\" rel=\"noopener\">Davis-Standard<\/a><br \/>\n<a href=\"tel:+44 (0) 1384 471930\" target=\"_blank\" rel=\"noopener\">+44 (0) 1384 471930<\/a><br \/>\n<a href=\"https:\/\/davis-standard.com\/\" target=\"_blank\" rel=\"noopener noreferrer\">Website<\/a><br \/>\n<a href=\"mailto:ndenerley@davis-standard.com\" target=\"_blank\" rel=\"noopener noreferrer\">Email<\/a><\/em><\/p>\n<ul>\n<li style=\"list-style-type: none;\"><\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>In this blog, Davis-Standard, a leader in high-performance converting and extrusion systems, has summarised thirteen common pellet quality issues with photo examples, defect names, possible causes and troubleshooting steps for correction.<\/p>\n","protected":false},"author":101012,"featured_media":1520,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-1516","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-plastikcity-blogs","post-preview"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.plastikcity.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1516","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.plastikcity.co.uk\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.plastikcity.co.uk\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.plastikcity.co.uk\/blog\/wp-json\/wp\/v2\/users\/101012"}],"replies":[{"embeddable":true,"href":"https:\/\/www.plastikcity.co.uk\/blog\/wp-json\/wp\/v2\/comments?post=1516"}],"version-history":[{"count":0,"href":"https:\/\/www.plastikcity.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1516\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.plastikcity.co.uk\/blog\/wp-json\/wp\/v2\/media\/1520"}],"wp:attachment":[{"href":"https:\/\/www.plastikcity.co.uk\/blog\/wp-json\/wp\/v2\/media?parent=1516"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.plastikcity.co.uk\/blog\/wp-json\/wp\/v2\/categories?post=1516"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.plastikcity.co.uk\/blog\/wp-json\/wp\/v2\/tags?post=1516"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}