{"id":3376,"date":"2026-09-07T19:20:37","date_gmt":"2026-09-07T11:20:37","guid":{"rendered":"http:\/\/www.constructings.com\/blog\/?p=3376"},"modified":"2026-09-07T19:20:37","modified_gmt":"2026-09-07T11:20:37","slug":"what-is-the-cause-of-sink-marks-in-products-made-by-a-pet-injection-molding-machine-4ff0-502e82","status":"publish","type":"post","link":"http:\/\/www.constructings.com\/blog\/2026\/09\/07\/what-is-the-cause-of-sink-marks-in-products-made-by-a-pet-injection-molding-machine-4ff0-502e82\/","title":{"rendered":"What is the cause of sink marks in products made by a PET injection molding machine?"},"content":{"rendered":"<p>As a provider of PET injection molding machines, I&#8217;ve encountered numerous inquiries from clients regarding sink marks in molded products. Sink marks, often appearing as shallow depressions on the surface of molded parts, can significantly impact the aesthetic and functional qualities of the final product. In this blog post, I&#8217;ll explore the root causes of sink marks in products made by PET injection molding machines, offering insights and suggestions to help you overcome these challenges and achieve optimal molding results. <a href=\"https:\/\/www.arleximm.com\/pet-injection-molding-machine\/\">PET Injection Molding Machine<\/a><\/p>\n<p><img decoding=\"async\" src=\"https:\/\/www.arleximm.com\/uploads\/47424\/page\/small\/658t-pet-plastic-injection-moulding-machine852fa.jpg\"><\/p>\n<h3>Understanding PET and Its Injection Molding Process<\/h3>\n<p>Before delving into the causes of sink marks, it&#8217;s essential to understand the properties of PET (polyethylene terephthalate) and the intricacies of the injection molding process. PET is a thermoplastic polymer known for its exceptional strength, clarity, and chemical resistance, making it a popular choice for a wide range of applications, including packaging, automotive components, and consumer goods.<\/p>\n<p>The injection molding process involves melting PET resin pellets in a heated barrel and injecting the molten plastic into a mold cavity under high pressure. Once the plastic fills the cavity, it cools and solidifies, taking on the shape of the mold. However, during the cooling and solidification process, various factors can contribute to the formation of sink marks on the surface of the molded part.<\/p>\n<h3>Causes of Sink Marks in PET Injection Molding<\/h3>\n<h4>1. Uneven Cooling<\/h4>\n<p>One of the primary causes of sink marks in PET injection molding is uneven cooling. As the molten plastic cools and solidifies, it undergoes a volume shrinkage. If the cooling rate is not uniform throughout the part, some areas may solidify faster than others, leading to differential shrinkage and the formation of sink marks.<\/p>\n<p>Several factors can contribute to uneven cooling, including:<\/p>\n<ul>\n<li><strong>Mold Design:<\/strong> Poorly designed molds with inadequate cooling channels or uneven wall thickness can impede the flow of coolant, resulting in uneven cooling rates.<\/li>\n<li><strong>Coolant Temperature:<\/strong> Inconsistent coolant temperature can also cause uneven cooling. If the coolant is too cold in some areas and too warm in others, it can lead to differential shrinkage and sink marks.<\/li>\n<li><strong>Part Geometry:<\/strong> Complex part geometries with thick and thin sections can pose challenges in achieving uniform cooling. Thick sections tend to cool more slowly than thin sections, increasing the risk of sink marks.<\/li>\n<\/ul>\n<h4>2. Insufficient Packing Pressure<\/h4>\n<p>Packing pressure is the pressure applied to the molten plastic after the cavity is filled to compensate for the volume shrinkage that occurs during cooling. Insufficient packing pressure can result in incomplete filling of the mold cavity, leaving voids and sink marks on the surface of the molded part.<\/p>\n<p>Several factors can contribute to insufficient packing pressure, including:<\/p>\n<ul>\n<li><strong>Inadequate Injection Volume:<\/strong> If the injection volume is too low, there may not be enough plastic to fill the cavity completely, leading to sink marks.<\/li>\n<li><strong>Short Packing Time:<\/strong> Packing time is the duration for which the packing pressure is applied. If the packing time is too short, the plastic may not have enough time to flow and fill all the cavities, resulting in sink marks.<\/li>\n<li><strong>Mold Venting Issues:<\/strong> Poor mold venting can prevent the escape of air and gases from the mold cavity, creating back pressure and reducing the effectiveness of the packing pressure.<\/li>\n<\/ul>\n<h4>3. High Melt Temperature<\/h4>\n<p>The melt temperature of the PET resin is a critical parameter in the injection molding process. If the melt temperature is too high, the plastic becomes more viscous and prone to shrinkage during cooling, increasing the risk of sink marks.<\/p>\n<p>Several factors can contribute to high melt temperature, including:<\/p>\n<ul>\n<li><strong>Barrel Temperature Settings:<\/strong> Incorrect barrel temperature settings can cause the PET resin to overheat, leading to high melt temperatures.<\/li>\n<li><strong>Screw Speed and Back Pressure:<\/strong> Excessive screw speed and back pressure can generate frictional heat, raising the melt temperature of the plastic.<\/li>\n<li><strong>Resin Drying:<\/strong> Inadequate drying of the PET resin can cause moisture to vaporize during the melting process, increasing the melt temperature and the risk of sink marks.<\/li>\n<\/ul>\n<h4>4. Material Selection and Quality<\/h4>\n<p>The quality and properties of the PET resin used in the injection molding process can also affect the formation of sink marks. Some PET resins have a higher shrinkage rate than others, making them more prone to sink marks. Additionally, the presence of impurities or additives in the resin can influence its flow behavior and cooling characteristics, increasing the risk of sink marks.<\/p>\n<h4>5. Machine Settings and Maintenance<\/h4>\n<p>The performance and settings of the PET injection molding machine can also play a role in the formation of sink marks. Poorly maintained machines with worn-out components can affect the accuracy and consistency of the injection molding process, leading to sink marks. Additionally, incorrect machine settings, such as injection speed, pressure, and cooling time, can contribute to the formation of sink marks.<\/p>\n<h3>Solutions to Prevent Sink Marks in PET Injection Molding<\/h3>\n<h4>1. Optimize Mold Design<\/h4>\n<ul>\n<li><strong>Uniform Wall Thickness:<\/strong> Design molds with uniform wall thickness to ensure even cooling and minimize the risk of sink marks.<\/li>\n<li><strong>Adequate Cooling Channels:<\/strong> Incorporate sufficient cooling channels in the mold design to ensure efficient heat transfer and uniform cooling.<\/li>\n<li><strong>Proper Venting:<\/strong> Ensure proper venting in the mold to allow the escape of air and gases during the injection molding process, reducing the risk of back pressure and sink marks.<\/li>\n<\/ul>\n<h4>2. Adjust Process Parameters<\/h4>\n<ul>\n<li><strong>Increase Packing Pressure and Time:<\/strong> Increase the packing pressure and time to ensure complete filling of the mold cavity and compensate for the volume shrinkage during cooling.<\/li>\n<li><strong>Optimize Melt Temperature:<\/strong> Adjust the barrel temperature settings, screw speed, and back pressure to maintain the optimal melt temperature for the PET resin, reducing the risk of shrinkage and sink marks.<\/li>\n<li><strong>Control Cooling Time:<\/strong> Optimize the cooling time to ensure uniform cooling and prevent the formation of sink marks.<\/li>\n<\/ul>\n<h4>3. Select the Right Material<\/h4>\n<ul>\n<li><strong>Choose Low-Shrinkage Resins:<\/strong> Select PET resins with low shrinkage rates to minimize the risk of sink marks.<\/li>\n<li><strong>Ensure Proper Resin Drying:<\/strong> Properly dry the PET resin before use to remove moisture and prevent vaporization during the melting process, reducing the risk of high melt temperature and sink marks.<\/li>\n<\/ul>\n<h4>4. Maintain the Injection Molding Machine<\/h4>\n<ul>\n<li><strong>Regular Maintenance:<\/strong> Perform regular maintenance on the PET injection molding machine to ensure optimal performance and accuracy.<\/li>\n<li><strong>Replace Worn-Out Components:<\/strong> Replace worn-out components, such as screws, barrels, and nozzles, to maintain the integrity of the injection molding process and minimize the risk of sink marks.<\/li>\n<\/ul>\n<h3>Conclusion<\/h3>\n<p>Sink marks in products made by PET injection molding machines can be a frustrating and costly issue for manufacturers. However, by understanding the root causes of sink marks and implementing the appropriate solutions, you can prevent their formation and achieve high-quality, defect-free molded parts.<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/www.arleximm.com\/uploads\/47424\/small\/screw-chiller1d9bd.jpg\"><\/p>\n<p>As a leading provider of PET injection molding machines, we are committed to helping our clients overcome these challenges and achieve optimal molding results. Our state-of-the-art machines are designed with advanced features and technologies to ensure precise control of the injection molding process, minimizing the risk of sink marks and other defects.<\/p>\n<p><a href=\"https:\/\/www.arleximm.com\/plastic-injection-moulding-machine\/\">Plastic Injection Moulding Machine<\/a> If you&#8217;re experiencing sink marks in your PET injection molding process or looking to upgrade your existing equipment, we invite you to contact us for a consultation. Our team of experts will work with you to understand your specific needs and provide customized solutions to meet your requirements. Let&#8217;s work together to take your PET injection molding process to the next level.<\/p>\n<h3>References<\/h3>\n<ul>\n<li>Tharammal, S., &amp; Kotnis, G. (2019). Injection Molding: Principles and Practices. Wiley.<\/li>\n<li>Rosato, D. V., &amp; Rosato, D. V. (2011). Injection Molding Handbook. Springer.<\/li>\n<li>Beaird, C. W. (2017). Injection Molding for Medical Applications. Hanser Publishers.<\/li>\n<\/ul>\n<hr>\n<p><a href=\"https:\/\/www.arleximm.com\/\">Ningbo Yalishi (Arlex) Plastic Machinery Co., Ltd.<\/a><\/p>\n<p>Address: No.63, Huangsu East Road, Industrial Zone, Dongqian Lake Tourist Resort, Ningbo, Zhejiang Province<br \/>E-mail: leo@arlex.cn<br \/>WebSite: <a href=\"https:\/\/www.arleximm.com\/\">https:\/\/www.arleximm.com\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>As a provider of PET injection molding machines, I&#8217;ve encountered numerous inquiries from clients regarding sink &hellip; <a title=\"What is the cause of sink marks in products made by a PET injection molding machine?\" class=\"hm-read-more\" href=\"http:\/\/www.constructings.com\/blog\/2026\/09\/07\/what-is-the-cause-of-sink-marks-in-products-made-by-a-pet-injection-molding-machine-4ff0-502e82\/\"><span class=\"screen-reader-text\">What is the cause of sink marks in products made by a PET injection molding machine?<\/span>Read more<\/a><\/p>\n","protected":false},"author":228,"featured_media":3376,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[3339],"class_list":["post-3376","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industry","tag-pet-injection-molding-machine-4e1c-509f84"],"_links":{"self":[{"href":"http:\/\/www.constructings.com\/blog\/wp-json\/wp\/v2\/posts\/3376","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.constructings.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.constructings.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.constructings.com\/blog\/wp-json\/wp\/v2\/users\/228"}],"replies":[{"embeddable":true,"href":"http:\/\/www.constructings.com\/blog\/wp-json\/wp\/v2\/comments?post=3376"}],"version-history":[{"count":0,"href":"http:\/\/www.constructings.com\/blog\/wp-json\/wp\/v2\/posts\/3376\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.constructings.com\/blog\/wp-json\/wp\/v2\/posts\/3376"}],"wp:attachment":[{"href":"http:\/\/www.constructings.com\/blog\/wp-json\/wp\/v2\/media?parent=3376"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.constructings.com\/blog\/wp-json\/wp\/v2\/categories?post=3376"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.constructings.com\/blog\/wp-json\/wp\/v2\/tags?post=3376"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}