--- title: "Injection Molding Defects: Brittleness" description: Purging Expert Jeremy Cooley talks about the injection molding defect of brittleness. image: https://www.asaclean.com/hubfs/AI-Generated%20Media/Images/This%20image%20depicts%20a%20shattered%20windshield-1.jpeg --- [ Order Online ](https://asaclean.my.site.com/b2bstore) [ Free Sample ](https://offers.asaclean.com/free-sample) ## [ Asaclean Blog ](https://www.asaclean.com/blog) Browse by Topic " aerospace asaclean asaclean news Asaclean® benefits asahi kasei automotive Best Practices black specks blisters blow molding blown-film extrusion buyers caps and closures carbon contamination cast-film extrusion Chemical Purging Compounds clear applications Color Changeovers Company News compounding consumer products contamination Cost savings custom molders Customer Success Story decreasing scrap defects electronics Energy Efficiency EX Grade extruder cleaning Extrusion fillament glass filled Glitter Grade Selection HDPE High and Low Temp Changeovers hold a bubble Hot Runners Injection Molding Injection Molding Tips LDPE Lightweight automotive components LLDPE low residue maintenance Material Changeovers Mechanical Purging Compounds medical Melt Flow Index NPE 24 nylons on the fly packaging PCR PEEK Polypropylene Post Consumer Resins preventative preventative purging processing tips profile extrusion Purge Program purge programs Purge Training Purge Trial purging purging compounds purging concentrates purging procedures Purging Tips quality recycled resins residue issues scrap reduction Screw Pulls sheet extrusion shutdown and sealing start-up super engineering resins Sustainability Tech Day technical support training trials Troubleshooting Twin Screw twin screw extrusion two step purging U Grade ULTEM venting Viscosity webinars wire extrusion - 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[LinkedIn Share ](https://www.linkedin.com/shareArticle?mini=true&url=https%3A%2F%2Fwww.asaclean.com%2Fblog%2Finjection-molding-defects-brittleness&title=Injection%20Molding%20Defects%3A%20Brittleness&summary=Purging+Expert+Jeremy+Cooley+talks+about+the+injection+molding+defect+of+brittleness.&source=) - [Pinterest Pin ](https://pinterest.com/pin/create/button/?url=https%3A%2F%2Fwww.asaclean.com%2Fblog%2Finjection-molding-defects-brittleness) - [Email Email ](mailto:?subject=Injection%20Molding%20Defects%3A%20Brittleness&body=https%3A%2F%2Fwww.asaclean.com%2Fblog%2Finjection-molding-defects-brittleness) ![Injection Molding Defects: Brittleness](https://www.asaclean.com/hs-fs/hubfs/AI-Generated%20Media/Images/This%20image%20depicts%20a%20shattered%20windshield-1.jpeg?width=640&height=500&name=This%20image%20depicts%20a%20shattered%20windshield-1.jpeg) ![Brittle Plastic](https://www.asaclean.com/hs-fs/hubfs/Brittle%20Plastic.jpg?width=344&name=Brittle%20Plastic.jpg) With injection molding there are many variables that go into a good part.  These include everything from the resin to the press to the mold and so forth. It also includes processes and drying and water temperature. Everything needs to be dialed in to get that repeatable, cycle after cycle quality product that can be shipped to the customer.  One injection molding defect that happens from time to time is part brittleness.  Brittleness appears when the part breaks or cracks upon ejection or after it is ejected during handling.  We will investigate this defect and the likely causes resulting from either Material, Mold, or Machine causes. **1.) Machine:**  With the process, the defect can be caused by several means.  Brittleness can be caused if the mold filling speed is too slow.  In this case increase the injection speed and be sure to maintain a consistent cushion.  The melt temperature of the resin could also be too low.  There are several things a molder can do to increase the melt temperature including increasing the heat profile to certain barrel zones or increasing the rpm which in turn increases the shear rate and melt temp. **2.) Mold: **When molding components, if the surface of the mold is too cold it can often cause brittleness in the part.  It is important that the correct water temp is used for quality molding.  The design of the mold can work against you as well.  If the runners and gates are too small for the application it can create excessive shear rates during filling which in turn can cause the brittleness. **3. )Material: ** In cases where the material being processed causes the brittleness of the part sometimes too much regrind is being added to the resin.  Regrinded resin breaks down significantly after a couple of generations of grinding.  In this case, reduce the amount of regrind percentage or mold with virgin resin for a while to see if the defect goes away.  Then the regrind can be added back into the process at a lower percentage that works with the process.  Contamination by foreign material can also cause brittleness.  Inspect the resin and perhaps run some tests to be sure that the resin isn’t contaminated with foreign matter or additives causing this defect. **Ready to reduce your ****production downtime**** to protect your profits? Learn more about how ****purging compounds**** and process efficiency work in tandem.** ![Yoko Tanaka](https://www.asaclean.com/hs-fs/hubfs/Yoko%20Tanaka%20Headshot%203-25-16.jpg?width=150&name=Yoko%20Tanaka%20Headshot%203-25-16.jpg) #### [ Yoko Tanaka ](https://www.asaclean.com/blog/author/yoko-tanaka) Yoko Tanaka is the Marketing Manager at Asaclean. She has been helping molders and extruders learn about Asaclean purging and how to improve their processes for the past eight years. - [Share On LinkedIn ](https://www.linkedin.com/in/yokotanaka/) ## Related Posts [![11 Ways to Prevent Degradation in Thermoplastic Extrusion](https://www.asaclean.com/hs-fs/hubfs/AI-Generated%20Media/Images/This%20image%20depicts%20someone%20writing%20the%20word%20DEFECTS%20and%20circling%20it%20with%20a%20red%20marker.jpeg?width=450&height=250&name=This%20image%20depicts%20someone%20writing%20the%20word%20DEFECTS%20and%20circling%20it%20with%20a%20red%20marker.jpeg) 11 Ways to Prevent Degradation in Thermoplastic Extrusion Purging Tips / 5 min read / August 10, 2018 ](https://www.asaclean.com/blog/11-tips-for-avoiding-material-degradation-in-your-thermoplastic-extruder) [![Injection Molders-Let's Vent!](https://www.asaclean.com/hs-fs/hubfs/AI-Generated%20Media/Images/this%20image%20depicts%20a%20steam%20engine%20with%20steam%20pumping%20out-1.jpeg?width=450&height=250&name=this%20image%20depicts%20a%20steam%20engine%20with%20steam%20pumping%20out-1.jpeg) Injection Molders-Let's Vent! Troubleshooting / 3 min read / November 09, 2018 ](https://www.asaclean.com/blog/injection-molders-lets-vent) ## Comments Get Started ## Ready to start improving your efficiency and increasing your profitability? - [Request a Consultation](https://www.asaclean.com/blog/injection-molding-defects-brittleness#) - [Contact Sales](https://www.asaclean.com/blog/injection-molding-defects-brittleness#) ![](https://www.asaclean.com/hubfs/assets/images/icons/icon-layers.svg) #### Free Sample Request a free sample of Asaclean® Purging Compounds for your plant and start saving today. [Request your free sample](https://offers.asaclean.com/en/free-sample?hsLang=en) ![](https://www.asaclean.com/hubfs/assets/images/icons/icon-calculator.svg) #### Cost Savings Calculator Use our free calculator to see how much you could be saving with Asaclean® Purging Compounds. [See your savings](https://www.asaclean.com/cost-savings-calculator) [ Back to Top ](https://www.asaclean.com/blog/injection-molding-defects-brittleness#top) ```json { "@context" : "https://schema.org", "@type" : "BlogPosting", "author" : { "@type" : "Person", "name" : "Yoko Tanaka", "url" : "https://www.asaclean.com/blog/author/yoko-tanaka" }, "dateModified" : "2025-07-07T18:18:58.581Z", "datePublished" : "2019-05-02T17:56:00.000Z", "headline" : "Injection Molding Defects: Brittleness", "image" : [ "https://www.asaclean.com/hubfs/AI-Generated%20Media/Images/This%20image%20depicts%20a%20shattered%20windshield-1.jpeg" ], "mainEntityOfPage" : { "@id" : "https://www.asaclean.com/blog/injection-molding-defects-brittleness", "@type" : "WebPage" }, "publisher" : { "@type" : "Organization", "logo" : { "@type" : "ImageObject", "url" : "https://www.asaclean.com/hubfs/Asaclean%20Logo%20TM.jpg" }, "name" : "Asahi Kasei Plastics North America" } } ``` ```json { "@context" : "http://schema.org", "@type" : "Article", "articleBody" : "With injection molding there are many variables that go into a good part. These include everything from the resin to the press to the mold and so forth. It also includes processes and drying and water temperature. Everything needs to be dialed in to get that repeatable, cycle after cycle quality product that can be shipped to the customer. One injection molding defect that happens from time to time is part brittleness. Brittleness appears when the part breaks or cracks upon ejection or after it is ejected during handling. We will investigate this defect and the likely causes resulting from either Material, Mold, or Machine causes. 1.) Machine: With the process, the defect can be caused by several means. Brittleness can be caused if the mold filling speed is too slow. In this case increase the injection speed and be sure to maintain a consistent cushion. The melt temperature of the resin could also be too low. There are several things a molder can do to increase the melt temperature including increasing the heat profile to certain barrel zones or increasing the rpm which in turn increases the shear rate and melt temp.", "author" : { "@type" : "Person", "name" : "Yoko Tanaka" }, "datePublished" : "May 02, 2019", "headline" : "Injection Molding Defects: Brittleness", "image" : "https://468726.fs1.hubspotusercontent-na1.net/hubfs/468726/AI-Generated%20Media/Images/This%20image%20depicts%20a%20shattered%20windshield-1.jpeg", "name" : "Injection Molding Defects: Brittleness", "url" : "https://www.asaclean.com/blog/injection-molding-defects-brittleness" } ```