[{"data":1,"prerenderedAt":565},["ShallowReactive",2],{"catalog:meta":3,"blog:article:\u002Fblog\u002Fsink-marks-injection-molding-causes-solutions":258,"blog:more:3:\u002Fblog\u002Fsink-marks-injection-molding-causes-solutions:Troubleshooting":534},{"categories":4,"machines":132,"zones":212,"totals":255},[5,35,59,122],{"id":6,"name":7,"slug":8,"description":9,"partCount":10,"subcategories":11},"EC","Electrical Components","electrical","Electrical systems and components for injection molding machines including heaters, thermocouples, servo motors, and controllers.",11,[12,17,22,27,31],{"id":13,"name":14,"slug":15,"partCount":16},"EC-CBC","Circuit Boards & Controllers","circuit-boards",4,{"id":18,"name":19,"slug":20,"partCount":21},"EC-CE","Connectors & Cables","connectors-cables",2,{"id":23,"name":24,"slug":25,"partCount":26},"EC-GEP","Servo Motors & Drives","servo-motors",1,{"id":28,"name":29,"slug":30,"partCount":21},"EC-HT","Heaters","heaters",{"id":32,"name":33,"slug":34,"partCount":21},"EC-SF","Safety Components","safety",{"id":36,"name":37,"slug":38,"description":39,"partCount":40,"subcategories":41},"HY","Hydraulic Components","hydraulic","Complete range of hydraulic system components including pumps, valves, motors, and pressure controls for injection molding machines.",14,[42,46,51,55],{"id":43,"name":44,"slug":45,"partCount":26},"HY-AU","Accumulators","accumulators",{"id":47,"name":48,"slug":49,"partCount":50},"HY-CV","Control Valves","control-valves",6,{"id":52,"name":53,"slug":54,"partCount":26},"HY-MO","Monitors & Gauges","monitors-gauges",{"id":56,"name":57,"slug":58,"partCount":50},"HY-PW","Pumps & Motors","pumps-motors",{"id":60,"name":61,"slug":62,"description":63,"partCount":64,"subcategories":65},"MC","Mechanical Components","mechanical","Mechanical parts and assemblies including barrels, screws, tie bars, bushings, platens, and clamping components.",42,[66,71,75,80,85,89,93,97,101,105,109,114,118],{"id":67,"name":68,"slug":69,"partCount":70},"MC-BC","Barrels & Cylinders","barrels-cylinders",5,{"id":72,"name":73,"slug":74,"partCount":16},"MC-SB","Screw Barrels & Seals","screws",{"id":76,"name":77,"slug":78,"partCount":79},"MC-TC","Tie Bars & Columns","tie-bars",7,{"id":81,"name":82,"slug":83,"partCount":84},"MC-GZ","Bushings & Guides","bushings-guides",8,{"id":86,"name":87,"slug":88,"partCount":26},"MC-PP","Platens","platens",{"id":90,"name":91,"slug":92,"partCount":70},"MC-TL","Toggle & Links","toggle-links",{"id":94,"name":95,"slug":96,"partCount":21},"MC-CC","Clamping Components","clamping",{"id":98,"name":99,"slug":100,"partCount":21},"MC-GMP","Tools & Accessories","tools-accessories",{"id":102,"name":103,"slug":104,"partCount":21},"MC-ES","End Caps & Plates","end-caps",{"id":106,"name":107,"slug":108,"partCount":26},"MC-SR","Seals & Rings","seals-rings",{"id":110,"name":111,"slug":112,"partCount":113},"MC-JM","Joints & Mounts","joints-mounts",3,{"id":115,"name":116,"slug":117,"partCount":26},"MC-SG","Safety Guards","safety-guards",{"id":119,"name":120,"slug":121,"partCount":26},"MC-CR","Clamping Mechanism","clamping-mechanism",{"id":123,"name":124,"slug":125,"description":126,"partCount":113,"subcategories":127},"O","Other Components","other","Additional components including filters, cooling systems, lubrication parts, and other auxiliary equipment.",[128],{"id":129,"name":130,"slug":131,"partCount":113},"O-TC","Filters & Cooling","filters-cooling",[133,143,161,172,180,188,194,200,205],{"id":134,"name":135,"slug":134,"series":136,"partCount":142},"haitian","Haitian International",[137,138,139,140,141],"Mars Series (MA)","Jupiter Series (JU)","Zhafir Venus Series (VE)","Zhafir Zeres Series (ZE)","Zhafir Jeres Series (JE)",68,{"id":144,"name":145,"slug":144,"series":146,"partCount":160},"yizumi","Yizumi",[147,148,149,150,151,152,153,154,155,156,157,158,159],"A6 Series","A5-EU Series","A5-N Series","SKIII Series","DP Series","D1 Series","FF Series","FF-M Series","P Series","CG-P Series","VM Series","SPET Series","LSR Series",12,{"id":162,"name":163,"slug":162,"series":164,"partCount":171},"chen-hsong","Chen Hsong",[165,166,167,168,169,170],"JETMASTER MK Series","JETMASTER SVP Series","SUPERMASTER Series","EASYMASTER Series","SPARK Series","JETMASTER C2 Series",10,{"id":173,"name":174,"slug":173,"series":175,"partCount":179},"tederic","Tederic",[176,177,178],"NEO Series","D Series (Two-Platen)","DE Series (All-Electric)",0,{"id":181,"name":182,"slug":181,"series":183,"partCount":179},"borch","Borch",[184,185,186,187],"BU Series (Two-Platen)","BS-III Series (Servo)","BE Series (All-Electric)","BM Series (Multi-color)",{"id":189,"name":190,"slug":189,"series":191,"partCount":179},"log-machine","LOG Machine",[192,193],"LOG-SE Series","LOG-EE Series (All-Electric)",{"id":195,"name":196,"slug":195,"series":197,"partCount":179},"donghua","Donghua",[198,199],"DH Series (Servo)","DH-TP Series (Two-Platen)",{"id":201,"name":202,"slug":201,"series":203,"partCount":179},"sunbun","Sunbun",[204],"Sunbun Servo Series",{"id":206,"name":207,"slug":206,"series":208,"partCount":179},"lijin","L.K. Machinery (Lijin)",[209,210,211],"POTENZA Series","FORZA Series (Two-Platen)","ELETTRICA Series (All-Electric)",[213,217,221,225,228,231,235,238,242,248,251],{"id":214,"number":26,"name":215,"role":216,"partCount":21},"clamp-cylinder","Clamping cylinder","The hydraulic cylinder behind the rear platen. It drives the crosshead that straightens the toggle links, which opens and closes the mold and builds the clamping force.",{"id":218,"number":21,"name":219,"role":220,"partCount":50},"toggle","Toggle mechanism","Links, pins and bushings between the rear and moving platens. They multiply the force of the clamping cylinder and lock the mold shut while plastic is injected.",{"id":222,"number":113,"name":223,"role":224,"partCount":113},"ejector","Ejector","A small cylinder behind the moving platen that pushes the ejector rods and plate forward to release the finished part from the mold.",{"id":78,"number":16,"name":226,"role":227,"partCount":40},"Tie bars & bushings","Four steel columns that join the platens, guide the moving platen and carry the clamping force. Tie bar nuts lock them in place; bushings guide the moving platen along them.",{"id":88,"number":70,"name":229,"role":230,"partCount":21},"Platens & mold plates","The fixed and moving platens carry the two halves of the mold; the rear platen anchors the toggle. Locating rings and clamping plates center and hold the mold.",{"id":232,"number":50,"name":233,"role":234,"partCount":50},"barrel-screw","Barrel, screw & nozzle","The screw turns inside the heated barrel to melt and mix the plastic, then moves forward to inject it through the nozzle into the mold. The screw tip and check ring stop melt from flowing back.",{"id":30,"number":79,"name":236,"role":237,"partCount":113},"Heater bands & sensors","Heater bands around the barrel and nozzle melt the plastic. Thermocouples measure each heating zone so the controller can hold the set temperature.",{"id":239,"number":84,"name":240,"role":241,"partCount":79},"injection-unit","Injection unit","Injection cylinders push the screw forward, the hydraulic (plasticizing) motor turns it, and the carriage moves the unit against the mold on its guide rails.",{"id":243,"number":244,"name":245,"role":246,"partCount":247},"hydraulics",9,"Hydraulic unit","The pump, motor, valves, accumulator, filters and oil cooler in the machine base. They supply and control the oil pressure for every movement of the machine.",16,{"id":8,"number":171,"name":249,"role":250,"partCount":244},"Electrical cabinet","The controller, I\u002FO and drive boards, servo drives, contactors and safety switches that run and protect the machine.",{"id":252,"number":10,"name":253,"role":254,"partCount":21},"feet","Machine feet","Leveling bolts and anti-vibration pads under the machine base that keep the machine level and stop vibration spreading to the floor.",{"parts":256,"subcategories":257},70,23,{"id":259,"title":260,"articleType":261,"author":262,"body":263,"category":516,"date":517,"description":518,"extension":519,"image":520,"lastModified":521,"meta":522,"navigation":523,"path":524,"seo":525,"seoTitle":520,"stem":526,"tags":527,"__hash__":533},"blog\u002Fblog\u002Fsink-marks-injection-molding-causes-solutions.md","Sink Marks on Injection Molded Parts: What's Really Going On","howto","IMSPARES Technical Team",{"type":264,"value":265,"toc":502},"minimark",[266,270,279,282,287,290,293,301,305,308,314,317,323,326,330,335,338,341,344,367,371,374,377,381,384,387,391,394,397,401,404,410,416,422,426,429,455,459,462,499],[267,268,260],"h1",{"id":269},"sink-marks-on-injection-molded-parts-whats-really-going-on",[271,272,273,278],"p",{},[274,275,277],"a",{"href":276},"\u002Ftroubleshooting\u002F#sink-marks","Sink marks",". Every molder has dealt with them. Those annoying depressions on the surface, usually opposite ribs, bosses, or thick sections.",[271,280,281],{},"They look like someone pressed a thumb into the plastic before it hardened. And in a sense, that's exactly what happened — the inside of the part shrunk more than the outside, pulling the surface inward.",[283,284,286],"h2",{"id":285},"the-physics-in-plain-language","The Physics in Plain Language",[271,288,289],{},"Plastic shrinks as it cools. More volume of plastic = more total shrinkage. When you have a thick section behind a visible surface — like a rib intersection or a boss — the thick area takes longer to cool and shrinks more than the surrounding thinner walls.",[271,291,292],{},"The surface solidifies first (it's against the cold mold wall). Then the interior continues cooling and shrinking. As it shrinks, it pulls the already-solidified surface inward. That's your sink mark.",[271,294,295,296,300],{},"The key insight: ",[297,298,299],"strong",{},"sink marks are a geometry problem first, and a process problem second."," You can sometimes eliminate them with process adjustments, but if the part design has a massive rib-to-wall ratio, no amount of packing pressure will fully compensate.",[283,302,304],{"id":303},"the-part-design-factor","The Part Design Factor",[271,306,307],{},"This is where the conversation gets uncomfortable, because fixing part design is harder than adjusting machine settings. But it's the truth:",[271,309,310,313],{},[297,311,312],{},"The #1 rule:"," Rib thickness should be 50-60% of the adjacent wall thickness. A 2mm wall should have ribs no thicker than 1.0-1.2mm at the base.",[271,315,316],{},"When ribs are thicker than this guideline, you get a thick zone at the rib-wall junction. That thick zone is the sink mark waiting to happen.",[271,318,319,322],{},[297,320,321],{},"Bosses"," create the same problem. The ring of material where a boss meets the wall is essentially a thick section.",[271,324,325],{},"If you have control over part design, this is where to focus. If you don't (you're molding someone else's part), then process adjustments are your only option.",[283,327,329],{"id":328},"process-solutions","Process Solutions",[331,332,334],"h3",{"id":333},"packing-pressure-and-time","Packing Pressure and Time",[271,336,337],{},"Packing (holding) pressure is the primary process control for sink marks. After injection fills the cavity, the screw maintains pressure to push additional material into the cavity as it shrinks.",[271,339,340],{},"Higher packing pressure forces more material in, compensating for shrinkage. Longer packing time maintains that pressure until the gate freezes and seals off.",[271,342,343],{},"But there are limits:",[345,346,347,351,359],"ul",{},[348,349,350],"li",{},"If the gate freezes before the thick section has cooled enough, packing pressure can't reach the problem area",[348,352,353,354,358],{},"Excessive packing pressure can cause ",[274,355,357],{"href":356},"\u002Ftroubleshooting\u002F#flash","flash",", sticking, or overpacking (its own set of problems)",[348,360,361,362,366],{},"On older machines with worn ",[274,363,365],{"href":364},"\u002Finjection-molding-machine-parts\u002Fbarrel-screw\u002Fcheck-ring\u002F","check rings",", maintaining consistent packing pressure is harder because the check valve leaks back",[331,368,370],{"id":369},"injection-speed","Injection Speed",[271,372,373],{},"Faster injection fills the cavity before much cooling happens. The surface layer is thinner at the time packing begins, making packing more effective.",[271,375,376],{},"However, too-fast injection can cause jetting, burn marks, or other issues. It's a balance.",[331,378,380],{"id":379},"mold-temperature","Mold Temperature",[271,382,383],{},"Higher mold temperature keeps the surface pliable longer, allowing packing pressure to work more effectively. This is particularly helpful for semi-crystalline materials (nylon, POM, PP) which shrink more than amorphous materials.",[271,385,386],{},"The trade-off: higher mold temperature = longer cooling time = longer cycle.",[331,388,390],{"id":389},"melt-temperature","Melt Temperature",[271,392,393],{},"Higher melt temperature reduces viscosity, allowing pack pressure to transmit further through the part. But excessively high melt temperature increases overall shrinkage (the plastic starts from a hotter, more expanded state and has further to shrink).",[271,395,396],{},"Usually, melt temperature adjustments have a smaller effect on sink marks compared to pack pressure and mold temperature.",[283,398,400],{"id":399},"material-considerations","Material Considerations",[271,402,403],{},"Some materials are more prone to sink marks than others:",[271,405,406,409],{},[297,407,408],{},"High shrinkage materials"," (PP, PE, nylon, POM): More prone, especially crystalline grades. These materials can shrink 1.5-2.5% and form distinct sink marks.",[271,411,412,415],{},[297,413,414],{},"Low shrinkage materials"," (PS, ABS, PC, PC\u002FABS): Less prone, but still possible with thick sections. Shrinkage is typically 0.4-0.7%.",[271,417,418,421],{},[297,419,420],{},"Glass-filled grades",": Less sink because the glass fiber reduces shrinkage and stiffens the part. A 30% glass-filled nylon rarely shows sink marks that would be visible on unfilled nylon.",[283,423,425],{"id":424},"when-you-cant-fix-it","When You Can't Fix It",[271,427,428],{},"Sometimes you just can't fully eliminate sink marks with process alone. The part design demands it, and the customer won't accept design changes. In those cases:",[345,430,431,437,443,449],{},[348,432,433,436],{},[297,434,435],{},"Texture the visible surface"," — a textured surface hides sink marks incredibly well. Mold texturing (EDM, chemical etch, laser) is a legitimate engineering solution, not a hack.",[348,438,439,442],{},[297,440,441],{},"Move the gate"," — gating closer to the thick section allows packing pressure to reach the problem area more effectively.",[348,444,445,448],{},[297,446,447],{},"Use gas-assist injection"," — nitrogen gas injected into the thick section creates a hollow channel, eliminating the thick mass that causes sinking. Requires equipment and mold modifications.",[348,450,451,454],{},[297,452,453],{},"Accept cosmetic limits"," — communicate honestly with the customer about what's physically achievable with the current design.",[283,456,458],{"id":457},"machine-condition-matters","Machine Condition Matters",[271,460,461],{},"On older machines, inconsistent sink marks (some shots fine, others not) often point to:",[345,463,464,470,480],{},[348,465,466,469],{},[297,467,468],{},"Worn check ring"," — inconsistent shot volume and pack pressure delivery. Check ring replacement is relatively inexpensive and can dramatically improve consistency.",[348,471,472,479],{},[297,473,474,475],{},"Worn ",[274,476,478],{"href":477},"\u002Finjection-molding-machine-parts\u002Fhydraulics\u002Fproportional-valve\u002F","proportional valves"," — inconsistent pressure control means inconsistent packing.",[348,481,482,488,489,493,494,498],{},[297,483,484],{},[274,485,487],{"href":486},"\u002Finjection-molding-machine-parts\u002Fhydraulics\u002F","Hydraulic issues"," — pressure spikes or drops during pack phase. Check ",[274,490,492],{"href":491},"\u002Fparts\u002Fhy-pw-06\u002F","hydraulic pump"," condition and ",[274,495,497],{"href":496},"\u002Fparts\u002Fo-tc-02\u002F","oil filter"," cleanliness.",[271,500,501],{},"Before chasing process parameters, make sure your machine can actually deliver consistent injection and packing. If the machine is inconsistent, process optimization is futile — you're chasing a moving target.",{"title":503,"searchDepth":21,"depth":21,"links":504},"",[505,506,507,513,514,515],{"id":285,"depth":21,"text":286},{"id":303,"depth":21,"text":304},{"id":328,"depth":21,"text":329,"children":508},[509,510,511,512],{"id":333,"depth":113,"text":334},{"id":369,"depth":113,"text":370},{"id":379,"depth":113,"text":380},{"id":389,"depth":113,"text":390},{"id":399,"depth":21,"text":400},{"id":424,"depth":21,"text":425},{"id":457,"depth":21,"text":458},"Troubleshooting","2026-10-08","Sink marks are depressions on the surface of molded parts. Learn what causes them and the practical solutions that actually work in production.","md",null,"2026-10-31",{},true,"\u002Fblog\u002Fsink-marks-injection-molding-causes-solutions",{"title":260,"description":518},"blog\u002Fsink-marks-injection-molding-causes-solutions",[528,529,530,531,532],"sink marks","molding defects","packing pressure","wall thickness","part design","1zWMRHc-ZNFzD8uXvIkNyfPn2_MHn2GJaULxGKNPRwY",[535,545,556],{"title":536,"path":537,"description":538,"date":521,"category":516,"tags":539},"Injection Nozzle Problems: Drooling, Stringing, and Blockages Explained","\u002Fblog\u002Finjection-nozzle-problems-troubleshooting","Common injection nozzle issues and how to fix them. Covers drool, stringing, cold slugs, nozzle blockages, and when to replace the nozzle tip or body.",[540,541,542,543,544],"injection nozzle","nozzle drool","stringing","nozzle replacement","cold slug",{"title":546,"path":547,"description":548,"date":549,"category":516,"tags":550},"Short Shots in Injection Molding: Causes and Fixes","\u002Fblog\u002Fshort-shots-injection-molding-causes-fixes","Short shots mean incomplete parts. Here are the real causes — not just the textbook answers — and what actually fixes them on the shop floor.","2026-09-30",[551,552,553,554,555],"short shots","incomplete fill","injection pressure","mold venting","troubleshooting",{"title":557,"path":558,"description":559,"date":549,"category":516,"tags":560},"Troubleshooting Hydraulic Pressure Loss in Injection Molding Machines","\u002Fblog\u002Ftroubleshooting-hydraulic-pressure-loss","Diagnose and fix hydraulic pressure loss problems in injection molding machines. Common causes, step-by-step troubleshooting, and replacement parts guide.",[38,561,555,562,563,564],"pressure loss","vane pump","piston pump","control valve",1793548985937]