Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. The total amount of scrap being produced during injection molding will usually be higher than that for compression molding because of the additional material loss created. Reduce the temperature of the mold and plastic being injected. Gas trapping/ poor venting. More about the knit lines in injection molding. RELATED CONTENT. This picture shows a. May happen at first shots while mold is being dialed in. a specific area on one side lens, a warp line, and a weft line. land and using maximum vent depths to get them as close to self-cleaning as possible. Flow Lines Knit or Weld Lines Cavity Gates Table 1 Knit line in a multi-injection-point cavity. Thick sections take longer to cool than thin ones. The above guidelines for initial heater band settings are for most injection molded parts. The main causes of Weld Line or Knit lines are: Convergence of two flowing polymer melt streams during injection molding process: This is the most common cause of weld lines, as the two melt streams coming from different runners or gates in the mold meet and do not fully mix, creating a weak point in the finished product. สาเหตุรองของการเกิดปัญหาการเกิดประกายเงิน (silver streak) 1. After the solidification of molten plastic, the finished part is ejected out. Inadequate injection pressure can result in knit lines and a surface that. Revisiting the '5 M's' of Molding. Depending on the material you use, the knit lines could be invisible or obvious—work with an injection molding company to figure out how to reduce the mold lines on your product. ”. The design of the mold, as well as the part being molded, has a significant impact on the success of the process. Any of the above can result in “knit lines” on final products, but mold flow analysis prior to mold machining can keep these issues from cropping up at all in iteration and production. Dedicated to strict quality management and thoughtful client services, our experienced staff customers are generally available to discuss your demands and guarantee full client pleasure for Knit Line Injection Molding, Electronics. Increase injection speed. As always, feel free to contact us at 877-479-3680 or [email protected] if questions or concerns emerge. The most common location of knit line formation is behind molded-in holes that are made by core pins in the mold. Table 2. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. In the 1947 book, Injection Molding of Plastics, the late Dr. Troubleshooting Injection Molding Weld Lines. Numerical results show that weld lines can be predicted accurately, and the formation and evolution processes of weld line can be shown more clearly by co-injection molding technique. Solution: People. Compression molded parts can vary in thickness without issue. Kurt W. Randy Kerkstra has been in the plastics industry for over 26 years, occupied frequently with troubleshooting injection molding. Submarine Gates. Anisotropy. Using restrictors helps push visible knit lines into less conspicuous areas. Steven. A knit line is the spot where two flows meet. Molding parts with multiple gates will almost certainly produce a weld line at right-angles to the line joining the two gates which could cause the weld lines to be exceptionally weak (see Figure 1. This article looks at the issues presented by a weld line in injection molding and the techniques manufacturers can use to avoid them. Meld and knit lines are actually both different types of weld lines. Reduce the injection pressure. Injection moulding is a manufacturing process that melts, injects and sets plastic into a metal mould. It is also one of the most important weapons in a molder’s arsenal for making process changes. They again get resolidified along the surface. Swirling can increase depending on the material you use, and the texture or polish of injection molding tools. The present. They again get resolidified along the surface. How weld lines form. More about the knit lines in injection molding. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary from virtually invisible to something that looks like cracks in the plastic. We originally thought it may be caused by a silicone release agent that was occasionally sprayed on the injection mold, but testing with minimal agent and later built-in slip agent showed no change. Weld line, also known as knit line or meld line, is a visible line or mark on the surface of a plastic part where two or more flow fronts of molten plastic meet and fuse together. While injection molding itself is a straightforward process involving melting thermoplastic resin and injecting it into a mold cavity, knit lines can pose. 203 in. The last cause of flow lines may be the operators running your daily operations. There are processes such as gas assist that do not require the injection unit to pressurize (pack out) the cavity, but for our discussion, we will stay with conventional injection molding. The areas in the cavity where such buildup tends to be common are at end-of-fill areas, details that trap gas, and knit lines. Achieving a high-quality surface finish can be challenging, and other methods, such as polishing or coating, may be required. plastic recycling machine, blown film extruder, filament extrusion line, injection molding machine, blow molding machine, injection blow molding machine, bag making machine, flexo. Take these steps to avoid knit lines. Knit lines generally occur around holes or other obstructions to the melt flow. Meld and knit lines are actually both different types of weld lines. Near-Net-Shape Molding enables us to eliminate knit lines, add undercuts, increase options for geometry and tolerances, and reduce tooling cost for low. 3. From the start of your project, you can count on The Toolroom to exceed your expectations for all of your plastic injection molding needs. Injection Pressure 0r Speed Too Low Explanation: If the injection speed or pressure is too low, the molten plastic will not be pushed into the mold cavity fast enough to fill and knit at converging flow fronts because it cools down and solidifies too soon. Adding vents, using overflows, or using porous metal. Having uniform wall thicknesses between 0. Bubbles are caused by melting flow fronts colliding in a mold cavity. But applying excessive force can create problems with the part, mold, and machine. Flow rate and flow speed are cut in half at every runner branch. Below is a list of items that should be checked both during normal molding operations and if defects are detected. These defects are not visible, like small. com. When injection molding complex parts, often knit-lines are formed during the mold filling stage. This slight depression is a tiny line called the weld line or knit line. If the part design’s wall thickness is constant, the magnitude of the plastic’s velocity will be the same at every. spelling: injection molding) is a process for producing parts by injecting molten material into a mould, or mold. It can also aid in material selection since fill. Poor Knit Lines. Increasing injection speed. It emerges and becomes visible when the flow fronts cannot mold or knit during the molding process. Proper venting is essential to molding a defect-free part. Also, since this part will likely be painted or chrome plated, knit lines are a concern. Increase the mold temperature and reduce the barrel temperature for injection molding of thin-walled products. An option to bluing agents, the long established means of gauging pressure distribution, comes via Pressurex, a thin, flexible, plastic film. He is currently a tooling manager for a large, multi-plant molding and manufacturing company. 197 in. Shear Controlled Orientation Injection Molding of Polymeric Composites with Enhanced Properties. They occur when melt flow fronts collide in a mold cavity. Over the years, I have developed two separate “5M” systems. Injection molding is the most cost-competitive technology for manufacturing high volumes of identical plastic parts. The knit lines are the result of poor molding conditions (likely molding at too low of a temperature). molding run to be sure that the temperature does not exceed the recommended limits . ICOMold is a plastic injection molding company that manufactures plastic injection molded parts. There are times when porous materials like Porcerax are used in problem or backfill areas. Final Report-Plastic Injection Molding - Free download as Word Doc (. [1] Here are a few ways to prevent knit lines in your plastic parts: Increase material temperature: Higher temperatures on both materials prevent one section from cooling too quickly. , Rallis, A. This month, we covered an array of topics including injection mold venting, business strategies and runnerless micro molds. Without adequate support pillars, flashing of the parting line faces and bowing of the plates may occur. The weld line can either be a minor cosmetic issue. Three terms that often get mixed up in injection molding are weld, meld and knit lines. As melt temperature, viscosity and abrasiveness rise, tool life will decline. In this case it would be 0. Knit/Weld Lines. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Misra A. Meld and knit lines are actually both different types of weld lines. While knit lines can be present it does not always mean the structural integrity of the plastic part is compromised. This was usually with a PC/ABS material at knit lines and high fill pressures from thin walls in the part. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. Weld lines also can be visible after a part is painted and can cause wrinkles on in-mold-label injection-molded products. By altering the part design, it may be possible to just have one flow front, and avoid multiple flow fronts having to come together. weld lines may form during the injection molding process and work closely with the plastic injection molder and tool builder to choose the best possible gate location. The resulting line has the. The point I am making here is, if you’re injecting 14. The depth of the texture or letters is somewhat limited, and extra draftInjection molding tool design and build for complex parts, with precision tooling and molding capabilities for industries demanding high-quality, critical components. Compression molding produces solid parts that are free of flow and knit lines. Draft. A knit line, also. Insufficient injection pressure and speed can cause weld lines. Weld line are formed whenever melt fronts separate and recombine at some downstream location. In the plastic injection moulding industry, we work with materials that are by-products of oil refinement and moulds made of metal casting, so our terminology is bound to be at least slightly confusing. These lines can manifest as visible marks on the component’s surface and potentially affect its structural integrity. The temperature might fall at some places like in the mold, runners leading to the mold and injection molding. Inappropriate temperature. Injection Molding Guide. Injection molding is a manufacturing process that involves injecting molten plastic into a mold cavity to create a specific shape or design. Parts molded with ABS are susceptible to forming knit lines, which are visible lines on the surface of the part. Design. Injection Molding: How to Set Second. Steven. Depending on the design of the mould and the material being injected, a knit line may: present no problem at all, be a cosmetic issue, or cause a potentially. They are formed downstream through holes, and between multiple gate locations. Contact Us. Using the design cube, learn how knit lines are formed on plastic parts and tips to avoid knit lines in your plastic injection molding design. Knit Lines 11: 1. The wall thicknesses of an injection molded part generally range from 2mm – 4mm (0. For those processes in which the plastic fills out a mold (cold press, compression, injection, reaction injection, resin transfer, structural foam, and transfer molding ), openings in the part can be molded into the part through the use of cores. Knit lines and other aesthetic characteristics of the part are strictly related to the plastic’s temperature during molding, so efficient filling time is essential for achieving proper welding lines and quality parts. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. Mold flow analysis is a software simulation that can show how resin will fill the mold during the injection molding process. Mold filling simulation software should be used to ensure that waterInjection Molding Problems and Solutions (17/17) – Weld or Knit Lines Sep 27, 2022Main causes of knit lines in injection molding: 1. There are two primary reasons for this occurrence: 1. Learn how to troubleshoot weld lines in injection molding. The comment on melt flow index is correct, but, I've molded straight PC down to . Material. This line does not normally impact the overall shape or dimensions of the item. Adding draft or slope to vertical walls of a part makes it easier to eject or remove the part from the mold. Recommended for the bonding of nylon (polyamide) and polypropylene materials, this thermoplastic elastomer delivers wide compatibility and thermal stability, allowing for use in demanding conditions. Figure 1: Knit lines in a cover plate. Remove the hardened material from the mold. If you have any issues getting. Participating in DFM and mold flow analysis is a good way to achieve this. Legend: a-in. (1. Prototype Tool In Soon As 10 Days; Production Tool In As Soon As 3 Weeks; 10k Parts in 10 Days; GET YOUR 30 SECOND QUOTE NOW. Determine the time duration of the molten state. Gates, vents, sliding cams, pick-out inserts, and any other place where the two sides of. The fluid path has an inlet and a radially continuous, downwardly. Knit lines occur at points where resin flows converge after molding around an obstruction or protrusion within the mold, usually away from the gate area. suppressed cooling and possibly warp. It is caused by the incomplete joining of the uncured. Too cool a melt. shows some obvious locations for vents, a brief molding trial should be conducted to observe where the gas voids occur. Very high quality and an extreme fit may. Highly ScalableVacuum on the mold does help and many times eliminates the weld line. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. Weld lines often leave witness marks in the moulding surface. Solution: People. H-13 Good general purpose tool steel. DFM Helps Prevent Sink Marks In Plastic Injection Molding. How to Eliminate Knit Lines In Injection Molding - Xcentric Mold Want to learn how to eliminate knit lines that form during the injection molding process? Then. 040-in. Weld lines may appear like seams or scratches, but that is not what they are. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. Dabei erreichen unsere Produkte zufriedene Käufer in mehr als 30 Ländern. 160"). For. Commonly seen at the edge of a hole or other cored feature, knit lines are—as a rule—purely cosmetic, but may create a physical failure point if present in an area of the part that receives substantial stress, such as the head of a screw. Industrial Knitting Machines. 5 mm) is ideal, according to injection molding engineer Jack Rulander of Protolabs in Maple Plain, MN. Cold weld line or known as “knit line” isWeld Line defect analysis, the most common of many defects in injection moulding products. Learn more. The difference between a knit and meld line is significant, dramatically impacting the part’s structural integrity. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. 3. You don't give us much to go on. The injection molding machine includes a fluid path extending through the first mold portion. The injection of molding compound into the parts through one or two gates may produce parts that have knit lines. In an injection mold, the plastic fluid flows and spreads out in many directions as it comes out of the gate. 3. Reduction of sink can possibly be had by switching to an ABS/PC-blended material. 02 in. Mold bases, ejector plates, and some cavities (if nickel or chrome plated to prevent rust). In the injection molding process, melting takes place via two factors that work together: shear and heat. Weld-line strength for plastics can vary from 20% to nearly 100% of the strength of the plastic itself. com TYPICAL PROPERTIES MECHANICAL THERMAL OPTICAL. You can avoid knit lines and other problems by creating designs with smooth geometries. They occur when two resin flows meet at different. Also known as a knit line, this is the point at which two flow formations meet and are unable to. 3. S. 2. 5 mm (0. Mold cores can be machined from a solid piece of copper alloy or inserted to aid in construction or allow for easier replacement if a com-ponent would ever be damaged in molding. Figures courtesy of CAE Services. And often, the mold is the same color as the plastic polymer, or can appear that way due to a lack of contrast caused by difficulties lighting the inside of the mold. Knit lines, also called parting lines, are any lines where two resin flows meet and may or may not be visible. directly! FCS Group, based in Taiwan, was established 40 years ago and is well known in Asia as a quality manufacturer of machinery, offering several lines of injection molding machines and other specialty and customized equipment. Introduction to Knit Line Injection Molding Knit Line Injection Molding is a process that allows manufacturers to produce parts more quickly, accurately, and at less cost than traditional injection molding. Know about the cause of these lines and the potential solutions. Weld lines are also known as “stitch lines” or “knit lines”. With over 50 years of experience, Universal Plastic Mold can help you avoid (or at least minimize) knit lines in your molded parts. Short shots and knit lines are two phenomena that are caused by using highly viscousHowever, they can also create weld lines or knit lines in the part where the flow fronts meet. Download : Download full-size image; 3. Conversely, texturing of part surfaces is often effective in hiding flaws and imparting a “grippy” or leather-like. Learn more. As. Brent Strong, p. In spite of its cosmetic attributes, a bad knit line can significantly. Criens}, journal={Materials Chemistry and Physics}, year={1986}, volume={14}, pages={69-83} }A structural automotive sub frame component ( 10 ) that is formed from a sheet molding compound having carbon fibers. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. Remove holes if possible. Knit lines. 12515 NE 95th Street , Vancouver, WA 98682 CALL TODAY: 1-800-839-0366Contact FU CHUN SHIN MACHINERY MANUFACTURE CO. Meld and knit lines are actually both different types of weld lines. Soft metals, such as aluminum and beryllium copper, can be used for prototype<br />. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. This type of molding uses a single tool to create both the part's geometry and surface finish in one step. By contrast, a slow injection speed will give you a matte finish and a cold mold, such as 50F, will give you a more flexible part. Runner Type. Plasti-Co ® manufactures a wide range of injection molding nozzles from standard nozzle tips, extended nozzle tips, nozzle bodies, extended nozzles bodies, custom bodies, general purpose to full taper, shut-off, mixing and filtering applications. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. The quality of the answer is directly proportional to the information we have to work with. Knit Lines. Potential Knit Lines • Knit lines occur where to or mold melt fronts come together-Holes, slots, multiple gates, variations in wall thickness-Meld lines occur when the melt comes together in the same flow direction • Knit lines are areas of weakness and should be located in low stress areas . The plastics used by injection molding processes are relatively cheap and can be used to achieve a wide variety of properties, so injection molding is popular for creating many packaging and consumer products, like LEGO! A weld line (weld point, flow line or a knit line) forms when separate melt fronts travelling in opposite directions meet. sinks, knit lines, and shrinkage,” Spalding says. Snake Lines: The appearance of snake lines is caused by the formation of a jet effect as the melt travels through a gate and into the mold cavity. With the right nozzle, you can boost cycle. Weld lines are a common imperfection to be found in most plastic injected molded parts. The pipe underwent brittle fracture into many pieces because of the high residual stresses in the wall of the pipe. 5-3. Thin wall injection molding can produce walls as thin as 0. But we can’t talk about the injection molding process without discussing the injection molding machine. Injection moulding can be performed with a host of materials mainly including metals (for which the process is called die-casting ), glasses, elastomers, confections, and most commonly thermoplastic and. Therefore, with the cooling process, the resin in the central part shrinks and expands to the surface, resulting in insufficient filling in the central part, which is called vacuum. In injection molding, it is often important to maintain consistent color throughout the part. Weld or knit lines occur when melt flow fronts collide in a mold cavity. From Plastic Materials and Processing by A. Polym Compos 1982; 3: 88–96. 6. Transfer molding also utilizes a press and a mold. 4. ” What else can you do about weld lines—besides redesigning the mold or gate locations or adjust the flow pattern during fill with sequential valve gating? I recently saw a report on this issue from Moldex3D, the maker of molding simulation software. Melt temperature does. A structural finite element analysis (FEA) can be used to compare locations of high stress to the locations of the knit lines identified in the mold-filling analysis. Knit lines don’t. This image shows a PVC pipe after it was accidentally dropped on the ground. Bubbles are caused by melting flow fronts colliding in a mold cavity. 250 in. Description: Flow lines are streaks, patterns, or lines - commonly off-toned in color - that show up on the prototype part as a consequence of the physical path and cooling profile of the molten plastic as it flows into the injection mold tooling cavity. Redesign the mold: Redesigning the mold to. Runner Type. ISO 9001:2015. Observation on a “trial and error” basis may be required. Plasti-Co. BURN MARKS Burn Marks: burn marks can occur when the design of a plastic part, and the subsequent injection mold design, causes air to be trapped during the injection (or filling stage) of the molding cycle. To prevent swirling, perform tests whenever possible and use pre-compounded resin to ensure identical color match across parts. Because they can be shut off independently you can control flow fronts and knit-line locations. Sink Marks Cause 5: Improper Part Geometry. plastic recycling machine, blown film extruder, filament extrusion line, injection molding machine, blow molding machine, injection blow molding machine, bag making machine, flexo. Also known as “stitch lines” or “weld lines”. Typical Tool Steel for Injection Mold Construction Steel Type Steel Properties Mold Component P-20 Pre-hardened, machines well, high carbon, general-purpose steel. The injection molding design process, much like all industrial design processes, deals primarily with the creation, look, and feel of a product. However, the weld line may not continue throughout the flow. Incompletely fused extrusion knit Line. Influence of injection-molding parameters on the morphology and mechanical properties of glass fiber-reinforced polypropylene composite. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no weld line. On a hydraulic machine you can program hold pressure: For example, if you set 850 psi (59 bar), you will get 850 psi hold pressure for the time you set on. Learn how small changes to an injection molding design like wall thickness or material choice can lead to more durable parts that are free of cosmetic defects. Influence of injection-molding parameters on the morphology and mechanical properties of glass fiber-reinforced polypropylene composite. In layman’s terms, injection molding boils down to four simple steps: Melt material. Still, they are almost always a cosmetic issue. Overall, injection molding is a relatively simple process. Part Design Summary Bosses:Welds and/or Knit lines can be defined as the inability of two or more flow fronts to “knit” together, or "weld", during the molding process. They are formed when two or more flow frontINJECTION MOLDING GUIDE V2. Injection moulding (U. To account for variations in viscosity, nylon injection molding machines need to maintain an appropriate injection pressure. For over four decades, our experienced team and leading edge technology have provided you with tooling solutions from start to finish. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. 5 to 3. It is. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. Knit line / Meld line / Transfer line Discoloured line where two flow fronts meet Mould or material temperatures set too low (the material is cold when they meet, so they don't bond). Each mold produces as specific part. When injection molding a part, a knit line may present no problem, or can cause a serious structural problem. PAPER ABSTRACT: Desktop injection molding machines and stereolithographic print ed molds make hands-on injection molding production possible in design studio classrooms and labs. Resin cools as it is injected into a mold. A majority of these investigations concern amorphous polymers, whereas a number of engineering polymers are semicrystalline and also contain reinforcing fillers and fibers. Direct experience designing molds and parts for injection molding and producing the molds and parts is valuable, relevant experience for design students. Weld lines or knit lines and meld lines formed when two melt fronts run into each other or join together can be improved by. (1987). 5 inches) dispersed throughout the structural automotive sub frame component ( 10 ). Using three test materials, polystyrene (PS), polycarbonate (PC) and polyoxymethylene (POM), the relationship between a design and a processing parameter and the effects of the knit-lines on the tensile properties of injection molded plates. Trapped air in a mold manifests itself as a burn mark on the molded part. PROBLEM: POOR ADHESION OF LSR MATERIAL TO. 140 in. Knit lines are most common downstream of holes created in parts where the molten material meets. However, product designers relying on this molding method encounter various challenges during tool design and development. In the present work, the micro specimens were investigated. Poorly constructed or worn out mold. If you need injection molding expertise, we’re here to help. By altering the part design, it may be possible to just have one flow front, and avoid multiple flow fronts having to come together. Weld lines have a significant effect on manufactured products. Meld and knit lines are actually both different types of weld lines. These lines occurs usually around holes or obstructions and cause locally weak areas in the molded part. SPI surface finishes are the most common set of injection molding finishing standards around the world with over 12 different grades. Trapped gas is one of the most common causes of part burns, and can also lead to short shots and voids, blemishes and discernible knit lines that weaken the part. Plastic injection molding is the industry’s most common way to manufacture parts. It’s also relatively inexpensive. Polym Compos 1982; 3: 88–96. Two major sources of weld lines are multiple gating and flow around pins. ISSUE FACED BY THE INJECTION MOLDING COMPANIES: FLOWLINES (ALSO CALLED WELD LINES OR KNIT LINES) Definition: Streaks, orange skin, or visible flow lines in parts. A knit line is what happens when plastic flows coming from two different directions meet inside of the mold and solidify. To ensure quality parts, injection molding companies must have the best injection mold design first + (91) 96067-70777 +(971) 547-161-112. Plastic injection molding is a process where a thermoplastic resin is heated to its melting point and injected into the cavity of an injection mold. Some of the most popular brands include:Harshal Bhogesra has 9+ years of combined experience in molding, customer & supplier development. Release of trapped air in those cases will. Remedies: Raise the temperature of the mold or molten plastic. In an injection molded structural plastic part, a weld line (also called a knit line) will result in a region of mechanical weakness as soon as the part is submitted to an external load. Misra A. This course outlines mold filling and how different gating configurations affect filling. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. The plastics used by injection molding processes are relatively cheap and can be used to achieve a wide variety of properties, so injection molding is popular for creating many packaging and consumer products, like LEGO!. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. The main types of injection molding defects are: 1. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. No matter the size of a production run, the presence of blemishes on the finished product leads to unhappy clients. In the 1947 book, Injection Molding of Plastics, the late Dr. It is also where a slide mechanism might meet where it shuts off on one of the mold halves. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Knit Lines. Weld Lines-3 Ways for Detecting and Correcting. Once the mold is created and the machine is set up, additional parts can be manufactured very fast and at a very low cost. In the world of injection molding, each weld. Knit lines form during the injection molding process when two resin flows meet. In fact, knit line strength will decrease with higher filler content and with longer fibers. Edge Gates. As these flow fronts come together. Below is a list of items that should be checked both during normal molding operations and if defects are detected. In injection molded parts, there are 2 types of weld lines: The first type of weld mark is called cold-melt joints and is formed when the melt front enters the cavity with different gates. Weld lines are among the most critical structural defects in parts made by the injection molding of fiber-reinforced thermoplastics, explained Sirmax in a press release. As a result, the portion has a faint, perhaps undetectable line. Meld and knit lines are actually both different types of weld lines. As the polymer resin is injected into a mold, it flows through all parts of the mold. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. Islyn Thomas summarized the need for a particular vent location better than I ever could. 030- to 0. ) or as thick as 25 mm (1 in. land and using maximum vent depths to get them as close to self-cleaning as possible. During injection, support pillars keep closed the two halves of the plastic injection mold. New blog post is up! What Are Knit Lines in Injection Molding, and How Do You Prevent Them? #injectionmolding #moldsmart #howto #rjg…Injection moulding is a well established mass production tool for polymeric products of all shapes and sizes which is now drawing the attention of companies and researchers who seek to utilise this high throughput fabrication technique to produce devices with nanoscale dimensions []. Three terms that often get mixed up are weld, meld, and knit lines. Check the diameter of the ejector pins and the pin hole tolerances, if the tolerance is too wide this could allow molten plastic to flow down between the pin and hole surface. The three dimensional structure is formed of a resin fiber mixture having a resin material infused with carbon fibers having a length of about 12. Weld lines, created in the areas of collision of two flow fronts of plastic in the injection mold cavity, are the reason of lower mechanical properties and a worse surface condition of molded parts. Without it, air and gas are trapped in the mold, which compress and heat as the cavity fills.