Meld and knit lines are actually both different types of weld lines. Gate design is another critical piece of part function in plastic injection molding. It is caused by the incomplete joining of the uncured. Fewer knit lines. Below is a list of items that should be checked both during normal molding operations and if defects are detected. 3. (knit) line and produces a latent, or obvious, part defect. When the plastic cools, it takes the shape of the mold and is then ejected and finished. Material contamination, for example, can cause several molding issues. 4. These materials have beenDetermining the correct tonnage provides a foundation that must be rock-solid to avoid flash and damage. ) are easy to produce. (1987). By altering the part design, it may be possible to just have one flow front, and avoid multiple flow fronts having to come together. The mold settings can run flawlessly until employees consistently open the machine for inspections, interrupt cycle times, or cause temperature. This will helpTroubleshooting Injection Molding Weld Lines. As a result, prototyping is strongly recommended for parts with. Meld and knit lines are actually both different types of weld lines. Here are some reasons why design is important for injection molding. occupied frequently with troubleshooting injection molding. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. In the 1947 book, Injection Molding of Plastics, the late Dr. . Injection molding is the most cost-competitive technology for manufacturing high volumes of identical plastic parts. With ABS injection molding, you get the collective benefits and properties of three monomers. The part is cooled in the mold until it is solid enough to be ejected. They occur when melt flow fronts collide in a mold cavity. Meld and knit lines are actually both different types of weld lines. Weld lines have a significant effect on manufactured products. Mold vents should function the same way. When 2 flows meet, small hair-like discolorations may develop. 6. Parts molded with ABS are susceptible to forming knit lines, which are visible lines on the surface of the part. For example, warping, sink marks, drag marks, and knit lines can all impact the visual appeal of the manufactured part. 040 and 0. 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. Injection Molding Problems and Solutions (17/17) – Weld or Knit Lines Sep 27, 2022 Injection Molding Problems and Solutions (16/17) – Warpage Sep 15, 2022. Improve venting and/or relocate to burned area. So what does the 140F mold temperature give us? The molding technician thought the 140F mold water was OK because the data sheet provided by the material supplier suggested mold temperatures from 75 to 180F. Having uniform wall thickness makes it possible for the melted plastic to fill the mold evenly, therefore not creating a part with warp, sink, thin knit lines, or other defects. Also known as knit lines. These knit-lines are well-known as particularly critical regions in the mold when mechanically. How weld lines form. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. Rapid heat-and-cool molding technologies have attracted increasing. The knit lines are the result of poor molding conditions (likely molding at too low of a temperature). Mold analysis tools are used by designers of molded plastic parts and by designers of the mold tools used to manufacture those parts. Meld and knit lines are actually both different types of weld lines. 120 in. and to identify potential knit lines. In fact, for a 32-cavity mold, the flow rate in this example drops down to 0. 060 and 0. Polym Compos 1982; 3: 88–96. Gating. Knit lines, also known as weld lines are areas in the. Injection moulding (U. The plastic melt that passes through the gate at high speed directly enters the cavity, then contacts the surface of the cavity to solidify, and then is pushed by the subsequent plastic melt, leaving traces of meandering. Release of trapped air in those cases will. Direct experience designing molds and parts for injection molding and producing the molds and parts is valuable, relevant experience for design students. This continues until the weld lines in plastic injection molding disappear. Polypropylene Consumer and Injection Molding Containers, Crates, Garden Furniture, Housewares, Luggage, TSL, TWIM lyondellbasell. As always, feel free to contact us at 877-479-3680 or [email protected] if questions or concerns emerge. Circular Loom Machine; Raschel Knitting Machines; Shade Net Making Machinery; Inspection Machines; Non Woven Production Line. To prevent swirling, perform tests whenever possible and use pre-compounded resin to ensure identical color match across parts. In the injection molding process, knit lines are a common occurrence when two or more plastic flow fronts collide and solidify, resulting in a visible seam or line on the molded part. Still, it can be seen to varied degrees depending on mold. 3 s, mold temperature of 60 °C and melt temperature of 250 °C. . They occur when two resin flows meet at different. Using abrasives in a pressurized air blast to create a surface texture on the part. Our glossary of terms provides definitions for a wide range of injection molding terms. This slight depression is a tiny line called the weld line or knit line. While injection molding itself is a straightforward process involving melting thermoplastic resin and injecting it into a mold cavity, knit lines can pose. While this process is largely efficient and reliable, it's not without its potential issues. Also known as a knit line, this is the point at which two flow formations meet and are unable to. 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. To prevent knit lines, injection molders can increase the temperature of the molten resin to prevent solidification from starting too soon, and increasing injection speeds and pressure are also potential solutions. 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. Koelling, Ronald C. Gate size can be increased or moved to a section with greater wall thickness to help eliminate. 2020-01-1306. The injection molding was carried out in a DK-Codim 175/410 injection molding machine. Using three test materials, polystyrene (PS), polycarbonate (PC) and polyoxymethylene (POM), the relationship between a design and a processing parameter. A weld line can also be called a knit line. Knit lines, also known as weld lines are areas in the molded part where two or more flow fronts converge. If I can answer any questions you may have on optimizing the plastic part design, CNC plastic prototype, mold manufacturing, and injection molding or if I can be of any other help, please feel. The cooler flow fronts of the resin aren’t forced into the mold surface texture as well as the hotter resin behind the flow front. Learn about the key characteristics of common injection molding materials, recommended applications, and how common thermoplastics compare to one another. 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. In this video, Chris Burda, applications engineer at Protolabs, shares what can be done to reduce knit lines and how they can impact your part's functionality. Designers are able to specify seamless design features with compression molding. The most common location of knit line formation is behind molded-in holes that are made by core pins in the mold. Also known as “stitch lines” or “weld lines”. Add a 0. Compression molding and injection molding are very similar, but they have one major difference. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. Find out more by calling 573-437-4154 today or email us. Swirling can increase depending on the material you use, and the texture or polish of injection molding tools. An injection mold that produces pieces while the final tool is being built. ) Mold Analysis Tools. An edge gate introduces material at the main parting line, or where the two halves of the mold meet, with a perpendicular runner. Part Shorts and has burn marks. As the polymer resin is injected into a mold, it flows through all parts of the mold. This image shows a PVC pipe after it was accidentally dropped on the ground. 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. A knit line is the spot where two flows meet. Weld lines are also known as “stitch lines” or “knit lines”. The Fusion of Weld Lines. 4. However, compression molding often provides poor product consistency and difficulty in controlling flashing, and it is not suitable for some types of parts. More about the knit lines in injection molding. 1. For example, increasing gate size can improve part filling. Another name given to weld lines is meld line. 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. 156 x 1. The specimens with a weld line at the center were obtained by double gate molding and the specimens without a weld line wereTherefore, changing the edges and corners of the mold core to make it buffer transition and keep the melt flow stable can prevent the occurrence of wavy lines. (1. The last cause of flow lines may be the operators running your daily operations. 3,000 ton machines can cost $700,000. The company provides an array of digital manufacturing expertise. Download : Download full-size image; 3. Whenever possible, vents should be located in the movable half of the mold wherever a gas void or knit line is seen on a part. J (left) shows embossed feature and S (right) shows debossed feature in plastics through injection molding. One common problem that occurs in injection molding is the formation of knit lines. 2. The second mold portion being movable relative to the first mold portion and together defining a mold cavity. . Proper venting is essential to molding a defect-free part. To account for variations in viscosity, nylon injection molding machines need to maintain an appropriate injection pressure. You can avoid knit lines and other problems by creating designs with smooth geometries. He is currently a tooling manager for a large, multi-plant molding and manufacturing company. Polym Compos 1982; 3: 88–96. All the while, the material could be the correct material," Hill says. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. Knit Lines. This occurs wherever there is a hole, notch, or any other feature on a part which divides the flow of plastic into 2 separate “flow fronts. Thin wall injection molding can produce walls as thin as 0. Injection molding is typically a better choice for more complex parts, while compression molding is a great option for relatively simple designs, including ultra-large basic shapes that cannot be produced using extrusion techniques. Viscosity represents a broad concept with huge effects on any efforts to standardize an injection molding process. A knit line is any line, visible or not, where two resin flows meet. 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. Injection molding is a popular manufacturing process used to fabricate parts in large volumes. Injection mold design and custom tooling can make or break the success of a finished plastic product. To learn more about us or to get a quote, click here or call 1-888-893-1587 now. Computer simulation packages of injection molding have had success in predicting filling behavior in extremely complicated geometries, capable of predicting weld lines’ location exactly. Incorrectly placed single gates may cause knit lines. Near-Net-Shape production uses injection molding to account for 70-90% of the final geometry of a part. Circular Loom Machine; Raschel Knitting Machines; Shade Net Making Machinery; Inspection Machines; Non Woven Production Line. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. 2. But we can’t talk about the injection molding process without discussing the injection molding machine. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. 3 /sec of material into a mold, don’t think the material is going into each cavity of a multi-cavity mold at the same 14. The area generally has lower strength than the other areas of the part. sinks, knit lines, and shrinkage,” Spalding says. 156 x 2 1/3 = 0. Knit lines, also known as weld lines or meld lines, are visible lines or seams that appear on a molded part where two or more flow fronts meet during the. Change gate locations. The GLS™ Injection Molding Guide provides in-depth information on part design, mold design and processing for styrenic block copolymer (SBC) thermoplastic elastomers (TPEs). 5 mm (0. weld line in injection molding. Behind the obstruction, the flows try to merge again, but this is made more difficult by a low temperature of the mold surface and a low melt pressure. Injection molding is the predominant manufacturing process used for producing transparent polymer products. matte or smooth texture on the part’s surface gives a more desirable aesthetic and hides small imperfections such as knit lines, flow lines, shadow marks, and sink marks that were caused by the mold. As. ) 2. Typical Tool Steel for Injection Mold Construction Steel Type Steel Properties Mold Component P-20 Pre-hardened, machines well, high carbon, general-purpose steel. Draft. Increase size of the vents. turbulent flow of Injection speed set too high. In the 1947 book, Injection Molding of Plastics, the late Dr. What causes knit lines? Knit lines are formed when the molten plastic flowing into the mold cavity runs into an obstruction, such as a core pin that forms the through hole on a flange of an enclosure. Knit lines don’t always compromise the structural integrity of plastic parts. While injection molding itself is a straightforward process involving melting thermoplastic resin and injecting it into a mold cavity, knit lines can pose. 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!. 08 KICKOFF PRODUCTION. Reduce the screw speed and adjust the backpressure. 02 in. Weld lines, melt lines or Knit lines could be caused by different causes: - Low temperature of molding machine barrel - Inadequate back pressure - Injection pressure or injection speed is too low - Low mold temperature - Small injection gates and/or runners - Improper location of injection gate - Excessive gate land length1. ABOUT THE AUTHOR. In a weld line, reinforcement fibers. Three terms that often get mixed up are weld, meld, and knit lines. Here is a look at the. Venting is required to allow the air in the sprue, runner and cavity to leave the tool as the melt flows into the cavity. In the plastic injection molding industry, we work with materials that are byproducts of oil refinement and molds made of metal casting, so our terminology is bound to be at least slightly confusing. Advantages Excellent moldability in thin sections Outstanding chemical resistance Heat resistance Limitations Cost Knit line strength OverviewLiquid crystal polymer (LCP) exhibits a highly ordered structure in both the melt and solid states. Molding Troubleshooting Guide Bond Readout Bond readout is a surface distortion similar to a hump or sink that occurs over a bond line Probable Cause Material Process • Mismatch of compliance between outer panel, inner panel and adhesive • Incompatible thermal expansion coefficients between the SM and the adhesivePrevents flow and knit lines. If the parting line is located on a sidewall of the part, it is nearly impossible to construct a mold without a slight mismatch between the force and the cavity. Knit lines, also known as weld lines, are fine lines that resemble hairline fractures or cracks. Cold weld line or known as “knit line” isWeld Line defect analysis, the most common of many defects in injection moulding products. Learn how HPP maximizes these specialized processes. Understanding types of injection molding process can help to avoid some design challenges early in the process. Plastic Injection Molding Part Design Guidelines, Plastic part Design Guidance, Parting Line Draft Undercuts Wall Thickness & Uniformity Bosses Gussets and Ribs Radii and Corners Material Shrinkage Gating Ventings Knit/Weld Lines. The knit line strength and other packing related properties both aesthetic and functional of injection molded polymeric products is improved by equipping the mold with packing pins. They are the result of fundamental physical effects taking place inside of the mold. These lines can manifest as visible marks on the component’s surface and potentially affect its structural integrity. Inappropriate temperature. Observation on a “trial and error” basis may be required. Avoid areas where the plastic must suddenly flow upward or downward. 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 []. Depending on the design of the mold and the material being injected, a knit line may: present no problem at all, be a cosmetic issue, or cause a potentially serious structural problem. Plastic injection molding is the industry’s most common way to manufacture parts. In the injection molding process, knit lines are a common occurrence when two or more plastic flow fronts collide and solidify, resulting in a visible seam or line on the molded part. These are caused by the shot of molten plastic moving at different speeds throughout the injection. It is. Design bosses with an outer diameter equal 2x the nominal diameter of the screw or insert. Flashing can be a common defect in injection moulding and can affect the appearance and functionality of the finished product. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no weld line. 0 mm) is crucial to ensuring that parts cool evenly. Fig. These defects are not visible, like small. In the world of injection molding, each weld. 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. In the injection molding process, knit lines are a common occurrence when two or more plastic flow fronts collide and solidify, resulting in a visible seam or line on the molded part. Plastic injection molding is the industry’s most common way to manufacture parts. The data suggest that either local sample thickening or grooves form at knit line when complete section solidification takes place first at weld zone or. There is no need to worry about flow or knit lines that may appear with injection molding. 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. Possible causes: Low temperature or fluidity of melted plastic during injection molding. 2) Vents in an injection mold should let the air out, but not the liquid plastic. Increase the injection speed. The injection molding process uses a granular plastic that is grav ity fed from a hopper. 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. The injection molding design process, much like all industrial design processes, deals primarily with the creation, look, and feel of a product. We complete the part to your precise specifications with CNC Milling operations. Still, they are almost always a cosmetic issue. 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 . Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. Injection speed and pressure. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. Each mold produces as specific part. The packing pins are sequentially. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. The pipe underwent brittle fracture into many pieces because of the high residual stresses in the wall of the pipe. Randy Kerkstra has been in the plastics industry for more than 26 years, occupied. CAUSE: 1. They again get resolidified along the surface. Additionally. Weld lines or knit lines and meld lines formed when two melt fronts run into each other or join together can be improved by. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. 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. 3. The knit line is generally opposite the gate in thermoset. Venting. May happen at first shots while mold is being dialed in. No matter the size of a production run, the presence of blemishes on the finished product leads to unhappy clients. Crossref. Let’s. 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. Increase injection speed. The defect may be in part appearance or mechanical strength. Because they can be shut off independently you can control flow fronts and knit-line locations. The injection molding process is on the surface is fairly simple, plastic resin is heated to its melting point and forced into the cavity of the mold to produce a plastic parts. mold venting is at the last filling point, whereby, while the melt flows forward in the cavity, air and gases flow out through the valve. An obstruction such as a core pin or holes will split the material flow and cause a weld line issue to form on the other side. For over four decades, our experienced team and leading edge technology have provided you with tooling solutions from start to finish. Design. 2. Place a vent in the weld line area to remove the entrapped air. Plastic melt and mold temperature. Notched weld lines then remain near the cavity walls. Misra A. Knit lines are most common downstream of holes created in parts where the molten material meets. 5. This normally occurs around holes or obstructions and causes locally weak areas in the molded parts. Three terms that often get mixed up are weld, meld, and knit lines. Remedies: Increasing the barrel temperatures will allow the flow fronts to stay hotter longer and. Increase the melt and/or mold temperature. Parting Lines. Also known as a knit line, this is the point at which two flow formations meet and are unable to. Knit Lines in Injection Molding. Injection molding machine and automation supplier Engel offers an array of technologies to simplify and speed up mold changes, including magnetic clamping platens and quick couplings; intelligent assistance systems; and the famox mold changing system for automating the set-up process. It can also aid in material selection since fill. By understanding material fill, injection mold designers can better position gates, anticipate where knit lines will appear, and locate difficult to fill spots in the mold. , LTD. It happens when the molten plastic material flows around obstacles, such as inserts or cores, and rejoins on the other side. 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. Many materials can be. Material. Figure 1: Knit lines in a cover plate. Also discussed are weld and meld lines and their effects on molded. 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. 3. Avoid adding threads directly on your injection molded part. This article looks at the issues presented by a weld line in injection molding and the techniques manufacturers can use to avoid them. Soft metals, such as aluminum and beryllium copper, can be used for prototype<br />. Encapsulating the metal insert with plastic creates a single molded plastic piece that’s generally stronger than one created using secondary assembly. ABS is a good choice for handheld consumer devices. a specific area on one side lens, a warp line, and a weft line. Knit lines. If the plastic has cooled too much during the injection process it can lead to knit lines in plastic parts when they meet past an the obstruction. Injection molding flow lines typically fall into one of the categories mentioned in the following table: Category: Type of Flow Line: Appearance (What It Looks Like) 1. weak knit lines and fracture points. Weak weld lines are perhaps the most common and difficult injection molding defect to eliminate. 5 to 3. 0 mm) is crucial to ensuring that parts cool evenly. 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. In compression molding, molds are closed around the charge, and in injection molding, the charge is injected into a closed mold cavity. A poor knit line can cause cosmetic blemishes and significantly weaken the structural integrity of a part. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. Achieving a high-quality surface finish can be challenging, and other methods, such as polishing or coating, may be required. Product designers encounter a wide range of challenges when. The utility model relates to a mold structure capable of eliminating the appearance of weld lines of a hole-shaped injection molded product. Parts with abrupt geometry changes or holes are more prone to knit lines. Based on the resin. Solid or semi‐solid, this material leaves a distinct border with adjacent melted material similar in. Contact Universal Plastic Mold Today. incomplete filling or shorts. On this page you will find the online, condensed version of this guide, offering quick answers to your injection molding questions. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. As the polymer resin is injected into a mold, it flows through all parts of the mold. With plastic finishing plugs and end caps, we can help you keep your products protected while giving. Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. 250 in. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. 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. ) or as thick as 25 mm (1 in. Exploring common molding defects and. 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. Weld lines can significantly reduce ultimate tensile strength (UTS) and fracture strain of talc filled polypropylene (PP). 827 Holes and Bosses. Knit lines are a common defect in injection molding that can affect the appearance and performance of plastic parts. In this case it would be 0. There are two primary reasons for this occurrence: 1. This article will discuss the importance of injection molding nozzles and what makes a good nozzle for a molding or injection. What Causes Knit and Meld Lines? Like many part inconsistencies, these unwanted features are rooted in product design. Place vents at last place to fill and at converging flow fronts. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. This defect is caused when the polymer resin is injected into a mold and flows around a solid piece and forms when the resin collides back together without completely fusing back together. 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. Knit lines appear to be a faint line or a crack in the finished part after it comes out of the injection mold. One solution is to use optimal wall thickness to help slow cooling during the ABS plastic molding process. Weld or Knit lines are a plane or section in an injection molding part where the flow of molten plastics meets from different directions. Specifically, by having a single, continuous injection outlet 140, molding material can be uniformly distributed throughout mold cavity 120 quickly and consistently without resulting in undesirable molding seams or knit lines. 020"). Typically, injection molded parts will be between 0. Fewer knit lines are produced and a smaller amount of fiber-length degradation is noticeable when compared to injection molding. com support@makenica. There. This can result in cosmetic defect or a weak point in the part. 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. Sprue bushing too long. Use gradients. 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. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. A thermoplastic resin is heated to its melting point and injected into the cavity of an injection mold to produce a specific part geometry. These seams or knit lines are avoided because the molding material flow does not a meet at an interface nor must. The melt is forced to split up during filling of the cavity. Depending on the design of the mold and the material being injected, a knit line may: present no problem at all,. Contact us. Comprehensive. lines are formed when there is an obstacle in the cavity of the injection mold. Left: L-shaped perform. Injection moulding (U. More about the knit lines in injection molding. Three terms that often get mixed up in the plastic injection molding industry are weld, meld, and knit lines. Determine the time duration of the molten state. 27-ounce shot size to 600-ton with a 105-ounce shot size. ITAR. (for example, a hole on the plastic part), the knit line will be unavoidable. A component of the injection-molding machine wherein the resin pellets are melted, compressed and injected into the mold's runner system. If the part design’s wall thickness is constant, the magnitude of the plastic’s velocity will be the same at every. The structural stability of. To ensure quality parts, injection molding companies must have the best injection mold design first + (91) 96067-70777 +(971) 547-161-112. After selecting resin material, the design and process control of injection mold directly influence the quality of formed products. 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. This will help the mold designer to determine the allowable gate and knit line locations. In the process of injection molding, when the wall thickness of the product is large, the cooling speed of the outer surface is faster than that of the central part. Weld Lines.