What Causes Knit and Meld Lines? Like many part inconsistencies, these unwanted features are rooted in product design. (for example, a hole on the plastic part), the knit line will be unavoidable. 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. Draft. Many materials can be. It is. Once the plastic cools, the mold is removed, and the object is ready for post-processing. 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. Insufficient injection pressure and speed can cause weld lines. Determine the time duration of the molten state. 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. Revisiting the '5 M's' of Molding. As the melted plastic fills the mold, there are locations where the molten plastic flow stream separates and then comes back together. Flow Lines Knit or Weld Lines Cavity Gates Table 1 Knit line in a multi-injection-point cavity. S. The specific method is that when the product is just filled and filled in the cavity, the insert. 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. Understanding Knit Lines in Injection Molding: Causes and Solutions. Parts as thin as 0. Increase the mold temperature and reduce the barrel temperature for injection molding of thin-walled products. Place a vent in the weld line area to remove the entrapped air. Mold venting is critical to the quality and consistency of the finished part. Thin wall injection molding can produce walls as thin as 0. Weld line in injection molding is line where two or more flow molten plastics knit together. 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 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. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. There is no need to worry about flow or knit lines that may appear with injection molding. Quotes for 25+ Manufacturing Processes. 3 /sec. In addition to the main factory and development. In places where the plastic flows around a solid piece of the mold, from a simple circle to forming complex shapes like rings or squares. 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. The goal is to create a uniform thickness and at the smallest (thinnest) level required. ABS. and Titomanlio, G. Meld and knit lines are actually both different types of weld lines. Also known as a knit line, this is the point at which two flow formations meet and are unable to. Adding vents, using overflows, or using porous metal. Injection molding is a plastic manufacturing process to achieve a high production rate. occupied frequently with troubleshooting injection molding. Consider adding mold release (can be added to the polymer itself by the polymer vendor) or at machine side Knit lines Weak knit lines Increase melt temperature Mold temperature too cold Increase injection speed Avoid nucleated products if possible Inadequate ventingWhat you should know is that there are various failure modes for injection molding. These defects are not visible, like small. injection-molding machine (Arburg allrounder 320C, Germany). This will help the mold designer to determine the allowable gate and knit line locations. Weld lines or knit lines and meld lines formed when two melt fronts run into each other or join together can be improved by. Legend: a-in. Knit lines are formed in injection molding when two flow fronts meet in the middle of a part (a line where two sides of the plastic are “knit” together). In addition, the force of the gas holds the appearance side of the part in contact with. injection molding. 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. Long shapes are produced without multiple drops or hot runner systems, eliminating knit lines and lowering tooling costs. For the production of these weld‐line specimens, a special mold was used and injection molding parameters were systematically varied, tensile (ISO 527‐2) and impact (ISO 179‐1/1eU. Gas trapping/ poor venting. What Are Knit Lines? When a product is produced through injection molding, a high-powered tool injects melted plastic into a custom, double-sided mold. POROUS MOLD MATERIALS. Raising the mold temperature will keep the material molten longer, resulting in stronger weld lines and even elimination of weld lines. Mold bases, ejector plates, and some cavities (if nickel or chrome plated to prevent rust). Kurt W. shows some obvious locations for vents, a brief molding trial should be conducted to observe where the gas voids occur. The fluid path has an inlet and a radially continuous, downwardly. 3 To get the most out of your Xometry Injection Molding experience, we offer the following part Design Guide with. Here’s a rundown of helpful tricks to keep in mind when designing and choosing a material for molded parts with walls: In general, ensuring your design has uniform wall thickness between 0. The process parameters were fixed as follows: Packing pressure of 40 MPa, injection time of 2. Having uniform wall thicknesses between 0. 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. 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 Molding Materials When using PolyJet molds, both tool life and part quality will be dependent on the thermoplastic material used during the injection molding process. 160"). Weld or knit lines occur when melt flow fronts collide in a mold cavity. Prevent Flow and Knit Lines Through Mold Adjustments. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. To avoid walls that are too fat or too thin, designing a wall thickness between 0. These knit lines affect the parts aesthetics, but also they generally decrease the strength. Because they can be shut off independently you can control flow fronts and knit-line locations. POROUS MOLD MATERIALS. In compression molding, molds are closed around the charge, and in injection molding, the charge is injected into a closed mold cavity. As. Avoid adding threads directly on your injection molded part. Influence of injection-molding parameters on the morphology and mechanical properties of glass fiber-reinforced polypropylene composite. Weld Lines-3 Ways for Detecting and Correcting. Knit lines, also known as weld lines, are fine lines that resemble hairline fractures or cracks. Mold venting should be checked and increased if necessary, injection molding service. Direct experience designing molds and parts for injection molding and producing the molds and parts is valuable, relevant experience for design students. Swirling can increase depending on the material you use, and the texture or polish of injection molding tools. This continues until the weld lines in plastic injection molding disappear. One solution is to use optimal wall thickness to help slow cooling during the ABS plastic molding process. Polym. SPI surface finishes are the most common set of injection molding finishing standards around the world with over 12 different grades. Contact Universal Plastic Mold Today. Table 2. These defects are not visible, like small. The plastic in the ‘flow front’ cannot pass through the core pin, so it flows around the core pin splitting into 2 distinct flow fronts. 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. This production method is particularly popular when manufacturing in large quantities. For injection molding of the multi-blade fans and various rotating plastic parts, the complex of multiple gating injection molding tools were used. Following lists causes and solutions for weld or knit lines. weak knit lines and fracture points. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. This can result in cosmetic defect or a weak point in the part. Submarine Gates. In this paper, two different injection molding tests were completed. It is important when selecting an injection molder that the right process conditions are used to reduce or eliminate the effects of. “A knit line in a colored part will result in glaring visual-effect problems, while a knit through a glass-filled part would have a negative effect on both the aesthetics and the performance,” agrees Kurt Weiss, manager of part performance and new material introductions at GE Plastics. Three terms that often get mixed up in injection molding are weld, meld and knit lines. Examples of different causes of PVC pipe failure. Increase the injection speed. Knit Lines in Injection Molding. 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. 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. A knit line in a plastic injection-molded part is created when two separate plastic flows meet within the mold and "resolidify" along their interface. Injection molding is a manufacturing process that involves injecting molten plastic into a mold cavity to create a specific shape or design. ”. The runner and gate system used in plastic injection molding is responsible for directing molten plastic from the nozzle of the molding machine into the cavity of the tool. Increase the injection speed. When injection molding complex parts, often knit-lines are formed during the mold filling stage. Getting started; Knit Line Injection Molding; Knit Line Injection Molding - China Manufacturers, Factory, Suppliers. However, the process involves forcing the material through small holes into the mold cavity. Make sure the venting is not too large. 1. The knit (weld) line is in the direction perpendicular to applied stress. 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. 0 mm) is crucial to ensuring that parts cool evenly. An option to bluing agents, the long established means of gauging pressure distribution, comes via Pressurex, a thin, flexible, plastic film. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. This range can be affected by the part wall thickness, melt temperature, mold temperature, injection speed, hold/pack pressures and also the time between molding and measuring. They occur when melt flow fronts collide in a mold cavity. 2020-01-1306. Possible causes: Low temperature or fluidity of melted plastic during injection molding. Inadequate injection pressure can result in knit lines and a surface that. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. Islyn Thomas summarized the need for a particular vent location better than I ever could. LCP can replace such materials as ceramics, metals, composites and other plastics because of its outstanding strength. Reduce the temperature of the mold and plastic being injected. However, with any practice, when the proper care and planning aren’t taken, problems can occur, and with injection molding, knit lines are one of the most common problems. Injection molding is capable of producing a lot of aesthetic options as well. 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 . 2. 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. Having uniform wall thicknesses between 0. Recent developments were oriented on the analysis of the mechanical performance at local (knit lines and welds) and bulk (molded part) areas, with the influence of molding and welding conditions. 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. TWIM=Thin Wall Injection Molding; TSL=Toys,Sports and Leisure; NB=No Break; IMR=Inter Material Replacement. 45 in. Cold weld line or known as “knit line” isWeld Line defect analysis, the most common of many defects in injection moulding products. For over four decades, our experienced team and leading edge technology have provided you with tooling solutions from start to finish. 3. weld line in injection molding. 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 comment on melt flow index is correct, but, I've molded straight PC down to . Whereas conventional injection molding uses. Remove the hardened material from the mold. 030- to 0. 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. Some of the most popular brands include:Harshal Bhogesra has 9+ years of combined experience in molding, customer & supplier development. . Learn more about the process by reading this white paper. Causes 1. (1. First, an injection mold with triangular inserts was built to study the influence of meeting angles on material properties at the weld line. Holes in plastic parts are normally cut with a router (or drilled if round. Our goal of 100% efficiency, zero scrap and repeatable processes can sometimes be hindered by poor setups or changes in the molding process. It can also aid in material selection since fill. 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. 5mm (0. Currently working with plastic, rubber, LSR, MIM molding companies to help them eliminate their complex molding challenges like air entrapment. POROUS MOLD MATERIALS. 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. This course outlines mold filling and how different gating configurations affect filling. With over 50 years of experience, Universal Plastic Mold can help you avoid (or at least minimize) knit lines in your molded parts. The utility model relates to a mold structure capable of eliminating the appearance of weld lines of a hole-shaped injection molded product. He is passionate about optimizing product design, tool development, molding processes, and quality. 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. The wall thicknesses of an injection molded part generally range from 2mm – 4mm (0. It tells them that you visualized how injection molded parts cool and harden. Reduce the screw speed and adjust the backpressure. Learn how to troubleshoot weld lines in injection molding. 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. This type of molding uses a single tool to create both the part's geometry and surface finish in one step. To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. Product designers encounter a wide range of challenges when. 26 = 0. Edge gates, which can include fan and tab-shaped gates, are the most common ways to gate a tool. Knit lines form when two or more plastic flow fronts collide and solidify or “knit” during the molding process. Weld lines occur where two flow fronts meet and always provide a source of weakness as the two fronts do not knit together. This was usually with a PC/ABS material at knit lines and high fill pressures from thin walls in the part. injection molding. An injection molding machine having a first mold portion and a second mold portion. Knit lines form when two or more plastic flow fronts collide and solidify or “knit” during the molding process. 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. For example, warping, sink marks, drag marks, and knit lines can all impact the visual appeal of the manufactured part. 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. Designers are able to specify seamless design features with compression molding. The adverse effect of knit-line formation on the mechanical properties of thermoplastics has been well documented for unfilled materials. The most common and one of the most challenging injection molding defects are weld and knit lines. Knit lines, also known as weld lines are areas in the molded part where two or more flow fronts converge. . Brent Strong, p. Weld / Knit Lines; Assumptions. Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. 2. Sink Marks Cause 4: High Mold Temperature. In the present work, the micro specimens were investigated. Injection molding is a simple and efficient process that produces high-quality plastic parts. Adjust the design for the flow pattern to be a single source flow. 5 mm (0. But we can’t talk about the injection molding process without discussing the injection molding machine. Therefore various injection molding defects can be eliminated. This is why the leading edge of the resin flow within a mold is always the coolest area of the resin, and, therefore, the closest to solidifying. Randy Kerkstra has been in the plastics industry for over 26 years, occupied frequently with troubleshooting injection molding. However, the weld line may not continue throughout the flow. Plastic injection force exceeding the clamping pressure of the press. wall thickness, knit lines, draft. Compression molded parts can vary in thickness without issue. ”. 0mm) throughout will ensure that the parts cool evenly and will prevent warping. Minimizing or eliminating flow and knit lines is an additional benefit of using this material. The only parts that count are the ones that meet quality standards, and keeping pressure evenly distributed across a mold’s parting lines is one of the many critical tasks to get those good parts molded. Draft. In a well-designed mold, this is generally not a problem. 7. Some. This most often occurs when you have a core or shutoff feature that the plastic needs to flow around. If the part design’s wall thickness is constant, the magnitude of the plastic’s velocity will be the same at every. Weld lines defects are formed when two flow fronts are merged together. Notched weld lines then remain near the cavity walls. The company provides an array of digital manufacturing expertise. Meld and knit lines are actually both different types of weld lines. The injection molding process uses a granular plastic that is grav ity fed from a hopper. One exception: ribs should be about 50. More about the knit lines in injection molding. Industrial Knitting Machines. Having a basic understanding of the injection molding process will aid in understanding how to design for injection molding as well as how to forecast production schedules. The part is cooled in the mold until it is solid enough to be ejected. 3. Table 2 lists the<br /> properties of common tool steels and the typical mold components for which they are<br /> used. ISO 9001:2015. Submarine gates are another injection molding types of gate that is located below the surface of the part, typically on the underside or back of the part. 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. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Using abrasives in a pressurized air blast to create a surface texture on the part. See full list on fathommfg. 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. These knit-lines are well-known as particularly critical regions in the mold when mechanically. This defect is caused from excessive lube or oily stock. 1016/0254-0584(86)90019-2 Corpus ID: 136712450; Impact strength of knit-lines in injection moulded parts @article{Criens1986ImpactSO, title={Impact strength of knit-lines in injection moulded parts}, author={R. That’s the air escaping out of the nozzle until the hose is full of pressurized water. Injection molding is the process of injecting liquid thermoplastic into a mold. 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. Injection moulding (U. While this process is largely efficient and reliable, it's not without its potential issues. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. One of these is knit lines, also called weld lines. 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. They are formed when two or more flow frontINJECTION MOLDING GUIDE V2. Soft metals, such as aluminum and beryllium copper, can be used for prototype<br />. However, compression molding often provides poor product consistency and difficulty in controlling flashing, and it is not suitable for some types of parts. Influence of injection-molding parameters on the morphology and mechanical properties of glass fiber-reinforced polypropylene composite. The design of the mold, as well as the part being molded, has a significant impact on the success of the process. Let’s. The Problems & Solutions course is designed to train injection molding personnel in. These flaws can affect the aesthetic and structural integrity of the. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. Tooling & Injection Molding Services High-Quality Complex Parts. The relationship between processing conditions, morphological structure and mechanical properties of knit lines of an injection molded semi-crystalline thermoplastic. With over 50 years of experience, Universal Plastic Mold can help you avoid (or at least minimize) knit lines in your molded parts. It can be determined by a visible line appearing on the surface of the plastic part where two flows of the plastic meet. These seams or knit lines are avoided because the molding material flow does not a meet at an interface nor must. Meld and knit lines are actually both different types of weld lines. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. . 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. The knit lines are the result of poor molding conditions (likely molding at too low of a temperature). Gating. In the world of injection molding, each weld. As the polymer resin is injected into a mold, it flows through all parts of the mold. These are imperfections in the part where separated flows of cooling material meet and. Computer simulation packages of injection molding have had success in predicting filling behavior in extremely complicated geometries, capable of predicting weld lines’ location exactly. If you turn on the spigot to a garden hose, you will hear a hissing sound at the nozzle end for the first few seconds. Without it, air and gas are trapped in the mold, which compress and heat as the cavity fills. 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. By altering the part design, it may be possible to just have one flow front, and avoid multiple flow fronts having to come together. Hartland, WI 53029. Plastic injection molding is the industry’s most common way to manufacture parts. The second mold portion being movable relative to the first mold portion and together defining a mold cavity. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. Moldflow is computer software that is widely used across the plastic injection molding industry to predict and optimize the injection molding process and assist with mold design. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. 1. suppressed cooling and possibly warp. Parts molded with ABS are susceptible to forming knit lines, which are visible lines on the surface of the part. 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. 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. Knit Lines. Also known as knit lines. There are times when porous materials like Porcerax are used in problem or backfill areas. Injection speed and pressure. Learn about the key characteristics of common injection molding materials, recommended applications, and how common thermoplastics compare to one another. When assessing issues with injection molded parts, we want to make sure some core aspects of molding are checked. Als einer der führenden deutschen Hersteller von Masterbatches stellen wir nicht nur Farb-Masterbatches, Additiv-Masterbatches und funktionelle Kunststoff-Compounds her – wir leben deutsches Forscher-, Ingenieurs- und Unternehmertum. Poor venting. In the 1947 book, Injection Molding of Plastics, the late Dr. Thicker parts require more cooling time and can lead to air becoming trapped in the mold and weld / knit lines to form. The point of meeting creates a weak spot because the edges of the molten plastic, already cooling, don’t mix together very well. We complete the part to your precise specifications with CNC Milling operations. They again get resolidified along the surface. Mechanical performance of knit lines and welded butt joints – A key factor in designing of multiple gated injection molded and subsequent welded. Depending on the resin, resin temperature, mold temperature, and filling. Molding analysis study: An example of the low patterns and knit (weld) lines formation (MoldFlow® data) of injection molded round plastic part with a complex shape and with a ring. Flash: All plastic injection molds contain parting lines, which create the potential for small amounts of molten plastic to escape the mold cavity’s boundaries. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. Using three test materials, polystyrene (PS), polycarbonate (PC) and polyoxymethylene (POM), the relationship between a design and a processing parameter. Yet a smooth finish sometimes actually highlights flaws like knit lines and blemishes in the part. Knit lines generally occur around holes or other obstructions to the melt flow. The weld-lines are undesirable from both aesthetic and functional points of view and their effect is different for varied materials, process conditions, loadings, forms. ) 2. Gas-assisted Injection Molding: Influence of Processing Conditions and Material Properties. Product designers encounter a wide range of challenges when creating and developing molded parts, such as stress factors, warp, and those pesky knit lines. Venting. The diameter of the secondary runner would be the diameter of the tertiary runner times the number of branches to the 1/3 power (cube root). Expand. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. Troubleshooting Injection Molding Weld Lines. Injection Molding Guide. In working with the injection molding service offered by Protolabs, you provide. Design. 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. When the plastic cools, it takes the shape of the mold and is then ejected and finished. After the solidification of molten plastic, the finished part is ejected out. 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. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. As always, feel free to contact us at 877-479-3680 or [email protected] if questions or concerns emerge. 4. Injection molding is the most cost-competitive technology for manufacturing high volumes of identical plastic parts. Temperature is another factor that can cause weld or knit lines in injection molding. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. 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. Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. This line does not normally impact the overall shape or dimensions of the item. For fiber-glass reinforced thermoplastics, the strength in these local areas (knit/weld and meld lines) is less than in bulk areas, dueMolding 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 adhesiveThe best option once you have the approximate tonnage required is to find a molding partner that has machines in that range. Knit Lines. If you have any issues getting. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. Edge Gates. 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. molding run to be sure that the temperature does not exceed the recommended limits . Compression molding produces solid parts that are free of flow and knit lines. There are times when porous materials like Porcerax are used in problem or backfill areas. The Bottom Line You might have come across the aforementioned terminology before and did not know what any of the words meant. The quality of the answer is directly proportional to the information we have to work with. A knit line, also. [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. 156 x 1. Randy Kerkstra has been in the plastics industry for more than 26 years, occupied. Knit lines are consideredmolding defects, and occur when the mold or/and materialtemperaturesare set too low:. 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. Final Report-Plastic Injection Molding - Free download as Word Doc (. When 2 flows meet, small hair-like discolorations may develop. Formation of knit line.