Melt delivery management has a major impact on final part quality and the ultimate success of the production line. process can be fully completed. The following advantages exist for the use of high injection speed in the injection process. For each investigated mould temperature, a linear relationship can be observed. Bad habits can cause many different problems with injection molding machines, and flow lines are included in that. This can be accomplished by reducing the substance’s viscosity. The mold material 6 can have several effects on. ; Warping – The structural deformation that occurs. Here are some of the most common scenarios for cracks in injection molded parts: Cracks in the Direction of Flow – If the crack develops in the direction of the plastic’s flow into the mold cavity, the cause is molecular orientation. Walls thicker than 8mm (0. Each material has a maximum flow length for a given injection pressure and wall thickness — this is known as the flow ratio. Cooling lines impact. 004 m, a characteristic velocity ν 0 =0. These are typically found near the narrow sections of the mould gate and can. Edge Gates. Thickness – Make the ribs 50% to 60% (0. 160"). Jetting occurs in a molded component when molten material is injected into the mold cavity and starts solidifying before it fills the cavity. Weld lines have been one of the common defects puzzling the injection molding industry. • u. If a mold cavity has a significant flow length-to-thickness ratio, the material should have a low enough viscosity to enable a continuous flow. The gate in injection molding is an essential component that directly connects to the plastic part and controls the flow of melted plastic resin into the cavity. Learn how mold flow analysis can support the development of complex and customized injection molded products by identifying defects, optimizing materials, enhancing performance, and reducing costs. Round the corners of the mold where wall thickness increases: This. Apart from the shape, it is important to design ribs for optimal mold performance. Injection molding is the most cost-competitive technology for manufacturing high volumes of identical plastic parts. Injection molding is a great technology for finished production on a massive scale. FLOW – A qualitative description of the fluidity of a plastic material during the process of molding. On-Line Solutions To Injection Molding Problems. In the process of injection molding, the quality of the mold plays a decisive role in the quality of the finished product. A look at how taking the time and data to analyze a mold problem will help you repair it right—and permanently—the first time. Polymer Injection Molding: Gas-assisted Molding. So when two. Mold Flow - Position ribs such that the plastic has an optimal flow path. thick, 0. Thus, as the flow continues, the two flow fronts may gradually rejoin to. Expand. Causes – Remedies. Thickness –Make the bottom of the boss 60% (0. This most often occurs when you have a core or shutoff feature that the plastic needs to flow around. Flow Lines The problem with flow lines is that they. Unexpected flow lines, so-called tear drops, occur. Most flow lines don’t impact the functio…Flow lines are a defect in injection molding and can be a significant issue for manufacturers. Manifesting as wavy lines or streaks on the surface of the molding, flow lines generally occur when molten material flows. 7 of the reference. 4 Injection Speed. In this guide, we cover evaluation and also the remedy of flow lines in injection molding. Parting Lines. 3). The article has been structured just for you to gain an understanding of the same so that when you plan to buy plastic injection molding, you do understand what it means to do so. The flow line is usually connected to injection specifications, mold and injection material, it can be defined as linear grooving, or round surges, on the surface of an injection molded part that shows the instructions of product flow within the cavity of the mold. Flow lines are a typical problem for injection molding faults that appear as visible streaks or lines on the surface of the molded part. After an hour of running, the steel temperature stabilized at 78°F. 182-185, 2013. By heating the solid material, it is converted into a fluid state with a low resistance to flow. The recommended minimum production volume for injection molding is 500 units. The type of resin used during injection molding plays a large role in whether or not a knit line will be present. At the high end of SOLIDWORKS Plastics simulation in Plastics Premium, mold-level analysis can be performed by representing the runners, cooling channels and a mold body around the cavity. The difference between a knit and meld line is significant, dramatically impacting the part’s structural integrity. This production method is particularly popular when manufacturing in large quantities. There are a few adjustments that you can make to your injection molding process to prevent flow lines, including: Increase the injection speed, pressure, or material temperature: Slow-moving molten plastic is more likely to cool. Increase molten plastic temperature during injection molding. The melt holds enough temperature to maintain a low enough viscosity. Low cushion and hold time. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible mark at the demarcating line. These flow fronts occur when the molten plastic material encounters obstacles, such as inserts, ribs, or other features within the mold cavity. mold and the blow molding process. In injection molding, it is often important to maintain consistent color throughout the part. Drain the hopper if you were working with 100% regrind, clean if necessary. As the material properties of. Midland, MI. Below are ways through which you can remove and prevent flow lines; a. ABS resin has low thermal deformation temperature, but poor heat resistance. Flow LinesWeld lines are the def ects in. Flow lines. The emergence of silver marks is generally due to the rapid start of the injection which causes the air in the melt and mold cavity unable to be discharged quickly enough. (1) Increase the injection pressure and prolong the injection time. Adjust the design for the flow pattern to be a single source flow. These lines form as a result of material flow and solidification during the injection molding process. Injection molding is one of the best plastic production methods. Co-injection molding technique is a useful way to study weld lines, which can offer more detailed information of the. . Known as thermolators, water cooling systems require a cooling source such as a tower. 025 100 120 140 160 180 200 220 240 Mold Temperature (F) LDPE PPWhen it comes to injection molding, the chances you might end up making a costly mistake is too high. These are off-tone streaks or lines on the surface of the plastic, and while they don’t affect the structural integrity, they are unattractive and prevent a uniform and consistent appearance. It is therefore important to work with reliable injection mold makers for quality services and products. Figures 3A, B and C depict different examples of “spot” vents. Turbulent Flow IS Always Better. Part walls thinner than 4mm (0. It explored the use of. 3 the path lines of selected material elements can be observed which are. The other parameters such as Mold temperature and Cooling Time also contribute in the defects appropriately. In this study, a new specimen design is introduced for the tensile testing of micro parts. The barrel temperature is too high. Use high-quality, temperature-controlled materials for better mold filling. Plastic injection molding is a complex and highly intricate process. The main. Higher numbers assure that water flow is adequate, and that turbulent flow is at an acceptable level. 025 100 120 140 160 180 200 220 240 Mold Temperature (F) LDPE PPFor 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) properties were measured, and statistical analyses were performed to gain insight on the correlation between melt flow rate and weld-line behavior. When the gate depth is much smaller than the cavity entrance depth, and the mold filling rate is very high, when the melt flow becomes unstable jet flow, the front jet has solidified and the later flowing melt fills the mold cavity, and the product will be Snake flow lines appear on the surface. Flow marks: Flow lines Directionally "off tone" wavy lines or patterns Injection speeds too slow (the plastic has cooled down. Utilize advanced injection molding machines with increased injection speed and pressure. 1. These streaks or patterns can affect a part's aesthetics, value, and. with a characteristic length χ 0 =0. Apart from the shape, it is important to design ribs for optimal mold performance. Flow Lines. Plastic is injected into a mold at a specific rate of flow—typically in. reduce the ability to positively influence the strength. It is generally a three phase process comprising filling, packing and cooling phases. Each gate type has specifications that significantly affect the end product’s structure and appearance. When designing a new injection mold, a moldmaker’s main goal should be to put its client in the best position to make quality parts consistently and efficiently. They again get resolidified along the surface. Results have shown that, although anisotropy is more pronounced in injection moldings, the mean of values for modulus along and at 90° to radial mold flow lines of an optimum modulus cure are the. The mold settings can run flawlessly until employees consistently open the machine for inspections, interrupt cycle times, or cause temperature. Mold makers should also pay attention to sprue, runner, or gate design. A gradual change in wall thickness is recommended to avoid any sudden change in the material flow direction. 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. Understanding the complexities of injection molding flow and solidification is a bit more challenging as. The formation of weld lines and their location along the flow path is a well-studied phenomenon in conventional injection molding; however, only a few papers are devoted to micro-injection molding [11,13,14,15,16]. 2) Material Changes. Vacuum on the mold does help and many times eliminates the weld line. Faster flow results in longer, thinner knits. The Plastic Troubleshooter Defect - Flow Lines. GPM: Measuring the amount of water passing through the mold every minute is a key measurable in determining turbulent flow. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. (2) Improving the flow of plastic and facilitating the molding of thin-walled parts. Knit and Meld lines are inherent to plastic injection. Lenticular, or Silver Dollar type pigments, are thicker than cornflakes, with a narrower particle size distribution. While the sprue is milled through the entire thickness of the injection mold, passing from the outer surface to the parting line (where the two mold halves meet), the runners are comparatively shallow channels milled into the face of one or two mold halves. to 0. A ‘parting line’ is the line of separation on the plastic part where the two halves of the plastic injection mold meet. Examine the flow pattern of each part to see if the plastic flow front is coming around on itself, or if there is a hesitation of the flow front in filling a thin section of the part. Fast injection gives you a glossy part, which is what we wanted in this. Conventional injection molding is widely used to produce plastic parts, mainly in the automotive industry, due to the high production ratios and quality of injection parts. Injection molding flow lines can also be caused by using material that has defects. This new process enables thinking differently about how parts and molds can be designed. Flow lines are the results of slow injection rate and disparities. On larger parts where knit lines or flow lines are a concern, you can use sequential valve gates to control the flow and move the knit lines. The proposed method is first applied to the simulation of HDPE melt in a classic Poiseuille flow case, and then two. This is a video excerpt from our Problems & Solutions Course - Jetting. These lines. Once the mold is created and the machine is set up, additional parts can be manufactured very fast and at a very low cost. These lines form as a result of material flow and solidification during the injection molding process. We started the mold with 100% water circulating at 60°F at a flow rate sufficient for turbulence. They may also appear as ring-shaped bands on a product’s surface near the entry points of the mold, or “gates”, which the molten material flows through. Injection molding gates occur in different forms, taking distinct sizes and shapes – appearing narrow, wide, tapered, etc. In this article, a multiscale simulation method of polymer melt injection molding filling flow is established by combining an improved smoothed particle hydrodynamics method and clustered fixed slip-link model. Reduce the injection pressure to prevent overpacking at the gate. Cooling lines have been placed in the cavity, core, and runner block following established guidelines for diameter/depth/pitch. The flexibility of rubber and its durability offers manufacturers and engineers ways to design cushioning components and seals. Injection molding could develop knit lines if one front cools before it reaches the other. 020 0. Some of these factors could be the flow rate, the pressure, or the temperature settings of plastic injection molding. c. Its popularity is typified by the numerous products produced in this way at the present time. The polymer material is melted by the heat from the heaters and viscous heating due to the screw rotation in the plasticization stage as shown in Fig. Thus, with an injection pressure of 1800 MPa, the flow length with 80°C is 47 mm and accordingly for. 030 0. They are best described as "off tone" wavy lines/streaks or patterns in the molded part around the injection ports. Mold Design. When the melt enters the cavity quickly, it is necessary to discharge the air quickly. This requires skilled labor to mold new parts that have less molding defects. A significant part of that is the cooling design, where there are many things to consider. Molds for investment casting are more accurate and have fewer defects, thanks to flow control over wax injection. Utilize hot. Flow lines are off-color lines, streaks, and other patterns that appear on the surface of a part. Using a thermoplastic that stays in a. 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. Injection molding (or injection moulding) is a widely used manufacturing process in many different industries such as aerospace, automotive, medical, and even. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. 1. Mold Venting. Flow fronts moving too slowly can lead to pressure in front of a flow front being too low to force gas through vents. Lower speeds allow gas more time to escape through vents. Flow lines are ripples in the plastic after the part is formed. (3) Improving the surface gloss of the product. This results in an incomplete part at the end of injection molding. Laminar flow in a plastic mold, described by. Weld lines can be a weak spot and have therefore to be taken into consideration in part design. Flow lines. Flow Rate. Investigate the mold for signs that a water leak is present, and correct the condition. MMT Chats. Pushing the air out or not is the difference between a good part or burns and flow lines. In this case the two flow fronts will meet and there will be very little molecular orientation across the weld. Using cooling simulation to circuit your cooling lines properly. In injection molding weldlines are generated when two separate melt streams join either. Factors within the tooling can also contribute to flow and knit lines, calling for mold modifications. We stopped the machine and added glycol to the chiller to a concentration of about 40%. 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. Sprues are usually tapered, and they come with ends that are bigger at the top. S. Mold design is a key aspect of injection molding. Add or increase vents as needed. In a weld line, reinforcement fibers. FOW Mould is one of the best companies that use injection molding. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. Contact us to learn more about SMARTFLOW flowmeters. If you have critical requirements for strength of knit lines, please call a Protolabs applications engineer at 877-479-3680 to discuss, or email at [email protected]. Taking proper care to design the mold properly, avoiding bottlenecks, and changing the number or location of gates can improve performance. Reposition gates and runners to allow resin to flow around the obstruction from a different direction. Edge Gates. We will now look at the problem you are likely to encounter and how to fix them. Too hot and the plastic will start to degrade, but too low and flow marks increase. These data were obtained from many andGenerally, injection molding resins are characterized as having medium, high or very high flow. In spite of its cosmetic attributes, a bad knit line can significantly. (3) Adjust the temperature of the barrel and nozzle: the viscosity. These are caused by the shot of molten plastic moving at different speeds throughout the injection mold, which ultimately causes the resin to solidify at different rates. It has larger cross-sectional regions that allow sufficient molten plastic flow into the cavity. Injection molding tool life is the number of production cycles that an injection mold can complete before it needs to be replaced. The wavy lines or patterns that form on the surface of the molded object are what we refer to as flow marks. The gate vestige for injection molding is usually narrow. Sufficient draft is an important part of any mold design, and quick-turn tooling is no exception. Circuit Identification. The injection speed should remain consistent as the plastic enters the mold, otherwise, it will slow down, cool, and cause flow marks. In addition to the recommended wall thickness, it’s important to consider a material’s flow characteristics. Flow lines appear as a wavy pattern on the surface of your plastic parts. Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. These marks remain and are visible in the cooled product. 3. Symptoms: Flow lines will typically appear as discolored “bands,” or sometimes “wavy. Increase the injection speed and mold/operational temperature to prevent fracture or surface breakdown. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. This most often occurs when you have a core or shutoff. The accompanying table lists the flow rates for various barrel diameters at various injection velocities. For example, filled resins and ABS are more likely to. Injection molded parts can have several different issues. If during the design and development stage,. Errors like these manifest when processing is done incorrectly. Weld‐line is a defect that arises in injection molding when two or more flow fronts collide. This action could indicate that one portion of the plastic flow will move more quickly than the other. We stopped the machine and added glycol to the chiller to a concentration of about 40%. They can be off-color or discolored material compared to the intended color of the part. Although injection molding is considered a fairly well-established manufacturing process, several independent parameters must be properly set to achieve a high quality of the molded parts. More about the knit lines in injection molding. Certain injection molding processes may not be effective for the production of some parts. Thereby creating localized pressure within the mold. 0010 in. Possible Causes & Remedies: Machine Cause. This method can be helpful in. Designers can easily set up and perform analysis with only a few clicks. When combined with low injection pressure, this problem leads to decreasing melt speeds and can cause flow lines. The melting temperature is 217–237 °C, and the thermal. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. If the cornflake pigment contains a large amount of fine particles, this will result in a higher definition of flow and weld lines. Cracking is commonly seen at the weld line area but sometimes on the entire surface. Imperfections in manufactured plastic goods, such as a flow line defect in injection molding, are unacceptable. Siemens PLM Software. In this way critical areas of the interface in regard to the lack of interdiffusion and the inappropriate molecular orientation were found to be placed near the surface of the finished parts. If you’re a mold designer with one of those vent-depth “rule-of. Before injection molding, there is a large amount of air in the flow path and the cavity. Solution: Utilize a material that has the stiffest flow possible without causing non-fill. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. Shortening the molding cycle time is a key factor in improving energy efficiency and since cooling occupies a major part of the cycle, effective design and operation of cooling systems is essential. Flow lines are unwanted streaks, waves, or lines on a part’s surface. Unraveling Flow Lines. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. The thermo-rheological findings were used to investigate the sources of weld line weakness. Sink Marks. 150 in. This means that the skin of the part is always formed by. 1mm (7/16"), coolant temperature of 30ºC and cycle time of 17 seconds (see Fig. The steel that cored out and created the notch was very thin—roughly 0. Then the melt is injected into the mold and the surface of injection-molded products is. The edge gate is the most popular and straightforward injection mold gate design. also utilized the co-injection molding technique to study the flow of polypropylene at the weld line behind an obstacle in injection molding; the weld line can be seen clearly from the Fig. The edge gate is the most popular and straightforward injection mold gate design. The parting line in injection molding is which one of the following: (a) the lines formed where polymer melt meets after flowing around a core in the mold, (b) the narrow gate sections where the parts are separated from the runner, (c) where the clamping unit is joined to the injection unit in the molding machine, or (d) where the two mold halves come. Strengthening. Kulkarni) During the fill phase (Fig. Injection molding has been the most popular method for making plastic products due to. 5. Injection Molding works with molten fluid created by heating the plastic granules above their melting point. spelling: injection molding) is a process for producing parts by injecting molten material into a mould, or mold. The weld lines are formed when there is an obstacle in the cavity of the injection mold. Adjust Injection Molding Parameters: Optimizing injection speed, pressure, and temperature can help ensure better melt flow and reduce the likelihood of weld line formation. There are several factors that can contribute to the formation of weld lines, including: Part design: The design of the part can impact the flow of the material and the likelihood of weld lines forming. The flow rate should ensure the material does not lose its. Before his present assignment, Bob managed a molding operation for 25. In some areas, the option is evident, while in others, it. 1) Snake flow lines. The plant water system is a critical component of an injection molding facility. Injection Molding of Multimaterial Systems. 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. Avoiding Voids and Sinks. Using a thermoplastic that stays in a. Causes: The issue might be varying flow rates as the molten plastic moves through the mold or changes in the thickness of the mold’s walls. 750 in. For runny, non-viscous, crystalline resins such as nylon, PE, or PP, the recommended vent depth can range from 0. Taking proper care to design the mold properly, avoiding bottlenecks, and changing the number or location of gates can improve performance. Weld lines, also known as knit lines, are a common defect in injection molding where two or more flow fronts of molten plastic meet but don’t properly fuse together. On that note, we. Water set-up and design are every bit as important as establishing and recording a repeatable process. Flow lines can be minimized in injection molding by optimizing the design of the part and the mold, as well as the processing conditions. All mold cooling lines must have adequate flow to produce a turbulent flow condition. Prevent Flow and Knit Lines During the Injection Molding Process. Facebook. In injection molding, it is often important to maintain consistent color throughout the part. The material is poured into a mold, which shapes the size and looks of the article. They appear as visible lines or streaks on the surface of the molded part and can negatively impact its aesthetics and mechanical properties. Weld-line strength for plastics can vary from 20% to nearly 100% of the strength of the plastic itself. They are visible on one side of the parts. The chart below shows recommended wall thicknesses for common injection molding resins. 2. The formation process of weld lines can be described as follows: Injection moulding (U. The Fill system analyzes the filling of each cavity by sensing the melt presence at the end of flow with a cavity temperature sensor and compares the fill-time. Give a good distance between mold gates and. 3. PROBLEM: FLASH ON PARTING LINE There are a few key reasons why flash appears on the parting line of a part. Molds separate into two sides at a parting line, the A side , and the B side , to permit the part to be extracted. Industry 4. If necessary, the mold designer may simulate the flow of solidification of resin using an injection molding simulation program. The Mold. Impurities in the resin will prevent a smooth flow through the mold. Flow marks in injection molding are defects that manifest as a line or series of lines forming a pattern different in color from the other parts of the molded material. 0010 in. In the area of lettering, ribs, domes or sharp wall thickness changes, air which cannot escape quickly enough is swept along, overrun by the melt and embedded. The materials used in the plastic injection molding process can vary in rigidity and pliability, among other differentiating characteristics. Flow Rate. If the mold itself has cracks or defects, the finished product will also have various problems. Make sure the venting is not too large. If performing a resin change from one polymer to another a difference in viscosity can cause flow lines or gels. Source: Google. 1, pp. Waterlines control heat within three diameters of themselves. 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. The Smartflow Reynolds Number Calculator is provided as a service to the injection molding community as an easy-to-use online resource. You can also adjust both pressure and temperature and make sure the clamp is strong enough to keep the material contained. When modeling injection molding, the global approach is necessary to take into account the solid polymer transport, polymer melting and the polymer melt flow. Typically, flow lines are caused by the liquid plastic cooling at different rates. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. Mold venting is critical to the quality and consistency of the finished part. 1. In the injection molding process, weld line regions occur when a molten polymer flow front is first separated and then rejoined. Weld lines can compromise the strength and aesthetics of the part, so it’s important to carefully design the mold and. Flow marks, also known as flow lines or weld lines, are common defects that can occur in plastic molded parts. The problem could be the result of machine settings made before the gate was installed. There are important differences between an injection mold sprue and its runner system. 1) Snake flow lines. com. They follow the flow of the molten resin from the gate along the finished part. (1) Reduction of injection time and shortening of the molding cycle. You might have come across the aforementioned terminology before and did not know what any of the words meant. Spatter lines formed on the surface of the plastic along the direction of melt flow are called silver marks. Features such as sharp corners or undercuts can. Commercial injection molding simulation packages, such as Moldflow and C-MOLD, have been incorporating GAIM options to provide computerized design and optimization tools for GAIM processes and. G. These streaks or patterns can affect a part's aesthetics, value, and overall quality. If the cornflake pigment contains a large amount of fine particles, this will result in a higher definition of flow and weld lines. The flow fronts at different times (Fig. In the injection molding process of plastic parts, flow mark is a common defect due to the defects of parts design and injection molding process [4]. Weld lines in injection molding are formed when two or more flow fronts of molten plastic material meet and merge during the molding process. Recently hired at plastic injection molding simulation software provider Moldex3D, Nicholson was spurred to undertake the research study following a conversation with a customer experiencing weld-line woes. Randy Kerkstra has been in the plastics industry for more than 26 years, occupied frequently with troubleshooting injection molding. In manufacturing, the Weld line or Knit line or Meld line is the line where two flow fronts meet when there is the inability of two or more flow fronts to "knit" together, or "weld", during the molding process. Plastic Injection Molding Process. Listed below are some factors to consider when designing ribs for injection-molded parts. Look for signs of stickiness or burning. 010 0. This can be achieved by connecting ribs to each other. However, the weld line may not continue throughout the flow. Excess Mold ReleasePoor mold design, including inappropriate mold wall thickness and faulty gate placements, is a common cause of weld line formation in injection molding. As far as the mold builders are concerned, having good flow through each circuit and having a good pressure leak test that they can perform is an. injection mould simulation at steady flow rate. Flow direction is essential for mold mapping because when water flow reverses, poor turbulence and hot spots occur. This “inside-out” flow of the plastic mimics the flow in a water fountain, therefore it is called fountain flow. These flow fronts occur when the molten plastic material encounters obstacles, such as inserts, ribs, or other features within the mold cavity. Obviously, as the resin front moves through the mold, the fill material will always be behind the front. It has larger cross-sectional regions that allow sufficient molten plastic flow into the cavity. Several factors contribute to the formation of flow marks in plastic molds: Mold Design:. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. When the gate depth is much smaller than the cavity entrance depth, and the mold filling rate is very high, when the melt flow becomes unstable jet flow, the front jet has solidified and the later flowing melt fills the mold cavity, and the product will be Snake flow lines appear on the surface. In this guide, we cover evaluation and also the remedy of flow lines in. From the perspective of the mold, when the molten plastic reaches the gate through a larger-sized runner, the flow resistance of the melt is greatly increased because the gate size is usually very small.