Locally black discolorations of the molded part occur in the area of the weld lines, at the end of the flow path or of individual areas of the molded part (for example, a rib). How to recognize, prevent, and counteract flow lines defects in injection molding? Learn flawless products from professional manufacturers. If near the gate, check the gate seal time. 5 gal/min through this circuit we will get turbulent flow—the optimum cooling situation. Flow lines, also referred to as flow marks or weld lines, are visible lines or patterns on the surface of a plastic component. If necessary, the mold designer may simulate the flow of solidification of resin using an injection molding simulation program. (4) It can improve the strength of the fusion line. Weld lines are formed during cavity filling whenever two separated melt flow font recombine. (1. This method can be helpful in. Flow lines are linear grooves or circular ripples on the surface of a molded object caused by uneven cooling, improper residence time, or cycle time, or low mold. Laminar flow in a plastic mold, described by. Plastic Purity. Each material has a maximum flow length for a given injection pressure and wall thickness — this is known as the flow ratio. 020 0. Increase the injection speed, pressure, or temperature of the material. Turbulent Flow IS Always Better. In this study, a fully automated. 0 is leading the productivity and efficiency of companies to minimize scrap rates and strive for zero-defect production, especially in the injection molding industry. Flow lines result from uneven cooling of the plastic within the mold. 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. Cooling lines impact. (All Illustrations: S. During the injection molding process, one of the most important requirements of the mold is to deliver melt from the barrel to the cavity. The plastic pellets must be. The plant water system is a critical component of an injection molding facility. html. The importance of understanding the causes of flow lines is critical for preventing them from occurring during the injection molding process. Typically, flow lines are caused by the liquid plastic cooling at different rates. Thus, as the flow continues, the two flow fronts may gradually rejoin to. Flow lines. Water set-up and design are every bit as important as establishing and recording a repeatable process. When incorporating multiple gates it’s important to consider where the flows will meet as the meeting area can cause aesthetic issues and part weakness. The strong molecular. Mold Flow - Position ribs such that the plastic has an optimal flow path. 3. Low mold temperatures are usually employed to decrease cycle molding time and final process costs; however, resulting surface defects include weld lines, sink marks,. tall, and 0. The best we can hope for is to pressurize the knit or meld line better through the combination of melt temperature, mold temperature, flow rate, and holding pressure. Flow lines are linear grooving or circular ripples on the surface of an injection molded part that indicate the direction of material flow within the cavity. Features such as sharp corners or undercuts can. 5° draft to each side of the rib. These defects include the following: 1. Prevent Flow and Knit Lines Through Mold Adjustments. Taking proper care to design the mold properly, avoiding bottlenecks, and changing the number or location of gates can improve performance. Weld lines have been one of the common defects puzzling the injection molding industry. The injection molding gate generates heat by dissipation. When two or more strands of molten plastics meet in the mold, a weld line will be produced at the junction [1,2]. Reduce the injection pressure to prevent overpacking at the gate. Leadtime Leader 2024. Also called “Weld Line. In spite of its cosmetic attributes, a bad knit line can significantly. Kulkarni) During the fill phase (Fig. Using a thermoplastic that stays in a. Common injection Mold Flow Lines. Flow Lines Defect in Injection Molding Process Flow lines can be defined as linear grooving, or circular ripples, on the surface of a molded part that indicate the. Conventional injection molding is widely used to produce plastic parts, mainly in the automotive industry, due to the high production ratios and quality of. In the injection molding process, weld line regions occur when a molten polymer flow front is first separated and then rejoined. Available with a number of options including thermometers, pressure gauges, liquid-filled pressure gauges and quick change socket and plug. The injection speed should remain consistent as the plastic enters the mold, otherwise, it will slow down, cool, and cause flow marks. When it comes to injection-molded products, here are several typical solutions for flow lines: To make sure the liquid reaches the mold fully before cooling, enhance the. Injection molding has been the most popular method for making plastic products due to. An improper flow rate and injection speed also cause flow marks. 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. If during the design and development stage,. Molds separate into two sides at a parting line, the A side , and the B side , to permit the part to be extracted. Let’s review some methods to prevent flow and knit lines in plastic injection molding. 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. This means that the skin of the part is always formed by. In this lesson we will focus on the meld and weld lines. 1) Snake flow lines. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. Weld lines not only affect the appearance and quality of products, but also cause negative influences on the mechanical properties. Weld‐line is a defect that arises in injection molding when two or more flow fronts collide. After an hour of running, the steel temperature stabilized at 78°F. Weld lines in injection molding occur when two flow fronts meet and create a visible line on the surface of the molded part. 100 to 0. 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. Poor mold surface n Refinish a poor or worn mold surface. Weld line. Flow Lines. Thus, as the flow continues, the two flow fronts may gradually rejoin to make one uninterrupted flow front. The injection molding process involves the injection of a polymer melt into a mold where the melt cools and solidifies to form a plastic product. Vents have three components. 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. It can help you reduce defects, improve quality, and save costs by simulating how. ” What else can you do about weld lines—besides redesigning the mold or gate locations or adjust the flow pattern during fill with sequential valve gating? I recently saw a report on this issue from Moldex3D, the maker of molding simulation software. Splay is a cosmetic defect that occurs in plastic injection molding, when silver or white streaks appear on the surface of the part. Drain the hopper if you were working with 100% regrind, clean if necessary. Weld lines are a common imperfection to be found in most plastic injected molded parts. The Reynolds number takes into account the pressure, volume and viscosity of the coolant, the resistance to flow, length and diameter of the channels and the pressure loss in the cir-cuit. 020"). Flow direction is essential for mold mapping because when water flow reverses, poor turbulence and hot spots occur. Here's a list of the commonest injection moulding defects and how you can avoid them: 1. Weld lines in injection molding are formed when two or more flow fronts of molten plastic material meet and merge during the molding process. The settings and optimization of the injection molding process dictate the geometric precision and mechanical properties of the final. The thermo-rheological findings were used to investigate the sources of weld line weakness. Several factors contribute to the formation of flow marks in plastic molds: Mold Design:. 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. Causes – Remedies. 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. With a minimum of 1. Shear; There are two causes of splay brought on by shear. The edge gate is the most popular and straightforward injection mold gate design. The part surface was observed in reflected light using optical microscope and the pictures of. Help prevent warping with these measures: Raise the mold or material cylinder temperature. 010 0. 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. Below, we’ll look at five of the most common types of injection molding defects, and how you can prevent or repair them. When modeling injection molding, the global approach is necessary to take into account the solid polymer transport, polymer melting and the polymer melt flow. 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]. These flow fronts occur when the molten plastic material encounters obstacles, such as inserts, ribs, or other features within the mold cavity. Increasing pack or hold pressure helps to eliminate low-pressure conditions at the weld line. Phone (630) 665-8590. Flow Rate. If the mold itself has cracks or defects, the finished product will also have various problems. Mold Flow Analysis. This continues until the weld lines in plastic injection molding disappear. Flow Lines and Flow Marks. Unraveling Flow Lines. If packing around a detail is causing cracks/ shorts/burns on the knit line, reduce the heat to improve knit line seal and strength. Flow Line. 1 m/s, and a zero-shear-rate viscosity η 0 (T 0)=3760 Pas. Let’s take a look at some defects that are caused purely due to faults in the injection molding process. Weld line. When molten plastic moves through an injection mold at different speeds, the resin solidifies at different rates, which causes this type of defect. to 0. Reduce the injection pressure. A. In this case the two flow fronts will meet and there will be very little molecular orientation across the weld. They can be unsightly and unpleasant in high-end sunglasses. A gradual change in wall thickness is recommended to avoid any sudden change in the material flow direction. ” Flow marks do not affect component integrity. The melt holds enough temperature to maintain a low enough viscosity. Surface Delamination. Definition: Off-tone streaks, patterns or lines that appear on parts. injection mould simulation at steady flow rate. How to solve flow lines in injection molded products?Injection molding is a heat-transfer process. Impurities in the resin will prevent a smooth flow through the mold. It is also useful for finalized prototypes that are used for consumer and/or product testing. ”. However, you can easily prevent such defects by simply adjusting the temperature, flow rate, or other mold parameters. New design is said to eliminate mold damage from nozzle stringing or work-arounds that slow cycles. Reducing injection speed will allow more time for the air to escape from the cavity through the vents, but this leads to other problems, such as short shots (incomplete parts). When injection molding a part, a knit line may present no problem, or can cause a serious structural problem. Optimize the runner system and locate gates near the thin walls. Mold Design. To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. Where wall thickness increases, round the corners of the mold in those regions. Adjust Injection Molding Parameters: Optimizing injection speed, pressure, and temperature can help ensure better melt flow and reduce the likelihood of weld line formation. The problem could be the result of machine settings made before the gate was installed. Vacuum on the mold does help and many times eliminates the weld line. Different gate sizes and locations using flow simulation have been detected for defects reduction such as weld lines and air traps, air traps and warpage can be managed by varying process parameters [17]. Mold flow marks, also known as flow lines or weld lines, are often caused by variations in the flow of molten plastic material during the injection molding process. Shear; There are two causes of splay brought on by shear. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. Flow lines appear as a wavy pattern on the surface of your plastic parts. Polymer Injection Molding: Gas-assisted Molding. Burn Marks. Below are ways through which you can remove and prevent flow lines; a. This injection molding defect appears as black or rust-colored discoloration on the molded part's surface or edge. Thin walls of greater length require greater pressure, which requires larger injection molding machines and. Features such as sharp corners or undercuts can. It is a well-known fact that weldlines are unavoidable in most injection-molded products of even moderate complexity. May 17, 2023. Injection molding gates occur in different forms, taking distinct sizes and shapes – appearing narrow, wide, tapered, etc. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. He is currently a tooling manager for a large, multi. The last cause of flow lines may be the operators running your daily operations. 10 in Nguyen-Chung et al. Flow Lines. 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. 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. mold and the blow molding process. 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. Select a plastic that is less prone to shrinkage. Injection molding (or injection moulding) is a widely used manufacturing process in many different industries such as aerospace, automotive, medical, and even. You can avoid having any weld lines with cascade injection moulding. Several factors contribute to the formation of flow lines, including material properties, mold design, and process parameters. Walls thicker than 8mm (0. 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. 3. Incorrect gate positions cause multiple flow fronts that struggle to merge seamlessly. These lines form as a result of material flow and solidification during the injection molding process. Clean all parting line and core vents. You can avoid having any weld lines with cascade injection moulding. They may also take the form of ring-shaped patterns when staying close to the mold's entry point, which is the plastic injection nozzle. Injection molding is one of the most significant material processing methods for mass production of plastic products. Imperfections in manufactured plastic goods, such as a flow line defect in injection molding, are unacceptable. The most common and one of the most challenging injection molding defects are weld and knit lines. Vacuum Voids. The weld line and the flow pattern of co-injection molding can be seen from Fig. The Bottom Line. I’ve been writing about plastic flow simulation since 1984, and I. Utilize hot. However, surface quality is difficult to predict due to many influencing factors and their complex interactions. The accompanying table lists the flow rates for various barrel diameters at various injection velocities. 015 0. Investigate the mold for signs that a water leak is present, and correct the condition. • u. Flow Lines. This review process showcases a company’s technical expertise, the capabilities of its design team, and overall quality. As a result this weld line will be a weak point in this part. Learn more. Thin wall injection molding can produce walls as thin as 0. Except for a few very simple injection molded parts, they occur on most injection molded parts (typically in the form of a line or V-groove), especially large complex items that require use of multi-gate molds and inserts. 020 0. Address 272 Commonwealth Drive, Carol Stream, IL 60188. 015 0. A mark on a molded piece made by the meeting of two flow fronts during molding. Flow lines and flow marks. GPM: Measuring the amount of water passing through the mold every minute is a key measurable in determining turbulent flow. They also can appear as ring-shaped patterns near the entry points of the mold. 16″) will be difficult to inject, leading to flow lines, surface imperfections, and short shots. This carbon will hang up in areas and is difficult to remove. Factors within the tooling can also contribute to flow and knit lines, calling for mold modifications. Also called “Weld Line. For each investigated mould temperature, a linear relationship can be observed. This can be accomplished by reducing the substance’s viscosity. Flow marks occur as circles or lines that occur around the gate. . Mold is not vented properly causing slow flow at knit lines. 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. c. They are off tone wavy lines/streaks or patterns in the molded part around the injection ports. Flow lines can occur if any of the following affect the mold: A runner, gate, or sprue that is too small for purpose creates more flow resistance. 030 0. Excess Mold Release Poor mold design, including inappropriate mold wall thickness and faulty gate placements, is a common cause of weld line formation in injection molding. 060 and 0. Prevent Flow and Knit Lines During the Injection Molding Process. The best we can hope for is to pressurize the knit or meld line better through the combination of melt temperature, mold temperature, flow rates, and holding pressures. Energy use by thermoplastics injection molding machines is estimated to result in global CO 2 emissions in the order of 80 million metric tons annually. Mold Design. Cascade Moulding Avoids Weld Lines. Height – Make the ribs 3 times the height of the nominal intersecting wall (3T). Certain injection molding processes may not be effective for the production of some parts. If the cornflake pigment contains a large amount of fine particles, this will result in a higher definition of flow and weld lines. The model of polymer melting is fundamental for the development of. Low melt temperature. 0010 in. 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. Polycarbonate is a tough, optically clear or opaque, biocompatible plastic with good thermal resistance. A method of melt flow visualization was used to record the weld line location on the surface of molding prepared at the proper injection conditions (method of "record grooves effect" formation. Peering into the Flow. After four years in development, an injection machine nozzle tip has been commercialized that is said to eliminate problems of stringing and all the compromises. ” FLOW MARKS – Wavy surface appearance on a molded object caused by improper flow of the material into the mold. Co-injection molding technique is a useful way to study weld lines, which can offer more detailed information of the. 4. 18/06/2021. RapidDirect – Your Best Injection Molding Partner. Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. Learn about prevention methods and references. Non-uniform cooling of mold causes warping, creating internal stresses within the part and resulting in distortions. This most often occurs when you have a core or shutoff feature that the plastic needs to flow around. Flow Rate. The type of resin used during injection molding plays a large role in whether or not a knit line will be present. There are important differences between an injection mold sprue and its runner system. Mold flow analysis is also used to help designers locate difficult spots to fill within the mold. Injection molding, in addition to extrusion, is the most important technology in the polymer processing industry. If the mold temperature is too low, the material temperature will drop very fast, so the injection pressure and the holding pressure will not be high enough to press the solidified layer against the mold surface, thus leaving flow lines along the melt flow direction. Lower speeds allow gas more time to escape through vents. Increase molten plastic temperature during injection molding. There is a level of insulation from the plastic layer on the wall. These lines can occur at the gate location, where the plastic enters the mold, or anywhere along the flow. 5. SMARTFLOW ® flowmeters effectively and accurately measure flow rate. Kobayashi et al. Mold flow analysis is a powerful tool for optimizing the design and performance of injection molding processes. 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. Thin walls often increase the pressure required to fill the part, and. Heat: Too much heat can have an appearance similar to moisture splay. At a theoretical flow distance of 10 mm it represented the measured values well but at a longer distance it underestimated the experimental scale. You might have come across the aforementioned terminology before and did not know what any of the words meant. Cooling for slender cores (≤3 mm) uses air cooling instead of water. Injection Molding (IM) Solutions 1019 Balfour St. 2), the plastic enters the mold at a relatively fast rate and forms the skin. Another solution may be to pull a vacuum on the mold just before injection. Mold flow analysis is a software simulation that can show how resin will fill the mold during the injection molding process. Sprues are usually tapered, and they come with ends that are bigger at the top. This allows the melt to keep enough velocity to ensure proper filing. The mold material 6 can have several effects on. A ‘parting line’ is the line of separation on the plastic part where the two halves of the plastic injection mold meet. Give a good distance between mold gates and. Reposition gates and runners to allow resin to flow around the obstruction from a different direction. 1 Injection molding From Wikipedia, the free encyclopedia Injection molding (British: moulding ) is a manufacturing technique for making parts from. 1) Snake flow lines. Increase the mold temperature. Spatter lines formed on the surface of the plastic along the direction of melt flow are called silver marks. Injection molding is one of the best plastic production methods. ; Warping – The structural deformation that occurs. It also may be that your injection speed is too low, which will cause the molten plastic to solidify at different rates. Add more cooling circuits. The Smartflow Reynolds Number Calculator is provided as a service to the injection molding community as an easy-to-use online resource. Select a plastic that is less prone to shrinkage. Minimum turbulent flow would be 12-14 GPM, while numbers in the 20’s would be identified as an excellent flow rate. This results in a much greater amount of vent flow area for the compressed air to exhaust through, and still protects the corners. The cause can vary. First, excessive injection pressures may be forcing the mold apart. If the mold itself has cracks or defects, the finished product will also have various problems. This can be achieved by reducing the flow. In this regard, the gate form with less shunt should be used, and the gate position should be selected reasonably. Sprue: This is what feeds the molten material into the runner that in tune reaches the casting by passing through the gates. 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. Make sure the venting is not too large. Setting the proper pressure on the injectors to push the plastic into the mold with enough speed that the plastic will coat the mold and fuse with other flow lines. Remedies: Raise the temperature of the mold or molten plastic. Increase the injection speed and mold/operational temperature to prevent fracture or surface breakdown. On that note, we. In narrow fields, a limited amount of molten liquid can solidify and block the flow. The Plastic Troubleshooter Defect - Flow Lines. Bubbles are caused by melting flow fronts colliding in a mold cavity. Unexpected flow lines, so-called tear drops, occur. 010 0. Before injection molding, there is a large amount of air in the flow path and the cavity. Flow lines. Request a same-day quote to see how our medical injection molding experts at Aberdeen Technologies can help move your project forward. Mold design is a key aspect of injection molding. Electronic flowmeters featuring FCI (Flow Characteristic Indicator). Adjustments to injection speeds are the best way to determine which of these two are the specific cause. 2. 3) Poor Preventative Maintenance. FIG 1 Depiction of fountain flow. In injection molding weld lines are formed whenever two flow fronts are joined. Understanding the complexities of injection molding flow and solidification is a bit more challenging as. (All Illustrations: S. In addition, when the melt is solidified in the cavity, there is a vacuum between the product and the cavity wall, also the air must enter the mold. Knit lines appear to be a faint line or a crack in the finished part after it comes out of the injection mold. 5. Plastic Injection Molding Defects series-Flow Marks or Flow Lines Aug 23, 2019 What should we keep in mind when designing for injection molding?1. Seven Common Defects and Solutions for PC/ABS injection molding Products,Flow Lines, Pitting,Product Delamination,Stretch Marks. This is achieved by using the needle valve nozzles to control mould filling so that only one flow front exists at a time. 1mm (7/16"), coolant temperature of 30ºC and cycle time of 17 seconds (see Fig. Flow lines appear as a wavy pattern often of a slightly different color than the surrounding area and generally on narrower sections of the molded component. Solution: Molding Process: This defect can be reduced by raising the material temperature and the nozzle temperature, and slowing down the injection speed, etc. Weld lines represent the region where two separated melt fronts recombine. Here are some ways to avoid. (2) Adjust the injection speed: high speed allows the melt to reach the confluence without cooling down, and low speed allows time for the air in the cavity to be discharged. Raising the temperature of the mold slightly can help to prevent flow lines, as it prevents the molten material from cooling immediately upon impact with the cavity walls. NX Mold Flow Analysis. Strengthening. The flow rate should ensure the material does not lose its. This may involve adjusting the temperature and pressure of the mold, using different mold materials, or adjusting the injection speed or cycle time. Parting Lines. Effects of mold temperature and pressure on shrinkage 0. The 7/16-inch size is a happy medium between many small lines and the fact that larger lines don’t particularly increase the heat exchange benefit. When creating the parting line, the mold design is the first place to look for the appropriate parting line for an injection molded product. This depends on a. Also, heating the material in the cylinder. Plastic is injected into a mold at a specific rate of flow—typically in. However, you can easily prevent such defects by simply adjusting the temperature, flow rate, or other mold parameters. Listed below are some factors to consider when designing ribs for injection-molded parts. As the weld line can significantly lower the mechanical strength of µIM parts, it is relevant to clarify the position of weld. Plugged or inadequate vents n Clean plugged or dirty vents, particularly those along the parting line. Heat Input and Cooling Calculator for Injection Molding. Flow lines. On-Line Solutions To Injection Molding Problems. Plastic injection molding is the industry’s most common way to manufacture parts. Study shows that the root cause of jetting is related to the mold design on the one hand and the viscoelasticity of the material on the other. 4) Extended Shutdowns. Thus, a right gate design raises polymer temperature to prevent the formation of weld lines and flow marks. MMT Chats. According to the design requirements of the back shell of mobile phone and the performance of materials, ABS is selected as the raw material for injection molding in consideration of economy [ 8 ]. In injection molding, it is often important to maintain consistent color throughout the part. These flow fronts occur when the molten plastic material encounters obstacles, such as inserts, ribs, or other features within the mold cavity. As the weld line can significantly lower the mechanical strength of µIM parts, it is relevant to clarify the position of weld. The moldability validation and flow analysis tools enable you to iden-tify and correct potential injection molding problems as you design the product. Its popularity is typified by the numerous products produced in this way at the present time. 7 of the reference. Tip #6: Pick Which Molding Defects Are Acceptable. Flow Linesparticles, during injection molding, will produce visible flow and weld lines. The differences between knit and meld lines are significant, and they can dramatically impact the part’s structural integrity. Flow Lines. Solution: Utilize a material that has the stiffest flow possible without causing non-fill. Sufficient draft is an important part of any mold design, and quick-turn tooling is no exception. Heat: Too much heat can have an appearance similar to moisture splay. Lookalikes include surface scratches, scuffs, flow lines, delamination from contamination, and flaking. Injection molding tool life is the number of production cycles that an injection mold can complete before it needs to be replaced. The linear mold shrinkage of injection molded parts will vary from 0. It can also aid in material selection since fill. The resulting defects don’t stop at flash only. Flow lines are ripples in the plastic after the part is formed. If you’re seeing flow lines, try extending the. 1. 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. Designers can easily set up and perform analysis with only a few clicks. Lesson 6: Meld and Weld Lines (Processing) When plastic flows into an injection mold, the internal flow pattern depends on the part design, mold design, and processing factors. This is achieved by using the needle valve nozzles to control mould filling so that only one flow front exists at a time. Randy Kerkstra has been in the plastics industry for more than 26 years, occupied frequently with troubleshooting injection molding. distance from the cooling lines and mold cavity surface varies and results in uneven cooling in molded part. [1]#TROUBLESHOOTING #FLOWLINES #INJECTIONMOLDINGStudy more about troubleshooting flow lines : lines occur when two flow fronts meet and fuse together in the injection molding process. with a characteristic length χ 0 =0. If possible, try to choose a little glue . Known as thermolators, water cooling systems require a cooling source such as a tower. 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. If so, look for an alternative resin. An on-line compounding injection molding machine, incorporating the co-rotating, intermeshing twin-screw extruder and a reciprocating screw injection molding machine fitted with the oscillating pressure valve, has been developed. Flow lines are surface irregularities, wavy patterns, or a rippled effect, perhaps of a slightly different color, that can appear in injection molded parts. Fast injection gives you a glossy part, which is what we wanted in this. 080" – 0. Part walls thinner than 4mm (0.