18/06/2021. Rynite® PET is usually processed with melt temperatures between 280 to 285 °C (535 to 545 °F) . Steven. This was usually with a PC/ABS material at knit lines and high fill pressures from thin walls in the part. The three dimensional structure is formed of a resin fiber mixture having a resin material infused with carbon fibers having a length of about 12. A thermoset injection molding process may save as much as 50% of machine time per shot with a faster cycle time compared to a thermoset compression molding process, allowing molders to produce high quantities of thermoset components per day in multi-cavity tools. When injection molding complex parts, often knit-lines are formed during the mold filling stage. New blog post is up! What Are Knit Lines in Injection Molding, and How Do You Prevent Them? #injectionmolding #moldsmart #howto #rjg…Injection moulding is a well established mass production tool for polymeric products of all shapes and sizes which is now drawing the attention of companies and researchers who seek to utilise this high throughput fabrication technique to produce devices with nanoscale dimensions []. Swirling can increase depending on the material you use, and the texture or polish of injection molding tools. ”. Sequential valve gate technology. Expand. Learn more. Shear Controlled Orientation Injection Molding of Polymeric Composites with Enhanced Properties. As these flow fronts come together. Kurt W. With plastic finishing plugs and end caps, we can help you keep your products protected while giving. These are imperfections in the part where separated flows of cooling material meet and. turbulent flow of Injection speed set too high. The injection molding design process, much like all industrial design processes, deals primarily with the creation, look, and feel of a product. While knit lines can be present it does not always mean the structural integrity of the plastic part is compromised. In the injection molding process, melting takes place via two factors that work together: shear and heat. In an injection molded structural plastic part, a weld line (also called a knit line) will result in a region of mechanical weakness as soon as the part is submitted to an external load. Based on the resin. 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. shows some obvious locations for vents, a brief molding trial should be conducted to observe where the gas voids occur. Islyn Thomas summarized the need for a particular vent location better than I ever could. It emerges and becomes visible when the flow fronts cannot mold or knit during the molding process. Holes in plastic parts are normally cut with a router (or drilled if round. This continues until the weld lines in plastic injection molding disappear. 030- to 0. Such molds or tools aren’t intended to be used in operation. You don't give us much to go on. Thin wall injection molding can produce walls as thin as 0. From: Polylactic Acid (Second Edition. 4. 2020-01-1306. 080" – 0. Koelling, Ronald C. com Three terms that often get mixed up in injection molding are weld, meld and knit lines. . Release of trapped air in those cases will. injection molding. They again get resolidified along the surface. Basic rule of thumb air in mold must be able to escape at theAbstract The knit line structure of injection moulded PA 6 samples was analysed by SEM and optical microscopy. This article will discuss the importance of injection molding nozzles and what makes a good nozzle for a molding or injection. The GLS™ Injection Molding Guide provides in-depth information on part design, mold design and processing for styrenic block copolymer (SBC) thermoplastic elastomers (TPEs). No matter the size of a production run, the presence of blemishes on the finished product leads to unhappy clients. Knit lines are consideredmolding defects, and occur when the mold or/and materialtemperaturesare set too low:. Why. 26 = 0. Some. Using three test materials, polystyrene (PS), polycarbonate (PC) and polyoxymethylene (POM), the relationship between a design and a processing parameter. Sink. Remedies: Increasing the barrel temperatures will allow the flow fronts to stay hotter longer and. Determine the time duration of the molten state. The injection molding process is on the surface is fairly simple, plastic resin is heated to its melting point and forced into the cavity of the mold to produce a plastic parts. Runner Type. Adding draft or slope to vertical walls of a part makes it easier to eject or remove the part from the mold. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. Part Shorts and has burn marks. Part Shorts No burn marks. While not always visible, weld lines (aka knit lines) are where two resin flows meet. Plastics Injection Molding Expert John Bozzelli covers. A screw-type plunger forces the material into a heated chambe r,. Knit Line occurs where different flow fronts of material meet while flowing through the mold. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. Edge Gates. Flow lines are off-color lines, streaks, and other patterns that appear on the surface of a part. 5. Causes 1. Comprehensive. Circular Loom Machine; Raschel Knitting Machines; Shade Net Making Machinery; Inspection Machines; Non Woven Production Line. Temperature is another factor that can cause weld or knit lines in injection molding. Industrial Knitting Machines. Material contamination, for example, can cause several molding issues. Injection moulding (U. Weak weld lines are perhaps the most common and difficult injection molding defect to eliminate. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. Also known as a knit line, this is the point at which two flow formations meet and are unable to. Parts molded with ABS are susceptible to forming knit lines, which are visible lines on the surface of the part. Thicker parts require more cooling time and can lead to air becoming trapped in the mold and weld / knit lines to form. Here are some reasons why design is important for injection molding. Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. Mold analysis tools are used by designers of molded plastic parts and by designers of the mold tools used to manufacture those parts. The resulting line has the. On average, larger injection molding machinery can cost from $50,000-$200,000 or more. Check the diameter of the ejector pins and the pin hole tolerances, if the tolerance is too wide this could allow molten plastic to flow down between the pin and hole surface. 4. 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. 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. Gates, vents, sliding cams, pick-out inserts, and any other place where the two sides of. 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. Bubbles are caused by melting flow fronts colliding in a mold cavity. These materials have beenDetermining the correct tonnage provides a foundation that must be rock-solid to avoid flash and damage. 015in wall. Finally, knit lines occur when molten plastic flows around an object and rejoins on the far side, a phenomenon that is quite possible when inserts. Weld lines are formed during cavity. sinks, knit lines, and shrinkage,” Spalding says. Gating. However, product designers relying on this molding method encounter various challenges during tool design and development. 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. Typically, injection molded parts will be between 0. 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. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. 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. 0 mm) is crucial to ensuring that parts cool evenly. A weld line refers to a line, notch or color change that is created on the molded part caused by the convergence of two separate flows of molten plastic. DOI: 10. When the plastic cools, it takes the shape of the mold and is then ejected and finished. Fig. Holes in the part will always cause knit lines. 5 to 3. Additional venting along the parting line perimeter will improve overall venting significantly. The cracking was always located in the weld/knit line and therefore caused by weakness in the bonding of the plastic at that line. Venting. The utility model relates to a mold structure capable of eliminating the appearance of weld lines of a hole-shaped injection molded product. Left: L-shaped perform. The fluid path has an inlet and a radially continuous, downwardly. More about the knit lines in injection molding. An option to bluing agents, the long established means of gauging pressure distribution, comes via Pressurex, a thin, flexible, plastic film. Injection Pressure 0r Speed Too Low Explanation: If the injection speed or pressure is too low, the molten plastic will not be pushed into the mold cavity fast enough to fill and knit at converging flow fronts because it cools down and solidifies too soon. 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. Poor Knit Lines. Meld and knit lines are actually both different types of weld lines. When venting stationary inserts or core pins in rib or part details with venting issues, I recommend no more than 0. Inadequate venting. Injection mold design and custom tooling can make or break the success of a finished plastic product. 5mm (0. Operating Conditions • Fast injection fill speeds, supporting short injection times (1–3 s), especially in thin sectionsGate and Knit Line Locations<br />. The injection molding was carried out in a DK-Codim 175/410 injection molding machine. Incompletely fused extrusion knit Line. weak knit lines and fracture points. Product designers encounter a wide range of challenges when. When designing for injection molding, consider these steps to prevent knit lines. Flashing can be a common defect in injection moulding and can affect the appearance and functionality of the finished product. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. There. But those key aspects can be viewed differently if you’re auditing mold changes before startup or troubleshooting changes for an already validated process. Weld lines, also known as knit lines or meld lines, occur when two or more flow fronts meet during the plastic injection molding process. Raising the mold temperature will keep the material molten longer, resulting in stronger weld lines and even elimination of weld lines. Product designers encounter a wide range of challenges when creating and developing molded parts, such as stress factors, warp, and those pesky knit lines. Insufficient injection pressure and speed can cause weld lines. Inject the molten material into a mold. As the polymer resin is injected into a mold, it flows through all parts of the mold. PAPER ABSTRACT: Desktop injection molding machines and stereolithographic print ed molds make hands-on injection molding production possible in design studio classrooms and labs. Sink Marks Cause 2: Low Pack and Hold time. For this study, a special injection mold was designed and constructed (Figure 1) in order to produce specimens of various thicknesses (from 2 to 6 mm). That’s the air escaping out of the nozzle until the hose is full of pressurized water. Mold cores can be machined from a solid piece of copper alloy or inserted to aid in construction or allow for easier replacement if a com-ponent would ever be damaged in molding. When the temperature is not very high, there are chances of premature solidification, which can cause weld lines to form. By altering the part design, it may be possible to just have one flow front, and avoid multiple flow fronts having to come together. Solid or semi‐solid, this material leaves a distinct border with adjacent melted material similar in. Figure 1 Flow Lines Knit or Weld Lines Cavity Gates Table 1 Knit line in a multi-injection-point cavity. 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. Flow Lines. Last month, in the first part of this two-part installment we focused on the reasons viscosity can change during injection molding. Let the molten material cool to a solid-state. Knit lines occur at points where resin flows converge after molding around an obstruction or protrusion within the mold, usually away from the gate area. Weld lines often leave witness marks in the moulding surface. What Causes Knit and Meld Lines? Like many part inconsistencies, these unwanted features are rooted in product design. These lines can manifest as visible marks on the component’s surface and potentially affect its structural integrity. Parting lines lie along the edge of the molded part, between the core and the cavity. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a 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. Venting. DFM Helps Prevent Sink Marks In Plastic Injection Molding. doc), PDF File (. 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. Brent Strong, p. This article looks at the issues presented by a weld line in injection molding and the techniques manufacturers can use to avoid them. Knit and Meld lines are inherent to plastic injection. Many materials can be. Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. Near-Net-Shape production uses injection molding to account for 70-90% of the final geometry of a part. Avoid adding threads directly on your injection molded part. 3,000 ton machines can cost $700,000. These defects are not visible, like small. In fact, strength at the knit line can be as little as 20 percent of the nominal strength of the part. With ABS injection molding, you get the collective benefits and properties of three monomers. The above guidelines for initial heater band settings are for most injection molded parts. This image shows a PVC pipe after it was accidentally dropped on the ground. The packing pins are similar in construction to mold ejector pins and may also be mold ejector pins depending on mold configuration. 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. As these flow fronts come together. 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. 2. Highly ScalableVacuum on the mold does help and many times eliminates the weld line. Three terms that often get mixed up are weld, meld, and knit lines. 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!. The thermo-rheological findings were used to investigate the sources of weld line weakness. 1. Insert injection molding is a process that requires an insert — typically metal — to be pre-placed in the tool for injected plastic to flow around. There are times when porous materials like Porcerax are used in problem or backfill areas. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. Because injection mold design and processing is complex, a set solution will not solve all problems. Influence of injection-molding parameters on the morphology and mechanical properties of glass fiber-reinforced polypropylene composite. In an injection mold, the plastic fluid flows and spreads out in many directions as it comes out of the gate. These defects are not visible, like small. Knit lines don’t. A weld line refers to a line, notch or color change that is created on the molded part caused by the convergence of two separate flows of molten plastic. Learn how to troubleshoot weld lines in injection molding. The main causes of Weld Line or Knit lines are: Convergence of two flowing polymer melt streams during injection molding process: This is the most common cause of weld lines, as the two melt streams coming from different runners or gates in the mold meet and do not fully mix, creating a weak point in the finished product. (See Fig. If the load is applied in the transverse direction relative to the knit line, matrix cracking is easily initiated, and the part can fail. Three terms that often get mixed up in injection molding are weld, meld and knit lines. As a result, prototyping is strongly recommended for parts with. Notched weld lines then remain near the cavity walls. 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. Plastic injection molding is the industry’s most common way to manufacture parts. Increase injection speed. Weld Lines-3 Ways for Detecting and Correcting. In addition to the main factory and development. When setting a heat profile, consider residence time, screw RPM and filler type. A poor design can lead to many visual defects in the final part. Rapid heat-and-cool molding technologies have attracted increasing. Reducing the dimensions of the runner system. the thin blades. Knit lines are a common defect in injection molding that can affect the appearance and performance of plastic parts. Injection Molding: How to Set Second. Most failures of injection molded plastic parts are caused by either improper design of the part or improper design of the mold. Knit lines. Knit lines form when two or more plastic flow fronts collide and solidify or “knit” during the molding process. Injection molded plastic parts have comparatively less strength in the weld line section and they also have an impact on product aesthetics. One common problem that occurs in injection molding is the formation of knit lines. 5-3. 453. 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. Depending on the resin, resin temperature, mold temperature, and filling. Plastic melt and mold temperature. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. Injection molded plastic begins its journey through the part tooling via an entry section called a. It is. Weld or knit lines occur when melt flow fronts collide in a mold cavity. a weld or knit line may develop on the opposite side of the obstruction as the two fronts of material join. 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. Misra A. Having uniform wall thicknesses between 0. – Change the thickness of the product. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. These knit lines affect the parts aesthetics, but also they generally decrease the strength. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. While mold-filling simulation is a very common tool for predicting the fill patterns of an injection mold, in our judgment there is not yet a commercially available, satisfactory filling simulation for microcellular foam molding. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Because they can be shut off independently you can control flow fronts and knit-line locations. For non-reinforced or non-filled nylon, the mechanical performance in the knit lines (planes) areas are approximately equal to the mechanical performance of the resin (polyamide) used. Thick sections take longer to cool than thin ones. One of the common defects that can occur in injection molded parts is weld line. A meld line occurs when two moving melt fronts converge and flow parallel to each other. Overall, injection molding is a relatively simple process. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. Industrial Knitting Machines. 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. An injection molding machine having a first mold portion and a second mold portion. See full list on fathommfg. This course outlines mold filling and how different gating configurations affect filling. 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. One exception: ribs should be about 50. cold and hot weld line. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. Yet a smooth finish sometimes actually highlights flaws like knit lines and blemishes in the part. After selecting resin material, the design and process control of injection mold directly influence the quality of formed products. Weld lines defects are formed when two flow fronts are merged together. ”. Be wary of saving too much weight or you might end up with: cracking. Knit lines generally occur around holes or other obstructions to the melt flow. These seams or knit lines are avoided because the molding material flow does not a meet at an interface nor must. An injection mold that produces pieces while the final tool is being built. and Titomanlio, G. When these areas are visible, it can pose no problem at all to the piece, be nothing more than a cosmetic flaw, or can be. The adverse effect of knit-line formation on the mechanical properties of thermoplastics has been well documented for unfilled materials. Trapped air in a mold manifests itself as a burn mark on the molded part. A knit line is the spot where two flows meet. An undercut is any indentation or protrusion that prohibits an ejection of a part from a one-piece mold. 4. Depending on the design of the mold and the material being injected, a knit line may: present no problem at all, be a cosmetic issue, or cause a potentially serious structural problem. Once the mold is created and the machine is set up, additional parts can be manufactured very fast and at a very low cost. He is currently a tooling manager for a large, multi-plant molding and manufacturing company. They again get resolidified along the surface. 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. While injection molding itself is a straightforward process involving melting thermoplastic resin and injecting it into a mold cavity, knit lines can pose. A knit line is any line, visible or not, where two resin flows meet. The structural stability of. Troubleshooting Injection Molding Weld Lines. Since our material is injected through a. ABS is a good choice for handheld consumer devices. The specimens with a weld line at the center were obtained by double gate molding and the specimens without a weld line wereTherefore, changing the edges and corners of the mold core to make it buffer transition and keep the melt flow stable can prevent the occurrence of wavy lines. 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. The specific method is that when the product is just filled and filled in the cavity, the insert. Proper mold cooling can eliminate warp, decrease cycle times, and increase part quality. Multiple parts with complex design and differing wall. com. If the part design’s wall thickness is constant, the magnitude of the plastic’s velocity will be the same at every. 2. Bad habits can cause many different problems with injection molding machines, and flow lines are included in that. Weld lines have a significant effect on manufactured products. They are formed downstream through holes, and between multiple gate locations. Too cool a melt. Prevent Flow and Knit Lines During the Injection Molding Process Timing and temperature are significant contributing factors when it comes to flow and knit line. 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. 2) Vents in an injection mold should let the air out, but not the liquid plastic. Contact us. BURN MARKS Burn Marks: burn marks can occur when the design of a plastic part, and the subsequent injection mold design, causes air to be trapped during the injection (or filling stage) of the molding cycle. Injection moulding can be performed with a host of materials mainly including metals (for which the process is called die-casting ), glasses, elastomers, confections, and most commonly thermoplastic and. To study the weld line formation of colliding flow fronts the filling of a mold cavity was simulated. This month, we covered an array of topics including injection mold venting, business strategies and runnerless micro molds. Submarine Gates. Polypropylene Consumer and Injection Molding Containers, Crates, Garden Furniture, Housewares, Luggage, TSL, TWIM lyondellbasell. 0 to 3. LCP can replace such materials as ceramics, metals, composites and other plastics because of its outstanding strength. Cold weld line or known as “knit line” isWeld Line defect analysis, the most common of many defects in injection moulding products. 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. Description: Flow lines are streaks, patterns, or lines - commonly off-toned in color - that show up on the prototype part as a consequence of the physical path and cooling profile of the molten plastic as it flows into the injection mold tooling cavity. The following are the conclusion drawn from the present research: 1. Design. Anisotropy. Contact Universal Plastic Mold Today. Take these steps to avoid knit lines. As a result, the portion has a faint, perhaps undetectable line. ISO 9001:2015. However, compression molding often provides poor product consistency and difficulty in controlling flashing, and it is not suitable for some types of parts. gate position or runner. Meld and knit lines are actually both different types of weld lines. These knit-lines are well-known as particularly critical regions in the mold when mechanically. On the other end of the scale, a desktop injection molding machine with 5 tons of force can cost between $30,000-50,000. Effect of Injection Moulding Conditions on Knit-line Formation, Plastics Rubber Processing and. They occur when melt flow fronts collide in a mold cavity. Macromol Symp 1988;21/21: 489-500. Injection Pressure 0r Speed Too Low Explanation: If the injection speed or pressure is too low, the molten plastic will not be pushed into the mold cavity fast enough to fill and knit at converging flow fronts because it cools down and solidifies too soon. All the while, the material could be the correct material," Hill says. TEFABLOC™ TESI 744 TPE compound for injection molding processing provides superior adhesion properties when processed using injection molding. For example, warping, sink marks, drag marks, and knit lines can all impact the visual appeal of the manufactured part. 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). So. The last cause of flow lines may be the operators running your daily operations. POROUS MOLD MATERIALS. 1050 Walnut Ridge Drive. Learn more. land and using maximum vent depths to get them as close to self-cleaning as possible. plastic recycling machine, blown film extruder, filament extrusion line, injection molding machine, blow molding machine, injection blow molding machine, bag making machine, flexo. Knit lines, also known as weld lines, are fine lines that resemble hairline fractures or cracks. Be wary of saving too much weight or you might end up with: cracking. Knit lines, also known as weld lines are areas in the. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. J (left) shows embossed feature and S (right) shows debossed feature in plastics through injection molding. The comment on melt flow index is correct, but, I've molded straight PC down to . incomplete filling or shorts. They are formed when two or more flow frontINJECTION MOLDING GUIDE V2. Since the intention is to preserve fiber length in LFRTs by reducing. This will help the mold designer to determine the allowable gate and knit line locations. Find out more by calling 573-437-4154 today or email us. Weld / Knit Lines; Assumptions. These are caused by the shot of molten plastic moving at different speeds throughout the injection. mixed manually and quickly stored in the tank of an injection machine just before the start of the resin injection or (2) the components are stored separately in different tanks of an injection machine with a mixing head. The area generally has lower strength than the other areas of the part. (knit) line and produces a latent, or obvious, part defect. A knit line is any line, visible or not, where two resin flows meet. Randy Kerkstra has been in the plastics industry for more than 26 years, occupied. 060 and 0. 3. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. 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. Gates, vents, sliding cams, pick-out inserts, and any other place where the two sides of. Bubbles are caused by melting flow fronts colliding in a mold cavity. 156 x 2 1/3 = 0. Having uniform wall thickness makes it possible for the melted plastic to fill the mold evenly, therefore not creating a part with warp, sink, thin knit lines, or other defects. Weld line, also known as knit line or meld line, is a visible line or mark on the surface of a plastic part where two or more flow fronts of molten plastic meet and fuse together. Knit lines appear to be a faint line or a crack in the finished part after it comes out of the injection mold. pdf), Text File (. In a weld line, reinforcement fibers. How weld lines form. To learn more about us or to get a quote, click here or call 1-888-893-1587 now.