. a specific area on one side lens, a warp line, and a weft line. Dedicated to strict quality management and thoughtful client services, our experienced staff customers are generally available to discuss your demands and guarantee full client pleasure for Knit Line Injection Molding, Electronics. Let the molten material cool to a solid-state. DFM Helps Prevent Sink Marks In Plastic Injection Molding. You can avoid knit lines and other problems by creating designs with smooth geometries. Having uniform wall thicknesses between 0. Material contamination, for example, can cause several molding issues. Learn how to troubleshoot weld lines in injection molding. "As soon as that part or material is stressed, it can be real conducive to fracture, cracking, breaking, just because of the way it's been molded. 197 in. This picture shows a. 45 in. 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. The resulting line has the. While injection molding itself is a straightforward process involving melting thermoplastic resin and injecting it into a mold cavity, knit lines can pose. The melt is forced to split up during filling of the cavity. Knit Mark – A witness mark on a molded part, often occurring at the midpoint between two transfer or injection sprue locations. Knit Lines: These occur when different flow fronts come together as plastic flows through the part cavities. Troubleshooting Injection Molding Weld Lines. Proper mold cooling can eliminate warp, decrease cycle times, and increase part quality. Polym. The knit lines are the result of poor molding conditions (likely molding at too low of a temperature). Inject the molten material into a mold. As the polymer resin is injected into a mold, it flows through all parts of the mold. incomplete filling or shorts. The company provides an array of digital manufacturing expertise. Temperature is another factor that can cause weld or knit lines in injection molding. Increase the size of the gate and runners to alter the mold design. Weld Lines. Many materials can be. and to identify potential knit lines. A structural finite element analysis (FEA) can be used to compare locations of high stress to the locations of the knit lines identified in the mold-filling analysis. Adding vents, using overflows, or using porous metal. In the plastic injection molding industry, we work with materials that are byproducts of oil refinement and molds made of metal casting, so our terminology is bound to be at least slightly confusing. ) or as thick as 25 mm (1 in. There. 27-ounce shot size to 600-ton with a 105-ounce shot size. Let’s. Wavy lines are another feature of weld lines. One solution is to use optimal wall thickness to help slow cooling during the ABS plastic molding process. Adjust the design for the flow pattern to be a single source flow. To prevent swirling, perform tests whenever possible and use pre-compounded resin to ensure identical color match across parts. Weld lines, melt lines or Knit lines could be caused by different causes: - Low temperature of molding machine barrel - Inadequate back pressure - Injection pressure or injection speed is too low - Low mold temperature - Small injection gates and/or runners - Improper location of injection gate - Excessive gate land length1. 5mm (0. Knit lines, also known as weld lines are areas in the molded part where two or more flow fronts converge. A weld line, or knit line, occurs when two flows of melted plastic meet and “knit” together. The Mold Tools toolbar provides tools for creating mold tooling (cores, cavities, etc. If the plastic has cooled too much during the injection process it can lead to knit lines in plastic parts when they meet past an the obstruction. 18/06/2021. – Change the thickness of the product. However, the weld line may not continue throughout the flow. Factors within the tooling can also contribute to flow and knit lines, calling for mold modifications. Mold Flow Analysis computer. The gate is the entry point to the part-forming cavity, where plastic material is injected from the molding machine barrel, through the sprue and runner, into the mold. ITAR. Weld Lines-3 Ways for Detecting and Correcting. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. 5 mm (0. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. Depending on the design of the mold and the material being injected, a knit line may: present no problem at all,. Knit lines. In fact, knit line strength will decrease with higher filler content and with longer fibers. Proper venting is essential to molding a defect-free part. Injection molding is the cost-effective method and is best suited for higher volumes. Randy Kerkstra has been in the plastics industry for more than 26 years, occupied. Much of this research has focussed on the materials which. Place a vent in the weld line area to remove the entrapped air. In an injection mold, the plastic fluid flows and spreads out in many directions as it comes out of the gate. An edge gate introduces material at the main parting line, or where the two halves of the mold meet, with a perpendicular runner. Using three test materials, polystyrene (PS), polycarbonate (PC) and polyoxymethylene (POM), the relationship between a design and a processing parameter and the effects of the knit-lines on the tensile properties of injection molded plates. 156 x 2 1/3 = 0. Avoid areas where the plastic must suddenly flow upward or downward. Knit Lines and Resins A knit line is any line, visible or not, where two resin flows meet (see Figure 2). To ensure quality parts, injection molding companies must have the best injection mold design first + (91) 96067-70777 +(971) 547-161-112. Neat polypropylene retains nearly 90% of its strength on a properly designed and molded weld line. 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. A component of the injection-molding machine wherein the resin pellets are melted, compressed and injected into the mold's runner system. Knit lines form when two or more plastic flow fronts collide and solidify or “knit” during the molding process. 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. And often, the mold is the same color as the plastic polymer, or can appear that way due to a lack of contrast caused by difficulties lighting the inside of the mold. Weld line. These seams or knit lines are avoided because the molding material flow does not a meet at an interface nor must. 6. suppressed cooling and possibly warp. Figure 1: Knit lines in a cover plate. Anisotropy. Venting is required to allow the air in the sprue, runner and cavity to leave the tool as the melt flows into the cavity. Inadequate injection pressure can result in knit lines and a surface that. , Rallis, A. Reducing the dimensions of the runner system. Increase size of the vents. (1. 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. In this way, the mold supports distribute the force and minimize the stresses on the mold plates. A poor knit line can cause cosmetic blemishes and significantly weaken the structural integrity of a part. Injection molding is capable of producing a lot of aesthetic options as well. The part is cooled in the mold until it is solid enough to be ejected. PROBLEM: FLOWLINES (ALSO CALLED WELD LINES OR KNIT LINES) Definition: Streaks, orange skin, or visible flow lines in parts . The relationship between processing conditions, morphological structure and mechanical properties of knit lines of an injection molded semi-crystalline thermoplastic. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. 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. The point of meeting creates a weak spot because the edges of the molten plastic, already cooling, don’t mix together very well. While injection molding itself is a straightforward process involving melting thermoplastic resin and injecting it into a mold cavity, knit lines can pose. Parts as thin as 0. Soft metals, such as aluminum and beryllium copper, can be used for prototype<br />. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. Such molds or tools aren’t intended to be used in operation. Vents for phenolic parts should be approximately ¼" (6 mm) wide and 0. Sink Marks Cause 4: High Mold Temperature. RELATED CONTENT. The runner and gate system used in plastic injection molding is responsible for directing molten plastic from the nozzle of the molding machine into the cavity of the tool. Because edge gates are easy to machine, they can be widened or modified to help material flow. 6 Monate. Quotes for 25+ Manufacturing Processes. Mechanical performance of knit lines and welded butt joints – A key factor in designing of multiple gated injection molded and subsequent welded. They occur when melt flow fronts collide in a mold cavity. All injection molding ultimately comes down to the “Man, Mold, Machine, Material and Method. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. Depending on the resin, resin temperature, mold temperature, and filling speed, knit lines can vary from virtually invisible to something that looks like cracks in the plastic. Product designers encounter a wide range of challenges when. Weld lines are formed during cavity. Fewer knit lines. com support@makenica. Knit lines are a common defect in injection molding that can affect the appearance and performance of plastic parts. See full list on fathommfg. Highly ScalableVacuum on the mold does help and many times eliminates the weld line. The following are the conclusion drawn from the present research: 1. 12515 NE 95th Street , Vancouver, WA 98682 CALL TODAY: 1-800-839-0366Contact FU CHUN SHIN MACHINERY MANUFACTURE CO. Knit / Weld Lines. The point I am making here is, if you’re injecting 14. Remedies: Raise the temperature of the mold or molten plastic. When injection molding complex parts, often knit-lines are formed during the mold filling stage. 1. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. How weld lines form. They have their origins in material choice, part design, tooling, and processingIn the injection molding process, knit lines are a common occurrence when two or more plastic flow fronts collide and solidify, resulting in a visible seam or line on the molded part. A majority of these investigations concern amorphous polymers, whereas a number of engineering polymers are semicrystalline and also contain reinforcing fillers and fibers. 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. And the lead-time for overmolded and insert molded parts is 15 days, a bit longer than FacFox’ single-part injection molding turnaround, but still much faster than traditional insert molding. Weld and meld lines are generally caused by holes or inserts in the part, multiple gates, variable wall thickness or hesitation and. Typically, injection molded parts will be between 0. Weld lines often leave witness marks in the moulding surface. Mold Venting. 2020-01-1306. More about the knit lines in injection molding. These defects are not visible, like small. and Titomanlio, G. Injection molding machine and automation supplier Engel offers an array of technologies to simplify and speed up mold changes, including magnetic clamping platens and quick couplings; intelligent assistance systems; and the famox mold changing system for automating the set-up process. After samples have been approved, it’s time to kickoff. The structural stability of. In the injection molding process, knit lines are a common occurrence when two or more plastic flow fronts collide and solidify, resulting in a visible seam or line on the molded part. Gates, vents, sliding cams, pick-out inserts, and any other place where the two sides of. S. Don’t forget to eliminate entrapped air in the weld line injection molding; otherwise, it’ll create unfilled portions in your part design, causing more weakening. In the injection molding process, melting takes place via two factors that work together: shear and heat. Also known as a knit line, this is the point at which two flow formations meet and are unable to. doc), PDF File (. Weld lines, which are also referred to as knit lines, are among the most common of these blemishes. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Weld / Knit Lines; Assumptions. land and using maximum vent depths to get them as close to self-cleaning as possible. Meld and knit lines are actually both different types of weld lines. 3. Be wary of saving too much weight or you might end up with: cracking. Having a basic understanding of the injection molding process will aid in understanding how to design for injection molding as well as how to forecast production schedules. In addition, the force of the gas holds the appearance side of the part in contact with. Currently working with plastic, rubber, LSR, MIM molding companies to help them eliminate their complex molding challenges like air entrapment. The primary rule is to apply 1 degree of draft per. Additionally, it may produce sinks and voids caused by localized shrinkage during the part’s cooling process. There is high defect rate (surface defects/knit line). The part weight x number of cavities + runner weight should. Specifically, by having a single, continuous injection outlet 140, molding material can be uniformly distributed throughout mold cavity 120 quickly and consistently without resulting in undesirable molding seams or knit lines. A poor design can lead to many visual defects in the final part. This can enable the manufacturer to increase the molten plastic temperature at the front of each flow and avoid the occurrence of weld lines. Depending on the design of the mould and the material being injected, a knit line may: present no problem at all, be a cosmetic issue, or cause a potentially. Potential Knit Lines • Knit lines occur where to or mold melt fronts come together-Holes, slots, multiple gates, variations in wall thickness-Meld lines occur when the melt comes together in the same flow direction • Knit lines are areas of weakness and should be located in low stress areas . Insufficient injection pressure and speed can cause weld lines. . We complete the part to your precise specifications with CNC Milling operations. Prototype Tool In Soon As 10 Days; Production Tool In As Soon As 3 Weeks; 10k Parts in 10 Days; GET YOUR 30 SECOND QUOTE NOW. 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. 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. The melt is forced to split up during filling of the cavity. What causes knit lines? Knit lines are formed when the molten plastic flowing into the mold cavity runs into an obstruction, such as a core pin that forms the through hole on a flange of an enclosure. Sprue bushing too long. Part thickness control is through stacking of. 0035"Weld lines:Witness line where 2 or more fronts of molten plastic converge, also called knit lines or flow lines, the weld around the holes, the line between the injection gate. SPI surface finishes are the most common set of injection molding finishing standards around the world with over 12 different grades. Misra A. Plastic injection molding is the process of injecting molten plastic material into a metal tool which then cools and ejects a plastic part from the machine. molding run to be sure that the temperature does not exceed the recommended limits . These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. When venting stationary inserts or core pins in rib or part details with venting issues, I recommend no more than 0. Designers are able to specify seamless design features with compression molding. Knit Lines. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a 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. Trapped gas is one of the most common causes of part burns, and can also lead to short shots and voids, blemishes and discernible knit lines that weaken the part. Weld-line is a defect that arises in injection molding when two or more flow fronts collide. Thus, as the flow continues, the two flow fronts may gradually rejoin to make one uninterrupted flow front. Increase the melt and/or mold temperature. 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. It tells them that you visualized how injection molded parts cool and harden. Weld line in injection molding is line where two or more flow molten plastics knit together. Very high quality and an extreme fit may. Weld lines also can be visible after a part is painted and can cause wrinkles on in-mold-label injection-molded products. During injection, support pillars keep closed the two halves of the plastic injection mold. As these flow fronts come together. shows some obvious locations for vents, a brief molding trial should be conducted to observe where the gas voids occur. Common causes of flashing in injection moulding. Avoid adding threads directly on your injection molded part. This article will discuss the importance of injection molding nozzles and what makes a good nozzle for a molding or injection. Additional venting along the parting line perimeter will improve overall venting significantly. Circular Loom Machine; Raschel Knitting Machines; Shade Net Making Machinery; Inspection Machines; Non Woven Production Line. They again get resolidified along the surface. POROUS MOLD MATERIALS. Holes in the part will always cause knit lines. excessive or premature wear at the parting line. Knit Line occurs where different flow fronts of material meet while flowing through the mold. 2. 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. Whenever possible, vents should be located in the movable half of the mold wherever a gas void or knit line is seen on a part. These materials have beenDetermining the correct tonnage provides a foundation that must be rock-solid to avoid flash and damage. Runner and gates must be balanced. It is also one of the most important weapons in a molder’s arsenal for making process changes. In fact, strength at the knit line can be as little as 20 percent of the nominal strength of the part. The quality of the answer is directly proportional to the information we have to work with. 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. Meld and knit lines are actually both different types of weld lines. So what does the 140F mold temperature give us? The molding technician thought the 140F mold water was OK because the data sheet provided by the material supplier suggested mold temperatures from 75 to 180F. Knit Lines 11: 1. turbulent flow of Injection speed set too high. As the polymer resin is injected into a mold, it flows through all parts of the mold. Swirling can increase depending on the material you use, and the texture or polish of injection molding tools. Weld Lines. Meld and knit lines are actually both different types of weld lines. Learn how to troubleshoot weld lines in injection molding. For over four decades, our experienced team and leading edge technology have provided you with tooling solutions from start to finish. When setting a heat profile, consider residence time, screw RPM and filler type. Check/add vacuum; Check mold lube; Check/increase venting. Take these steps to avoid knit lines. Numerical results show that weld lines can be predicted accurately, and the formation and evolution processes of weld line can be shown more clearly by co-injection molding technique. Weld lines can significantly reduce ultimate tensile strength (UTS) and fracture strain of talc filled polypropylene (PP). Raising the mold temperature will keep the material molten longer, resulting in stronger weld lines and even elimination of weld lines. Plastics Technology article (June 2018): Technical capabilities of the process have advanced to erase former cycle-time penalties, and ongoing developments address creation of a materials database and new applications in hybrid composite injection overmolding. Use gradients. 3—Another issue with the four-gate design was that knit lines ended on or near mounting holes, causing a. Solution: People. But applying excessive force can create problems with the part, mold, and machine. They occur when two resin flows meet at different. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. PROBLEM: POOR ADHESION OF LSR MATERIAL TO. Knit Line – A molding defect resembling a flow-line found at the point where the rubber meets between the injections. The thermo-rheological findings were used to investigate the sources of weld line weakness. A weld line, also known as a knit line, is a visible line or mark that occurs in an injection-molded part where two or more melt fronts meet and fuse together during the molding process. Operating Conditions • Fast injection fill speeds, supporting short injection times (1–3 s), especially in thin sectionsGate and Knit Line Locations<br />. He said, “Vent cavities at weld lines or junction points where two or more material streams meet and fuse into a solid mass. Let’s. Also known as “stitch lines” or “weld lines”. 120 in. , LTD. injection molding. It happens when the molten plastic material flows around obstacles, such as inserts or cores, and rejoins on the other side. 2. Support pillar suppliers can help determine the. Some of the most popular brands include:Harshal Bhogesra has 9+ years of combined experience in molding, customer & supplier development. 5-3. 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. Venting at Weld Lines. Influence of injection-molding parameters on the morphology and mechanical properties of glass fiber-reinforced polypropylene composite. Material contamination, for example, can cause several molding issues. With over 50 years of experience, Universal Plastic Mold can help you avoid (or at least minimize) knit lines in your molded parts. Having uniform wall thicknesses between 0. Reducing the dimensions of the runner system. Given the cosmetic requirements, there is a good chance the mold would require. Venting. The data suggest that either local sample thickening or grooves form at knit line when complete section solidification takes place first at weld zone or. 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. Our plastic injection molding glossary provides key terms. RapidDirect – Your Best. Our glossary of terms provides definitions for a wide range of injection molding terms. This line does not normally impact the overall shape or dimensions of the item. 08 KICKOFF PRODUCTION. ”. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no weld line. This was usually with a PC/ABS material at knit lines and high fill pressures from thin walls in the part. ICOMold is a plastic injection molding company that manufactures plastic injection molded parts. ABOUT THE AUTHOR. It’s also relatively inexpensive. In the world of injection molding, each weld. Weld lines create visible marks, but this type of injection molding defect can also reduce a part’s strength and durability. 4. The wall thicknesses of an injection molded part generally range from 2mm – 4mm (0. The last cause of flow lines may be the operators running your daily operations. 203 in. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. Contact Universal Plastic Mold Today. 060 and 0. The difference between a knit and meld line is significant, dramatically impacting the part’s structural integrity. 250 in. Runner Type. Compression molding produces solid parts that are free of flow and knit lines. (1987). Knit Lines. First, an injection mold with triangular inserts was built to study the influence of meeting angles on material properties at the weld line. injection molding. 1 in. To briefly describe, weld lines are also called knit lines. With over 50 years of experience, Universal Plastic Mold can help you avoid (or at least minimize) knit lines in your molded parts. Any of the above can result in “knit lines” on final products, but mold flow analysis prior to mold machining can keep these issues from cropping up at all in iteration and production. 040 and 0. Make sure the venting is not too large. 040-in. The goal is to create a uniform thickness and at the smallest (thinnest) level required. Solution: People. Conversely, texturing of part surfaces is often effective in hiding flaws and imparting a “grippy” or leather-like. Considerations: ABS-molded parts will show knit lines and can have sink and voids in thick areas. Use a thread with a pitch greater than 0. If the load is applied in the transverse direction relative to the knit line, matrix cracking is easily initiated, and the part can fail. Weld lines, knit lines, and meld lines are terminologies to describe the imperfections of finished parts in plastic injection molding processing. 8 mm (32 threads per inch) Use a trapezoidal or buttress thread. By contrast, a slow injection speed will give you a matte finish and a cold mold, such as 50F, will give you a more flexible part. Figures courtesy of CAE Services. There are times when porous materials like Porcerax are used in problem or backfill areas. Polym Compos 1982; 3: 88–96. Melt temperature does. In the case of mold. 17. sinks, knit lines, and shrinkage,” Spalding says. Plastic injection molding has long been an affordable and efficient process for producing custom prototypes and end-use production parts. The cooler flow fronts of the resin aren’t forced into the mold surface texture as well as the hotter resin behind the flow front. Recommended for the bonding of nylon (polyamide) and polypropylene materials, this thermoplastic elastomer delivers wide compatibility and thermal stability, allowing for use in demanding conditions. (Overpacking. The cracking was always located in the weld/knit line and therefore caused by weakness in the bonding of the plastic at that line. Injection Molding Problems and Solutions (17/17) – Weld or Knit Lines Sep 27, 2022 Injection Molding Problems and Solutions (16/17) – Warpage Sep 15, 2022. com TYPICAL PROPERTIES MECHANICAL THERMAL OPTICAL. A wide variety of tool steels are available for injection mold construction. They occur when melt flow fronts collide in a mold cavity. 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. Understanding Knit Lines in Injection Molding: Causes and Solutions. land and using maximum vent depths to get them as close to self-cleaning as possible. 4. As a result, molten plastic takes the injection mold core and cavity shape. 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. Design bosses with an outer diameter equal 2x the nominal diameter of the screw or insert. Material. Revisiting the '5 M's' of Molding. These defects are not visible, like small. Table 2. Dabei erreichen unsere Produkte zufriedene Käufer in mehr als 30 Ländern. The plastic melt that passes through the gate at high speed directly enters the cavity, then contacts the surface of the cavity to solidify, and then is pushed by the subsequent plastic melt, leaving traces of meandering. The Goldilocks principle applied to wall thickness. J (left) shows embossed feature and S (right) shows debossed feature in plastics through injection molding. While injection molding itself is a straightforward process involving melting thermoplastic resin and injecting it into a mold cavity, knit lines can pose. The packing pins are sequentially. Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Direct experience designing molds and parts for injection molding and producing the molds and parts is valuable, relevant experience for design students. Influence of injection-molding parameters on the morphology and mechanical properties of glass fiber-reinforced polypropylene composite. Knit line / Meld. 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. To prevent knit lines, injection molders can increase the temperature of the molten resin to prevent solidification from starting too soon, and increasing injection speeds and pressure are also potential solutions. Brent Strong, p. ) are easy to produce. 060 and 0. 1050 Walnut Ridge Drive. Encapsulating the metal insert with plastic creates a single molded plastic piece that’s generally stronger than one created using secondary assembly. Be wary of saving too much weight or you might end up with: cracking. The knit line is generally opposite the gate in thermoset. Cold weld line or known as “knit line” isWeld Line defect analysis, the most common of many defects in injection moulding products. Notched weld lines then remain near the cavity walls. Injection molding is a simple and efficient process that produces high-quality plastic parts. Gating. SEA-LECT Plastics has 16 MILACRON injection molding machines that range from 33-ton with a 2. It is important when selecting an injection molder that the right process conditions are used to reduce or eliminate the effects of. A screw-type plunger forces the material into a heated chambe r,. weld lines may form during the injection molding process and work closely with the plastic injection molder and tool builder to choose the best possible gate location. Place vents at last place to fill and at converging flow fronts. These defects are not visible, like small. These are imperfections in the part. Contact Us. Injection molding is the most cost-competitive technology for manufacturing high volumes of identical plastic parts. occupied frequently with troubleshooting injection molding. Consider adding mold release (can be added to the polymer itself by the polymer vendor) or at machine side Knit lines Weak knit lines Increase melt temperature Mold temperature too cold Increase injection speed Avoid nucleated products if possible Inadequate ventingWhat you should know is that there are various failure modes for injection molding. plastic recycling machine, blown film extruder, filament extrusion line, injection molding machine, blow molding machine, injection blow molding machine, bag making machine, flexo. One of these is knit lines, also called weld lines.