Three terms that often get mixed up in injection molding are weld, meld and knit lines. He is currently a tooling manager for a large, multi-plant molding and manufacturing company. Weld lines defects can also form when the flow fronts from two gates merge or when thick and thin sections in a part cause a flow to split and merge. land and using maximum vent depths to get them as close to self-cleaning as possible. 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. Knit Lines. 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). Using abrasives in a pressurized air blast to create a surface texture on the part. What Are Knit Lines in Injection Molding, and How Do You Prevent Them? - RJG, Inc. Observation on a “trial and error” basis may be required. Another name given to weld lines is meld line. Troubleshooting Injection Molding Weld Lines. Swirling can increase depending on the material you use, and the texture or polish of injection molding tools. The structural stability of. 6. Injection molding is the process of injecting liquid thermoplastic into a mold. An injection mold that produces pieces while the final tool is being built. 5 to 3. On the other end of the scale, a desktop injection molding machine with 5 tons of force can cost between $30,000-50,000. Gas-assisted Injection Molding: Influence of Processing Conditions and Material Properties. Remove holes if possible. 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. Three terms that often get mixed up are weld, meld, and knit lines. This defect is caused when the polymer resin is injected into a mold and flows around a solid piece and forms when the resin collides back together without completely fusing back together. Some. Vacuum. S. We then. 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 Injection Molding Part Design Guidelines, Plastic part Design Guidance, Parting Line Draft Undercuts Wall Thickness & Uniformity Bosses Gussets and Ribs Radii and Corners Material Shrinkage Gating Ventings Knit/Weld Lines. When injection molding complex parts, often knit-lines are formed during the mold filling stage. Strength at the knit line can be as little as 20% of the. 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. Two major sources of weld lines are multiple gating and flow around pins. To prevent swirling, perform tests whenever possible and use pre-compounded resin to ensure identical color match across parts. Based on the resin temperature, filling speed, and resin, there is a variation in the knit lines. But add 30% glass and weld-line strength retention drops to only 34% as high as the compound with no weld line. 8 mm (32 threads per inch) Use a trapezoidal or buttress thread. The GLS™ Injection Molding Guide provides in-depth information on part design, mold design and processing for styrenic block copolymer (SBC) thermoplastic elastomers (TPEs). These flaws can affect the aesthetic and structural integrity of the. As the polymer resin is injected into a mold, it flows through all parts of the mold. POROUS MOLD MATERIALS. Get a free des. Notched weld lines then remain near the cavity walls. I am working on a thin PC/ASA injection moulded component which has a tendency to snap at the Knit-point (the final point of travel at which the…Here are a few of the most common defects that may occur in plastic injection molding — and how product teams can avoid them. Weld lines, which are also referred to as knit lines, are among the most common of these blemishes. The quality of the answer is directly proportional to the information we have to work with. Compression molding produces solid parts that are free of flow and knit lines. 1 in. ) Mold Analysis Tools. If you have any issues getting. Comprehensive. So. Knit lines. 030- to 0. 26 = 0. Because viscosity is a variable, keeping fill time constant minimizes the influence of these variations and provides a more stable process, and therefore. Reduce the temperature of the mold and plastic being injected. 3 /sec. LOCATION: Along any parting line. 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. Knit Lines. To prevent swirling, perform tests whenever possible and use pre-compounded resin to ensure identical color match across parts. Knit lines are a common defect in injection molding that can affect the appearance and performance of plastic parts. The mold maker may think that some minor defects are acceptable, or they may not even consider them from the beginning, which can cause problems when the injection mold is being manufactured. thick. The part weight x number of cavities + runner weight should. 2. 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. “A knit line in a colored part will result in glaring visual-effect problems, while a knit through a glass-filled part would have a negative effect on both the aesthetics and the performance,” agrees Kurt Weiss, manager of part performance and new material introductions at GE Plastics. While injection molding itself is a straightforward process involving melting thermoplastic resin and injecting it into a mold cavity, knit lines can pose. Parts with abrupt geometry changes or holes are more prone to knit lines. An obstruction such as a core pin or holes will split the material flow and cause a weld line issue to form on the other side. Polypropylene Consumer and Injection Molding Containers, Crates, Garden Furniture, Housewares, Luggage, TSL, TWIM lyondellbasell. 6. The melt is forced to split up during filling of the cavity. In the case of mold. Gas trapping/ poor venting. An undercut is any indentation or protrusion that prohibits an ejection of a part from a one-piece mold. If you turn on the spigot to a garden hose, you will hear a hissing sound at the nozzle end for the first few seconds. Mechanical performance of knit lines and welded butt joints – A key factor in designing of multiple gated injection molded and subsequent welded. Flow Lines. ICOMold is a plastic injection molding company that manufactures plastic injection molded parts. It is one of the most common blemishes for manufactured products. 040 and 0. Transfer molding also utilizes a press and a mold. Conclusion The formation of weld lines in micro injection molding of plastic depends on different parameters such as melt temperature, injection pressure and fabrication method. Inadequate injection pressure can result in knit lines and a surface that. A poor knit line can cause only cosmetic blemishes or it can significantly weaken the structural integrity of a part. The above guidelines for initial heater band settings are for most injection molded parts. The mold settings can run flawlessly until employees consistently open the machine for inspections, interrupt cycle times, or cause temperature. 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. Since our material is injected through a. Product designers encounter a wide range of challenges when. 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. While not always visible, weld lines (aka knit lines) are where two resin flows meet. Edge Gates. (1. Holes in plastic parts are normally cut with a router (or drilled if round. Kurt W. 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. Recent developments were oriented on the analysis of the mechanical performance at local (knit lines and welds) and bulk (molded part) areas, with the influence of molding and welding conditions. Knit line / Meld line / Transfer line Discoloured line where two flow fronts meet Mould or material temperatures set too low (the material is cold when they meet, so they don't bond). 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. The packing pins are similar in construction to mold ejector pins and may also be mold ejector pins depending on mold configuration. More about the knit lines in injection molding. Injection molded plastic begins its journey through the part tooling via an entry section called a. 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. They are formed when two or more flow frontINJECTION MOLDING GUIDE V2. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding. Contact Universal Plastic Mold Today. (1. Knit lines. 060 and 0. Let’s. 040-in. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. Increase the injection speed. อุณหภูมิของพลาสติกเหลวสูงเกินไปจนก๊าซหรือความชื้นแยกตัวออกมาได้. No matter the size of a production run, the presence of blemishes on the finished product leads to unhappy clients. Understanding types of injection molding process can help to avoid some design challenges early in the process. 08 KICKOFF PRODUCTION. The Mold Tools toolbar provides tools for creating mold tooling (cores, cavities, etc. 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. Considerations: ABS-molded parts will show knit lines and can have sink and voids in thick areas. Thermoplastic Elastomer Molding Guidelines. It is caused by the incomplete joining of the uncured. Plastic injection force exceeding the clamping pressure of the press. Compression molding produces solid parts that are free of flow and knit lines. Solution: People. 18/06/2021. Randy Kerkstra has been in the plastics industry for over 26 years, occupied frequently with troubleshooting injection molding. The cracking was always located in the weld/knit line and therefore caused by weakness in the bonding of the plastic at that line. Knit lines are typically much weaker. occupied frequently with troubleshooting injection molding. 45 in. In spite of its cosmetic attributes, a bad knit line can significantly. 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. Runner Type. Mold bases, ejector plates, and some cavities (if nickel or chrome plated to prevent rust). The depth of the texture or letters is somewhat limited, and extra draftInjection molding tool design and build for complex parts, with precision tooling and molding capabilities for industries demanding high-quality, critical components. Below is a list of items that should be checked both during normal molding operations and if defects are detected. Participating in DFM and mold flow analysis is a good way to achieve this. (See Fig. Weld lines, created in the areas of collision of two flow fronts of plastic in the injection mold cavity, are the reason of lower mechanical properties and a worse surface condition of molded parts. Inadequate venting may cause short-shots, poor surface appearance, or weak weld-lines. The mold settings can run flawlessly until employees consistently open the machine for inspections, interrupt cycle times, or cause. 5-3. The adverse effect of knit-line formation on the mechanical properties of thermoplastics has been well documented for unfilled materials. 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. Revisiting the '5 M's' of Molding. Meld and knit lines are actually both different types of weld lines. It explored the use of. 18/06/2021. In fact, knit line strength will decrease with higher filler content and with longer fibers. When injection molding complex parts, often knit-lines are formed during the mold filling stage. sinks, knit lines, and shrinkage,” Spalding says. 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 majority of these investigations concern amorphous polymers, whereas a number of engineering polymers are semicrystalline and also contain reinforcing fillers and fibers. , 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. Knit Lines: These occur when different flow fronts come together as plastic flows through the part cavities. ISO 9001:2015. The effect of holding variables and of injection and mould temperature was explored. a weld or knit line may develop on the opposite side of the obstruction as the two fronts of material join. There are times when porous materials like Porcerax are used in problem or backfill areas. Sequential valve gate technology. ”. Holes in the part will always cause knit lines. 0mm) throughout will ensure that the parts cool evenly and will prevent warping. One of the common defects that can occur in injection molded parts is weld line. 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. This was usually with a PC/ABS material at knit lines and high fill pressures from thin walls in the part. Soft metals, such as aluminum and beryllium copper, can be used for prototype<br />. Sprue bushing too long. With ABS injection molding, you get the collective benefits and properties of three monomers. They are the result of fundamental physical effects taking place inside of the mold. "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. Contact Universal Plastic Mold Today. The Problems & Solutions course is designed to train injection molding personnel in. 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. 4. As a result, prototyping is strongly recommended for parts with. Whereas conventional injection molding uses. 160"). Possible causes: Low temperature or fluidity of melted plastic during injection molding. A knit line may only be a cosmetic issue and affect. This production method is particularly popular when manufacturing in large quantities. , Rallis, A. ) or as thick as 25 mm (1 in. Resin cools as it is injected into a mold. Design. Influence of injection-molding parameters on the morphology and mechanical properties of glass fiber-reinforced polypropylene composite. Meld and knit lines are actually both different types of weld lines. Also, since this part will likely be painted or chrome plated, knit lines are a concern. Molding parts with multiple gates will almost certainly produce a weld line at right-angles to the line joining the two gates which could cause the weld lines to be exceptionally weak (see Figure 1. 7. 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. Mold venting is critical to the quality and consistency of the finished part. 120 in. Without adequate support pillars, flashing of the parting line faces and bowing of the plates may occur. While injection molding itself is a straightforward process involving melting thermoplastic resin and injecting it into a mold cavity, knit lines can pose. A weld or meld line is a weakness or visible. Kaminski, in Specialized Molding Techniques,. Incorrectly placed single gates may cause knit lines. Three terms that often get mixed up are weld, meld, and knit lines. Also known as a knit line, this is the point at which two flow formations meet and are unable to. Download : Download full-size image; 3. The area generally has lower strength than the other areas of the part. Knit Lines. Some of the most popular brands include:Harshal Bhogesra has 9+ years of combined experience in molding, customer & supplier development. Using three test materials, polystyrene (PS), polycarbonate (PC) and polyoxymethylene (POM), the relationship between a design and a processing parameter. a knit line will form 180°on the opposite side from the gate location. 5. 12515 NE 95th Street , Vancouver, WA 98682 CALL TODAY: 1-800-839-0366Contact FU CHUN SHIN MACHINERY MANUFACTURE CO. Snake Lines: The appearance of snake lines is caused by the formation of a jet effect as the melt travels through a gate and into the mold cavity. Dabei erreichen unsere Produkte zufriedene Käufer in mehr als 30 Ländern. Adding vents, using overflows, or using porous metal. Cold weld line or known as “knit line” isWeld Line defect analysis, the most common of many defects in injection moulding products. This is why the leading edge of the resin flow within a mold is always the coolest area of the resin, and, therefore, the closest to solidifying. Improve venting and/or relocate to burned area. One of these is knit lines, also called weld lines. Degassing – Degassing is the simple operation of opening and closing an injection mold to allow any trapped air (or gas) to escape. The plastics used by injection molding processes are relatively cheap and can be used to achieve a wide variety of properties, so injection molding is popular for creating many packaging and consumer products, like LEGO! A weld line (weld point, flow line or a knit line) forms when separate melt fronts travelling in opposite directions meet. Most failures of injection molded plastic parts are caused by either improper design of the part or improper design of the mold. Considerations: ABS-molded parts will show. Meld and knit lines are actually both different types of weld lines. As a result, prototyping is strongly recommended for parts with. By altering the part design, it may be possible to just have one flow front, and avoid multiple flow fronts having to come together. The recommended minimum production volume for injection molding is 500 units. Weld Lines-3 Ways for Detecting and Correcting. 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. Short shots and knit lines are two phenomena that are caused by using highly viscousHowever, they can also create weld lines or knit lines in the part where the flow fronts meet. Bead Blasting. Sink Marks Cause 2: Low Pack and Hold time. Adding draft or slope to vertical walls of a part makes it easier to eject or remove the part from the mold. Sink Marks Cause 3: Improper Pack or Hold Pressure. To avoid walls that are too fat or too thin, designing a wall thickness between 0. The injection molding design process, much like all industrial design processes, deals primarily with the creation, look, and feel of a product. The knit line itself (the vertical line in the middle) is visible in this lighting, but the biggest issue is with the texture. There are times when porous materials like Porcerax are used in problem or backfill areas. Criens}, journal={Materials Chemistry and Physics}, year={1986}, volume={14}, pages={69-83} }A structural automotive sub frame component ( 10 ) that is formed from a sheet molding compound having carbon fibers. Meld and knit lines are actually both different types of weld lines. "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. In the process of injection molding, when the wall thickness of the product is large, the cooling speed of the outer surface is faster than that of the central part. Prevent Flow and Knit Lines Through Mold Adjustments. Tooling & Injection Molding Services High-Quality Complex Parts. The knit lines are the result of poor molding conditions (likely molding at too low of a temperature). 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. Three terms that often get mixed up are weld, meld, and knit lines. However, with any practice, when the proper care and planning aren’t taken, problems can occur, and with injection molding, knit lines are one of the most common problems. Near-Net-Shape production uses injection molding to account for 70-90% of the final geometry of a part. Highly ScalableVacuum on the mold does help and many times eliminates the weld line. Having uniform wall thicknesses between 0. 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. Meld and knit lines are actually both different types of weld lines. Injection Molding: How to Set Second. And like all manufacturing industries, plastic injection molding lines are more profitable the shorter the cycle time — so long as they produce quality parts. 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. 3,000 ton machines can cost $700,000. N174W21430 Alcan Dr Jackson, WI 53037 262-677-9700; 16685. com support@makenica. As a result, the portion has a faint, perhaps undetectable line. 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. Contact us. This article will discuss the importance of injection molding nozzles and what makes a good nozzle for a molding or injection. It is also one of the most important weapons in a molder’s arsenal for making process changes. [8] Bevis, MJ, Reis RL, Cunha AM. 1. Based on the resin. Getting started; Knit Line Injection Molding; Knit Line Injection Molding - China Manufacturers, Factory, Suppliers. Mold venting should be checked and increased if necessary, injection molding service. In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. It can also aid in material selection since fill. These are imperfections in the part where separated flows of cooling material meet and. J (left) shows embossed feature and S (right) shows debossed feature in plastics through injection molding. molding run to be sure that the temperature does not exceed the recommended limits . [1] Here are a few ways to prevent knit lines in your plastic parts: Increase material temperature: Higher temperatures on both materials prevent one section from cooling too quickly. Minimizing or eliminating flow and knit lines is an additional benefit of using this material. 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. These lines occur usually around holes or obstructions and cause locally weak areas in the molded part. The wall thicknesses of an injection molded part generally range from 2mm – 4mm (0. ”. For example, warping, sink marks, drag marks, and knit lines can all impact the visual appeal of the manufactured part. Injection moulding (U. Venting. Injection molding is the cost-effective method and is best suited for higher volumes. (knit) line and produces a latent, or obvious, part defect. Advantages Excellent moldability in thin sections Outstanding chemical resistance Heat resistance Limitations Cost Knit line strength OverviewLiquid crystal polymer (LCP) exhibits a highly ordered structure in both the melt and solid states. 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. Knit/Weld Lines. Mold Flow Analysis computer. It is. A wide variety of tool steels are available for injection mold construction. The packing pins are sequentially. 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. H-13 Good general purpose tool steel. 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. Solution: People. The plastics used by injection molding processes are relatively cheap and can be used to achieve a wide variety of properties, so injection molding is popular for creating many packaging and consumer products, like LEGO!. A poor design can lead to many visual defects in the final part. It’s also relatively inexpensive. Weld line. Piccarolo, S. Injection molding is an efficient, often cost-effective way to manufacture custom plastics that are strong, durable, and long-lasting. suppressed cooling and possibly warp. 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. The company provides an array of digital manufacturing expertise. When setting a heat profile, consider residence time, screw RPM and filler type. 3. As melt temperature, viscosity and abrasiveness rise, tool life will decline. By using this method, theHowever, injection molding is not without its challenges. The most common and one of the most challenging injection molding defects are weld and knit lines. Effect of Injection Moulding Conditions on Knit-line Formation, Plastics Rubber Processing and. These defects are not visible, like small. In injection molding, it is often important to maintain consistent color throughout the part. Weld lines may appear like seams or scratches, but that is not what they are. 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. If I can answer any questions you may have on optimizing the plastic part design, CNC plastic prototype, mold manufacturing, and injection molding or if I can be of any other help, please feel. Reducing the dimensions of the runner system. 27-ounce shot size to 600-ton with a 105-ounce shot size. Weld lines have a significant effect on manufactured products. Weld Line Phenomenon: Surface defect in which the weld, or the part where the flows of melted plastic meet inside the mold, shows up on the surface as a groove or pattern. Such molds or tools aren’t intended to be used in operation. Bad habits can cause many different problems with injection molding machines, and flow lines are included in that. lines are formed when there is an obstacle in the cavity of the injection mold. 2. The main types of injection molding defects are: 1. Depends how hard you want to push it. 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 . Poorly constructed or worn out mold. 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. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. Submarine Gates. In addition, the force of the gas holds the appearance side of the part in contact with. 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. Additional venting along the parting line perimeter will improve overall venting significantly. Be wary of saving too much weight or you might end up with: cracking. Polym. Use gradients. This line does not normally impact the overall shape or dimensions of the item. The injection molding process offers a vast array of plastic resins to work with. All the while, the material could be the correct material," Hill says. Place vents at last place to fill and at converging flow fronts. Thick sections take longer to cool than thin ones. 5 mm (0. Temperature is another factor that can cause weld or knit lines in injection molding. In this way, the mold supports distribute the force and minimize the stresses on the mold plates. The total amount of scrap being produced during injection molding will usually be higher than that for compression molding because of the additional material loss created. directly! FCS Group, based in Taiwan, was established 40 years ago and is well known in Asia as a quality manufacturer of machinery, offering several lines of injection molding machines and other specialty and customized equipment. Knit lines don’t always compromise the structural integrity of plastic parts. Knit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. 156 x 1. DFM Helps Prevent Sink Marks In Plastic Injection Molding. Mold flow analysis is a software simulation that can show how resin will fill the mold during the injection molding process. Alter the mold design. When injection molding a part, a knit line may present no problem, or can cause a serious structural problem. Let’s review what causes meld and knit line imperfections, how they’re different, and how they affect part durability. Weld lines can significantly reduce ultimate tensile strength (UTS) and fracture strain of talc filled polypropylene (PP). In a plastic injection-molded component, a knit line occurs when 2 different plastic flows emerge in a mold. Design bosses with an outer diameter equal 2x the nominal diameter of the screw or insert. com. 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.