When injection molding a part, a knit line may present no problem, or can cause a serious structural problem. We will now look at the problem you are likely to encounter and how to fix them. 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. Plastic Baffles provide better temperature stabilization. Weld lines are among the most critical structural defects in parts made by the injection molding of fiber-reinforced thermoplastics, explained Sirmax in a press release. Take these steps to avoid knit lines. Flow lines are lines or streaks visible on the surface of a part. These streaks or patterns can affect a part's. The. 50 mm, material of plastic part is HI-PS, shrinkage rate is 1. • Chapter 4 discusses Moldflow design principles and how they relate to making qualityFlow velocity is very high in the area of the gate as it enters the mold, but slows down as the flow front extends away from the gate and into the cavity on a widening circle. DEFINITION: Excess plastic squeezing out perpendicular to the part at parting line. If it does not, the lack of fluidity of the material. Depends on wall thickness, viscosity, gating system, etc. When trying to establish process control in plastic injection, watering the tool is a key variable that is often overlooked. MFR values for polypropylenes are determined at the same load but at a higher temperature 230°C (446°F). Injection speed is so slow that the molten plastics becomes solid before it flows to the end of the mold. x 15 in. Flow Lines. Learn more. After running a Flow analysis, you can view results of interest both during and at the end of the filling phase. However, like any manufacturing process, it is not without its challenges. Increase injection speeds and pressure to ensure the cavities are filled properly. If you’re a mold designer with one of those vent-depth “rule-of-thumb” charts for different types of materials tacked to your wall, keep in mind that it is only a guideline. While the second model showed negligible particle flow length after weld-line formation, the third model showed movement of. Co-injection molding technique is a useful way to study weld lines, which can offer more detailed information of the. 002 mm to 0. Solution. Just multiply the area of the barrel × the injection velocity. By understanding material fill, injection mold designers can better position gates, anticipate where. Here are some common fixes for injection molding splay: Moisture-related: Ensuring that all material is thoroughly dry before beginning the injection mold process is crucial. The mold cavity is an exact hollow negative of the part to be produced. They often appear in a wavy pattern and might be a slightly different color than the rest of the piece. These data were obtained from many andTroubleshooting Injection Molding Flash. In injection molded parts, there are 2 types of weld lines: The first type of weld mark is. This can prevent the opportunity for trapping air. They were amazed when all the molding technicians had to do was lower the barrel melt temperatures, warm up the mold, and turn down the injection pressures, just like we suggested. Capabilities. 010 0. particles, during injection molding, will produce visible flow and weld lines. May happen at first shots while. A knit line may be unnoticeable or may look like a crack. The chart below shows recommended wall. Weld lines can impact the strength and appearance of the final part, and are often considered a defect. This will help them achieve a smooth and consistent finish on their products. 005, and weight of plastic part is 179. 3C) is to put a vent along the entire edge, but just shy of the corners. Injection molding is one of the best plastic production methods. Flow lines (sometimes called flow marks) are lines commonly caused by a variation in the cooling speed of the molten plastic as it flows through the mold. The problem could be the result of machine settings made before the gate was installed. Next we need to determine a cooling or energy flow rate, represented by the letter Q. For instance, the plastic used for gears must be completely smooth. In addition to accurate temperature control, optimizing flow through a mold is critical and, quite often, results in decreased cycle times and increased product quality and repeatability,. High pressure is associated with the high-speed flow. Low shrinkage: 0. About Press Copyright Contact us Creators Advertise Developers Terms Privacy Policy & Safety How YouTube works Test new features Press Copyright Contact us Creators. Burn Marks. Increase the injection speed, pressure, or temperature of the material. Several mold design issues can lead to the formation of a weld line in injection molding. 025 inches per inch, depending on the particular resin, molding conditions, part design, part wall thickness, and direction of flow. Reduce the temperature of the mold and plastic being injected. Electronic flowmeters featuring FCI (Flow Characteristic Indicator). Increase the amount of cooling in the mold. When combined with low injection pressure, this problem leads to decreasing melt speeds and can cause flow lines. One must increase injection speed, pressure, and material temperature to ensure the material fills the mold. If the. Commercial injection molding simulation packages, such as Moldflow and C-MOLD, have been incorporating GAIM options to provide computerized design and optimization tools for GAIM processes and. Reasons and solutions. Optical Insert. Shorten the. The Injection Moulding Process is a manufacturing process used for producing parts or components by injecting molten material into the mold cavity. The convective fluxes are evaluated using Eq. Below are ways through which you can remove and prevent flow lines; a. S. Voids, Sink Marks, Shrinkage Figure 8: Use of ribs instead of a solid section. to 0. Easy-flow polyethylene and polypropylene gate depths are based on just 50 percent of the part wall thickness. Increase. If not taken care of, removal of material is tough. The injected plastic solidifies in the mold upon cooling and can be released subsequently. Flow. 0030 in. For optimal cooling, these waterlines are located as close as possible to the surface of the molded part. Avoid knit lines when designing a molded part to improve cosmetic appearance and functionality. Complexities in the design and intricate pathways in the mold can also create flash in injection molded parts. Increase the mold wall thickness and switch to a grade where the melt flows easily. To avoid this, manufacturers must ensure that they use the right injection speed for their process. 2% to 0. Knit lines are hard to eliminate for injection molded plastic parts but designers can minimize cosmetic defects. Some of these factors could be the flow rate, the pressure, or the temperature settings of plastic injection molding. 40 * 52. Spatter lines formed on the surface of the plastic along the direction of melt flow are called silver marks. We will assume here that the mass is injected perpendicular to the boundary. Flow of hot fluid must be smooth. Tip #5: Always Design Resin Flow from Thick to Thin Sections. This flow tab has to be cut off after molding, which is another operation and expense but does provide a valuable vent for trapped air as the flow fronts meet. Chart 1: Diameter versus turbulent flow. Laminar flow and shear rates are the two most common categories for injection molding plastic flow. Lower the melt and mold temperature to prevent overheating. 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. 080" – 0. valve in the gas line just prior to the location of attachment of the gas line to the resin injection. The molten plastic may start to cool before the mold cavity is filled. 1. Injection Molding (IM) Solutions 1019 Balfour St. They can be off-color or discolored material compared to the intended color of the part. To. FLOW RATE. This allows the melt to keep enough velocity to ensure proper filing. Here is a look at the differences between them, the causes of meld and knit line imperfections, and their impact on part durability. A thermoplastic resin is heated to its melting point and injected into the cavity of an injection mold to produce a specific part geometry. Impurity. The use of high-pressure and low-speed injection can maintain the stability of the melt flow and prevent the appearance of wave patterns. Sometimes designing injection molded parts requires thicker sections for structure and strength. The wall thicknesses of an injection molded part generally range from 2mm – 4mm (0. 56 BTU. Flow lines result from uneven cooling of the plastic within the mold. III. That’s an easy calculation to perform. Flow Lines. Consequently, it causes viscous dissipation that leads to the generation of heat. Flow LinesKnit 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). Knit lines are formed when two or more plastic flow fronts collide and solidify or “knit” together during the molding process. In this case the two flow fronts will meet and. The edge gate is the most popular and straightforward injection mold gate design. Known as thermolators,. Obviously, as the resin front moves through the mold, the fill material will always be behind the front. The injection molding process involves melting (above glass transition temperature) and injecting thermoplastic polymers into a mold cavity that has preexisting features that need to be replicated. Figure 1 presents the shrinkage of polypropylene versus wall thickness in injection molded parts. In the world of plastics, Design for Manufacturing (DFM) is the combination of art, science and technologies necessary for designing a plastic part or product prior to tooling and. Injection molding is a widely used manufacturing process for producing large quantities of plastic parts. Utilize hot. Flow lines can be defined as linear grooving, or circular ripples, on the surface of molded parts that indicate the direction of material flow within the mould cavity. Optimize the runner system and locate gates near the thin walls. Similar to flow lines, discoloration occurs when the color of the resulting product is different from the original intention. b. The molding process is the leading cause of defects in injection molding parts. Insufficient mold cooling. 5 to 2. This injection molding defect appears as black or rust-colored discoloration on the molded part's surface or edge. 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. 5. Depending on the extent, these can become defects in the case of molded products in which their external appearance is an important aspect of quality, such as in the case of home electrical appliances, containers for. It is permissible to adapt. Cooling lines impact. They occur as a result of different flow rates of molten plastic in the mold cavity. 030 0. This is where the melt fronts divided by an insert, such as a pin or a block,. We offer this Mold Cooling Calculator tool as a free service to the injection molding industry. , 1 IN, 1 OUT, 2 IN, 2 OUT). Laminar flow in a plastic mold, described by Reynolds numbers below 2,000, indicates conditions whereby heat is not efficiently transferred. It can be difficult to determine what is truly splay, as its appearance is very similar to other defects. In this lesson we will focus on the meld and weld lines. Also known simply as blush, or gate shear or halos, gate blush is a dull or discolored portion usually found just inside the gate location of a part. Mould Cause LOW MOLD TEMPERATURE. (3-1) Increasing the Resin Temperature at the Weld Line Section. Once you have a cool shell formed the rest of the mold entering absorbs heat from the layer next to the wall. In some cases, voids can also cause the part to fail during use. 8. (Overpacking. The injection speed should remain consistent as the plastic enters the mold, otherwise, it will slow down, cool, and cause flow marks. Also called “Weld Line. Water set-up and design are every bit as important as establishing and recording a. The differences between knit and meld lines are significant, and they can dramatically impact the part’s structural integrity. It involves using specialized software to simulate the design of the component. 015 0. Well, what this simply implies is that injection polycarbonate molding makes it possible for you to create a wide range of part sizes. They are usually hardened metal examples include; aluminum,. Flow marks are a phenomenon in which a pattern of the flow tracks of the molten plastic remains on the surface of the molded product. Weld lines are formed when there is an inability of two or more flow fronts to ‘knit’ or ‘weld,’ together during the molding process. Traditional cooling channel is straight drilled lines manufactured by CNC shown in Fig. The Weld line result itself has a scale associated with the placement of the weld line that is directly relative to how severe the weld line will be based on the angle in which the two flow fronts meet. However, the weld line may not continue throughout the flow. 1) Snake flow lines. When you notice off-color streaks or other patterns on your product, these are the result of “flow lines. SBC TPEs will flow more easily into thin areas of the mold at high shear rates. The resulting defects don’t stop at flash only. Increasing pack or hold pressure helps to eliminate low-pressure conditions at the weld line. A gradual change in wall thickness is recommended to avoid any sudden change in the material flow direction. Injection of gas through the. Thin wall injection molding has lots to offer, but you’ll want to follow these injection molding design tips to achieve the best results. The process involves the injection of heated, liquefied plastic into a temperature-controlled mold under high pressure. V. Guideline for Design, Material Selection and General Application of Encapsulation of Electronic Circuit Assembly by Low Pressure Molding with ThermoplasticsThe location of the crack can tell us a lot about its specific cause. One way to reduce the changes in speed of the flow front is to tailor the injection-speed profile. 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. Injection molding machine . The air cooling system transfers heat from the flowing water in the injection molding machine assembly line to the air around the assembly line in the cooler. Laminar. A detailed guide of injection molding, detailing some of the terminology and terms and definitions of the same. Clean water. Plastic Defect # 2: Flow Lines. ³/sec. low clamping pressure. 6 in. To open the Flow Results PropertyManager, do one of the following: In the PlasticsManager tree, expand Results, and double-click Flow Results. No matter which manufacturing process you use, from bi-oriented film extrusion to injection molding, we can support you with additives that will improve your efficiency. Injection molded plastic begins its journey through the part tooling via an entry section called a “gate. A single fundamental rule of injection molding is that. top 10 injection molding machine manufacturers in china; Top 10 Plastic Injection Molding Companies In United States; Top 6 injection Molding Machine Manufacturers;. This is expected to achieve. Packing pressure: up to 100MPa. Prior to injection molding, moldflow analysis is essential. Plexiglass. 006 mm or 0. 020 0. We have shown how to calculate the cooling energy for one shot. 1 – Snake Lines Snake lines occur when a jet effect is created as the melt enters through a. 34 BTU/lb-°F x (464-212) °F = 0. A plastics molding plant runs on more than electricity—it runs on water. Contact us to learn more about SMARTFLOW flowmeters. November 1984. Injection molding flow lines can also be caused by using material that has defects. This chart shows clearly that BTU/gal decreases as flow-rate increases, even as the flow transitions to turbulent. 1 Injection molding. Lots of it. 1. This should happen. This makes the rubber much more ideal for molding fuel lines, hoses,. ) 2. Determined by shape, aperture, etc. Factors. Plastic is injected into a mold at a specific rate of flow—typically in. If larger gates are used, expect a longer molding cycle time. 2. Pack (hold time) is usually 2 to 3 times the mold fill times, depending on gate size. Flow Lines. Flow marks occur as circles or lines that occur around the gate. 020"). 6 in. Mold temperature: 68°F to 158°F. 020 0. ”. 010 0. There is a level of insulation from the plastic layer on the wall. Imperfections in manufactured plastic goods, such as a flow line defect in injection molding, are unacceptable. 7 of the reference. Plugged or inadequate vents n Clean plugged or dirty vents, particularly those along the parting line. The flow line is usually connected to injection specifications, mold and injection material, it can be defined as linear grooving, or round surges, on the surface of an injection molded part that shows the. If the cornflake pigment contains a large amount of fine particles, this will result in a higher definition of flow and weld lines. also contribute to gas permeation into the thinner product walls adjacent to the intended gas flow path. Plastic injection force exceeding the clamping pressure of the press. Weld line defects – also known as knit lines – is a defect that occurs when the injected plastic meets within a mold. When designing a cooling system for a new injection mold, there are a few concerns to address for maximum cooling and reduced cycle time: All cooling channels within the mold need to be in close proximity to the thickest part of what is being formed. Improve the exhaust system of the mold. Flow lines are frequently the result of changes. While some molds or inserts have simple, straightforward. 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. Flow lines and weld lines are lines or streaks in the final molded part. 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) properties were. Mold leaks also can. This occurs wherever there is a. The best we can hope for is to pressurize the knit or meld line better through the combination of melt temperature, mold temperature, flow rate, and holding pressure. As the name implies, it is usually positioned along the edge of the workpiece, forming a visible. Avoid Drag in Molded Parts. Improve injection speed and melt flow. Flow lines can occur if any of the following affect the mold: A runner, gate, or sprue that is too small for purpose creates more flow resistance. 95. 2 (a). ” It then flows through the tool. Gas assist injection molding has been practiced at some level for about 20 years, and there have. Figure 1 below shows the development of a weld line. Manifesting as wavy lines or streaks on the surface of the molding, flow lines generally occur when molten material flows unevenly and when some areas of the molding cool faster than others. Because air doesn’t transmit heat the way water does, this fan-cooled air typically consumes 10 percent more electricity. Another tactic to promote more chain entangling at the weld line is to raise the mold temperature 10° C (50° F). The. Each typically. 025 100 120 140 160 180 200 220 240 Mold Temperature (F) LDPE PPThe injection molding process is one where molten plastic material is forced into a mold cavity under high pressure. Flow lines or flow marks are a common visual defect in injection molding. Vertical walls, meaning those part surfaces parallel to the direction of mold operation, should have a. Weld Lines. This can be achieved by reducing. Prevent Flow and Knit Lines During the Injection Molding Process. The parts were glossy, the glass filler had been buried, and a resin-rich surface that we all strive for had been achieved. Reducing the dimensions of the runner system. This common injection molding defect typically happens due to leftover pellets contained in the. Here are some ways manufacturers can avoid quality issues during the plastic injection molding process: Inadequate Injection/Holding Pressure: If injection and. 000 0. improper venting. The material temperature is too high, which causes decomposition. 2023年1月3日 / by admin. Website: UNDERSTANDING QUALITY ISSUES WITH INJECTION MOLDED PARTS Glossary of terms used to identify defects: Short Shot – injection of insufficient material, causing mold cavity not to pack out creating flow lines. This can be caused by a poor mold design, or plastic temperatures, mold temperatures, injection speeds, or. Flow lines occur as a wavering or ring-shaped pattern on the plastic part that. personnel to assess cooling lines in the mold design. Edge Gates. Source: Google. If a mold cavity has a significant flow length-to-thickness ratio, the material. Where. The flow rate should ensure the material does not lose its. low viscosity. The gate in injection molding is an essential component that directly connects to the plastic part and controls the flow of melted plastic resin into the cavity. 45 lb x 0. Injection molding flow lines can also be caused by using material that has defects. If the pressure in the mold is greater than the clamping pressure of the. Consider the following examples of cooling channel configurations in P20 mold steel with a water line diameter (D) of 11. (7/16 in. An on-line compounding injection molding machine, incorporating the co-rotating, intermeshing twin-screw extruder and a reciprocating screw injection molding machine fitted with the oscillating pressure valve, has been developed. Because air traps defects are seldom thought of in the design process, it is almost routine for plastic molds to have venting put in after the mold is initially sampled! However, mold flow analysis can be used to. Thus, a right gate design raises polymer temperature to prevent the formation of weld lines and flow marks. Drying temperature 75°F to 90°F. Flow lines – A common plastic injection molding defect in which discolored ring-shaped streaks, patterns, or wavy lines appear around gates or narrow sections of the finished product. 5. Proper mold venting is essential for producing quality parts. The emergence of silver marks is generally due to the rapid start of the. 34 x 252 = 38. Flow is split 6 ways: Q AB ≡ Q Q BC = 2 3 Q Q CD = 1 3 Q Q BE = Q. As your needs evolve, HTI Plastics is using the latest technology to set the pace for the plastics injection molding and blow molding industries. Turbulent Flow IS Always Better. Reposition gates and runners to allow resin to flow around the obstruction from a different. Certain injection molding processes may not be effective for the production of some parts. Sink Marks. Bubblers and Baffles. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Solution: The. The mold leaks oil, water, and air into the mold cavity, which easily causes silver streaks on the part surface. Flow lines. The mold designer cannot know your goals without your input, which is why you will be asked to approve a gate and ejector layout prior to manufacturing a mold. When incorporating multiple gates it’s important to consider where the flows will meet as the meeting area can cause aesthetic issues and part weakness. Weld lines defects are formed when two flow fronts are merged together. Flow Rate of PVC Pipes; CPVC VS PVC; Sch 40 PVC Pipe Dimensions; Schedule 80 PVC Pipe Dimensions; PVC Fittings | PVC Connection; Versus. More viscous amorphous materials, such as PC, TPU or PEEK, can have a recommended vent depth range from 0. Flow Lines in Injection Molding . Weld lines are injection molding defects that can be mitigated by a number of tactics that depend on your part design. Poor mold surface n Refinish a poor or worn mold surface. 1mm (7/16"), coolant temperature of 30ºC and cycle time of 17 seconds (see Fig. process and provides background on the inje ction-molding process and plastic materials. A special mold provided with a glass window was used in order to directly evaluate the flow progression during the filling phase of the injection molding process in a thin-wall cavity and to. The Mold. It also may be that your injection speed is too low, which will cause the molten plastic to solidify at different rates. An air cooling system will discharge hot air into your plant. Impurities in the resin will prevent a smooth flow through the mold. Understanding the complexities of injection molding flow and solidification is a bit more challenging as. An improper flow rate and injection speed also cause flow marks. Weld lines typically appear in a part when an obstruction of some kind separates the melt flow and prevents it from "knitting" together. They appear as waves or lines, usually of a different color tone from the surrounding area. Weld lines are the def ects in. Water cooler bubbler and baffle are sections of cooling lines that divert the coolant flow into areas that would normally lack cooling. Until the mold is up to temperature, the TCU will need to heat the heat. Injection molding can be performed with only one of these. diam. As molten resin flows through the injection mold it loses pressure and temperature. If it is farther down the flow part, increase injection speed to decrease viscosity and allow more packing pressure. All weld lines trap air, and it is a critical. SMARTFLOW ® flowmeters effectively and accurately measure flow rate. 182-185, 2013. In the SOLIDWORKS Plastics CommandManager, click Flow Results. July 18, 2023 Flow lines are a defect in injection molding and can be a significant issue for manufacturers. The type of resin used during injection molding plays a large role in whether or not a knit line will be present. FLOW – A qualitative description of the fluidity of a plastic material during the process of molding. parting line mismatches. 127 mm; average thickness of plastic part is 2. Voids can affect the moulded part’s strength and appearance, increasing material waste and production costs. Occasionally, gate blush will show up in areas where there’s a wall-stock. 005 0. Mandrel as part of an. Adjust the sprue bushing length: If the face of the sprue bushing is sealing off on the parting line, adjust the length to ensure that nozzle pressure or thermal expansion does not hold the mold open and. Wavy lines are another feature of weld lines. #TROUBLESHOOTING #FLOWLINES #INJECTIONMOLDINGStudy more about troubleshooting flow lines : molding is a manufacturing technology for the mass-production of identical plastic parts with good tolerances. 2. of the optic. 4, no. Check the diameter of the ejector pins and the pin hole tolerances, if the tolerance is too wide this could allow. Peter Reitmann. Flash – excess plastic, usually found around the area of the mold parting line on a. Patented side wipers prevent coolant blow-by ensuring coolant flow to. The influence of coolant flow rate on heat transfer efficiency. Aesthetics, such as injection molding gate marks, sink marks, voids and flow lines In some cases, more than one gate may be necessary to achieve the desired outcome. The mold, however, may consist of areas too far away to accommodate regular cooling channels. This paper describes the polymer melt flow in molds during. Enlarge gas vents and gates to allow trapped air to escape the mold. We practice continuous process improvement, and HTI Plastics keeps costs low and. Here are some of the most common scenarios for cracks in injection molded parts: Cracks in the Direction of Flow – If the crack develops in. The mold should have a fine matte finish to allow air to vent quickly and the parison to conform to the mold surface while it is still hot. Mold flow analysis is a software simulation that can show how resin will fill the mold during the injection molding process. 3,000 ton machines can cost $700,000. Splay is a cosmetic defect that occurs in plastic injection molding, when silver or white streaks appear on the surface of the part. Flow marks are caused by a variety of factors in the injection molding making technology, and they happen at the gate. Pre-wrapped with PTFE tape, the product has a maximum coolant temperature of 212° F. 3). In any case, you’d prefer to create. For injection molding grades, the MFR (MI) values for polyethylenes are generally determined at 190°C (374°F) using a static load of 2,160 g. 025 100 120 140 160 180 200 220 240 Mold Temperature (F) LDPE PPKnit lines, weld lines, mold lines, or flow lines in injection molding are faint lines that become visible on certain plastic parts. An injection molding machine. Picture the flow of a liquid resin filled with, for example, glass fiber. Principles of Injection Molding. For this we must take into account the rate at which the material flows through the mold. Application: The SWAP Valve is well-suited for cooling water Supply lines up to 2-inch NPT on frequently changed tools that are hung on small to medium tonnage injection molding machines. A mold that flows from thin tight sections to a larger wall thickness will have trouble completely. Injection. Sufficient draft is an important part of any mold design, and quick-turn tooling is no exception. Possible Sources of Weld/Knit Lines: Temperature from the injection molding machine, runners, and/or the mold itself in order to ensure the plastic resin flows properly; Insufficient pressure resulting in the flow fronts not being merged back together with strong enough; Mold design, especially location of gates and runners impacting the. Setting the proper pressure on the injectors to push the plastic into the mold with enough speed that the plastic will coat the mold and fuse with other flow lines. Flow lines are aesthetic defects that occur on plastic products. Allows you to accommodate a variety of part sizes. This requires skilled labor to mold new parts that have less molding defects. Increase the temperature of the material as well as the mold temperature. 2. The injection velocity and other flow variables are computed from the given mass flow rate m ˙ and the injection temperature T inj. Expert molding team members can process out flow lines and other issues before producing customer parts from a new mold. Check for proper cooling flow through the mold. Imagine a river splitting to go around a rock, then meeting up again on the other side. Figure 21. Timing and temperature are significant contributing factors when it comes to flow and knit line defects. ; Burn marks – Often. They usually appear as a slightly different color than the rest of the part. E = 0. The Solutions for Poor Welding Lines. 160"). A look at how taking the time and data to analyze a mold problem will help you repair it right—and permanently—the first time. Injection moulding defect voids, also known as air pockets, vacuum voids, or bubbles, are trapped pockets of air or gas in the moulded part. Maximum dimension of product is 239. 5mm (0. g.