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C P Defect Identification and Troubleshooting T A 6 Defect Identification and Troubleshooting 6.1 Defects Table The following table contains a list of some of the most frequent molding problems, their possible causes and met
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  EN C PT A Master Language is English Hot Runner System Instruction Manual SVC-17-0001_EN-Rev03 RESTRICTED: Property of Synventive. - 85 - All rights reserved. Errors and omissions exceptedFor limited third party distribution based on need and intended use. © 2015 Synventive Molding Solutions Defect Identication and Troubleshooting 6 Defect Identication and Troubleshooting 6.1 Defects Table The following table contains a list of some of the most frequent molding problems, their possible causes and methods of rectify.  Although the description is made to the best of our knowledge, we cannot guarantee that the problems will be successfully rectied using these measures. The list is to be used as a general guideline. The operator should make a detailed analysis of the defect on-site. Table 6: List of defects SignPossible causeResolution Sink marks on the molded part Cushion too small.Sink marks close to the gate or in thick-wall areas.Shot-size increaseIncrease backpressure, optimize backpressure time.Increase backpressure.Decrease mold wall temperature.Increase melt temperature.Decrease shot speed. Adjust gate diameter.Sink marks far from the gate or in thin-wall areas.Optimize backpressure time.Increase backpressure.Increase shot speed.Increase melt temperature.Increase mold wall temperature. Adjust gate diameter. Deformation during ejection.Increase cooling time.Melt too cold, resulting in too high shear stress.Increase melt temperature.Increase hot runner temperature.Melt too hot, resulting in damage to the molded part due to high temperature.Decrease material setpoint temperature.Decrease hot runner temperature (do not decrease nozzle temperature too much, could cause freezing-off).Decrease shot speed. Adjust gate diameter.Temperature sensor of the hot runner (inlet bushing, manifold, nozzle).Temperature sensor position: Sensor too far from heating, in a cold area. Place the sensor closer to heating.Temperature sensor function: Correct sensor type (K, J)? Correctly calibrated controller (K, J)?  EN C PT A Master Language is English Hot Runner System Instruction Manual SVC-17-0001_EN-Rev03 RESTRICTED: Property of Synventive. - 86 - All rights reserved. Errors and omissions exceptedFor limited third party distribution based on need and intended use. © 2015 Synventive Molding Solutions Defect Identication and Troubleshooting SignPossible causeResolution Burnt smudges (brown or silver) Cushion too large.Reduce cushion.Shear stress on the actuator too high.Decrease screw rotation speed. Long residence time in plastication unit under critical conditions.Decrease cycle time.Increase delay at feeding. Use a smaller plastication unit. Shear stress at gate too high.Decrease shot speed.Check / adjust gate diameter.Remove transitions with sharp edges from the hot runner system.Material too dry.Check/reduce temperature/drying time. See drying instructions from material producer.Differences in hot runner diameter too big Channel diameter for the melt too big (long residence time).Clean the hot runner. Adjust the channels for the melt in the hot runner.Wrong, excessive dimensioning.Contact between hot runner nozzles and manifold, resulting in overheating (noticeable on the high load of the heating zone).Check the cut out and the contact surfaces of the hot runner and the manifold vs. the injection mold.Increase the isolation gap (Joint Z).Cut out dimensions as per the customer drawing The cavity stops filling with material after more than 5 shots Check the cut out and the contact surfaces or the hot runner and the manifold vs. the injection mold.Cold nozzles, frozen gate.Check if the nozzle does not bear on the cut out (take into account thermal expansion), correct, if needed.Check injection mold, machine nozzle and inlet bushing for tightness.Check the function of heaters and replace them, if needed.Check the temperature at mold gate using a pyrometer.Increase temperature at mold gate by 28-56°C (50-I00°F) above operating temperature until all cavities are lled, and decrease to normal operating temperature. Caution is required: not all plastics withstand this temperature increase. If this is the case do not set such a high temperature.  EN C PT A Master Language is English Hot Runner System Instruction Manual SVC-17-0001_EN-Rev03 RESTRICTED: Property of Synventive. - 87 - All rights reserved. Errors and omissions exceptedFor limited third party distribution based on need and intended use. © 2015 Synventive Molding Solutions Defect Identication and Troubleshooting SignPossible causeResolution Dark spots Granulate contaminated.Prevent contamination. Clean the plastication unit and the hot runner. Melt temperature too high.Decrease melt temperature.Decrease hot runner temperature.Decrease screw rotation speed.Decrease hot runner temperature (avoid nozzle freezing).Decrease dynamic pressure.Too long melt residence time in the system.Decrease cycle time.Increase delay at feeding. Use a smaller plastication unit. Check the channel diameter in the hot runner.PC processing.When production is interrupted, decrease hot runner and actuator temperature to max.160°C (320°F).If temperature is to drop in general, it is essential to ush the hot runner and the plastication unit in advance (natural PP or natural PE).Wearing, dead spots. Check plastication unit, gate system and hot runner for contamination, wearing and dead spots. Stringing in the gate area Melt temperature too high.Decrease melt temperature.Decrease hot runner temperature.Decrease screw rotation speed.Decrease hot runner temperature (avoid nozzle freezing).Gate area too hot.Decrease mold temperature.Check contact tightness between nozzle tip and mold.Check mating between nozzle tip and mold.Check isolation cap thickness.Use colder nozzle / cone point insert.Temperature sensor position:Sensor too far from heating, in a cold area. Place the sensor closer to heating.Temperature sensor function:Correct sensor type (K, J)? Correctly calibrated controller (K, J)? Part deformation Injection pressure too low.Increase injection pressure.Increase cooling time.Increase injection mold surface temperature.Decrease regrind percentage.Increase gate diameter. Afterpressure time too short.Heating defect. Smudges Material too cold.Increase material temperature.Increase injection mold surface temperature.Increase gate or runner channel.Gate or channel too small.Injection mold too cold.Nozzle hole too small. Matt surfaces Material / injection mold too cold.Increase material / injection mold temperature. Molded parts are brittle Material / injection mold too cold / hot.Injection speed too high. Gate or ow channel too small. Increase material/ injection mold temperature.Decrease injection speed.Increase/decrease injection mold temperature. Increase gate or ow channel.  EN C PT A Master Language is English Hot Runner System Instruction Manual SVC-17-0001_EN-Rev03 RESTRICTED: Property of Synventive. - 88 - All rights reserved. Errors and omissions exceptedFor limited third party distribution based on need and intended use. © 2015 Synventive Molding Solutions Defect Identication and Troubleshooting SignPossible causeResolution Actual temperature does not reach the required value: Heating power does not cover heat losses due to support elements, center rings and inlet bushing.Verify correct Hot Runner System installation in mold.Nozzle heating in contact with the injection mold. Unstable value of actual temperature Unstable value of actual temperature.Check temperature controller Notify ServicesVerify correct assembly dimensions.Unsuitable sensor position.Defective sensor.Unstable system contact, synchronization with injection cycle. Max. heating power cannot be reached Weak temperature control.Heating power limited by manual setting.Increase heating power set manually. Gate freezing Gate too small. Check for presence of cold / non-plastied material.Check injection mold and processing temperature.Check for presence of foreign material.Check temperature controller.Notify Services.Contact surfaces too large.Foreign body in the gate.Nozzle run, cold plug.Defective sensor or heating.Heating in contact with the mold.Irregular injection cycle.Mold temp too low. Plastic leakage Temperature too high.Check temperature.Increase screw decompression.Check pressure.Gate too large.Matt places around the gate or at sharp edges.Contact surfaces too small.Replace tips Matt places around the gate or at sharp edges Shot speed too high. Graduated injection speed prole slow – medium – fast.Increase injection pressure.Increase mold temperature.Increase mold temperature. Signicantly decrease shot speed before the ow face reaches sharp edges in the mold. Melt temperature too low.Mold temperature too low / uneven.Melt face speed too high.
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