Troubleshooting guide of plastic injection molding

Posted by TINA at 22.11.2019
Injection molding is a process of shaping plastic by melting it and injecting it into a predesigned mold. The process was first designed in the 1930s and was originally based on metal die casting designs. The process uses large injection molding machines, it consists of two basic elements: the injection unit and the clamping unit. The process starts with a mold, which is clamped under pressure to accommodate the injection and cooling process. There are many problems during the process.
Quick link of the Troubleshooting Guide:
1) Dark brown spots
2) Brittle fracture
3) Bubbles (Or Steelyard balance : stranded gas)
4) Burn marks
5) Plastic injection molding machine of mucosa
6) Grain crack
7) Plastic degradation
8) Injection molded parts deforms
9) Injection molded cloak
10) Injection molded parts does not shrink
11) Surface roughness
12) Silver streak
13) Surface wrinkled skin texture
14) Color distribution
15) Fusion line location decline
16) Insufficient filling
17) Injection molded parts size differences
18) Systolic trace
19) Dirt marks
20) Sprue adhesion
21) Empty hole
22) Curved injection molded parts
23) Spraying trace
24) Surface layer (peeling)


Dark brown spots
Spots and stripes still visible even the molding parts have the correct color.

Troubleshooting Solution Guide
Injection molding machine 1. The last production of degradable plastics materials in the cylinder, screw, valve adapter maybe curing inside the aggregate hot runner pipe. Use cleaning compounds or high molecular weight PMMA material to clean the injection cylinder unit.
2. Plastic material traps in the cylinder device's dead area or stagnant area, causing it to stay too long in the high temperature.

1. cylinder and screw should be removed and thoroughly clean the surfaces in contact with the polymer melt.
2. Check whether the nozzle is located correctly in injection cylinder.
3. Use open or direct type nozzle to replace opening and closing nozzle.
4. Check the stop valve for cracks, etc. Change a new device if necessary.
3. Plastic enters the mould cavity too fast causing excessive shear polymer. Reduce the injection speed.
4. Melt temperature is too high. 1. Reduce fire zone melt temperature in a feed tank. Check the flow rate if its sufficient for cooling the hopper locking device, adjust the flow rate if necessary.
2. Reduce the cycle time to increase plastic that is passed by the cylinder device.
5. Using the incorrect screw surface speed and back pressure, causing the molten plastic over cut. Use minimum back pressure and the correct use of the screw surface speed
6. Use a correct type of screw design in the process of plastic. Use a lower rate of a extrusion screw.
Mold 1. Grease or oil occur within the mold. Mold and nozzle should be removed and thoroughly cleaned.
2. Gate is too small. Increase the gate size.
3. Wall injection molded too thin, so that plastic flow is not sufficient to pass through, so it causes no degradation. Check the correctness and consistency of wall thickness, if necessary, will be modified.
4. Hot runner mold produces impurities. The hot runner mold aggregates tube completely remove and clean.
Plastic 1. PET or other heat-sensitive plastic appear impurities. Check the source of impurities, especially with PET manufacturing and conveying plastic pipe part.
2. Excessive heating of the back using the previous materials. Strict inspection after the separation of impurities in materials.
3. Due to the lack of room cleaning or plastic dry cause plastic blended with burnt particles. Dry cleaning and reuse of some materials.
4. Poor plastic flow characteristics caused by Insufficient lubrication of plastic. Adda certain amount of external lubricant (such as 0. 05% to 0. 1% stearate).

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Brittle fracture
Injection parts split or easily broken in the process of molding.

Troubleshooting Solution Guide
Injection molding machine Melt temperature is too low. Increase temperature in tank and injection mouth.
Reduce the speed of the screw or adjust the screw speed to get the correct surface speed
The breakdown of the molecular structure of plastics caused by degradation in cylinder. In all regions to reduce injection cylinder temperature.
Reduced back pressure.
Mold filling is too slow.
Increase injection speed.
On the automatic injection molding machine remains stable bedding.
Mold Cold mold surface Increase mold temperature.
Limit the speed of cooling flows through the mold.
Runner and the gate are too small, so the mold filling produced excessive shear rate. Use full-round runners and increase the size of runner and gate to provide acceptable mold filling phase shear rate.
Plastic The pressure of injection molded parts without proper release or not be processed. Injection molded parts annealed, if nylon plastic products, which dipped in warm water.
Injection molded parts is not sufficient for a particular plastic. If possible, design the product in order to improve the weak sections.
Adding too much regrind. Reduced the mixture proportion of recycle materials with the new plastic materials.
Heterogeneous plastic impurities. Check the plastics for impurities.
Thoroughly clean shot cylinder.
Hopper or filling machines to be removed and cleaned thoroughly.
Regrind may have poor quality. Double check the signs of impurities when recycle material being separated.
Ensure dust removing material.
Check for strict implementation of recycling programs.

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Bubbles ( Or Steelyard balance : stranded gas)
If melt temperature contains gases (volatile compounds), then packing disappears in the injection molded parts also contain air bubbles.

Troubleshooting Solution Guide
Injection molding machine 1. Trapped in the injection of air in the cylinder. Reduced melt temperature, particularly the latter.
Increase back pressure.
2. Mold filling speed is too fast. Reduce the speed of the screw, and reduce cable volume.
Reduce the injection speed.
Increase injection pressure.
3. Fill pressure insufficient Increase injection speed.
On the injection molding machine remains stable bedding.
Mold 1. Mold exhausting not enough. Inserted in mold venting or expand existing vent depth.
2. Plastic flow in the mold of uneven air trapped in it.
Using vacuum exhaust method on the die.
Change the location of the gate.
Runner diameter increase.
Plastic Workshop of plastic into the warm air moisture condenses on the cold plastic. Drying of plastic.
Put plastic factory for at least six hours before injection.

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Burn marks
Changing color of plastic (from yellow to black), usually appeared in runner tails or compressed areas.

Troubleshooting Solution Guide

Injection molding machine
1. Plastic is so hot. Reduced melt temperature.
2. Mold filling speed is too fast. Reduce the injection speed
3. Back pressure is too high. 1. Reduced back pressure.
2. Check a screw surface speeds are correct.
4. Melting volatile in excess. 1. Ensure that the air not incident with tank and plastic.
2. Check the hopper is always filled with plastic to a stable height
5. Using too much clamping force. Slightly reduced clamping force.
6. In the previous production operation with an incorrect machine clearance procedures therefore the plastic cooked in cylinder. Strict customs clearance procedures.
7. Plastic injection cylinders in heated for too long. On the blow molding machine, it also have the heater to heating PET preform. Reduce cycle times.
Mould 1. Mould exhausted or is closed Check and clean exhaust.
2. Surrounded by molten plastic mould in the air and air trapped in it. Formation of trapped air is compressed and combustion burn marks. 1. On the mould using vacuum exhaust.
2. By reducing injection part walls or injection moulded parts to increase mobile guide on changing the way mould filling
3. Gate size too small. Increasing the depth or width of the gate, or increase the gate area area.
Plastic Incomplete drying of plastic, so left a trace of water. 1. Drying plastic according to correct procedures.
2. Use a vacuum or with desiccant dryers.

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Plastic injection molding machine of mucosa
Injection molding parts sticked inside the mold made injection molding parts very difficult to move out.

Troubleshooting Solution Guide
Injection molding machine
Mold plastic packing. Lower injection pressure and injection quantities.
Injection cylinder temperature is too high.
Injection pressure is maintained for too long. Reduce screw forward time.
Mold Porous mould surface scratches, or abrasions. Remove stains and polished surfaces of the injection mould.
Mould angle is insufficient. Using every edge is 0. 5 degrees minimum angle (angle larger, goes against the easier, faster operation).
Poor collapse designed No frontal angle area guaranteed.
Injection molded parts stuck high Polish mold surface. Using exhaust valve to remove pressure from highly polished surfaces of injection molded parts produced in vacuum.
Exhaled air, the secondary crest.
Crest of inappropriate equipment. Increasing the number of crest or put on a different system.
Plastic Plastic lubrication is insufficient. Use parting agent. Increasing external lubricant, such as zinc stearate (0. 05%).

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Grain crack
Injection molding cells have small cracks, their transparent injection parts formed white / silver color appearance.

Troubleshooting Solution Guide
Injection molding machine Injection pressure is too high. Lower injection pressure.
Reduced screw Rod forward time.
Mold filling speed is too slow. Increase injection speed.
Melt glue inconsistencies (melting glue viscosity difference). Increase melt glue temperature (increasing after firing tank zone temperature).
Increase the total cycle time.
Increasing back-pressure or multi-level back-pressure
Finnish to make mold plastic on a larger shot injection molding machine.
Mold Injection molded parts from the mold when ejection under high pressure Use additional ejector.
Guaranteed top out after launch to a unified, flat land for process.
If you need to increase the diameter of the ejector.
Reduce the speed of ejection.
Caused sharp crack on the surface of the preform mold. Cleaning and checking of grain crack caused by preform mold surface.
Metal insert supercooled and or greasy. They skim and pre-out insert mold before.
Oil traces from extrusion machinery to the mold surface. Ejection system to be removed and washed thoroughly, checking hydraulic ejection if there are any leaks.
Within the cavity or core is leaking. Core-mold cavity, mold or template, check the signs of cracks.
Check for any leaks caused because the poor quality of rubber ring.
Gate dimensions too Ambassador plastics packing too much due to excessive pressure. Reducing the gate depth.

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Plastic degradation
Injection molded parts or certain parts of injection molded parts usually changed color in the degradation, color from yellow to black.

Troubleshooting Solution Guide
Injection molding machine In cylinder of injection plastic too heated. Reduced melt temperature.
Temperature controller is not functioning properly. Check injection cylinder controlled by temperature controller is in the correct area.
More positive temperature controller and check again whether there is a contact adhesive.
Using an incorrect thermocouple types. Check whether the types of thermocouples used or available on temperature controller, such as FeCon consistent.
Check whether all electric running with satisfaction.

Plastic injection cylinders in the residence time is too long.
Injection weight, if it is less than the injection pressure of injection molding machine 25%, the mold will transfer to the smaller plastic injection molding machine.
If there are no smaller injection molding machine can be used for the injection cylinder temperature dropped below the minimum value, which will meet the quality requirements of injection molded parts. So, before we buy the new injection machine, we should choose a right injection machine first.
At the time of cessation of the production of plastic stuck in cylinder of injection. When you stop the production, to clean up the shot cylinder, screw the most forward position.
Somewhere in the plastic injection tank "stranded" and degradation. Check shot cylinder, removal of land of any residual stains.
Mold Mold shot is too small. The mold is moved to the smaller of the injection molding machine.
Plastic Water content in the plastic is too high. Use the correct baking programs.

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Injection molded parts deforms
Injection molded parts that cannot be copied exactly as cavity size, some parts are torn, bent or deformed.

Troubleshooting Solution Guide
Injection molding machine Parts eject while they are too hot. 1. Increase cool down.
2. Reduce melt temperature.
3. Increase the total cycle time.
4. Reduce mold temperature.
Mold 1. Mold sinks too deeply. Reduce the depth of the depression, and RADIUS.
2. Apex PIN number is too small or too little. Increase the number of top pin diameter or.
3. The movement of the machinery is not uniform. Check out balance and smooth nature of mechanical movement.
4. The ribs use in injection molding line or the wheel design was incorrect. Rib used on lines, hubs and networks, such as the maximum allowable slope.
5. Mold surface finish difference. Polish mold surface.

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Injection molded cloak
Injection molded parts have excess materials such as edges or neighboring fin, they usually appeared in mold part dividing line or mold on da, or holes.

Troubleshooting Solution Guide
Injection molding machine 1. Injection pressure is too great. 1. Reduce injection pressure and injection pressure change to packing.
2. Reduce time to screw moves forward.
3. Reduce the injection speed.
2. Too many plastic injection into molds.
Reduce the injection capacity.
3. Plastic is so hot. 1. Reduce melt temperature.
2. Reduce total cycle time.
3. Reduce the injection speed.
4. Intermittent pauses in the production run. When production stops, check the injection molding operation, especially melt temperature.
Mold 1. Injection pressure within the mold is skewed. 1. Cavity layout should be balanced.
2. Check whether the injection part wall thickness on average.
2. Become a prominent part in the mold surface. 1. If cloak appears in the side of injection molded parts, check whether the land balance each other.
2. Check mold junction area, where there is needed to clean.
3. Then use blue ink check balance again.
3. Injection molded parts in the mold or mold surface without registration. Open mold, a close-up view, repair and make correction to obtain balance padding mode.
4. Projected area is too large. Total projected area of the mold (mold cavity and runner) for use of the clamping force is too big.
5. Improper exhaust so plastic leaves the cavity area. 1. Inspect and clean the vent.
2. 0. 0005in or 0. 01mm expanded mold vent until the amount of increase will correctly fill the injection mold.

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Injection molded parts does not shrink
Injection molded parts are not showing normal shrinkage value associated with the plastic.

Troubleshooting Solution Guide
Injection molding machine 1. The injection pressure within the cavity is too low.
Rise injection pressure, check the size of the injection molding parts each time the pressure rises, until the injection molded parts slightly appear.
2. Insufficient plastic inside the cavity. Increase the amount of plastic injection molding or check the bedding.
3. Mold temperature is too high. Reduce mold temperature.
4. Unusual injection molding conditions. 1. Using an incorrect injection molding conditions (temperature and pressure, and so on).
2. In the absence of stability samples before the injection process. For example, when the PET bottle preform is finished, then the bottle blow molding process is coming, all of them will be done in the whole PET line.
5. Injection hole is too small. Increase the diameter of injection nozzle hole.
6. Mold cavity filling speed is too slow. Increase injection speed or multistage fill rate.
7. Gate no condensation within the mold.
Increase the screw forward time and increases measurement samples at a time.
8. Melt temperature is different inside the injection volume. 1. Lower the screw rotation speed to return the screw just before the cooling is completed.
2. Increase the back pressure.
Mold 1. The gate is too small or poorly designed. Increase the gate size or reduce the length of the junction area.
2. Improper design of runner system. 1. Circular or ladder-shaped flow path.
2. Increase the viscosity of runners to fit plastic or plastic flow characteristics.
3. Insufficient cooling pipe design of the mold. 1. Measure the cavity surface temperature and actual temperature with the corresponding shrinkage value.
2. If there is a clear difference, the new design of cooling pipe in order to overcome the problem.
Plastic Plastic liquid is too low (that is, plastic flow is too difficult). With a lower viscosity (ie: easier flow levels) of polymers.

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Surface roughness
Injection molded parts have excess materials such as edges or neighboring fin, they usually appeared in mold part dividing line or mold on da, or holes.

Possible cause Recommendations to resolve
Injection molding machine 1. Cold material in the nozzle. 1. Check the nozzle installation to see if its dripping.
2. Increase the jet nozzle temperature.
3. If using closed fire mouth, check that it is operating correctly.
4. Nozzle back taper allows the separation of plastic and mold.
2. Melt temperature is too low. Increase melt temperature.
3. Injection molded parts are not fully populated. 1. Increase the injection molding of plastic injection molding machine.
2. Increase injection pressure.
4. Clamping force is not sufficient for use in molding surface. Increasing effective clamping force.
Mold 1. Without prior establishment of cold material points. Opposite the note process a plastic plug or deepen existing plastic plug.
2. Mold temperature too low. Increase the mold temperature.
3. Plastic rapid changes in flow direction. In any place in the mold to avoid sharp edges.
4. The spiral cavity (mixed plastics more obvious). Increasing the diameter of the gate or gate with slice types.
5. Use release agent. Avoid the use of release agents.
6. In the gate area, bad cold material by hot runner device due to rough surfaces. With elevated temperature or correct nozzle improved hot runner injection nozzle.
Plastic Plastic contains extra lubricants or other processing auxiliary. Test the same plastic to identify whether its a faulty good.

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Silver streak
Injection molded parts surface finish is inconsistent in some other jurisdictions, appeared a silver surface.

Possible cause Recommendations to resolve
Injection molding machine 1. Melt surface temperature is too high. Reduce injection cylinder temperature.
2. Plastic stranded in cylinder of injection is taking too long. 1. Reduce the total cycle time.
2. Injection volume on PET injection  machines is too small.
3. Melt temperature is too low causes mold filling time unstable. 1. Increase injection cylinder temperatures.
2. Increased jet nozzle temperature.
3. Increase mold filling velocity.
4. Not enough injection pressure. Increase injection pressure.
5. Inaccurate temperature controller, control was mixed. Check the temperature controller for precision and control.
Mold 1. Mold surface temperature is too low. 1. Increase plastic mold temperature.
2. Limit the speed of coolant flow through the die.
2. Injection molded parts have some no-plastic-plastic. 1. Increase the size of cold material hole.
2. Extended tail to form additional cold stream hole.
3. Electric heats nozzle and note muzzle.
3. Runner and gate length is too small or too long, plastic at the time of delivery caused by condensation. If necessary, increase the runner diameter and depth of the gate.
4. Too many release agents on mold surface. Thoroughly clean mold surface with white alcohol.

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Surface wrinkled skin texture
Constantly on the plastic flow marks, or around the end of gate area appeared wrinkled skin texture.

Possible cause Recommendations to resolve
Injection molding machine 1. Temperature glue temperature is too low. Increase the temperature of injection cylinder in the first two sections.
2. Mold filling speed is too slow. 1. Increase the injection speed.
2. Increase the injection pressure.
3. Mold temperature too low. Increase the plastic mould temperature.
Mold Runner and gate are too small. Increase the gate and runner diameter.
Plastic Plastic viscosity is too high. Select the easy plastic flow level.

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Color distribution
Injection molded parts have inconsistent color, that is, there is bias differences, colored streaks or patches.

Possible cause Recommendations to resolve
Injection molding machine Pigments mixed in cylinder of injection molding machine not inadequate. 1. Increase the back pressure.
2. Reduce the injection cylinder temperature of plastic for better mixing.
Plastic 1. Pigment not evenly covered with the plastic particles. lubricant used before injection mixed with plastic.
2. Colorant particles are too thick. Polishing dyes to obtain the powder.
3. Color master batch concentration level is too low. Use the correct concentration of colorant, color master batch or liquid stains.
4. Liquid coloring agent, the ingredients are not unified. Check the send tubes for air jam, and check for slide screw.
5. Amount of difference in plastic. Mixture of new material and material rendering to get rid of all "powder" and dust.

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Fusion line location decline
Injection molded parts containing the fusion line, injection molded parts to top out or damaged or broken when used in these places.

Troubleshooting Recommendations to resolve
Injection molding machine 1. In the fusion line of plastic temperature is too low. 1. Increase the melt temperature.
2. Increase the jet nozzle temperature.
3. Adjust the screw back in time.
4. Increase the back pressure.
2. Effective cavity pressure is too low. 1. Increase the injection pressure.
2. Increase the screw forward time.
3. To maintain the correct melting bedding.
3. Melt fusion is too slow or too fast. 1. Adjust the injection speed.
2. Adjust the screw speed to provide a higher degree of melt temperature on the surface.
Mold 1. Use a lot of release agents. Clean mold; reduced or no use of release agent
2. Mold surface is too cold. 1. Increase plastic mold temperature.
2. Limit the speed of coolant flow through the die.
3. Lack of exhaust in the mold. Vents added or reduced gate junction zone length.
4. Gate and runner size are too small. 1. Runner diameter increase.
2. Increase the size of gate or gate junction area of reduced length.
5. Fusion line is too far away from the gate area location. 1. Change the location of gate to get a different injection mold filling (gate and the splice line some distance too long).
2. Raising with hot water and reduced gate length of the note.
Plastic Plastic viscosity is too high and not fill the hot runner mold. Change to more easy-flow plastic level.

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Insufficient filling
Plastic injection molding process does not complete, because the cavity is not filled with plastic or injection process lacks some details.

Troubleshooting Recommendations to resolve
Injection molding machine 1. Injection speed is insufficient. Increase the injection speed.
2. Shortage of plastic. 1. Check the amount of plastic in the hopper.
2. Check that you correctly set the injection stroke.
3. Screw didn't leave a screw litter. Check valve for wear or cracks.
4. Changes in operating hours. Check the operation is stable.
5. Injection cylinder temperature is too low. 1. Increase the melt temperature.
2. Increase the back pressure.
6. Injection speed is insufficient. Increase the injection speed.
7. Nozzle part is sealed. Check the nozzle hole for foreign object or plastic.
8. Nozzle or injection cylinder heater damage. Check the heater outer and check the energy output is correct.
9. Injection time is too short. Increase the screw forward time.
10. Plastic against the pipe wall and the hopper. Increase the cooling capacity of hopper throat area, or lower the the injection cylinder temperatures.
11. Injection molding machine capacity is too small (that is, injections or weight plasticizing capacity). Use a large plastic injection molding machine.
Mold 1. Insufficient mold exhaust. Check the vent if its block or not.
2. Insufficient mold filling. 1. Increase the gate size or reduce the length of gate junction area.
2. Add cold material to the runner to prevent non-plasticized plastic seal.
Plastic 1. Injection part wall is too thin, plastic cannot flow. Use low viscosity (namely to flow more easily) plastic.
2. Plastic flow's length is too large, plastic does not fill properly in injection molded parts. Change the location of the gate in order to reduce the length of plastic flow.

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Injection molded parts size differences
In the injection molding process, the weight and size are over the tooling / injection / plastic production capacity.

Troubleshooting Recommendations to resolve
Injection molding machine 1. Cylinder with a inequality plastic material. Check for adequate cooling water flow through the hopper throat in order to maintain the correct temperature.
2. Cylinder's temperature fluctuation range is too large. 1. Check whether there are inferior or even and loose electrical heating.
2. Check with temperature controller used with electric heating is a correct type.
3. Injection molding machine's capacity is too small. Check the injection and plasticizing capacity of plastic injection molding machine, and then compared with the actual quantity of injection molding and plastics consumption per hour.
4. Injection pressure instable. 1. Ensure stable melt bedding operation.
2. Check the back flow valve for leaking, if there is a need for a replacement.
3. Check for wrong feed settings.
5. Screw restart instable. Make sure the operation screw at each recurrence position is stable, that is not more than 0. 4mm(0. 016in).
6. Changes in operating hours, inconsistent melt viscosity. 1. Check the operating hours for inconsistency.
2. Using back pressure.
Mold 1. Some blocked gate. Check whether there are any indication of gate residues remain in the sprue hole, especially diving-gate
2. Inconsistent mold temperature control. 1. Checks whether the cooling medium for mold cooling with temperature changes.
2. Check the PET preform mould cooling pipe plug.
3. Check the cooling pipes are properly linked.
Plastic Plastic change. 1. Check the feed size changes.
2. Make sure the powder is sieve.
3. Checks whether the two groups of plastic mixed.

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Systolic trace
It usually associated with surface trace, and formation of plastic shrinkage detachment from the mold surface.

Troubleshooting Recommendations to resolve
Injection molding machine 1. The melting temperature is too high or too low. 1. Adjust the injection cylinder temperatures.
2. Adjust the screw speed to get the correct surface speed.
2. Insufficient plastic in cavity. 1. Increase the amount of plastic injection molding.
2. Ensure proper bedding.
3. Increase the screw forward time.
4. Increase the injection pressure.
5. Increase the injection speed.
6. Check that the valve is installed properly.
7. Because of abnormal operation may cause pressure loss.
3. Plastic surface is overheated in cooling stage. Lower mold surface temperature.
Mold 1. Feed system is too small. Increase the size of runner diameter and gate. (Depth, width and length).
2. Injection molded parts' temperature is too hot. 1. Increased the cool down.
2. Immersion in warm water immediately after crest, cooling of injection molded parts
3. Product's walls are too thick or large disproportionate. 1. Use thinner and more uniform wall to redesign the injection molded parts.
2. Position the gate in injection parts on the most thick-walled parts.
4. Lack of mold cooling pipes. 1. Blank the thick molds if possible.
2. Insert additional cooling pipes inside the mold and thin core / Add thermal Rod rods.

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Dirt marks
It usually related to the gate area: its surface is dark and sometimes the stripes appeared.

Troubleshooting Recommendations to resolve
Injection molding machine 1. The melting temperature is too high. Reduce the temperature of injection cylinder in the first two sections.
2. Mold filling's speed is too fast. 1. Reduce the injection speed.
2. Lower the injection pressure.
3. The temperature is too high. Reduce the mold temperature.
Mold The gate signs of burning or additional process the rest of the area. Drop the gate area of rough, and polish it.
Plastic Plastic viscosity is too low. Select the easy plastic flow.

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Sprue adhesion
Sprue links sprue bushing.

Troubleshooting Recommendations to resolve
Injection molding machine 1. The sprue bushing is not aligned with the nozzle. Re-link muzzle and nozzle.
2. Inner plastic packing too much. 1. Lower the injection pressure.
2. Reduce the screw forward time.
3. Jet nozzle temperature is too low. Increased the jet nozzle temperature or heating an independent temperature controller.
4. Plastic injection is not fully cured, especially large diameter pouring sprue. Increase the cooling time, but the better way is to use a smaller mouth note instead of the original.
Mold 1. Sprue bushing hole's diameter appearing hair. Check if any burr, which may lead to depression. The reason of burr is sprue bushing area and noozle area have an incorrect RADIUS .
2. Nozzle is incorrect. Rework the process of nozzle so that it has the correct RADIUS (typically 0. 55m larger than the RADIUS of noozle).
3. Nozzle's diameter larger than the sprue aperture. Install a new shoot the mouth or smaller aperture to increase injection sleeve bore diameter.
4. Sprue bushing lack of taper. Increase the angle of the sleeve at 3 to 5 degrees.
5. Improper use of injection needles. Check if you are using the correct type of injection needle. Wherever possible, use the inverted cone design of the injection needle or "z"-shaped needle, check the "z"-type needle is in the top-left mold in the process, "z" corner of the needle or the runner and note precede circle alone.
6. Poor surface accuracy. Polishing internal surfaces.
7. Sprue bushing's diameter is too small. Increase the diameter of mouth.

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Empty hole
Easily seen "air wells" in transparent plastics, but can also appear in an opaque plastic. This is about the thickness, and often caused by plastic shrink from the center of injection molding parts.

Troubleshooting Recommendations to resolve
Injection molding machine 1. Mold is not fully populated. 1. Increase the amount of shot.
2. Increase the injection pressure.
3. Increase the screw forward time.
4. Reduce the melting temperature.
5. Decrease or increase injection speed. (such as amorphous class plastic increases 45 speed ).
2. Valve is not function properly. Checks whether the valve dehiscence or malfunctioning.
Mold 1. Gate is too small. Increase the size of gate to prevent the plastic at the gate being solidified earlier.
2. Flow path design or size is not correct. 1. Use round or trapezoidal channel.
2. Runner's diameter increase.
3. Gate location error. Change the location of the gate, so plastic enter the thickest part of the mold.
Plastic Plastic contains too much water. 1. Plastic dry for a long time to reduce the water content of plastics.
2. Use a vacuum or desiccant dryer.

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Curved injection molded parts
Injection molded parts have similar shape to cavity parts but the shape is distorted version of the cavity parts.

Troubleshooting Recommendations to resolve
Injection molding machine Bent is because the excessive internal stresses in injection molded parts. Lower the injection pressure.
Reduce the screw forward time.
Increase the cycle time (in particular, cooling time). Especially the thick injection molded parts within the mold. Immersed in warm water (38° c or 100degrees c) immediately after Crest and slowly cooling the injection molded parts.
Mold filling is slow. Increase the injection speed.
Lack of plastic in mold cavity. Increase the volume of the shooting.
Plastic's temperature is too low or inconsistent. Increase the temperature of plastics.
Injection molded parts is too hot when inject. Cool the equipment.
Mold Mold cooling's capacity is not enough. Increased the cooling capacity (speed of the cooling liquid mold).
Stains remove in a cooling pipe.
Mold cooling pipes imbalances so as to bring to injection molded parts of uneven cooling rates. Check the mold surface temperature, if it needs to be two halves of the mold parts with different temperatures.
Installing the cooling pipes and cavity surface close to each other.
Improper design of the gate location. Injection molded parts the thickest part of the open gate.
Use thin gate where possible (the smaller the width of the gate, bent more).
Feed system size is too small. Increase the size of runner or note.
Do not use the half circle runner.
Because of the mold core offset or movement, it causes thick injection part wall. Check that the core or cavity position, if its incorrect just correct them.
Plastic All types of filler in plastics. In the glass reinforced plastics use glass spheres instead of glass in tow.
Improper design of the injection molded parts (that is, not the thickness and sudden changes in thick-walled) Use consistent thickness of wall and gradually shift wall to redesign the injection molded parts.
Design a correct selection of plastic injection molded parts (like gate types and the liquidity wall thickness of plastic to the flow of long scale).

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Spraying trace
Injection molded parts of the surface trace of plastics in injection molding process.

Troubleshooting Recommendations to resolve
Injection molding machine 1. Filling speed is too fast. 1. Reduce the injection speed.
2. Increase the plastic melting temperature.
3. Increase the mold temperature.
4. Increase the back pressure.
2. Plastic injection molding machines' plasticize capacity is insufficient. Better Plasticize capacity injection molding machine.
Mold The runner and gate is too small. 1. To increase the runner diameter and gate width if needed.
2. Change the gate location or increase the barrier before the gate.

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Surface layer (peeling)
Injection molded surface peeling phenomenon, the cause is the recipe for injection molded parts (Including additives and color powder) Incomplete fusion or exclusion after fragmentation.

Troubleshooting Recommendations to resolve
Injection molding machine 1. Melt temperature is too high. Reduce the melt temperature.
2. Mold filling speed is too fast. Reduce the injection speed.
3. Screw rotation speed is insufficient. Increase the speed of rotation of the screw.
Mold Mold temperature is insufficient. Increase the mold temperature.
Plastic 1. Plastics enters the warm workshop, moisture condenses on the cold plastic. Dry the plastic according to correct procedures.
2. Color particle or additives cannot fully integrated or excluse. Replace another particle or additives

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