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Trouble shooting

Problem Content: 1Resin does not charge

Main cause Main measures
1. Pellet size or crushed products are too large in diameter than the groove depth of the screw. Reduce pellet size or grind or replace machine or screw.
2. Cylinder temperature is too low to melt resin. Increase cylinder temperature.
3. The screw under the hopper is wrapped with solidified resin
(This may be occurred at molding without cooling under the hopper).		 The solidified resin is removed.

2Problem Content: Resin does not come out of the nozzle

Main cause Main measures
1. Nozzle clogging may occur due to unmelted resin. Increase cylinder temperature.
2. The melting resin may have solidified at the nozzle and become clogged. Increase nozzle temperature.
3. Nozzle clogging due to foreign matter is suspected. Disassemble and clean the nozzle and take measures to prevent foreign matter from entering the nozzle.

3Problem Content: Foamed resin comes out of the nozzle

Main cause Main measures
1. The temperature of the cylinder is too high and the resin may have decomposed. Decrease cylinder temperature.
2. Moisture is high and moisture vaporization or hydrolysis of the resin is considered. Dry the pellets or recycled material.

4Problem Content: There is a resin dripping from the nozzle

Main cause Main measures
1. It may be caused resins with low melt viscosity. Make the screw-suck-back properly.
2. It is probable that the resin was hydrolyzed and the melt viscosity was lowered due to the high moisture content. Dry the pellets or recycled material.

5Problem Content: There is a solid resin in the melting resin that comes out of the nozzle

Main cause Main measures
1. The resin may not be melted enough. Increase cylinder temperature.
2. If the screw speed is too fast, heat transfer from the cylinder wall will be poor. Reduce screw rotation speed or increase back pressure to delay resin passage time.
3. It may be caused different resins mixed in. Check for the foreign resin contamination with a high melting point.

6Problem Content: Poor mold release

Main cause Main measures
1. This may occur if the mold is scratched. Correct the scraches.
2. It may happen when over packing occurs. Reduce injection pressure.
3. The taper angle may be too small to pull out. Increase the taper angle.

7Problem Content: Sprue remains in the fixed-side mold

Main cause Main measures
1. Scratches may occur in the sprue (special attention is paid to the nozzle tip). Correct the scraches.
2. This may occur when the center ring of the nozzle is not aligned to mold sprue hole. Starting over the mold attachment procedure to align the centers.

8Problem Content: Resin cannot be filled in the cylinder

Main cause Main measures
1. Resins with low melt viscosity may cause by resin dripping.
  1. When filling with resin, fill the resin with the nozzle touch.
  2. Decrease nozzle temperature.
  3. Reduces back pressure.
2. The high moisture content in resin may make resin hydrolysis, resulting in a decrease in melt viscosity. Drying the plastic is performed.

9Problem Content: The cushion of resin cannot be taken enough

Main cause Main measures
1. Problems with the anti-reflux valve (wear, etc.) may occur. Replace the check valve.
2. Resin may have leaked from the nozzle tip. Prevent resin leaks in an appropriate manner (e.g. the curvature of the nozzle touch matched).

10Problem Content: Yarn from sprue

Main cause Main measures
1. The resin at the nozzle tip does not solidify, and the viscosity is large, so that the molding parts cannot be pulled off when the mold is opened.
  1. Lower the nozzle temperature to allow the resin in the nozzle touch to solidify.
  2. Increase the cooling time.
  3. Take the screw-suck-back properly.
2. Resin may have leaked from the nozzle tip. Prevent resin leaks in an appropriate manner (e.g. the curvature of the nozzle touch matched).

11Problem Content: Gate clogged

Main cause Main measures
1. Before resin is fully filled in the cavity, the resin solidifies at the gate. Raise the cylinder temperature and mold temperature to increase the injection speed.
2. Cold slag well is too shallow, cold slag clogged the gate. Make cold slag well big.
3. The gate may be clogged by unmelted pellets or recycled materials by mixing different resins with high melting points. Removes different resins.

12Problem Content: Parts size become small

Main cause Main measures
1. If the injection pressure is too low, the molding shrinkage increases and the dimension decreases. Increase injection pressure.
2. The mold temperature is too high, the crystallinity at the time of solidification is increased, and the molding shrinkage is large and the dimension is reduced. Lower the mold temperature.
3. When the molded article is exposed to high heat, crystallinity increases and dimensions decrease. Avoid unnecessary exposure to high temperatures.

13Problem Contents: Warpage

Main cause Main measures
1. Variation occurs due to uneven mold cooling. Improve the position of the cooling hole (groove) or adjust with the amount of cooling water and temperature.
2. Grades with large anisotropy of molding shrinkage tend to have large warpage.
  1. Choose a resin with a small anisotropy (glass fiber reinforced grade has a large anisotropy and a small amount with an inorganic filler). Review the product shape, mold shape, cooling groove position, etc.
  2. Product shape: Shape to allow the melting resin to flow in a well-balanced manner. Bring to a uniform thickness and a symmetrical shape (the thinner part becomes larger in orientation).
    Position of the cooling groove: Position the cooling groove so that the surface temperature of the mold is as uniform as possible. Use of CAE is effective.
    Mold shapes: Position the gate so that melting resin flows in the longitudinal direction of the product. The gate should be a film gate to ensure that the resin flow is parallel and wide.
    Molding conditions: Lower mold temperature and longer cooling time are appropriate.

14Problem Content: Poor Appearance a. Rough surface

Main cause Main measures
1. It is easy to be occurred when the mold temperature is low and the resin is solidified while not conforming to the mold surface. Increase mold temperature.
2. It is easy to be occurred when the injection pressure is low and the resin is solidified while not conforming to the mold surface. Increase injection pressure.
3. It is easy to be occurred when the cylinder temperature is low and the resin is solidified while not conforming to the mold surface. Increase cylinder temperature.
4. It is easy to be occurred when recycled material is not suitable use. (contamination of foreign matter, insufficient melting, etc.) The use of recycled materials consider be stooped.

15Problem Content: Poor Appearance b. Weldline

Main cause Main measures
1. When the flow tip resin with a lowered temperature merges, the confluence is not completely fused, and a thin linear mark occures on the surface.
  1. Higher mold temperature and faster injection speed.
  2. Product shape: The shape is designed to allow the resin to flow easily, and the number of gates is increased to the extent that the resin temperature at the merge section does not drop too much by reducing the area where it merges as much as possible. In addition, design the merge section so that it is at a position where no load is applied.
  3. Mold designing: It is also effective to provide an adequate air vent to improve the resin flow, and sometimes to provide an overflow tab to eject the low-temperature resin section from the product section.

16Problem Content: Poor Appearance c. Jetting

Main cause Main measures
1. It may be occurred that some of the solidified resin was pushed by the melting resin that came later in the mold and moved in a serpentine fashion.
  1. Reduce the injection speed.
  2. Increase the gate size.

17Problem Content: Poor Appearance d. Short Shot

Main cause Main measures
1. There is a lack of weighing. Increase the weighing (strokes).
2. This occurs when the injection pressure is low and the resin does not flow sufficiently. Increase injection pressure.
3. This occurs when the mold temperature is low and the resin solidifies rapidly and does not flow sufficiently. Increase mold temperature.
4. This occurs when the resin temperature is low and the resin solidifies rapidly and does not flow sufficiently. Increase cylinder temperature.
5. When the injection rate is slow and solidification occurs before resin sticks to the tip of the cavity. Increase injection speed.
6. The injection time is too short. Increase the injection time.
7. Product shape: In extreme thin walls, the resin flow becomes poor and solidifies. Eliminate extremely thin sections.
8. Mold shapes: In the case of multiple cavity, short shots may occur in some cavities due to poor runner balance or gate balance. Make better runner balance and gate halance.
9. If the viscosity of the resin is too high, the flow becomes poor, which tends to occur. Choose a resin of appropriate viscosity.
10. Injection pressure may not increase due to defective reverse flow prevention ring. Replace the anti-reflux ring.
11. The air vent in the cavity may be poor and the resin may not reach the tip. Provide sufficient venting.

18Problem Content: Poor Appearance e. Silver Streak

Main cause Main measures
1. It is occurred when it contains vaporized moisture, decomposed gas, air, etc.
  1. Dry the pellet thoroughly.
  2. Reduce the cylinder temperature to prevent resin from decomposing (avoid any long stay area of melting resin in the cylinder).
  3. Reduce the injection speed or make it easy to flow to prevent air entrainment.

19Problem Content: Poor Appearance f. Splash

Main cause Main measures
1. Sharp corners may cause resin to splash. Eliminate sharp corners.
2. Cold slag may scatter into the product and be generated. Take enough cold slag wells.
3. The injection speed may be too fast. Reduce the injection speed.

20Problem Content: Poor Appearance g.Flow Mark

Main cause Main measures
1. It is occurred when it contains vaporized moisture, decomposed gas, air, etc.
  1. Delays solidification time by increasing mold temperature.
  2. Reduce the injection speed.
2. It occurs at sharp corners and over-thin and over-thick areas (too thin is likely to occur at the flow end and over-thick is likely to occur near the gate). Eliminate sharp corners to make wall thickness suitable.

21Problem Content: Poor Appearance h.Color unevenness

Main cause Main measures
1. It occurs when kneading is insufficient.
  1. The screw L/D should be at least 18.
  2. Increase the back pressure of the screw and reduce the rotational speed.
  3. Reduce the mixture ratio by preventing the recycled material shape from becoming larger.
2. The color of resin may be occurred color change due to the long stay area of resin in the cylinder. Prevent the resin long stay area.
3. This may occur due to improper filling balance when multiple cavity are used or when multiple gates are used. Adjust gate position and size to allow simultaneous filling.

22Problem Content: Poor appearance i. Black dots, etc.

Main cause Main measures
1. If the color of the stain point is black or brown, it is considered that the stain generated inside the cylinder and deposited or deteriorated, etc., is mixed into the peeled product. The inside of the cylinder must be disassembled and cleaned or purged sufficiently.
2. If the stain point is white, unfused resin or solidified resin may be considered.
  1. Increase the cylinder temperature to sufficiently dissolve.
  2. Make the cold slag well deep enough.

23Problem Content: Poor Appearance j. Bubbles (voids)

Main cause Main measures
1. When resin flows at high speed, air in the cavity may be entrained and formed in or on the surface of the molded article. Reduce the injection speed.
2. There is a large difference in wall thickness, and air may be entrained when the resin flows from a thin place to a thick place at a high speed. Design flow paths to prevent sudden flow changes.

24Problem Content: Poor Appearance k. Poor gloss

Main cause Main measures
1. This occurs because the melting resin does not adhere to the surface of the mold when the temperature of the resin is low. Increase cylinder temperature.
2. This occurs because the melting resin does not adhere to the surface of the mold when the molding temperature is low. Increase mold temperature.
3. Gas in the cavity adheres to the surface of the product and ,makes rough surface. Enhance degassing or make shallow texture.
4. Die surface may be dirty and cloudy. Clean the mold surface.
5. This happens because the injection pressure is low and the melting resin does not adhere sufficiently to the mold surface. Increase injection pressure.
6. Injection switching position is inappropriate and the melting resin does not adhere sufficiently to the mold surface. Adjust the VP switching position.
7. This occurs because the gate size is small, so the melting resin does not adhere sufficiently to the mold surface. Increase the gate size.

25Problem Content: Poor Appearance l.Wrinkle

Main cause Main measures
1. This happens because the injection pressure is low and the melting resin does not adhere sufficiently to the mold surface. Increase injection pressure.
2. The injection rate is slow and solidification occurs before the melting resin adheres well to the surface of the mold. Increase injection speed.
3. Die surface may be dirty and wrinkle. Clean the mold surface.
4. This occures the gate size may be small, so the melting resin does not adhere sufficiently to the mold surface. Increase the gate size.

26 Problem Content: Poor Appearance m. Whitening

Main cause Main measures
1. Die surface may be dirty. Clean the mold surface.
2. This may occur when the gate size is too small. Increase the gate size.
3. May occur due to poor degassing. Improve gas removal.
4. Excessive kneading may generate decomposition gas and cause whitening. Decrease the screw speed and back pressure.
5. The resin may contain gases that cause whitening. Dry the resin thoroughly.
6. When the molded product is forcibly removed from the mold, it may become white.
  1. Take sufficient taper angle.
  2. Increase the R at the corner of the molded article and at the base of the boss, rib, etc.

27Problem Content: Poor Appearance n. Peeling

Main cause Main measures
1. Inclusion of incompatible heterologous resins.
  1. Prevent contamination with different resins and purge thoroughly.
  2. Choice of compatible heterologous resins.
  3. Increase the amount of purging and the number of discarded.
  4. Increase the resin temperature.
2. Mixing of dripping resin, yarns from sprue, and cold slag. Prevention of dripping resin and yarns from sprue, and modification of cold slag wells.

28Problem Content: Poor Appearance o. Burn

Main cause Main measures
1. Resin accumulates locally in cylinder. Disassemble and clean the cylinder.
2. The resin burns due to the heat of compression of the gas due to poor degassing.
  1. Allow sufficient degassing from the mold.
  2. Decrease injection speed.
3. Too high a resin temperature may cause brown discoloration. Decrease cylinder temperature.

29Problem Content: Poor Appearance p. Bubbule

Main cause Main measures
1. When the mold is opened before the resin solidifies sufficiently.
  1. Increase the cooling time.
  2. Lower the mold temperature.
2. When the thick portion is not sufficiently solidified. Lower the mold temperature.

30Problem Content: Poor Appearance q.Burr

Main cause Main measures
1. Generated when melting resin flows into parting line or between mating surfaces of molding blocks.
  1. Increase the clamping force.
  2. Reduce injection pressure.
  3. Lower resin temperature and mold temperature are appropriate, but the effect is not significant.
  4. Correct the flatness of the parting line and the mating surface of molding blocks.
  5. Balance runners and gates to avoid resin pressure bias.

31Problem Content: Poor Appearance r. Sink mark

Main cause Main measures
1. The volume shrinks when the melting resin solidifies. Crystalline resins generally have a large degree of crystallinity. When this solidification shrinkage occurs at the thick wall portion, the surface of the product is pulled toward the center of the thick wall portion, resulting in a sink mark.
  1. Increase the retention time.
  2. Lower the mold temperature.
  3. Increase the cooling time.
  4. Make the thickness thinner (the maximum thickness is about 5mm.).
  5. Gates should be placed close to the sink mark area, and the size of the gate should be greater.
  6. Be careful when designing ribs and bosses.

32Problem Content: The expected strength does not come out: a. Corner part breaks

Main cause Main measures
1. The corner area is where stress concentration occurs easily. Corner Radius should be big.
2. If the wall thickness is too thin, it becomes weak. Increase the thickness of the wall to an appropriate value.
3. Scratches can cause stress concentration and break easily. Prevent it from being scratched.

33Problem Content: The expected strength does not come out: b. Void inside the parts

Main cause Main measures
1. Voids can cause stress concentration. Voids may be caused by resin shrinkage or air entrapment.
​
  1. Reduce the thickness of the wall.
  2. Increase the retention time.
  3. Change the position and size of the gate.
  4. Reduce injection speed and design products without rapid flow changes.

34Problem Content: The expected strength does not come out: c. Location where it will break or crack is determined

Main cause Main measures
1. The mold has been scratched, and cracking has occurred from the portion. Repair scratches on the mold.
2. It is easy to occur crack at thin portions with weak strength. Thicken the wall.

35Problem Content: The expected strength does not come out: d. There is a crack from the poor appearance parts

Main cause Main measures
1. Cold slag may be mixed in. Make the cold slag well deep enough.
2. Cracking occurs at the wrinkled part due to insufficient injection pressure. Increase injection pressure, mold temperature, and resin temperature.

36Problem Content: The expected strength does not come out: e. A foreign substance is seen on the fracture surface

Main cause Main measures
1. Foreign substance is taken stress concentration.
  1. Disassemble and clean the inside of the cylinder or purge it thoroughly.
  2. If there are other sources of contamination, measures will be taken.
2. Cold slag may be mixed in. Make the cold slag well deep enough.

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