Improper operation method, broken-down machine and mold may produce many mold defects. Some solutions for reference are given as follows.
In order to reduce machine vacant time and find the reason of operation questions as soon as possible, operators should record all injection molding conditions on “Record table of injection molding condition” for reference of solving subsequent questions.
We know that the attached documents are not completely correct. We will be not responsible for the validity and completeness. The user should decide whether it can be used for reference.
(1) Incomplete products
| Reasons of malfunctions | Solutions |
| Too low temperature of plastics | Increase the temperature of plastic-melting barrel |
| Too low shooting pressure | Increase shooting pressure |
| Not enough shooting quantity | Increase shooting quantity |
| Ill match between inlet sleeve and shooting sleeve, plastic leakage. | Re-adjust the match between them |
| Too short shooting time | Increase shooting time |
| Too slow shooting speed | Add shooting speed |
| Improper low-pressure adjustment | Re-adjust |
| Too low mold temperature | Increase mold temperature |
| Uneven mold temperature | Readjust water pipe of the mold |
| Ill exhaust of the mold | Add exhaust holes at right position |
| The temperature of shooting nozzle is not high enough | Increase shooting nozzle temperature |
| Uneven plastic feeding | Re-open outlet position |
| Too small casting channel or overflow mouth | Enlarge the casting channel or overflow mouth |
| No enough lubricant in plastic | Increase lubricant |
| No enough back pressure | Add pressure |
| Plastic inlet ring and plastic-melting screw are worn | Dismantle and amend |
| No enough shooting quantity | Replace with injection mold machine with large specification |
| Too thin product | Use nitrogen for shooting |
(2) Shrinkage of product
| Reasons of malfunctions | Solutions |
| No enough plastic feeding in the mold | Increase shooting pressure |
| No enough melt plastic | Add the quantity of melt plastic |
| Too low shooting pressure | Increase shooting pressure |
| Too low back pressure | Increase back pressure |
| Too shooting time | Increase shooting time |
| Too slow shooting speed | Increase shooting speed |
| Uneven overflow mouth | Adjust size and position of overflow mouth size |
| The shooting nozzle is too small, plastics coagulates in the sleeve of casting channel, the back pressure is too low | Adjust mold or replace shooting nozzle |
| The material temperature is too high | Lower temperature |
| Improper mold temperature | Adjust mold temperature properly |
| No enough cooling time | Prolong cooling time |
| Too many pressure accumulation sections | The shooting process should be terminated at the most front part. |
| The product, rib or column are too thick | Examine product design |
| Too much shooting quantity | Replace with smaller injection mold machine |
| The plastic feeding ring and plastic-melting screw are worn out | Dismantle, examine and repair |
| The casting mouth is too small, the plastic solidification loses the back pressure | Increase the size of casting mouth |
(3) Mold conglutination of product
| Reasons of malfunctions | Solutions |
| Too much feeding material | Lower shooting pressure |
| Too high shooting pressure | Lower shooting pressure |
| Too much shooting quantity | Reduce shooting quantity |
| The shooting time is too long | Reduce shooting time |
| The temperature of feeding material is too high | Lower temperature |
| Uneven feeding induces partial saturation | Change the size or position of overflow mouth |
| The mold temperature is too high or too low | Adjust the temperature of mold and the two sides |
| Mold-severing rounded angle in the mold | Repair mold and remove rounded angle |
| The surface of mold is not smooth | Polish mold |
| Vacuum induced by mold-severing | Slow Mold-open or ejection, or add gas equipment |
| Too short injection cycle | Strengthen cooling |
| No enough mold-severing reagent | Add the quantity of mold-severing reagent |
(4) Mold conglutination of casting channel
| Reasons of malfunctions | Solutions |
| Too high shooting pressure | Lower shooting pressure |
| Too high injection temperature | Lower plastic temperature |
| The casting channel is too big | Modify mold |
| The cooling of casting channel is not enough | Prolong cooling time or lower cooling temperature |
| The mold-severing angle of casting channel is not enough | Modify mold and add angle |
| Ill match between sleeve of casting channel and shooting nozzle | Re-adjust match |
| The inner surface of casting channel is not smooth or there is mold-severing rounded angle | Examine and repair mold |
| The outer hole of the casting channel is damaged | Examine and repair mold |
| No holding-pin of casting channel | Add holding-pin |
| The feeding material is too saturated | Reduce shooting quantity, time and speed |
| No enough mold-severing reagent | Add the quantity of mold-severing reagent |
(5)Burr and flying edge
| Reasons of malfunctions | Solutions |
| Too high plastic temperature | Lower temperature of plastic and mold |
| Too high shooting speed | Reduce shooting speed |
| Too high shooting pressure | Reduce shooting pressure |
| The feeding material is too saturated | Reduce shooting time, speed and quantity |
| Ill Mold-close line or match surface | Examine and repair mold |
| No enough mold-lock force | Add mold-lock force or replace injection molding machine with larger mold-lock force |
(6) Product cracking during mold open or ejection
| Reasons of malfunctions | Solutions |
| Feeding material is too saturated | Reduce shooting pressure, time, speed and quantity |
| Too low mold temperature | Improve mold temperature |
| Some mold-severing angles are not enough | Examine and repair mold |
| Mold-severing rounded angle | Examine and repair mold |
| Unbalanced severance during product mold-severing process | Examine and repair mold |
| Ejector is not enough or its location is not proper | Examine and repair mold |
| Partial vacuum during mold-severing | Slow Mold-open ejection speed, add gas equipment |
| No enough mold-severing reagent | Add mold-severing reagent |
| Ill mold design, too much residual stress | Improve product design |
| Improper time or location of side sliding block | Examine and repair mold |
(7) Joint line
| Reasons of malfunctions | Solutions |
| Plastic is not melted well | Increase plastic temperature, back pressure and screw rotation speed |
| Too low mold temperature | Improve mold temperature |
| Too low shooting nozzle temperature | Improve shooting nozzle temperature |
| Too slow shooting speed | Increase shooting speed |
| Plastic is not pure or mixed with impurities | Examine plastic |
| Too much mold-severing grease | Reduce quantity of grease or do not use it |
| Casting channel and overflow mouth are too big or too small | Adjust mold |
| The joint location of melting plastic is too far from the casting channel mouth | Adjust mold |
| Air in the mold can not be remove timely | Add exhaust holes or check if original exhaust holes are blocked |
| No enough plastic melting quantity | Apply larger injection molding machine |
| Too much mold-severing reagent | Reduce the quantity of mold-severing reagent or do not use it |
(8) Flow trail
| Reasons of malfunctions | Solutions |
| Plastic material is not melted well | Improve plastic temperature, back pressure and screw rotation speed |
| Too low mold temperature | Increase mold temperature |
| Mold is cooled improperly | Readjust mold water pipe |
| The shooting speed is too slow or too fast | Adjust proper shooting speed |
| The shooting pressure is too high or too low | Adjust proper shooting pressure |
| Plastic is not pure or mixed with impurities | Examine plastic |
| The overflow mouth is too small and crack is produced | Enlarge overflow mouth |
| The difference between the thin section and the thick section of the product is too much | Change product design or location of overflow mouth |
(9) Silver line, air bubble
| Reasons of malfunctions | Solutions |
| The plastic is mixed with water | Dry the plastic completely and improve back pressure |
| The plastic temperature is too high, or the plastic stays in the barrel for too long time | Lower plastic temperature, replace injection mold machine with smaller shooting quantity, lower temperature of shooting nozzle and the front section |
| The additives such as lubricant and dyes in the plastic decompose | Reduce their dosage or use replacement with high temperature resistance. |
| Other additives in the plastic are not mixed evenly | Mix them completely even |
| Too fast shooting speed | Slow shooting speed |
| Too high shooting pressure | Reduce shooting pressure |
| The melting speed is too slow | Improve melting speed |
| Too low mold temperature | Improve mold temperature |
| The size of plastic particles is not even | Use materials with even particle size |
| Air is mixed in the melting barrel | Reduce temperature of the back section of melting barrel, improve back pressure, reduce the length of compressed section |
| Improper flow of the plastic in the mold | Adjust the size and location of the overflow mouth, mold temperature, keep the thickness of product even. |
(10) No polish in the product surface
| Reasons of malfunctions | Solutions |
| Too low mold temperature | Improve mold temperature |
| No enough plastic dosage | Increase shooting pressure, speed, time and dosage |
| Too much mold-severing grease | Clean |
| The plastic is dried improperly | Improve the process of drying treatment |
| Water on the mold surface | Wipe up and check if there is water leakage |
| The inner mold surface is not smooth | Polish the mold |
(11) Product deformation
| Reasons of malfunctions | Solutions |
| The product is still not cooled down when ejected out. | Reduce mold temperature, prolong cooling time, lower plastic temperature |
| Too low plastic temperature | Improve the temperature of plastics and mold |
| Uneven shape and thickness of product | Control the mold temperature by partition, fix the product after mold-severing, change shape design |
| Too much feeding material | Reduce shooting pressure, speed, time and dosage |
| Uneven material feeding at several overflow mouths | Modify overflow mouths |
| Unbalance ejector system | Improve ejector system |
| Uneven mold temperature | Adjust mold temperature |
| The plastic near the overflow mouth is too tight or too loose | Increase or reduce shooting time |
| Ill pressure keep | Increase pressure-keeping time |
(12) Air bubble inside the product
| Reasons of malfunctions | Solutions |
| No enough feeding quantity to avoid over shrinkage of the product | Improve shooting pressure |
| The product section, rib or column are too thick | Change product design or the location of overflow mouth |
| Too low shooting pressure | Increase shooting pressure |
| No enough shooting quantity and time | Increase shooting quantity and shooting time |
| The overflow mouth of the casting channel is too small | Enlarge casting channel and overflow mouth |
| Too fast shooting speed | Slow shooting speed |
| Water mixed in the plastic | Dry the plastic completely |
| Too high temperature make the plastic decompose | Lower plastic temperature |
| Uneven mold temperature | Adjust mold temperature |
| Too long cooling time | Reduce cooling time, use water shower to cool |
| Too violent water cooling | Reduce shower time or improve water shower temperature |
| No enough back pressure | Improve back pressure |
| Improper melting barrel temperature | Lower the temperature of shooting nozzle and front part, improve back part temperature |
| Too shrinkage ratio of the plastic | Apply other kind of plastic with smaller shrinkage ratio |
(13) Speckle
| Reasons of malfunctions | Solutions |
| Plastic overheated | Lower plastic temperature |
| Too high plastic temperature | Lower plastic temperature |
| Too fast melting speed | Reduce melting speed |
| The eccentricity screw and melting barrel induce too much friction heat | Examine and repair machine |
| The size of shooting nozzle is too small or the temperature is too high | Re-adjust nozzle size or temperature |
| Too much shooting quantity | Replace small-type injection mold machine |
| Dead corner that make plastic overheated inside the melting barrel | Check contact surface between shooting nozzle and melting barrel to see if there is clearance or erosion. |
(14) Unstable cycle
The causes and solutions of all the above listed shape defects of injection molding machines are related with the stability of cycle. The proper plastizing in the melting barrel or the control of mold temperature is the result of heat transfer balance. That is to say, during the whole injection molding cycle, the plastic in the melting barrel will accept friction heat from the screw rotation and electric-heating ring. The heat will enter into the mold with the plastic. The heat energy of the mold comes from plastic and the machine of constant temperature of the mold. The heat energy will lose in the mold-severing of the product, the air or be brought away but cooling water. So if the temperature of melting plastic and mold need to be kept constant, the output and input heat transfer should be balanced. If the time of injection cycle is shorter and shorter, the heat energy of the melting barrel can not be balanced and the plastic can not be melted, while the energy that is input into the mold will be more than that being output, the mold temperature will rise, so in any operation of injection mold process, especially to manual operation, the cycle time must be controlled stably and the unstable cycle time should be avoided. If other conditions are kept constantly, then:
The acceleration of the cycle will cause: short shooting, product shrinkage and deformation, mold conglutination.
The prolongation of the cycle will cause: material overflow, burr, mold conglutination, deformation, plastic overheat, singing, the residual singed material will damage the mold. The overheat plastic in the melting barrel may erode barrel and speckle and black line will be found in the product.