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 plasticsIncrease the temperature of plastic-melting barrel
Too low shooting pressureIncrease shooting pressure
Not enough shooting quantityIncrease shooting quantity
Ill match between inlet sleeve and shooting sleeve, plastic leakage.Re-adjust the match between them
Too short shooting timeIncrease shooting time
Too slow shooting speedAdd shooting speed
Improper low-pressure adjustmentRe-adjust
Too low mold temperatureIncrease mold temperature
Uneven mold temperatureReadjust water pipe of the mold
Ill exhaust of the moldAdd exhaust holes at right position
The temperature of  shooting nozzle is not high enoughIncrease shooting nozzle temperature
Uneven plastic feedingRe-open outlet position
Too small casting channel or overflow mouthEnlarge the casting channel or overflow mouth
No enough lubricant in plasticIncrease lubricant
No enough back pressureAdd pressure
Plastic inlet ring and plastic-melting screw are wornDismantle and amend
No enough shooting quantityReplace with injection mold machine with large specification
Too thin productUse nitrogen for shooting

 

(2) Shrinkage of product

Reasons of malfunctionsSolutions
No enough plastic feeding in the moldIncrease shooting pressure
No enough melt plasticAdd the quantity of melt plastic
Too low shooting pressureIncrease shooting pressure
Too low back pressureIncrease back pressure
Too shooting timeIncrease shooting time
Too slow shooting speedIncrease shooting speed
Uneven overflow mouthAdjust 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 lowAdjust mold or replace shooting nozzle
The material temperature is too highLower temperature
Improper mold temperatureAdjust mold temperature properly
No enough cooling timeProlong cooling time
Too many pressure accumulation sectionsThe shooting process should be terminated at the most front part.
The product, rib or column are too thickExamine product design
Too much shooting quantityReplace with smaller injection mold machine
The plastic feeding ring and plastic-melting screw are worn outDismantle, examine and repair
The casting mouth is too small, the plastic solidification loses the back pressureIncrease the size of casting mouth

 

(3) Mold conglutination of product

Reasons of malfunctionsSolutions
Too much feeding materialLower shooting pressure
Too high shooting pressureLower shooting pressure
Too much shooting quantityReduce shooting quantity
The shooting time is too longReduce shooting time
The temperature of feeding material is too highLower temperature
Uneven feeding induces partial saturationChange the size or position of overflow mouth
The mold temperature is too high or too lowAdjust the temperature of mold and the two sides
Mold-severing rounded angle in the moldRepair mold and remove rounded angle
The surface of mold is not smoothPolish mold
Vacuum induced by mold-severingSlow Mold-open or ejection, or add gas equipment
Too short injection cycleStrengthen cooling
No enough mold-severing reagentAdd the quantity of mold-severing reagent

 

(4) Mold conglutination of casting channel

Reasons of malfunctionsSolutions
Too high shooting pressureLower shooting pressure
Too high injection temperatureLower plastic temperature
The casting channel is too bigModify mold
The cooling of casting channel is not enoughProlong cooling time or lower cooling temperature
The mold-severing angle of casting channel is not enoughModify mold and add angle
Ill match between sleeve of casting channel and shooting nozzleRe-adjust match
The inner surface of casting channel is not smooth or there is mold-severing rounded angleExamine and repair mold
The outer hole of the casting channel is damagedExamine and repair mold
No holding-pin of casting channelAdd holding-pin
The feeding material is too saturatedReduce shooting quantity, time and speed
No enough mold-severing reagentAdd the quantity of mold-severing reagent

 

(5)Burr and flying edge

Reasons of malfunctionsSolutions
Too high plastic temperatureLower temperature of plastic and mold
Too high shooting speedReduce shooting speed
Too high shooting pressureReduce shooting pressure
The feeding material is too saturatedReduce shooting time, speed and quantity
Ill Mold-close line or match surfaceExamine and repair mold
No enough mold-lock forceAdd mold-lock force or replace injection molding machine with larger mold-lock force

 

(6) Product cracking during mold open or ejection

Reasons of malfunctionsSolutions
Feeding material is too saturatedReduce shooting pressure, time, speed and quantity
Too low mold temperatureImprove mold temperature
Some mold-severing angles are not enoughExamine and repair mold
Mold-severing rounded angleExamine and repair mold
Unbalanced severance during product mold-severing processExamine and repair mold
Ejector is not enough or its location is not properExamine and repair mold
Partial vacuum during mold-severingSlow Mold-open ejection speed, add gas equipment
No enough mold-severing reagentAdd mold-severing reagent
Ill mold design, too much residual stressImprove product design
Improper time or location of side sliding blockExamine and repair mold

 

(7) Joint line

Reasons of malfunctionsSolutions
Plastic is not melted wellIncrease plastic temperature, back pressure and screw rotation speed
Too low mold temperatureImprove mold temperature
Too low shooting nozzle temperatureImprove shooting nozzle temperature
Too slow shooting speedIncrease shooting speed
Plastic is not pure or mixed with impuritiesExamine plastic
Too much mold-severing greaseReduce quantity of grease or do not use it
Casting channel and overflow mouth are too big or too smallAdjust mold
The joint location of melting plastic is too far from the casting channel mouthAdjust mold
Air in the mold can not be remove timelyAdd exhaust holes or check if original exhaust holes are blocked
No enough plastic melting quantityApply larger injection molding machine
Too much mold-severing reagentReduce the quantity of mold-severing reagent or do not use it

 

(8) Flow trail

Reasons of malfunctionsSolutions
Plastic material is not melted wellImprove plastic temperature, back pressure and screw rotation speed
Too low mold temperatureIncrease mold temperature
Mold is cooled improperlyReadjust mold water pipe
The shooting speed is too slow or too fastAdjust proper shooting speed
The shooting pressure is too high or too lowAdjust proper shooting pressure
Plastic is not pure or mixed with impuritiesExamine plastic
The overflow mouth is too small and crack is producedEnlarge overflow mouth
The difference between the thin section and the thick section of the product is too muchChange product design or location of overflow mouth

 

(9) Silver line, air bubble

Reasons of malfunctionsSolutions
The plastic is mixed with waterDry the plastic completely and improve back pressure
The plastic temperature is too high, or the plastic stays in the barrel for too long timeLower 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 decomposeReduce their dosage or use replacement with high temperature resistance.
Other additives in the plastic are not mixed evenlyMix them completely even
Too fast shooting speedSlow shooting speed
Too high shooting pressureReduce shooting pressure
The melting speed is too slowImprove melting speed
Too low mold temperatureImprove mold temperature
The size of plastic particles is not evenUse materials with even particle size
Air is mixed in the melting barrelReduce temperature of the back section of melting barrel, improve back pressure, reduce the length of compressed section
Improper flow of the plastic in the moldAdjust 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 malfunctionsSolutions
Too low mold temperatureImprove mold temperature
No enough plastic dosageIncrease shooting pressure, speed, time and dosage
Too much mold-severing greaseClean
The plastic is dried improperlyImprove the process of drying treatment
Water on the mold surfaceWipe up and check if there is water leakage
The inner mold surface is not smoothPolish the mold

 

(11) Product deformation

Reasons of malfunctionsSolutions
The product is still not cooled down when ejected out.Reduce mold temperature, prolong cooling time, lower plastic temperature
Too low plastic temperatureImprove the temperature of plastics and mold
Uneven shape and thickness of productControl the mold temperature by partition, fix the product after mold-severing, change shape design
Too much feeding materialReduce shooting pressure, speed, time and dosage
Uneven material feeding at several overflow mouthsModify overflow mouths
Unbalance ejector systemImprove ejector system
Uneven mold temperatureAdjust mold temperature
The plastic near the overflow mouth is too tight or too looseIncrease or reduce shooting time
Ill pressure keepIncrease pressure-keeping time

 

(12) Air bubble inside the product

Reasons of malfunctionsSolutions
No enough feeding quantity to avoid over shrinkage of the productImprove shooting pressure
The product section, rib or column are too thickChange product design or the location of overflow mouth
Too low shooting pressureIncrease shooting pressure
No enough shooting quantity and timeIncrease shooting quantity and shooting time
The overflow mouth of the casting channel is too smallEnlarge casting channel and overflow mouth
Too fast shooting speedSlow shooting speed
Water mixed in the plasticDry the plastic completely
Too high temperature make the plastic decomposeLower plastic temperature
Uneven mold temperature Adjust mold temperature
Too long cooling timeReduce cooling time, use water shower to cool
Too violent water coolingReduce shower time or improve water shower temperature
No enough back pressureImprove back pressure
Improper melting barrel temperatureLower the temperature of shooting nozzle and front part, improve back part temperature
Too shrinkage ratio of the plasticApply other kind of plastic with smaller shrinkage ratio

 

(13) Speckle

Reasons of malfunctionsSolutions
Plastic overheatedLower plastic temperature
Too high plastic temperatureLower plastic temperature
Too fast melting speedReduce melting speed
The eccentricity screw and melting barrel induce too much friction heatExamine and repair machine
The size of shooting nozzle is too small or the temperature is too highRe-adjust nozzle size or temperature
Too much shooting quantityReplace small-type injection mold machine
Dead corner that make plastic overheated inside the melting barrelCheck 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.