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Description:Delamination-defect-injection-molding.jpg


Delamination can be defined as a separation of the layers within a molded part. It can also appear as fish-scaling.



Possible Causes & Remedies:


Machine Cause


◇ INJECTION SPEED TOO SLOW


Remedies: Increase the injection fill speed in small increments (two percent of total) until the delamination tendency disappears. If burning or flashing occurs, the injection speed is too high and delamination is being caused by other factors.


◇ INADEQUATE CUSHION


Remedies: Establish a cushion of at least 1/8'' and not more than 1/4''. Too little a cushion causes under-packing while too great a cushion results in uncontrolled packing of the sprue area.


◇ INJECTION HOLD TIME TOO SHORT


Remedies: Maintain the holding pressure until the gate freezes. Once that happens, the holding pressure will no longer have any effect on the material in the cavity.


◇ LOW BARREL TEMPERATURE


Remedies: Each material has a range in which it can be molded and the barrel temperature should be adjusted to accommodate the specific material being used and the product and mold design being incorporated. The material supplier is the best source of information for this data. Be sure to use the proper profile and heat the material progressively from the rear to the front of the barrel.


Mould Cause


◇ LOW MOLD TEMPERATURE


Remedies: Each material has an ideal mold temperature that should be used for proper molding. The material supplier is the best source for this information, but most material should run in molds that are between 120 - 180 degrees F.


◇ SHARP CORNERS IN GATES AND RUNNERS


Remedies: It is always a good idea to utilize a radius at every turn in a runner system and at each gate entrance to the cavity. This will help to minimize shear and reduce the chance of resin separation during injection.


◇ EXCESSIVE MOLD RELEASE


Remedies: The remedy is to keep the mold as clean as possible and make every effort to eliminate the use of external mold releases.


Material Cause


◇ CONTAMINATED RAW MATERIAL


Remedies: This type of contamination can be minimized by dealing with high quality, reputable suppliers and by using good housekeeping practices. Properly trained material handlers will also help reduce contamination.


◇ FOREIGN MATERIALS OR IMPROPER ADDITIVES


Remedies: Use only compatible additives for all base resins. Use reputable, proven compounders especially when specifying non-standard formulations.


◇ EXCESSIVE MOISTURE


Remedies: Although it is commonly understood that non-hygroscopic material does not require drying, do not take chances. Dry all materials. It may be that fillers used in the material ARE hygroscopic and they will absorb moisture. Every plastic material requires specific drying conditions. And each material should be dried according to the material suppliers recommendations. The desired moisture content is between 1/10th of 1 percent and 1/20th of 1 percent by weight. This means the dry air being used to take moisture from the material should have a dew point of -20 to -40 degrees F.


Operator Cause


◇ POOR HOUSEKEEPING


Remedies: If possible, run the machine on automatic cycle, using the operator only to interrupt the cycle if an emergency occurs. Use a robot if an “operator” is really necessary. And, instruct all employees on the importance of maintaining consistent cycles. 


(Source: plastictroubleshooter.com)

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