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Mould problems solution

Cutlery mould exhaust problem

Oct. 30, 2019

In the process of producing plastic disposable cutlery, sometimes will have unfilled parts, air bubbles etc, this is caused by air exhaust.


1. The source of air in the injection cutlery mold.

(1) The air contained in the gating system and the mould cavity. 

(2) Some raw materials contain moisture that is not removed by drying, and they are vaporized into water vapor at a high temperature. 

(3) Air generated by decomposition of some unstable plastics due to excessive temperature during injection molding. 

(4) Air formed by volatilization or chemical reaction of certain additives in plastic raw materials. 


Poor exhaust of the knife and fork mold will bring a series of hazards to the quality of the plastic parts. The main performance is as follows:

(1) In the injection molding process, the melt will replace the air in the cavity. If the air is not discharged in time, the melt filling will be difficult, resulting in insufficient injection volume to fill the cavity. 

(2) Excluding the unsatisfactory air will form a high pressure in the cavity and penetrate into the plastic inside under a certain degree of compression, resulting in quality defects such as pores, voids, tissue sparseness, and silver streaks. 

(3) Due to the high compression of the air, the temperature in the cavity rises sharply, which causes decomposition and burning of the surrounding melt, causing local carbonization and charring of the plastic part. It mainly occurs at the junction of the two melts at the gate flange. 

(4) The air is not well removed, so that the melt velocity entering each cavity is different, so flow marks and fusion marks are easily formed, and the mechanical properties of the plastic parts are lowered. 

(5) Due to the obstruction of air in the cavity, the filling speed will be reduced, the molding cycle will be affected, and the taxation efficiency will be reduced.


Distribution of bubbles in plastic parts


(1) The bubbles generated by the accumulation of air in the mould cavity of the cutlery spoon are often distributed on the opposite part of the gate. 

(2) Bubbles generated by decomposition or chemical reaction in the plastic raw material are distributed along the thickness of the plastic part. 

(3) The bubbles generated by the vaporization of residual water in the plastic raw material are irregularly distributed on the entire plastic part.


From the distribution of the bubbles in the above-mentioned plastic parts, it is possible to judge not only the nature of the bubbles but also whether the exhaust portion of the cutlery mold is correct and reliable.

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