Plastic shrinkage of common problems and solutions under

8 scorching, airlines

Analysis of the causes: generally known as scorching (Burn Mark) includes the surface of the product due to plastic degradation resulting in discoloration and the filling end of the product scorched black phenomenon. Scorching is trapped in the cavity of the air in the plastic melt filling is not quickly discharged (trapped air), is compressed and significantly heated up, the material will be scorched. 

Poor air discharge. Countermeasures: Strengthen the air exhaust in the trapped air area, so that the air is discharged promptly. Reduce the injection pressure, but it should be noted that the injection speed slows down after the pressure drops, which can easily cause flow marks fusion marks, and fusion marks to deteriorate.

①Adopt multi-stage control filling, and adopt the multi-stage deceleration method at the end of the molding process to facilitate gas discharge.
②Use a vacuum pump to extract air from the cavity, so that the cavity is filled under vacuum. Clean up the exhaust slot to prevent blockage.
③The gate is too thin or too long, which leads to plastic degradation. p Exhaust slots, exhaust inserts, etc.

9 surface flow patterns (flow marks), water ripples

Analysis of the causes: plastic melt flow traces to the gate as the center of the striped wave pattern. The surface occurs in the vertical flow of numerous fine lines, resulting in the surface of the product being similar to fingerprints ripples.

Countermeasure: The flow marks are caused by the melt flowing into the cavity at the beginning cooling too fast and forming a boundary with the melt flowing after it. Cold material left in the front of the injection molding machine nozzle, if directly into the cavity, resulting in flow marks. The low temperature of the plastic melt increases the viscosity and causes flow marks. Low mold temperature takes away a lot of plastic melt heat, so that the plastic melt temperature drops, viscosity increases and flow marks occur. 

Injection speed is too slow, filling process plastic melt temperature decreases more, viscosity increases, and the occurrence of flow marks. In the mold filling process, the temperature of the plastic melt in the cavity decreases to a high viscosity state filling, contact with the mold surface of the plastic melt to semi-solid state pressed into the surface of the vertical flow of numerous fine lines, resulting in the surface of the product similar to fingerprint ripples. When the temperature of the plastic melt then drops, the filling is not completely cured, resulting in underfilling. Ripples often occur near the edge of the product and fill the end.

10 clip water lines (fusion marks), spray lines (snake lines)

Reason analysis: When the mold adopts multiple gates into the pouring scheme, the rubber flow front converges with each other; hole and obstacle area, the rubber flow front will also be divided into two; uneven wall thickness will also lead to melting marks. 

The plastic melt passing through the gate at high speed enters the cavity directly, then touches the surface of the cavity and cures, then is pushed by the subsequent plastic melt, thus leaving snaking marks. Side gates, plastic after the gate without stagnant area or stagnant area is not sufficient, easy to produce spray marks.

Countermeasure: Reduce the number of gates. Add material overflow wells near the fusion section, move the fusion line to the overflow wells, and then remove them. Adjust the gate position. Change the location and number of gates, and move the location where the fusion line occurs to another location. Intensify the exhaust in the area of the fusion line to quickly evacuate the air and volatiles in this part. Increase the material temperature and mold temperature to enhance the fluidity of the plastic and increase the material temperature when fusing. Increase the injection pressure and increase the size of the pouring system. Increase the injection speed. Shorten the distance between the gate and the fusion area. 

Shorten the distance between the gate and the fusion area. Reduce the use of mold release agents. Adjust the gate position so that the plastic melt collides with the pin type or wall after passing through the gate. Change the gate form, use overlapping gates or lug gates, set enough stagnant area in the gate area. This can slow down the initial injection speed of the melt. Increase the gate thickness/cross-sectional area so that the flow front forms immediately. Raise the mold temperature to prevent rapid material curing.