Effect of plastic structure on shrinkage of products

April 11, 2019

Effect of plastic structure on shrinkage of products
(1) Thick-walled plastic parts have higher shrinkage than thin-walled plastic parts (but most plastic 1mm thin-walled parts have a larger shrinkage than 2mm, which is due to the increased resistance of the melt in the cavity);
(2) The shrinkage rate of the insert with the insert on the plastic part is smaller than that without the insert;
(3) The shape of the plastic part is complicated, and the shrinkage rate is simpler than that of the simple shape;
(4) The height direction of the plastic part is generally smaller than the horizontal direction;
(5) The shrinkage rate of the elongated plastic part in the longitudinal direction is small;
(6) The dimension in the longitudinal direction of the plastic part is smaller than the shrinkage ratio in the thickness direction dimension;
(7) The inner hole shrinkage rate is large, and the shape shrinkage rate is small.

 

 

Effect of plastic properties on shrinkage of products
(1) The shrinkage rate of crystalline plastics is greater than that of amorphous plastics;
(2) Plastics with good fluidity, small molding shrinkage;
(3) Adding filler to the plastic, the molding shrinkage rate is significantly reduced;
(4) The same plastics in different batches have different molding shrinkage rates.

Effect of plastic mold structure on heat shrinkage rate
(1) The gate size is large and the shrinkage rate is reduced;
(2) The vertical gate direction shrinkage rate is reduced, and the parallel gate direction shrinkage rate is increased;
(3) The shrinkage rate away from the gate is smaller than that of the near gate;
(4) The shrinkage rate of the plastic part having the mold restriction is small, and the shrinkage rate of the unrestricted plastic part is large. ..

 

Effect of molding process on shrinkage of plastic products
(1) Barrel temperature: When the temperature of the cylinder is high, the pressure transmission is good and the contraction force is reduced. However, when a small gate is used, the shrinkage rate is still large due to the early curing of the gate. For wall-thick plastic parts, even if the barrel temperature is higher, the shrinkage rate is still large.
(2) Feeding: In the molding conditions, the feeding is minimized to keep the size of the plastic parts stable. However, if the feed is insufficient, the pressure cannot be maintained, and the shrinkage rate is also increased.
(3) Injection pressure: The injection pressure is a factor that has a large influence on the shrinkage rate, especially the pressure holding pressure after the filling is completed. Under normal circumstances, when the pressure is large, the density of the material is large, and the shrinkage rate is small.
(4) Injection speed: The injection speed has little effect on the shrinkage rate. However, when the thin-walled plastic part or gate is very small, and when the reinforcing material is used, the injection speed is increased and the shrinkage rate is small.
Mold temperature: Generally, the shrinkage rate is also large when the mold temperature is high. However, for thin-walled plastic parts, if the mold temperature is high, the flow resistance of the melt is small, and the shrinkage rate is rather small.
(5) Molding cycle: There is no direct relationship between the molding cycle and the shrinkage rate. However, it should be noted that when the molding cycle is accelerated, the mold temperature, the melt temperature, and the like are also inevitably changed, thereby affecting the change in the shrinkage rate.
(6) Mold temperature: the higher the mold temperature, the greater the shrinkage rate

 

 

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