The formula for calculating shrinkage is (R before - R after) / R before *100%. Shrinkage percentage.
Shrinkage S is expressed by the following formula: S={(D-M)/D}×100%(1)
Where: S-shrinkage; D-mold size; M-mold size.
The following are the shrinkage rates of plastics in (%)
PP(1.0-2.5);
PMMA(0.1-0.4);
PC(0.5-0.7);
PA6(0.5-1.5);
PA6-GF(0.4-0.6);
PA66(0.8-1.5);
PA66-GF(0.5);
PS(0.4-0.7);
ABS(0.4-0.9);
ABS-GF(0.1-0.2);
POM(2-2.5);
PBT(1.5- 2.0);
PET (2-2.5).
The above are the shrinkage ratios of commonly used plastics, there is a range, usually manufacturers do not specify, take the middle value!
Expanded Information:
1, mold structure on the plastic products shrinkage
(1)? Shrinkage decreases with large gate size;
(2) Shrinkage decreases in the direction of perpendicular gates and increases in the direction of parallel gates;
(3) Shrinkage is smaller away from the gate than close to the gate;
(4) Shrinkage is small in the part of the plastic part which is restricted by the mold, and large in the part of the plastic part which is unrestricted.
2, the nature of the plastic products on the impact of shrinkage
(1) crystalline plastic shrinkage is greater than amorphous plastics;
(2) good fluidity of the plastic, molding shrinkage is small;
(3) the addition of filler in the plastic, the molding shrinkage decreased significantly;
(4) different batches of the same plastics, the molding shrinkage is not the same. The molding shrinkage rate is also different for different batches of the same plastic.
3, the plastic structure of the product shrinkage
(1) thick-walled plastic parts than thin-walled plastic shrinkage (but most plastics 1mm thin-walled parts than 2mm shrinkage, this is due to the melt in the mold cavity resistance increases the cause);
(2) plastic parts with inserts on the shrinkage than the inserts of the contraction of the small;
(3) the shape of the plastic parts than the complex shape of the simple shrinkage;
(3) the shape of the plastic parts, the shrinkage of the molded part is not the same. Complex shape is smaller than the shape of a simple shrinkage;
(4) the height direction of the part is generally smaller than the horizontal direction of the shrinkage;
(5) slender parts in the length direction of the shrinkage is small;
(6) the length of the part dimensions than the thickness direction of the shrinkage of the dimensions of the shrinkage is small;
(7) the shrinkage of the inner hole shrinkage is large, the shape of the shrinkage is small.
Baidu Encyclopedia - Plastic Shrinkage
Baidu Encyclopedia - Shrinkage