What factors affect the shrinkage TPE injection products
Shrinkage factor S represented by the formula: S = {(D-M) / D} × 100%
Where: S- shrinkage; D- die size; M- size plastic parts.
Like ordinary plastic injection, SBS / SEBS mold design must take into account the shrinkage characteristics of the material.
SBS or SEBS material shrinkage and other by formula, in the range of 0.5% to 2% range. Melt flow back into the mold shrinkage will be higher. In general, SBS shrinkage to be smaller, and SEBS shrinkage is slightly larger higher density (the filled material) of material shrinkage rate than low-density material shrinkage smaller.
An impact on the plastics molding shrinkage
(1) maintaining the pressure increases, the shrinkage decreases;
(2) the molding temperature is constant, the injection pressure increases, the shrinkage rate decreased;
(3) the melt temperature is increased, the shrinkage is reduced;
(4) the mold temperature is high, shrinkage increases;
(5) long-mold cooling time, reduce shrinkage;
(6) packing a long time, reduce shrinkage, but does not affect the shrinkage of the gate closed;
(7) injection speed is high, shrinkage tends to increase slightly less affected;
(8) molding shrinkage after shrinkage. Two days after the beginning of the large contraction in a week or so stable. Plunger-type injection molding machine shrinkage.
2, the impact of plastic shrinkage rate structure
(1) thick plastic parts greater than the thin-walled plastic parts shrinkage (but most of the thin-walled plastic parts but larger than 1mm 2mm shrinkage, which is due to increased resistance of melt in the mold cavity sake);
(2) on the plastic parts with inserts smaller than the shrinkage without inserts;
(3) Plastic height direction generally smaller than the shrinkage in the horizontal direction;
(4) plastic parts of complex shape than the shape of a simple shrinkage is smaller;
(5) small slender plastic shrinkage in the longitudinal direction;
(6) the size of the longitudinal direction of the plastic parts is smaller than the thickness direction dimension of shrinkage;
(7) bore shrinkage, small outline shrinkage.
3, the impact of structure on the plastic mold shrinkage
(1) gate size large, shrinkage is reduced;
(2) the direction perpendicular to the gate reduce shrinkage, shrinkage in the direction parallel to the gate increases;
(3) away from the gate is smaller than near the gate of shrinkage;
(4) has a mold shrinkage rate limiting portion small plastic parts, plastic parts shrinkage unlimited large portion.
4, the impact of the nature of the products, plastic shrinkage
(1) crystalline plastic shrinkage greater than amorphous plastics;
(2) good mobility plastic molding shrinkage;
(3) adding a plastic filler, mold shrinkage decreased;
(4) different batches of the same plastic, the mold shrinkage rate is not the same. Some processing conditions such as mold temperature, melt temperature, injection velocity and thickness of the product will affect the product shrinkage.
