Home > Technical Support > How to judge the internal and external lubrication balance in the processing of PVC plastics?

How to judge the internal and external in the processing of PVC plastics?

(1) If internal and external lubrication are both insufficient. It will be high melt viscosity, high plasticizing

torque, serious melt wall sticking phenomenon and non-smooth inner surface; serious thermal

decomposition in advance, low mechanical properties of products. If the internal and external lubrication

are balanced, the melting test material will come down as soon as it touches, and the surface of the rotor

will not stick to the melt material.


(2) If internal and external lubricants are both excessive. The plasticizing torque is small and have

precipitation occurs. Although the product has good smoothness, but its mechanical properties are low ,

easy broke. When it is serious, the surface of plastics will feel oily when wiped by hand.


(3) If less internal lubricants and more external lubricants. The plasticizing time is obviously prolonged,

because the internal lubricant is less, the internal friction of resin is larger, and it is easy to cause

thermal decomposition. The plasticizing torque increases. Sometimes it feels oily on the surface of the

sample by hand, and the product  becomes broke


(4) If more internal lubricants and less external lubricants. The plasticizing time is obviously shortened,

so that the resin is plasticized ahead of time, resulting in the high viscosity melt being subjected to

shear force for too long, at the same time, there is a serious adhesion phenomenon, the rotor is not

easy to clean, also resulting in the shortening of thermal stability time, products have decomposition

yellow line.


In a word, if the amount of external lubricant is insufficient, there will be adhesion, short plasticizing

time and non-smooth surface of the sample; if the amount of external lubricant is excessive, plasticizing

time will beobviously prolonged, mechanical properties will be reduced, brittle, precipitation may occur,

and oil-like feeling will be felt when the exterior lubricant is excessive. When the amount of internal

lubricant is insufficient, the plasticizing torque will be larger and the plasticizing time will be longer;

when the amount of internal lubricantis excessive, the plasticizing time will be shorter and the

plasticizing torque will be smaller, but the thermal stability time will also be shorter, and there will be

thermal decomposition phenomenon, and the inner wall of the sample will not be smooth.


Usually the tensile strength is the highest when the plasticity is 60%, the impact strength is the highest

when the plasticity is 65%, and the elongation at break is the highest when the plasticity is 70%.


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