The influencing factors of plastic produce internal stress
the polarity of the molecular chain. The greater the polarity of the molecular chain, the greater the force of attraction between the molecules, so that the intermolecular interaction increases difficulty moving, restore reversible elastic deformation degree is reduced, cause a large residual internal stress.
replace groups of steric effect. Macromolecular side base instead of the volume of a group, the greater the freedom of movement, the obstruction of macromolecular chain cause residual internal stress increased.
molecular chain rigidity. The higher the molecular chain rigidity, the greater the melt viscosity, polymer molecular chain mobility is poor, so for the reversible high elastic deformation recovery is poor, easy to produce residual internal stress.
plastic low internal stress and dispersion
raw materials formula design. The polymer molecular weight, the greater the degree of macromolecular chain inter-atomic forces and tangles increased, its products, strong stress cracking resistance of polymer molecular weight distribution is wider, the low molecular weight compounds, the greater the first form micro tear, cause stress concentration, make the products cracking.
select resin of low content of impurities. Polymer in the stress concentration of impurity is body, will reduce the original strength of plastic, impurity content should be reduced to a minimum.
blending modification. Prone to stress cracking resin and other resin suitable blending, can reduce the degree of the existence of internal stress.
enhancement modification. Enhanced with enhanced fibers, can reduce the internal stress of products, this is because the fiber tangles a lot of macromolecular chain, so as to improve the ability of stress cracking.
nucleation modification. To join in the crystalline plastics suitable nucleating agent, can be formed in the products of many small spherulites, reduce internal stress and dispersed.
plastic molding process, that can reduce the forming factors of polymer molecular orientation of products can reduce stress orientation, who can make the products in the polymer process conditions of uniform cooling can reduce the internal stress of cooling, all help to plastic products processing method of demoulding are beneficial to reduce internal stress of demoulding.
affect machining conditions
the injection pressure of internal stress. High injection pressure, melt in the process of mold filling by shear force is big, also bigger chance of producing a stress orientation. Therefore, in order to reduce the orientation stress and eliminate mold release stress, should be appropriate to reduce the injection pressure.
cylinder temperature. High cylinder temperature is advantageous to the orientation of stress is reduced, this is because the high cylinder temperature, uniform plasticizing, melt viscosity, liquidity increases, in the process of the melt filled cavity, molecular orientation effect is small, less stress and orientation. Cylinder and at lower temperature, higher melt viscosity, molecular orientation in the process of mold filling, cooling after finalize the residual internal stress is larger. Cylinder temperature is too high, however, is not good, too easy to cause insufficient cooling, easy to cause deformation when parting, although the orientation stress decreases, but the cooling stress and stripping stress increase instead.
the discretion of the mold temperature on orientation stress and cooling effect of internal stress is very big. Die a great influence on plastic crystallization temperature, die temperature is higher, the more grain pile close together, the inside of the crystal defects to reduce or eliminate, so as to reduce internal stress.
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