Plastic product processing is a complex process, in which process parameters such as temperature and pressure play a key role. They directly affect the rheological behavior, molecular orientation of plastics, and the physical properties, mechanical properties and appearance quality of the final product. In-depth understanding of the impact of these parameters is of great significance for optimizing plastic product processing technology and improving product quality.
Temperature is crucial in plastic product processing. First, it affects the fluidity of plastics. When the temperature rises, the force between plastic molecules weakens, the melt viscosity decreases, and the fluidity increases, which is conducive to the filling and molding of plastics in the mold. For example, in injection molding, the appropriate barrel temperature can make the plastic uniformly plasticized and smoothly injected into the mold cavity. However, too high a temperature may cause plastic degradation and reduce product performance, such as yellowing of color and reduced mechanical properties. On the contrary, too low a temperature will make the plastic have poor fluidity, resulting in problems such as unsatisfactory filling and rough surface.
Secondly, temperature affects the crystallinity of the product. For crystalline plastics, the processing temperature determines the speed and degree of crystallization. Appropriate cooling temperature can control the crystallinity, which in turn affects the density, hardness, strength and heat resistance of the product. Generally speaking, a slower cooling rate will result in higher crystallinity, increased hardness and strength of the product, but may reduce toughness.
Pressure is also an indispensable parameter in plastic products processing. During the injection molding process, the injection pressure determines whether the plastic melt can quickly and evenly fill the mold cavity. Higher injection pressure helps to overcome the melt flow resistance, so that the details of the product can be clearly formed, and the dimensional accuracy and surface quality of the product can be improved. However, too high injection pressure may cause increased mold wear, flash, deformation and other problems in the product.
Holding pressure plays a key role in the density and dimensional stability of the product. During the cooling and shrinkage of the plastic melt, the holding pressure can supplement the gaps caused by volume shrinkage and prevent defects such as shrinkage marks and voids in the product. Appropriate holding pressure can make the product density uniform, dimensional stability, and improve the mechanical properties of the product.
Temperature and pressure are often interrelated and synergistic. For example, in extrusion molding, the rotation speed of the screw and the back pressure jointly affect the plasticization quality and extrusion pressure of the plastic. Higher screw speeds generate more frictional heat and increase the temperature of the plastic, while back pressure can subject the plastic to higher pressure in the extruder for further uniform plasticization. If the temperature and pressure are not properly controlled, problems such as unstable dimensions, rough surfaces, or internal stress may occur in the extruded product.
Reasonable control of temperature and pressure can significantly improve the mechanical properties of the product. Appropriate processing temperature and pressure can fully orient and arrange the plastic molecular chains, improve the tensile strength, bending strength, and impact strength of the product. For example, in blow molding, by precisely controlling the blow molding pressure and mold temperature, the molecular chains of the plastic bottle can be uniformly oriented in the circumferential and axial directions, thereby improving the impact resistance and pressure resistance of the bottle.
Temperature and pressure also have an important impact on the appearance quality of the product. Uneven temperature or pressure fluctuations may cause defects such as flow marks, moire, and bubbles on the product surface. For example, in injection molding, if the mold temperature is uneven, the cooling speed of the product surface will be inconsistent, resulting in obvious temperature difference marks. Unstable pressure may cause turbulence in the plastic melt during the filling process, affecting the surface finish of the product.
In the process of plastic products processing, process parameters such as temperature and pressure have many specific effects on product performance. From product fluidity, crystallinity, mechanical properties to appearance quality, each link is closely related to these parameters. Therefore, in the processing of plastic products, temperature and pressure must be accurately controlled, and process parameters must be reasonably adjusted according to different plastic varieties, product structures and mold characteristics to obtain plastic products with excellent performance and stable quality.
