PP air duct is produced by stamping method and high-speed extrusion method. The punching method is to punch holes with a punch, roll with a roll at the same time, flatten with a mandrel continuous rolling mill, and indirectly extrude in an extruder with a high-speed extrusion method. The pipe processed by this method has low dimensional accuracy and defects such as cracks, wrinkles, delamination and inclusions. For thick wall and small diameter pipes, ingots can also be forged and rolled. Under natural or artificial conditions, the appearance of PP ducts whose function degrades with time is called the appearance of plastic aging, resulting in a sharp increase in the resistance to deformation.
During the shrinkage process of the runner, since the runner rolls on the surface of the tube blank at a high speed, if there are other tiny obstacles, it will cause vibration and wrinkle the appearance of the tube. The aging of PP air ducts is manifested as changes in the appearance of plastic products, such as surface darkening, deformation, cracking or mildew, falling off, etc. As well as changes in physical and chemical functions such as solubility, glass transition temperature, melt activity rate and group content. Changes in mechanical properties such as tensile strength, impact strength, crack growth, etc. ; Changes in electrical operation such as insulation resistance, dielectric constant, breakdown voltage, etc.
There are internal and external factors in the aging process of PP air duct, and the internal factor is the influence of chemical scheme. However, the aging difficulty of pp air duct depends on the strength of its chemical bonds. Different keys have different key energies, and they vary widely. In polymer molecules, the presence of branched chains and pendant groups can reduce the bond strength and make it difficult for the plastic to age. The plastic aging reaction only needs reactants, and only those entering the polymer planner have a certain reaction speed, otherwise the aging speed is very slow and only on the surface. So the service life is very long.
In order to improve the weak circumferential strength of the pipe, new pipe extrusion dies have emerged, such as cutting empty pipe extrusion dies, replacing extruded pipe extrusion dies, etc. The axial tensile stress field during disassembly can slightly increase the axial tensile strength of the pipeline, and the circumferential shear stress field during disassembly can improve the circumferential tensile strength of the pipe well. In the shear stress field, the axial tensile strength of the pp air duct generally increases with the increase of the rotation speed of the shear sleeve. When the shear sleeve just rotates, the axial tensile strength of the PP air duct decreases slightly, and the extrusion temperature in the shear stress field should be around 200 °C.
