Carbon fiber defects are diverse and varied, and the defects can be divided into two categories: surface defects and internal defects. The effect of surface defects on the tensile strength of the same size is greater than that of internal defects. Today, give you a brief introduction of carbon fiber surface defects and reasons.
It is observed under the microscope if there is a circular spot deposit on the surface of the carbon fiber. This may be produced in the process of the formation of the wet spinning process, that is, the micro suspension in the solidification bath is deposited on the surface of the primary fiber by preoxidation and carbonization. Therefore, the circulating solidified liquid should be filtered and filtered out to prevent the contamination of primary fibers. In addition, the surface is a circular speckled deposit, and it is likely to be caused by the deposition of tiny spinning droplets.
Some also have internal cracks or obvious skin core structures. This internal crack is likely to be the result of the thermal degradation of the core in the carbonization process without fully preoxidized and trapezoid structures. In other words, the dense epidermis is the result of the pyrolysis and condensation of the trapezoid structure, and the core is composed of the thermal degradation of the linear molecular chain of resin carbon. The decomposition of thermal degradation is much, and the residue is less, which leads to the formation of loose structures and cracks.
A large hole that may exist inside the carbon fiber. There is no doubt that the existence of these large holes reduces the effective section of the loading load and reduces the tensile strength. If the hole has reduced the effective section area by 23.6%, the tensile strength can not reach the level of T300 carbon fiber. There may be two reasons for the formation of these large pores. One is that there are large central holes in the PAN precursor, and the other is that there is a serious skin core structure in the pre oxidation process. During the carbonization process, the core structure of the trapezoid structure is not evaporating rapidly. The structure of the core is very volatile.
In the process of carbonization, the fiber is transformed from flexibility to brittleness, and the broken fragments can not be retained. Therefore, the surface scratching is likely to be produced during the preoxidation process, and then the probability of retaining the debris in situ is the greatest in the straight run carbonization. The cause of the scratch is due to the poor smoothness of the conveyor roller surface, so the roller should be treated by spraying ceramic. Grinding and polishing, removing burr, sharp angle.
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