The sheet products produced by sheet machines are directly affecting its appearance and quality. There are many reasons for this defect, which can be summarized as the following categories:

First of all, improper control of the mold thermal system will lead to the occurrence of ripples. The uneven distribution of the mold temperature field will cause the cooling rate of the melt in the mold cavity, and then the contracted uneven wavy defect occurs. If the temperature fluctuation range of the tube is too large, the melt temperature change entering the mold will also cause ripples. Studies have shown that if the temperature fluctuations of the mold exceed ± 2 ° C, the probability is greater than 80%.

Secondly, changes in the characteristics of the melt may also cause ripples. If raw material problems cause uneven distribution of melt viscosity and liquidity, the flow rate difference in the high and low viscosity area will directly form a wavy pattern of high and low. Further studies have shown that for the PP material, when the MFR index changes more than 10%, the severity of the ripple of the sheet can reach 90%.

Furthermore, the deviation of each component of the sheet machine will also affect the occurrence of ripples. For example, the unstable control of the three -roller speed will change the stretch rate; the depth of the mold cavity or the design of the cooling water channel may become a cause. Data show that when the speed of the three -roller fluctuates is greater than 2%, the ripple incurring chance exceeds 85%. In addition, residues in the mold cavity and three -roller working surface are not cleaned well, which is also related to ripples.

In order to eliminate wavy defects, we must start with melting pre -processing, temperature control optimization, and equipment control, strictly manage key process parameters, and improve the stability of the process. At the same time, optimize the structure of the mold, standardize the operation and maintenance, to fundamentally prevent and reduce the occurrence of ripples.