Correcting Tiger Striping…

When these are in the mold surface, small changes such as reduced melt temperature, slower injection speed, and reduced packing pressure tend to help. These reduce the polymer’s ability to duplicate the cavity detail will improve the overall appearance, but do not fix the underlying problems. 
Question: Are Tiger Stripes Solvable? All the processing changes such as increasing melt , mold temperature , adjusting velocity did not yield result to eliminate however improved the condition. 
My Response: ‘Tiger Stripes’ is a visual condition on the final part related to poor surface finish. Since the location of material-related defects are not predictable and consistent form shot to shot, this is not likely to be caused by the material since material coloring defects are more random and not consistent in appearance. Some high viscosity and low gloss grades of material may show less cavity detail, and therefor hide the problem, but they will not ‘fix’ the problem. Three of the most common causes are listed below:
1) Poor Sandblasting – The texture was not well applied to the mold. In this case, the striping is likely parallel with the edge of the mold base. This is because the employee would have passed their hand  back and forth when sandblasting, causing lines in the finish if they hold the blaster too close or do not spray evenly. If this is the case, the mold surface needs to be repaired and returned to its original condition
2) Poor Venting (New Problem) – When air cannot escape from the mold it becomes trapped against the mold surface. These tend to occur perpendicular to the direction of flow. When this happens, the polymer does not properly adhere to the mold surface causing it to ‘skip’, giving the cavity a rippled appearance. If this is a new problem, improving the venting, reducing the tonnage, and thoroughly cleaning the mold surface with safe solvents should significantly improve the situation. 
3) Poor Venting (Old Problem) – Unfortunately, if this has been occurring for a long period of time, the mold surface will actually become damaged due to the slipping polymer and buildup of corrosive volatiles on the mold surface. If this is the case, the mold surface needs to be repaired and returned to its original condition and much more venting needs to be added.

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